Fundamentals of Vacuum Technology

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FUNDAMENTALS

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Fundamentals of Vacuum Technology General

Fundamentals of Vacuum Technology

revised and compiled by Dr. Walter Umrath with contributions from

Dr. Hermann Adam †, Alfred Bolz, Hermann Boy, Heinz Dohmen, Karl Gogol, Dr. Wolfgang Jorisch, Walter Mönning, Dr. Hans-Jürgen Mundinger, Hans-Dieter Otten, Willi Scheer, Helmut Seiger, Dr. Wolfgang Schwarz, Klaus Stepputat, Dieter Urban, Heinz-Josef Wirtzfeld, Heinz-Joachim Zenker

Preface

A great deal has transpired since the final reprint of the previous edition of Fundamen- tals of Vacuum Technology appeared in 1987. LEYBOLD has in the meantime introduced a number of new developments in the field. These include the dry-running ALL·ex chemicals pump, the COOLVAC-FIRST cryopump systems with quick regeneration feature, turbomolecular pumps with magnetic bearings, the A-Series vacuum gauges, the TRANSPECTOR and XPR mass spectrometer transmitters, leak detectors in the UL series, and the ECOTEC 500 leak detector for refrigerants and many other gases. Moreo- ver, the present edition of the “Fundamentals” goes into much greater detail on some topics. Among these are residual gas analyses at low pressures, measurement of low pressures, pressure monitoring, open- and closed-loop pressure control, and leaks and their detection. Included for the first time are the sections covering the devices used to measure and control the application of coatings and uses for vacuum technology in the coating process. Naturally LEYBOLD’s “Vacuum Technology Training Center” at Cologne was dependent on the invaluable support of numerous associates in collating the literature on hand and preparing new sections; I would like to expressly thank all those indi- viduals at this juncture. A special word of appreciation is due the Communications Department for its professional contribution in preparing this document for publishing. Regrettably Dr. Hermann Adam, who at one time compiled the very first version of the “Fundamentals”, did not live to see the publication of this edition. Though he had been in retirement for many years, he nonetheless labored over the corrections and editing of this current edition until shortly before his death. I hope that this volume will enjoy a response as favorable as the previous version.

Dr. Walter Umrath Cologne, August, 1998

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Contents Fundamentals of Vacuum Technology

1. Vacuum physics Quantities, 2.1.6.4 Pump fluid backstreaming 2.3.4 Evacuation of a chamber their symbols, units of and its suppression where gases and vapors measure and definitions . . .7 (Vapor barriers, baffles) . . .39 are evolved ...... 66 1.1 Basic terms and concepts 2.1.6.5 Water jet pumps and 2.3.5 Selection of pumps for in vacuum technology ...... 7 steam ejectors ...... 40 drying processes ...... 66 1.2 Atmospheric air ...... 10 2.1.7 Turbomolecular pumps . . . .41 2.3.6 Flanges and their seals . . . .67 1.3 Gas laws and models . . . . .11 2.1.8 Sorption pumps ...... 45 2.3.7 Choice of suitable valves . . .68 1.3.1 Continuum theory ...... 11 2.1.8.1 Adsorption pumps ...... 45 2.3.8 Gas locks and seal-off 1.3.2 Kinetic gas theory ...... 11 2.1.8.2 Sublimation pumps ...... 46 fittings ...... 69 1.4 The pressure ranges in 2.1.8.3 Sputter-ion pumps ...... 46 vacuum technology and 2.1.8.4 Non evaporable getter 3. Vacuum measurement, their characterization . . . . . 12 pumps (NEG pumps) . . . . .48 monitoring, control and 1.5 Types of flow and 2.1.9 Cryopumps ...... 49 regulation ...... 70 conductance ...... 12 2.1.9.1 Types of cryopump ...... 49 3.1 Fundamentals of low- 1.5.1 Types of flow ...... 12 2.1.9.2 The cold head and its pressure measurement . . . .70 1.5.2 Calculating conductance operating principle ...... 50 3.2 Vacuum gauges with values ...... 13 2.1.9.3 The refrigerator cryopump .51 pressure reading that is 1.5.3 Conductance for piping 2.1.9.4 Bonding of gases to cold independent of the type and openings ...... 14 surfaces ...... 51 of gas ...... 72 1.5.4 Conductance values for 2.1.9.5 Pumping speed and position 3.2.1 Bourdon vacuum gauges . . .72 other elements ...... 15 of the cryopanels ...... 52 3.2.2 Diaphragm vacuum 2.1.9.6 Characteristic quantities of a gauges ...... 72 2. Vacuum Generation . . . . .16 cryopump ...... 53 3.2.2.1 Capsule vacuum gauges . . .72 2.1 Vacuum pumps: A survey .16 2.2 Choice of pumping 3.2.2.2 DIAVAC diaphragm vacuum 2.1.1 Oscillation displacement process ...... 56 gauge ...... 72 vacuum pumps ...... 17 2.2.1 Survey of the most usual 3.2.2.3 Precision diaphragm 2.1.1.1 Diaphragm pumps ...... 17 pumping processes ...... 56 vacuum gauges ...... 72 2.1.2 Liquid sealed rotary 2.2.2 Pumping of gases 3.2.2.4 Capacitance diaphragm displacement pumps ...... 17 (dry processes) ...... 57 gauges ...... 73 2.1.2.1 Liquid ring pumps ...... 17 2.2.3 Pumping of gases and 3.2.3 Liquid-filled (mercury) 2.1.2.2 Oil sealed rotary vapors (wet processes) . . . .58 vacuum gauges ...... 74 displacement pumps ...... 18 2.2.4 Drying processes ...... 60 3.2.3.1 U-tube vacuum gauges . . . .74 2.1.2.2.1 Rotary vane pumps 2.2.5 Production of an oil-free 3.2.3.2 Compression vacuum (TRIVAC A, TRIVAC B, (hydrocarbon-free) gauges (according to TRIVAC E, SOGEVAC) . . . . .18 vacuum ...... 60 McLeod) ...... 74 2.1.2.2.2 Rotary plunger pumps 2.2.6 Ultrahigh vacuum working 3.3 Vacuum gauges with (E-Pumps) ...... 20 Techniques ...... 61 gas-dependent pressure 2.1.2.2.3 Trochoid pumps ...... 21 2.3 Evacuation of a vacuum reading ...... 75 2.1.2.2.4 The gas ballast ...... 21 chamber and determination 3.3.1 Spinning rotor gauge 2.1.3 Dry compressing rotary of pump sizes ...... 62 (SRG) (VISCOVAC) ...... 75 displacement pumps ...... 24 2.3.1 Evacuation of a vacuum 3.3.2 Thermal conductivity 2.1.3.1 Roots pumps ...... 24 chamber (without additional vacuum gauges ...... 76 2.1.3.2 Claw pumps ...... 27 sources of gas or vapor) . . .62 3.3.3 Ionization vacuum gauges . .77 2.1.3.2.1 Claw pumps with internal 2.3.1.1 Evacuation of a chamber 3.3.3.1 Cold-cathode ionization compression for the in the rough vacuum vacuum gauges (Penning semiconductor industry region ...... 62 vacuum gauges) ...... 77 (“DRYVAC Series”) ...... 28 2.3.1.2 Evacuation of a chamber 3.3.3.2 Hot-cathode ionization 2.1.3.2.2 Claw pump without internal in the high vacuum vacuum gauges ...... 78 compression for chemistry region ...... 63 3.4 Adjustment and calibration; applications (“ALL·ex”) . . . .31 2.3.1.3 Evacuation of a chamber in DKD, PTB national 2.1.4 Accessories for oil-sealed the medium vacuum standards ...... 81 rotary displacement region ...... 63 3.4.1 Examples of fundamental pumps ...... 33 2.3.2 Determination of a suitable pressure measurement 2.1.5 Condensers ...... 33 backing pump ...... 64 methods (as standard 2.1.6 Fluid-entrainment pumps . .35 2.3.3 Determination of methods for calibrating 2.1.6.1 (Oil) Diffusion pumps . . . . .36 pump-down time from vacuum gauges ...... 81 2.1.6.2 Oil vapor ejector pumps . . .38 nomograms ...... 65 3.5 Pressure monitoring, control D00 2.1.6.3 Pump fluids ...... 39 and regulation in vacuum systems ...... 83

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3.5.1 Fundamentals of pressure 4.6.4 Quantitative gas analysis . .101 5.5.2.4 Leak detectors with monitoring and control . . . .83 4.7 Software ...... 102 quadrupole mass 3.5.2 Automatic protection, 4.7.1 Standard SQX software spectrometer monitoring and control (DOS) for stand-alone (ECOTEC II) ...... 113 of vacuum systems ...... 83 operation(1 MS plus, 5.5.2.5 Helium leak detectors 3.5.3 Pressure regulation and 1 PC, RS 232) ...... 102 with 180° sector mass control in rough and 4.7.2 Multiplex/DOS software spectrometer medium vacuum MQX (1 to 8 MS plus (UL 200, UL 500) ...... 114 systems ...... 84 1 PC, RS 485) ...... 102 5.5.2.6 Direct-flow and 3.5.4 Pressure regulation in 4.7.3 Process-oriented software – counter-flow leak high and ultrahigh Transpector-Ware for detectors ...... 115 vacuum systems ...... 87 Windows ...... 102 5.5.2.7 Partial flow operation . . . .115 3.5.5 Examples of applications 4.7.4 Development software 5.5.2.8 Connection to vacuum with diaphragm TranspectorView ...... 102 systems ...... 116 controllers ...... 88 4.8 Partial pressure 5.5.2.9 Time constants ...... 116 regulation ...... 102 5.6 Limit values / Specifications 4. Analysis of gas at low 4.9 Maintenance ...... 103 for the leak detector . . . . .117 pressures using mass 5.7 Leak detection techniques spectrometry ...... 89 5. Leaks and their using helium leak 4.1 General ...... 89 detection ...... 104 detectors ...... 117 4.2 A historical review ...... 89 5.1 Types of leaks ...... 104 5.7.1 Spray technique 4.3 The quadrupole mass 5.2 Leak rate, leak size, (local leak test) ...... 117 spectrometer mass flow ...... 104 5.7.2 Sniffer technology (TRANSPECTOR) ...... 89 5.2.1 The standard helium (local leak testing using 4.3.1 Design of the sensor ...... 90 leak rate ...... 106 the positive pressure 4.3.1.1 The normal (open) 5.2.2 Conversion equations . . . .106 method) ...... 118 ion source ...... 90 5.3 Terms and definitions . . . .106 5.7.3 Vacuum envelope test 4.3.1.2 The quadrupole 5.4 Leak detection methods (integral leak test) ...... 118 separation system ...... 91 without a leak detector 5.7.3.1 Envelope test – test 4.3.1.3 The measurement unit ...... 107 specimen pressurized system (detector) ...... 92 5.4.1 Pressure rise test ...... 107 with helium ...... 118 4.4 Gas admission and 5.4.2 Pressure drop test ...... 108 a) Envelope test with pressure adaptation ...... 93 5.4.3 Leak test using vacuum concentration measur 4.4.1 Metering valve ...... 93 gauges which are sensitive ement and subsequent 4.4.2 Pressure converter ...... 93 to the type of gas ...... 108 leak rate calculation . . .118 4.4.3 Closed ion source (CIS) . . .93 5.4.4 Bubble immersion test . . .109 b) Direct measurement of 4.4.4 Aggressive gas monitor 5.4.5 Foam-spray test ...... 109 the leak rate with the (AGM) ...... 94 5.4.6 Vacuum box check bubble .109 leak detector 4.5 Descriptive values in 5.4.7 Krypton 85 test ...... 109 (rigid envelope) ...... 118 mass spectrometry 5.4.8 High-frequency vacuum 5.7.3.2 Envelope test with test (specifications) ...... 94 test ...... 109 specimen evacuated . . . . .118 4.5.1 Line width (resolution) . . . .94 5.4.9 Testing with chemical a) Envelope = 4.5.2 Mass range ...... 95 reactions and dye “plastic tent” ...... 118 4.5.3 Sensitivity ...... 95 penetration ...... 110 b) Rigid envelope ...... 119 4.5.4 Smallest detectable 5.5 Leak detectors and how 5.7.4 “Bombing” test, partial pressure ...... 95 they work ...... 110 “Storage under pressure” .119 4.5.5 Smallest detectable 5.5.1 Halogen leak detectors 5.8 Industrial leak testing . . . .119 partial pressure ratio (HLD 4000, D-Tek) ...... 110 (concentration) ...... 95 5.5.2 Leak detectors with 6. Thin film controllers and 4.5.6 Linearity range ...... 95 mass spectrometers (MS) .110 control units with quartz 4.5.7 Information on surfaces 5.5.2.1 The operating principle oscillators ...... 120 and amenability to for a MSLD ...... 111 6.1 Introduction ...... 120 bake-out ...... 95 5.5.2.2 Detection limit, background, 6.2 Basic principles of coating 4.6 Evaluating spectra ...... 96 gas storage in oil (gas ballast), thickness measurement 4.6.1 Ionization and fundamental floating zero-point with quartz oscillators . . . .120 problems in gas analysis . . .96 suppression ...... 111 6.3 The shape of quartz 4.6.2 Partial pressure 5.5.2.3 Calibrating leak detectors; oscillator crystals ...... 121 measurement ...... 100 test leaks ...... 112 6.4 Period measurement . . . . .122 4.6.3 Qualitative gas analysis . . .100 6.5 The Z match technique . . .122

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6.6 The active oscillator . . . . .122 8.3.1.4 Operating defects while Tab VI Conversion of pumping 6.7 The mode-lock oscillator . .123 pumping with gas ballast – speed (volume flow rate) 6.8 Auto Z match technique . .124 potential sources of error units ...... 144 6.9 Coating thickness where the required ultimate Tab VII Conversion of throughput regulation ...... 125 pressure is not achieved . .137 (a,b) QpV units; leak rate 6.10 INFICON instrument 8.3.2 Roots pumps ...... 137 units ...... 144 variants ...... 127 8.3.2.1 General operating Tab VIII Composition of instructions, installation atmospheric air ...... 145 7. Application of vacuum and commissioning ...... 137 Tab IX Pressure ranges used in technology for coating 8.3.2.2 Oil change, maintenance vacuum technology and their techniques ...... 128 work ...... 137 characteristics ...... 145 7.1 Vacuum coating 8.3.2.3 Actions in case of Tab X Outgassing rate of technique ...... 128 operational disturbances . .138 materials ...... 145 7.2 Coating sources ...... 128 8.3.3 Turbomolecular pumps . . .138 Tab XI Nominal internal diameters 7.2.1 Thermal evaporators 8.3.3.1 General operating (DN) and internal diameters (boats, wires etc.) ...... 128 instructions ...... 138 of tubes, pipes and apertures 7.2.2 Electron beam 8.3.3.2 Maintenance ...... 138 with circular cross-section evaporators 8.3.4 Diffusion and vapor-jet (according to PNEUROP). .146 (electron guns) ...... 129 vacuum pumps ...... 139 Tab XII Important data for 7.2.3 Cathode sputtering ...... 129 8.3.4.1 Changing the pump fluid common solvents ...... 146 7.2.4 Chemical vapor and cleaning the pump . . .139 Tab XIII Saturation pressure and deposition ...... 129 8.3.4.2 Operating errors with density of water ...... 147 7.3 Vacuum coating diffusion and vapor-jet Tab XIV Hazard classificationof technology/coating pumps ...... 139 fluids ...... 148 systems ...... 130 8.3.5 Adsorption pumps ...... 139 Tab XV Chemical resistance of 7.3.1 Coating of parts ...... 130 8.3.5.1 Reduction of adsorption commonly used elastomer 7.3.2 Web coating ...... 130 capacity ...... 139 gaskets and sealing 7.3.3 Optical coatings ...... 131 8.3.5.2 Changing the molecular materials ...... 149 7.3.4 Glass coating ...... 132 sieve ...... 139 Tab XVI Symbols used invacuum 7.3.5 Systems for producing 8.3.6 Titanium sublimation technology ...... 152 data storage disks ...... 132 pumps ...... 140 Tab XVII Temperature comparison 8.3.7 Sputter-ion pumps ...... 140 and conversion table . . . . .154 8. Instructions for vacuum 8.4 Information on working Fig. 9.1 Variation of mean free path equipment operation . . . .134 with vacuum gauges . . . . .140 l (cm) with pressure for 8.1 Causes of faults where the 8.4.1 Information on installing various gases ...... 154 desired ultimate pressure vacuum sensors ...... 140 Fig. 9.2 Diagram of kinetics of is not achieved or is 8.4.2 Contamination at the gases for air at 20 °C . . . .154 achieved too slowly . . . . .134 measurement system and Fig. 9.3 Decrease in air pressure 8.2 Contamination of vacuum its removal ...... 141 and change in vessels and eliminating 8.4.3 The influence of magnetic temperature as a contamination ...... 134 and electrical fields ...... 141 function of altitude ...... 155 8.3 General operating infor- 8.4.4 Connectors, power pack, Fig. 9.4 Change in gas composition mation for vacuum measurement systems . . .141 of the atmosphere as a pumps ...... 134 function of altitude ...... 155 8.3.1 Oil-sealed rotary vacuum 9. Tables, formulas, Fig. 9.5 Conductance values for pumps (Rotary vane nomograms, diagrams piping of commonly used pumps and rotary piston and symbols ...... 142 nominal internal diameters pumps) ...... 135 Tab I Permissible pressure units with circular cross-section 8.3.1.1 Oil consumption, oil including the torr and its for molecular flow ...... 155 contamination, oil conversion ...... 142 Fig. 9.6 Conductance values for change ...... 135 Tab II Conversion of pressure piping of commonly used 8.3.1.2 Selection of the pump oil units ...... 142 nominal internal diameters when handling Tab III Mean free path ...... 142 with circular cross-section aggressive vapors ...... 135 Tab IV Compilation of important for molecular flow ...... 155 8.3.1.3 Measures when pumping formulas pertaining to the Fig. 9.7 Nomogram for various chemical kinetic theory of gases . . .143 determination of substances ...... 136 Tab V Important values ...... 143 pump-down time tp of a D00 vessel in the rough vacuum pressure range . . .156

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Fig. 9.8 Nomogram for 10.3 Remarks on alphabetical determination of the list in Section 10.2 ...... 168 conductance of tubes with 10.4 Tables ...... 170 a circular cross-section 10.4.1 Basic SI units ...... 170 for air at 20 °C in the 10.4.2 Derived coherent SI units region of molecular flow . .157 with special names Fig. 9.9 Nomogram for and symbols ...... 170 determination of 10.4.3 Atomic units ...... 170 conductance of tubes in 10.4.4 Derived noncoherent SI the entire pressure range .158 units with special names Fig. 9.10 Determination of and symbols ...... 170 pump-down time in the medium vacuum range 11. National and international taking into account the standards and evolution of gas from recommendations the walls ...... 159 particularly relevant to Fig.9.11 Saturation vapor vacuum technology . . . . .171 pressure of various 11.1 National and international substances ...... 160 standards and Fig. 9.12 Saturation vapor pressure recommendations of of pump fluids for oil and special relevance to mercury fluid entrainment vacuum technology ...... 171 pumps ...... 160 Fig. 9.13 Saturation vapor pressure 12. References ...... 174 of major metals used in vacuum technology ...... 160 13. Index ...... 184 Fig. 9.14 Vapor pressure of nonmetallic sealing materials (the vapor pressure curve for fluoro rubber lies between the curves for silicone rubber and Teflon)...... 161 Fig. 9.15 Saturation vapor pressure ps of various substances relevant for cryogenic technology in a temperaturerange of T = 2 – 80 K...... 161 Fig. 9.16 Common working ranges of vacuum pumps ...... 161 Fig. 9.16a Measurement ranges of common vacuum gauges ...... 162 Fig. 9.17 Specific volume of saturated water vapor . . . .163 Fig. 9.18 Breakdown voltage between electrodes for air (Paschen curve) ...... 163 Fig 9.19 Phase diagram of water . . .164

10. The statutory units used in vacuum technology . . . . .165 10.1 Introduction ...... 165 10.2 Alphabetical list of variables, symbols and units frequently used in vacuum technology and its applications ...... 165

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all the non-condensable components temperature is gas in equilibrium with the 1. Quantities, present in the mix – in case of the “parti- liquid phase of the same substance. A al ultimate pressure” at a rotary vane strict differentiation between gases and their symbols, pump, for example. vapors will be made in the comments units of which follow only where necessary for Saturation vapor pressure ps complete understanding. The pressure of the saturated vapor is measure and referred to as saturation vapor pressure Particle number density n (cm-3) ps. ps will be a function of temperature for According to the kinetic gas theory the definitions any given substance. number n of the gas molecules, referenced to the volume, is dependent on pressure p Vapor pressure p (cf. DIN 28 400, Part 1, 1990, d and thermodynamic temperature T as Partial pressure of those vapors which can expressed in the following: DIN 1314 and DIN 28 402) be liquefied at the temperature of liquid p = n · k · T (1.1) nitrogen (LN2). n = particle number density 1.1 Basic terms and Standard pressure pn k = Boltzmann’s constant Standard pressure pn is defined in DIN concepts in At a certain temperature, therefore, the 1343 as a pressure of pn = 1013.25 mbar. vacuum technology pressure exerted by a gas depends only on the particle number density and not on the Ultimate pressure pend Pressure p (mbar) The lowest pressure which can be achie- nature of the gas. The nature of a gaseous of fluids (gases and liquids). (Quantity: ved in a vacuum vessel. The socalled ulti- particle is characterized, among other factors, by its mass m . pressure; symbol: p; unit of measure: mate pressure pend depends not only on T millibar; abbreviation: mbar.) Pressure is the pump’s suction speed but also upon ρ -3 -3 defined in DIN Standard 1314 as the the vapor pressure pd for the lubricants, Gas density (kg · m , g · cm ) quotient of standardized force applied to a sealants and propellants used in the pump. The product of the particle number densi- surface and the extent of this surface If a container is evacuated simply with an ty n and the particle mass mT is the gas (force referenced to the surface area). oil-sealed rotary (positive displacement) density ρ: Even though the Torr is no longer used as vacuum pump, then the ultimate pressure ρ = n · m (1.2) a unit for measuring pressure (see Section which can be attained will be determined T 10), it is nonetheless useful in the interest primarily by the vapor pressure of the of “transparency” to mention this pressure pump oil being used and, depending on The ideal gas law unit: 1 Torr is that gas pressure which is the cleanliness of the vessel, also on the The relationship between the mass mT of a able to raise a column of mercury by 1 mm vapors released from the vessel walls and, gas molecule and the molar mass M of this at 0 °C. (Standard atmospheric pressure is of course, on the leak tightness of the gas is as follows: 760 Torr or 760 mm Hg.) Pressure p can vacuum vessel itself. M = N · m (1.3) be more closely defined by way of sub- A T Ambient pressure pamb scripts: Avogadro’s number (or constant) NA or (absolute) atmospheric pressure indicates how many gas particles will be Absolute pressure pabs contained in a mole of gas. In addition to Absolute pressure is always specified in Overpressure pe or gauge pressure this, it is the proportionality factor between vacuum technology so that the “abs” index (Index symbol from “excess”) the gas constant R and Boltzmann’s can normally be omitted. constant k: pe = pabs – pamb R = NA · k (1.4) Total pressure pt Here positive values for pe will indicate The total pressure in a vessel is the sum of overpressure or gauge pressure; negative Derivable directly from the above the partial pressures for all the gases and values will characterize a vacuum. equations (1.1) to (1.4) is the correlation vapors within the vessel. between the pressure ρ and the gas Working pressure pW density ρ of an ideal gas. During evacuation the gases and/or vapors Partial pressure pi are removed from a vessel. Gases are R · T The partial pressure of a certain gas or p = ρ ⋅ ––––– (1.5) vapor is the pressure which that gas or understood to be matter in a gaseous state M vapor would exert if it alone were present which will not, however, condense at in the vessel. working or operating temperature. Vapor In practice we will often consider a certain is also matter in a gaseous state but it may enclosed volume V in which the gas is Important note: Particularly in rough be liquefied at prevailing temperatures by present at a certain pressure p. If m is the D00 vacuum technology, partial pressure in a increasing pressure. Finally, saturated mass of the gas present within that mix of gas and vapor is often understood vapor is matter which at the prevailing volume, then to be the sum of the partial pressures for

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m ture this is always equivalent to reducing Quantity of gas (pV value), (mbar ⋅ l) ρ = ––– (1.6) the gas pressure p. Explicit attention must V The quantity of a gas can be indicated by at this point be drawn to the fact that a way of its mass or its weight in the units of The ideal gas law then follows directly reduction in pressure (maintaining the measure normally used for mass or from equation (1.5): volume) can be achieved not only by weight. In practice, however, the product reducing the particle number density n but of p · V is often more interesting in vacu- m p ⋅ V = ––– ⋅ R ⋅ T = ν ⋅ R ⋅ T (1.7) also (in accordance with Equation 1.5) by um technology than the mass or weight of M reducing temperature T at constant gas a quantity of gas. The value embraces an density. This important phenomenon will energy dimension and is specified in Here the quotient m / M is the number of always have to be taken into account millibar·liters (mbar·l) (Equation 1.7). moles u present in volume V. where the temperature is not uniform Where the nature of the gas and its The simpler form applies for m / M = 1, i.e. throughout volume V. temperature are known, it is possible to for 1 mole: use Equation 1.7b to calculate the mass m The following important terms and for the quantity of gas on the basis of the p · V = R · T (1.7a) concepts are often used in vacuum product of p · V: technology: The following numerical example is intended to illustrate the correlation p·V= m ·R·T (1.7) Volume V (l, m3, cm3) between the mass of the gas and pressure M The term volume is used to designate for gases with differing molar masses, a) the purely geometric, usually predeter- drawing here on the numerical values in p·V ·M mined, volumetric content of a vacuum m = (1.7b) Table IV (Chapter 9). Contained in a R ·T chamber or a complete vacuum system 10-liter volume, at 20 °C, will be including all the piping and connecting a) 1g of helium spaces (this volume can be calculated); Although it is not absolutely correct, b) 1g of nitrogen b) the pressure-dependent volume of a reference is often made in practice to the When using the equation (1.7) there gas or vapor which, for example, is “quantity of gas” p · V for a certain gas. results then at V = 10 l , m = 1 g, moved by a pump or absorbed by an This specification is incomplete; the R = 83.14 mbar·l·mol-1·K-1, adsorption agent. temperature of the gas T, usually room T = 293 K (20 °C) temperature (293 K), is normally implicitly assumed to be known. In case a) where M = 4 g · mole-1 Volumetric flow (flow volume) qv 3 3 (monatomic gas): (l/s, m /h, cm /s) Example: The term “flow volume” designates the The mass of 100 mbar · l of nitrogen (N2) 1··g· 83. 14 mbar··` mol––11 · K ·· 293 K volume of the gas which flows through a p = = at room temperature (approx. 300 K) is: 10···`·Kgmol 4 · –1 piping element within a unit of time, at the −1 = 609 mbar pressure and temperature prevailing at the 100mbar··` 28 g ·mol m= −− = particular moment. Here one must realize 83mbar ··`mol 11 ·K · 300K In case b), with M = 28 ≠ g mole-1 (diato- that, although volumetric flow may be 2800 mic gas): identical, the number of molecules moved = gg=0. 113 may differ, depending on the pressure and 300· 83 1··g· 83. 14 mbar··` mol––11 · K ·· 293 K p = = temperature. –1 10···`·Kgmol 28 · Analogous to this, at T = 300 K: = 87 mbar Pumping speed S (l/s, m3/h, cm3/s) -3 The pumping speed is the volumetric flow 1 mbar · l O2 = 1.28 · 10 g O2 The result, though appearing to be through the pump’s intake port. paradoxical, is that a certain mass of a -1 dV 70 mbar · l Ar = 1.31 · 10 g Ar light gas exerts a greater pressure than the S = –––– (1.8a) same mass of a heavier gas. If one takes dt The quantity of gas flowing through a into account, however, that at the same piping element during a unit of time – in If S remains constant during the pumping gas density (see Equation 1.2) more accordance with the two concepts for gas process, then one can use the difference particles of a lighter gas (large n, small m) quantity described above – can be indica- quotient instead of the differential quoti- will be present than for the heavier gas ted in either of two ways, these being: ent: (small n, large m), the results become more understandable since only the ∆V Mass flow qm (kg/h, g/s), S = ––– (1.8b) this is the quantity of a gas which flows particle number density n is determinant ∆t for the pressure level, assuming equal through a piping element, referenced to temperature (see Equation 1.1). (A conversion table for the various units of time measure used in conjunction with m The main task of vacuum technology is to q = ––– or as pumping speed is provided in Section 9, m reduce the particle number density n insi- t Table VI). de a given volume V. At constant tempera-

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Vacuum Physics Fundamentals of Vacuum Technology

-1 -1 -1 pV flow qpV (mbar·l·s ). Conductance C (l · s ) Leak rate qL (mbar·l·s ) pV flow is the product of the pressure and The pV flow through any desired piping According to the definition formulated volume of a quantity of gas flowing element, i.e. pipe or hose, valves, nozzles, above it is easy to understand that the size through a piping element, divided by time, openings in a wall between two vessels, of a gas leak, i.e. movement through unde- i.e.: etc., is indicated with sired passages or “pipe” elements, will also be given in mbar·l·s-1. A leak rate is q = C(p1 – p2) = ∆p · C (1.11) p · V d (p · V) pV often measured or indicated with atmos- qpV = –––––– = –––––––– t dt Here ∆p = (p1 – p2) is the differential bet- pheric pressure prevailing on the one side ween the pressures at the inlet and outlet of the barrier and a vacuum at the other pV flow is a measure of the mass flow of ends of the piping element. The proportio- side (p < 1 mbar). If helium (which may be the gas; the temperature to be indicated nality factor C is designated as the con- used as a tracer gas, for example) is pas- here. ductance value or simply “conductance”. It sed through the leak under exactly these is affected by the geometry of the piping conditions, then one refers to “standard Pump throughput qpV element and can even be calculated for helium conditions”. The pumping capacity (throughput) for a some simpler configurations (see Section Outgassing (mbar·l) pump is equal either to the mass flow 1.5). through the pump intake port: The term outgassing refers to the liberati- In the high and ultrahigh vacuum ranges, on of gases and vapors from the walls of a m C is a constant which is independent of q = –––– (1.9) vacuum chamber or other components on m pressure; in the rough and medium-high t the inside of a vacuum system. This quan- regimes it is, by contrast, dependent on tity of gas is also characterized by the pro- or to the pV flow through the pump’s inta- pressure. As a consequence, the calculati- duct of p · V, where V is the volume of the ke port: on of C for the piping elements must be vessel into which the gases are liberated, carried out separately for the individual and by p, or better ∆p, the increase in p · V pressure ranges (see Section 1.5 for more pressure resulting from the introduction of qpV = –––––– t detailed information). gases into this volume. From the definition of the volumetric flow It is normally specified in mbar·l·s-1. Here Outgassing rate (mbar·l·s-1) it is also possible to state that: The p is the pressure on the intake side of the This is the outgassing through a period of conductance value C is the flow volume pump. If p and V are constant at the intake time, expressed in mbar·l·s-1. side of the pump, the throughput of this through a piping element. The equation (1.11) could be thought of as “Ohm’s law pump can be expressed with the simple Outgassing rate (mbar·l·s-1 · cm-2) for vacuum technology”, in which q equation pV (referenced to surface area) corresponds to current, ∆p the voltage and In order to estimate the amount of gas q = p · S (1.10a) C the electrical conductance value. Analo- pV which will have to be extracted, knowledge gous to Ohm’s law in the science of elec- of the size of the interior surface area, its where S is the pumping speed of the pump tricity, the resistance to flow at intake pressure of p. material and the surface characteristics, 1 their outgassing rate referenced to the sur- (The throughput of a pump is often indica- R = ––– C face area and their progress through time ted with Q, as well.) are important. The concept of pump throughput is of has been introduced as the reciprocal major significance in practice and should value to the conductance value. The Mean free path of the molecules λ (cm) not be confused with the pumping speed! equation (1.11) can then be re-written as: and collision rate z (s-1) The pump throughput is the quantity of 1 The concept that a gas comprises a large ⋅ ∆ gas moved by the pump over a unit of qpV = —— p (1.12) number of distinct particles between which time, expressed in mbar ≠ l/s; the pum- R – aside from the collisions – there are no ping speed is the “transportation capacity” The following applies directly for connec- effective forces, has led to a number of which the pump makes available within a tion in series: theoretical considerations which we sum- specific unit of time, measured in m3/h marize today under the designation “kine- or l/s. R∑ = R1 + R2 + R3 . . . (1.13) tic theory of gases”. The throughput value is important in deter- When connected in parallel, the following One of the first and at the same time most mining the size of the backing pump in applies: beneficial results of this theory was the relationship to the size of a high vacuum calculation of gas pressure p as a function pump with which it is connected in series 1 1 1 1 ––– = –– + –– + –– + ⋅ ⋅ ⋅ ⋅ (1.13a) of gas density and the mean square of in order to ensure that the backing pump 2 R∑ R1 R2 R3 velocity c for the individual gas molecules will be able to “take off” the gas moved by in the mass of molecules mT: D00 the high vacuum pump (see Section 2.32).

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1 --- 1 --- Impingement rate z (cm-2 ⋅ s-1) and ρ ⋅ 2 ⋅ ⋅ ⋅ 2 A 1.2 Atmospheric air p = –– c = –– n mT c (1.14) τ 3 3 monolayer formation time (s) A technique frequently used to characteri- Prior to evacuation, every vacuum system where ze the pressure state in the high vacuum on earth contains air and it will always be regime is the calculation of the time requi- surrounded by air during operation. This k · T red to form a monomolecular or monoato- makes it necessary to be familiar with the c2 = 3 ⋅ ——– (1.15) m mic layer on a gas-free surface, on the physical and chemical properties of T assumption that every molecule will stick atmospheric air. to the surface. This monolayer formation The gas molecules fly about and among The atmosphere is made up of a number of time is closely related with the so-called each other, at every possible velocity, and gases and, near the earth’s surface, water impingement rate z . With a gas at rest the bombard both the vessel walls and collide A vapor as well. The pressure exerted by impingement rate will indicate the number (elastically) with each other. This motion of atmospheric air is referenced to sea level. of molecules which collide with the surfa- the gas molecules is described numerical- Average atmospheric pressure is ce inside the vacuum vessel per unit of ly with the assistance of the kinetic theory 1013 mbar (equivalent to the “atmos- time and surface area: of gases. A molecule’s average number of phere”, a unit of measure used earlier). collisions over a given period of time, the n·c Table VIII in Chapter 9 shows the compo- so-called collision index z, and the mean z = (1.20) A 4 sition of the standard atmosphere at relati- path distance which each gas molecule ve humidity of 50 % and temperature of covers between two collisions with other If a is the number of spaces, per unit of 20 °C. In terms of vacuum technology the molecules, the so-called mean free path surface area, which can accept a specific following points should be noted in regard λ length , are described as shown below as gas, then the monolayer formation time is to the composition of the air: - a function of the mean molecule velocity c a) The water vapor contained in the air, a 4·a the molecule diameter 2r and the particle τ = = (1.21) varying according to the humidity level, z n·c number density molecules n – as a very A plays an important part when evacua- good approximation: ting a vacuum plant (see Section 2.2.3). -3 -1 C Collision frequency zv (cm · s ) b) The considerable amount of the inert Z = (1.16) gas argon should be taken into account λ This is the product of the collision rate z and the half of the particle number density in evacuation procedures using sorpti- where n, since the collision of two molecules is to on pumps (see Section 2.1.8). be counted as only one collision: c) In spite of the very low content of heli- 8· k ·T 8· R ·T um in the atmosphere, only about 5 c = = π (1.17) n ppm (parts per million), this inert gas ·mT π · M zV = ·z (1.21a) 2 makes itself particularly obvious in ultrahigh vacuum systems which are and sealed with Viton or which incorporate 1 glass or quartz components. Helium is λ = (1.18) π · 2 ·n ·(2r)2 able to permeate these substances to a measurable extent. Thus the mean free path length λ for the The pressure of atmospheric air falls with particle number density n is, in accordan- rising altitude above the earth’s surface ce with equation (1.1), inversely proportio- (see Fig. 9.3 in Chapter 9). High vacuum nal to pressure p. Thus the following rela- prevails at an altitude of about 100 km and tionship holds, at constant temperature T, ultrahigh vacuum above 400 km. The com- for every gas position of the air also changes with the distance to the surface of the earth (see λ ⋅ p = const (1.19) Fig. 9.4 in Chapter 9). Used to calculate the mean free path length λ for any arbitrary pressures and various gases are Table III and Fig. 9.1 in Chapter 9. The equations in gas kinetics which are most important for vacuum technology are also summarized (Table IV) in chapter 9.

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1.3 Gas laws and Ideal gas Law change of direction through 180 °, will be equal to 2 · m · c. The sum of the pulse m T p ·V = ·R ·T = ν·R ·T changes for all the molecules impinging on models M the wall will result in a force effective on 1.3.1 Continuum theory this wall or the pressure acting on the wall, Also: Equation of state for ideal gases per unit of surface area. Model concept: Gas is “pourable” (fluid) (from the continuum theory) n 1 and flows in a way similar to a liquid. The 2 ·c·2·mT ·c = ·n·c ·mT = p continuum theory and the summarization van der Waals’ Equation 6 3 of the gas laws which follows are based on a − experience and can explain all the proces- (p + )·(Vm b) = R·T where V2 ses in gases near atmospheric pressure. m N Only after it became possible using ever n = V better vacuum pumps to dilute the air to a, b = constants the extent that the mean free path rose far (internal pressure, covolumes) beyond the dimensions of the vessel were Vm = Molar volume Derived from this is Also: Equation of state for real gases more far-reaching assumptions necessary; 1 p·V = · N · m ·c2 these culminated in the kinetic gas theory. 3 T The kinetic gas theory applies throughout Clausius-Clapeyron Equation the entire pressure range; the continuum dp theory represents the (historically older) LT= áá()VV− Ideal gas law (derived from the kinetic dT mv,, ml special case in the gas laws where atmos- gas theory) 2 –2 pheric conditions prevail. L = Enthalpy of evaporation, If one replaces c with c then a compari- T = Evaporation temperature, son of these two “general” gas equations Summary of the most important gas laws V V = Molar volumes of vapor will show: (continuum theory) m,v, m,l or liquid m 1 p·V = · R ·T = · N · m · c2 or Boyle-Mariotte Law M 3 T p ⋅ V = const. 1.3.2 Kinetic gas theory 2 for T = constant (isotherm) m · R 2 m · c With the acceptance of the atomic view of p· V = N · ( T ) ·T = · N ·( T ) the world – accompanied by the necessity M 3 2 Gay-Lussac’s Law (Charles’ Law) to explain reactions in extremely dilute V = V (1+ β · t) gases (where the continuum theory fails) – The expression in brackets on the left- 0 the “kinetic gas theory” was developed. hand side is the Boltzmann constant k; that Using this it is possible not only to derive for p = constant (isobar) on the right-hand side a measure of the the ideal gas law in another manner but molecules’ mean kinetic energy: also to calculate many other quantities Amonton’s Law involved with the kinetics of gases – such Boltzmann constant p = p (1+ γ t) as collision rates, mean free path lengths, 0 · m · R − J monolayer formation time, diffusion con- k = T = 1.38 · 10 23 M K for V = constant (isochor) stants and many other quantities. Model concepts and basic assumptions: Mean kinetic energy of the molecules Dalton’s Law 1. Atoms/molecules are points. m · c2 ∑ 2. Forces are transmitted from one to T pi = p total E = i another only by collision. kin 2 3. The collisions are elastic. thus 4. Molecular disorder (randomness) Poisson’s Law 2 prevails. p·V = N·k ·T = ·N · E 3 kin k p ⋅ V = const A very much simplified model was develo- (adiabatic) ped by Krönig. Located in a cube are N In this form the gas equation provides a particles, one-sixth of which are moving gas-kinetic indication of the temperature! Avogadro’s Law toward any given surface of the cube. If m m The mass of the molecules is 1: 2 = M :M the edge of the cube is 1 cm long, then it V V 1 2 1 2 will contain n particles (particle number M Mass / mol density); within a unit of time n · c · ∆t/6 m = = D00 T N Molecules / mol molecules will reach each wall where the A change of pulse per molecule, due to the

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where NA is Avogadro’s number 1.5 Types of flow and (previously: Loschmidt number).   p   ∆p = p 1−  2  conductance crit 1  p  (1.22) Avogadro constant  1 crit ⋅ –1 NA = 6.022 1023 mol Three types of flow are mainly encountered in vacuum technology: viscous or con- A further rise in ∆p > ∆p would not n crit z = · tinuous flow, molecular flow and – at the result in any further rise in gas flow; any For 1 mole, V 2 and transition between these two – the so-cal- increase is inhibited. For air at 20,°C the V = Vm = 22.414 l (molar volume); led Knudsen flow. gas dynamics theory reveals a critical value of Thus from the ideal gas law at standard   conditions 1.5.1 Types of flow p2   = 0.528 (1.23) (Tn = 273.15 K and pn = 1013.25 mbar):  p1 Viscous or continuum flow crit m p·V = ·R·T This will be found almost exclusively in the The chart in Fig. 1.1 represents sche- M rough vacuum range. The character of this matically the venting (or airing) of an eva- type of flow is determined by the interac- cuated container through an opening in the For the general gas constant: tion of the molecules. Consequently inter- envelope (venting valve), allowing ambient nal friction, the viscosity of the flowing 1013.25 mbar · 22.4 `·mol −1 air at p = 1000 mbar to enter. In accordan- R = = substance, is a major factor. If vortex moti- 273.15 K ce with the information given above, the on appears in the streaming process, one resultant critical pressure is mbar · ` speaks of turbulent flow. If various layers ∆ ⋅ ≈ = 83.14 pcrit = 1000 (1–0.528) mbar 470 mbar; mol · K of the flowing medium slide one over the i.e. where ∆p > 470 mbar the flow rate will other, then the term laminar flow or layer be choked; where ∆p < 470 mbar the gas flux may be applied. flow will decline. Laminar flow in circular tubes with para-

bolic velocity distribution is known as Poi- ∆ 1.4 The pressure p qm seuille flow. This special case is found mbar % ranges in vacuum frequently in vacuum technology. Viscous 1 flow will generally be found where the 100 technology and their molecules’ mean free path is considerab- characterization ly shorter than the diameter of the pipe: 2 75 λ « d. 1000 qm (See also Table IX in Chapter 9.) It is com- ∆p 50 mon in vacuum technology to subdivide its A characteristic quantity describing the viscous flow state is the dimensionless wide overall pressure range – which spans 470 more than 16 powers of ten – into smaller Reynolds number Re. 25 individual regimes. These are generally Re is the product of the pipe diameter, flow defined as follows: velocity, density and reciprocal value of the 0 s viscosity (internal friction) of the gas Rough vacuum (RV) 1000 – 1 mbar venting time (t) which is flowing. Flow is turbulent where Medium vacuum (MV) 1 – 10-3.mbar Re > 2200, laminar where Re < 2200. High vacuum (HV) 10-3 – 10-7 mbar 1 Gas flow rate qm choked = constant The phenomenon of choked flow may also (maximum value) Ultrahigh vacuum (UHV) 2 Gas flow not impeded, qm drops to ∆p = 0 10-7 – (10-14) mbar be observed in the viscous flow situation. It plays a part when venting and evacua- This division is, naturally, somewhat arbit- ting a vacuum vessel and where there are Fig. 1.1 Schematic representation of venting an rary. Chemists in particular may refer to leaks. evacuated vessel the spectrum of greatest interest to them, lying between 100 and 1 mbar, as “inter- Gas will always flow where there is a diffe- Molecular flow ∆ mediate vacuum”. Some engineers may rence in pressure p = (p1 – p2) > 0. The Molecular flow prevails in the high and not refer to vacuum at all but instead speak intensity of the gas flow, i.e. the quantity of ultrahigh vacuum ranges. In these regimes of “low pressure” or even “negative pres- gas flowing over a period of time, rises the molecules can move freely, without sure”. The pressure regimes listed above with the pressure differential. In the case any mutual interference. Molecular flow is can, however, be delineated quite satisfac- of viscous flow, however, this will be the present where the mean free path length torily from an observation of the gas-kine- case only until the flow velocity, which also for a particle is very much larger than the tic situation and the nature of gas flow. The rises, reaches the speed of sound. This is diameter of the pipe: λ >> d. operating technologies in the various ran- always the case at a certain pressure diffe- ges will differ, as well. rential and this value may be characterized as “critical”:

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Knudsen flow ratory equipment the collisions of the gas 1.5.2 Calculating The transitional range between viscous particles among each other will predomi- conductance values flow and molecular flow is known as Knud- nate in the rough vacuum range whereas sen flow. It is prevalent in the medium in the high and ultrahigh vacuum ranges The effective pumping speed required to vacuum range: λ ≈ d. impact of the gas particles on the contai- evacuate a vessel or to carry out a process ner walls will predominate. inside a vacuum system will correspond to The product of pressure p and pipe diame- the inlet speed of a particular pump (or the ter d for a particular gas at a certain tem- In the high and ultrahigh vacuum ranges pump system) only if the pump is joined perature can serve as a characterizing the properties of the vacuum container directly to the vessel or system. Practically quantity for the various types of flow. wall will be of decisive importance since speaking, this is possible only in rare situa- -3 Using the numerical values provided in below 10 mbar there will be more gas tions. It is almost always necessary to Table III, Chapter 9, the following equiva- molecules on the surfaces than in the include an intermediate piping system com- lent relationships exist for air at 20 °C: chamber itself. If one assumes a mono- prising valves, separators, cold traps and molecular adsorbed layer on the inside the like. All this represents an resistance to Rough vacuum – Viscous flow wall of an evacuated sphere with 1 l volu- flow, the consequence of which is that the me, then the ratio of the number of d effective pumping speed Seff is always less λ < ⇔ p ⋅ d > 6.0 ⋅ 10-1 mbar ⋅ cm adsorbed particles to the number of free 100 than the pumping speed S of the pump or molecules in the space will be as follows: the pumping system alone. Thus to ensure at 1 mbar 10-2 a certain effective pumping speed at the Medium vacuum – Knudsen flow at 10-6 mbar 10+4 vacuum vessel it is necessary to select a d d -11 +9 pump with greater pumping speed. The < λ < ⇔ at 10 mbar 10 correlation between S and S is indicated 100 2 For this reason the monolayer formation eff by the following basic equation: time t (see Section 1.1) is used to charac- ⇔ 6 ⋅ 10-1 > p ⋅ d > 1.3 ⋅ 10-2 mbar ⋅ cm terize ultrahigh vacuum and to distinguish 1 1 1 = + this regime from the high vacuum range. (1.24) Seff S C High and ultrahigh vacuum – Molecular The monolayer formation time τ is only a flow fraction of a second in the high vacuum Here C is the total conductance value for range while in the ultrahigh vacuum range the pipe system, made up of the individual λ > d ⇔ p ⋅ d < 1.3 ⋅ 10-2 mbar · cm it extends over a period of minutes or values for the various components which 2 hours. Surfaces free of gases can therefo- are connected in series (valves, baffles, In the viscous flow range the preferred re be achieved (and maintained over lon- separators, etc.): ger periods of time) only under ultrahigh speed direction for all the gas molecules 1 1 1 1 1 will be identical to the macroscopic direc- vacuum conditions. = + + + . . . C C C C C (1.25) tion of flow for the gas. This alignment is Further physical properties change as 1 2 3 n compelled by the fact that the gas particles pressure changes. For example, the ther- Equation (1.24) tells us that only in the are densely packed and will collide with mal conductivity and the internal friction of situation where C = ∞ (meaning that the one another far more often than with the gases in the medium vacuum range are flow resistance is equal to 0) will S = S . boundary walls of the apparatus. The highly sensitive to pressure. In the rough eff A number of helpful equations is available macroscopic speed of the gas is a “group and high vacuum regimes, in contrast, to the vacuum technologist for calculating velocity” and is not identical with the “ther- these two properties are virtually indepen- the conductance value C for piping sec- mal velocity” of the gas molecules. dent of pressure. tions. The conductance values for valves, In the molecular flow range, on the other Thus, not only will the pumps needed to cold traps, separators and vapor barriers hand, impact of the particles with the walls achieve these pressures in the various will, as a rule, have to be determined empi- predominates. As a result of reflection (but vacuum ranges differ, but also different rically. also of desorption following a certain resi- vacuum gauges will be required. A clear It should be noted that in general that the dence period on the container walls) a gas arrangement of pumps and measurement conductance in a vacuum component is particle can move in any arbitrary direction instruments for the individual pressure not a constant value which is independent in a high vacuum; it is no longer possible ranges is shown in Figures 9.16 and 9.16a of prevailing vacuum levels, but rather to speak of “flow” in the macroscopic in Chapter 9. depends strongly on the nature of the flow sense. (continuum or molecular flow; see below) It would make little sense to attempt to and thus on pressure. When using con- determine the vacuum pressure ranges as ductance indices in vacuum technology a function of the geometric operating calculations, therefore, it is always neces- situation in each case. The limits for the sary to pay attention to the fact that only individual pressure regimes (see Table IX the conductance values applicable to a cer- D00 in Chapter 9) were selected in such a way tain pressure regime may be applied in that when working with normal-sized labo- that regime.

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3 1.5.3 Conductance for piping d (1.28b) pumping speeds S*visc and S*mol refer- C = 12.1· `/s and orifices l enced to the area A of the opening and as δ a function of = p2/p1. The equations Conductance values will depend not only given apply to air at 20 °C. The molar mas- In the molecular flow region the conduc- on the pressure and the nature of the gas ses for the flowing gas are taken into con- tance value is independent of pressure! which is flowing, but also on the sectional sideration in the general equations, not The complete Knudsen equation (1.26) will shape of the conducting element (e.g. cir- shown here. cular or elliptical cross section). Other fac- have to be used in the transitional area –2 – -1 Ð1 Ð2 tors are the length and whether the ele- 10 < d · p < 6 · 10 mbar · cm. Conduc- l á s á cm ment is straight or curved. The result is tance values for straight pipes of standard that various equations are required to take nominal diameters are shown in Figure 9.5 into account practical situations. Each of (laminar flow) and Figure 9.6 (molecular these equations is valid only for a particu- flow) in Chapter 9. Additional nomograms lar pressure range. This is always to be for conductance determination will also be considered in calculations. found in Chapter 9 (Figures 9.8 and 9.9). a) Conductance for a straight pipe, which is not too short, of length l, with a circular cross section of diameter d for the laminar, Knudsen and molecular flow ranges, valid for air at 20 °C (Knudsen equation):

d4 d3 1+ 192 ·d · p C = 135 p +12.1 · `/s (1.26) l l 1+ 237 ·d · p Fig. 1.2 Flow of a gas through an opening (A) at high pressures (viscous flow) where b) Conductance value C for an orifice A p + p 2 p = 1 2 (A in cm ): For continuum flow (viscous 2 flow) the following equations (after Prandtl) apply to air at 20 °C where d = Pipe inside diameter in cm p /p = δ: l = Pipe length in cm (l ≥ 10 d) 2 1 δ ≥ p1 = Pressure at start of pipe for 0.528 (1.29) (along the direction of flow) in mbar A ` p = Pressure at end of pipe δ 0.712 −δ 0.288 2 Cvisc = 76.6· · 1 · −δ Fig. 1.3 Conductance values relative to the area, (along the direction of flow) in mbar 1 s C*visc, C*mol, and pumping speed S*visc and S* for an orifice A, depending on the δ ≤ mol If one rewrites the second term in (1.26) in for 0.528 (1.29a) pressure relationship p2/p1 for air at 20 °C. the following form A ` C = 20· When working with other gases it will be visc − δ d3 1 s necessary to multiply the conductance C = 12.1· · f (d · p) (1.26a) l values specified for air by the factors and for δ ≤ 0,03 (1.29b) shown in Table 1.1. with ` Gas (20 °C) Molecular flow Laminar flow 1+ 203·d ·p + 2.78·103 · d2 · p 2 C = 20 · A f (d ·p) = (1.27) visc s Air 1.00 1.00 1+ 237 ·d · p Oxygen 0.947 0.91 δ = 0.528 is the critical pressure Neon 1.013 1.05 it is possible to derive the two important Helium 2.64 0.92 limits from the course of the function f situation for air – Hydrogen 3.77 2.07 (d · p): Carbon dioxide 0.808 1.26  p   2  Water vapor 1.263 1.7  p  Limit for laminar flow 1 crit Table 1.1 Conversion factors (see text) (d · –p > 6 · 10-1 mbar · cm): Flow is choked at δ < 0.528; gas flow is d4 C = 135· · p `/ s (1.28a) thus constant. In the case of molecular l flow (high vacuum) the following will apply for air: Limit for molecular flow -1 2 (d · –p < 6 · 10-2 mbar · cm): Cmol = 11,6 · A · l · s (A in cm ) (1.30) Given in addition in Figure 1.3 are the

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Nomographic determination of conduc- The technical data in the Leybold catalog tance values states the conductance values for vapor The conductance values for piping and barriers, cold traps, adsorption traps and openings through which air and other valves for the molecular flow range. At hig- gases pass can be determined with nomo- her pressures, e.g. in the Knudsen and graphic methods. It is possible not only to laminar flow ranges, valves will have about determine the conductance value for the same conductance values as pipes of piping at specified values for diameter, corresponding nominal diameters and length and pressure, but also the size of axial lengths. In regard to right-angle val- the pipe diameter required when a pum- ves the conductance calculation for an ping set is to achieve a certain effective elbow must be applied. pumping speed at a given pressure and In the case of dust filters which are used to given length of the line. It is also possible protect gas ballast pumps and roots to establish the maximum permissible pipe pumps, the percentage restriction value length where the other parameters are for the various pressure levels are listed in known. The values obtained naturally do the catalog. Other components, namely the not apply to turbulent flows. In doubtful condensate separators and condensers, situations, the Reynolds number Re (see are designed so that they will not reduce Section 1.5.) should be estimated using pumping speed to any appreciable extent. the relationship which is approximated below The following may be used as a rule of qpV thumb for dimensioning vacuum lines: Re = 15· (1.31) d The lines should be as short and as wide as possible. They must exhibit at least the Here qpV = S · p is the flow output in mbar same cross-section as the intake port at l/s, d the diameter of the pipe in cm. the pump. If particular circumstances pre- A compilation of nomograms which have vent shortening the suction line, then it is proved to be useful in practice will be advisable, whenever this is justifiable from found in Chapter 9. the engineering and economic points of view, to include a roots pump in the suction line. This then acts as a gas entrain- 1.5.4 Conductance values for ment pump which reduces line impedance. other elements Where the line contains elbows or other curves (such as in right-angle valves), these can be taken into account by assuming a greater effective length leff of the line. This can be estimated as follows:

θ l = l +1.33· ·d (1.32) eff axial 180°

Where laxial : axial length of the line (in cm) leff : Effective length of the line (in cm) d : Inside diameter of the line (in cm) θ : Angle of the elbow (degrees of angle)

Axial length D00

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the atmosphere (compression pumps). 2. Pumps which transport quantities of 2. Vacuum The gas particles are pumped by means gas from the low pressure side to the of displacement or pulse transfer. high pressure side without changing generation b) Vacuum pumps where the gas particles the volume of the pumping chamber which are to be removed condense on (Roots pumps, turbomolecular pumps) or are bonded by other means (e.g. 3. Pumps where the pumping effect is 2.1. Vacuum pumps: A chemically) to a solid surface, which based mainly on the diffusion of gases often is part of the boundary forming into a gas-free high speed vapor jet survey volume itself. (vapor pumps) 4. Pumps which pump vapors by means of A classification which is more in line with Vacuum pumps are used to reduce the gas condensation (condensers) and pumps the state-of-the-art and practical applica- pressure in a certain volume and thus the which pump permanent gases by way tions makes a difference between the gas density (see equation 1.5). Conse- of condensation at very low tempera- following types of pumps, of which the quently consider the gas particles need to tures (cryopumps) first three classes belong to the compres- be removed from the volume. Basically 5. Pumps which bond or incorporate ga- sion pumps and where the two remaining differentiation is made between two ses by adsorption or absorption to classes belong to the condensation and classes of vacuum pumps: surfaces which are substantially free of getter pumps: a) Vacuum pumps where – via one or gases (sorption pumps). several compression stages – the gas 1. Pumps which operate with periodically particles are removed from the volume increasing and decreasing pump cham- A survey on these classes of vacuum which is to be pumped and ejected into ber volumes (rotary vane and rotary pumps is given in the diagram of Table 2.1. plunger pumps; also trochoid pumps)

Vacuum pump (Operating principle)

Gas transfer Entrapment vacuum pump vacuum pump Positive displacement Kinetic vacuum pump vacuum pump

Reciprocating Rotary Drag Fluid entrainment Ion transfer Adsorption positive displacement vacuum pump vacuum pump vacuum pump vacuum pump pump vacuum pump

Diaphragm Liquid sealed Gaseous ring Ejector Getter pump vacuum pump vacuum pump vacuum pump vacuum pump

Liquid ring Piston Turbine Liquid jet vacuum pump Bulk getter pump vacuum pump vacuum pump vacuum pump

Rotary vane vacuum pump Axial flow Gas jet Sublimation vacuum pump vacuum pump pump

Multiple vane vacuum pump Radial flow Vapor jet Getter ion pump vacuum pump vacuum pump

Rotary piston vacuum pump Molecular drag vacuum pump Diffusion pump Evaporation ion pump

Rotary plunger vacuum pump

Turbomolecular pump Self-purifying Sputter-ion pump diffusion pump

Dry compressing vacuum pump

Fractionating diffusion pump Cryopump Roots vacuum pump

Diffusion ejector Condenser pump Claw vacuum pump

Scroll pump

Table 2.1 Classification of vacuum pumps

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2.1.1 Oscillation displacement pumping chamber so that it remains free mbar. Two-stage pumps such as the vacuum pumps of oil and lubricants (dry compressing DIVAC from LEYBOLD can attain about vacuum pump). Diaphragm and valves are 10 mbar (see Fig. 2.2), three-stage pumps 2.1.1.1 Diaphragm pumps the only components in contact with the can attain about 2 mbar and four-stage medium which is to be pumped. When diaphragm pumps can reach about Recently, diaphragm pumps have coating the diaphragm with PTFE (Teflon) 5·10-1 mbar. becoming ever more important, mainly for and when manufacturing the inlet and environmental reasons. They are alterna- exhaust valves of a highly fluorinated Diaphragm pumps offering such a low tives to water jet vacuum pumps, since elastomer as in the case of the DIVAC from ultimate pressure are suited as backing diaphragm pumps do not produce any LEYBOLD, it is then possible to pump pumps for turbomolecular pumps with fully waste water. Overall, a diaphragm vacuum aggressive vapors and gases. It is thus integrated Scroll stages (compound or wide pump can save up to 90 % of the operating well suited for vacuum applications in the range turbomolecular pumps, such as the costs compared to a water jet pump. chemistry lab. TURBOVAC 55 from LEYBOLD). In this way Compared to rotary vane pumps, the a pump system is obtained which is ab- pumping chamber of diaphragm pumps Due to the limited elastic deformability of solutely free of oil, this being of great im- are entirely free of oil. By design, no oil the diaphragm only a comparatively low portance to measurement arrangements immersed shaft seals are required. pumping speed is obtained. In the case of involving mass spectrometer systems and Diaphragm vacuum pumps are single or this pumping principle a volume remains leak detectors. In contrast to rotary vane multi-stage dry compressing vacuum at the upper dead center – the so called pumps this combination of pumps for leak pumps (diaphragm pumps having up to “dead space” – from where the gases can detectors offers the advantage that four stages are being manufactured). Here not be moved to the exhaust line. The naturally no helium is dissolved in the the circumference of a diaphragm is quantity of gas which remains at the ex- diaphragm pump thereby entirely avoiding tensioned between a pump head and the haust pressure expands into the expanding a possible build up of a helium background. casing wall (Fig. 2.1). It is moved in an pumping chamber during the subsequent oscillating way by means of a connecting suction stroke thereby filling it, so that as rod and an eccentric. The pumping or the intake pressure reduces the quantity of 2.1.2 Liquid sealed rotary compression chamber, the volume of inflowing new gas reduces more and displacement pumps which increases and decreases periodi- more. Thus volumetric efficiency worsens cally, effects the pumping action. The continuously for this reason. Diaphragm valves are arranged in such a way that vacuum pumps are not capable of 2.1.2.1 Liquid ring pumps attaining a higher compression ratio than during the phase where the volume of the Due to the pumping principle and the the ratio between “dead space” and pumping chamber increases it is open to simple design, liquid ring vacuum pumps maximum volume of the pumping cham- the intake line. During compression, the are particularly suited to pumping gases ber. In the case of single-stage diaphragm pumping chamber is linked to the exhaust and vapors which may also contain small vacuum pumps the attainable ultimate line. The diaphragm provides a hermetic amounts of liquid. Air, saturated with water pressure amounts to approximately 80 seal between the gear chamber and the vapors or other gases containing conden-

IN EX

(1) Casing lid (5) Diaphragm 1st stage 2nd stage (2) Valves (6) Diaphragm support disk (3) Lid (7) Connecting rod Opening and closing of the valves, path and pumping mechanism (4) Diaphragm disk (8) Eccentric disk during four subsequent phases of a turn of the connecting rod (a-d) D00

Fig. 2.1 Schematic on the design of a diaphragm pump stage (Vacuubrand) Fig. 2.2 Principle of operation for a two-stage diaphragm pump (Vacuubrand)

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Fundamentals of Vacuum Technology Vacuum Generation

sable constituents, may be pumped 2.1.2.2.1 Rotary vane pumps without problems. By design, liquid ring (TRIVAC A, TRIVAC B, pumps are insensitive to any contamina- TRIVAC E, SOGEVAC) tion which may be present in the gas flow. Rotary vane pumps (see also Figs. 2.5 and The attainable intake pressures are in the 2.6) consist of a cylindrical housing region between atmospheric pressure and (pump-ing ring) (1) in which an eccentri- the vapor pressure of the operating liquid cally suspended and slotted rotor (2) turns used. For water at 15 °C it is possible to in the direction of the arrow. The rotor has attain an operating pressure of 33 mbar. A vanes (16) which are forced outwards typical application of water ring vacuum usually by centrifugal force but also by pumps is venting of steam turbines in springs so that the vanes slide inside the power plants. Liquid ring vacuum pumps Constant, minimum clearance a for the entire housing. Gas entering through the intake (Fig. 2.3) are rotary displacement pumps sealing passage b (4) is pushed along by the vanes and is which require an operating liquid which finally ejected from the pump by the oil rotates during operation to pump the gas. Fig. 2.4 Arrangement of the sealing passage in rotary vane pumps sealed exhaust valve (12). also known as “duo seal” The older range of TRIVAC A pumps (Fig. 1. Removal of the heat produced by the 2.5) from LEYBOLD has three radial vanes compression process. offset by 120°. The TRIVAC B range (Fig. 2. Uptake of liquids and vapors 2.6) has only two vanes offset by 180°. In (condensate). 3. Providing the seal between the blade wheel and the casing.

2.1.2.2 Oil sealed rotary displacement pumps 1 Rotor 4 Intake channel 2 Rotor shaft 5 Liquid ring A displacement vacuum pump is generally 3 Casing 6 Flex. discharge channel a vacuum pump in which the gas which is Fig. 2.3 Liquid ring vacuum pump, schematic to be pumped is sucked in with the aid of (Siemens) pistons, rotors, vanes and valves or similar, possibly compressed and then The blade wheel is arranged eccentrically discharged. The pumping process is in a cylindrical casing. When not in opera- effected by the rotary motion of the piston tion, approximately half of the pump is inside the pump. Differentiation should be filled with the operating fluid. In the axial made between oiled and dry compressing direction the cells formed by the blade displacement pumps. By the use of sealing wheel are limited and sealed off by oil it is possible to attain in a single-stage 1 Pump housing 9 Exhaust port 2 Rotor 10 Air inlet silencer “control discs”. These control discs are high compression ratios of up to about 3 Oil-level sight glass 11 Oil filter 5 equipped with suction and ejection slots 10 . Without oil, “inner leakiness” is 4 Suction duct 12 Exhaust valve which lead to the corresponding ports of considerably greater and the attainable 5 Anti-suckback valve 13 Exhaust duct the pump. After having switched on such a compression ratio is correspondingly less, 6 Dirt trap 14 Gas ballast duct 7 Intake port 15 Oil injection pump the blade wheel runs eccentrically about 10. 8 Lid of gas ballast 16 Vane within the casing; thus a concentrically As shown in the classification Table 2.1, valve rotating liquid ring is created which at the the oil sealed displacement pumps include narrowest point fully fills the space rotary vane and rotary plunger pumps of Fig. 2.5 Cross section of a single-stage rotary vane between the casing and the blade wheel single and two-stage design as well as pump (TRIVAC A) and which retracts from the chambers as single-stage trochoid pumps which today the rotation continues. The gas is sucked are only of historic interest. Such pumps both cases the vanes are forced outwards in as the chambers empty and compres- are all equipped with a gas ballast facility by the centrifugal forces without the use of sion is obtained by subsequent filling. The which was described in detail (for details springs. At low ambient temperatures this limits for the intake or discharge process see 2.1.2.2.4) for the first time by Gaede possibly requires the use of a thinner oil. are set by the geometry of the openings in (1935). Within specified engineering The A-Series is lubricated through the the control discs. limits, the gas ballast facility permits arising pressure difference whereas the B- Series pumps have a geared oil pump for In addition to the task of compression, the pumping of vapors (water vapor in pressure lubrication. The TRIVAC B-Series operating fluid fulfills three further particular) without condensation of the is equipped with a particularly reliable anti- important tasks: vapors in the pump. suckback valve; a horizontal or vertical

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Vacuum Generation Fundamentals of Vacuum Technology

the oil box (user friendly design). In combination with the TRIVAC BCS system it may be equipped with a very com- Valve stop prehensive range of accessories, designed chiefly for semiconductor applications. The oil reservoir of the rotary vane pump and also that of the other oil sealed Leaf displacement pumps serves the purpose spring of the of lubrication and sealing, and also to fill valve dead spaces and slots. It removes the heat of gas compression, i.e. for cooling I High vacuum stage purposes. The oil provides a seal between II Second forevacuum stage rotor and pump ring. These parts are Fig. 2.7 Cross section of a two-stage rotary vane “almost” in contact along a straight line pump, schematic (cylinder jacket line). In order to increase the oil sealed surface area a so-called two-stage oil sealed pumps it is possible sealing passage is integrated into the 1 Intake port 8 Orifice, connec- to attain lower operating and ultimate 2 Dirt trap tion for inert gas pumping ring (see Fig. 2.4). This provides pressures ompared to the corresponding 3 Anti-suckback ballast a better seal and allows a higher com- valve 9 Exhaust duct single-stage pumps. The reason for this is pression ratio or a lower ultimate pres- 4 Intake duct 10 Exhaust valve that in the case of single-stage pumps, oil sure. LEYBOLD manufactures three 5 Vane 11 Demister is unavoidably in contact with the 6 Pumping cham- 12 Spring different ranges of rotary vane pumps atmosphere outside, from where gas is ber 13 Orifice; connec- which are specially adapted to different 7 Rotor tion for oil filter taken up which partially escapes to the applications such as high intake pressure, vacuum side thereby restricting the low ultimate pressure or applications in Fig. 2.6 Cross section of a single-stage rotary vane attainable ultimate pressure. In the oil pump (TRIVAC B) the semiconductor industry. A summary of sealed two-stage displacement pumps the more important characteristics of manufactured by LEYBOLD, oil which has these ranges is given in Table 2.2. The arrangement for the intake and exhaust already been degassed is supplied to the TRIVAC rotary vane pumps are produced ports. The oil level sight glass and the gas stage on the side of the vacuum (stage 1 in as single-stage (TRIVAC S) and two-stage ballast actuator are all on the same side of Fig. 2.7): the ultimate pressure lies almost (TRIVAC D) pumps (see Fig. 2.7). With the

TRIVAC A TRIVAC B TRIVAC BCS TRIVAC E SOGEVAC Vanes per stage 3 2 2 2 3 (tangential) 1 – 1.5 1.6 – – 16 – 25 Pumping speed 2 – 4 4 – 8 16 – 25 2.5 40 – 100

[m3/h] 8 – 16 16 – 25 40 – 65 – 180 – 280 30 – 60 40 – 65 – – 585 – 1200 Sealing passage yes yes yes yes no

Ultimate pressure, < 2 · 10–2 < 2 · 10–2 < 2 · 10–2 – < 5 · 10–1 single-stage [mbar] Ultimate pressure < 2.5 · 10–4 < 1 · 10–4 < 1 · 10–4 < 1 · 10–4 – two-stage [mbar] Oil supply Pressure difference Gear pump Gear pump Eccentric pump Pressure difference Slots Comparable for all types: about 0.01 to 0.05 mm Bearing/lubrication Axial face / oil Axial face / oil Axial face / oil Ball / grease Ball / oil Special – Hydropneumatic Coated parts in Many Cost-effective characteristics anti-suckback valve contact with medium accessories Media No ammonia Clean to Aggressive and Clean to Clean light particles corrosive light particles Main areas of Multi- Multi- Semiconductor Multi- Packaging D00 application purpose purpose industry purpose industry

Table 2.2 Rotary vacuum pump ranges

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Fig. 2.8a Cross section of a two-stage rotary vane Fig. 2.8b SOGEVAC pump SV 300 with three tangen- pump (TRIVAC E) tial vanes

in the high vacuum range, the lowest direction of the arrow moves along the operating pressures lie in the range chamber wall. The gas which is to be between medium vacuum / high vacuum. pumped flows into the pump through the Note: operating the so called high vacuum intake port (11), passes through the intake stage (stage 1) with only very little oil or channel of the slide valve (12) into the 1 Casing 8 Exhaust pot 2 Cylindrical piston 9 Gas ballast valve no oil at all will – in spite of the very low pumping chamber (14). The slide valve 3 Eccentric 10 Dirt trap ultimate pressure – in practice lead to forms a unit with the piston and slides to 4 Compression 11 Intake port considerable difficulties and will signifi- and fro between the rotatable valve guide chamber 12 Slide valve cantly impair operation of the pump. in the casing (hinge bar 13). The gas 5 Oil sealed pressure 13 Hinge bar valve 14 Pumping chamber drawn into the pump finally enters the 6 Oil-level sight glass (air is flowing in) compression chamber (4). While turning, 7 Gas ballast channel 2.1.2.2.2 Rotary plunger pumps the piston compresses this quantity of gas (E-Pumps) until it is ejected through the oil sealed Fig. 2.9 Cross section of a single-stage rotary plun- valve (5). As in the case of rotary vane ger pump (monoblock design) Shown in Fig. 2.9 is a sectional view of a pumps, the oil reservoir is used for rotary plunger pump of the single block lubrication, sealing, filling of dead spaces each turn completes an operating cycle type. Here a piston (2) which is moved and cooling. Since the pumping chamber (see Fig. 2.10). Rotary plunger pumps are along by an eccentric (3) turning in the is divided by the piston into two spaces, manufactured as single and two-stage pumps. In many vacuum processes combining a Roots pump with a single- stage rotary plunger pump may offer more advantages than a two-stage rotary plunger pump alone. If such a combination or a two-stage pump is inadequate, the use of a Roots pump in connection with a two-stage pump is recommended. This does not apply to combinations involving rotary vane pumps and Roots pumps.

Motor power The motors supplied with the rotary vane and rotary plunger pumps deliver enough power at ambient temperatures of 12 °C and when using our special oils to cover 1 Upper dead point 4 Slot in suction channel is clo- – commencement of gas bal- the maximum power requirement (at about 2 Slot in suction channel of sed again by swivelling hinge last inlet 400 mbar). Within the actual operating slide valve is freed – begin- bar – end of suction period 7 Gas ballast opening is quite ning of suction period 5 Upper dead point – maximum free range of the pump, the drive system of the 3 Lower dead point – slot in space between rotating 8 End of gas ballast inlet warmed up pump needs to supply only suction channel is quite free, piston and stator 9 End of pumping period. about one third of the installed motor and pumped-in gas (arrow) 6 Shortly before beginning of power (see Fig. 2.11). enters freely into the pum- compression period, the front ping chamber (shown sha- surface of the rotating plun- ded) ger frees gas ballast opening

Fig. 2.10 Operating cycle of a rotary plunger pump (for positions 1 to 9 of the plunger)

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att] Discharge n io s s e r p

m o

C Gas ballast inlet

Gas ballast Position inlet of the leading vane Power of the drive motor [W

Suction

Pressure [mbar]

1 Operating temp. 5 Theoretic curve for 1 Toothed wheel fixed to the driving shaft curve 1 32°C, adiabatic compres- 2 Toothed wheel fixed to the piston 2 Operating temp. sion 1–2 Suction 3 Elliptic piston curve 2 40°C, 6 Theoretic curve for 2–5 Compression 4 Inner surface of the pump 3 Operating temp. isotherm compres- 3–4 Gas ballast inlet 5 Driving shaft curve 3 60°C, sion 5–6 Discharge 6 Eccentric 4 Operating temp. curve 4 90°C,

Fig. 2.11 Motor power of a rotary plunger pump (pumping speed 60 m3/h) as a function of intake pressure and operating temperature. The curves for gas ballast pumps of other sizes are Fig. 2.13 Working process within a rotary vane pump similar. Fig. 2.12 Cross section of a trochoid pump with gas ballast

2.1.2.2.3 Trochoid pumps the area of manufacturing, so that today the pump’s oil. This very rapidly impairs LEYBOLD does not produce trochoid the lubricating properties of the oil and the Trochoid pumps belong to the class of so pumps any more. Operation of such a pump may even seize when it has taken up called rotary piston pumps, which (see pump is shown in the sectional diagram of too much water. The gas ballast facility overview of Table 2.1) in turn belong to the Fig. 2.12. developed in 1935 by Wolfgang Gaede group of rotary pumps. With rotary piston inhibits the occurrence of condensation of pumps, the piston’s center of gravity runs the vapor in the pump as follows. Before along a circular path about the rotational 2.1.2.2.4 The gas ballast the actual compression process begins axis (hence rotary piston machines). A (see Fig. 2.13), a precisely defined quantity rotary piston pump can – in contrast to the The gas ballast facility as used in the rotary of air (“the gas ballast”) is admitted into rotary plunger pump – be completely vane, rotary plunger and trochoid pumps the pumping chamber of the pump. The balanced dynamically. This offers the permits not only pumping of permanent quantity is such that the compression ratio advantage that larger pumps can operate gases but also even larger quantities of of the pump is reduced to 10:1 max. Now without vibration so that they can be condensable gases. vapors which have been taken in by the installed without needing foundations. The gas ballast facility (see Fig. 2.13) pump may be compressed together with Moreover, such pumps may be operated at prevents condensation of vapors in the the gas ballast, before reaching their higher speed, compared to rotary plunger pump chamber of the pump. When condensation point and ejected from the pumps (see below). The volume of the pumping vapors these may only be pump. The partial pressure of the vapors pumping chamber with respect to the compressed up to their saturation vapor which are taken in may however not volume of the entire pump – the so called pressure at the temperature of the pump. exceed a certain value. It must be so low specific volume – is, in the case of If pumping water vapor, for example, at a that in the case of a compression by a trochoid pumps, approximately twice of pump temperature of 70 °C, the vapor may factor of 10, the vapors can not condense that of rotary plunger pumps. Larger only be compressed to 312 mbar at the operating temperature of the pump. rotary plunger pumps run at speeds of (saturation vapor pressure of water at When pumping water vapor this critical 500 rpm. The trochoid pump may run at 70 °C (see Table XIII in Section 9)). When value is termed the “water vapor 1000 rpm and this applies also to larger compressing further, the water vapor tolerance”. designs. It is thus about four times smaller condenses without increasing the compared to a rotary plunger pump having Shown schematically in Fig. 2.14 is the pressure. No overpressure is created in the same pumping speed and runs without pumping process with and without gas the pump and the exhaust valve is not producing any vibrations. Unfortunately ballast as it takes place in a rotary vane D00 opened. Instead the water vapor remains the advantages in the area of engineering pump when pumping condensable vapors. as water in the pump and emulsifies with are combined with great disadvantages in

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∆ Two requirements must be met when pexhaust filter = is the pressure difference pumping vapors: across the exhaust filter 1) the pump must be at operating amounting to 0 ... 0.5 bar temperature. 2) the gas ballast valve must be open. Example 1: With a rotary vane pump with an external (With the gas ballast valve open the oil mist filter in series, a mixture of water temperature of the pump increases by vapor and air is being pumped. The follo- about 10 °C. Before pumping vapors the wing values are used for applying eq. (2.1): pump should be operated for half an hour with the gas ballast valve open). pexhaust = 1 bar ∆p + ∆p = 0.35 bar, Simultaneous pumping of gases and valve exhaust filter vapors temperature of the pump 70 °C When simultaneously pumping permanent Hence: gases and condensable vapors from a vacuum system, the quantity of permanent psum = 1.35 bar; pvapor sat (H2O) gas will often suffice to prevent any = 312 mbar condensation of the vapors inside the (see Table XIII in chapter 9) pump. The quantity of vapor which may be pumped without condensation in the Using eq. (2.1) follows: pump can be calculated as follows: a) Without gas bal- b) With gas ballast pvapour , H O 312 p 2 < = 0.23 last 1) Pump is connected pvapour vapour, sat + < (2.1) pvapour , H O pair 1350 1) Pump is connected to the vessel, which + 2 pvapour pperm psum to the vessel, which is already almost is already almost empty of air The pressure of the water vapor in the empty of air (70 mbar) – it must Where: air/water vapor mixture must not exceed (70 mbar) – it must thus transport pvapor = is the partial pressure of 23 % of the total pressure of the mixture. thus transport mostly vapor vapor at the intake of the mostly vapor particles particles 2) Pump chamber is pump Example 2: 2) Pump chamber is separated from the pperm = is the total pressure of all Ethanoic acid is to be pumped with a separated from the vessel – now the pumped permanent gases rotary plunger pump. vessel – compres- gas ballast valve, at the intake of the pump sion begins through which the pexhaust = 1.1 bar (taking into 3) Content of pump pump chamber is pvapor, sat = is the saturation pressure chamber is already filled with additio- of the pumped vapor, consideration the flow so far compressed nal air from outsi- depending on temperatu- resistance of the pipes) that the vapor con- de, opens – this re (see Fig. 2.15) ∆p = 0.25 bar denses to form additional air is cal- ∆ valve droplets – over- led gas ballast psum = pexhaust + pvalve + ∆ ∆ pressure is not yet 3) Discharge valve is pexhaust filter pexhaust filter = 0.15 bar reached pressed open, and ∆ pvalve = is the pressure difference (pressure loss in the oil 4) Residual air only particles of vapor across the exhaust valve now produces the and gas are pushed mist trap) required overpres- out – the overpres- which amounts depen- sure and opens the sure required for ding on type of pump and Hence: discharge valve, this to occur is rea- operating conditions to psum = 1.5 bar. but the vapor has ched very early 0.2 ... 0.4 bar already condensed because of the sup- and the droplets plementary gas By controlled cooling the pump and oil are precipitated in ballast air, as at the temperature is set at 100 °C. The saturati- the pump. beginning the enti- on pressure of the acid therefore is – see

re pumping pro- r] Fig. 2.15 – p = 500 mbar. cess condensation or vapor, sat e [mbar] cannot occur e [T 4) The pump dischar- From eq. (2.1) follows: essur ges further air and essur p 0.5 1 vapor vapour, acid = < = pvapour, acid + pair 1.5 3

Returning to the question of pumping water vapor in a mixture with air, the ratio Saturation vapor pr Fig. 2.14 Diagram of pumping process in a rotary vane Saturation vapor pr Temperature [° C] pump without (left) and with (right) gas bal- 3 parts of permanent gases to 1 part of last device when pumping condensable sub- water vapor, as indicated in example 1, can stances Fig. 2.15 Saturation vapor pressures be for guidance only. In actual practice it is

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recommended to run up a rotary pump of Water vapor tolerance the gas ballast B would result in an increa- the types described hitherto always with An important special case in the general sed water vapor tolerance pW,0. In prac- the gas ballast valve open, because it takes considerations made above relating to the tice, an increase in B, especially in the case some time until the pump has reached its topic of vapor tolerance is that of pumping of single-stage gas ballast pumps is final working temperature. water vapor. According to PNEUROP water restricted by the fact that the attainable vapor tolerance is defined as follows: ultimate vacuum for a gas ballast pump From eq. (2.1) follows for the permissible operated with the gas ballast valve open partial pressure p of the pumped “Water vapor tolerance is the highest vapor becomes worse as the gas ballast B vapor the relation pressure at which a vacuum pump, under increases. Similar considerations also normal ambient temperatures and apply to the general equation 2.3 for the p pressure conditions (20 °C, 1013 mbar), p ≤ vapour, sat p vapor tolerance p . vapour − á perm (2.2) can continuously take in and transport vapor psum pvapour, sat pure water vapor. It is quoted in mbar”. It At the beginning of a pump down process, is designated as p . the gas ballast pump should always be This relation shows that with pperm = 0 no W,O vapors can be pumped without condensa- operated with the gas ballast valve open. Applying eq. (2.3) to this special case tion in the pump, unless the gas-ballast In almost all cases a thin layer of water will means: concept is applied. The corresponding for- be present on the wall of a vessel, which only evaporates gradually. In order to mula is: pperm = 0 and pvapor, sat = ps (H2O), thus: − attain low ultimate pressures the gas ≤ B(pVa pour, sat pvapour , g.b. ) ppvapour sumá − + − ballast valve should only be closed after Sppsum vapour , sat B ps (H 2O) pvapour, g.b. p = p (2.4) pvapour sat (2.3) W,O sum − ( ) the vapor has been pumped out. LEYBOLD + − pperm S psum ps H 2O ppsum vapour sat pumps generally offer a water vapor tolerance of between 33 and 66 mbar. Two- If for the gas ballast gas atmospheric air of Where: stage pumps may offer other levels of 50 % humidity is used, then B = is the volume of air at water vapor tolerance corresponding to p = 13 mbar; with B/S = 0.10 1013 mbar which is admitted vapor, g.b. the compression ratio between their – a usual figure in practice – and p to the pump chamber per unit sum stages – provided they have pumping (total exhaust pressure) = 1330 mbar, the time, called in brief the “gas chamber of different sizes. water vapor tolerance p as function of ballast” W,0 the temperature of the pump is represen- S = is the nominal speed of the Other gases as ballast ted by the lowest curve in diagram Fig. pump (volume flow rate) Generally atmospheric air is used as the 2.16. The other curves correspond to the p = is the pressure at the gas ballast medium. In special cases, sum pumping of water vapor-air mixtures, discharge outlet of the pump, when pumping explosive or toxic gases, hence p = p ≠ O), indicated by the assumed to be a maximum at perm air for example, other permanent gases like symbol p in millibar. In these cases a hig- 1330 mbar L noble gases or nitrogen, may be used (see her amount of water vapor partial pressu- p = Saturation vapor pressure of Section 8.3.1.3). vapor, sat re p can be pumped as shown in the dia- the vapor at the pump’s w gram. The figures for p given in the exhaust port W,0 catalogue therefore refer to the lower limit p = is the partial pressure of any vapor, g.b. and are on the safe side. vapor that might be present in the gas used as gas ballast According to equation 2.4 an increase in (e.g. water vapor contained in

the atmospheric air when pL [mbar] used as gas ballast) pperm = is the total pressure of all permanent gases at the inlet port of the pump

Eq. (2.3) shows that when using gas [mbar] W ballast (B ≠ 0) vapors can also be pumped p without condensation if no gas is present at the intake of the pump. The gas ballast Temperature of the pump may also be a mixture of non-condensable gas and condensable vapor as long as the Fig. 2.16 Partial pressure p of water vapor that can partial pressure of this vapor (pvapor, g.b.) is W less than the saturation pressure p be pumped with the gas ballast valve open vapor, sat without condensation in the pump, as a fun- of the pumped vapor at the temperature of ction of the pump temperature for various the pump. D00 partial pressures pL of air. The lowest curve corresponds to the water vapor tolerance pW, O of the pump

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Fundamentals of Vacuum Technology Vacuum Generation

2.1.3 Dry compressing rotary without mechanical wear. In contrast to SiR = n · ViR (2.9) displacement pumps rotary vane and rotary plunger pumps, Roots pumps are not oil sealed, so that the i.e. the product of speed n and internal leakage volume V . 2.1.3.1 Roots pumps internal leakage of dry compressing iR pumps by design results in the fact that Volumetric efficiency of a Roots pumps is The design principle of the Roots pumps compression ratios only in the range 10 – given by was already invented in 1848 by Isaiah 100 can be attained. The internal leakage Davies, but it was 20 years later before it of Roots pumps, and also other dry Qeff was implemented in practice by the η = compressing pumps for that matter, is Q (2.10) Americans Francis and Philander Roots. mainly based on the fact that owing to the th Initially such pumps were used as blowers operating principle certain surface areas of By using equations 2.5, 2.6, 2.7 and 2.8 for combustion motors. Later, by inverting the pump chamber are assigned to the one obtains the drive arrangement, the principle was intake side and the compression side of p S employed in gas meters. Only since 1954 the pump in alternating fashion. During the η = 1− V · iR (2.11) has this principle been employed in compression phase these surface areas pa Sth vacuum engineering. Roots pumps are (rotors and casing) are loaded with gas used in pump combinations together with (boundary layer); during the suction phase When designating the compression pv/pa backing pumps (rotary vane- and rotary this gas is released. The thickness of the as k one obtains plunger pumps) and extend their operating traveling gas layer depends on the S range well into the medium vacuum range. clearance between the two rotors and η = 1− k iR S (2.11a) With two stage Roots pumps this extends between the rotors and the casing wall. th into the high vacuum range. The operating Due to the relatively complex thermal Maximum compression is attained at zero principle of Roots pumps permits the conditions within the Roots pump it is not throughput (see PNEUROP and assembly of units having very high possible to base one’s consideration on DIN 28 426, Part 2). It is designated as k : pumping speeds (over 100,000 m3/h) the cold state. The smallest clearances and 0 which often are more economical to S thus the lowest back flows are attained at ( th ) k0 = η = 0 (2.12) operate than steam ejector pumps running operating pressures in the region of SiR in the same operating range. 1 mbar. Subsequently it is possible to A Roots vacuum pump (see Fig. 2.17) is a attain in this region the highest com- k0 is a characteristic quantity for the Roots rotary positive-displacement type of pump pression ratios, but this pressure range is pump which usually is stated as a function where two symmetrically-shaped impel- also most critical in view of contacts of the forevacuum pressure pV (see Fig. lers rotate inside the pump casing past between the rotors and the casing. 2.18). k0 also depends (slightly) on the each other in close proximity. The two type of gas. rotors have a cross section resembling Characteristic quantities of roots pumps For the efficiency of the Roots pump, the approximately the shape of a figure 8 and The quantity of gas Qeff effectively pumped are synchronized by a toothed gear. The by a Roots pump is calculated from the clearance between the rotors and the theoretically pumped quantity of gas Qth casing wall as well as between the rotors and the internal leakage QiR (as the themselves amounts only to a few tenths quantity of gas which is lost) as: of a millimeter. For this reason Roots Qeff = Qth – QiR (2.5) pumps may be operated at high speeds The following applies to the theoretically pumped quantity of gas:

1 Qth = pa · Sth (2.6) 2 2 Fig. 2.18 Maximum compression k0 of the Roots pump where pa is the intake pressure and Sth is RUVAC WA 2001 as a function of fore vacu- the theoretical pumping speed. This in turn um pressure pV is the product of the pumping volume VS and the speed n: generally valid equation applies: S = n · V (2.7) th S k η = 1− (2.13) Similarly the internal leakage Q is ko 3 iR 5 calculated as: Normally a Roots pump will be operated in 4 Q = n · V (2.8) iR iR connection with a downstream rough 1 Intake flange 4 Exhaust flange where pV is the forevacuum pressure vacuum pump having a nominal pumping 2 Rotors 5 Casing (pressure on the forevacuum side) and S speed S . The continuity equation gives: 3 Chamber iR V is a (notional) “reflow” pumping speed S · p = S · p = η · S · p (2.14) Fig. 2.17 Schematic cross section of a Roots pump with V V eff a th a

D00.24 LEYBOLD VACUUM PRODUCTS AND REFERENCE BOOK 2001/2002 D00 E 19.06.2001 21:36 Uhr Seite 25

Vacuum Generation Fundamentals of Vacuum Technology

From this b) the max. compression as a function of Power requirement of a roots pump the fore vacuum pressure: k (p ) Compression in a Roots pump is perfor- pV Sth 0 V k = = η· (2.15) med by way of external compression and pa S c) the pumping speed characteristic of the V is termed as isochoric compression. backing pump SV (pV) Experience shows that the following equa- The ratio S /S (theoretical pumping th V The way in which the calculation is carried tion holds approximately: speed of the Roots pump / pumping speed out can be seen in Table 2.3 giving the data of the backing pump) is termed the N = S (p – p ) (2.18) for the combination of a Roots pump compression th v a gradation k . From (2.15) one obtains th RUVAC WA 2001 / E 250 (single-stage ro- In order to determine the total power (so- η k = · kth (2.16) tary plunger pump, operated without gas called shaft output) of the pump, mecha- ballast). In this the following is taken for nical power losses N (for example in the Equation (2.16) implies that the compres- V S : bearing seals) must be considered: sion k attainable with a Roots pump must th N = N + ∑ N (2.19) always be less than the grading kth S = 2050 – 2.5 % = 2000 m3/h tot compression V between Roots pump and backing pump th The power losses summarized in NV are – since volumetric efficiency is always < 1. The method outlined above may also be as shown by experience – approximately When combining equations (2.13) and applied to arrangements which consist of a proportional to S , i.e.: (2.16) one obtains for the efficiency the rotary pump as the backing pump and th ∑ well known expression several Roots pumps connected in series, Nv = const · Sth (2.20) for example. Initially one determines – in k0 Depending on the type of pump and its η = (2.17) line with an iteration method – the k + k design the value of the constant ranges o th pumping characteristic of the backing between 0.5 and 2 Wh / m3 . pump plus the first Roots pump and then The characteristic quantities to be found in considers this combination as the backing The total power is thus: equation 2.17 are only for the combination pump for the second Roots pump and so of the Roots pump and the backing pump, Ntot = Sth (pv – pa + const.) on. Of course it is required that the namely maximum compression k of the 0 theoretical pumping speed of all pumps of The corresponding numerical value equa- Roots pump and gradation k between th the arrangement be known and that the tion which is useful for calculations is: Roots pump and backing pump. compression at zero throughput k0 as a -2 With the aid of the above equations the function of the backing pressure is also Ntot = Sth (pv – pa + const.) · 3 · 10 Watt pumping speed curve of a given combi- known. As already stated, it depends on (2.21) nation of Roots pump and backing pump the vacuum process which grading will be with p , p in mbar, S in m3 / h and may be calculated. For this the following most suitable. It may be an advantage v a th must be known: when backing pump and Roots pump both the constant “const.” being between a) the theoretical pumping speed of the have the same pumping speed in the 18 and 72 mbar. Roots pump: Sth rough vacuum range.

η Forevacuum Pumping speed kth = Sth / Sv k0 (pv) of = k0 / k0+kth Intake pressure η pressure Sv of the = 2001/Sv the RUVAC (Volumetric. Seff = Sth pa = pv · Sv / Seff Pv E 250 WA 2001 efficiency) (equation 2.14) 100 250 8.0 12.5 0.61 1.220 21 40 250 8.0 18 0.69 1.380 7.2 10 250 8.0 33 0.8 1.600 1.6 5 250 8.0 42 0.84 1.680 0.75 1 250 8.0 41 0.84 1.680 0.15 5 · 10–1 220 9.1 35 0.79 1.580 7 · 10–2 1 · 10–1 120 16.6 23 0.6 1.200 1 · 10–2 4 · 10–2 30 67 18 0.21 420 3 · 10–3 ↓ ↓

The values taken from the two right-hand columns give point by point the pumping speed curve for Pumping speed characteristic the combination WA 2001/E250 (see Fig. 2.19, topmost curve) for the combination D00 WA 2001 / E250

Table 2.3

LEYBOLD VACUUM PRODUCTS AND REFERENCE BOOK 2001/2002 D00.25 D00 E 19.06.2001 21:36 Uhr Seite 26

Fundamentals of Vacuum Technology Vacuum Generation Pumping speed S

→ Intake pressure pa

Fig. 2.19 Pumping speed curves for different pump combinations with the corresponding backing pumps

Load rating of a roots pump Integral leak tightness of this version is Maintaining the allowed pressure The amount of power drawn by the pump < 10-4 mbar·l·s-1. difference determines its temperature. If the tempe- In the case of standard Roots pumps, In the case of better leak tightness rature increases over a certain level, measures must be introduced to ensure requirements of < 10-5 mbar·l·s-1 the determined by the maximum permissible that the maximum permissible pressure Roots pump is equipped with a canned pressure difference p – p , the danger difference between intake and exhaust port V a motor. The rotor is seated in the vacuum exists that the rotors may seize in the due to design constraints is not exceeded. on the drive shaft of the pump and is casing due to their thermal expansion. The This is done either by a pressure switch, separated from the stator by a vacuum- maximum permissible pressure difference which cuts the Roots pump in and out tight non-magnetic tube. The stator coils ∆p is influenced by the following fac- depending on the intake pressure, or by max are cooled by a fan having its own drive tors: forevacuum or compression pressure using a pressure difference or overflow motor. Thus shaft seals which might be p , pumping speed of the backing pump valve in the bypass of the Roots pumps V subject to wear are no longer required. The S , speed of the Roots pump n, gradation (Fig. 2.20 and 2.21). The use of an V use of Roots pumps equipped with canned k and the adiabatic exponent κ of the overflow valve in the bypass of the Roots th motors is especially recommended when pumped gas. ∆p increases when p pump is the better and more reliable max V pumping high purity-, toxic- or radioactive and S increase and decreases when n and solution. The weight and spring loaded V gases and vapors. kth increase. Thus the maximum difference valve is set to the maximum permissible between forevacuum pressure and intake pressure, pV – pa must – during continuous operation – not exceed a certain value depending on the type of pump. Such values are in the range between 130 and 50 mbar. However, the maximum permissible pressure difference for continuous operation may be exceed for brief WAU 2001 periods. In the case of special designs, which use gas cooling, for example, high pressure differences are also permissible during continuous operation.

Types of motors used with roots pumps SOGEVAC SV 1200 Standard flange-mounted motors are used as the drive. The shaft feedthroughs are sealed by two oil sealed radial shaft seals running on a wear resistant bushing in order to protect the drive shaft. Flange motors of any protection class, voltage or Fig. 2.20 Cross section of a Roots pumps with Fig. 2.21 Vacuum diagram – Roots pump with integra- bypass line ted bypass line and backing pump frequency may be used.

D00.26 LEYBOLD VACUUM PRODUCTS AND REFERENCE BOOK 2001/2002 D00 E 19.06.2001 21:36 Uhr Seite 27

Vacuum Generation Fundamentals of Vacuum Technology

1 a

4 b 4 Z P Z P 3 Z P c

1 Intake port 2 Discharge port 3 Gas cooler 1 Rotors 4 Exhaust slot 4 Flow of cold gas 2 Compression 5 Intake slot chamber 6 Intermediate stage purge Fig. 2.24 Arrangement of the pumps and guiding of 3 Intake space gas Fig. 2.22 Diagram of a Roots pump with pre-admis- the gas flow. P = Pump stage Z = Interme- sion cooling Fig. 2.23 Principle of operation diate ring

pressure difference of the particular pump. the case of single-stage compression is work cycle in position a, the right rotor just This ensures that the Roots pump is not taken from the atmosphere and admitted opens the intake slot (5). Gas now flows overloaded and that it may be operated in from the pre-admission cooler, and which into the continually increasing intake space any pressure range. In practice this means in the case of multi-stage pump systems is (3) in position b until the right rotor seals that the Roots pump can be switched on, taken from downstream gas coolers, off the intake slot (5) in position c. After together with the backing pump, at performs a pre-compression and removes both claws have passed through the center atmospheric pressure. In the process any by “inner cooling” the heat of compression position, the gas which has entered is then pressure increases will not adversely affect at the point of time it occurs. compressed in the compression chamber combined operation, i.e. the Roots pump (2) (position a) so long until the left rotor is not switched off in such circumstances. releases the discharge slot (4) (position b) 2.1.3.2 Claw pumps thereby discharging the gas. Immediately Pre-admission cooling (Fig. 2.22) after the compression process has started Like Roots pumps, claw pumps belong to In the case of Roots pumps with pre- (position a) the intake slot (5) is opened the group of dry compressing rotary admission cooling, the compression pro- simultaneously and gas again flows into piston vacuum pumps (or rotary vacuum cess basically is the same as that of a nor- the forming intake space (3) (position b). pumps). These pumps may have several mal Roots pump. Since greater pressure Influx and discharge of the gas is stages; their rotors have the shape of differences are allowed more installed performed during two half periods. Each claws. power is needed, which at the given speed rotor turns twice during a full work cycle. and the pressure difference between inlet The design principle of a claw pump is Located between the pumping stages are and discharge port is directly proportional explained by first using an example of a intermediate discs with flow channels and is composed of the theoretical work four-stage design. The cross section inside which run from the discharge side of the done on compression and various power the pump’s casing has the shape of two upper stage to the intake side of the next losses. The compression process ends partly overlapping cylinders (Fig. 2.23). stage, so that all inlet or exhaust sides are normally after opening of the pumping Within these cylinders there are two freely arranged vertically above each other (Fig. chamber in the direction of the discharge rotating rotors in each pump stage: (1) 2.24). Whereas in a Roots pump the in- port. At this moment warmed gas at higher with their claws and the matching recesses coming gas is pumped through the pump pressure flows into the pumping chamber rotating in opposing directions about their at a constant volume and compression is and compresses the transported volume of vertical axes. The rotors are synchronized only performed in the forevacuum line gas. This compression process is perfor- by a gear just like a Roots pump. In order (see Section 2.1.3.1), the claw pump med in advance in the case of pre-admis- to attain an optimum seal, the clearance compresses the gas already within the sion cooling. Before the rotor opens the between the rotor at the center of the pumping chamber until the rotor releases pumping chamber in the direction of the casing and the amount of clearance with the discharge slot. Shown in Fig. 2.25 are discharge port, compressed and cooled respect to the inside casing wall is very the average pressure conditions in the gas flows into the pumping chamber via small; both are in the order of magnitude individual pumping stages of a DRYVAC at the pre-admission channel. Finally the of a few 0.01 mm. The rotors periodically an intake pressure of 1 mbar. In order to D00 rotors eject the pumped medium via the open and close the intake and discharge meet widely differing requirements discharge port. The cooled gas, which in slots (5) and (4). At the beginning of the LEYBOLD manufactures two different

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Fundamentals of Vacuum Technology Vacuum Generation

IN 1 mbar OUT P P Stage 1 W 3 mbar W Compr. 1 Compr. 1 2 2

IN 3 mbar OUT 15 mbar Stage 2

IN 15 mbar OUT 150 mbar Stage 3 3

IN 150 mbar OUT 1000 mbar Stage 4 4 3

V V

Fig. 2.27 Compression curve for a claw pump without Fig. 2.26 Compression curve for a claw pump with internal compression Fig. 2.25 Pressures in pump stages 1 to 4 internal compression (“isochoric compression”)

series of claw pumps, which chiefly differ which is applied from the outside after 2.1.3.2.1 Claw pumps with internal in the type of compression process used: completion of the intake process. This is compression for the 1) Pumps with internal compression, similar to the admission of a gas ballast semiconductor industry multi-stage for the semiconductor when opening the gas ballast valve after (“DRYVAC series”) industry (DRYVAC Series) and completion of the intake phase. From the 2) Pumps without internal compression, diagram it is apparent that in the case of Design of DRYVAC Pumps two-stage for chemistry applications isochoric compression the work done on Due to the work done on compression in (“ALL·ex”). compression must be increased, but cold the individual pumping stages, multi-stage gas instead of hot exhaust gas is used for claw pumps require water cooling for the Figs. 2.26 and 2.27 demonstrate the venting. This method of direct gas cooling four stages to remove the compression differences in design. Shown is the course results in considerably reduced rotor heat. Whereas the pumping chamber of of the pressure as a function of the volume temperatures. Pumps of this kind are dis- the pump is free of sealants and lubri- of the pumping chamber by way of a pV cussed as “ALL·ex” in Section 2.1.3.2.2. cants, the gear and the lower pump shaft diagram. are lubricated with perfluoropolyether Fig. 2.26 shows the (polytropic) course of (PFPE). The gear box is virtually herme- the compression for pumps with internal tically sealed from the pumping chamber compression. The pressure increases until by piston rings and a radial shaft seal. The the discharge slot is opened. If at that bearings in the upper end disk are point the exhaust back pressure has not lubricated with PFPE grease. In order to been reached, the compression space is protect the bearings and shaft seals suddenly vented with hot exhaust gas. As against aggressive substances, a barrier the volume is reduced further, the gas at 1 gas facility is provided. A controlled water exhaust pressure is ejected. The work 2 cooling system allows the control of the done on compression is represented by casing temperature over a wide range as the area under the p-v curve 1-2-3-4. It is the pump is subjected to differing gas almost completely converted into heat. In loads coming from the process. The four the case of dry compressing vacuum stage design is available in several pumps not much of this heat can be lost to pumping speed and equipment grades of 3 the cooled casing due to the low density of 25, 50 and 100 m3/h DRYVAC pumps: the gas. This results in high gas tempe- a) as the basic version for non-aggressive ratures within the pump. Experiences with clean processes: DRYVAC 25 B, 50 B claw pumps show that the highest tem- and 100 B (Fig. 2.29a) peratures occur at the rotors. b) as a version for semiconductor processes: DRYVAC 25 P, 50 P and Shown in Fig. 2.27 is the principle of 100 P (Fig. 2.29b) isochoric compression in a p-v diagram. 1 Intake port c) as a system version with integrated self Here the compression is not performed by 2 Front panel / electronics 3 Main switch monitoring: DRYVAC 50 S and 100 S reducing the volume of the pumping d) as a system version with integrated self chamber, but by venting with cold gas Fig. 2.28 DRYVAC pump

D00.28 LEYBOLD VACUUM PRODUCTS AND REFERENCE BOOK 2001/2002 D00 E 19.06.2001 21:36 Uhr Seite 29

Vacuum Generation Fundamentals of Vacuum Technology

Intake Casing Casing Intake line suction suction line Cooling 100 P only Cooling water water

Exhaust Exhaust line line

Inert gas

Fig. 2.29a Vacuum diagram for the DRYVAC B Fig. 2.29b Vacuum diagram for the DRYVAC P Fig. 2.29c Vacuum diagram for the DRYVAC S

monitoring offering an increased need to meet a variety of special require- strongly on their size. The mean velocity pumping speed in the lower pressure ments. In semiconductor processes, as in (VGas) of the flowing gas during the range: DRYVAC 251 S and 501 S (Fig. many other vacuum applications, the compression phase is given by the 2.29c) formation of particles and dusts during the following equation: process and/or in the course of compres- The ultimate pressure attainable with the q mbar · `·s−1 sing the pumped substances to atmos- v = pV · = DRYVAC 251 S or 501 S is – compared to Gas p· A 2 pheric pressure within the pump, is una- mbar · cm the versions without integrated Roots (2.22) voidable. In the case of vacuum pumps 10·qpV m pump – by approximately one order of = · operating on the claw principle it is p· A s magnitude lower (from 2·10-2 mbar to possible to convey particles through the 3·10-3 mbar) and the attainable throughput pump by means of so called “pneumatic qpV = gas throughput is also considerably increased. It is of conveying”. This prevents the deposition p = pressure course possible to directly flange mount of particles and thus the formation of A = surface area LEYBOLD RUVAC pumps on to the layers within the pump and reduces the DRYVAC models (in the case of semi- One can see that with increasing pressure risk that the claw rotor may seize. Care conductor processes also mostly with a the velocity of the pumped gas flow slows must be taken to ensure that the velocity of PFPE oil filling for the bearing chambers). down and attains the order of magnitude the gas flow within the individual pumping of the settling speed of the particles in the The pumps of the DRYVAC family are the stages is at all times greater than the gas flow (Fig. 2.32). This means that the classic dry compressing claw vacuum settling speed of the particles entrained in risk of depositing particles in the operating pumps that are preferably used in the se- the gas flow. As can be seen in Fig. 2.31, chamber of the pump and the resulting miconductor industry, whereby the pumps the settling speed of the particles depends

To be provided by the customer Stage 2 Stage 3 Stage 4 2 500 mbar·l/s 8 300 mbar·l/s 20 000 mbar·l/s

TSH Temperature switch

PSL Pressure switch Particle size

PSH Pressure switch

FSL Flow switch Throughput in MPS Motor protection switch mbar·l/s Limit speed Gas velocity PT 100 Temperature sensor Throughput cross sec- For DRYVAC with LIMS tion 6.5 cm2, constant Pressure CS Current sensor Pressure EPS Exhaust pressure sensor D00 Fig. 2.32 Mean gas velocity vg during compression Fig. 2.31 Settling speed as a function of pressure p. without purge gas (left) and with purge gas Fig. 2.30 Key to Figures 2.29a – 2.29c Parameter: particle size (right) in stages 2, 3 and 4

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Fundamentals of Vacuum Technology Vacuum Generation

mbar e essur

Stage 2 2 500 mbar · l/s Ultimate pr Stage 3 8 300 mbar · l/s Pumping speed Stage 4 20 000 mbar · l/s Purge gas flow

Pressure Fig. 2.33 Ultimate pressure of the DRYVAC 100S as a function of pure gas flow in stages 2 – 4 Fig. 2.34 Pumping speed with and without purge gas

impairment increases with increasing ate discs to the exhaust, it is possible to method several effects can be noted: pressure. In parallel to this the potential reduce the influence of the purge gas on • The admitted purge gas dilutes the for the formation of particles from the the ultimate pressure to a minimum. Test pumped mixture of substances, par- gaseous phase increases at increasing results (Fig. 2.33) indicate that the in- ticle-forming reactions will not occur, or compression levels. In order to keep the fluence of purge gas in the fourth stage is are at least delayed. size of the forming particles small and thus – as to be expected – of the lowest level • The risk of an explosion through self- their settling speed low and to maintain a since there are located between this stage igniting substances is significantly high velocity for the gas, an additional and the intake side the three other pum- reduced. quantity of gas is supplied into the pump ping stages. The admission of purge gas • Particles which have formed are con- via the individual intermediate discs (purge via the second and third stages (Fig. 2.33) veyed pneumatically through the pump gas). For this, the inflowing quantity of has a comparatively small influence on the • Losses in pumping speed and a reduc- purge gas is matched to the pressure ultimate pressure as can be seen from the tion in ultimate pressure can be kept conditions prevailing in the individual pumping speed curve in Fig. 2.34. Finally it very small due to the special way in pumping stages (see top right part of Fig. can be said that the formation of particles which the gas is made to pass through 2.32). This keeps the velocity of the gas is to be expected in most CVD processes. the pump. flow high enough within the entire pump When using dry compressing claws by so-called pneumatic pumping. Through vacuum pumps, the controlled admission the way in which the gas is lead within the of purge gas via the individual intermediate pump, i.e. from the intake through the four discs is the best approach to avoid the pumping stages with the related intermedi- formation of layers. When applying this

Intake port Motor

1st stage Claws 2nd stage

Coupling Axial face seals

Gear, complete with shafts and bearings

Fig. 2.35 Simple arrangement of the dry compression “ALL·ex” pump

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Vacuum Generation Fundamentals of Vacuum Technology

2.1.3.2.2 Claw pumps without internal view of protection against internal explo- compression for chemistry sions, something which was also taken applications (“ALL·ex” ) into account by direct cooling with cold gas (see operating principle). A special The chemical industry requires vacuum Cooling gas feature of the “ALL·ex” is that both shafts pumps which are highly reliable and which have their bearings exclusively in the gear. do not produce waste materials such as On the pumping side, the shafts are free contaminated waste oil or waste water. If (cantilevered). This simple design allows this can be done, the operating costs of the user to quickly disassemble the pump such a vacuum pump are low in view of for cleaning and servicing without the Exhaust gas the measures otherwise required for pro- need for special tools. tecting the environment (disposal of waste oil and water, for example). For operation In order to ensure a proper seal against of the simple and rugged “ALL·ex” pump the process medium in the pumping Fig. 2.37 Circulation of the cold gas in the “ALL·ex” from LEYBOLD there are no restrictions as chamber the shaft seal is of the axial face with cooler / condenser to the vapor flow or the pressure range seal type – a sealing concept well proven during continuous operation. The “ALL·ex” in chemistry applications. This type of seal rotor. The process gas then flows into the may be operated within the entire pressure is capable of sealing liquids against intake chamber which increases in size. The range from 5 to 1000 mbar without liquids, so that the pump becomes intake process is caused by the pressure restrictions. rinseable and insensitive to forming gradient produced by increasing the condensate. Fig. 2.36 shows the compo- volume of the pumping chamber. The Design of the “ALL·ex” pump nents supplied with the “ALL·ex”, together maximum volume is attained after 3/4 of a The design of the two-stage “ALL·ex” is with a gas cooler and a receiver. revolution of the rotors (Fig. 2.38-2). After shown schematically in Fig. 2.35. The gas the end of the intake process, the control flows from top to bottom through the Operating principle edge of the left rotor opens the cold gas vertically arranged pumping stages in Isochoric compression, which also serves inlet and at the same time the control edge order to facilitate the ejection of con- the purpose of limiting the temperature of the right rotor opens the intake slot (Fig. densates and rinsing liquids which may ultimately attained during compression, 2.38-3) once more. In Fig. 2.38-4 the have formed. The casing of the pump is especially in the stage on the side of the control edge of the left rotor terminates the water cooled and permits cooling of the atmosphere, and which ensures protection discharge of the gas which has been first stage. There is no sealed link between against internal explosions, is performed compressed to 1000 mbar with the cold gas chamber and cooling channel so that by venting the pumping chamber with cold gas; at the same time the control edge of the entry of cooling water into the gas from a closed refrigerating gas cycle the right rotor completes an intake process pumping chamber can be excluded. The (Fig. 2.37). Fig. 2.38-1 indicates the start of again. pressure-burst resistant design of the the intake process by opening the intake entire unit underlines the safety concept in slot through the control edge of the right The total emissions from the system are

1 3

1000 4

m3 . h-1 2 5 100 mˆgen er 6 10

7 Saugv 8 6 Pumping speed 4 2 1 2 4 6 8 1 10 100 mbar 1000 IntakeAnsaugdr pressurucek 1 Motor 5 Exhaust cooler 2 Pump 6 Cooling water 3 Intake port connection D00 4 Exhaust port 7 Cooling receiver

Fig. 2.36 “ALL·ex” pump Fig. 2.39 Pumping speed characteristic of an ALL·ex” 250

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Fundamentals of Vacuum Technology Vacuum Generation

Vmax

Exhaust slot Intake Volume of the pump slot 1 chamber starts to increase Suction Cold gas inlet Vmin

100 1000 Pmbar (10) (100)

Vmax

Volume of the pump 2 chamber at maximum End of suction

Vmin

100 1000 Pmbar (10) (100)

Cold gas inlet Vmax

Volume of the pump chamber stars to decrease (without compression). Pressure increase to 1000 mbar 3 only by admitting cold gas.

Vmin

Beginning of admitting cold gas 100 1000 Pmbar (10) (100)

Vmax

Ejection of the mixture Exhaust slot composed of sucked in gas and cold gas. 4

Cold gas inlet Vmin

100 1000 Pmbar (10) (100)

Fig. 2.38 Diagrams illustrating the pumping principle of the ALL·ex” pump (claw pump without inner compression)

not increased by the large quantities of cold solvent recovery. The method of direct gas ly. The rinsing liquids are usually applied to gas, since a closed refrigerating cycle is cooling, i.e. venting of the pumping cham- the pump after completion of the connec- maintained by way of an externally arran- ber with cold gas supplied from outside ted process (batch operation) or while the ged gas cooler and condenser (Fig. 2.37). (instead of hot exhaust gas) results in the process is in progress during brief blocking The hot exhaust gas is made to pass case of the “ALL·ex” in rotor temperatures phases. Even while the “ALL·ex” is at through the cooler and is partly returned in which are so low that mixtures of substa- standstill and while the pumping chamber the form of cold gas for pre-admission nces rated as ExT3 can be pumped reliably is completely filled with liquid it is possible cooling into the pump. The pump takes in under all operating conditions. The to start this pump up. Shown in Fig. 2.39 is the quantity of cold process gas needed for “ALL·ex” thus fully meets the requirements the pumping speed characteristic of an venting the pumping chamber back into the of the chemical industry concerning the “ALL·ex” 250. This pump has a nominal compression space on its own. This pro- protection against internal explosions. A pumping speed of 250 m3/h and an cess, however, has no influence on the certain degree of liquid compatibility makes ultimate pressure of < 10 mbar. At pumping speed of the “ALL·ex” because the the “ALL·ex” rinseable, thus avoiding the 10 mbar it still has a pumping speed of intake process has already ended when the formation of layers in the pump, for examp- 100 m3/h. The continuous operating venting process starts. Designing the le, or the capability of dissolving layers pressure of the pump may be as high as cooler as a condenser allows for simple which may already have formed respective- 1000 mbar; it consumes 13.5 kW of electric power.

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2.1.4 Accessories for Elimination of oil vapor oil-sealed rotary The attainable ultimate pressure with oil- sealed rotary pumps is strongly influenced displacement pumps by water vapor and hydrocarbons from the During a vacuum process, substances pump oil. Even with two-stage rotary vane harmful to rotary pumps can be present in pumps, a small amount of back-streaming a vacuum chamber. of these molecules from the pump interior into the vacuum chamber cannot be Elimination of water vapor avoided. For the production of hydrocar- Water vapor arises in wet vacuum proces- bon-free high and ultrahigh vacuum, for ses. This can cause water to be deposited example, with sputter-ion or turbomolecu- in the inlet line. If this condensate reaches lar pumps, a vacuum as free as possible of the inlet port of the pump, contamination oil is also necessary on the forevacuum of the pump oil can result. The pumping side of these pumps. To obtain this, me- performance of oil-sealed pumps can be dium vacuum adsorption traps (see Fig. significantly impaired in this way. More- 2.40) filled with a suitable adsorption over, water vapor discharged through the material (e.g., LINDE molecular sieve 13X) outlet valve of the pump can condense in are installed in the inlet line of such oil- the discharge outlet line. The condensate sealed forepumps. The mode of action of a can, if the outlet line is not correctly ar- sorption trap is similar to that of an ad- ranged, run down and reach the interior of sorption pump. For further details, see the pump through the discharge outlet Section 2.1.8. If foreline adsorption traps valve. Therefore, in the presence of water are installed in the inlet line of oil-sealed vapor and other vapors, the use of rotary vane pumps in continuous opera- condensate traps is strongly recommen- tion, two adsorption traps in parallel are ded. If no discharge outlet line is connec- recommended, each separated by valves. ted to the gas ballast pump (e.g., with Experience shows that the zeolite used as smaller rotary vane pumps), the use of the adsorption material loses much of its 1 Housing 2 Basket holding the sieve discharge filters is recommended. These adsorption capacity after about 10 – 14 3 Molecular sieve (filling) catch the oil mist discharged from the days of running time, after which the 4 Sealing flanges pump. other, now-regenerated, adsorption trap 5 Intake port with small flange can be utilized; hence the process can 6 Upper section Some pumps have easily exchangeable fil- continue uninterrupted. By heating the 7 Vessel for the heater or refrigerant ter cartridges that not only hold back oil 8 Connection on the side of the pump with adsorption trap, which is now not connec- small flange mist, but clean the circulating pump oil. ted in the pumping line, the vapors Whenever the amount of water vapor pre- escaping from the surface of the zeolite sent is greater than the water vapor tole- can be most conveniently pumped away Fig. 2.40 Cross section of a medium vacuum rance of the pump, a condenser should with an auxiliary pump. In operation, pum- adsorption trap always be installed between the vessel and ping by the gas ballast pump generally the pump. (For further details, see Section leads to a covering of the zeolite in the 2.1.5 Condensers 2.1.5) other, unheated adsorption trap and thus to a premature reduction of the adsorption For pumping larger quantities of water Elimination of dust capacity of this trap. vapor, the condenser is the most econo- Solid impurities, such as dust and grit, mical pump. As a rule, the condenser is significantly increase the wear on the Reduction of the effective pumping cooled with water of such temperature that pistons and the surfaces in the interior of speed the condenser temperature lies sufficiently the pump housing. If there is a danger that All filters, separators, condensers, and below the dew point of the water vapor and such impurities can enter the pump, a dust valves in the inlet line reduce the effective an economical condensation or pumping separator or a dust filter should be in- pumping speed of the pump. On the basis action is guaranteed. For cooling, however, stalled in the inlet line of the pump. Today of the values of the conductances or media such as brine and refrigerants (NH3, not only conventional filters having fairly resistances normally supplied by Freon) can also be used. large casings and matching filter inserts manufacturers, the actual pumping speed When pumping water vapor in a large are available, but also fine mesh filters of the pump can be calculated. For further industrial plant, a certain quantity of air is which are mounted in the centering ring of details, see Section 1.5.2. always involved, which is either contained the small flange. If required, it is recom- in the vapor or originates from leaks in the mended to widen the cross section with KF plant (the following considerations for air adaptors. and water vapor obviously apply also in D00 general for vapors other than water vapor). Therefore, the condenser must be backed

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Fundamentals of Vacuum Technology Vacuum Generation

of the gas ballast pump – should not condenser, the water vapor pressure pD2 at (when the quantity of permanent gas the exit of the condenser is always lower described in more detail in Section than that at the entrance; for (2.23) to be 2.2.3 is not pumped simultaneously) be fulfilled, the partial pressure of air pp2 at greater than the water vapor tolerance the exit must be higher than at the for the gas ballast pump involved. If – entrance pp1, (see Fig. 2.43), even when as cannot always be avoided in practice no throttle is present. – a higher water vapor partial pressure The higher air partial pressure p at the is to be expected at the condenser exit, p2 condenser exit is produced by an accumu- it is convenient to insert a throttle bet- 1 Inlet of the condenser lation of air, which, as long as it is present ween the condenser exit and the inlet 2 Discharge of the condenser at the exit, results in a stationary flow port of the gas ballast pump. The 3 See text equilibrium. From this accumulation of air, conductance of this throttle should be the (eventually throttled) gas ballast pump variable and regulated (see Section Fig. 2.41 Condenser (I) with downstream gas ballast in equilibrium removes just so much as 1.5.2) so that, with full throttling, the pump (II) for pumping of large quantities of streams from the entrance (1) through the pressure at the inlet port of the gas water vapor in the rough vacuum range (III) condenser. – adjustable throttle ballast pump cannot become higher than the water vapor tolerance. Also, All calculations are based on (2.23a) for by a gas ballast pump (see Fig. 2.41) and the use of other refrigerants or a de- which, however, information on the hence always works – like the Roots pump crease of the cooling water temperature quantity of pumped vapors and permanent – in a combination. The gas ballast pump may often permit the water vapor pres- gases, the composition, and the pressure has the function of pumping the fraction of sure to fall below the required value. should be available. The size of the condenser and gas ballast pump can be air, which is often only a small part of the For a mathematical evaluation of the calculated, where these two quantities are, water-vapor mixture concerned, without combination of condenser and gas ballast indeed, not mutually independent. Fig. 2.42 simultaneously pumping much water pump, it can be assumed that no loss of represents the result of such a calculation vapor. It is, therefore, understandable that, pressure occurs in the condenser, that the as an example of a condenser having a within the combination of condenser and total pressure at the condenser entrance condensation surface of 1 m2, and at an gas ballast pump in the stationary con- ptot 1, is equal to the total pressure at the dition, the ratios of flow, which occur in the inlet pressure pv1, of 40 mbar, a condenser exit, ptot 2: region of rough vacuum, are not easily condensation capacity that amounts to 15 kg / h of pure water vapor if the fraction assessed without further consideration. ptot 1 = ptot 2 (2.23) of the permanent gases is very small. 1 m3 The simple application of the continuity The total pressure consists of the sum of equation is not adequate because one is no of cooling water is used per hour, at a line the partial pressure portions of the air pp overpressure of 3 bar and a temperature of longer concerned with a source or sink-free and the water vapor p : field of flow (the condenser is, on the basis v 12 °C. The necessary pumping speed of the of condensation processes, a sink). This is p + p = p + p (2.23a) gas ballast pump depends on the existing p1 v1 p2 v2 operating conditions, particularly the size of emphasized especially at this point. In a As a consequence of the action of the practical case of “non-functioning” of the the condenser. Depending on the efficiency condenser – gas ballast pump combination, it might be unjustifiable to blame the condenser for the failure. ] In sizing the combination of condenser -1 and gas ballast pump, the following points P’ must be considered: v2 P Pv2 a) the fraction of permanent gases (air) v1 pumped simultaneously with the water

vapor should not be too great. At partial P’p2 Pp2 pressures of air that are more than Pp1 about 5 % of the total pressure at the Condensation capacity [kg · h exit of the condenser, a marked accumulation of air is produced in front of Intake pressure pD1 the condenser surfaces. The condenser Fig. 2.43 Schematic representation of the pressure dis- then cannot reach its full capacity (See Fig. 2.42 Condensation capacity of the condenser tribution in the condenser. The full lines corre- also the account in Section 2.2.3 on the (surface area available to condensation 1 m2) spond to the conditions in a condenser in simultaneous pumping of gases and as a function of intake pressure pD1 of the which a small pressure drop takes place water vapor. Curve a: Cooling water tempera- (ptot 2 < ptot 1). The dashed lines are those for vapors). ≈ ture 12 °C. Curve b: Temperature 25 °C. an ideal condenser (ptot 2 ptot 1). pD: Partial b) the water vapor pressure at the 3 Consumption in both cases 1 m /h at 3 bar pressure of the water vapor, pL: Partial pressu- condenser exit – that is, at the inlet side overpressure re of the air

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of the condenser, the water vapor partial front, but generally only behind the 2.1.6 Fluid-entrainment pumps pressure pv2 lies more or less above the condenser. saturation pressure p which corresponds Basically, a distinction is made between S If the starting time of a process is shorter to the temperature of the refrigerant. (By ejector pumps such as water jet pumps than the total running time, technically the cooling with water at 12 °C, p , would be (17 mbar < p < 1013 mbar), vapor ejector S simplest method – the roughing and the 15 mbar (see Table XIII in Section 9)). vacuum pumps holding pump – is used. Processes with -3 -1 Correspondingly, the partial air pressure (10 mbar < p < 10 mbar) and diffusion strongly varying conditions require an -3 p that prevails at the condenser exit also pumps (p < 10 mbar). Ejector vacuum p2 adjustable throttle section and, if needed, varies. With a large condenser, pumps are used mainly for the production ≈ an adjustable air admittance. of medium vacuum. Diffusion pumps pv2 pS, the air partial pressure pp,2 is thus large, and because p · V = const, the On the inlet side of the gas ballast pump a produce high and ultrahigh vacuum. Both p types operate with a fast-moving stream of volume of air involved is small. Therefore, water vapor partial pressure pv2 is always only a relatively small gas ballast pump is present, which is at least as large as the pump fluid in vapor or liquid form (water necessary. However, if the condenser is saturation vapor pressure of water at the jet as well as water vapor, oil or mercury small, the opposite case arises: coolant temperature. This ideal case is vapor). The pumping mechanism of all fluid-entrainment pumps is basically the pv2 > pS · pp2, is small. Here a relatively realizable in practice only with a very large large gas ballast pump is required. Since condenser (see above). same. The pumped gas molecules are removed from the vessel and enter into the the quantity of air involved during a With a view to practice and from the stated pumping process that uses condensers is pump fluid stream which expands after fundamental rules, consider the two passing through a nozzle. The molecules not necessarily constant but alternates following cases: within more or less wide limits, the of the pump fluid stream transfer by way considerations to be made are more 1. Pumping of permanent gases with of impact impulses to the gas molecules in difficult. Therefore, it is necessary that the small amounts of water vapor. Here the the direction of the flow. Thus the gas pumping speed of the gas ballast pump size of the condenser – gas ballast pump which is to be pumped is moved to a space effective at the condenser can be regulated combination is decided on the basis of the having a higher pressure. within certain limits. pumped-off permanent gas quantity. The In fluid-entrainment pumps corresponding condenser function is merely to reduce the In practice, the following measures are vapor pressures arise during operation water vapor pressure at the inlet port of usual: depending on the type of pump fluid and the gas ballast pump to a value below the a) A throttle section is placed between the the temperature as well as the design of water vapor tolerance. gas ballast pump and the condenser, the nozzle. In the case of oil diffusion which can be short-circuited during 2. Pumping of water vapor with small pumps this may amount to 1 mbar in the rough pumping. The flow resistance of amounts of permanent gases. Here, to boiling chamber. The backing pressure in the throttle section must be adjustable make the condenser highly effective, as the pump must be low enough to allow the so that the effective speed of the pump small as possible a partial pressure of the vapor to flow out. To ensure this, such can be reduced to the required value. permanent gases in the condenser is pumps require corresponding backing This value can be calculated using the sought. Even if the water vapor partial pumps, mostly of the mechanical type. The equations given in Section 2.2.3. pressure in the condenser should be vapor jet cannot enter the vessel since it b) Next to the large pump for rough pum- greater than the water vapor tolerance of condenses at the cooled outer walls of the ping a holding pump with low speed is the gas ballast pump, a relatively small gas pump after having been ejected through installed, which is of a size corres- ballast pump is, in general, sufficient with the nozzle. ponding to the minimum prevailing gas the then required throttling to pump away Wolfgang Gaede was the first to realize quantity. The objective of this holding the prevailing permanent gases. that gases at comparatively low pressure pump is merely to maintain optimum Important note: During the process, if the can be pumped with the aid of a pump operating pressure during the process. pressure in the condenser drops below the fluid stream of essentially higher pressure c) The necessary quantity of air is ad- saturation vapor pressure of the conden- and that, therefore, the gas molecules mitted into the inlet line of the pump sate (dependent on the cooling water from a region of low total pressure move through a variable-leak valve. This temperature), the condenser must be into a region of high total pressure. This additional quantity of air acts like an blocked out or at least the collected apparently paradoxical state of affairs enlarged gas ballast, increasing the condensate isolated. If this is not done, the develops as the vapor stream is initially water vapor tolerance of the pump. gas ballast pump again will pump out the entirely free of gas, so that the gases from However, this measure usually results vapor previously condensed in the a region of higher partial gas pressure (the in reduced condenser capacity. More- condenser vessel) can diffuse into a region of lower over, the additional admitted quantity of partial gas pressure (the vapor stream). air means additional power consump- This basic Gaede concept was used by tion and (see Section 8.3.1.1) increased Langmuir (1915) in the construction of the oil consumption. As the efficiency of the first modern diffusion pump. The first D00 condenser deteriorates with too great a diffusion pumps were mercury diffusion partial pressure of air in the condenser, pumps made of glass, later of metal. In the the admission of air should not be in Sixties, mercury as the medium was

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almost completely replaced by oil. To generally with water. Smaller oil diffusion 2.1.6.1 (Oil) Diffusion pumps obtain as high a vapor stream velocity as pumps can, however, also be cooled with These pumps consist basically (see Fig. possible, he allowed the vapor stream to an air stream because a low wall tempe- 2.44) of a pump body (3) with a cooled emanate from a nozzle with supersonic rature is not so decisive to the efficiency as wall (4) and a three- or four-stage nozzle speed. The pump fluid vapor, which con- for mercury diffusion pumps. Oil diffusion system (A – D). The oil serving as pump stitutes the vapor jet, is condensed at the pumps can operate well with wall tempera- fluid is in the boiler (2) and is vaporized cooled wall of the pump housing, whereas tures of 30 °C, whereas the walls of mer- from here by electrical heating (1). The the transported gas is further compressed, cury diffusion pumps must be cooled to pump fluid vapor streams through the usually in one or more succeeding stages, 15 °C. To protect the pumps from the riser tubes and emerges with supersonic before it is removed by the backing pump. danger of failure of the cooling water – speed from the ring-shaped nozzles (A – The compression ratios, which can be insofar as the cooling-water coil is not D). Thereafter the jet so-formed widens obtained with fluid entrainment pumps, controlled by thermally operated protec- like an umbrella and reaches the wall are very high: if there is a pressure of 10-9 tive switching – a water circulation moni- where condensation of the pump fluid mbar at the inlet port of the fluid- tor should be installed in the cooling water occurs. The liquid condensate flows entrainment pump and a backing pressure circuit; hence, evaporation of the pump downward as a thin film along the wall and of 10-2 mbar, the pumped gas is com- fluid from the pump walls is avoided. finally returns into the boiler. Because of pressed by a factor of 107! this spreading of the jet, the vapor density Basically the ultimate pressure of fluid is relatively low. The diffusion of air or any entrainment pumps is restricted by the pumped gases (or vapors) into the jet is so value for the partial pressure of the fluid rapid that despite its high velocity the jet used at the operating temperature of the pump. In practice one tries to improve this by introducing baffles or cold traps. These are “condensers” between fluid entrainment pump and vacuum chamber, so that the ultimate pressure which can be attained in the vacuum chamber is now only limited by the partial pressure of the fluid at the temperature of the baffle. The various types of fluid entrainment pumps are essentially distinguished by the density of the pump fluid at the exit of the top nozzle facing the high vacuum side of the pump: 1. Low vapor density: Diffusion pumps Oil diffusion pumps (Series: LEYBODIFF, DI and DIP) Mercury diffusion pumps 2. High vapor density: Vapor jet pumps Water vapor pumps Oil vapor jet pumps Mercury vapor jet pumps 3. Combined oil diffusion/ vapor jet pumps 4. Water jet pumps

Cooling of fluid entrainment pumps The heater power that is continuously supplied for vaporizing the pump fluid in 1 Heater 5 High vacuum flange A 2 Boiler 6 Gas molecules B fluid-entrainment pumps must be dissipa- 3 Pump body 7 Vapor jet Cဲ Nozzles ted by efficient cooling. The energy 4 Cooling coil 8 Backing vacuum connection D required for pumping the gases and vapors is minimal. The outside walls of the Fig. 2.44 Mode of operation of a diffusion pump casing of diffusion pumps are cooled,

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becomes virtually completely saturated lowest diffusion stage, to allow the volatile To characterize the effectiveness of a with the pumped medium. Therefore, over components to evaporate and be removed diffusion pump, the so called HO factor is a wide pressure range diffusion pumps by the backing pump. Therefore, the re- defined. This is the ratio of the actually have a high pumping speed. This is evaporating pump fluid consists of only obtained specific pumping speed to the practically constant over the entire the less volatile components of the pump theoretical maximum possible specific working region of the diffusion pump oil. pumping speed. In the case of diffusion (≤ 10-3 mbar) because the air at these low pumps from LEYBOLD optimum values pressures cannot influence the jet, so its Pumping speed are attained (of 0.3 for the smallest and up course remains undisturbed. At higher The magnitude of the specific pumping to 0.55 for the larger pumps). inlet pressures, the course of the jet is speed S of a diffusion pump – that is, the The various oil diffusion pumps manufac- altered. As a result, the pumping speed pumping speed per unit of area of the tured by LEYBOLD differ in the following decreases until, at about 10-1 mbar, it actual inlet surface – depends on several design features (see Fig. 2.45 a and b). becomes immeasurably small. parameters, including the position and The forevacuum pressure also influences dimensions of the high vacuum stage, the a) LEYBODIFF series velocity of the pump fluid vapor, and the This series of pumps is equipped with a the vapor jet and becomes detrimental if - its value exceeds a certain critical limit. mean molecular velocity c of the gas being fractionating device. The various consti- This limit is called maximum backing pumped (see equation 1.17 in Section tuents of the pump fluid are selected so pressure or critical forepressure. The 1.1). With the aid of the kinetic theory of that the high vacuum nozzle is supplied capacity of the chosen backing pump must gases, the maximum attainable specific only by the fraction of the pump fluid that be such (see 2.3.2) that the amount of gas pumping speed at room temperature on has the lowest vapor pressure. This discharged from the diffusion pump is pumping air is calculated to assures a particularly low ultimate pres- -1 -2 pumped off without building up a backing Smax = 11.6 l · s · cm . This is the spe- sure. Fractionating occurs because the pressure that is near the maximum cific (molecular) flow conductance of the degassed oil first enters the outer part of backing pressure or even exceeding it. intake area of the pump, resembling an the boiler, which serves the nozzle on the aperture of the same surface area (see backing vacuum side. Here a part of the The attainable ultimate pressure depends equation 1.30 in Section 1.5.3). Quite more volatile constituents evaporates. on the construction of the pump, the vapor generally, diffusion pumps have a higher Hence the already purified pump fluid pressure of the pump fluid used, the pumping speed for lighter gases compared reaches the intermediate part of the boiler, maximum possible condensation of the to heavier gases. which serves the intermediate nozzle. Here pump fluid, and the cleanliness of the vessel. Moreover, backstreaming of the pump fluid into the vessel should be reduced as far as possible by suitable baffles or cold traps (see Section 2.1.6.4).

Degassing of the pump oil In oil diffusion pumps it is necessary for the pump fluid to be degassed before it is returned to the boiler. On heating of the pump oil, decomposition products can arise in the pump. Contamination from the vessel can get into the pump or be contained in the pump in the first place. These constituents of the pump fluid can significantly worsen the ultimate pressure attainable by a diffusion pump, if they are not kept away from the vessel. Therefore, the pump fluid must be freed of these impurities and from absorbed gases. 1 2 This is the function of the degassing section, through which the circulating oil passes shortly before re-entry into the a) LEYBODIFF-Pump with fractionating b) DI pump; side view on to the boiler. In the degassing section, the most facility internal heater volatile impurities escape. Degassing is 1 Center 1 Thermostat sensor obtained by the carefully controlled 2 Middle section 2 Heating cartridge 3 Outer part of the boiler temperature distribution in the pump. The (fractionation) D00 condensed pump fluid, which runs down the cooled walls as a thin film, is raised to Fig. 2.45 Diagram showing the basic differences in LEYBOLD oil diffusion pumps a temperature of about 130 °C below the

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boiling. Those parts of the thermal conductivity panels above the oil level supply additional energy to the vapor. Owing to the special design of the heating system, the heater cartridges may be exchanged also while the pump is still hot.

1 Nozzle (Laval) 2.1.6.2 Oil vapor ejector pumps 2 Diffuser nozzle (Venturi) 3 Mixing chamber The pumping action of a vapor ejector 4 Connection to the vacuum chamber stage is explained with the aid of Fig. 2.46. The pump fluid enters under high pressure Fig. 2.46 Operation of a vapor jet pump p1 the nozzle (1), constructed as a Laval nozzle. There it is expanded to the inlet the lighter constituents are evaporated in pressure p2. On this expansion, the greater quantities than the heavier con- sudden change of energy is accompanied stituents. When the oil enters the central by an increase of the velocity. The region of the boiler, which serves the high consequently accelerated pump fluid vacuum nozzle, it has already been freed of vapor jet streams through the mixer region 1 High vacuum port the light volatile constituents. (3), which is connected to the vessel (4) 2 Diffusion stages being evacuated. Here the gas molecules 3 Ejector stages b) DI series emerging from the vessel are dragged In these pumps an evaporation process for along with the vapor jet. The mixture, Fig. 2.47 Diagram of an oil jet (booster) pump the pump fluid which is essentially free of pump fluid vapor – gas, now enters the bursts is attained by the exceptional heater diffuser nozzle constructed as a Venturi The oil vapor ejector pumps used in design resulting in a highly constant nozzle (2). Here the vapor – gas mixture is present-day vacuum technology have, in pumping speed over time. The heater is of compressed to the backing pressure p3 general, one or more diffusion stages and the internal type and consists of heating with simultaneous diminution of the several subsequent ejector stages. The cartridges into which tubes with soldered velocity. The pump fluid vapor is then con- nozzle system of the booster is construc- on thermal conductivity panels are densed at the pump walls, whereas the ted from two diffusion stages and two introduced. The tubes made of stainless entrained gas is removed by the backing ejector stages in cascade (see Fig. 2.47). steel are welded horizontally into the pump. Oil vapor ejector pumps are ideally The diffusion stages provide the high pump’s body and are located above the oil suited for the pumping of larger quantities pumping speed between 10-4 and 10-3 level. The thermal conductivity panels of gas or vapor in the pressure region mbar (see Fig. 2.48), the ejector stages, -3 made of copper are only in part immersed between 1 and 10 mbar. The higher the high gas throughput at high pressures in the pump fluid. Those parts of the density of the vapor stream in the nozzles (see Fig. 2.49) and the high critical backing thermal conductivity panels are so rated ensures that the diffusion of the pumped pressure. Insensitivity to dust and vapors that the pump fluid can evaporate gas in the vapor stream takes place much dissolved in the pump fluid is obtained by intensively but without any retardation of more slowly than in diffusion pumps, so a spacious boiler and a large pump fluid that only the outer layers of the vapor stream are permeated by gas. Moreover, the surface through which the diffusion occurs is much smaller because of the special construction of the nozzles. The ] –1 ]

specific pumping speed of the vapor ] –1 ejector pumps is, therefore, smaller than –1 r · l s

that of the diffusion pumps. As the pum- or ped gas in the neighborhood of the jet under the essentially higher inlet pressure decisively influences the course of the flow

Pumping speed [l · s lines, optimum conditions are obtained

only at certain inlet pressures. Therefore, Pumping speed [T

the pumping speed does not remain con- Pumping speed [mbar ·l · s

Intake pressure pa stant toward low inlet pressures. As a Intake pressure pa Fig. 2.48 Pumping speed of various vapor pumps as a consequence of the high vapor stream function of intake pressure related to a nomi- velocity and density, oil vapor ejector nal pumping speed of 1000 l/s. pumps can transport gases against a rela- End of the working range of oil vapor ejector tively high backing pressure. Their critical Fig. 2.49 Pumping speed of various vapor pumps pumps (A) and diffusion pumps (B) backing pressure lies at a few millibars. (derived from Fig. 2.48)

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reservoir. Large quantities of impurities tion neither decomposes nor becomes sed at) the inner cooled surfaces of these can be contained in the boiler without de- strongly oxidized when air is admitted. devices. Second, the condensation sur- terioration of the pumping characteristics. However, at room temperature it has a faces must be so constructed and geome- comparatively high vapor pressure of trically arranged that the flow conductance 10-3 mbar. If lower ultimate total pressures of the baffles or cold traps is as large as 2.1.6.3 Pump fluids are to be reached, cold traps with liquid possible for the pumped gas. These two nitrogen are needed. With their aid, requirements are summarized by the term a) Oils ultimate total pressures of 10-10 mbar can “optically opaque”. This means that the The suitable pump fluids for oil diffusion be obtained with mercury diffusion pumps. particles cannot enter the baffle without pumps are mineral oils, silicone oils, and Because mercury is toxic, as already hitting the wall, although the baffle has a oils based on the polyphenyl ethers. mentioned, and because it presents a high conductance. The implementation of Severe demands are placed on such oils hazard to the environment, it is nowadays this idea has resulted in a variety of which are met only by special fluids. The hardly ever used as a pump fluid. designs that take into account one or the properties of these, such as vapor pres- LEYBOLD supplies pumps with mercury as other requirement. sure, thermal and chemical resistance, the pump fluid only on request. The vapor A cold cap baffle is constructed so that it particularly against air, determine the pressure curves of pump fluids are given in can be mounted immediately above the choice of oil to be used in a given type of Fig. 9.12, Section 9. pump or to attain a given ultimate vacuum. high vacuum nozzle. The cold cap baffle is The vapor pressure of the oils used in made of metal of high thermal conductivity vapor pumps is lower than that of mer- 2.1.6.4 Pump fluid backstreaming and in good thermal contact with the cooled cury. Organic pump fluids are more sen- its suppression (vapor pump wall, so that in practice it is main- sitive in operation than mercury, because barriers, baffles) tained at the cooling-water temperature or, the oils can be decomposed by long-term with air-cooled diffusion pumps, at ambi- In the vapor stream from the topmost admission of air. Silicone oils, however, ent temperature. In larger types of pumps, nozzle of a diffusion pump, pump fluid withstand longer lasting frequent admis- the cold cap baffle is water cooled and molecules not only travel in the direction sions of air into the operational pump. permanently attached to the pump body. of streaming to the cooled pump wall, but The effective pumping speed of a diffusion Typical mineral oils are DIFFELEN light, also have backward components of pump is reduced by about 10 % on normal and ultra. The different types of velocity because of intermolecular colli- installation of the cold cap baffle, but the DIFFELEN are close tolerance fractions of a sions. They can thus stream in the direc- oil backstreaming is reduced by about 90 high quality base product (see our cata- tion of the vessel. In the case of to 95 %. log). LEYBODIFF and DI pumps, the oil-backstreaming amounts to a few micrograms Shell baffles consist of concentrically Silicone oils (DC 704, DC 705, for examp- per minute for each square centimeter of arranged shells and a central baffle plate. le) are uniform chemical compounds inlet cross-sectional area. To reduce this With appropriate cooling by water or (organic polymers). They are highly backstreaming as much as possible, refrigeration, almost entirely oil vapor-free resistant to oxidation in the case of air various measures must be undertaken vacua can be produced by this means. The inrushes and offer special thermal stability simultaneously: effective pumping speed of the diffusion characteristics. a) the high vacuum-side nozzle and the pump remains at least at 50 %, although DC 705 has an extremely low vapor pres- shape of the part of the pump body shell baffles are optically opaque. This type sure and is thus suited for use in diffusion surrounding this nozzle must be of baffle has been developed by LEYBOLD pumps which are used to attain extremely constructed so that as few as possible in two different forms: with a stainless- low ultimate pressures of < 10-10 mbar. vapor molecules emerge sideways in steel cooling coil or – in the so-called Astrotorus baffles – with cooling inserts of ULTRALEN is a polyphenylether. This fluid the path of the vapor stream from the copper. The casing of the former type is is recommended in all those cases where a nozzle exit to the cooled pump wall. made entirely of stainless steel. particularly oxidation-resistant pump fluid b) the method for cooling the pump wall must be used and where silicone oils must allow as complete as possible For the smaller air-cooled, oil diffusion would interfere with the process. condensation of the pump fluid vapor pumps, plate baffles are used. The air- and, after condensation, the fluid must cooled arrangement consists of a copper APIEZON AP 201 is an oil of exceptional be able to drain away readily. plate with copper webs to the housing thermal and chemical resistance capable c) one or more pump-fluid traps, baffles, wall. The temperature of the plate baffle of delivering the required high pumping or cold traps must be inserted between remains nearly ambient during the speed in connection with oil vapor ejector the pump and the vessel, depending on operation of the diffusion pump. pumps operating in the medium vacuum the ultimate pressure that is required. range. The attainable ultimate total pres- Hydrocarbon-free vacuum sure amounts to about 10-4 mbar. Two chief requirements must be met in the construction of baffles or cold traps for oil If extreme demands are made on freedom b) Mercury diffusion pumps. First, as far as possible, from oil vapor with vacuum produced by D00 Mercury is a very suitable pump fluid. It is all backstreaming pump-fluid vapor mole- oil diffusion pumps, cold traps should be a chemical element that during vaporiza- cules should remain attached to (conden- used that are cooled with liquid nitrogen

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The temperature increase at the vessel Note: containing the refrigerant is so slight over It must be noted that data on back- the operating time that – as the liquid level streaming as specified in catalogs apply drops – no significant desorption of the only to continuously-operated oil diffusion condensate takes place. Located on the pumps. Shortly after starting a pump the pumping side is an impact panel made of uppermost nozzle will not eject a well copper. The low temperature of this panel directed vapor jet. Instead oil vapor ensures that the greater part of the spreads in all directions for several se- condensed pump fluid remains in the conds and the backstreaming effect is liquid state and may drip back into the strong. When switching a diffusion pump pump. Today the oils used to operate dif- on and off frequently the degree of oil fusion pumps have a very low vapor pres- brackstreaming will be greater. sure at room temperature (for example DIFFELEN light, 2 · 10-8 mbar; DC 705, 4 · 10-10 mbar). The specified provisions 2.1.6.5 Water jet pumps and steam with a liquid-nitrogen-cooled baffle or cold ejectors trap would enable an absolutely oil-free Included in the class of fluid-entrainment vacuum to be produced. pumps are not only pumps that use a fast- In practice, however, complete suppres- streaming vapor as the pump fluid, but sion of oil-backstreaming is never at- also liquid jet pumps. The simplest and tained. There are always a few pump-fluid cheapest vacuum pumps are water jet molecules that, as a result of collisions pumps. As in a vapor pump (see Fig. 2.46 with one another, reach the vessel without or 2.51), the liquid stream is first released having hit one of the cooled surfaces of the from a nozzle and then, because of baffle or the cold trap. Moreover, there are turbulence, mixes with the pumped gas in always a few highly volatile components of 1 Diffusion pump with cold the mixing chamber. Finally, the movement cap baffle (cooled by contact), the pump fluid that do not remain attached of the water – gas mixture is slowed down 2 Shell or chevron baffle to the very low temperature surfaces. The in a Venturi tube. The ultimate total 3 Anticreep barrier temperature and the vapor molecules pressure in a container that is pumped by 4 Sealing gasket adsorbed at the surface of the vessel 5 Bearing ring a water jet pump is determined by the determine exactly the pressure in the 6 LN2 cold trap, vapor pressure of the water and, for 7 Vacuum chamber vessel. If, the surfaces are not fully cove- example, at a water temperature of 15 °C red with adsorbed pump-fluid molecules amounts to about 17 mbar. Fig. 2.50 Schematic arrangement of baffle, anticreep after a bake-out process, their vapor barrier and cold trap above a diffusion pump pressure contributes only insignificantly to Essentially higher pumping speeds and the pressure in the vessel. lower ultimate pressures are produced by steam ejector pumps. The section so that they are maintained at a tempera- After a certain time, the “stay-down time”, through one stage is shown in Fig. 2.51. ture of -196 °C. a continuous layer of oil molecules builds The markings correspond with those Low-temperature baffles or cold traps up, and the ultimate pressure is practically shown in Fig. 2.46. In practice, several should always be used with a cold cap in determined by the vapor pressure of the pumping stages are usually mounted in place. On this the greatest part of the pump fluid at the temperature of the vessel cascade. For laboratory work, two-stage backstreaming oil is condensed, so that walls. This “stay-down” time can even pump combinations are suitable and the inevitable loss of pump fluid from the amount to several hours, indeed even to consist of a steam ejector stage and a condensation of the pump fluid on the low- days, with the use of low-temperature water jet (backing) stage, both made of temperature surface is kept at a minimum. baffles. glass. The water jet backing stage enables With longer-term operation it is always ad- Oil can reach the vessel not only as vapor, operation without other backing pumps. visable to install, in place of the cold cap, a but also as a liquid film, because oil wets With the help of a vapor stream at water-cooled shell or chevron baffle readily and thus creeps up the wall. overpressure, the vacuum chamber can be between the diffusion pump and the low- evacuated to an ultimate pressure of about temperature baffle or cold trap (see Fig. By installation of an anticreep barrier (see 3 mbar. The condensate from the steam is 2.50). Fig. 2.50) made of Teflon polymer, a mate- led off through the drain attachment. The rial that is not wetted by oil and can stand water jet stage of this pump is cooled with LEYBOLD manufactures cold traps made a bake-out temperature up to 200 °C, water to increase its efficiency. Steam of metal so called LN2 cold traps. These further creeping of the oil can be effecti- ejector pumps are especially suitable for cold traps are to be used in those cases vely prevented. It is most appropriate to work in laboratories, particularly if very where a cold trap is to be operated for arrange the anticreep barrier above the aggressive vapors are to be pumped. prolonged periods of time without re- upper baffle (see Fig. 2.50). Steam ejector pumps, which will operate quiring a filling facility for liquid nitrogen. at a pressure of a few millibars, are

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2.1.7 Turbomolecular pumps Whereas the dependence of the pumping speed_ on the _type_ of gas is fairly low The principle of the molecular pump – well (S ∼ c ∼ 1 / Eǰ M ), the dependence of the known since 1913 – is that the gas par- compression k at zero throughput and ticles to be pumped receive, through 0 thus also the compression__ k, because impact with the rapidly moving surfaces of ∼ ǰM ∼ of k0 e log k0 ǰ M , is greater as a rotor, an impulse in a required flow direc- shown by the experimentally-determined tion. The surfaces of the rotor – usually relationship in Fig. 2.55. disk-shaped – form, with the stationary Example: surfaces of a stator, intervening spaces in which the gas is transported to the backing from theory it follows that port. In the original Gaede molecular log k (He) pump and its modifications, the inter- 0 = 4 = 1 = 1 vening spaces (transport channels) were log k0(N2) 28 7 2.65 very narrow, which led to constructional ⇒ = log k0(N 2) 2.65·logk0(He) difficulties and a high degree of sus- ceptibility to mechanical contamination. 3 this with k0 (He) = 3 · 10 from Fig. 2.55 At the end of the Fifties, it became possible results in: – through a turbine-like design and by 3 modification of the ideas of Gaede – to log k0 (N2) = 2.65 · log (3 · 10 ) = 9.21 produce a technically viable pump the so- or k (N ) = 1.6 · 109. called “turbomolecular pump”. The 0 2 spaces between the stator and the rotor This agrees – as expected – well (order of disks were made in the order of magnitude) with the experimentally determined value for k (N ) = 2.0 · 108 1 Steam inlet millimeters, so that essentially larger 0 2 2 Jet nozzle tolerances could be obtained. Thereby, from Fig. 2.55. In view of the optimizations 3 Diffuser greater security in operation was achieved. for the individual rotor stages common 4 Mixing region However, a pumping effect of any today, this consideration is no longer 5 Connection to the vacuum chamber significance is only attained when the correct for the entire pump. Shown in Fig. circumferential velocity (at the outside 2.56 are the values as measured for a Fig. 2.51 Schematic representation of the operation rim) of the rotor blades reaches the order modern TURBOVAC 340 M. of a steam ejector pump of magnitude of the average thermal In order to meet the condition, a circumfe- velocity of the molecules which are to be rential velocity for the rotor of the same especially recommended for pumping pumped. Kinetic gas theory supplies for -c order of magnitude as -c high rotor speeds laboratory distillation apparatus and of the equation 1.17: are required for turbomolecular pumps. similar plants when the pressure from a They range from about 36,000 rpm for simple water jet pump is insufficient. In 8· R ·T pumps having a large diameter rotor c = π this instance, the use of rotary pumps · M (TURBOVAC 1000) to 72,000 rpm in the would not be economical. case of smaller rotor diameters in which the dependency on the type of gas Even in spite of their low investment costs (TURBOVAC 35 / 55). Such high speeds as a function of molar mass M is contained. water jet pumps and steam ejectors are naturally raise questions as to a reliable The calculation involving cgs-units being replaced in the laboratories more bearing concept. LEYBOLD offers three (where R = 83.14 · 106 mbar · cm3/mol · K) and more by diaphragm pumps because of concepts, the advantages and disadvan- results in the following Table: the environmental problems of using water tages of which are detailed in the follo- as the pump fluid. Solvent entering the Gas Molar Mean thermal wing: Mass M velocity (m/s) • Oil lubrication / steel ball bearings water can only be removed again through ————————————–———— complex cleaning methods (distillation). + Good compatibility with particles by H2 2 1761 circulating oil lubricant He 4 1245 - Can only be installed vertically H2O 18 587 + Low maintenance Ne 20 557 • Grease lubrication / hybrid bearings CO 28 471 + Installation in any orientation N 28 471 2 + Suited for mobile systems Air 28.96 463 ± Air cooling will do for many applica- O 32 440 2 tions Ar 40 394 + Lubricated for life (of the bearings) D00 CO2 44 375 CC13F (F11) 134.78 68 Table 2.4 -c as a function of molar mass M

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• Free of lubricants / magnetic suspen- Jülich” permitted the magnetic suspen- stages, whose blades have shorter radial sion sion concept to spread widely. In this spans, where the gas is compressed to + No wear system the rotor is maintained in a stable backing pressure or rough vacuum pres- + No maintenance position without contact during operation, sure. The turbine rotor (6) is mounted on + Absolutely free of hydrocarbons by magnetic forces. Absolutely no lubri- the drive shaft, which is supported by two + Low noise and vibration levels cants are required. So-called touch down precision ball bearings (8 and 11), accom- + Installation in any orientation bearings are integrated for shutdown. modated in the motor housing. The rotor shaft is directly driven by a medium-fre- Steel ball bearings / hybrid ball bearings Fig. 2.52 shows a sectional drawing of a quency motor housed in the forevacuum (ceramic ball bearings): Even a brief tear typical turbomolecular pump. The pump is space within the rotor, so that no rotary in the thin lubricating film between the an axial flow compressor of vertical shaft lead-through to the outside atmos- balls and the races can – if the same type design, the active or pumping part of phere is necessary. This motor is powered of material is used – result in microwelding which consists of a rotor (6) and a stator and automatically controlled by an external at the points of contact. This severely re- (2). Turbine blades are located around the frequency converter, normally a solid-state duces the service life of the bearings. By circumferences of the stator and the rotor. frequency converter that ensures a very using dissimilar materials in so called hy- Each rotor – stator pair of circular blade low noise level. For special applications, brid bearings (races: steel, balls: ceramics) rows forms one stage, so that the for example, in areas exposed to radiation, the effect of microwelding is avoided. assembly is composed of a multitude of motor generator frequency converters are stages mounted in series. The gas to be The most elegant bearing concept is that used. pumped arrives directly through the of the magnetic suspension. As early as aperture of the inlet flange (1), that is, The vertical rotor – stator configuration 1976 LEYBOLD delivered magnetically without any loss of conductance, at the provides optimum flow conditions of the suspended turbomolecular pumps – the active pumping area of the top blades of gas at the inlet. legendary series 550M and 560M. At that the rotor – stator assembly. This is equip- time a purely active magnetic suspension To ensure vibration-free running at high ped with blades of especially large radial (i.e. with electromagnets) was used. Ad- rotational speeds, the turbine is dyna- span to allow a large annular inlet area. vances in electronics and the use of per- mically balanced at two levels during its The gas captured by these stages is manent magnets (passive magnetic assembly. transferred to the lower compression suspension) based on the “System KFA

Turbomole- cular pump stage 3

Siegbahn stage 5

8 1

1 High vacuum inlet flange 7 Pump casing 1 Vacuum port 5 Bearing 2 Stator pack 8 Ball bearings 2 High vacuum flange 6 Motor 3 Venting flange 9 Cooling water connection 3 Rotor 7 Fan 4 Forevacuum flange 10 3-phase motor 4 Stator 8 Bearing 5 Splinter guard 11 Ball bearings 6 Rotor

Fig. 2.52 Schematic diagram of a grease lubricated TURBOVAC 151 Fig. 2.52a Cross section of a HY.CONE turbomolecular pump turbomolecular pump

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10000 l · s–1 l · s–1

600 1000/1000 MC

1000 500 S 361 200 340M 151 100 50/55

10 2 4 6 8 ñ6 ñ5 ñ4 ñ3 ñ2 ñ1 10 10 10 p 10 10 mbar 10

Fig. 2.53 Pumping speed for air of different turbomolecular pumps Fig. 2.54 Pumping speed curves of a TURBOVAC 600 for H2, He, N2 and Ar

The pumping speed (volume flow rate) forevacuum flange of the pump and that at the aid of one or more cooled baffles or characteristics of turbomolecular pumps the high vacuum flange: maximum com- traps and without the risk of a measurable are shown in Fig. 2.53. The pumping pression k0 is to be found at zero partial pressure for hydrocarbons in the speed remains constant over the entire throughput. For physical reasons, the vacuum chamber (hydrocarbon-free working pressure range. It decreases at compression ratio of turbomolecular vacuum! – see also Fig. 2.57: residual gas intake pressures above 10-3 mbar, as this pumps is very high for heavy molecules spectrum above a TURBOVAC 361). As the threshold value marks the transition from but considerably lower for light molecules. hydrogen partial pressure attained by the the region of molecular flow to the region The relationship between compression rotary backing pump is very low, the of laminar viscous flow of gases. Fig. 2.54 and molecular mass is shown in Fig. 2.55. turbomolecular pump is capable of shows also that the pumping speed Shown in Fig. 2.56 are the compression attaining ultimate pressures in the 10-11 depends on the type of gas. curves of a TURBOVAC 340 M for N2, He mbar range in spite of its rather moderate and H as a function of the backing pres- compression for H . To produce such ex- The compression ratio (often also simply 2 2 sure. Because of the high compression tremely low pressures, it will, of course, be termed compression) of turbomolecular ratio for heavy hydrocarbon molecules, necessary to strictly observe the general pumps is the ratio between the partial turbomolecular pumps can be directly rules of UHV technology: the vacuum pressure of one gas component at the connected to a vacuum chamber without chamber and the upper part of the turbo-

M = Mass number = Relative molar mass at an ionization 1 √M I = Ion current D00 Fig. 2.56 Maximum compression k0 of a turbomolecular Fig. 2.55 TURBOVAC 450 – Maximum compression pump TURBOVAC 340 M for H2, He and N2 as k0 as a function of molar mass M a function of backing pressure Fig. 2.57 Spectrum above a TURBOVAC 361

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molecular pump must be baked out, and pump should be vented (except in the case metal seals must be used. At very low of operation with a barrier gas) via the pressures the residual gas is composed venting flange which already contains a mainly of H2 originating from the metal sintered metal throttle, so that venting may walls of the chamber. The spectrum in Fig. be performed using a normal valve or a 2.57 shows the residual gas composition power failure venting valve. in front of the inlet of a turbomolecular pump at an ultimate pressure of 7 · 10-10 Barrier gas operation mbar nitrogen equivalent. It appears that In the case of pumps equipped with a the portion of H2 in the total quantity of barrier gas facility, inert gas – such as dry gas amounts to approximately 90 to 95 %. nitrogen – may be applied through a The fraction of “heavier” molecules is con- special flange so as to protect the motor siderably reduced and masses greater than space and the bearings against aggressive 44 were not detected. An important crite- media. A special barrier gas and venting rion in the assessment of the quality of a valve meters the necessary quantity of residual gas spectrum are the measurable barrier gas and may also serve as a ven- hydrocarbons from the lubricants used in ting valve. the vacuum pump system. Of course an Fig. 2.58 Determination of the cut-in pressure for “absolutely hydrocarbon-free vacuum” turbomolecular pumps when evacuating Decoupling of vibrations large vessels can only be produced with pump systems TURBOVAC pumps are precisely balanced which are free of lubricants, i.e. for exam- and may generally be connected directly to ple with magnetically-suspended turbo- pump sets and large vacuum chambers. At the apparatus. Only in the case of highly molecular pumps and dry compressing a known pumping speed for the backing sensitive instruments, such as electron 3 backing pumps. When operated correctly pump SV (m /h) and a known volume for microscopes, is it recommended to install 3 (venting at any kind of standstill) no hy- the vacuum chamber (m ) it is possible to vibration absorbers which reduce the drocarbons are detectable also in the spec- estimate the cut-in pressure for the present vibrations to a minimum. For mag- trum of normal turbomolecular pumps. turbomolecular pump: netically suspended pumps a direct A further development of the turbomo- Simultaneous start when connection to the vacuum apparatus will usually do because of the extremely low lecular pump is the hybrid or compound S v > 40h−1 vibrations produced by such pumps. turbomolecular pump. This is actually two V pumps on a common shaft in a single For special applications such as opera- casing. The high vacuum stage for the mo- and delayed start when tion in strong magnetic fields, radiation lecular flow region is a classic turbo- hazard areas or in a tritium atmosphere, S molecular pump, the second pump for the v < 40h−1 please contact our Technical Sales Depart- viscous flow range is a molecular drag or V ment which has the necessary experience friction pump. and which is available to you at any time. at a cut-in pressure of: LEYBOLD manufactures pumps such as  S  the TURBOVAC 55 with an integrated  V  6 ·V (2.24) Holweck stage (screw-type compressor) pV,Start = e mbar and, for example, the HY.CONE 60 or HY.CONE 200 with an integrated Siegbahn When evacuating larger volumes the cut-in stage (spiral compressor). The required pressure for turbomolecular pumps may backing pressure then amounts to a few also be determined with the aid of the mbar so that the backing pump is only diagram of Fig. 2.58. required to compress from about 5 to 10 mbar to atmospheric pressure. A sectional Venting view of a HY.CONE is shown in Fig. 2.52a. After switching off or in the event of a power failure, turbomolecular pumps Information on the operation of turbomo- should always be vented in order to lecular pumps prevent any backdiffusion of hydrocarbons from the forevacuum side into the vacuum Starting chamber. After switching off the pump the As a rule turbomolecular pumps should cooling water supply should also be generally be started together with the switched off to prevent the possible backing pump in order to reduce any condensation of water vapor. In order to backstreaming of oil from the backing protect the rotor it is recommended to pump into the vacuum chamber. A delayed comply with the (minimum) venting times start of the turbomolecular pump, makes stated in the operating instructions. The sense in the case of rather small backing

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2.1.8 Sorption pumps particle diameter compared with the pore size of 13 Å for zeolite 13X. These gases The term “sorption pumps” includes all are, therefore, very poorly adsorbed. arrangements for the removal of gases and vapors from a space by sorption means. The adsorption of gases at surfaces is The pumped gas particles are thereby dependent not only on the temperature, bound at the surfaces or in the interior of but more importantly on the pressure these agents, by either physical tempera- above the adsorption surface. The ture-dependent adsorption forces (van der dependence is represented graphically for Waals forces), chemisorption, absorption, a few gases by the adsorption isotherms or by becoming embedded during the given in Fig. 2.60. In practice, adsorption course of the continuous formation of new pumps are connected through a valve to sorbing surfaces. By comparing their ope- the vessel to be evacuated. It is on rating principles, we can distinguish immersing the body of the pump in liquid between adsorption pumps, in which the nitrogen that the sorption effect is made sorption of gases takes place simply by technically useful. Because of the different temperature-controlled adsorption pro- adsorption properties, the pumping speed cesses, and getter pumps, in which the and ultimate pressure of an adsorption sorption and retention of gases are 1 Inlet port 5 Thermal conducting pump are different for the various gas 2 Degassing port vanes essentially caused by the formation of 3 Support 6 Adsorption material molecules: the best values are achieved for chemical compounds. Gettering is the 4 Pump body (e.g. Zeolith) nitrogen, carbon dioxide, water vapor, and bonding of gases to pure, mostly metallic hydrocarbon vapors. Light noble gases are surfaces, which are not covered by oxide Fig. 2.59 Cross section of an adsorption pump hardly pumped at all because the diameter or carbide layers. Such surfaces always of the particles is small compared to the form during manufacture, installation or 1 m2. For nitrogen molecules with a pores of the zeolite. As the sorption effect while venting the system. The mostly relative molecular mass Mr = 28 that decreases with increased coverage of the metallic highest purity getter surfaces are corresponds to about 2 · 10-4 g or 0.20 zeolite surfaces, the pumping speed falls continuously generated either directly in mbar · l (see also Section 1.1). Therefore, off with an increasing number of the the vacuum by evaporation (evaporator an adsorption surface of 1000 m2 is particles already adsorbed. The pumping pumps) or by sputtering (sputter pumps) capable of adsorbing a monomolecular speed of an adsorption pump is, therefore, or the passivating surface layer of the layer in which more than 133 mbar · l of dependent on the quantity of gas already getter (metal) is removed by degassing the gas is bound. pumped and so is not constant with time. vacuum, so that the pure material is Hydrogen and light noble gases, such as The ultimate pressure attainable with exposed to the vacuum. This step is called helium and neon, have a relatively small adsorption pumps is determined in the activation (NEG pumps NEG = Non Eva- porable Getter).

Pressure [Torr]

2.1.8.1 Adsorption pumps ] –1 Adsorption pumps (see Fig. 2.59) work according to the principle of the physical adsorption of gases at the surface of molecular sieves or other adsorption materials (e.g. activated Al2O3). Zeolite 13X is frequently used as an adsorption material. This alkali aluminosilicate possesses for a mass of the material an extraordinarily large surface area, about 1000 m2/g of solid substance. Corres- pondingly, its ability to take up gas is considerable. The pore diameter of zeolite 13X is about 13 Å, which is within the order of size of water vapor, oil vapor, and larger gas

molecules (about 10 Å). Assuming that the Adsorbed quantity of gas per adsorbent [mbar ·l · g mean molecular diameter is half this value, D00 Pressure [mbar] 5 · 10-8 cm, about 5 · 1018 molecules are adsorbed in a monolayer on a surface of Fig. 2.60 Adsorption isotherms of zeolite 13X for nitrogen at -195 °C and 20 °C, as well as for helium and neon at -195 °C

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first instance by those gases that prevail in an extraordinarily high pumping speed for the vessel at the beginning of the pumping active gases, which, particularly on star- process and are poorly or not at all ting processes or on the sudden evolution adsorbed (e.g. neon or helium) at the of greater quantities of gas, can be rapidly zeolite surface. In atmospheric air, a few pumped away. As sublimation pumps parts per million of these gases are function as auxiliary pumps (boosters) to present. Therefore, pressures < 10-2 mbar sputter-ion pumps and turbomolecular can be obtained. pumps, their installation is often indispensable (like the “boosters” in vapor If pressures below 10-3 mbar exclusively ejector pumps; see Section 2.1.6.2). are to be produced with adsorption pumps, as far as possible no neon or helium PZ should be present in the gas mixture. 2.1.8.3 Sputter-ion pumps After a pumping process, the pump must The pumping action of sputter-ion pumps be warmed only to room temperature for ← ⊕ Direction of motion of the ionized gas the adsorbed gases to be given off and the is based on sorption processes that are molecules zeolite is regenerated for reuse. If air (or initiated by ionized gas particles in a Pen- • → Direction of motion of the sputtered damp gas) containing a great deal of water ning discharge (cold cathode discharge). titanium By means of “paralleling many individual - – – - Spiral tracks of the electrons vapor has been pumped, it is recom- PZ Penning cells mended to bake out the pump completely Penning cells” the sputter ion pump dry for a few hours at 200 °C or above. attains a sufficiently high pumping speed for the individual gases. Fig. 2.61 Operating principle of a sputter-ion pump To pump out larger vessels, several adsorption pumps are used in parallel or in Operation of sputter-ion pumps series. First, the pressure is reduced from The ions impinge upon the cathode of the sures) is sufficient to maintain a self- atmospheric pressure to a few millibars by cold cathode discharge electrode system sustained gas discharge. A supply of elec- the first stage in order to “capture” many and sputter the cathode material (titanium). trons from a hot cathode is not required. noble gas molecules of helium and neon. The titanium deposited at other locations Because of their great mass, the After the pumps of this stage have been acts as a getter film and adsorbs reactive movement of the ions is unaffected by the saturated, the valves to these pumps are gas particles (e.g., nitrogen, oxygen, hydro- magnetic field of the given order of mag- closed and a previously closed valve to a gen). The energy of the ionized gas par- nitude; they flow off along the shortest further adsorption pump still containing ticles is not only high enough to sputter the path and bombard the cathode. clean adsorbent is opened so that this cathode material but also to let the The discharge current i is proportional to pump may pump down the vacuum impinging ions penetrate deeply into the the number density of neutral particles n , chamber to the next lower pressure level. 0 cathode material (ion implantation). This the electron density n-, and the length l of This procedure can be continued until the sorption process “pumps” ions of all types, the total discharge path: ultimate pressure cannot be further including ions of gases which do not – σ improved by adding further clean adsorp- chemically react with the sputtered titanium i = n0 · n · · l (2.25) tion pumps. film, i.e. mainly noble gases. The effective cross section s for ionizing The following arrangement is used to collisions depends on the type of gas. According to (2.25), the discharge current 2.1.8.2 Sublimation pumps produce the ions: stainless-steel, cylindrical anodes are closely arranged between, i is a function of the number particle Sublimation pumps are sorption pumps in with their axes perpendicular to, two density n0, as in a Penning gauge, and it which a getter material is evaporated and parallel cathodes (see Fig. 2.61). The can be used as a measure of the pressure -4 -8 deposited on a cold inner wall as a getter cathodes are at negative potential (a few in the range from 10 to 10 mbar. At film. On the surface of such a getter film kilovolts) against the anode. The entire lower pressures the measurements are not the gas molecules form stable com- electrode system is maintained in a strong, reproducible due to interferences from pounds, which have an immeasurably low homogeneous magnetic field of a flux field emission effects. vapor pressure. The active getter film is density of B = 0.1 T, (T = Tesla = 104 In diode-type, sputter-ion pumps, with an renewed by subsequent evaporations. Gauss) produced by a permanent magnet electrode system configuration as shown Generally titanium is used in sublimation attached to the outside of the pump’s in Fig. 2.62, the getter films are formed on pumps as the getter. The titanium is casing. The gas discharge profduced by the anode surfaces and between the evaporated from a wire made of a special the high tension contains electrons and sputtering regions of the opposite alloy of a high titanium content which is ions. Under the influence of the magnetic cathode. The ions are buried in the heated by an electric current. Although the field the electrons travel along long spiral cathode surfaces. As cathode sputtering optimum sorption capacity (about one tracks (see Fig. 2.61) until they impinge on proceeds, the buried gas particles are set nitrogen atom for each evaporated tita- the anode cylinder of the corresponding free again. Therefore, the pumping action nium atom) can scarcely be obtained in cell. The long track increases ion yield, for noble gases that can be pumped only practice, titanium sublimation pumps have which even at low gas densities (pres- by ion burial will vanish after some time

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pumping speed Sn is given by the maximum of the pumping speed curve for air whereby the corresponding pressure must be stated. For air, nitrogen, carbon dioxide and water vapor, the pumping speed is practically the • Titanium atoms same. Compared with the pumping speed Ö Gas molecules for air, the pumping speeds of sputter-ion ⊕ Ions pumps for other gases amount to ü Electrons approximately: B Magnetic field Hydrogen 150 to 200 % Methane 100 % Other light hydrocarbons 80 to 120 % Oxygen 80 % Argon 30 % Fig. 2.62 Electrode configuration in a diode sputter-ion pump Helium 28 % and a “memory effect” will occur. and from which they travel to the target Sputter-ion pumps of the triode type excel plate at an energy still considerably higher in contrast to the diode-type pumps in Unlike diode-type pumps, triode sputter- than the thermal energy 1/2 · k · T of the high-noble gas stability. Argon is pumped ion pumps exhibit excellent stability in gas particles. The energetic neutral stably even at an inlet pressure of their pumping speed for noble gases particles can penetrate into the target 1 · 10-5 mbar. The pumps can be started because sputtering and film forming surface layer, but their sputtering effect is without difficulties at pressures higher than surfaces are separated. Fig. 2.63 shows only negligible. These buried or implanted 1 · 10-2 mbar and can operate continuously the electrode configuration of triode particles are finally covered by fresh at an air inlet producing a constant air sputter-ion pumps. Their greater efficiency titanium layers. As the target is at positive pressure of 5 · 10-5 mbar. A new kind of for pumping noble gases is explained as potential, any positive ions arriving there design for the electrodes extends the follows: the geometry of the system favors are repelled and cannot sputter the target service life of the cathodes by 50 %. grazing incidence of the ions on the layers. Hence the buried noble gas atoms titanium bars of the cathode grid, whereby are not set free again. The pumping speed Influence on processes in the vacuum the sputtering rate is considerably higher of triode sputter-ion pumps for noble chamber by magnetic stray fields and than with perpendicular incidence. The gases does not decrease during the stray ions from the sputter-ion pump. sputtered titanium moves in about the operation of the pump. The high-magnetic-field strength required same direction as the incident ions. The for the pumping action leads inevitably to getter films form preferentially on the third The pumping speed of sputter-ion pumps stray magnetic fields in the neighborhood electrode, the target plate, which is the depends on the pressure and the type of of the magnets. As a result, processes in actual wall of the pump housing. There is gas. It is measured according to the the vacuum chamber can be disturbed in an increasing yield of ionized particles that methods stated in DIN 28 429 and some cases, so the sputter-ion pump are grazingly incident on the cathode grid PNEUROP 5615. The pumping speed concerned should be provided with a where they are neutralized and reflected curve S(p) has a maximum. The nominal screening arrangement. The forms and kinds of such a screening arrangement can be regarded as at an optimum if the processes taking place in the vacuum chamber are disturbed by no more than the earth’s magnetic field which is present • Titanium atoms in any case. Ö Gas molecules ⊕ Ions Fig. 2.64 shows the magnetic stray field at ü Electrons the plane of the intake flange of a sputter- A Anode cylinder ion pump IZ 270 and also at a parallel (same as in the diode pump) plane 150 mm above. If stray ions from the B Magnetic field discharge region are to be prevented from F Target plate reaching the vacuum chamber, a suitable (pump housing) screen can be set up by a metal sieve at as the third electrode K Cathode grid opposite potential in the inlet opening of the sputter-ion pump (ion barrier). This, however, reduces the pumping speed of D00 the sputter-ion pump depending on the Fig. 2.63 Electrode configuration in a triode sputter-ion pump mesh size of the selected metal sieve.

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then need no electrical energy • no interference by magnetic fields • hydrocarbon-free vacuum • free of vibrations • low weight NEG pumps are mostly used in combination with other UHV pumps (turbomolecular and cryopumps). Such combinations are especially useful when wanting to further reduce the ultimate pressure of UHV systems, since hydrogen contributes mostly to the ultimate pressure in an UHV system, and for which NEG pumps have a particularly high pumping speed, whereas the pumping effect for H2 of other pumps is low. Some typical examples for applications in which NEG pumps are used are particle accelerators and similar research systems, surface Fig. 2.64 Stray magnetic field of a sputter-ion pump analysis instruments, SEM columns and in two places parallel to the inlet flange (inserts) curves show lines of constant sputtering systems. NEG pumps are magnetic induction B in Gauss. manufactured offering pumping speeds of 1 Gauss = 1 · 10–4 Tesla several l/s to about 1000 l/s. Custom pumps are capable of attaining a pumping 2.1.8.4 Non evaporable getter pumps speed for hydrogen which is by several (NEG Pumps) orders of magnitude higher. The non evaporable getter pump operates with a non evaporable, compact getter material, the structure of which is porous at the atomic level so that it can take up large quantities of gas. The gas molecules adsorbed on the surface of the getter material diffuse rapidly inside the material thereby making place for further gas molecules impinging on the surface. The non evaporable getter pump contains a heating element which is used to heat the getter material to an optimum temperature depending on the type of gas which is preferably to be pumped. At a higher temperature the getter material which has been saturated with the gas is regenerated (activated). As the getter material, mostly zirconium-aluminum alloys are used in the form of strips. The special properties of NEG pumps are: • constant pumping speed in the HV and UHV ranges • no pressure restrictions up to about 12 mbar • particularly high pumping speed for hydrogen and its isotopes • after activation the pump can often operate at room temperature and will

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2.1.9 Cryopumps engineering in that the temperatures pumped by way of condensation. A involved in cryo engineering are in the surface cooled with liquid helium As you may have observed water range below 120 K (< -153 °C). Here we (T ≈ 4.2 K) is capable of condensing all condenses on cold water mains or are dealing with two questions: gases except helium. windows and ice forms on the evaporator a) What cooling principle is used in cryo In continuous flow cryopumps the cold unit in your refrigerator. This effect of engineering or in cryopumps and how surface is designed to operate as a heat condensation of gases and vapors on cold is the thermal load of the cold surface exchanger. Liquid helium in sufficient surfaces, water vapor in particular, as it is lead away or reduced? quantity is pumped by an auxiliary pump known in every day life, occurs not only at b) What are the operating principles of the from a reservoir into the evaporator in order atmospheric pressure but also in vacuum. cryopumps? to attain a sufficiently low temperature at This effect has been utilized for a long time the cold surface (cryopanel). in condensers (see 2.1.5) mainly in The liquid helium evaporates in the heat connection with chemical processes; 2.1.9.1 Types of cryopump exchanger and thus cools down the previously the baffle on diffusion pumps Depending on the cooling principle a cryopanel. The waste gas which is used to be cooled with refrigerating difference is made between generated (He) is used in a second heat machines. Also in a sealed space (vacuum • Bath cryostats exchanger to cool the baffle of a thermal chamber) the formation of condensate on • Continuous flow cryopumps radiation shield which protects the system a cold surface means that a large number • Refrigerator cryopumps from thermal radiation coming from the of gas molecules are removed from the outside. The cold helium exhaust gas volume: they remain located on the cold In the case of bath cryostats – in the most ejected by the helium pump is supplied to surface and do not take part any longer in simple case a cold trap filled with LN (li- 2 a helium recovery unit. The temperature at the hectic gas atmosphere within the quid nitrogen) – the pumping surface is the cryopanels can be controlled by vacuum chamber. We then say that the cooled by direct contact with a liquefied controlling the helium flow. particles have been pumped and talk of gas. On a surface cooled with LN2 cryopumps when the “pumping effect” is ≈ Today refrigerator cryopumps are being (T 77 K) H2O and CO2 are able to attained by means of cold surfaces. condense. On a surface cooled to ≈ 10 K used almost exclusively (cold upon demand). These pumps operate basically Cryo engineering differs from refrigeration all gases except He and Ne may be much in the same way as a common household refrigerator, whereby the following thermodynamic cycles using 1 helium as the refrigerant may be employed: 3 • Gifford-McMahon process • Stirling process 2 • Brayton process • Claude process The Gifford-McMahon process is mostly used today and this process is that which has been developed furthest. It offers the possibility of separating the locations for the large compressor unit and the expansion unit in which the refrigeration process takes place. Thus a compact and low vibration cold source can be designed. The cryopumps series-manufactured by LEYBOLD operate with two-stage cold heads according to the Gifford-McMahon process which is discussed in detail in the following. The entire scope of a refrigerator cryopump is shown in Fig. 2.65 and consists of the compressor unit (1) which is linked via flexible pressure lines (2) – and thus vibration-free – to the cryopump (3). The cryopump itself consists of the pump 1 Compressor unit 3 Cold head (without 2 Flexible pressure condensation casing and the cold head within. Helium is D00 lines surfaces) used as the refrigerant which circulates in a closed cycle with the aid of the compressor. Fig. 2.65 All items of a refrigerator cryopump

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2.1.9.2 The cold head and its opera- located inside the displacer. The regenera- In two series connected stages the ting principle (Fig. 2.66) tor is a heat accumulator having a large temperature of the helium is reduced to heat exchanging surface and capacity, about 30 K in the first stage and further to Within the cold head, a cylinder is divided which operates as a heat exchanger within about 10 K in the second stage. The into two working spaces V and V by a 1 2 the cycle. Outlined in Fig. 2.66 are the four attainable low temperatures depend displacer. During operation the right space phases of refrigeration in a single-stage among other things on the type of V is warm and the left space V is cold. At 1 2 refrigerator cold head operating according regenerator. Commonly copperbronze is a displacer frequency f the refrigerating to the Gifford-McMahon principle. used in the regenerator of the first stage power W of the refrigerator is: and lead in the second stage. Other W = (V2,max – V2,min) · (pH – pN) · f (2.26) The two-stage cold head materials are available as regenerators for The series-manufactured refrigerator special applications like cryostats for The displacer is moved to and fro pneuma- cryopumps from LEYBOLD use a two- extremely low temperatures (T < 10 K). tically so that the gas is forced through the stage cold head operating according to the The design of a two-stage cold head is displacer and thus through the regenerator Gifford-McMahon principle (see Fig. 2.67). shown schematically in Fig. 2.67. By

V2 (cold) V1 (warm) Phase 1: The displacer is at the left dead center; V2 where the cold is produced has its minimum size. Valve N remains closed, H is opened. Gas at the pressure pH Regenerator Displacer flows through the regenerator into V2. There the gas warms up by the pressure increase in V1.

V2 (cold) V1 (warm) Phase 2: Valve H remains open, valve N closed: the displacer moves to the right and ejects the gas from V1 through the regenerator to V2 where it cools down at the Regenerator Displacer cold regenerator.; V2 has its maximum volume.

V2 (cold) V1 (warm) Phase 3: Valve H is closed and the valve N to the low pressure reservoir is opened. The gas expands from pH to pN and thereby cools down. This removes heat from the Regenerator Displacer vicinity and it is transported with the expanding gas to the compressor.

V2 (cold) V1 Phase 4: With valve N open the displacer moves to the left; the gas from V2,max flows through the regenerator, cooling it down and then flows into the volume V1 and Regenerator Displacer into the low pressure reservoir. This completes the cycle.

Fig. 2.66 Refrigerating phases using a single-stage cold head operating according to the Gifford-McMahon process

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1 Electric connections and current 11 Regenerator, 2nd stage 1 High vacuum flange 9 1st stage of the cold head feedthrough for the motor in the 12 Expansion volume, 2nd stage 2 Pump casing (≈ 50 – 80 K) cold head 13 2nd (cooling) stage 3 Forevacuum flange 10 Gauge for the hydrogen vapor 2 He high pressure connection (copper flange) 4 Safety valve for gas discharge pressure thermometer 3 He low pressure connection 14 Measurement chamber for the 5 Thermal radiation shield 11 Helium gas connections 4 Cylinder, 1st stage vapor pressure 6 Baffle 12 Motor of the cold head 5 Displacer, 1st stage 15 Control piston 7 2nd stage of the cold head with casing and electric 6 Regenerator, 1st stage 16 Control volume (≈10 K); connections 7 Expansion volume, 1st stage 17 Control disk 8 Cryopanels 8 1st (cooling) stage (copper 18 Control valve flange) 19 Gauge for the hydrogen vapor 9 Cylinder, 2nd stage pressure thermometer 10 Displacer, 2nd stage 20 Motor in the cold head Fig. 2.67 Two-stage cold head Fig. 2.68 Design of a refrigerator cryopump (schematic)

means of a control mechanism with a is surrounded by the thermal radiation stage (7) of the cold head are coated with motor driven control valve (18) with shield (5) which is black on the inside and activated charcoal on the inside in order to control disk (17) and control holes first the polished as well as nickel plated on the be able to pump gases which do not easily pressure in the control volume (16) is outside. Under no-load conditions the condense and which can only be pumped changed which causes the displacers (6) baffle and the thermal radiation shield by cryosorption (see 2.1.9.4). of the first stage and the second stage (11) (first stage) attain a temperature ranging to move; immediately thereafter the between 50 to 80 K at the cryopanels and pressure in the entire volume of the about 10 K at the second stage. The 2.1.9.4 Bonding of gases to cold cylinder is equalized by the control surface temperatures of these cryopanels surfaces mechanism. The cold head is linked via are decisive to the actual pumping The thermal conductivity of the condensed flexible pressure lines to the compressor. process. These surface temperatures (solid) gases depends very much on their depend on the refrigerating power structure and thus on the way in which the supplied by the cold head, and the thermal condensate is produced. Variations in 2.1.9.3 The refrigerator cryopump conduction properties in the direction of thermal conductivity over several orders of the pump’s casing. During operation of the Fig. 2.68 shows the design of a cryopump. magnitude are possible! As the condensa- cryopump, loading caused by the gas and It is cooled by a two-stage cold head. The te increases in thickness, thermal resis- the heat of condensation results in further thermal radiation shield (5) with the baffle tance and thus the surface temperature warming of the cryopanels. The surface (6) is closely linked thermally to the first increase subsequently reducing the pum- temperature does not only depend on the stage (9) of the cold head. For pressures ping speed. The maximum pumping speed temperature of the cryopanel, but also on below 10-3 mbar the thermal load is of a newly regenerated pump is stated as the temperature of the gas which has caused mostly by thermal radiation. For its nominal pumping speed. The bonding D00 already been frozen on to the cryopanel. this reason the second stage (7) with the process for the various gases in the The cryopanels (8) attached to the second condensation and cryosorption panels (8) cryopump is performed in three steps: first

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not arrive at the second stage and consume capacity there), the situation arises as shown in Fig. 2.69. The gas molecules entering the pump produce the area related theoretical pumping speed according the equation 2.29a with T = 293 K. The different pumping speeds have been combined for three representative gases H2, N2 and H20 taken from each of the aforementioned groups. Since water Hydrogen Water vapor Nitrogen vapor is pumped on the entire entry area of Area related conductance of the intake flange in l / s · cm2: the cryopump, the pumping speed 43.9 14.7 11.8 measured for water vapor corresponds Area related pumping speed of the cryopump in l / s · cm2: almost exactly to the theoretical pumping 13.2 14.6 7.1 speed calculated for the intake flange of Ratio between pumping speed and conductance: 30 % 99 % 60 % the cryopump. N2 on the other hand must first overcome the baffle before it can be Fig. 2.69 Cryopanels – temperature and position define the efficiency in the cryopump bonded on to the cryocondensation panel. Depending on the design of the baffle, 30 the mixture of different gases and vapors pressure. Cryosorption is the physical and to 50 percent of all N2 molecules are meets the baffle which is at a temperature reversible bonding of gas molecules reflected. of about 80 K. Here mostly H O and CO through Van der Waals forces on suffici- 2 2 H2 arrives at the cryosorption panels after are condensed. The remaining gases ently cold surfaces of other materials. The further collisions and thus cooling of the penetrate the baffle and impinge in the bond energy is equal to the heat of gas. In the case of optimally designed outside of the cryopanel of the second adsorption which is greater than the heat cryopanels and a good contact with the ac- stage which is cooled to about 10 K. Here of vaporization. As soon as a monolayer tive charcoal up to 50 percent of the H2 gases like N2, O2 or Ar will condense. Only has been formed, the following molecules which has overcome the baffle can be H2, He and Ne will remain. These gases impinge on a surface of the same kind bonded. Due to the restrictions regarding can not be pumped by the cryopanels and (sorbent) and the process transforms into access to the pumping surfaces and these pass after several impacts with the cryocondensation. The higher bond energy cooling of the gas by collisions with the thermal radiation shield to the inside of for cryocondensation prevents the further walls inside the pump before the gas these panels which are coated with an growth of the condensate layer thereby reaches the pumping surface, the measu- adsorbent (cryosorption panels) where restricting the capacity for the adsorbed red pumping speed for these two gases they are bonded by cryosorption. Thus for gases. However, the adsorbents used, like amounts only to a fraction of the theoreti- the purpose of considering a cryopump activated charcoal, silica gel, alumina gel cal pumping speed. The part which is not the gases are divided into three groups and molecular sieve, have a porous pumped is reflected chiefly by the baffle. depending at which temperatures within structure with very large specific surface Moreover, the adsorption probability for 6 2 the cryopump their partial pressure drops areas of about 10 m /kg. Cryotrapping is H differs between the various adsorbents -9 2 below 10 mbar: understood as the inclusion of a low and is < 1, whereas the probabilities for the boiling point gas which is difficult to pump ≈ 1st group: condensation of water vapor and N2 1. such as hydrogen, in the matrix of a gas p < 10-9 mbar at T ≈ 77K (LN ): H O, CO s 2 2 2 having a higher boiling point and which Three differing capacities of a pump for the gases which can be pumped result from 2nd group: can be pumped easily such as Ar, CH4 or -9 ≈ the size of the three surfaces (baffle, ps < 10 mbar at T 20K: N2, O2, Ar CO2. At the same temperature the condensate mixture has a saturation vapor condensation surface at the outside of the 3rd group: pressure which is by several orders of second stage and sorption surface at the p < 10-9 mbar at T < 4.2K: H , He, Ne s 2 magnitude lower than the pure condensate inside of the second stage). In the design A difference is made between the different of the gas with the lower boiling point. of a cryopump, a mean gas composition bonding mechanisms as follows: (air) is assumed which naturally does not apply to all vacuum processes (sputtering Cryocondensation is the physical and re- 2.1.9.5 Pumping speed and position of processes, for example. See 2.1.9.6 versible bonding of gas molecules through the cryopanels “Partial Regeneration”). Van der Waals forces on sufficiently cold surfaces of the same material. The bond Considering the position of the cryopanels energy is equal to the energy of vaporiza- in the cryopump, the conductance from tion of the solid gas bonded to the surface the vacuum flange to this surface and also and thus decreases as the thickness of the the subtractive pumping sequence (what condensate increases as does the vapor has already condensed at the baffle can

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2.1.9.6 Characteristic quantities of a TK (K) Ultimate pressure Ult. press. (mbar) Ult. press.(mbar) cryopump (according to equ. 2.28) H2 N2 –14 The characteristic quantities of a cryo- 2.5 10.95 · ps 3.28 · 10 immeasurably low –9 pump are as follows (in no particular 4.2 8.66 · ps 4.33 · 10 immeasurably low order): +3 –11 20 3.87 · ps 3.87 · 10 3.87 · 10 • Cooldown time Table 2.6 Ultimate temperatures at a wall temperature of 300 K • Crossover value

• Ultimate pressure Ultimate pressure pend: For the case of refrigerating power for the first stage at 80 cryocondensation (see Section 2.1.9.4) K and for the second stage at 20 K when • Capacity the ultimate pressure can be calculated by: simultaneously loading both stages • Refrigerating power and net thermally. During the measurement of refrigerating power TG refrigerating power the thermal load is pend = ps(TK)· (2.28) TK generated by electric heaters. The refrige- • Regeneration time rating power is greatest at room temperature and is lowest (Zero) at ultimate tem- • Throughput and maximum pV flow pS is the saturation vapor pressure of the gas or gases which are to be pumped at perature. • Pumping speed . the temperature TK of the cryopanel and TG Net refrigerating power Q (W): In the • Service life / duration of operation is the gas temperature (wall temperature in case of refrigerator cryopumps the net the vicinity of the cryopanel). refrigerating power available at the usual • Starting pressure Example: With the aid of the vapor operating temperatures Cooldown time: The cooldown time of (T1 < 80 K, T2 < 20 K) substantially defines pressure curves in Fig. 9.15 for H2 and N2 cryopumps is the time span from start-up the ultimate pressures summarized in the throughput and the crossover value. until the pumping effect sets in. In the case The net. refrigerating power is – depen- Table 2.6 at TG = 300 K result. of refrigerator cryopumps the cooldown ding on the configuration of the pump – time is stated as the time it takes for the The Table shows that for hydrogen at much lower than the refrigerating power of second stage of the cold head to cool temperatures T < 3 K at a gas temperature the cold head used without the pump. down from 293 K to 20 K. of TG= 300 K (i.e. when the cryopanel is exposed to the thermal radiation of the pV flow see 1.1 Crossover value: The crossover value is a wall) sufficiently low ultimate pressures Regeneration time: As a gas trapping characteristic quantity of an already cold can be attained. Due to a number of inter- device, the cryopump must be regenerated refrigerator cryopump. It is of significance fering factors like desorption from the wall after a certain period of operation. Rege- when the pump is connected to a vacuum and leaks, the theoretical ultimate pres- neration involves the removal of condens- chamber via an HV / UHV valve. The sures are not attained in practice. ed and adsorbed gases from the cryopa- crossover value is that quantity of gas with nels by heating. The regeneration can be respect to T = 293 K which the vacuum Capacity C (mbar · l): The capacity of a n run fully or only partially and mainly differs chamber may maximally contain so that cryopump for a certain gas is that quantity by the way in which the cryopanels are the temperature of the cryopanels does of gas (pV value at Tn = 293 K) which can heated. not increase above 20 K due to the gas be bonded by the cryopanels before the burst when opening the valve. The pumping speed for this type of gas G In the case of total regeneration a diffe- crossover value is usually stated as a pV drops to below 50 % of its initial value. rence is made between: value in in mbar · l. The capacity for gases which are pumped 1. Natural warming: after switching off the The crossover value and the chamber by means of cryosorption depends on the compressor, the cryopanels at first volume V result in the crossover pressure quantity and properties of the sorption warm up only very slowly by thermal pc to which the vacuum chamber must be agent; it is pressure dependent and conduction and then in addition evacuated first before opening the valve generally by several orders of magnitude through the released gases. leading to the cryopump. The following lower compared to the pressure 2. Purge gas method: the cryopump is may serve as a guide: independent capacity for gases which are warmed up by admitting warm purging pumped by means of cryocondensation. gas. 35 · p ≤ ·Q (20K) mbar (2.27) . 3. Electric heaters: the cryopanels of the c V 2 Refrigerating power Q (W): The refrige- cryopump are warmed up by heaters at rating power of a refrigeration source at a V = Volume of the vacuum chamber (l), the first and second stages. The temperature T gives the amount of heat . released gases are discharged either that can be extracted by the refrigerating Q2(20K) = Net refrigerating capacity in through an overpressure valve (purge source whilst still maintaining this Watts, available at the second stage of the gas method) or by mechanical backing temperature. In the case of refrigerators it cold head at 20 K. pumps. Depending on the size of the D00 has been agreed to state for single-stage pump one will have to expect a cold heads the refrigerating power at 80 K regeneration time of several hours. and for two-stage cold heads the

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p >> pend the expression in brackets approaches 1 so that in the oversaturated case p >> pend > Ps so that: e (K) Sth = AK · SA (2.29a) 2 1 with emperatur T R ·T T S = c = G = 3.65 G `/s·cm2 A 4 2· π · M M (2) (1) TG Gas temperature in K 40 minutes Time about 6 hours M Molar mass Fig. 2.70 Comparison between total (1) and partial (2) regeneration Given in Table 2.7 is the surface area- -1 -2 related pumping speed SA in l · s · cm Partial regeneration: Since the limitation The maximum pV flow at which the for some gases at two different gas ≈ in the service life of a cryopump depends cryopanels are warmed up to T 20 K in temperatures TG in K determined accor- in most applications on the capacity limit the case of continuous operation, de- ding to equation 2.29a. The values stated for the gases nitrogen, argon and pends on the net refrigerating power of the in the Table are limit values. In practice the hydrogen pumped by the second stage, it pump at this temperature and the type of condition of an almost undisturbed will often be required to regenerate only gas. For refrigerator cryopumps and equilibrium (small cryopanels compared this stage. Water vapor is retained during condensable gases the following may be to a large wall surface) is often not true, partial regeneration by the baffle. For this, taken as a guide: because large cryopanels are required to the temperature of the first stage must be . attain short pumpdown times and a good Qmax = 2.3 Q 2 (20 K) mbar · l/s maintained below 140 K or otherwise the . end vacuum. Deviations also result when partial pressure of the water vapor would Q 2 (20 K) is the net refrigerating power in the cryopanels are surrounded by a cooled become so high that water molecules Watts available at the second stage of the baffle at which the velocity of the would contaminate the adsorbent on the cold heat at 20 K. In the case of inter- penetrating molecules is already reduced second stage. mittent operation, a higher pV flow is per- by cooling. missible (see crossover value). In 1992, LEYBOLD was the first manufac- Service life / duration of operation top (s): turer of cryopumps to develop a method The duration of operation of the cryopump Pumping speed S : The following applies permitting such a partial regeneration. th for a particular gas depends on the to the (theoretical) pumping speed of a This fast regeneration process is micro- equation: cryopump: processor controlled and permits a partial top, G regeneration of the cryopump in about 40  p  α − end = ∫ with Sth = AK · SA · · 1  CG QG (t)dt minutes compared to 6 hours needed for a  p  (2.29) 0 total regeneration based on the purge gas C = Capacity of the cryopump for the method. A comparison between the typical A Size of the cryopanels G cycles for total and partial regeneration is K gas G S Surface area related pumping speed shown in Fig. 2.70. The time saved by the A Q (t) =Throughput of the cryopump for (area related impact rate according to G Fast Regeneration System is apparent. In a the gas at the point of time t production environment for typical sput- equations 1.17 and 1.20, proportional tering processes one will have to expect to the mean velocity of the gas If the constant__ mean over time for the one total regeneration after 24 partial molecules in the direction of the throughput QG is known, the following regenerations. cryopanel) applies: C C Throughput and maximum pV flow: a Probability of condensation t = G = G op, G p ·S (2.30) (mbar l/s): the throughput of a cryopump (pumping) QG G G for a certain gas depends on the pV flow of pend Ultimate pressure (see above) the gas G through the intake opening of After the period of operation top,G has the pump: p Pressure in the vacuum chamber elapsed the cryopump must be regenerated with respect to the type of gas G. Q = q the following equation The equation (2.29) applies to a cryopanel G pV,G; built into the vacuum chamber, the surface applies Starting pressure po: Basically it is area of which is small compared to the possible to start a cryopump at atmosphe- QG = pG · SG with surface of the vacuum chamber. At ric pressure. However, this is not desirable sufficiently low temperatures α = 1 for all for several reasons. As long as the mean pG = intake pressure, gases. The equation (2.29) shows that for free path of the gas molecules is smaller SG = pumping capacity for the gas G

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M SA SA TS Triple point Symbol Gas Molar at 293 K at 80 K Boiling point (= melting point) mass gas temp. gas temp. 1013 mbar Tt pt g/mol l/s · cm2 l/s · cm2 K K mbar

H2 Hydrogen 2.016 43.88 22.93 20.27 13.80 70.4

He Helium 4.003 31.14 16.27 4.222 2.173 50.52

CH4 Methane 4.003 15.56 8.13 111.67 90.67 116.7

H2O Water 18.015 14.68 – 373.15 273.16 6.09

Ne Neon 20.183 13.87 7.25 27.102 24.559 433.0 CO Carbon monoxide 28.000 11.77 6.15 81.67 68.09 153.7

N2 Nitrogen 28.013 11.77 6.15 77.348 63.148 126.1 Air 28.96 11.58 6.05 ≈ 80.5 ≈ 58.5 –

O2 Oxygen 31.999 11.01 5.76 90.188 54.361 1.52 Ar Argon 39.948 9.86 5.15 87.26 83.82 687.5 Kr Krypton 83.80 6.81 3.56 119.4 115.94 713.9 Xe Xenon 131.3 5.44 2.84 165.2 161.4

Table 2.7 Surface-related pumping speeds for some gases

than the dimensions of the vacuum chamber (p > 10-3 mbar), thermal conductivity of the gas is so high that an unacceptably large amount of heat is transferred to the cryopanels. Further, a relatively thick layer of condensate would form on the cryopanel during starting. This would markedly reduce the capacity of the cryopump available to the actual operating phase. Gas (usually air) would be bonded to the adsorbent, since the bonding energy for this is lower than that for the condensation surfaces. This would further reduce the already limited capacity for hydrogen. It is recommended that cryopumps in the high vacuum or ultrahigh vacuum range are started with the aid of a backing pump at pressures of p < 5 · 10-2 mbar. As soon as the starting pressure has been attained the backing pump may be switched off.

D00

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2.2 Choice of pumping Dry processes work primarily in a narrow resin-casting plants, as well as in and limited pressure region. molecular distillation, the production of as process The system is usually evacuated to a large a liquid surface as possible is suitable characteristic pressure before the important. In all wet processes the provi- 2.2.1 Survey of the most usual actual working process begins. This sion of the necessary heat for evapo- pumping processes happens, for example, in plants for evaporation of the moisture is of great impor- rative coating, electron-beam welding, and tance. crystal pulling; in particle accelerators, Vacuum technology has undergone rapid Basic pumping procedures are given in the mass spectrometers, electron micro- development since the Fifties. In research following paragraphs. and in most branches of industry today, it scopes; and others. If you have specific questions, you should is indispensable. Further, there are dry processes in which get in touch with a specialist department in degassing in vacuum is the actual Corresponding to the many areas of ap- LEYBOLD where experts are available to technical process. These include work in plication, the number of technical proce- you who can draw on many years of induction- and arc furnaces, steel degas- dures in vacuum processes is extraordi- experience. narily large. These cannot be described sing plants, and plants for the manufacture of pure metals and electron tubes. within the scope of this section, because Classifications of typical vacuum proces- the basic calculations in this section cover ses and plants according to the pressure Wet processes are undertaken primarily mainly the pumping process, not the regions. in a prescribed working operation that process taking place in the vessel. A Rough vacuum 1013 mbar – 1 mbar covers a wider pressure region. survey of the most important processes in • Drying, distillation, and steel degassing. vacuum technology and the pressure This is especially important in the drying of -3 mbar regions in which these processes are solid materials. If, for instance, work is Medium vacuum 1 -10 • Molecular distillation, freeze-drying, chiefly carried out is given in the diagrams undertaken prematurely at too low a (Figures 2.71 and 2.72). pressure, the outer surfaces dry out too impregnation, melting and casting quickly. As a result, the thermal contact to furnaces, and arc furnaces. Generally, the pumping operation for these the moisture to be evaporated is impaired High vacuum 10-3 – 10-7 mbar processes can be divided into two and the drying time is considerably • Evaporative coating, crystal pulling, categories – dry- and wet – vacuum proce- increased. Predominantly processes that mass spectrometers, tube production, dures, that is, into processes in which no are carried out in drying, impregnating, electron microscopes, electron beam significant amounts of vapor have to be and freeze-drying plants belong in this plants, and particle accelerators. pumped and those in which vapors category. Ultrahigh vacuum: < 10-7 mbar (mostly water or organic) arise. • Nuclear fusion, storage rings for In the removal of water vapor from liquids Distinctions between the two categories or in their distillation, particularly in accelerators, space research, and are described briefly: degassing columns, vacuum filling, and surface physics.

Ultrahigh vacuum High vacuum Medium vacuum Rough vacuum

Mass spectrometers Molecular beam apparatus Ion sources Particle accelerators Electron microscopes Electron diffraction apparatus Vacuum spectographs Low-temperature research Production of thin films Surface physics Plasma research Nuclear fusion apparatus Space simulation Material research Preparations for electron microscopy

10–13 10–10 10–7 10–3 100 103

Pressure [mbar] Fig. 2.71 Pressure ranges (p < 1000 mbar) of physical and chemical analytical methods

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Ultrahigh vacuum High vacuum Medium vacuum Rough vacuum

Annealing of metals Melting of metals Degassing of molten metals Steel degassing Electron-beam melting Electron-beam welding Evaporation coating Sputtering of metals Zone melting and crystal growing in high-vacuum Molecular distillation Degassing of liquids Sublimation Casting of resins and lacquers Drying of plastics Drying of insulating papers Freeze-drying of mass materials Freeze-drying of pharmaceutical products Production of incandescent lamps Production of electron tubes Production of gas-discharge tubes

10–10 10–7 10–3 100 103

Pressure [mbar] Fig. 2.72 Pressure ranges of industrial vacuum processes

2.2.2 Pumping of gases be pumped above 80 mbar over long still amounts to about 50 % of the nominal (dry processes) periods, one should use, particularly on pumping speed. economic grounds, jet pumps, water ring For dry processes in which a non conden- pumps or dry running, multi-vane pumps. Between 1 and 10-2 mbar at the onset of sable gas mixture (e.g., air) is to be Rotary vane and rotary piston pumps are large quantities of gas, Roots pumps with pumped, the pump to be used is clearly especially suitable for pumping down rotary pumps as backing pumps have characterized by the required working vessels from atmospheric pressure to optimum pumping properties (see Section pressure and the quantity of gas to be pressures below 80 mbar, so that they can 2.1.3.1). For this pressure range, a single- pumped away. The choice of the required work continuously at low pressures. If stage rotary pump is sufficient, if the chief working pressure is considered in this large quantities of gas arise at inlet working region lies above 10-1 mbar. If it section. The choice of the required pump pressures below 40 mbar, the connection lies between 10-1 and 10-2 mbar, a two- is dealt with in Section 2.3. in series of a Roots pump is recommen- stage backing pump is recommended. -2 Each of the various pumps has a charac- ded. Then, for the backing pump speed Below 10 mbar the pumping speed of teristic working range in which it has a required for the process concerned, a single-stage Roots pumps in combination much smaller rotary vane or piston pump with two-stage rotary pumps as backing particularly high efficiency. Therefore, the -2 most suitable pumps for use in the follo- can be used. pumps decreases. However, between 10 and 10-4 mbar, two-stage Roots pumps (or wing individual pressure regions are des- -3 cribed. For every dry-vacuum process, the b) Medium vacuum (1 – 10 mbar) two single-stage Roots pumps in series) vessel must first be evacuated. It is quite If a vacuum vessel is merely to be eva- with two-stage rotary pumps as backing possible that the pumps used for this may cuated to pressures in the medium vacu- pumps still have a very high pumping be different from those that are the um region, perhaps to that of the required speed. Conversely, this pressure region is optimum choices for a process that is backing pressure for diffusion or sputter- the usual working region for vapor ejector undertaken at definite working pressures. ion pumps, single- and two-stage rotary pumps. For work in this pressure region, pumps are adequate for pressures down to they are the most economical pumps to In every case the choice should be made -1 -3 with particular consideration for the 10 and 10 mbar, respectively. It is es- purchase. As backing pumps, single-stage pressure region in which the working sentially more difficult to select the rotary positive displacement pumps are process predominantly occurs. suitable type of pump if medium vacuum suitable. If very little maintenance and val- processes are concerned in which gases veless operation are convenient (i.e., small or vapors are evolved continuously and vessels in short operation cycles are to be a) Rough vacuum (1013 – 1 mbar) -4 The usual working region of the rotary must be pumped away. An important hint pumped to about 10 mbar or large pumps described in Section 2 lies below may be given at this point. Close to the vessels are to be maintained at this pres- 80 mbar. At higher pressures these pumps attainable ultimate pressure, the pumping sure unattended for weeks), the previously have a very high power consumption (see speed of all rotary pumps falls off rapidly. mentioned two-stage Roots pumps with D00 Fig. 2.11) and a high oil consumption (see Therefore, the lowest limit for the normal two-stage rotary pumps as backing pumps Section 8.3.1.1). Therefore, if gases are to working pressure region of these pumps are the suitable combinations. Allthough, should be that at which the pumping speed such a combination does not work as

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economically as the corresponding vapor 2.2.3 Pumping of gases and sisting of a Roots pump, condenser, and ejector pump, it can operate for a much vapors (wet processes) backing pump, which can transport 100 longer time without maintenance. kg/h of vapor and 18 kg/h of air at an inlet When vapors must be pumped, in addition pressure of 50 mbar, has a power c) High vacuum (10-3 to 10-7 mbar) to the factors working pressure and requirement of 4 – 10 kW (depending on Diffusion, sputter-ion, and turbomolecular pumping speed, a third determining factor the quantity of air involved). A steam pumps typically operate in the pressure is added namely the vapor partial pressure ejector pump of the same performance region below 10-3 mbar. If the working – which may vary considerably in the requires about 60 kW without altering the region varies during a process, different course of a process. This factor is decisive quantity of air involved. pumping systems must be fitted to the in determining the pumping arrangement For the pumping of water vapor, gas ballast vessel. There are also special diffusion to be installed. In this regard, the con- pumps and combinations of gas ballast pumps that combine the typical properties densers described in Section 2.15 are very pumps, Roots pumps, and condensers are of a diffusion pump (low ultimate pres- important adjuncts to rotary displacement especially suitable. sure, high pumping speed in the high pumps. They have a particularly high vacuum region) with the outstanding pumping speed when pumping vapors. Pumping of water vapor with gas ballast properties of a vapor ejector pump (high The next section covers pumping of water pumps throughput in the medium vacuum region, vapor (the most frequent case). The The ratio of vapor partial pressure p to air high critical backing pressure). If the considerations apply similarly to other v partial pressure p is decisive in the working region lies between 10-2 and 10-6 non-aggressive vapors. p evaluation of the correct arrangement of mbar, these diffusion pumps are, in gas ballast pumps, as shown previously by general, specially recommended. Pumping of Water Vapor Water vapor is frequently removed by equations 2.2 and 2.3. Therefore, if the water vapor tolerance of the gas ballast d) Ultrahigh vacuum (< 10-7 mbar) pumps that operate with water or steam as pump is known, graphs may be obtained For the production of pressures in the a pump fluid, for example, water ring that clearly give the correct use of gas ultrahigh vacuum region, sputter-ion, and pumps or steam ejector pumps. This de- ballast pumps for pumping water vapor sublimation pumps, as well as turbomole- pends considerably on circumstances, (see Fig. 2.73). Large single-stage rotary cular pumps and cryopumps, are used in however, because the economy of steam plunger pumps have, in general, an combination with suitable forepumps. The ejector pumps at low pressures is gene- operating temperature of about 77 °C and pump best suited to a particular UHV rally far inferior to that of rotary pumps. hence a water vapor tolerance of about 60 process depends on various conditions For pumping a vapor – gas mixture in mbar. This value is used to determine the (for further details, see Section 2.5). which the vapor portion is large but the air portion is small, the vapor can be pumped different operating regions in Fig. 2.73. In by condensers and the permanent gases, addition it is assumed that the pressure at by relatively small gas ballast pumps (see the discharge outlet port of the gas ballast Section 2.1.5). pump can increase to a maximum of 1330 mbar until the discharge outlet valve Comparatively, then, a pump set con- opens.

Region A: Single-stage, rotary plunger pumps without gas ballast inlet. At a saturation vapor pressure pS of 419 mbar at 77 °C, according to equation 2.2, the requirement is given that pv < 0.46 pp, where

v pv is the water vapor partial pressure e p pp is the partial pressure of air

essur pv + pp = ptot total pressure

tial pr This requirement is valid in the whole working region of the single-stage rotary pv/pp = 0.46 plunger pump – hence, at total pressures -1

ater vapor par between 10 and 1013 mbar. W Region B: Single-stage rotary plunger pumps with gas ballast and an inlet condenser. In this region the water vapor pressure Air partial pressure pp exceeds the admissible partial pressure at Fig. 2.73 Areas of application for gas ballast pumps and condensers pumping water vapor (o.G. = without gas ballast) the inlet. The gas ballast pump must,

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therefore, have a condenser inserted at the Pumping of water vapor with roots pumps denser must decrease the vapor partial inlet, which is so rated that the water vapor Normally, Roots pumps are not as pressure below 60 mbar. Hence, the gas partial pressure at the inlet port of the economical as gas ballast pumps for ballast pump should be large enough only rotary pump does not exceed the continuous operation at pressures above to prevent the air partial pressure behind admissible value. The correct dimensions 40 mbar. With very large pump sets, which the intermediate condenser from ex- of the condenser are selected depending work with very specialized gear ratios and ceeding a certain value; for example, if the on the quantity of water vapor involved. are provided with bypass lines, however, total pressure behind the Roots pump For further details, see Section 2.1.5. At a the specific energy consumption is indeed (which is always equal to the total water vapor tolerance of 60 mbar, the more favorable. If Roots pumps are pressure behind the intermediate conden- lower limit of this region is installed to pump vapors, as in the case of ser) is 133 mbar, the gas ballast pump gas ballast pumps, a chart can be given must pump at least at a partial air pressure p > 6O + 0.46 p mbar v p that includes all possible cases (see Fig. of 73 mbar, the quantity of air transported 2.74). to it by the Roots pump. Otherwise, it must Region C: Single-stage rotary plunger take in more water vapor than it can pumps with a gas ballast. Region A: A Roots pump with a single- tolerate. This is a basic requirement: the The lower limit of region C is characterized stage rotary plunger pump without gas use of gas ballast pumps is wise only if by the lower limit of the working region of ballast. air is also pumped! this pump. It lies, therefore, at about As there is merely a compression between With an ideally leak-free vessel, the gas ptot = 1 mbar. If large quantities of vapor the Roots pump and the rotary plunger ballast pump should be isolated after the arise in this region, it is often more pump, the following applies here too: economical to insert a condenser: 20 kg of required operating pressure is reached and vapor at 28 mbar results in a volume of pv < 0.46 pp pumping continued with the condenser 3 only. Section 2.1.5 explains the best about 1000 m . It is not sensible to pump The requirement is valid over the entire possible combination of pumps and this volume with a rotary pump. As a rule working region of the pump combination condensers. of thumb: and, therefore, for total pressures between 10-2 and 40 mbar (or 1013 mbar for Roots A condenser should always be inserted at Region C: A Roots pump, an intermediate pumps with a bypass line). the pump’s inlet if saturated water vapor condenser, and a gas ballast pump. arises for a considerable time. Region B: A main condenser, a Roots The lower limit of the water vapor partial As a precaution, therefore, a Roots pump pump with a bypass line, an intermediate pressure is determined through the should always be inserted in front of the condenser, and a gas ballast pump. compression ratio of the Roots pump at condenser at low inlet pressures so that This combination is economical only if the backing pressure, which is determined the condensation capacity is essentially large water vapor quantities are to be by the saturation vapor pressure of the enhanced. The condensation capacity does pumped continuously at inlet pressures condensed water. Also, in this region the not depend only on the vapor pressure, above about 40 mbar. The size of the main intermediate condenser must be able to but also on the refrigerant temperature. At condenser depends on the quantity of reduce the vapor partial pressure to at low vapor pressures, therefore, effective vapor involved. The intermediate con- least 60 mbar. The stated arrangement is condensation can be obtained only if the refrigerant temperature is correspondingly low. At vapor pressures below 6.5 mbar, for example, the insertion of a condenser is sensible only if the refrigerant temperature is less than 0 °C. Often at low pressures a gas – vapor mixture with unsaturated water vapor is pumped (for v e p further details, see Section 2.1.5). In

general, then, one can dispense with the essur condenser. tial pr

Region D: Two-stage gas ballast pumps, Roots pumps, and vapor ejector pumps,

always according to the total pressure ater vapor par

W = 0.46 concerned in the process. /p p It must again be noted that the water vapor p v tolerance of two-stage gas ballast pumps is frequently lower than that of corresponding single-stage pumps. D00 Air partial pressure p Air partial pressurep pp

Fig. 2.74 Areas of application for Roots pumps and condensers pumping water vapor (o.G. = without gas ballast)

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suitable – when cooling the condenser E. If the drying process should terminate with known properties with that of a with water at 15 °C – for water vapor at still lower pressures material with different properties. pressures between about 4 and 40 mbar. When a pressure below 10-2 mbar is reached a previously bypassed oil vapor Fundamentally, in the drying of a Region D: A roots pump and a gas ballast ejector pump should be switched on in material, a few rules are noteworthy: pump. addition. Experience has shown that shorter drying In this region D the limits also depend times are obtained if the water vapor essentially on the stages and ratios of Drying of solid substances partial pressure at the surface of the sizes of the pumps. In general, however, As previously indicated, the drying of solid material is relatively high, that is, if the this combination can always be used substances brings about a series of further surface of the material to be dried is not between the previously discussed limits – problems. It no longer suffices that one yet fully free of moisture. This is possible therefore, between 10-2 and 4 mbar. simply pumps out a vessel and then waits because the heat conduction between the until the water vapor diffuses from the source of heat and the material is greater solid substance. This method is indeed at higher pressures and the resistance to technically possible, but it would intorably diffusion in a moist surface layer is smaller increase the drying time. than in a dry one. To fulfill the conditions of a moist surface, the pressure in the 2.2.4 Drying processes It is not a simple technical procedure to drying chamber is controlled. If the neces- keep the drying time as short as possible. Often a vacuum process covers several of sary relatively high water vapor partial Both the water content and the layer thick- the regions quoted here. In batch drying pressure cannot be maintained perma- ness of the drying substance are im- the process can, for example (see Fig. nently, the operation of the condenser is portant. Only the principles can be stated 2.74), begin in region A (evacuation of the temporarily discontinued. The pressure in here. In case of special questions we empty vessel) and then move through the chamber then increases and the advise you to contact our experts in our regions B, C, and D in steps. Then the surface of the material becomes moist Cologne factory. course of the process would be as follows: again. To reduce the water vapor partial A. Evacuating the vessel by a gas ballast The moisture content E of a material to be pressure in the vessel in a controlled way, pump and a Roots pump with a bypass dried of which the diffusion coefficient it may be possible to regulate the re- line. depends on the moisture content (e.g. with frigerant temperature in the condenser. In plastics) as a function of the drying time t this way, the condenser temperature B. Connecting the two condensers is given in close approximation by the attains preset values, and the water vapor because of the increasing vapor pressure following equation: partial pressure can be reduced in a con- produced by heating the material. trolled manner. The choice of the pumping System is E0 E = % (2.31) decided by the highest vapor partial (1 + K · t)q pressure occurring and the lowest air partial pressure at the inlet. E0 where E is the moisture content before C. Bypassing the main condenser drying 2.2.5 Production of an oil-free It will now not have an effect. Instead it q is the temperature-dependent coef- (hydrocarbon-free) would only be pumped empty by the ficient. Thus equation (2.31) serves vacuum pumping system with a further drop in only for the temperature at which q vapor pressure. was determined Backstreaming vapor pump fluids, vapors K is a factor that depends on the of oils, rotary pump lubricants, and their D. Bypassing the intermediate condenser cracking products can significantly disturb Roots pumps and gas ballast pumps alone temperature, the water vapor partial pressure in the vicinity of the material, various working processes in vacuum. can now continue pumping. With short- Therefore, it is recommended that certain term drying, the separation of the the dimensions, and the properties of the material. applications use pumps and devices that condenser filled with condensed water is reliably exclude the presence of hydro- particularly important, because the gas With the aid of this approximate equation, carbon vapors. ballast pump would continue to pump the drying characteristics of many from the condenser the previously substances can be assessed. If K and q a) Rough vacuum region condensed water vapor at the saturation have been determined for various (1013 to 1 mbar) vapor pressure of water. temperatures and water vapor partial Instead of rotary pumps, large water jet, With longer-term drying processes, it pressures, the values for other steam ejector, or water ring pumps can be suffices to shut off the condensate temperatures are easily interpolated, so used. For batch evacuation, and the pro- collector from the condenser. Then only that the course of the drying process can duction of hydrocarbon-free fore vacuum the remaining condensate film on the be calculated under all operating for sputter-ion pumps, adsorption pumps cooling tubes can reevaporate. Depending conditions. With the aid of a similarity (see Section 2.1.8.1) are suitable. If the on the size of the gas ballast pump, this transformation, one can further compare use of oil-sealed rotary vane pumps reevaporation ensues in 30 – 60 min. the course of drying process of a material cannot be avoided, basically two-stage

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rotary vane pumps should be used. The pumps with diaphragm pumps or classic of the vacuum vessel and of the small amount of oil vapor that back- turbomolecular pumps combined with attached components (e.g., connecting streams out of the inlet ports of these scroll pumps should be used as oil-free tubulation; valves, seals) can be made pumps can be almost completely removed backing pumps. extremely small, by a sorption trap (see Section 2.1.4) c) suitable means (cold traps, baffles) are inserted in the pumping line. provided to prevent gases or vapors or their reaction products that have origi- b) Medium vacuum region nated from the pumps used from (1 to 10-3 mbar) 2.2.6 Ultrahigh vacuum reaching the vacuum vessel (no For the pumping of large quantities of gas working Techniques backstreaming). in this pressure region, vapor ejector To fulfill these conditions, the individual pumps are by far the most suitable. With The boundary between the high and ultra- components used in UHV apparatus must mercury vapor ejector pumps, completely high vacuum region cannot be precisely be bakeable and extremely leaktight. oil-free vacua can be produced. As a pre- defined with regard to the working me- Stainless steel is the preferred material for caution, the insertion of a cold trap chilled thods. In practice, a border between the UHV components. with liquid nitrogen is recommended so two regions is brought about because that the harmful mercury vapor does not pressures in the high vacuum region may The construction, start-up, and operation enter the vessel. With the medium vacuum be obtained by the usual pumps, valves, of an UHV system also demands special sorption traps described under a), it is seals, and other components, whereas for care, cleanliness, and, above all, time. The possible with two-stage rotary vane pressures in the UHV region, another assembly must be appropriate; that is, the pumps to produce almost oil-free vacua technology and differently constructed individual components must not be in the down to below 10-4 mbar. components are generally required. The least damaged (i.e. by scratches on “border” lies at a few 10-8 mbar. Therefore, precision-worked sealing surfaces). Fun- Absolutely oil-free vacua may be produced pressures below 10-7 mbar should ge- damentally, every newly-assembled UHV in the medium vacuum region with nerally be associated with the UHV region. apparatus must be tested for leaks with a adsorption pumps. Since the pumping helium leak detector before it is operated. action of these pumps for the light noble The gas density is very small in the UHV Especially important here is the testing of gases is only small, vessels initially filled region and is significantly influenced by demountable joints (flange connections), with air can only be evacuated by them to outgasing rate of the vessel walls and by glass seals, and welded or brazed joints. about 10-2 mbar. Pressures of 10-3 mbar the tiniest leakages at joints. Moreover, in After testing, the UHV apparatus must be or lower can then be produced with connection with a series of important baked out. This is necessary for glass as adsorption pumps only if neither neon nor technical applications to characterize the well as for metal apparatus. The bake-out helium is present in the gas mixture to be UHV region, generally the monolayer time extends not only over the vacuum vessel, pumped. In such cases it can be useful to (see also equation 1.21) has become but frequently also to the attached parts, expel the air in the vessel by first flooding important. This is understood as the time t particularly the vacuum gauges. The with nitrogen and then pumping it away. that elapses before a monomolecular or monatomic layer forms on an initially individual stages of the bake-out, which c) High- and ultrahigh vacuum region ideally cleaned surface that is exposed to can last many hours for a larger system, and the bake-out temperature are arranged (< 10-3 mbar) the gas particles. Assuming that every gas according to the kind of plant and the When there is significant evolution of gas particle that arrives at the surface finds a ultimate pressure required. If, after the in the pressure regions that must be pum- free place and remains there, a convenient apparatus has been cooled and the other ped, turbomolecular pumps, or cryo- formula for τ is necessary measures undertaken (e.g., pumps should be used. A sputter-ion 3.2 τ = ·10– 6 s (p in mbar) cooling down cold traps or baffles), the pump is especially suitable for maintaining p ultimate pressure is apparently not the lowest possible pressure for long obtained, a repeated leak test with a periods in a sealed system where the -7 Therefore, in UHV (p < 10 mbar) the helium leak detector is recommended. process does not release large quantities monolayer formation time is of the order Details on the components, sealing of gas. Magnetically-suspended turbomo- of minutes to hours or longer and thus of methods and vacuum gauges are provided lecular pumps also guarantee hydrocar- the same length of time as that needed for in our catalog. bon-free vacua. However, while these experiments and processes in vacuum. pumps are switched off, oil vapors can The practical requirements that arise have enter the vessel through the pump. By become particularly significant in solid- suitable means (e.g., using an isolating state physics, such as for the study of thin valve or venting the vessel with argon), films or electron tube technology. A UHV contamination of the vessel walls can be system is different from the usual high impeded when the pump is stationary. If vacuum system for the following reasons: the emphasis is on generating a “hydroc- a) the leak rate is extremely small (use of D00 arbon-free vacuum” with turbomolecular metallic seals), pumps, then hybrid turbomolecular b) the gas evolution of the inner surfaces

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quantities of gas and vapor at a certain V 1013 V 1013 2.3. Evacuation of a S = · `n = ·2.3·log pressure. eff t p t p (2.34) vacuum chamber 3. Pumping of the gases and vapors produced during a process by variation Introducing the dimensionless factor and determination of temperature and pressure. 1013 1013 σ= `n = 2.3·log (2.34a) of pump sizes Initial evacuation of a vacuum chamber is p p influenced in the medium-, high-, and Basically, two independent questions ultrahigh vacuum regions by continually into equation (2.34), the relationship arise concerning the size of a vacuum evolving quantities of gas, because in between the effective pumping speed Seff, system: these regions the escape of gases and and the pump-down time t is given by 1. What effective pumping speed must the vapors from the walls of the vessel is so V S = ·σ (2.35) pump arrangement maintain to reduce significant that they alone determine the eff t the pressure in a given vessel over a dimensions and layout of the vacuum given time to a desired value? system. The ratio V/Seff is generally designated as 2. What effective pumping speed must the a time constant τ. Thus the pump-down pump arrangement reach during a time of a vacuum chamber from atmospheric pressure to a pressure p is vacuum process so that gases and 2.3.1 Evacuation of a vacuum vapors released into the vessel can be given by: quickly pumped away while a given chamber (without t = τ · s (2.36) pressure (the operating pressure) in the additional sources of gas vessel, is maintained and not or vapor) V with τ = exceeded? S Because of the factors described above, an eff During the pumping-out procedure of assessment of the pump-down time must 1013 certain processes (e.g., drying and hea- be basically different for the evacuation of σ = `n and p ting), vapors are produced that were not a container in the rough vacuum region originally present in the vacuum chamber, from evacuation in the medium- and high The dependence of the factor from the so that a third question arises: vacuum regions. desired pressure is shown in Fig. 2.75. It 3. What effective pumping speed must the should be noted that the pumping speed of pump arrangement reach so that the single-stage rotary vane and rotary piston process can be completed within a 2.3.1.1 Evacuation of a chamber in the pumps decreases below 10 mbar with gas certain time? rough vacuum region ballast and below 1 mbar without gas ballast. This fundamental behavior is The effective pumping speed of a pump In this case the required effective pumping different for pumps of various sizes and arrangement is understood as the actual speed Seff, of a vacuum pump assembly is pumping speed of the entire pump ar- dependent only on the required pressure rangement that prevails at the vessel. p, the volume V of the container, and the The nominal pumping speed of the pump pump-down time t. can then be determined from the effective With constant pumping speed Seff and pumping speed if the flow resistance assuming that the ultimate pressure pend (conductances) of the baffles, cold traps, attainable with the pump arrangement is filters, valves, and tubulations installed such that pend << p, the decrease with time between the pump and the vessel are of the pressure p(t) in a chamber is given known (see Sections 1.5.2 to 1.5.4). In the by the equation:

determination of the required nominal → e pumping speed it is further assumed that dp Seff − = ·p (2.32)

the vacuum system is leaktight; therefore, dt V essur the leak rate must be so small that gases Pr Beginning at 1013 mbar at time t = 0, the flowing in from outside are immediately effective pumping speed is calculated removed by the connected pump arrange- depending on the pump-down time t from ment and the pressure in the vessel does equation (2.32) as follows: not alter (for further details, see Section 5). The questions listed above under 1., 2. p dp Seff ∫ = − · t σ and 3. are characteristic for the three most p V (2.33a) Dimensionless factor essential exercises of vacuum technology 1013 Fig. 2.75 Dependency of the dimensionless factor s for 1. Evacuation of the vessel to reach a calculation of pumpdown time t according to p S equation 2.36. The broken line applies to specified pressure. `n = − eff ·t (2.33b) 1013 V single-stage pumps where the pumping 2. Pumping of continuously evolving speed decreases below 10 mbar

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types but should not be ignored in the condition. Useful data are collected in A pumping speed of 100 l/s alone is determination of the dependence of the Table X (Section 9). The gas evolution can required to continuously pump away the pump-down time on pump size. It must be be determined experimentally only from quantity of gas flowing in through the pointed out that the equations (2.32 to case to case by the pressure-rise method: leaks or evolving from the chamber walls. 2.36) as well Fig. 2.75 only apply when the the system is evacuated as thoroughly as Here the evacuation process is similar to ultimate pressure attained with the pump possible, and finally the pump and the the examples given in Sections 2.3.1.1. used is by several orders of magnitude chamber are isolated by a valve. Now the However, in the case of a diffusion pump lower than the desired pressure. time is measured for the pressure within the pumping process does not begin at the chamber (volume V) to rise by a atmospheric pressure but at the forevacu- Example: A vacuum chamber having a certain amount, for example, a power of um pressure pV instead. Then equation volume of 500 l shall be pumped down to 10. The gas quantity Q that arises per unit (2.34) transforms into: 1 mbar within 10 minutes. What effective time is calculated from: pumping speed is required? p S = V ·`n V = V · `nK ∆p ·V eff t p t 500 l = 0.5 m3; 10 min = 1/6 h Q = t (2.37) -3 According to equation (2.34) it follows At a backing pressure of pV = 2 · 10 mbar that: (∆p = measured pressure rise ) “compression” K is in our example: 0.5 1013 The gas quantity Q consists of the sum of 2⋅10–3 S = ·2.3·log K = = 200 eff 1/6 1 all the gas evolution and all leaks possibly 1⋅10–5 = 3·2.3·3.01 = 20.8m3/h present. Whether it is from gas evolution or leakage may be determined by the In order to attain an ultimate pressure of following method: 1 · 10-5 mbar within 5 minutes after For the example given above one reads off starting to pump with the diffusion pump the value of 7 from the straight line in Fig. The gas quantity arising from gas evolu- an effective pumping speed of 2.75. However, from the broken line a tion must become smaller with time, the value of 8 is read off. According to quantity of gas entering the system from 500 ≈ ` Seff = ·2.3·log 200 9 equation (2.35) the following is obtained: leakage remains constant with time. 5·60 s Experimentally, this distinction is not 0.5 S = ·7 = 21m3/h or always easily made, since it often takes a is required. This is much less compared to eff 1 considerable length of time – with pure the effective pumping speed needed to 6 gas evolution – before the measured pres- maintain the ultimate pressure. Pump- 0.5 3 Seff = ·8 = 24 m /h sure-time curve approaches a constant (or down time and ultimate vacuum in the 1 almost a constant) final value; thus the 6 high vacuum and ultrahigh vacuum ranges beginning of this curve follows a straight depends mostly on the gas evolution rate line for long times and so simulates and the leak rates. The underlying mathe- under consideration of the fact that the leakage (see Section 5, Leaks and Leak matical rules can not be covered here. For pumping speed reduces below 10 mbar. Detection). these please refer to books specializing on The required effective pumping speed thus that topic. amounts to about 24 m3/h. If the gas evolution Q and the required pressure pend are known, it is easy to determine the necessary effective pumping 2.3.1.2 Evacuation of a chamber in the speed: 2.3.1.3 Evacuation of a chamber in the high vacuum region medium vacuum region Q S = In the rough vacuum region, the volume of It is considerably more difficult to give eff p (2.38) general formulas for use in the high vacu- end the vessel is decisive for the time involved um region. Since the pumping time to in the pumping process. In the high and reach a given high vacuum pressure Example: A vacuum chamber of 500 l may ultrahigh vacuum regions, however, the depends essentially on the gas evolution have a total surface area (including all gas evolution from the walls plays a from the chamber’s inner surfaces, the systems) of about 5 m2. A steady gas significant role. In the medium vacuum condition and pre-treatment of these evolution of 2 · 10-4 mbar · l/s is assumed region, the pumping process is influenced surfaces are of great significance in per m2 of surface area. This is a level by both quantities. Moreover, in the vacuum technology. Under no circums- which is to be expected when valves or medium vacuum region, particularly with tances should the material used exhibit rotary feedthroughs, for example are rotary pumps, the ultimate pressure pend porous regions or – particularly with connected to the vacuum chamber. In attainable is no longer negligible. If the regard to bake-out – contain cavities; the order to maintain in the system a pressure quantity of gas entering the chamber is inner surfaces must be as smooth as of 1 · 10-5 mbar, the pump must have a known to be at a rate Q (in millibars liter possible (true surface = geometric sur- pumping speed of per second) from gas evolution from the walls and leakage, the differential equation D00 face) and thoroughly cleaned (and 5·2·10–4 mbar ·`/ s degreased). Gas evolution varies greatly S = = 100 `/s (2.32) for the pumping process becomes eff 1·10–5 mbar with the choice of material and the surface

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  The required pumping speed of the 1·10–4 S p − p − Q S = · 200 = 0.1`/s = 0.36m3/h dp eff  end  (2.39) backing pump is calculated from: V –1 = − 2·10 dt V pA SV = · Seff (2.41a) Integration of this equation leads to pV Theoretically in this case a smaller backing pump having a pumping speed of about 1   3  p − p  − Q / S m /h could be used. But in practice a V  o end eff Example: In the case of a diffusion pump t = larger backing pump should be installed `n   having a pumping speed of 400 l/s the S  p − p  − Q / S (2.40) because, especially when starting up a eff  end eff effective pumping speed is 50 % of the vacuum system, large amounts of gas may value stated in the catalog when using a where occur for brief periods. Operation of the shell baffle. The max. permissible backing p is the pressure at the beginning of the high vacuum pump is endangered if the 0 pressure is 2 · 10-1 mbar. The pumping pumping process quantities of gas can not be pumped away speed required as a minimum for the p is the desired pressure immediately by the backing pump. If one backing pump depends on the intake works permanently at very low inlet pres- In contrast to equation 2.33b this equation pressure p according to equation 2.41a. A sures, the installation of a ballast volume does not permit a definite solution for S , eff At an intake pressure of p = 1 · 10-2 mbar (backing-line vessel or surge vessel) therefore, the effective pumping speed for A the pumping speed for the high vacuum between the high vacuum pump and the a known gas evolution cannot be deter- pump as stated in the catalog is about 100 backing pump is recommended. The mined from the time – pressure curve l/s, subsequently 50 % of this is 50 l/s. backing pump then should be operated for without further information. Therefore the pumping speed of the short times only. The maximum admis- In practice, therefore, the following backing pump must amount to at least sible backing pressure, however, must method will determine a pump with never be exceeded. 1·10–2 sufficiently high pumping speed: S = · 50 = 2.5`/s = 9 m3/h V –1 The size of the ballast volume depends on a) The pumping speed is calculated from 2·10 the total quantity of gas to be pumped per equation 2.34 as a result of the volume At an intake pressure of p = 1 · 10-3 mbar unit of time. If this rate is very low, the rule of the chamber without gas evolution A the pump has already reached its nominal of thumb indicates that 0.5 l of ballast and the desired pump-down time. pumping speed of 400 l/s; the effective volume allows 1 min of pumping time with b The quotient of the gas evolution rate pumping speed is now S = 200 l/s; thus the backing pump isolated. and this pumping speed is found. This eff the required pumping speed for the quotient must be smaller than the For finding the most adequate size of backing pump amounts to required pressure; for safety, it must be backing pump, a graphical method may be about ten times lower. If this condition 1·10–3 used in many cases. In this case the S = · 200 =1`/s = 3.6m3/h is not fulfilled, a pump with corres- V 2·10–1 starting point is the pumping speed cha- pondingly higher pumping speed must racteristic of the pumps according to be chosen. If the high vacuum pump is to be used for equation 2.41. pumping of vapors between 10-3 and 10-2 mbar, then a backing pump offering a The pumping speed characteristic of a nominal pumping speed of 12 m3/h must pump is easily derived from the measured be used, which in any case must have a pumping speed (volume flow rate) 2.3.2 Determination of a pumping speed of 9 m3/h at a pressure of characteristic of the pump as shown for a suitable backing pump 2 · 10-1 mbar. If no vapors are to be 6000 l/s diffusion pump (see curve S in Fig. 2.76). To arrive at the throughput The gas or vapor quantity transported pumped, a single-stage rotary vane pump operated without gas ballast will do in characteristic (curve Q in Fig. 2.76), one through a high vacuum pump must also be must multiply each ordinate value of S by handled by the backing pump. Moreover, most cases. If (even slight) components of vapor are also to be pumped, one should its corresponding pA value and plotted in the operation of the high vacuum pump against this value. If it is assumed that the (diffusion pump, turbomolecular pump), in any case use a two-stage gas ballast pump as the backing pump which offers – inlet pressure of the diffusion pump does the maximum permissible backing -2 also with gas ballast – the required not exceed 10 mbar, the maximum pressure must never, even for a short time, -1 throughput is 9.5 mbar · l/s be exceeded. If Q is the effective quantity pumping speed at 2 · 10 mbar. of gas or vapor, which is pumped by the If the high vacuum pump is only to be Hence, the size of the backing pump must high vacuum pump with an effective used at intake pressures below 10-3 mbar, be such that this throughput can be handled by the pump at an intake pressure pumping speed Seff at an inlet pressure pA, a smaller backing pump will do; in the case this gas quantity must certainly be trans- of the example given this will be a pump (of the backing pump) that is equal to or ported by the backing pump at a pumping offering a pumping speed of 6 m3/h. If the preferably lower than the maximum speed of S at the backing pressure p . For permissible backing pressure of the dif- V V continuous intake pressures are even -1 the effective throughput Q, the continuity lower, below 10-4 mbar, for example, the fusion pump; that is, 4 · 10 mbar for the equation applies: required pumping speed for the backing 6000 l/s diffusion pump. pump can be calculated from equation Q = pA · Seff = pv · SV (2.41) After accounting for the pumping speed 2.41a as: D00.64 LEYBOLD VACUUM PRODUCTS AND REFERENCE BOOK 2001/2002 D00 E 19.06.2001 21:38 Uhr Seite 65

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characteristics of commercially available 2.3.3 Determination of pump- the pressure at which the Roots pump is two-stage rotary plunger pumps, the down time from switched on. throughput characteristic for each pump is nomograms In the medium vacuum region, the gas calculated in a manner similar to that used evolution or the leak rate becomes to find the Q curve for the diffusion pump In practice, for instance, when estimating significantly evident. From the nomogram in Fig. 2.76 a. The result is the group of Q the cost of a planned vacuum plant, cal- 9.10 in Section 9, the corresponding curves numbered 1 – 4 in Fig. 2.76 b, culation of the pump-down time from the calculations of the pump-down time in this whereby four 2-stage rotary-plunger effective pumping speed S , the required eff vacuum region can be approximated. pumps were considered, whose nominal pressure p, and the chamber volume V by speeds were 200, 100, 50, and 25 m3/h, formulas presented would be too trouble- In many applications it is expedient to respectively. The critical backing pressure some and time-consuming. Nomograms relate the attainable pressures at any given of the 6000 l/s diffusion pump is marked as are very helpful here. By using the nomo- time to the pump-down time. This is easily V.B. (p = 4 · 10-1 mbar). Now the maximum gram in Fig. 9.7 in Section 9, one can possible with reference to the nomogram throughput Q = 9.5 mbar · l/s is shown as quickly estimate the pump-down time for 9.7 in Section 9. horizontal line a. This line intersects the vacuum plants evacuated with rotary As a first example the pump-down cha- four throughput curves. Counting from pumps, if the pumping speed of the pump racteristic – that is, the relationship pres- right to left, the first point of intersection concerned is fairly constant through the sure p (denoted as desired pressure p ) that corresponds to an intake pressure pressure region involved. By studying the end versus pumping time tp – is derived from below the critical backing pressure of examples presented, one can easily under- the nomogram for evacuating a vessel of 4 · 10-1 mbar is made with throughput stand the application of the nomogram. 5 m3 volume by the single-stage rotary characteristic 2. This corresponds to the The pump-down times of rotary vane and plunger pump E 250 with an effective two-stage rotary plunger pump with a rotary piston pumps, insofar as the pum- pumping speed of S = 250 m3/h and an nominal pumping speed of 100 m3/h. eff ping speed of the pump concerned is con- ultimate pressure p = 3 · 10-1 mbar Therefore, this pump is the correct backing end,p stant down to the required pressure, can when operated with a gas ballast and at pump for the 6000 l/s diffusion pump be determined by reference to example 1. -2 pend,p = 3 · 10 mbar without a gas ballast. under the preceding assumption. τ In general, Roots pumps do not have The time constant = V / Seff (see equation However, if the pumping process is such constant pumping speeds in the working 2.36) is the same in both cases and that the maximum throughput of 9.5 region involved. For the evaluation of the amounts as per nomogram 9.7 to about mbar · l/s is unlikely, a smaller backing pump-down time, it usually suffices to 70 s (column 3). For any given value of pump can, of course, be used. This is self- assume the mean pumping speed. pend > pend,p the straight line connecting explanatory, for example, from line b in Examples 2 and 3 of the nomogram show, the “70 s point” on column 3 with the Fig. 2.76 b, which corresponds to a in this context, that for Roots pumps, the (pend – pend,p) value on the right-hand maximum throughput of only 2 mbar l/s. compression ratio K refers not to the scale of column 5 gives the corresponding 3 In this case a 25 m /h two-stage rotary- atmospheric pressure (1013 mbar), but to tp value. The results of this procedure are plunger pump would be sufficient. shown as curves a and b in Fig. 2.77. ] –1 s · l ] · –1 ] s · –1 s · l · oughput Q [mbar Q [mbar Thr Pumping speed S [l

Intake pressure pa [mbar] a) Pumping speed characteristic of a 6000 l/s diffusion pump b) Series of throughput curves for two-stage rotary D00 plunger pumps (V.B. = critical forevacuum pressure) Fig. 2.76 Diagram for graphically determining a suitable backing pump

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2001 / E 250 in Fig. 2.19), one introduces, evolving and pumped vapors is known. as an approximation, average values of However, since this is seldom the case Seff, related to defined pressure ranges. In except with drying processes, a quantita- the case of the WA 1001/ E 250 tive consideration of this question is combination the following average figures abandoned within the scope of this apply: publication. 3 Seff = 800 m /h in the range 10 – 1 mbar, 3 Seff = 900 m /h in the range 1 mbar to 5 · 10-2 mbar, 2.3.5 Selection of pumps for 3 -2 Seff = 500 m /h in the range 5 · 10 to drying processes 5 · 10-3 mbar Fundamentally, we must distinguish bet- The ultimate pressure of the combination ween short-term drying and drying pro- WA 1001 / E 250 is: P = 3 · 10-3 mbar. end,p cesses that can require several hours or From these figures the corresponding time even days. Independently of the duration constants in the nomogram can be of drying, all drying processes proceed determined; from there, the pump-down approximately as in Section 2.24 time tp can be found by calculating the pressure reduction R on the left side of As an example of an application, the drying column 5. The result is curve c in Fig. 2.77. of salt (short-term drying) is described, this being an already well-proven drying Computer aided calculations at LEYBOLD process. Of course calculations for our industrial systems are performed by computer Drying of salt programs. These require high per- First, 400 kg of finely divided salt with a formance computers and are thus usually water content of about 8 % by mass is to not available for simple initial calculations. be dried in the shortest possible time (about 1 h) until the water content is less than 1 % by mass. The expected water evolution amounts to about 28 kg. The salt 2.3.4 Evacuation of a chamber in the chamber is continuously agitated during the drying process and heated to where gases and vapors about 80 °C. The vacuum system is 3 Fig. 2.77 Pumpdown time, tp, of a 5 m vessel using a are evolved schematically drawn in Fig. 2.78. rotary plunger pump E 250 having a nominal pumping speed of 250 m3/h with (a) and The preceding observations about the During the first quarter of drying time far without (b) gas ballast, as well as pump-down time are significantly altered if more than half the quantity of water vapor Roots/rotary plunger pump combination WA vapors and gases arise during the is evolved. Then the condenser is the 1001 / E250 for a cut-in pressure of 10 mbar evacuation process. With bake-out pro- actual main pump. Because of the high for the WA 1001 (e) cesses particularly, large quantities of water vapor temperature and, at the vapor can arise when the surfaces of the beginning of the drying, the very high It is somewhat more tedious to determine chamber are cleared of contamination. The water vapor pressure, the condensation the (pend,tp) relationship for a combination resulting necessary pump-down time efficiency of the condenser is significantly of pumps. The second example discussed depends on very different parameters. increased. In Fig. 2.78 it is understood that in the following deals with evacuating a Increased heating of the chamber walls is two parallel condensers each of 1 m2 con- 3 vessel of 5 m volume by the pump accompanied by increased desorption of densation surface can together condense combination Roots pump WA 1001 and gases and vapors from the walls. However, about 15 l of water at an inlet pressure of the backing pump E 250 (as in the because the higher temperatures result in 100 mbar in 15 min. However, during this preceding example). Pumping starts with an accelerated escape of gases and vapors initial process, it must be ensured that the the E 250 pump operated without gas from the walls, the rate at which they can water vapor pressure at the inlet port of ballast alone, until the Roots pump is be removed from the chamber is also in- the rotary piston pump does not exceed 60 switched on at the pressure of 10 mbar. As creased. mbar (see Section 2.15 for further details). the pumping speed characteristic of the Since the backing pump has only to pump The magnitude of the allowable tempera- combination WA 1001/ E 250 – in contrast away the small part of the noncondensable ture for the bake-out process in question to the characteristic of the E 250 – is no gases at this stage, a single-stage rotary will, indeed, be determined essentially by longer a horizontal straight line over the piston pump TRIVAC S 65 B will suffice. the material in the chamber. Precise pump- best part of the pressure range (compare With increasing process time, the water down times can then be estimated by this to the corresponding course of the vapor evolution decreases, as does the characteristic for the combination WA calculation only if the quantity of the

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water vapor pressure in the condenser. the desired pump-down time. This pump- pressure. The relationship between the After the water pressure in the chamber down time is arranged according to the ultimate pressure and the remaining falls below 27 mbar, the Roots pump (say, desired process duration: if the process is moisture is fixed for every product but dif- a Roots pump RUVAC WA 501) is to be finished after 12 – 15 h, the pump- ferent from product to product. LEYBOLD switched in. Thereby the water vapor is down time should not last longer than 1 h. has many years of experience to its record pumped more rapidly out of the chamber, The size of the backing pump may be regarding applications in this area. the pressure increases in the condensers, easily calculated according to Section Assume that a 0.1 % residual moisture and their condensation efficiency again 2.3.1. content is required, for which the neces- increases. The condensers are isolated by sary ultimate pressure is 6 · 10-2 mbar. a valve when their water vapor reaches its 2. Predrying During the last 5 h the remaining 6 % of saturation vapor pressure. At this point, During predrying – depending on the the moisture content, or 5 kg of water, is there is a water vapor pressure in the pressure region in which the work is removed. At a mean pressure of about chamber of only about 4 mbar, and carried out – about 75 % of the moisture is 0.65 mbar, 2000 m3/h of vapor is evolved. pumping is accomplished by the Roots drawn off. This predrying should occupy Two possibilities are offered: pump with a gas ballast backing pump the first third of the drying time. The rate at a) One continues working with the above- until the water vapor pressure reaches which predrying proceeds depends almost mentioned Roots pump WA 1001. The about 0.65 mbar. From experience it can exclusively on the sufficiency of the heat ultimate total pressure settles at a value be assumed that the salt has now reached supply. For predrying 1 ton of paper in 5 h, according to the water vapor quantity the desired degree of dryness. 60 kg of water must be evaporated; that is, evolving. One waits until a pressure of an energy expenditure of about 40 kWh is about 6.5 · 10-2 mbar is reached, which Drying of paper needed to evaporate water. Since the paper naturally takes a longer time. If the pumps are to be of the correct size must be heated to a temperature of about b From the beginning, a somewhat larger for a longer process run, it is expedient to 120 °C at the same time, an average of Roots pump is chosen (e.g., the break down the process run into charac- about 20 kW must be provided. The mean RUVAC WA 2001 with a pumping speed teristic sections. As an example, paper vapor evolution per hour amounts to of 2000 m3/h is suitable). For larger drying is explained in the following where 12 kg. Therefore, a condenser with a capa- quantities of paper (5000 kg, for the paper has an initial moisture content of city of 15 kg/h should be sufficient. If the example) such a pumping system will 8 %, and the vessel has the volume V. paper is sufficiently preheated (perhaps by be suitable which at a pumping speed air-circulation drying) before evacuation, for water vapor of up to 20,000 m3/h 1. Evacuation in the first hour of drying, double vapor automatically lowers the pressure from The backing pump must be suitably rated evolution must be anticipated. 27 to 10-2 mbar. The entire time need with regard to the volume of the vessel and for drying is significantly reduced when 3. Main drying using such pumps. If, in the second stage, the pressure in a further 5 h is to fall from 20 to about 5.3 mbar and 75 % of the total moisture (i.e., 19 % of the total moisture of 15 kg) is to be drawn off, the pump must, accor- 2.3.6 Flanges and their seals ding to equations (2.37) and (2.38), have a In general, demountable joints in metallic pumping speed of vacuum components, pumps, valves, V · ∆p tubulations, and so on are provided with S = eff t·p flanges. Vacuum components for rough, medium, and high vacuum from LEYBOLD According to equation 1.7, 15 kg of water are equipped with the following stan- vapor corresponds at 15 °C to a quantity of dardized flange systems: water vapor of • Small flanges (KF) (quick-action con- m·R·T 15·83.14·288 nections to DIN 28 403) of nominal V ·∆p = = ≈ M 18 widths 10, 16, 20, 25, 32, 40 and 50 mm. The values 10, 16, 25 and 40 are ≈ 20000 mbar · m3 subsequently 1 Vacuum chamber with salt filling preferred widths according to the 2 RUVAC WA 501 PNEUROP recommendations and the 3 Condensers 20000 3 ISO recommendations of the technical 4 Throttle valve Seff = = 750 m /h 5 Rotary plunger pump 5 ·5.3 committee ISO/TC 112 (see also Sec- tion 11). For a complete connection of Hence the Roots pump RUVAC WA 1001 two identical flanges one clamping ring Fig. 2.78 Vacuum diagram for drying of salt. Pump D00 combination consisting of Roots pump, con- would be the suitable pump. The and one centering ring are required. denser and rotary plunger pump for stepwise permissible remaining moisture in the • Clamp flanges (ISO-K) of nominal switching of the pumping process (see text) product determines the attainable ultimate widths 65, 100, 160, 250, 320, 400,

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500 and 630 mm. Also, these flanges impairment. However, then Perbunan Valves are constructed so that they will not correspond to the nominal widths and sealing material is not suitable as a flange throttle pumping speed. Hence, when construction of the PNEUROP and sealant. Rather, VITILAN® (a special FPM) opened fully, their conductance in the ISO/TC 112 recommendations. Clamp sealing rings and also aluminum seals, rough and medium vacuum regions equals flanges are joined together by clamps which allow heating processes up to that of corresponding tube components. or collar rings. Centering rings or gas- 150 °C and 200 °C respectively, should be For example, the conductance of a right- kets are needed for sealing. used. After such degassing, pressures angle valve will equal the conductance of a down to 10-8 mbar, i.e. down to the UHV bent tube of the same nominal bore and • Bolted flanges (ISO-F) for the same range, can be attained in vacuum systems. angle. Similarly, the conductance of the nominal widths as above (according to valve for molecular flow (i. e., in the high PNEUROP and ISO/TC 112). In special Generating pressures below 10-8 mbar and ultrahigh vacuum regions), is so high cases bolted flanges having a smaller requires higher bake-out temperatures. As that no significant throttling occurs. Actual nominal width are used. Clamp flanges explained above (see Section 2.2.6) work values for the conductance of various and bolted flanges are in accordance in the UHV range requires a basically components are given in the catalog. with DIN 28 404. different approach and the use of CF flanges fitted with metallic sealing rings. To meet stringent leak-tightness demands, The nominal width is approximately equal high-quality vacuum valves are designed to the free inner diameter of the flange in so that gas molecules adhering to the millimeters; greater deviations are excep- surface of the valve shaft are not tions, so the clamp flange DN 63 has an transferred from the outer atmosphere into inner diameter of 70 mm. See also Table XI 2.3.7 Choice of suitable valves the vacuum during operation. Such valves in Section 9). are therefore equipped with metal bellows Vacuum technology puts great demands for isolating the valve shaft from the High vacuum components are made of on the functioning and reliability of the atmosphere, or alternatively, they are fully aluminum or stainless steel. Stainless valves, which are often needed in large encapsulated, that is, only static seals exist steel is slightly more expensive but offers numbers in a plant. The demands are between atmosphere and vacuum. This a variety of advantages: lower degassing fulfilled only if correct shut-off devices are group is comprised of all medium and high rate, corrosion resistant, can be degassed installed for each application, depending vacuum valves from LEYBOLD that are at temperatures up to 200 °C, metal seals on the method of construction, method of operated either manually or electro- are possible and stainless steel is much operation, and size. Moreover, in the pneumatically (Fig. 2.80) and (Fig. 2.79). more resistant to scratching compared to construction and operation of vacuum The leak rate of these valves is less than aluminum. plants, factors such as the flow 10-9 mbar · l/s. conductance and leak-tightness of valves Ultrahigh vacuum components are made are of great importance. Valves sealed with oil or grease can be of stainless steel and have CF flanges bakeable to a high temperature. These components, including the flanges, are manufactured in a series production, starting with a nominal width of 16 up to 250 mm. CF flanges are available as fixed flanges or also with rotatable collar flanges. They may be linked with CONFLAT flanges from almost all manufacturers. Copper gaskets are used for sealing purposes. Basically, the flanges should not be smaller than the connecting tubes and the components that are joined to them. When no aggressive gases and vapors are pumped and the vacuum system is not exposed to a temperature above 80 °C, sealing with NBR (Perbunan) or CR (Neo- prene) flange O-rings is satisfactory for work in the rough-, medium-, and high vacuum regions. This is often the case 1 Casing 3 Compression spring 1 Casing 4 Compressed air supply when testing the operation of vacuum 2 Valve disk 4 Solenoid coil 2 Valve disk 5 Piston systems before they are finally assembled. 3 Bellows

All stainless steel flanges may be degassed Fig. 2.79 Right angle vacuum valve with Fig. 2.80 Right angle vacuum valve with at temperatures up to 200 °C without solenoid actuator electropneumatic actuator

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used for highly stringent demands. Their Typical are variable leak valves, which 2.3.8 Gas locks and seal-off leakage rate is also about 10-9 mbar · l/s. cover the leakage range from 10-10 cm3/s fittings However, a special case is the pendulum- (NTP) up to 1.6 · 103 cm3/s (NTP). These type gate valve. Despite its grease-covered valves are usually motor driven and In many cases it is desirable not only to be seal, the leak rate between vacuum and suitable for remote control and when they able to seal off gas-filled or evacuated ves- external atmosphere is virtually the same are connected to a pressure gauge, the sels, but also to be in a position to check as for bellows-sealed valves because when process pressures can be set and the pressure or the vacuum in these the valve is in operation the shaft carries maintained. Other special valves fulfill vessels at some later time and to post-eva- out only a rotary motion so that no gas safety functions, such as rapid, automatic cuate or supplement or exchange the gas molecules are transferred into the vacuum. cut-off of diffusion pumps or vacuum filling. Pendulum-type gate valves are not manu- systems in the event of a power failure. For This can be done quite easily with a seal-off factured by LEYBOLD. example, SECUVAC valves belong to this fitting from LEYBOLD which is actuated via group. In the event of a power failure, they For working pressures down to 10-7 mbar, a corresponding gas lock. The small flange cut off the vacuum system from the valves of standard design suffice because connection of the evacuated or gas-filled pumping system and vent the forevacuum their seals and the housing materials are vessel is hermetically sealed off within the system. The vacuum system is enabled such that permeation and outgassing are tube by a small closure piece which forms only after a certain minimum pressure insignificant to the actual process. If the actual valve. The gas lock required for (about 200 mbar) has been attained once pressures down to 10-9 mbar are required, actuation is removed after evacuation or the power has been restored. baking up to 200 °C is usually necessary, filling with gas. Thus one gas lock will do to which requires heat resistant sealing When aggressive gases or vapors have to actuate any number of seal-off fittings. materials (e.g., VITILAN®) and materials be pumped, valves made of stainless steel Shown in Fig. 2.81 is a sectional view of of high mechanical strength, with prepared and sealed with VITILAN® sealant are such an arrangement. Gas locks and seal- (inner) surfaces and a low outgassing rate. usually used. For nuclear technology, off fittings are manufactured by LEYBOLD Such valves are usually made of stainless valves have been developed that are sealed having a nominal width of DN 16 KF, DN 25 steel. Flange connections are sealed with with special elastomer or metal gaskets. KF and DN 40 KF. They are made of stain- aluminum gaskets, so permeation pro- We will be pleased to provide further less steel. The leak rate of the seal-off fit- -9 blems of elastomer seals are avoided. In design information for your area of tings is less than 1 · 10 mbar l/s. They the UHV range these issues are of special application upon request. can sustain overpressures up to 2.5 bar, significance so that mainly metallic seals are temperature resistant up to 150 °C and must be used. The gas molecules bonded may be protected against dirt by a standard to the surface of the materials have, at blank flange. pressures below 10-9 mbar, a very great Typical application examples are double- influence. They can only be pumped away walled vessels with an insulating vacuum, within a reasonable period of time by like Dewar vessels, liquid gas vessels simultaneous degassing. Degassing (tanks) or long distance energy pipelines temperatures up to 500 °C required in UHV and many more. They are also used for systems, pose special requirements on the evacuation or post-evacuation of reference sealing materials and the entire sealing and support vacua in scientific instruments geometry. Gaskets made of gold or copper seal-off fittings with gas locks are often must be used. used. Previously it was necessary to have a The various applications require valves pump permanently connected in order to with different drives, that is, valves that are post-evacuate as required. Through the manually operated, electropneumatically- use of gas locks with seal-off fittings a or magnetically-operated, and motor vacuum-tight seal is provided for the vessel and the pump is only required from driven, such as variable-leak valves. The h variety is even more enhanced by the time to time for checking or post- various housing designs. In addition to the evacuation. various materials used, right-angle and DN straight-through valves are required. a Depending on their nominal width and intended application, flanges fitted to valves may be small (KF), clamp (ISO-K), a bolted (ISO-F), or UHV (CF).

In addition to the vacuum valves, which h1 h2 perform solely an isolation function (fully d D00 open – fully closed position), special valves are needed for special functions. Fig. 2.81 Gas lock with centering ring and seal-off fitting, sectional view

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Fundamentals of Vacuum Technology Vacuum Measurement

3. Vacuum 3.1 Fundamentals of measurement, low-pressure measurement monitoring, Vacuum gauges are devices for measuring control and gas pressures below atmospheric pressure (DIN 28 400, Part 3, 1992 issue). In regulation many cases the pressure indication depends on the nature of the gas. With The pressures measured in vacuum tech- Analogy analysis nology today cover a range from 1013 compression vacuum gauges it should be -12 Determination by Absolute noted that if vapors are present, condensa- mbar to 10 mbar, i.e. over 15 orders of means of pressure Length magnitude. The enormous dynamics invol- tion may occur due to the compression, as empirical world a result of which the pressure indication is ved here can be shown through an analo- of human beings 1 bar 1 m gy analysis of vacuum pressure measure- falsified. Compression vacuum gauges simple measuring measure the sum of the partial pressures ment and length measurement, as depic- methods > 1 mbar > 1 mm ted in Table 3.1. of all gas components that do not conden- mechanical se during the measurement procedure. In Measuring instruments designated as measuring the case of mechanically compressing methods > 10–3 mbar > 1 mm vacuum gauges are used for measurement pumps, the final partial pressure can be in this broad pressure range. Since it is indirect measured in this way (see 1.1). Another –9 ≈ impossible for physical reasons to build a methods 10 mbar 1/100 way of measuring this pressure, is to free- atom ∅ vacuum gauge which can carry out quanti- ze out the condensable components in an ≈ tative measurements in the entire vacuum extreme indirect 0.18 LN cold trap. Exact measurement of par- –12 ∅ 2 range, a series of vacuum gauges is avai- methods 10 mbar electron tial pressures of certain gases or vapors is lable, each of which has a characteristic Table 3.1 carried out with the aid of partial pressure measuring range that usually extends over measuring instruments which operate on several orders of magnitude (see Fig. the mass spectrometer principle (see sec- 9.16a). In order to be able to allocate the tion 4). largest possible measuring ranges to the individual types of vacuum gauges, one Dependence of the pressure indication accepts the fact that the measurement on the type of gas uncertainty rises very rapidly, by up to A distinction must be made between the 100 % in some cases, at the upper and following vacuum gauges: lower range limits. This interrelationship is 1. Instruments that by definition measure shown in Fig. 3.1 using the example of the the pressure as the force which acts on VISCOVAC. Therefore, a distinction must an area, the so-called direct or absolu- be made between the measuring range as te vacuum gauges. According to the stated in the catalogue and the measuring kinetic theory of gases, this force, range for “precise” measurement. The which the particles exert through their measuring ranges of the individual vacu- impact on the wall, depends only on the um gauges are limited in the upper and number of gas molecules per unit volu- lower range by physical effects. me (number density of molecules n) and their temperature, but not on their molar mass. The reading of the measuring instrument is independent of the 20 type of gas. Such units include liquid- filled vacuum gauges and mechanical “favorable measuring range” 15 vacuum gauges. (relative measurement uncertainty < 5%) 2. Instruments with indirect pressure 10 measurement. In this case, the pressure is determined as a function of a pres-

5 sure-dependent (or more accurately,

Relative measurement uncertainty (%) Relative measurement density-dependent) property (thermal

1 conductivity, ionization probability, 10–6 10–5 10–4 10–3 10–2 10–1 1 electrical conductivity) of the gas. Pressure (mbar) These properties are dependent on the molar mass as well as on the pressure. Fig. 3.1 Measurement uncertainty distribution over the measuring range: VISCOVAC

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The pressure reading of the measuring vacuum ranges with a measurement (of the order of 10-2 to 10-1 l/s). Contami- instrument depends on the type of gas. uncertainty of less than 50 %, the person nation of the measuring system, interfe- conducting the experiment must proceed The scales of these pressure measuring ring electrical and magnetic fields, insula- with extreme care. Pressure measure- instruments are always based on air or tion errors and inadmissibly high ambient ments that need to be accurate to a few nitrogen as the test gas. For other gases or temperatures falsify pressure measure- percent require great effort and, in general, vapors correction factors, usually based ment. The consequences of these avoida- the deployment of special measuring on air or nitrogen, must be given (see ble errors and the necessary remedies are instruments. This applies particularly to all Table 3.2). For precise pressure measure- indicated in the discussion of the individu- pressure measurements in the ultrahigh ment with indirectly measuring vacuum al measuring systems and in summary vacuum range (p < 10-7 mbar). gauges that determine the number density form in section 8.4. through the application of electrical energy To be able to make a meaningful statement Selection of vacuum gauges (indirect pressure measurement), it is about a pressure indicated by a vacuum The desired pressure range is not the only important to know the gas composition. In gauge, one first has to take into account at factor considered when selecting a suita- practice, the gas composition is known what location and in what way the measu- ble measuring instrument. The operating only as a rough approximation. In many ring system is connected. In all pressure conditions under which the gauge works cases, however, it is sufficient to know areas where laminar flows prevail -1 also play an important role. If measure- whether light or heavy molecules predomi- (1013 > p > 10 mbar), note must be ments are to be carried out under difficult nate in the gas mixture whose pressure is taken of pressure gradients caused by operating conditions, i.e. if there is a high to be measured (e.g. hydrogen or pump pumping. Immediately in front of the risk of contamination, vibrations in the fluid vapor molecules). pump (as seen from the vessel), a lower tubes cannot be ruled out, air bursts can pressure is created than in the vessel. Even Given the presence Correction factor be expected, etc., then the measuring components having a high conductance of predominantly based on N instrument must be robust. In industrial 2 may create such a pressure gradient. (type of gas) (nitrogen = 1) facilities, Bourdon gauges, diaphragm Finally, the conductance of the connecting vacuum gauges, thermal conductivity He 6.9 line between the vacuum system and the Ne 4.35 vacuum gauges, hot cathode ionization measuring system must not be too small vacuum gauges and Penning vacuum gau- Ar 0.83 because the line will otherwise be evacua- Kr 0.59 ges are used. Some of these measuring ted too slowly in the pressure region of instruments are sensitive to adverse ope- Xe 0.33 laminar flow so that the indicated pressure Hg 0.303 rating conditions. They should and can is too high. only be used successfully if the above H2 2.4 mentioned sources of errors are excluded CO 0.92 The situation is more complicated in the as far as possible and the operating CO 0.69 case of high and ultrahigh vacuum. 2 According to the specific installation fea- instructions are followed. CH 0.8 4 tures, an excessively high pressure or, in higher the case of well-degassed measuring hydrocarbons 0.1 – 0.4 tubes, an excessively low pressure may be recorded due to outgassing of the walls of Table 3.2 Correction factors the vacuum gauge or inadequate degassing of the measuring system. In high and Example: If the pressure of a gas essenti- ultrahigh vacuum, pressure equalization ally consisting of pump fluid molecules is between the vacuum system and the mea- measured with an ionization vacuum suring tubes may take a long time. If pos- gauge, then the pressure reading (applying sible, so-called nude gauges are used. The to air or N2), as shown in Table 3.2, is too latter are inserted directly in the vacuum high by a factor of about 10. system, flange-mounted, without a connecting line or an envelope. Special Measurement of pressures in the rough consideration must always be given to the vacuum range can be carried out relatively influence of the measuring process itself precisely by means of vacuum gauges with on the pressure measurement. For exam- direct pressure measurement. Measure- ple, in ionization vacuum gauges that work ment of lower pressures, on the other with a hot cathode, gas particles, especial- hand, is almost always subject to a num- ly those of the higher hydrocarbons, are ber of fundamental errors that limit the thermally broken down. This alters the gas measuring accuracy right from the start so composition. Such effects play a role in that it is not comparable at all to the connection with pressure measurement in degree of accuracy usually achieved with the ultrahigh vacuum range. The same D00 measuring instruments. In order to mea- applies to gas clean-up in ionization vacu- sure pressure in the medium and high um gauges, in particular Penning gauges

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3.2 Vacuum gauges 3.2.2 Diaphragm vacuum The closure to the vessel is in the form of a gauges corrugated diaphragm (4) of special steel. with pressure As long as the vessel is not evacuated, this 3.2.2.1 Capsule vacuum gauges diaphragm is pressed firmly against the reading that is wall (1). As evacuation increases, the diffe- independent of the The best-known design of a diaphragm rence between the pressure to be measu- vacuum gauge is a barometer with an red px and the reference pressure decrea- type of gas aneroid capsule as the measuring system. ses. The diaphragm bends only slightly at It contains a hermetically sealed, evacu- first, but then below 100 mbar to a greater Mechanical vacuum gauges measure the ated, thin-walled diaphragm capsule made degree. With the DIAVAC the diaphragm pressure directly by recording the force of a copper-beryllium alloy. As the pressu- deflection is again transmitted to a pointer which the particles (molecules and atoms) re drops, the capsule diaphragm expands. (9). In particular the measuring range bet- in a gas-filled space exert on a surface by This movement is transmitted to a point by ween 1 and 20 mbar is considerably exten- virtue of their thermal velocity. a lever system. The capsule vacuum ded so that the pressure can be read quite gauge, designed according to this princi- accurately (to about 0.3 mbar). The sensi- ple, indicates the pressure on a linear tivity to vibration of this instrument is scale, independent of the external atmos- somewhat higher than for the capsule 3.2.1 Bourdon vacuum gauges pheric pressure. vacuum gauge. The interior of a tube bent into a circular arc (so-called Bourdon tube) (3) is 3.2.2.2 DIAVAC diaphragm vacuum 3.2.2.3 Precision diaphragm vacuum connected to the vessel to be evacuated gauge gauges (Fig. 3.2). Through the effect of the exter- A significantly higher measuring accuracy nal air pressure the end of the tube is The most accurate pressure reading possi- than that of the capsule vacuum gauge and deflected to a greater or lesser extent ble is frequently required for levels below the DIAVAC is achieved by the precision during evacuation and the attached pointer 50 mbar. In this case, a different diaphragm diaphragm vacuum gauge. The design of mechanism (4) and (2) is actuated. Since vacuum gauge is more suitable, i.e. the these vacuum gauges resembles that of the pressure reading depends on the exter- DIAVAC, whose pressure scale is consider- capsule vacuum gauges. The scale is line- nal atmospheric pressure, it is accurate ably extended between 1 and 100 mbar. ar. The obtainable degree of precision is only to approximately 10 mbar, provided The section of the interior in which the the maximum possible with present-day that the change in the ambient atmosphe- lever system (2) of the gauge head is loca- state-of-the-art equipment. These instru- ric pressure is not corrected. ted (see Fig. 3.3) is evacuated to a reference pressure pref of less than 10-3 mbar. ments permit measurement of 10-1 mbar with a full-scale deflection of 20 mbar. The greater degree of precision also means a higher sensitivity to vibration. Capsule vacuum gauges measure pressure accurately to 10 mbar (due to the linear scale, they are least accurate at the low pressure end of the scale). If only pressures below 30 mbar are to be measured, the DIAVAC is recommended because its reading (see above) is considerably more accurate. For extremely precise measuring accuracy requirements precision diaphragm vacuum gauges should be used. If low pressures have to be measured accurately and for this reason a measuring range of, for example, up to 20 mbar is selected, higher pressures can no longer be measured since these gauges have a 1 Base plate 7 Mirror sheet linear scale. All mechanical vacuum gau- 1 Connecting tube to 2 Lever system 8 Plexiglass sheet ges are sensitive to vibration to some connection flange 3 Connecting flange 9 Pointer 2 Pointer 4 Diaphragm 10 Glass bett extent. Small vibrations, such as those that 3 Bourdon tube 5 Reference 11 Mounting plate arise in the case of direct connection to a 4 Lever system pressure pref, 12 Housing backing pump, are generally not detrimen- 6 Pinch-off end tal.

Fig. 3.3 Cross-section of DIAVAC DV 1000 Fig. 3.2 Cross-section of a Bourdon gauge diaphragm vacuum gauge

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1 2

C1 C2

p1 p2

Fig. 3.4 Piezoelectric sensor (basic diagram) Fig. 3.5 Capacitive sensor (basic diagram)

3.2.2.4 Capacitance diaphragm capacitance of a plate capacitor: one elec- If the pressures to be measured exceed gauges trode is fixed, the other is formed by the these range limits, it is recommended that diaphragm. When the diaphragm is deflec- a multichannel unit with two or three sen- Deflection of a diaphragm can also be elec- ted, the distance between the electrodes sors be used, possibly with automatic trically measured as “strain” or as a chan- and thus capacitance of the capacitor is channel changeover. The capacitance dia- ge in capacitance. In the past, four strain altered. Fig. 3.5 illustrates the principle of phragm gauge thus represents, for all gauges, which change their resistance this arrangement. A distinction is made practical purposes, the only absolute pres- when the diaphragm is deflected, i.e. between sensors with metallic and those sure measuring instrument that is inde- under tensile load, were mounted on a with ceramic diaphragms. The structure of pendent of the type of gas and designed metallic diaphragm in a bridge circuit. At the two types is similar and is shown on for pressures under 1 mbar. Today two LEYBOLD such instruments have been the basis of two examples in Fig. 3.6. types of capacitive sensors are available: given a special designation, i.e. Capacitance diaphragm gauges are used 1) Sensors DI 200 and DI 2000 with MEMBRANOVAC. Later, silicon dia- from atmospheric pressure to 1·10-3 mbar aluminum oxide diaphragms, which are phragms that contained four such “strain (from 10-4 mbar the measurement uncer- particularly overload-free, with the resistances” directly on their surface were tainty rises rapidly). To ensure sufficient MEMBRANOVAC DM 11 and DM 12 used. The electrical arrangement again deflection of the diaphragms at such low units. consisted of a bridge circuit, and a con- pressures, diaphragms of varying thickn- 2) Sensors with Inconel diaphragms CM 1, stant current was fed in at two opposite esses are used for the various pressure DM 10, CM 100, CM 1000 with extre- corner points while a linear voltage signal levels. In each case, the pressure can be mely high resolution, with the DM 21 proportional to the pressure was picked up measured with the sensors to an accuracy and DM 22 units. at the two other corner points. Fig. 3.4 illu- of 3 powers of ten: strates the principle of this arrangement. 1013 to 1 mbar Such instruments were designated as 100 to 10–1 mbar PIEZOVAC units and are still in use in 10 to 10–2 mbar und many cases. Today the deflection of the 1 to 10–3 mbar. diaphragm is measured as the change in

C ~ A/d C = capacitance Diaphragm A = area (Inconel) Reference chamber closure d = distance C ~ A/d C = capacitance Grid + reference chamber A = area closure d = distance Amplifier + 15 V DC Capacitor plates Diaphragm Sensor body Signal converter – 15 V DC (ceramic) (ceramic) + amplifier 0 – 10 V Electrode 24 V DC, 4 – 20 mA D00 left: CAPACITRON (Inconel diaphragm) right: MEMBRANOVAC (aluminum oxide diaphragm)

Fig. 3.6 Capacitive sensors (basic diagram)

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3.2.3 Liquid-filled (mercury) racy. The pressure is measured by com- Principle of measurement with compres- vacuum gauges pressing a quantity of gas that initially sion vacuum gauges occupies a large volume into a smaller If h is the difference in the mercury level 3.2.3.1 U-tube vacuum gauges volume by raising a mercury level. The between the measurement capillary and increased pressure obtained in this man- the reference capillary (measured in mm), U-tube vacuum gauges filled with mercury ner can be measured in the same way as in then it follows from the Boyle-Mariotte are the simplest and most exact instru- a U-tube manometer and from it the origi- law: ments for measuring pressure in the rough nal pressure is calculated (see equations p · V = (p + h) · Vc (3.1) vacuum range (1013 to a few mbar). below). Unfortunately their use in technical plants V is limited because of their size and pro- According to the type of scale division, a p = h⋅ c V −V (3.1a) neness to breakage (see 3.4.1a). distinction is made between two forms of c compression vacuum gauges: those with a In the evacuated limb of the U-tube vacu- linear scale (see Fig. 3.7) and those with a p measured in mm of mercury (= torr). um gauge a constant pressure is maintai- square-law scale (see Fig. 3.8). In the case If Vc << V, then: ned equal to the vapor pressure of mercu- of the compression vacuum gauges of the -3 V ry at room temperature (about 10 mbar). McLeod linear-scale type, the ratio of the p = h⋅ c (3.1b) The other limb is connected to the volume enclosed residual volume Vc to the total V in which the pressure is to be measured. volume V must be known for each height V and V must be known, h is read off From the difference in the levels of the two of the mercury level in the measurement c (linear scale). columns, the pressure to be measured can capillary; this ratio is shown on the scale be determined on the mbar scale provided. provided with the instrument. In the case These relationships remain unchanged if The reading is independent of the atmos- of compression vacuum gauges with a the difference in level is read off a scale pheric pressure. square-law scale, the total volume and the with mbar division. The pressure is then capillary diameter d must be known. obtained in mbar: Nowadays a “shortened” McLeod type 3.2.3.2 Compression vacuum gauges p = 4 ⋅h⋅Vc h in mm (3.1c) (according to McLeod) compression vacuum gauge according to 3 V Kammerer is used to measure the “partial The compression vacuum gauge develo- final pressure” of mechanically com- If during measurement the mercury level ped by McLeod in 1874 is a very rarely pressing pumps. Through the high degree in the measurement capillary is always set used type of vacuum gauge today. In its of compression the condensable gas com- so that the mercury level in the reference refined form the instrument can be used ponents (vapors) are discharged as liquid capillary corresponds to the upper end of for absolute pressure measurement in the (the volume of the same mass is then the measurement capillary (see Figs. 3.7 -5 high vacuum range down to 10 mbar. In smaller by a factor of around 105 and can and 3.8), the volume Vc is always given by: the past it was frequently used as a refe- π be neglected in the measurement) so that V = h⋅ ⋅d2 (3.1d) rence instrument for the calibration of only the pressure of the permanently c 4 medium and sometimes also of high vacu- gaseous components is measured (this is um gauges. For such measurements, where the expression permanent gases h ....difference in level, see Fig. 3.5 however, numerous precautionary rules comes from). d ....inside diameter of measurement had to be taken into account before it was capillary possible to assess the measuring accu-

Upper limit for: torr torr 3 Vcmax. = 1 cm hmax. = 100 mm Upper limit for: d = 2.5 mm Upper limit for: 3 Upper limit for: Vcmax. = 0.1 cm hmax. = 100 mm d = 1 mm measuring range measuring range e p Lower limit for:

essur d = 2.5 mm Pr measuring range

Lower limit for: measuring range –3 3 Lower limit for: Vcmin. = 5 · 10 cm d = 1 mm hmin. = 1 mm

3 Volume V [cm3] Volume V [cm ]

Fig. 3.7 McLeod compression vacuum gauge with linear scale (equation 3.1b) Fig. 3.8 McLeod compression vacuum gauge with square-law scale (equation 3.1f)

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If this term is substituted for Vc in equati- 3.3 Vacuum gauges vided until after supply of this signal to the on (3.1b), the result is: computer and processing by the appro- with priate software and is then displayed direc- π d2 p = h2 ⋅ ⋅ (3.1e) tly on the screen. 4 V gas-dependent

that is, a square-law scale in mm (torr) if d pressure reading 3 and V are measured in mm or mm . If the This type of vacuum gauge does not mea- 3.3.1 Spinning rotor gauge scale is to be divided into mbar, then the sure the pressure directly as an area-rela- (SRG) (VISCOVAC) equation is: ted force, but indirectly by means of other physical variables that are proportional to Pressure-dependent gas friction at low gas π 2 p = h2 ⋅ ⋅ d (3.1f) the number density of particles and thus to pressures can be utilized to measure pres- 3 V the pressure. The vacuum gauges with sures in the medium and high vacuum where h in mm gas-dependent pressure reading include: range. In technical instruments of this kind d in mm the decrement gauge (3.3.1), the thermal a steel ball that has a diameter of several and V in mm3 conductivity vacuum gauge (3.3.2) and the millimeters and is suspended without ionization vacuum gauge having different contact in a magnetic field (see Fig. 3.9) is Compression vacuum gauges ensure a designs (3.3.3). used as the measuring element. The ball is reading of the sum of all partial pressures set into rotation through an electro- The instruments consist of the actual sen- of the permanent gases, provided that no magnetic rotating field: after reaching a sor (gauge head, sensor) and the control vapors are present that condense during starting speed (around 425 Hz), the ball is unit required to operate it. The pressure the compression procedure. left to itself. The speed then declines at a scales or digital displays are usually based rate that depends on the prevailing pressu- The measuring range between the top and on nitrogen pressures; if the true pressure re under the influence of the pressure- bottom ends is limited by the maximum p of a gas (or vapor) has to be determi- T dependent gas friction. The gas pressure and minimum ratios of the capillary volu- ned, the indicated pressure p must be I is derived from the relative decline of the me to the total volume (see Figs. 3.7 and multiplied by a factor that is characteristic speed f (slowing down) using the follo- 3.8). The accuracy of the pressure mea- for this gas. These factors differ, depen- wing equation: surement depends to a great extent on the ding on the type of instrument, and are eit- reading accuracy. By using a vernier and ⋅σ her given in tabular form as factors inde- − ⋅ df 10 ⋅ p f = (3.2) mirror, pressure measurements with an pendent of pressure (see Table 3.2) or, if dt π c ⋅ r ⋅ ρ accuracy of ± 2 % can be achieved. In the they depend on the pressure, must be low pressure range, where h is very small, determined on the basis of a diagram (see p = gas pressure this accuracy is no longer attainable, chief- Fig. 3.11). r = radius of the ball ly because small geometric deviations ρ In general, the following applies: = density of the ball material have a very noticeable effect at the closed -c = mean speed of the gas particles, end of the capillary (systematic error). True pressure dependent on type of gas The presence of vapors that may conden- pT = indicated pressure pI · correction factor σ = coefficient of friction of the ball, inde- se during compression influences the pendent of the type of gas, nearly 1. If the pressure is read off a “nitrogen measurement, often in an indefinite man- scale” but not corrected, one refers to ner. One can easily determine whether “nitrogen equivalent” values. vapors having a pressure that is not negligible are present. This can be done by set- In all electrical vacuum gauges (they inclu- ting different heights h in the measure- de vacuum gauges that are dependent on ment capillary under constant pressure the type of gas) the increasing use of com- while using the linear scale and then cal- puters has led to the wish to display the culating p according to equation 3.1b. If no pressure directly on the screen, e.g. to ins- vapors are present, or only those whose ert it at the appropriate place in a process pressure is negligible at room temperature flow diagram. To be able to use the most (such as mercury), then the same value of standardized computer interfaces possi- p must result for each h. ble, so-called transmitters (signal converters with standardized current outputs) are The scale of compression vacuum gauges built instead of a sensor and display unit 1 Ball 3 Permanent magnets can be calculated from the geometric (e.g. THERMOVAC transmitter, Penning 2 Measuring tube, 4 Stabilization coils dimensions. This is why they were used in closed at one end, 5 4 drive coils transmitter, IONIVAC transmitter). Trans- the past by official calibration stations as welded into 6 Bubble level mitters require a supply voltage (e.g. +24 normal pressure (see equation 3.4.1a). connection flange 7 7 Connection flange volts) and deliver a pressure-dependent D00 current signal that is linear over the entire Fig. 3.9 Cross-section of the gauge head of a measuring range from 4 to 20 mA or VISCOVAC VM 212 spinning rotor gauge (SRG) 0 – 10 V. The pressure reading is not pro-

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As long as a measurement uncertainty of 3.3.2 Thermal conductivity dent on the density and thus on the pres- 3 % is sufficient, which is usually the case, vacuum gauges sure. Below 10-3 mbar the mean free path one can apply σ = 1 so that the sensitivity of a gas roughly corresponds to the size of Classical physics teaches and provides of the spinning rotor gauge (SRG) with radius r2 of the measuring tubes. The sen- rotating steel ball is given by the calculable experimental confirmation that the thermal sing filament in the gauge head forms a physical size of the ball, i.e. the product conductivity of a static gas is independent branch of a Wheatstone bridge. In the radius x density r · ρ (see equation 3.2). of the pressure at higher pressures (par- THERMOTRON thermal conductivity gau- Once a ball has been “calibrated”, it is sui- ticle number density), p > 1 mbar. At lower ges with variable resistance which were table for use as a “transfer standard”, i.e. pressures, p < 1 mbar, however, the ther- commonly used in the past, the sensing as a reference device for calibrating ano- mal conductivity is pressure-dependent filament was heated with a constant cur- ther vacuum gauge through comparison, (approximately proportional 1 / ͱȉM). It de- rent. As gas pressure increases, the tem- and is characterized by high long-term sta- creases in the medium vacuum range star- perature of the filament decreases because bility. Measurements with the VISCOVAC ting from approx. 1 mbar proportionally to of the greater thermal conduction through are not limited to measurement of the the pressure and reaches a value of zero in the gas so that the bridge becomes out of pressure, however. Other variables invol- the high vacuum range. This pressure balance. The bridge current serves as a ved in the kinetic theory of gases, such as dependence is utilized in the thermal con- measure for the gas pressure, which is mean free path, monolayer time, particle ductivity vacuum gauge and enables preci- indicated on a measuring scale. In the number density and impingement rate, can se measurement (dependent on the type of THERMOVAC thermal conductivity gau- also be measured. The instrument permits gas) of pressures in the medium vacuum ges with constant resistance which are storage of 10 programs and easy change- range. almost exclusively built today, the sensing over between these programs. The measu- The most widespread measuring instru- filament is also a branch of a Wheatstone ring time per slowing-down operation is ment of this kind is the Pirani vacuum bridge. The heating voltage applied to this between 5 seconds for high pressures and gauge. A current-carrying filament with a bridge is regulated so that the resistance about 40 seconds for lower pressures. The radius of r1 heated up to around 100 to and therefore the temperature of the fila- measurement sequence of the instrument 150 °C (Fig. 3.10) gives off the heat gene- ment remain constant, regardless of the is controlled fully automatically by a rated in it to the gas surrounding it heat loss. This means that the bridge is microprocessor so that a new value is dis- through radiation and thermal conduction always balanced. This mode of regulation played after every measurement (slowing- (as well as, of course, to the supports at involves a time constant of a few millise- down procedure). The programs additio- the filament ends). In the rough vacuum conds so that such instruments, in con- nally enable calculation of a number of sta- range the thermal conduction through gas trast to those with variable resistance, res- tistical variables (arithmetic mean, stan- convection is virtually independent of pond very quickly to pressure changes. dard deviation) after a previously specified pressure (see Fig. 3.10). If, however, at a The voltage applied to the bridge is a mea- number of measurements. few mbar, the mean free path of the gas is sure of the pressure. The measuring voltage is corrected electronically such that an While in the case of the kinetic theory of of the same order of magnitude as the fila- approximately logarithmic scale is obtai- gases with VISCOVAC the counting of par- ment diameter, this type of heat transfer ned over the entire measuring range. Ther- ticles directly represents the measuring declines more and more, becoming depen- principle (transferring the particle pulses to the rotating ball, which is thus slowed down). With other electrical measuring I II III methods that are dependent on the type of gas, the particle number density is measu- r2 - red indirectly by means of the amount of l ‹‹ r 2 – r1 r1 - heat lost through the particles (thermal - l ‹‹ r1 l Յ r conductivity vacuum gauge) or by means 2 - of the number of ions formed (ionization l ›› r1

vacuum gauge). Heat loss Abgeführter Wärmefluß

10–5 10–4 10–3 10–2 10–1 1 10 100 PressurDrucke [mbar] [mbar]

I Thermal dissipation due to radiation and conduction in the metallic ends II Thermal dissipation due to the gas, pressure-dependent III Thermal dissipation due to radiation and convection

Fig. 3.10 Dependence of the amount heat dissipated by a heated filament (radius r1) in a tube (radius r2) at a constant temperature difference on the gas pressure (schematic diagram)

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mal conductivity vacuum gauges with con- pheric pressure” pT with a THERMOVAC as is proportional to the particle number den- stant resistance have a measuring range a pressure measuring instrument. Argon sity and thus to the pressure. from 10-4 to 1013 mbar. Due to the very might escape from the vessel (cover The formation of ions is a consequence of short response time, they are particularly opens, bell jar rises). For such and similar either a discharge at a high electric field suitable for controlling and pressure moni- applications, pressure switches or vacuum strength (so-called cold-cathode or Pen- toring applications (see section 3.5). The gauges that are independent of the type of ning discharge, see 3.3.3.1) or the impact measurement uncertainty varies in the dif- gas must be used (see section 3.2). of electrons that are emitted from a hot ferent pressure ranges. The maximum cathode (see 3.3.3.2). error at full-scale deflection is about 1 to 2 %. In the most sensitive range, i.e. bet- Under otherwise constant conditions, the ween 10-3 and 1 mbar, this corresponds to ion yield and thus the ion current depend around 10 % of the pressure reading. The 3.3.3 Ionization vacuum on the type of gas since some gases are measurement uncertainty is significantly gauges easier to ionize than others. As all vacuum greater outside this range. gauges with a pressure reading that is Ionization vacuum gauges are the most dependent on the type of gas, ionization As in all vacuum gauges dependent on the important instruments for measuring gas vacuum gauges are calibrated with nitro- type of gas, the scales of the indicating pressures in the high and ultrahigh vacu- gen as the reference gas (nitrogen equiva- instruments and digital displays in the um ranges. They measure the pressure in lent pressure, see 3.3). To obtain the true case of thermal conductivity vacuum gau- terms of the number density of particles pressure for gases other than nitrogen, the ges also apply to nitrogen and air. Within proportional to the pressure. The gas read-off pressure must be multiplied by the limits of error, the pressure of gases whose pressure is to be measured enters the correction factor given in Table 3.2 for with similar molecular masses, i.e. O , CO 2 the gauge heads of the instruments and is the gas concerned. The factors stated in and others, can be read off directly. Cali- partially ionized with the help of an electric Table 3.2 are assumed to be independent bration curves for a series of gases are field. Ionization takes place when electrons of the pressure, though they depend shown in Fig. 3.11. are accelerated in the electric field and somewhat on the geometry of the electro- An extreme example of the discrepancy attain sufficient energy to form positive de system. Therefore, they are to be regar- between true pressure p and indicated ions on impact with gas molecules. These ded as average values for various types of T ions transmit their charge to a measuring pressure pI in pressure measurement is ionization vacuum gauges (see Fig. 3.16). the admission of air to a vacuum system electrode (ion collector) in the system. The with argon from a pressure cylinder to ion current, generated in this manner (or, avoid moisture (pumping time). According more precisely, the electron current in the 3.3.3.1 Cold-cathode ionization feed line of the measuring electrode that is to Fig. 3.11, one would obtain a pI reading vacuum gauges (Penning of only 40 mbar on reaching an “Ar atmos- required to neutralize these ions) is a mea- vacuum gauges) sure of the pressure because the ion yield Ionization vacuum gauges which operate with cold discharge are called cold-cathode- or Penning vacuum gauges. The discharge process in a measuring tube is,

N2, O2 air – pI = pT in principle, the same as in the electrode system of a sputter ion pump (see section 2.1.8.3). A common feature of all types of cold-cathode ionization vacuum gauges is that they contain just two unheated p < p I T electrodes, a cathode and an anode, between which a so-called cold discharge is W initiated and maintained by means of a d.c. voltage (of around 2 kV) so that the discharge continues at very low pressures. e [mbar] p This is achieved by using a magnetic field essur to make the paths of the electrons long p > p ue pr I T enough so that the rate of their collision r T with gas molecules is sufficiently large to form the number of charge carriers required to maintain the discharge. The magnetic field (see Fig. 3.12) is arranged such that the magnetic field lines of force cross the electric field lines. In this way the elec- D00 Indicated pressure [mbar] pI trons are confined to a spiral path. The Fig. 3.11 Calibration curves of THERMOVAC gauges for various gases, based on nitrogen equivalent reading positive and negative charge carriers pro-

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duced by collision move to the correspon- tive to the sudden admission of air and to i+ produced in the measuring system is ding electrodes and form the pressure- vibrations; and third, the instrument is defined by: dependent discharge current, which is easy to operate. i+ = C · i– · p und (3.3) indicated on the meter. The reading in mbar depends on the type of gas. The i + p= upper limit of the measuring range is given − ⋅ (3.3a) 3.3.3.2 Hot-cathode ionization vacuum i C by the fact that above a level of several gauges 10-2 mbar the Penning discharge changes The variable C is the vacuum gauge con- to a glow discharge with intense light out- Generally speaking, such gauges refer to stant of the measuring system. For nitro- put in which the current (at constant volta- measuring systems consisting of three gen this variable is generally around ge) depends only to a small extent on the electrodes (cathode, anode and ion collec- 10 mbar-1. With a constant electron cur- pressure and is therefore not suitable for tor) where the cathode is a hot cathode. rent the sensitivity S of a gauge head is measurement purposes. In all Penning Cathodes used to be made of tungsten but defined as the quotient of the ion current gauges there is considerably higher gas are now usually made of oxide-coated iri- and the pressure. For an electron current -1 sorption than in ionization vacuum gauges dium (Th2O3, Y2O3) to reduce the electron of 1 mA and C = 10 mbar , therefore, the that operate with a hot cathode. A Penning output work and make them more resi- sensitivity S of the gauge head is: stant to oxygen. Ionization vacuum gauges measuring tube pumps gases similarly to a S = i+ / p = C · i- = 10 mbar-1 · 1 mA sputter ion pump (S ≈ 10-2 l/s). Here again of this type work with low voltages and = 10 mbar-1 · 10-3 A the ions produced in the discharge are without an external magnetic field. The hot -2 accelerated towards the cathode where cathode is a very high-yield source of elec- = 1 · 10 A/mbar. they are partly retained and partly cause trons. The electrons are accelerated in the Hot-cathode ionization vacuum gauges sputtering of the cathode material. The electric field (see Fig. 3.13) and receive also exhibit gas sorption (pumping sputtered cathode material forms a gette- sufficient energy from the field to ionize action), which, however, is considerably ring surface film on the walls of the gauge the gas in which the electrode system is smaller than with Penning systems, i.e. tube. In spite of these disadvantages, located. The positive gas ions formed are approx. 10-3 l/s. Essentially this gas sorp- which result in a relatively high degree of transported to the ion collector, which is tion takes place on the glass wall of the inaccuracy in the pressure reading (up to negative with respect to the cathode, and gauge head and, to a lesser extent, at the around 50 %), the cold-cathode ionization give up their charge there. The ion current ion collector. Here use is made of nude gauge has three very outstanding advanta- thereby generated is a measure of the gas gauges that are easy to operate because an - ges. First, it is the least expensive of all density and thus of the gas pressure. If i external magnet is not needed. The upper high vacuum measuring instruments. is the electron current emitted by the hot limit of the measuring range of the hot- Second, the measuring system is insensi- cathode, the pressure-proportional current cathode ionization gauge is around 10-2 mbar (with the exception of special designs). It is basically defined by the scatter processes of ions at gas molecules Anode due to the shorter free path at higher pressures (the ions no longer reach the ion Cathode Ion collector collector = lower ion yield). Moreover, uncontrollable glow or arc discharges may form at higher pressures and electrostatic discharges can occur in glass tubes. In these cases the indicated pressure pI may deviate substantially from the true pressu- UC UA (+ 50V) (+ 200V) re pT. At low pressures the measuring range is limited by two effects: by the X-ray effect and by the ion desorption effect. These

UA effects results in loss of the strict proportionality between the pressure and the ion current and produce a low pressure threshold that apparently cannot be crossed U C (see Fig. 3.14). 1 Small flange 4 Ceramic washer DN 25 KF; 5 Current leadthrough DN 40 KF 6 Connecting bush i+: ion current The X-ray effect (see Fig. 3.15) 2 Housing 7 Anode pin i-: electron current The electrons emitted from the cathode 3 Ring anode with 8 Cathode plate impinge on the anode, releasing photons ignition pin (soft X-rays). These photons, in turn, Fig. 3.13 Schematic diagram and potential curve in a trigger photoelectrons from surfaces they Fig. 3.12 Cross-section of PENNINGVAC PR 35 gauge hot-cathode ionization vacuum gauge

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strike. The photoelectrons released from collector and lead to a pressure indication the Bayard-Alpert system is usually the the ion collector flow to the anode, i.e. the that is initially independent of the pressure standard system. ion collector emits an electron current, but rises as the electron current increases. which is indicated in the same manner as If such a small electron current is used so a) The conventional ionization vacuum a positive ion current flowing to the ion that the number of electrons incident at the gauge collector. This photocurrent simulates a surface is small compared to the number of A triode of conventional design (see Fig. pressure. This effect is called the positive adsorbed gas particles, every electron will 3.16 a) is used as the gauge head, but it is X-ray effect, and it depends on the anode be able to desorb positive ions. If the elec- slightly modified so that the outer electro- voltage as well as on the size of the surfa- tron current is then increased, desorption de serves as the ion collector and the grid ce of the ion collector. will initially increase because more elec- within it as the anode. With this arrange- trons impinge on the surface. This finally ment the electrons are forced to take very Under certain circumstances, however, leads to a reduction in adsorbed gas par- long paths (oscillating around the grid there is also a negative X-ray effect. Pho- ticles at the surface. The reading falls again wires of the anode) so that the probability tons which impinge on the wall surroun- and generally reaches values that may be of ionizing collisions and thus the sensiti- ding the gauge head release photoelec- considerably lower than the pressure rea- vity of the gauge are relatively high. Becau- trons there, which again flow towards the ding observed with a small electron cur- se the triode system can generally only be anode, and since the anode is a grid struc- rent. As a consequence of this effect in used in high vacuum on account of its ture, they also flow into the space within practice, one must ascertain whether the strong X-ray effect, the gas sorption (pum- the anode. If the surrounding wall has the pressure reading has been influenced by a ping) effect and the gas content of the same potential as the ion collector, e.g. desorption current. This can be done most electrode system have only a slight effect ground potential, a portion of the electrons simply by temporarily altering the electron on the pressure measurement. released at the wall can reach the ion current by a factor of 10 or 100. The rea- collector. This results in the flow of an ding for the larger electron current is the electron current to the ion collector, i.e. a more precise pressure value. a) negative current flows which can compensate the positive ion current. This negative In addition to the conventional ionization Conventional ionization X-ray effect depends on the potential of the gauge, whose electrode structure resemb- vacuum gauge outer wall of the gauge head. les that of a common triode, there are system various ionization vacuum gauge systems The ion desorption effect (Bayard-Alpert system, Bayard-Alpert b) Adsorbed gases can be desorbed from a system with modulator, extractor system) ionization vacu- surface by electron impact. For an ionizati- which more or less suppress the two um gauge system for higher on gauge this means that, if there is a layer effects, depending on the design, and are pressures (up to of adsorbed gas on the anode, these gases therefore used for measurement in the 1 mbar) are partly desorbed as ions by the impin- high and ultrahigh vacuum range. Today ging electrons. The ions reach the ion c)

Bayard-Alpert ionization vacuum gauge system

d) e mbar Bayard-Alpert ionization essur vacuum gauge system with modulator

Indicated pr e) Actual pressure mbar extractor I Pressure reading without X-ray effect ionization II Apparent low pressure limit due to X-ray effect C Cathode vacuum gauge III Sum of I and II A Anode system I Ion collector I ion collector A anode Fig. 3.15 Explanation of the X-ray effect in a conventio- Sc screen C cathode nal ionization gauge. The electrons e- emitted M modulator R reflector by the cathode C collide with anode A and D00 trigger a soft X-ray radiation (photons) there. Fig. 3.16 Schematic drawing of the electrode This radiation strikes, in part, the ion collec- arrangement of various ionization vacuum Fig. 3.14 Apparent low pressure limit due to X-ray Ð effect in a normal ionization vacuum gauge tor and generates photoelectrons es there gauge measuring systems

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b) The high-pressure ionization vacuum as that on the ion collector, part of the ion Another advantage is that the measuring gauge (up to 1 mbar) current formed flows to the modulator and system is designed as a nude gauge with a A triode is again used as the electrode the current that flows to the ion collector diameter of only 35 mm so that it can be system (see Fig. 3.16 b), but this time with becomes smaller. The indicated pressure installed in small apparatus. an unmodified conventional design. Since pI of the ionization gauge with modulator the gauge is designed to allow pressure set to the anode potential consists of the measurements up to 1 mbar, the cathode portion due to the gas pressure pg and that must be resistant to relatively high oxygen due to the X-ray effect pγ: pressure. Therefore, it is designed as a so- p = p + p (3.4) called non-burnout cathode, consisting of A g γ an yttria-coated iridium ribbon. To obtain a After switching the modulator from the rectilinear characteristic (ion current as a anode potential over to the ion collector linear function of the pressure) up to a potential, the modulated pressure reading pressure of 1 mbar, a high-ohmic resistor pM is lower than the pI reading because a is installed in the anode circuit. portion of the ions now reaches the modulator. Hence: c) Bayard-Alpert ionization vacuum p = α · p + pγ (3.5) gauge (the standard measuring M g system used today) with α < 1. To ensure linearity between the gas pressure and the ion current over as large a The pg share of the X-ray effect is the same pressure range as possible, the X-ray in both cases. After determining the diffe- effect must be suppressed as far as possi- rence between (3.4) and (3.5), we obtain ble. In the electrode arrangement develo- the equation for the gas pressure pg: ped by Bayard and Alpert, this is achieved p − p p = A M (3.6) by virtue of the fact that the hot cathode is g 1− α located outside the anode and the ion collector is a thin wire forming the axis of α can immediately be determined by expe- the electrode system (see Fig. 3.16 c). The riment at a higher pressure (around X-ray effect is reduced by two to three 10-6 mbar) at which the X-ray effect and orders of magnitude due to the great thus pγ are negligible. The pressure corre- reduction in the surface area of the ion sponding to the two modulator potentials collector. When pressures in the ultrahigh are read off and their ratio is formed. This vacuum range are measured, the inner modulation method has the additional surfaces of the gauge head and the advantage that the ion desorption effect is connections to the vessel affect the pres- determined in this way. It permits pressu- sure reading. The various effects of ad- re measurements up to the 10-11 mbar sorption, desorption, dissociation and flow range with relatively little effort. phenomena cannot be dealt with in this context. By using Bayard-Alpert systems e) Extractor ionization vacuum gauge as nude gauge systems that are placed Disruptive effects that influence pressure directly in the vessel, errors in measure- measurement can also be extensively eli- ment can be extensively avoided because minated by means of an ion-optical system of the above mentioned effects. first suggested by Redhead. With this extractor system (see Fig. 3.16 e) the ions d) Bayard-Alpert ionization vacuum gauge from the anode cylinder are focused on a with modulator very thin and short ion collector. The ion The Bayard-Alpert system with modulator collector is set up in a space, the rear wall (see Fig. 3.16 d), introduced by Redhead, of which is formed by a cup-shaped elec- offers pressure measurement in which trode that is maintained at the anode errors due to X-ray and ion desorption potential so that it cannot be reached by effects can be quantitatively taken into ions emanating from the gas space. Due to account. In this arrangement there is a the geometry of the system as well as the second thin wire, the modulator, near the potential of the of individual electrodes, anode in addition to the ion collector insi- the disruptive influences through X-ray de the anode. If this modulator is set at the effects and ion desorption are almost com- anode potential, it does not influence the pletely excluded without the need of a measurement. If, on the other hand, the modulator. The extractor system measures same potential is applied to the modulator pressures between 10-4 and 10-12 mbar.

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3.4 Adjustment and gauges), are calibrated directly by the PTB 3.4.1 Examples of fundamental at regular intervals. Vacuum gauges of all pressure measurement calibration; DKD, makes are calibrated on an impartial basis methods (as standard by LEYBOLD in Cologne according to PTB national customer order. A DKD calibration certifi- methods for calibrating standards cate is issued with all characteristic data vacuum gauges) on the calibration. The standards of the Definition of terms: Since these terms are Federal Physical-Technical Institute are the a) Measuring pressure with a reference often confused in daily usage, a clear defi- so-called national standards. To be able to gauge nition of them will first be provided: guarantee adequate measuring accuracy An example of such an instrument is the or as little measurement uncertainty as U-tube vacuum gauge, with which the Adjustment or tuning refers to the correct possible in its calibrations, the PTB largely measurement of the pressure in the mea- setting of an instrument. For example, set- carries out its measurements through the surement capillary is based on a measure- ting 0 and 100 % in THERMOVACs or set- application of fundamental methods. This ment of the weight over the length of the ting the mass spectrometer to mass 4 in means, for example, that one attempts to mercury column. describe the calibration pressures through the helium leak detector. In the past the McLeod vacuum gauge was the measurement of force and area or by also used for calibration purposes. With a thinning the gases in strict accordance Calibration inspection refers to com- precision-made McLeod and carefully exe- with physical laws. The chain of the recali- parison with a standard in accordance with cuted measurements, taking into account bration of standard instruments carried certain statutory regulations by specially all possible sources of error, pressures out once a year at the next higher qualified authorized personnel (Bureau of Stand- down to 10-4 mbar can be measured with calibration facility up to the PTB is called ards). If the outcome of this regular ins- considerable accuracy by means of such “resetting to national standards”. In other pection is positive, an operating permit for an instrument. the next operation period (e.g. three years) countries as well, similar methods are carried out by the national standards institu- Another reference gauge is the VISCOVAC is made visible for outsiders by means of a decrement gauge with rotating ball (see sticker or lead seal. If the outcome is nega- tes as those applied by the Federal Physi- cal-Technical Institute (PTB) in Germany. 3.3.1) as well as the capacitance dia- tive, the instrument is withdrawn from phragm gauge (see 3.2.2.4). operation. Fig. 3.17 shows the pressure scale of the PTB. Calibration guidelines are specified in b) Generation of a known pressure; static Calibration refers to comparison with a DIN standards (DIN 28 416) and ISO pro- posals. expansion method standard in accordance with certain On the basis of a certain quantity of gas statutory regulations by specially authori- whose parameters p, V and T are known zed personnel (calibration facility). The exactly – p lies within the measuring range result of this procedure is a calibration cer- of a reference gauge such as a U-tube or tificate which contains the deviations of the readings of the instrument being calibrated from the standard.

Calibration facilities carry out this calibra- 30 tion work. One problem that arises is the Dynamic question of how good the standards are expansion and where they are calibrated. Such stan- 10 dards are calibrated in calibration facilities of the German Calibration Service (DKD). The German Calibration Service is mana- 3 ged by the Federal Physical-Technical Molecular beam Institute (PTB). Its function is to ensure Static expansion that measuring and testing equipment 1 used for industrial measurement purposes U-Tube is subjected to official standards. Calibrati-

on of vacuum gauges and test leaks within 0.3 the framework of the DKD has been assigned to LEYBOLD, as well as other compa- Relative uncertainly [%] of the pressure determination

nies, by the PTB. The required calibration 0.1 pump bench was set up in accordance 10–12 10–9 10–6 10–3 100 103 with DIN 28 418 (see Table 11.1) and then inspected and accepted by the PTB. The Pressure [mbar] D00 standards of the DKD facilities, so-called Fig. 3.17 Pressure scale of Federal Physical-Technical Institute (PTB), Berlin, (status as at August 1984) for inert gases, transfer standards (reference vacuum nitrogen and methane

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McLeod vacuum gauge – a lower pressure c) Dynamic expansion method L1 = conductance of the valve. The pum- within the working range of ionization gau- (see Fig. 3.19) ping system consists of a precisely mea- ges is reached via expansion in several According to this method, the calibration sured aperture with the conductance L2 in stages. pressure p is produced by admitting gas at a wall that is as thin as possible (screen a constant throughput rate Q into a va- conductance) and a pump with a pumping If the gas having volume V1 is expanded to cuum chamber while gas is simultaneous- speed of PS : a volume (V + V ), and from V to p 1 2 2 ly pumped out of the chamber by a pump (V + V ), etc., one obtains, after n stages L ⋅ S L 2 3 unit with a constant pumping speed S. At 2 p 2 of expansion: S = = (3.8) equilibrium the following applies accor- L + S L 2 p 1+ 2 V V V − ding to equation 1.10 a: S p = p ⋅ 1 ⋅ 2 ⋅⋅ ⋅⋅ n 1 (3.7) p n 1 + + + V1 V2 V2 V3 Vn −1 Vn p = Q/S and thus p1 = initial pressure measured directly in Q is obtained either from the quantity of L L L mbar gas that flows into the calibration chamber p = p ⋅ 1 = p ⋅ 1 ⋅ (1 + 2) 2 1 1 (3.9) pn = calibration pressure from a supply vessel in which constant S L2 Sp pressure prevails or from the quantity of The volumes here must be known as pre- gas flowing into the calibration chamber at This method has the advantage that, after cisely as possible (see Fig. 3.18) and the a measured pressure through a known reaching a state of equilibrium, sorption temperature has to remain constant. This conductance. The pressure in front of the effects can be ignored and this procedure method requires that the apparatus used inlet valve must be high enough so that it can therefore be used for calibrating gau- be kept very clean and reaches its limit at can be measured with a reference gauge. ges at very low pressures. pressures where the gas quantity can be The inlet apertures of the valve (small altered by desorption or adsorption effects capillaries, sintered bodies) must be so beyond the permissible limits of error. small that the condition d << λ is met, i.e. According to experience, this lower limit is a molecular flow and hence a constant around 5 · 10-7 mbar. This method is cal- conductance of the inlet valve are obtained led the static expansion method because (see Section 1.5). The quantity of gas is the pressure and volume of the gas at rest then defined by p1 · L1, where are the decisive variables. p1 = pressure in front of the inlet valve and

IM IM

3 V2 = 1000 cm + p1 p3 V4 = 3 + + + 13000 cm p + 3 3 4 V1 = 25 cm V3 = 25 cm p2 + L p2 = p1 1 (Sp >> L2) S +

1 Volume 1 10 LN2 cold trap 16 to pump 2 Volume 2 11 to pump system (pumping speed 3 Inlet valve 12 U-tube vacuum PSp) (conductance L1) gauge 17 Gas inlet 4 Aperture with 13 McLeod vacuum 18 Mass spectrometer conductance L2 gauge 19,20 Gauges to be 5 Valve 14 Valve calibrated 6 to pump system 15 Calibrated 21 Nude gauge to be 7 Valve ionization gauge calibrated 8 to gas reservoir tube 22 Bake-out furnace 9 Valve

Fig. 3.18 Generation of low pressures through static expansion Fig. 3.19 Apparatus for calibration according to the dynamic expansion method

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3.5 Pressure 3.5.2 Automatic protection, actuated from a control panel with push- monitoring and control of buttons. The pump system is to be protec- monitoring, control vacuum systems ted against the following malfunctions: and regulation in a) power failure Protection of a vacuum system against b) drop in pressure in the compressed air vacuum systems malfunctions is extremely important. In network the event of failure, very high material c) failure of cooling water to the diffusion 3.5.1 Fundamentals of pressure values may be at risk, whether through pump loss of the entire system or major compo- d) fault in diffusion pump heating system monitoring and control nents of it, due to loss of the batch of e) failure of backing pump In all vacuum processes the pressure in material to be processed or due to further f) pressure rise in the vessel above a the system must be constantly checked production down time. Adequate operatio- maximum permissible value and, if necessary, regulated. Modern plant nal control and protection should therefo- g) pressure rise above a maximum control additionally requires that all mea- re be provided for, particularly in the case backing pressure (critical forepressure sured values which are important for of large production plants. The individual of the diffusion pump) monitoring a plant are transmitted to cen- factors to be taken into account in this The measures to be taken in order to fore- tral stations, monitoring and control cen- connection are best illustrated on the basis stall such malfunctions will be discussed ters and compiled in a clear manner. Pres- of an example: Fig. 3.20 shows the sche- in the same order: sure changes are frequently recorded over matic diagram of a high vacuum pump a) Measures in the event of power failure: time by recording equipment. This means system. The vessel (11) can be evacuated All valves are closed so as to prevent that additional demands are placed on by means of a Roots pump (14) or a diffu- admission of air to the vacuum vessel vacuum gauges: sion pump (15), both of which operate in and protect the diffusion pump against a) continuous indication of measured conjunction with the backing pump (1). damage. values, analog and digital as far as pos- The Roots pump is used in the medium b) Protection in the event of a drop in sible vacuum range and the diffusion pump in pressure in the compressed air net- b) clear and convenient reading of the the high vacuum range. The valves (3), (8) work: The compressed air is monitored measured values and (16) are operated electropneuma- by a pressure monitoring device (5). If c) recorder output to connect a recording tically. The individual components are instrument or control or regulation equipment d) built-in computer interface (e.g. RS 232) e) facility for triggering switching operations through built-in trigger points These demands are generally met by all vacuum gauges that have an electric measured value display, with the exception of Bourdon, precision diaphragm and liquid- filled vacuum gauges. The respective control units are equipped with recorder outputs that supply continuous voltages between 0 and 10 V, depending on the pressure reading on the meter scale, so that the pressure values can be recorded over time by means of a recording instrument. If a pressure switching unit is connected to the recorder output of the gauge, switching operations can be triggered when the values go over or below specified setpoints. The setpoints or switch threshold values for triggering switching operations directly in the gauges are called trigger 6 Temperature monitoring device 12 High-vacuum gauge values. Apart from vacuum gauges, there 1 Backing pump 2 Backing pressure 7 Cooling water monitoring device 13 Limit switches are diaphragm pressure switches that trig- monitoring device 8 Electropneumatic valve 14 Roots pump ger a switching operation (without display 3 Electropneumatic valve 9 Recorder 15 Diffusion pump of a measured value) via a contact ampli- 4 Compressed air connection 10 High-vacuum monitoring device 16 Electropneumatic valve 11 Vessel 17 Venting valve fier when a certain pressure is reached. 5 Pressure monitoring device D00 Valves, for example, can also be controlled Fig. 3.20 Schematic diagram of a high vacuum pump system with optional operation of a Roots pump or through such switching operations. a diffusion pump

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Fundamentals of Vacuum Technology Vacuum Measurement

the pressure falls under a specified system protected against all malfunctions ce is the controller in which the setpoint value, a signal can initially be emitted or to a fully automatic, program-controlled and the actual value are compared. The the valves can be automatically closed. plant, though the complexity of the electri- totality of all elements involved in the con- In this case, a sufficient reserve supply cal circuits, of course, increases signifi- trol process forms the control circuit. The of compressed air is necessary (not cantly. terms and characteristic variables for shown in Fig. 3.20), which allows all describing control processes are stipula- valves to be actuated at least once. ted in DIN 19226. c) Measures in the event of failure of coo- Generally a distinction is made between ling water to the diffusion pump: The discontinuous control (e.g. two-step or cooling water is monitored by a flow or 3.5.3 Pressure regulation and three-step control) with specification of a temperature monitoring device (6) and control in rough and pressure window, within which the pressu- (7). If the flow of cooling water is ina- medium vacuum systems re may vary, and continuous control (e.g. dequate, the heater of the diffusion PID control) with a specified pressure set- pump is switched off and a signal is Control and regulation have the function of point, which should be maintained as pre- given; the valve (8) closes. giving a physical variable – in this case the cisely as possible. We have two possible d) Protection against failure of the diffusi- pressure in the vacuum system – a certain ways of adjusting the pressure in a vacu- on pump heater: Interruption of the dif- value. The common feature is the actuator um system: first, by changing the pumping fusion pump heating system can be which changes the energy supply to the speed (altering the speed of the pump or monitored by a relay. If the temperature physical variable and thus the variable its- throttling by closing a valve); second, rises above a maximum permissible elf. Control refers to influencing a system through admission of gas (opening a value, a temperature monitoring device or unit through commands. In this case valve). This results in a total of 4 procedu- (6) responds. In both cases the valve the actuator and hence the actual value of res. (8) closes and a signal is given. the physical variable is changed directly e) Protection in the event of backing pump with a manipulated variable. Example: Discontinuous pressure regulation failure: Belt-driven backing pumps Actuation of a valve by means of a pressu- Although continuous regulation undoub- must have a centrifugal switch which re-dependent switch. The actual value may tedly represents the more elegant proce- shuts down the entire system in the change in an undesirable way due to addi- dure, in many cases two-step or three-step event of belt breakage or another tional external influences. The controlled regulation is fully adequate in all vacuum malfunction. Monoblock pumps for unit cannot react to the control unit. For ranges. To specify the pressure window, which the drive is mounted directly on this reason control systems are said to two or three variable, pressure-dependent the shaft can be monitored by current have an open operating sequence. In the switch contacts are necessary. It does not relays and the like. case of regulation, the actual value of the matter here whether the switch contacts f) Protection against a pressure rise in the physical variable is constantly compared are installed in a gauge with display or in a vessel above a certain limit value: The to the specified setpoint and regulated if downstream unit or whether it is a pressu- high vacuum monitoring device (10) there is any deviation so that it completely re switch without display. Fig. 3.21 illust- emits a signal when a specified pressu- approximates the setpoint as far as possi- rates the difference between two-step re is exceeded. ble. For all practical purposes regulation regulation through pumping speed thrott- g) Ensuring the critical forepressure of the always requires control. The main differen- ling, two-point regulation through gas diffusion pump: When a certain backing pressure is exceeded, all valves are closed by the backing pressure monitoring device (2), the pumps are switched off and again a signal is given. The position Two-step regulation through Three-step regulation through of the valves (3), (8) and (16) is indica- pumping speed throttling gas admission pumping speed throttling ted on the control panel by means of and gas admission Pressure Pressure Pressure limit switches (13). The pressure in the p p p vessel is measured with a high vacuum Atm Atm Atm gauge (12) and recorded with a recorder (9). Protection against operating pmax errors can be provided by interlocking p p p the individual switches so that they can min max mitte only be actuated in a predetermined pmin pmin sequence. The diffusion pump, for example, may not be switched on when Time Time Time the backing pump is not running or the required backing pressure is not maintained or the cooling water circulation is not functioning. Fig. 3.21 Schematic diagram of two-step and three-step regulation In principle, it is not a big step from a

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➀ Gauge with two Fu Fuse ➀ Gauge with two Fu Fuse switching points R, Mp Mains connection 220 V/50 Hz switching points R, Mp Mains connection 220 V/50 Hz ➁ Throttle valve Smax Switching point for maximum value ➁ Variable-leak valve Smax Switching point for maximum value ➂ ➂ Vacuum pump Smin Switching point for minimum value Inlet valve Smin Switching point for minimum value ➃ Pump valve PV Pump valve ➃ Gas supply EV Inlet valve ➄ Vacuum vessel R1 Auxiliary relay for pump valve ➄ Throttle valve R2 Auxiliary relay for inlet valve K1 Relay contact of R1 ➅ Vacuum pump K2 Relay contact of R2 M Measuring and switching device ➆ Vacuum vessel M Measuring and switching device

Fig. 3.22 Two-step regulation through pumping speed throttling Fig. 3.23 Two-step regulation through gas admission

admission and three-point regulation In the case of two-step regulation through As the name indicates, two switching through a combination of pumping speed gas admission, the inlet valve is initially points, the lower switching point of the throttling and gas admission. Figures 3.22 closed. If the upper pressure switching regulation system through pumping speed and 3.23 show the circuit and structure of point is not reached, nothing changes; throttling and the upper switching point of the two two-step regulation systems. In only when the pressure falls below the the gas inlet regulation system, were com- the case of two-step regulation through lower switching point, do the “make bined. pumping speed throttling (Fig. 3.22), vol- contacts” open the gas inlet valve and To avoid the complicated installation with tage is supplied to pump valve 4, i.e. it is actuate the auxiliary relay with self-holding auxiliary relays, many units offer a facility open when the relay contacts are in the function simultaneously. Return to the idle for changing the type of function of the release condition. At a level below the state with closing of the gas inlet valve is built-in trigger values via software. Initially upper switching point the valve remains not effected until after the upper switching one can choose between individual swit- open because of the self-holding function point is exceeded due to the release of the ching points (so-called “level triggers”) of the auxiliary relay. Only at a level below relay self-holding function. and interlinked switching points (“interval the lower switching point is the relay lat- Fig. 3.24 shows the corresponding three- triggers”). These functions are explained ching released. If the pressure subse- step regulation system which was created in Fig. 3.25. With interval triggers one can quently rises, the valve is opened again at with the two components just described. also select the size of the hysteresis and the upper switching point.

Fu Fuse ➀ Gauge with three R, Mp Mains connection 220 V/50 Hz switching points Smax Switching point for maximum value ➁ Variable-leak valve Smitte Switching point for mean value ➂ Variable-leak valve Smin Switching point for minimum value T TORROSTAT® S 020 ➃ Inlet valve ➄ PV Pump valve Gas supply EV Inlet valve ➅ Throttle valve R1 Auxiliary relay for pump interval ➆ Vacuum pump R2 Auxiliary relay for inlet interval ➇ Pump valve K1 Relay contact of R1 D00 ➈ Vacuum vessel K2 Relay contact of R2 M Measuring and switching device Fig. 3.24 Three-step regulation system Fig. 3.25 Diagram of level triggers and interval triggers

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process chamber connection measuring connection for process pressure reference chamber control chamber diaphragm controller seat measuring connection for reference pump connection chamber

reference pressure adjustment valve

Fig. 3.26 LEYBOLD-A series, equipment with level and interval triggers Fig. 3.27 Principle of a diaphragm controller

the type of setpoint specification, i.e. either rence pressure > process pressure) or such a connection of 3 MR 50 diaphragm fixed setting in the unit or specification released (for reference pressure < process controllers. through an external voltage, e.g. from 0 – pressure) so that in the latter case, a To control a vacuum process, it is fre- 10 volts. A three-step regulation system connection is established between the pro- quently necessary to modify the pressure (without auxiliary relay), for example, can cess side and the vacuum pump. This ele- in individual process steps. With a dia- be set up with the LEYBOLD MEMBRANOVAC gant and more or less “automatic” regula- phragm controller this can be done either of the A series. Fig. 3.26 shows different tion system has excellent control characte- manually or via electric control of the refe- units of the new LEYBOLD A series, which, ristics (see Fig. 3.28). rence pressure. although they function according to diffe- To achieve higher flow rates, several dia- rent measuring methods, all display a uni- Electric control of the reference pressure phragm controllers can be connected in form appearance. of a diaphragm controller is relatively easy parallel. This means that the process because of the small reference volume that chambers and the reference chambers are Continuous pressure regulation always remains constant. Fig. 3.31 shows also connected in parallel. Fig. 3.29 shows We have to make a distinction here bet- such an arrangement on the left as a pic- ween electric controllers (e.g. PID controllers) with a proportional valve as actuator and mechanical diaphragm controllers. In a regulation system with electric controllers the coordination between controller and actuator (piezoelectric gas inlet valve, inlet valve with motor drive, butterfly control valve, throttle valve) is difficult because of the very different boundary conditions (volume of the vessel, effective pumping speed at the vessel, pressure control range). Such control circuits tend to vibrate easily when process malfunctions occur. It is virtually impossible to specify generally valid standard values. Many control problems can be better solved with a diaphragm controller. The function of the diaphragm controller (see Fig. 3.27) can be easily derived from that of a diaphragm vacuum gauge: the blunt end of

a tube or pipe is either closed off by means P1 = process pressure, P2 = pressure in pump, Pref = reference pressure of an elastic rubber diaphragm (for refe- Fig. 3.28 Control characteristics of a diaphragm controller

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3.5.4 Pressure regulation in high and ultrahigh vacuum systems If the pressure is to be kept constant within certain limits, an equilibrium must be established between the gas admitted to the vacuum vessel and the gas simultaneously removed by the pump with the aid of valves or throttling devices. This is not very difficult in rough and medium vacu- Fig. 3.29 Triple connection of diaphragm controllers um systems because desorption of adsorbed gases from the walls is generally neg- ture and on the right schematically, see ligible in comparison to the quantity of gas 3.5.5 for application examples with flowing through the system. Pressure diaphragm controllers. regulation can be carried out through gas inlet or pumping speed regulation. Howe- To be able to change the reference pressu- ver, the use of diaphragm controllers is DC Diaphragm controller P Vacuum pump re and thus the process pressure towards only possible between atmospheric pres- higher pressures, a gas inlet valve must M Measuring and switching device sure and about 10 mbar. PS Pressure sensor additionally be installed at the process V1 Pump valve chamber. This valve is opened by means of In the high and ultrahigh vacuum range, V2 Gas inlet valve a differential pressure switch (not shown on the other hand, the gas evolution from TH Throttle the vessel walls has a decisive influence on RC Reference chamber in Fig. 3.31) when the desired higher pro- PC Process chamber cess pressure exceeds the current process the pressure. Setting of specific pressure CV Internal reference pressure control valve pressure by more than the pressure diffe- values in the high and ultrahigh vacuum rence set on the differential pressure range, therefore, is only possible if the gas Fig. 3.30 Control of vacuum drying processes by regu- switch. evolution from the walls is negligible in lation of the intake pressure of the vacuum relation to the controlled admission of gas pump according to the water vapor tolerance by means of the pressure-regulating unit. For this reason, pressure regulation in this variable-leak valves are used as actuators. range is usually effected as gas admission Only bakeable all-metal gas inlet valves regulation with an electric PID controller. should be used for pressure regulation Piezoelectric or servomotor-controlled below 10-6 mbar.

DC Diaphragm controller PS Process pressure sensor RS Reference pressure sensor V1 Gas inlet valve V2 Pump valve V3 Gas inlet variable-leak valve TH Throttle M Measuring and switching device PP Process pump RC Reference chamber PC Process chamber D00 AP Auxiliary pump CV Internal reference pressure control valve Fig. 3.31 Diaphragm controller with external automatic reference pressure regulation

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3.5.5 Examples of applications The material to be dried is usually heated “caught” as the reference pressure in the with diaphragm to intensify and speed up the drying pro- reference chamber (RC) of the diaphragm cess. If a certain amount of water vapor is controller (DC). Now the process pressure controllers produced, the intake pressure rises above is automatically maintained at a constant 1) Regulation of a drying/distillation pro- the two switching points. As a result, valve level according to the set reference pres- cess, taking into account the maximum V2 first closes and V1 opens. Through sure by means of the diaphragm controller water vapor tolerance of a vane type incoming air or protective gas the pressu- (DC). If the reference pressure should rise rotary pump re in the reference chamber is raised and in the course of the process due to a leak, the throughput at the diaphragm controller this is automatically detected by the mea- In a drying process it is frequently desira- thus throttled until the intake pressure of suring and switching device and corrected ble to carry out drying solely by means of the vacuum pump has dropped below the by briefly opening pump valve V2. This vacuum pumps without inserting conden- set maximum switching point again. Then additional control function enhances the sers. In view of the limited water vapor valve V1 closes. operational reliability and extends the tolerance of vacuum pumps – approx. range of application. Correcting the increa- Depending on the quantity of vapor that 30 mbar as a rule – this would result in sed reference pressure to the originally set accumulates, the throughput of the condensation of the vapors produced wit- value is of special interest for regulated diaphragm controller is set by increasing hin the vacuum pump, given non-throttled helium circuits because the pressure rise or decreasing the reference pressure in or non-regulated pumping speed. One can in the reference chamber (RC) of the dia- each case so that the maximum permissi- avoid this through process-dependent phragm controller can be compensated for ble partial water vapor pressure at the inlet remote control of a diaphragm controller through this arrangement as a consequen- connection of the vacuum pump is never with auxiliary control valves and a measu- ce of the unavoidable helium permeability exceeded. ring and switching device with a pressure of the controller diaphragm of FPM. sensor at the inlet connection of the vacu- As soon as the pressure in the process To be able to change the reference pressu- um pump if the intake pressure is adapted chamber drops below the set minimum re and thus increase the process pressure to the pumps water vapor tolerance switching point towards the end of the dry- to higher pressures, a gas inlet valve must through automatic monitoring of the inta- ing process, valve V2 opens and remains be additionally installed at the process ke pressure of the vacuum pump and by open. In this way the unthrottled cross- chamber. This valve is opened by means of throttling the pumping speed. Fig. 3.30 section of the diaphragm controller is avai- a differential pressure switch (not shown shows the principle of this arrangement. lable again for rapid final drying. At the in Fig. 3.31) when the desired higher pro- same time the final drying procedure can Mode of operation: Starting from atmos- cess pressure exceeds the current process be monitored by means of the pressure pheric pressure with the process heating pressure by more than the pressure diffe- sensor PS. switched off, valve V1 is initially open rential set at the differential pressure (maximum switching point exceeded) so switch. that atmospheric pressure also prevails in 2) Pressure regulation by means of dia- the reference chamber. phragm controller with external automatic reference pressure adjust- The diaphragm controller is therefore clo- ment (see Fig. 3.31) sed. When the system is started up, the connecting line between the vacuum pump For automatic vacuum processes with and pump valve V2 is first evacuated. As regulated process pressure, presetting of soon as the pressure drops below the the desired set pressure must often func- maximum switching point, valve V1 clo- tion and be monitored automatically. If a ses. When the pressure falls below the diaphragm controller is used, this can be minimum switching point, valve V2 opens. done by equipping the reference chamber with a measuring and switching device and In this manner the pressure in the referen- a control valve block at the reference ce chamber is slowly lowered, the thrott- chamber. The principle of this arrange- ling of the diaphragm controller is reduced ment is shown in Fig. 3.31. accordingly and thus the process pressure is lowered until the quantity of process gas Mode of operation: Starting with atmos- is greater than the quantity conveyed by pheric pressure, gas inlet valve V1 is clo- the pump so that the minimum switching sed at the beginning of the process. Pump point is again exceeded. Valve V2 closes valve V2 opens. The process chamber is again. This interaction repeats itself until now evacuated until the set pressure, the pressure in the process chamber has which is preset at the measuring and swit- dropped below the minimum switching ching device, is reached in the process point. After that, valve V2 remains open so chamber and in the reference chamber. that the process can be brought down to When the pressure falls below the set swit- the required final pressure with a comple- ching threshold, pump valve V2 closes. As tely open diaphragm controller. a result, the pressure value attained is

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which are in common use comprise the 4. Analysis of gas measurement system proper (the sensor) and the control device required for its ope- at low ration. The sensor contains the ion source, the separation system and the ion trap. pressures The separation of ions differing in masses and charges is often effected by utilizing using mass phenomena which cause the ions to reso- spectrometry nate in electrical and magnetic fields. Initially, the control units were quite clum- sy and offered uncountable manipulation options. It was often the case that only 4.1 General physicists were able to handle and use them. With the introduction of PCs the Analyses of gases at low pressures are requirements in regard to the control units useful not only when analyzing the residu- became ever greater. At first, they were fit- al gases from a vacuum pump, leak testing ted with interfaces for linkage to the com- at a flange connection or for supply lines puter. Attempts were made later to equip a c (compressed air, water) in a vacuum. They a PC with an additional measurement circuit b are also essential in the broader fields of board for sensor operation. Today’s sen- vacuum technology applications and pro- a: High-performance sensor with Channeltron sors are in fact transmitters equipped with b: Compact sensor with Micro-Channelplate cesses. For example in the analysis of pro- an electrical power supply unit attached c: High-performance sensor with Faraday cup cess gases used in applying thin layers of direct at the atmosphere side; communica- Fig. 4.1a TRANSPECTOR sensors coatings to substrates. The equipment tion with a PC from that point is via the used for qualitative and/or quantitative standard computer ports (RS 232, RS analyses of gases includes specially deve- 485). Operating convenience is achieved metry in vacuum-assisted process techno- loped mass spectrometers with extremely by the software which runs on the PC. logy applications presumably date back to small dimensions which, like any other Backus’ work in the years 1943 / 44. He vacuum gauge, can be connected directly carried out studies at the Radiographic to the vacuum system. Their size distin- Laboratories at the University of California. guishes these measurement instruments Seeking to separate uranium isotopes, he from other mass spectrometers such as 4.2 A historical review used a 180° sector field spectrometer after those used for the chemical analyses of Following Thomson’s first attempt in 1897 Dempster (1918), which he referred to as gases. The latter devices are poorly suited, to determine the ratio of charge to mass a “vacuum analyzer”. Even today a similar for example, for use as partial pressure e/m for the electron, it was quite some term, namely the “residual gas analyzer” measurement units since they are too time (into the 1950s) before a large num- (RGA), is frequently used in the U.S.A. and large, require a long connector line to the ber and variety of analysis systems came the U.K. instead of “mass spectrometer”. vacuum chamber and cannot be baked out into use in vacuum technology. These Today’s applications in process monitoring with the vacuum chamber itself. The in- included the Omegatron, the Topatron and are found above all in the production of vestment for an analytical mass spectro- ultimately the quadrupole mass spectro- semiconductor components. meter would be unjustifiably great since, meter proposed by Paul and Steinwedel in for example, the requirements as to reso- 1958, available from INFICON in its stan- lution are far less stringent for partial pres- dard version as the TRANSPECTOR (see sure measurements. Partial pressure is Fig. 4.1). The first uses of mass spectro- understood to be that pressure exerted by 4.3 The quadrupole a certain type of gas within a mix of gases. mass spectrometer The total of the partial pressures for all the types of gas gives the total pressure. The (TRANSPECTOR) distinction among the various types of The ion beam extracted from the electron gases is essentially on the basis of their impact ion source is diverted into a qua- molar masses. The primary purpose of drupole separation system containing four analysis is therefore to register qualita- rod-shaped electrodes. The cross sections tively the proportions of gas within a of the four rods form the circle of curvatu- system as regards the molar masses and re for a hyperbola so that the surrounding determine quantitatively the amount of the electrical field is nearly hyperbolic. Each of individual types of gases associated with the two opposing rods exhibits equal the various atomic numbers. D00 potential, this being a DC voltage and a Partial pressure measurement devices superimposed high-frequency AC voltage Fig. 4.1b TRANSPECTOR XPR sensor

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Anode

Quadrupole exit Focussing plate diaphragm Cathode (extractor diaphragm) Ion source exit diaphragm Cathode (total pressure measurement) Anode

Shielding Reflec- Ion trap tor

Ion source Quadrupole separation system Ion detector Extractor measurement system

Transpector measurement head Fig. 4.2 Schematic for quadrupole mass spectrometer Fig. 4.3 Quadrupole mass spectrometer – Extractor ionization vacuum gauge

(Fig. 4.2). The voltages applied induce XPR sensor had to be raised from about 2 of the cathode, anode and several baffles. transverse oscillations in the ions traver- MHz to approximately 6 times that value, The electron emission, kept constant, causing the center, between the rods. The namely to 13 MHz. In spite of the reduction ses partial ionization of the residual gas, amplitudes of almost all oscillations in the length of the rod system, ion yield is into which the ion source is “immersed” as escalate so that ultimately the ions will still reduced due to dispersion processes completely as possible. The vacuum in the make contact with the rods; only in the at such high pressures. Additional electro- vicinity of the sensor will naturally be influ- case of ions with a certain ratio of mass to nic correction is required to achieve per- enced by baking the walls or the cathode. charge m/e is the resonance condition fect depiction of the spectrum. The dimen- The ions will be extracted through the baf- which allows passage through the system sions of the XPR sensor are so small that fles along the direction of the separation satisfied. Once they have escaped from the it can “hide” entirely inside the tubulation system. One of the baffles is connected to separation system the ions move to the ion of the connection flange (DN 40, CF) and a separate amplifier and – entirely inde- trap (detector, a Faraday cup) which may thus occupies no space in the vacuum pendent of ion separation – provides con- also take the form of a secondary electron chamber proper. Fig. 4.1a shows the size tinuous total pressure measurement (see multiplier pick-up (SEMP). comparison for the normal high-perfor- Fig. 4.4). The cathodes are made of iridium mance sensors with and without the Chan- wire and have a thorium oxide coating to The length of the sensor and the sepa- neltron SEMP, the normal sensor with reduce the work associated with electron ration system is about 15 cm. To ensure channel-plate SEMP. Fig. 4.1b shows the discharge. (For some time now the thori- that the ions can travel unhindered from XPR sensor. The high vacuum required for um oxide has gradually been replaced by the ion source to the ion trap, the mean the sensor is often generated with a yttrium oxide.) These coatings reduce the free path length inside the sensor must be TURBOVAC 50 turbomolecular pump and electron discharge work function so that considerably greater than 15 cm. For air a D 1.6 B rotary vane pump. With its great the desired emission flow will be achieved and nitrogen, the value is about compression capacity, a further advantage even at lower cathode temperatures. Avai- p · λ = 6 · 10–3 mbar · cm. At p = 1 · 10-4 of the turbomolecular pump when lable for special applications are tungsten bar this corresponds to a mean free path handling high molar mass gases is that the cathodes (insensitive to hydrocarbons but length of λ = 60 cm. This pressure is gene- sensor and its cathode are ideally pro- sensitive to oxygen) or rhenium cathodes rally taken to be the minimum vacuum for tected from contamination from the (insensitive to oxygen and hydrocarbons mass spectrometers. The emergency shut- direction of the forepump. but evaporate slowly during operation due down feature for the cathode (responding to the high vapor pressure). to excessive pressure) is almost always set for about 5 · 10-4 mbar. The desire to be able to use quadrupole spectrometers Cathode at higher pressures too, without special 4.3.1 Design of the sensor pressure convertors, led to the development of the XPR sensor at Inficon (XPR One can think of the sensor as having been Shielding standing for extended pressure range). To derived from an extractor measurement Anode enable direct measurement in the range of system (see Fig. 4.3), whereby the about 2 · 10-2 mbar, so important for sput- separation system was inserted between Extractor diaphragm ter processes, the rod system was reduced the ion source and the ion trap. from 12 cm to a length of 2 cm. To ensure Total pressure that the ions can execute the number of diaphragm transverse oscillations required for sharp 4.3.1.1 The normal (open) ion source mass separation, this number being about The ion source comprises an arrangement 100, the frequency of the current in the Fig. 4.4 Open ion source

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Mass Spectrometry Fundamentals of Vacuum Technology

4.3.1.2 The quadrupole separation the amplitude of the transverse oscilla- system xz plane yz plane tions will be smaller than the clearance + Rod: - Rod: +U –U between the rods and the ion can pass Here the ions are separated on the basis of 1 + + Transmission: Transmission: to the collector at very large V. their mass-to-charge ratio. We know from + full - none + Rod: - Rod: +U+V, cos ω –U–V · cos ω + + physics that the deflection of electrically + + 3. Ion emission i = i (V) for a fixed mass 2 Transmission: Transmission: charged particles (ions) from their trajec- + low-pass - high-pass of M: tory is possible only in accordance with i+ i+ 3 xz plane (left): For voltages of V < V1 the their ratio of mass to charge, since the V V V V 1 1 deflection which leads to an escalation attraction of the particles is proportional to + + i i of the oscillations is smaller than V , i.e. the charge while the inertia (which resists 4 1 M M M M change) is proportional to its mass. The 1 1 still in the “pass” range. Where V > V1 separation system comprises four cylin- Superimposition of the xy and yz planes the deflection will be sufficient to U induce escalation and thus blockage. + yz xz fixed drical metal rods, set up in parallel and iso- i ( V ) lated one from the other; the two opposing 5 I III yz plane (right): For voltages of V < V II M 1

rods are charged with identical potential. U .. Selectivity (resolution) Sensitivity the deflection which leads to the dam- V Fig. 4.2 shows schematically the arrange- ping of the oscillations is smaller than ment of the rods and their power supply. V1, i.e. still in the “block” range. Where The electrical field Φ inside the separation Fig. 4.5 Phenomenological explanation of the V > V1 the damping will be sufficient to system is generated by superimposing a separation system settle oscillations, allowing passage. DC voltage and a high-frequency AC volta- 4. Ion flow i+ = i+ (M) for a fixed ratio of ge: paration system and observe the deflec- U / V: tion of a singly ionized, positive ion with Φ = (U + V ⋅ cos ωt) · (x2 – y2) / r 2 0 atomic number M, moving in two planes, Here the relationships are exactly oppo- + + r0 = radius of the cylinder which can be which are perpendicular one to the other site to those for i = i (V) since the inscribed inside the system of rods and each passing through the centers of influence of V on light masses is great- Exerting an effect on a single charged ion two opposing rods. We proceed step-by- er than on heavy masses. step and first observe the xz plane (Fig. moving near and parallel to the center line xz plane: For masses of M < M the 4.5, left) and then the yz plane (Fig.4.5, 1 inside the separation system and perpen- deflection which results in escalation of right): dicular to its movement are the forces the oscillations is greater than at M , 1. Only DC potential U at the rods: 1 which means that the ions will be − 2e ⋅ ⋅ ω ⋅ Fx = x cos ( t) xz plane (left): Positive potential of +U blocked. At M > M the deflection is no r 2 1 0 at the rod, with a repellant effect on the longer sufficient for escalation, so that 2e Fy = − ⋅ y⋅ cos (ω ⋅ t) ion, keeping it centered; it reaches the the ion can pass. r 2 0 collector (→ passage). yz plane: For masses of M < M1 the Fz = 0 yz plane (right): Negative potential on deflection which results in damping of the rod -U, meaning that at even the the oscillations is greater than at M1, The mathematical treatment of these equa- tiniest deviations from the center axis which means that the ion will pass. At tions of motion uses Mathieu’s differential the ion will be drawn toward the nearest M > M1 the damping is not sufficient to equations. It is demonstrated that there rod and neutralized there; it does not calm the system and so the ion is are stable and unstable ion paths. With the reach the collector (→ blocking). blocked. stable paths, the distance of the ions from 5. Combination of the xz and yz planes. In the separation system center line always 2. Superimposition of high-frequency ω the superimposition of the ion currents remains less than r (passage condition). voltage V · cos t: o i+ = i+ (M) for both pairs of rods (U / V With unstable paths, the distance from the xz plane (left): being fixed) there are three important axis will grow until the ion ultimately colli- ω Rod potential +U + V · cos t. With ranges: des with a rod surface. The ion will be rising AC voltage amplitude V the ion discharged (neutralized), thus becoming will be excited to execute transverse Range I : No passage for M due to the unavailable to the detector (blocking con- oscillations with ever greater amplitu- blocking behavior of the xz pair of rods. dition). des until it makes contact with a rod Range II : The pass factor of the rod Even without solving the differential equa- and is neutralized. The separation systems for mass M is determined by tion, it is possible to arrive at a purely phe- system remains blocked for very large the U/V ratio (other ions will not pass). nomenological explanation which leads to values of V. We see that great permeability (corre- an understanding of the most important yz plane (right): sponding to high sensitivity) is bought characteristics of the quadrupole sepa- Rod potential -U -V · cos ω t. Here again at the price of low selectivity (= resolu- ration system. D00 superimposition induces an additional tion, see Section 4.5). Ideal adjustment If we imagine that we cut open the se- force so that as of a certain value for V of the separation system thus requires a compromise between these two prop-

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Positive ion Separation system output Collector Electron suppressor

Faraday cup

Connection Amplifier to front end of the inside surface Resistance of the inner surface

≈ 8 Ω Amplifier Resistance 10 Negative high voltage R ≈ 4 · 106 Ω

Fig. 4.6 Left: principle of the Faraday cup; right: configuration of the Channeltron

erties. To achieve constant resolution, Channeltrons or Channelplates can be TRANSPECTOR the otherwise unlimited the U/V ratio will remain constant over used as SEMPs. SEMPs are virtually iner- selection of the scanning period and the the entire measurement range. The tia-free amplifiers with gain of about 10+6 amplifier time constants will be restricted “atomic number” M (see 4.6.1) of the at the outset; this will indeed drop off by microprocessor control to logical pairs ions which can pass through the sepa- during the initial use phase but will then of values. ration system must satisfy this condi- become virtually constant over a long peri- tion: od of time. Fig. 4.6 shows at the left the m V basic configuration of a Faraday ion trap ≈ M = and, on the right, a section through a e 14.438 ⋅ f 2 ⋅r 2 o Channeltron. When recording spectra the scanning period per mass line t0 and the V = High-frequency amplitude, time constants of the amplifier t should r = Quadrupole inscribed radius τ O satisfy the condition that t0 = 10 . In f = High-frequency modern devices such as the As a result of this linear dependency there results a mass spectrum with linear mass scale due to simultaneous, proportional modification of U and V. Non-segregating gas inlet system Range III : M cannot pass, due to the blocking characteristics of the yz pair of Stage B Stage A rods. p ≤ 10 –4 mbar p = 1 ... 10 mbar p = 10 ... 1000 mbar L L Mass ^2 Capillary 3 spectrometer _ 4.3.1.3 The measurement system QHV

(detector) ^ _ L1 Seff Q Pumping No Molecular flow Laminar flow Once they have left the separation system segregation the ions will meet the ion trap or detector L molecular λ d which, in the simplest instance, will be in 2 → À L2 1 QHV QPumping the form of a Faraday cage (Faraday cup). L2 ~ ¿ ȈȉM (Transition laminar/molecular) In any case the ions which impinge on the 1 L detector will be neutralized by electrons 1 ~ ȈȉM 1 from the ion trap. Shown, after electrical Seff L1 Se f f ~ amplification, as the measurement signal À → ȈȉM

itself is the corresponding “ion emission S S compensates for L No segregation stream”. To achieve greater sensitivity, a eff 2 → secondary electron multiplier pickup (SEMP) can be employed in place of the Faraday cup. Fig. 4.7 Principle of the pressure converter (stage B only in the single-stage version and stages A and B in two-stage units)

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4.4 Gas admission and a. Process pressure < 1 mbar: Single- A falsification of the gas composition stage pressure converter. resulting from adsorption and condensati- pressure Gas is allowed to pass out of the vacuum on can be avoided by heating the pressure vessel in molecular flow, through a dia- converter and the capillary. adaptation phragm with conductance value L and 2 To evaluate the influence on the gas com- into the “sensor chamber” (with its own position by the measurement unit itself, 4.4.1 Metering valve high vacuum system). Molecular flow cau- information on the heating temperature, ses segregation but this will be indepen- The simplest way to adapt a classical mass the materials and surface areas for the dent of the pressure level (see Section spectrometer to pressures exceeding metallic, glass and ceramic components 1.5). A second diaphragm with molecular 1 · 10-4 mbar is by way of a metering will be needed along with specifications on flow, located between the sensor chamber valve. The inherent disadvantage is, howe- the material and dimensions of the catho- and the turbomolecular pump, will com- ver, that since the flow properties are not de (and ultimately regarding the electron pensate for the segregation occurring at unequivocally defined, a deviation from the impact energy for the ion source as well). L . original gas composition might result. 2 b. Process pressure > 1 mbar: Two-stage pressure converter. Using a small (rotary vane) pump a laminar stream of gas is diverted from the rough vacuum area 4.4.3 Closed ion source (CIS) 4.4.2 Pressure converter through a capillary or diaphragm (conduc- In order to curb – or avoid entirely – influ- In order to examine a gas mix at total pres- tance value L3). Prior to entry into the ences which could stem from the sensor sure exceeding 1 · 10-4 mbar it is neces- pump, at a pressure of about 1 mbar, a chamber or the cathode (e.g. disturbance small part of this flow is again allowed to sary to use pressure converters which will of the CO-CO2 equilibrium by heating the not segregate the gases. Figure 4.7 is used enter the sensor chamber through the dia- cathode) a closed ion source (CIS) will be to help explain how such a pressure con- phragm with conductance value L2, again used in many cases (see Fig 4.8). verter works: as molecular flow.

Process: 10-2 mbar Process: 10-2 mbar

(Elastomer) Valve (Metal) Inlet diaphragm

Impact chamber 10-5 10-5 10-5 10-3 Cathode chamber Example of the sputter „Exit diaphragm“ process

To be detected is 1 ppm N 2 as contamination in argon, the working gas 10-5 10-5 10-5 10-5

1 ppm N 2 at the inlet: 1 ppm N 2 at the inlet:

10-6 ·10-5 mbar = 10-11 mbar 10-6 · 10-3 mbar = 10-9 mbar Exit diaphragm Background: Background: Residual gas (valve closed) 10-6 mbar total Residual gas (valve closed) 10-7 mbar total total, including 1% by mass 28 : 10-8 mbar Pump Pump total, including 1% by mass 28 : 10-9 mbar

Background noise 1 ppm

Signal at 1‰ of background Background noise cannot be detected Signal twice the background noise amplitude; can just be clearly detected D00

Fig. 4.8 Open ion source (left) and closed ion source (right)

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Impact chamber Working gas for the process (Ar) Cathode chamber “Exit diaphragms” AGM protective gas valve

10-5

Process: -3 -5 e. g. 50 mbar 10 10

Diaphragm Pump 10-5

Fig. 4.9 Principle behind the aggressive gas monitor (AGM)

The CIS is divided into two sections: a 4.4.4 Aggressive gas monitor 4.5 Descriptive values cathode chamber where the electrons are (AGM) emitted, and an impact chamber, where in mass the impact ionization of the gas particles In many cases the process gas to be takes place. The two chambers are pum- examined is so aggressive that the catho- spectrometry ped differentially: the pressure in the de would survive for only a short period of (specifications) cathode chamber comes to about time. The AGM uses the property of lami- 10-5 mbar, that in the impact room about nar flow by way of which there is no A partial pressure measurement unit is 10-3 mbar. The gas from the vacuum “reverse” flow of any kind. Controlled with characterized essentially by the following chamber is allowed to pass into the impact a separate AGM valve, a part of the wor- properties (DIN 28 410): chamber by way of a metal-sealed, bakea- king gas fed to the processes is introduced ble valve (pressure converter, ultrahigh as “purging gas”, ahead of the pressure vacuum technology). There high-yield converter, to the TRANSPECTOR; this sets ionization takes place at about 10-3 mbar. up a flow toward the vacuum chamber. The electrons exerting the impact are emit- Thus process gas can reach the TRANS- 4.5.1 Line width (resolution) ted in the cathode chamber at about PECTOR only with the AGM valve closed. 10-5 mbar and pass through small ope- When the valve is open the TRANSPEC- The line width is a measure of the degree nings from there into the impact chamber. TOR sees only pure working gas. Fig. 4.9 to which differentiation can be made bet- The signal-to-noise ratio (residual gas) via shows the AGM principle. ween two adjacent lines of the same à vis the open ion source will be increased height. The resolution is normally indica- ∆ overall by a factor of 10+3 or more. Figure ted. It is defined as: R = M / M and is con- 4.8 shows the fundamental difference bet- stant for the quadrupole spectrometer ween the configurations for open and clo- across the entire mass range, slightly ∆ sed ion sources for a typical application in greater than 1 or M < 1. sputter technology. With the modified Often an expression such as “unit resoluti- design of the CIS compared with the open on with 15% valley” is used. This means ion source in regard to both the geometry that the “bottom of the valley” between and the electron energy (open ion source two adjacent peaks of identical height 102 eV, CIS 75 or 35 eV), different frag- comes to 15 % of the height of the peak or, ment distribution patterns may be found put another way, at 7.5 % of its peak where a lower electron energy level is sel- height the line width DM measured across ++ ected. For example, the argon36 isotope an individual peak equals 1 amu (atomic at mass of 18 cannot be detected at elec- mass unit); see in this context the sche- tron energy of less than 43.5 eV and can matic drawing in Fig. 4.10. + therefore not falsify the detection of H2O at mass 18 in the sputter processes using argon as the working gas – processes which are of great importance in industry.

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+ 100% log i Regulation

+ Exact measurement i range

Automatic shut-down: ≈5 · 10 –4

15% 1 amu 7,5%

M M + 1 Atomic number

–8 –7 –6 –5 –4 –3 log P ∆M 10 10 10 10 10 10

Fig. 4.10 Line width – 15 % valley Fig. 4.11 Detection of Argon36 Fig. 4.12 Qualitative linearity curve

4.5.2 Mass range 4⋅10– 14A which are to be specified (± 10 % for par- p (FC) = = 4⋅10 –10 mbar min ⋅ – 4 tial pressure measurement devices). The mass range is characterized by the 1 10 A/mbar atomic numbers for the lightest and hea- In the range below 1 · 10-6 mbar the rela- viest ions with a single charge which are tionship between the ion flow and partial -6 detected with the unit. 4.5.5 Smallest detectable pressure is strictly linear. Between 1 · 10 mbar and 1 · 10-4 mbar there are minor partial pressure ratio deviations from linear characteristics. 4.5.3 Sensitivity (concentration) Above 1 · 10-4 mbar these deviations grow -2 The definition is: until, ultimately, in a range above 10 Sensitivity E is the quotient of the measu- mbar the ions for the dense gas atmos- red ion flow and the associated partial SDPPR = pmin / pΣ (ppm) phere will no longer be able to reach the pressure; it is normally specified for argon This definition, which is somewhat “clum- ion trap. The emergency shut-down for the or nitrogen: sy” for practical use, is to be explained cathode (at excessive pressure) is almost always set for 5 · 10-4 mbar. Depending on i+  A  using the detection of argon36 in the air as   the information required, there will be dif- E =   (4.1) the example: Air contains 0.93 % argon by pG mbar volume; the relative isotope frequency of fering upper limits for use. -6 Typical values are: Ar40 to Ar36 is 99.6 % to 0.337 %. Thus In analytical applications, 1 · 10 mbar the share of Ar36 in the air can be calcula- should not be exceeded if at all possible. A ted as follows: -6 -4 Faraday cup: E = 1⋅10–4 The range from 1 · 10 mbar to 1 · 10 mbar 0.93 · 10–2 · 0.337 · 10–2 = 3.13 · 10–5 = mbar is still suitable for clear depictions of 31.3 ppm the gas composition and partial pressure A regulation (see Fig. 4.12). SEM: E = 1⋅10+2 mbar Figure 4.11 shows the screen print-out for the measurement. The peak height for Ar36 in the illustration is determined to be 1.5 · 10-13 A and noise amplitude ∆ · i+ to R be 4 · 10-14 A. The minimum detectable 4.5.7 Information on surfaces 4.5.4 Smallest detectable concentration is that concentration at which and amenability to partial pressure the height of the peak is equal to the noise bake-out amplitude. This results in the smallest mea- The smallest detectable partial pressure is surable peak height being Additional information required to evaluate defined as a ratio of noise amplitude to 1.5 · 10-13 A/2.4 · 10-14 A = 1.875. The a sensor includes specifications on the sensitivity: smallest detectable concentration is then bake-out temperature (during measurement or with the cathode or SEMP swit- ∆⋅i+ derived from this by calculation to arrive at: P = R (mbar) ched off), materials used and surface min 31.3 · 10–6 / 1.875 = 16.69 · 10–6 E areas of the metal, glass and ceramic com- = 16.69 ppm. ponents and the material and dimensions Æ á i+ = Noise amplitude R for the cathode; data is also needed on the Example (from Fig. 4.11): electron impact energy at the ion source (and on whether it is adjustable). These A 4.5.6 Linearity range Sensitivity E = 1⋅10–4 values are critical to uninterrupted operati- D00 mbar The linearity range is that pressure range on and to any influence on the gas compo- for the reference gas (N , Ar) in which sen- sition by the sensor itself. Noise amplitude Æ á i+ = 4 · 10–14 A 2 R sitivity remains constant within limits

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4.6 Evaluating spectra Element Ordinal- Atomic Relative Element Ordinal- Atomic Relative number number frequency number number frequency 4.6.1 Ionization and fundamen- H 1 1 99.985 S 16 32 95.06 2 0.015 33 0.74 tal problems in gas ana- He 2 3 0.00013 34 4.18 lysis 4 ≈ 100.0 36 0.016 B 5 10 19.78 Cl 17 35 75.4 Continuous change in the voltages applied 11 80.22 37 24.6 to the electrodes in the separation system C 6 12 98.892 Ar 18 36 0.337 (“scanning”) gives rise to a relationship 13 1.108 38 0.063 + between the ion flow I and the “atomic N 7 14 99.63 40 99.60 number” which is proportional to the m/e 15 0.37 Kr 36 78 0.354 ratio and expressed as: O 8 16 99.759 80 2.27 M 17 0.0374 82 11.56 M = r (4.2) ne 18 0.2039 83 11.55 F 9 19 100.0 84 56.90 (Mr = relative molar mass, Ne 10 20 90.92 86 17.37 ne = number of elementary charges e) 21 0.257 Xe 54 124 0.096 22 8.82 126 0.090 Na 11 23 100.0 128 1.919 This is the so-called mass spectrum, Al 13 27 100.0 129 26.44 i+ = i+(M). The spectrum thus shows the Si 14 28 92.27 130 4.08 peaks i+ as ordinates, plotted against the 29 4.68 131 21.18 atomic number M along the abscissa. One 30 3.05 132 26.89 of the difficulties in interpreting a mass P 15 31 100.0 134 10.44 spectrum such as this is due to the fact 136 8.87 that one and the same mass as per the equation (4.2) may be associated with Table 4.2 Relative frequency of isotopes Table 4.2 Relative frequency of isotopes various ions. Typical examples, among many others, are: The atomic number yield is greatest at an electron energy level 4) Finally, gas molecules are often broken + ++ M = 16 corresponds to CH4 and O2 ; between about 80 and 110 eV; see Fig. down into fragments by ionization. The + + + M = 28 for CO , N2 and C2H ! Particular 4.14. fragment distribution patterns thus crea- attention must therefore be paid to the fol- ted are the so-called characteristic spectra In practice the differing ionization rates for lowing points when evaluating spectra: (fingerprint, cracking pattern). the individual gases will be taken into 1) In the case of isotopes we are dealing account by standardization against nitro- Important: In the tables the individual frag- with differing positron counts in the nucle- gen; relative ionization probabilities ments specified are standardized either us (mass) of the ion at identical nuclear (RIP) in relationship to nitrogen will be against the maximum peak (in % or ‰ of charge numbers (gas type). Some values indicated (Table 4.3). the highest peak) or against the total of all for relative isotope frequency are compiled peaks (see the examples in Table 4.4). in Table 4.2.

2) Depending on the energy of the impac- 12 ting electrons (equalling the potential differential, cathode – anode), ions may be eit- 10 + her singly or multiply ionized. For example, Ar one finds Ar+ at mass of 40, Ar++ at mass 8 of 20 and Ar+++ at mass of 13.3. At mass of 20 one will, however, also find neon, 6 Ne+. There are threshold energy levels for the impacting electrons for all ionization 4 states for every type of gas, i.e., each type of ion can be formed only above the asso- 2 ciated energy threshold. This is shown for · mbar per cm Ions formed Ar in Fig. 4.13. 0 100 200 300 400 500 3) Specific ionization of the various Electron energy (eV) gases Sgas, this being the number of ions Threshold formed, per cm and mbar, by collisions energy Ar+ 15,7 eV Ar++ 43,5 eV Ar3+ 85,0 eV Ar4+ 200 eV with electrons; this will vary from one type for argon ions of gas to the next. For most gases the ion Fig. 4.13 Number of the various Ar ions produced, as a factor of electron energy level

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+ quarter of the share of N2 with its mass of 28. If, on the other hand, no oxygen is detected in the spectrum, then the peak at atomic number 28 would indicate carbon monoxide. In so far as the peak at atomic number 28 reflects the CO+ fragment of CO2 (atomic number 44), this share is 11 % of the value measured for atomic number 44 (Table 4.5). On the other hand, in all cases where nitrogen is present, ato- ++ med per cm · mbar mic number 14 (N2 ) will always be found in the spectrum in addition to the atomic +

Ions for number 28 (N2); in the case of carbon monoxide, on the other hand, there will always appear – in addition to CO+ – the fragmentary masses of 12 (C+) and ++ 16 (O2 )). Figure 4.15 uses a simplified example of a Electron energy (eV) “model spectrum” with superimpositions of hydrogen, nitrogen, oxygen, water Fig. 4.14 Specific ionization S for various gases by electrons exhibiting energy level E vapor, carbon monoxide, carbon dioxide, neon and argon to demonstrate the diffi- Both the nature of the fragments created obtained using devices made by different culties involved in evaluating spectra. and the possibility for multiple ionization manufacturers. will depend on the geometry (differing ion Often the probable partial pressure for one number, depending on the length of the of the masses involved will be estimated ionization path) and on the energy of the through critical analysis of the spectrum. impacting electrons (threshold energy for Thus the presence of air in the vacuum certain types of ions). Table values are vessel (which may indicate a leak) is mani- always referenced to a certain ion source + fested by the detection of a quantity of O with a certain electron energy level. This is 2 (with mass of 32) which is about one- why it is difficult to compare the results

CO+ O+

O+ H + ++ 2 Ar CO+ H O+ O + + + 2 2 Ar CO2

H + 2 O+ N+ + H OH+ Ne+ + N2 C+ O+ H O+ 13 + 13C+ 3 22Ne+ CO + + ++ C 16 18 + 36 + 13 16 + H Ne O O Ar C O2 14N15N+

0 5 10 15 20 25 30 35 40 45 50 Hydrogen Oxygen Carbon dioxide Argon Nitrogen Water Neon Carbon monoxide

Evaluation problems: The peak at atomic number 16 may, for example, be due to oxygen fragments resulting from O2, H2O, CO2 and CO; the peak at atomic number 28 from contributions by N2 as well as by CO and CO as a fragment of CO2; the peak at atomic number 20 could result from singly ionized Ne and double-ionized Ar D00

Fig. 4.15 Model spectrum

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Type of gas Symbol RIP Type of gas Symbol RIP

Acetone (Propanone) (CH3)2CO 3.6 Hydrogen chloride HCl 1.6 Air 1.0 Hydrogen fluoride HF 1.4

Ammonia NH3 1.3 Hydrogen iodide HI 3.1 Argon Ar 1.2 Hydrogen sulfide H2S 2.2 Benzene C6H6 5.9 Iodine I2 Benzoic acid C6H5COOH 5.5 Krypton Kr 1.7 Bromine Br 3.8 Lithium Li 1.9

Butane C4H10 4.9 Methane CH4 1.6 Carbon dioxide CO2 1.4 Methanol CH3OH 1.8 Carbon disulfide CS2 4.8 Neon Ne 0.23 Carbon monoxide CO 1.05 Nitrogen N2 1.0 Carbon tetrachloride CCl4 6.0 Nitrogen oxide NO 1.2 Chlorobenzene C6H4Cl 7.0 Nitrogen dioxide N2O 1.7 Chloroethane C2H3Cl 4.0 Oxygen O2 1.0 Chloroform CHCl3 4.8 n-pentane C5H17 6.0 Chlormethane CH3Cl 3.1 Phenol C6H5OH 6.2 Cyclohexene C6H12 6.4 Phosphine PH3 2.6 Deuterium D2 0.35 Propane C3H8 3.7 Dichlorodifluoromethane CCl2F2 2.7 Silver perchlorate AgClO4 3.6 Dichloromethane CH2Cl2 7.8 Tin iodide Snl4 6.7 Dinitrobenzene C6H4(NO2)2 7.8 Sulfur dioxide SO2 2.1 Ethane C2H6 2.6 Sulfur hexafluoride SF6 2.3 Ethanol C2H5OH 3.6 Toluene C6H5CH3 6.8 Ethylene oxide (CH2)2O 2.5 Trinitrobenzene C6H3(NO2)3 9.0 Helium He 0.14 Water vapor H2O 11.0 Hexane C6H14 6.6 Xenon Xe 3.0 Hydrogen H2 0.44 Xylols C6H4(CH3)2 7.8 Table 4.3 Relative ionization probabilities (RIP) vis à vis nitrogen, electron energy 102 eV

Electron energy : 75 eV (PGA 100) 102 eV (Transpector) Gas Symbol Mass Σ = 100 % Greatest peak = 100 % Σ = 100 % Greatest peak = 100 % Argon Ar 40 74.9 100 90.9 100 20 24.7 33.1 9.1 10 36 0.3 Carbon dioxide CO2 45 0.95 1.3 0.8 1 44 72.7 100 84 100 28 8.3 11.5 9.2 11 16 11.7 16.1 7.6 9 12 6.15 8.4 5 6 Carbon monoxide CO 29 1.89 2.0 0.9 1 28 91.3 100 92.6 100 16 1.1 1.2 1.9 2 14 1.7 1.9 0.8 12 3.5 3.8 4.6 5 Neon Ne 22 9.2 10.2 0.9 11 20 89.6 100 90.1 100 10 0.84 0.93 9 4 Oxygen O2 34 0.45 0.53 32 84.2 100 90.1 100 16 15.0 17.8 9.9 11 Nitrogen N2 29 0.7 0.8 0.9 1 28 86.3 100 92.6 100 14 12.8 15 6.5 12 Water vapor H2O 19 1.4 2.3 18 60 100 74.1 100 17 16.1 27 18.5 25 16 1.9 3.2 1.5 2 2 5.0 8.4 1.5 2 1 15.5 20 4.4 6 Table 4.4 Fragment distribution for certain gases at 75 eV and 102 eV

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No Gas Symbol 1 = 100 2 3 4 5 6

1 Acetone (CH3)2CO 43/100 15/42 58/20 14/10 27/19 42/8 2 Air 28/100 32/27 14/6 16/3 40/1 -

3 Ammonia NH3 17/100 16/80 15/8 14/2 - - 4 Argon Ar 40/100 20/10 - - - -

5 Benzene C6H6 78/100 77/22 51/18 50/17 52/15 39/10 6 Carbon dioxide CO2 44/100 28/11 16/9 12/6 45/1 22/1 7 Carbon monoxide CO 28/100 12/5 16/2 29/1 - -

8 Carbon tetrachloride CCl4 117/100 119/91 47/51 82/42 35/39 121/29 9 Carbon tetrafluoride CF4 69/100 50/12 31/5 19/4 - - 10 Diff. pump oil, DC 705 78/100 76/83 39/73 43/59 91/32 - 11 Diff. pump oil, Fomblin 69/100 20/28 16/16 31/9 97/8 47/8 12 Diff. pump oil, PPE 50/100 77/89 63/29 62/27 64/21 38/7

13 Ethanol CH3CH2OH 31/100 45/34 27/24 29/23 46/17 26/8 14 Halocarbon 11 CCl3F 101/100 103/60 35/16 66/15 47/12 31/10 15 Halocarbon 12 CCl2F2 85/100 87/32 50/16 35/12 - -

16 Halocarbon 13 CClF3 69/100 85/15 50/14 31/9 35/7 87/5 17 Halocarbon 14 CF4 69/100 12/7 19/6 31/5 50/8 - 18 Halocarbon 23 CHF3 51/100 31/58 69/40 50/19 52/1 21/1 19 Halocarbon 113 C2C13F3 101/100 103/62 85/55 31/50 151/41 153/25 20 Helium He 4/100 - - - - -

21 Heptane C7H16 43/100 41/62 29/49 27/40 57/34 71/28 22 Hexane C6H14 41/100 43/92 57/85 29/84 27/65 56/50

23 Hydrogen H2 2/100 1/5 - - - - 24 Hydrogen sulfide H2S 34/100 32/44 33/42 36/4 35/2 - 25 Isopropyl alcohol C3H8O 45/100 43/16 27/16 29/10 41/7 39/6 26 Krypton Kr 84/100 86/31 83/20 82/20 80/4 -

27 Methane CH4 16/100 15/85 14/16 13/8 1/4 12/2 28 Mehtyl alcohol CH3OH 31/100 29/74 32/67 15/50 28/16 2/16

29 Methyl ethyl ketone C4H8O 43/100 29/25 72/16 27/16 57/6 42/5 30 Mechanical pump oil 43/100 41/91 57/73 55/64 71/20 39/19 31 Neon Ne 20/100 22/10 10/1 - - -

32 Nitrogen N2 28/100 14/7 29/1 - - - 33 Oxygen O2 32/100 16/11 - - - - 34 Perfluorokerosene 69/100 119/17 51/12 131/11 100/5 31/4

35 Perfluor-tributylamine C12F27N 69/100 131/18 31/6 51/5 50/3 114/2 36 Silane SiH4 30/100 31/80 29/31 28/28 32/8 33/2 37 Silicon tetrafluoride SiF4 85/100 87/12 28/12 33/10 86/5 47/5 38 Toluene C6H5CH3 91/100 92/62 39/12 65/6 45.5/4 51/4 39 Trichloroethane C2H3Cl3 97/100 61/87 99/61 26/43 27/31 63/27 40 Trichloroethylene C2HCl3 95/100 130/90 132/85 97/64 60/57 35/31

41 Trifluoromethane CHF3 69/100 51/91 31/49 50/42 12/4 - 42 Turbomolecular pump oil 43/100 57/88 41/76 55/73 71/52 69/49

43 Water vapor H2O 18/100 17/25 1/6 16/2 2/2 - 44 Xenon Xe 132/100 129/98 131/79 134/39 136/33 130/15 Table 4.5 Spectrum library of the 6 highest peaks for the TRANSPECTOR D00

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Fundamentals of Vacuum Technology Mass Spectrometry

4.6.2 Partial pressure + only after the spectrum has been standar- pgas = igas, m (measured )⋅ measurement 2 dized, by setting the height of the highest 1 1 line equal to 100 or 1000 (see Table 4.5 as The number of ions i+ produced from a ⋅ gas EN BFgas,m ⋅RIPgas ⋅TF (m) (4.3) an example). gas in the ion source is proportional to the 2 2 emission current i–, to the specific ioni- The comparison can be made manually on The partial pressure is calculated from the zation S , to a geometry factor f repre- the basis of collections of tables (for gas ion flow measured for a certain fragment senting the ionization path inside the example, A. Cornu & R. Massot: Compil- by multiplication with two factors. The first ionization source, to the relative ionization ation of Mass Spectral Data) or may be factor will depend only on the nitrogen probability RIP , and to the partial pres- effected with computer assistance; large gas sensitivity of the detector and thus is a sure p . This number of ions produced databases can be used (e.g. Mass Spectral gas constant for the device. The second will is, by definition, made equal to the sensi- Data Base, Royal Society of Chemistry, depend only on the specific ion properties. Cambridge). tivity Egas times the partial pressure pgas: These factors will have to be entered sepa- When making comparisons with library i+ (produced) = i- · S · f · RIP · p gas gas gas gas rately for units with direct partial pressure information, it is necessary to pay attenti- = Egas · pgas indication (at least for less common types on to whether identical ion sources or at of ions). least identical electron impact energies due to RIPN2 = 1 were used. – EN2 is equal to i · SN2 · f All these capabilities are, however, generally too elaborate for the problems and Egas is equal to EN2 · RIPgas 4.6.3 Qualitative gas analysis encountered in vacuum technology. Many Almost all gases form fragments during commercial mass spectrometers can show ionization. To achieve quantitative evalu- The analysis of spectra assumes certain a number of library spectra in the screen ation one must either add the ion flows at working hypotheses: so that the user can see immediately whether the “library substance” might be the appropriate peaks or measure (with a 1. Every type of molecule produces a cer- contained in the substance measured. known fragment factor [FF]) one peak and tain, constant mass spectrum or frag- Usually the measured spectrum was the calculate the overall ion flow on that basis: ment spectrum which is characteristic result of a mix of gases and it is particu- + for this type of molecule (fingerprint, igas,m i + (produced )= i + + i + +....= 1 larly convenient if the screen offers the gas gas,m1 gas,m2 cracking pattern). + BFgas,m1 capacity for subtracting (by way of trial) igas,m = 2 =....= E ⋅p 2. The spectrum of every mixture of gases the spectra of individual (or several) gases BF gas gas gas,m2 is the same as would be found through from the measured spectrum. The gas can linear superimposition of the spectra of be present only when the subtraction does In order to maintain the number of ions the individual gases. The height of the not yield any negative values for the major arriving at the ion trap, it is necessary to peaks will depend on the gas pressure. peaks. Figure 4.16 shows such a step-by- multiply the number above with the trans- step subtraction procedure using the 3. The ion flow for each peak is proportio- mission factor TF(m), which will be depen- Transpector-Ware software. dent on mass, in order to take into account nal to the partial pressure of each com- the permeability of the separation system ponent responsible for the peak. Since Regardless of how the qualitative analysis for atomic number m (analogous to this, the ion flow is proportional to the parti- is prepared, the result is always just a there is the detection factor for the SEMP; al pressure, the constant of proportio- “suggestion”, i.e. an assumption as to it, however, is often already contained in nality (sensitivity) varies from one gas which gases the mixture might contain. TF). The transmission factor (also: ion- to the next. This suggestion will have still to be examined, e.g. by considering the likelihood that optical transmission) is thus the quotient Although these assumptions are not a certain substance would be contained in of the ions measured and the ions produ- always correct (see Robertson: Mass the spectrum. In addition, recording a new ced. Spectrometry) they do represent a useful spectrum for this substance can help to working hypothesis. Thus achieve clarity. + ( ) In qualitative analysis, the unknown spec- igas,m produced p = 2 trum is compared with a known spectrum gas BF ⋅ E gas,m2 gas in a library. Each gas is “definitively deter- + mined” by its spectrum. The comparison igas, m (measured ) ⇒ p = 2 with library data is a simple pattern reco- gas BF ⋅ E ⋅TF (m) gas , m2 gas gnition process. Depending on the availability, the comparison may be made using and with any of a number ancillary aids. So, for example, in accordance with the position, Egas = EN2 · RIPgas size and sequence of the five or ten highest the ultimate result is: peaks. Naturally, comparison is possible

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4.6.4 Quantitative gas analysis Particular difficulties are encountered when interpreting the spectrum of an Parent spectrum unknown mixture of gases. The proportions of ion flow from various sources can be offset one against the other only after all the sources have been identified. In many applications in vacuum technology one will be dealing with mixtures of a few A AP=arent simple gases of known identity, with ato- range mic numbers less of than 50 (whereby the process-related gases can represent exceptions). In the normal, more complicated case there will be a spectrum with a multitude of superimpositions in a com- Parent spectrum Assumption: pletely unknown mixture of many gas Groups components; here a qualitative analysis 2 1 1K=rypton+ will have to be made before attempting 2K=rypton++ quantitative analysis. The degree of diffi- culty encountered will depend on the number of superimpositions (individual/a few/ Library spectrum: many). Krypton In the case of individual superimpositions, mutual, balancing of the ion flows during measurement of one and the same type of gas for several atomic numbers can often Parent spectrum without krypton Assumption: be productive. + 3Argon Where there is a larger number of super- 4 ++ 3 4Argon impositions and a limited number of gases overall, tabular evaluation using correction factors vis à vis the spectrum of a calibration gas of known composition can often Library spectrum: be helpful. Argon In the most general case a plurality of gases will make a greater or lesser contribution to the ion flow for all the masses. The share of a gas g in each case for the Parent spectrum without argon Assumption: atomic number m will be expressed by the 5Neon+ fragment factor Ff . In order to simplify 5 m,g calculation, the fragment factor Ffm,g will also contain the transmission factor TF and the detection factor DF. Then the ion current to mass m, as a function of the Library spectrum: overall ion currents of all the gases invol- Neon ved, in matrix notation, is:

 +   +  i BFj,k ⋅ ⋅ ⋅ ⋅ ⋅ BFj,o  I  j     k  ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅        ⋅   ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅   ⋅  Parent spectrum after detection  +     +  i = ⋅ ⋅ ⋅ FF ⋅ ⋅ ⋅ I of krypton, argon and neon  m  m,g  ·  g   ⋅   ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅   ⋅   ⋅   ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅   ⋅        + BF ⋅ ⋅ ⋅ ⋅ ⋅ BF  + iu  u,k u,o Io  D00 The ion current vector for the atomic num- Fig. 4.16 Subtracting spectra contained in libraries bers m (resulting from the contributions by the fragments of the individual gases) is LEYBOLD VACUUM PRODUCTS AND REFERENCE BOOK 2001/2002 D00.101 D00 E 19.06.2001 21:39 Uhr Seite 102

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equal to the fragment matrix times the vec- 4.7 Software in particular to analyze interesting process tor of the sum of the flows for the indivi- sections exactly, both during the process dual gases. and retroactively, once the process has run to completion, without having to interrupt 0 4.7.1 Standard SQX software + + the measurement operations which are or: im = ∑BFm, g · Ig g=k (DOS) for stand-alone running in the background. Where operation (1 MS plus ongoing monitoring of identical processes (in simplified notation: i = FF · I) 1 PC, RS 232) is undertaken the program can generate where + = ion flow vector for the atomic statistics (calculating mean values and im The conventional software package (SQX) numbers, resulting from contributions of standard deviations) from which a band- contains the standard routines for the fragments of various individual gases width for “favorable process operation” operation of the mass spectrometer can be derived. Error reports are issued (MS)– various spectra depictions, queries 0 where limit values are exceeded. of individual channels with the correspon- ∑BFm,g = fragment matrix g=k ding screen displays as tables or bar charts, partial pressure conversion, trend + Ig = Vector of the sum of the flows for the displays, comparison with spectra libra- individual gases or: ries (with the capability for trial subtrac- 4.7.4 Development software – tion of library spectra), leak testing mode TranspectorView Ff m, g etc. – and for sensor balancing, as well. 6444474448 Using PCs as the computer and display This software used to for develop custom i + = ∑ p ⋅ E ⋅ RIP ⋅ FF ⋅ TF m g N2 g m m unit naturally makes available all the usual software versions for special situations. It Transmission factor functions including storing and retrieving is based on the LabView development for the mass m data, printing, etc. Characteristic of the Fragment factor package and includes the drivers required for the gas to mass m conventional software package is that spe- to operate the Transpector. Relative ionization probability for the gas cific individual spectra will be measured, Nitrogen sensitivity (equipment constant) even though the measurement is fully Partial pressure of the gas automated and takes place at a point in Ion current for atomic number m time which is specified in advance. A spectrum of this type can thus be only a One sees that the ion flow caused by a gas “snapshot” of a process in progress. 4.8 Partial pressure is proportional to the partial pressure. The linear equation system can be solved only regulation for the special instance where m = g Some processes, such as reactive sputter (square matrix); it is over-identified for processes, require the most constant pos- m > g. Due to unavoidable measurement sible incidence rates for the reacting gas error (noise, etc.) there is no set of overall 4.7.2 Multiplex/DOS software molecules on the substrate being coated. + MQX (1 to 8 MS plus ion flow Ig (partial pressures or concentra- The “incidence rate” is the same as the tions) which satisfies the equation system 1 PC, RS 485) “impingement rate” discussed in Chapter exactly. Among all the conceivable soluti- The first step toward process-oriented 1; it is directly proportional to the partial ons it is now necessary to identify set +* Ig software by INFICON is the MQX. It makes pressure. The simplest attempt to keep the which after inverse calculation to the parti- possible simultaneous monitoring of a partial pressure for a gas component con- al ion flows I+* will exhibit the smallest maximum of eight sensors and you can stant is throughput by regulating with a m apply all the SQX functions at each sensor. squared deviation from the partial ion cur- flow controller; it does have the disadvan- + tage that the regulator cannot determine rents i actually measured. Thus: m whether, when and where the gas con-

+ + sumption or the composition of the gas in ∑ − * 2 (im im) = min the vacuum chamber changes. The far 4.7.3 Process-oriented soft- superior and more effective option is parti- This minimization problem is mathematic- ware –Transpector-Ware al pressure control using a mass spectro- ally identical to the solution of another for Windows meter via gas inlet valves. Here the signifi- equation system cant peaks of the gases being considered FFT · i = FFT · FF · I Transpector-Ware is based on an entirely are assigned to channels in the mass spec- new philosophy. During the course of the trometer. Suitable regulators compare the which can be evaluated direct by the com- process (and using settings – the “recipe” analog output signals for these channels puter. The ion current vector for the indivi- – determined beforehand) data will be with set-point values and derive from the dual gases is then: recorded continuously – like the individual difference between the target and actual –1 [FF T ⋅ i]⋅ [FFT ⋅ BF] frames in a video. These data can be sto- values for each channel the appropriate I = red or otherwise evaluated. It is possible det[FF T ⋅ BF] actuation signal for the gas inlet valve for

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Mass Spectrometry Fundamentals of Vacuum Technology

the channel. A configuration of this kind

has been realized to control six channels in t4 t the QUADREX PPC. Gas inlet valves mat- 5 Mass spectrometer ching the unit can also be delivered. The gas used to measure the impingement rate (partial pressure) must naturally be Pressure stage Regulation valve t ୴^୵ drawn from a representative point in the 1 _ Sensor t t t vacuum chamber. When evaluating the ୴ 6 Vacuum vessel 2 3

୴ ୴୵ time constant for a regulation circuit of this type it is important to take into account all TMP50CF the time aspects and not just the electrical signal propagation and the processing in the mass spectrometer, but also the vacuum-technology time constants and flow velocities, as illustrated in Figure 4.17. Pressure converters or unfavorably instal- Fig. 4.17 Partial shares for overall time constants led gas inlet lines joining the control valve and the vacuum vessel will make particu- Sensor balancing at the mass axis (often grime, then the adjustment of the rods larly large contributions to the overall time erroneously referred to as calibration) is which will be required afterwards will have constant. It is generally better to establish done today in a very easy fashion with the to be carried out at the factory. a favorable S/N ratio with a large signal (i.e. software (e.g. SQX, Transpector-Ware) through an inlet diaphragm with a large and can be observed directly in the screen. opening) rather than with long integration Naturally, not only the arrangement along periods at the individual channels. Contra- the mass axis will be determined here, but sted in Figure 4.18 are the effects of boo- also the shape of the lines, i.e. resolution sting pressure and lengthening the integra- and sensitivity (see Section 4.5). tion time on signal detectability. In depictions a, b and c only the integration period It will be necessary to clean the sensor was raised, from 0.1 to 1.0 and 10 seconds only in exceptional cases where it is heavi- (thus by an overall factor of 100), respec- ly soiled. It is usually entirely sufficient to tively. By comparison, in the sequence a-d- clean the ion source, which can be easily e-f, at constant integration time, the total dismantled and cleaned. The rod system pressure was raised in three steps, from can be cleaned in an ultrasonic bath once 7.2 · 10-6 mbar to 7.2 · 10-5 mbar (or by a it has been removed from the config- factor of just 10 overall). uration. If dismantling the system is unavoidable due to particularly stubborn

a b c 4.9 Maintenance (Cathode service life, sensor balancing, cleaning the ion source and rod system) The service life of the cathode will depend greatly on the nature of the loading. Expe- rience has shown that the product of operating period multiplied by the operating pressure can serve as a measure for the d e f loading. Higher operating pressures (in a range of 1 · 10-4 to 1 · 10-3 mbar) have a particularly deleterious effect on service life, as do certain chemical influences such as refrigerants, for example. Changing out the cathode is quite easy, thanks to the simple design of the sensor. It is advisable, however, to take this opportunity to D00 change out or at least clean the entire ion source. Fig. 4.18 Improving the signal-to-noise ratio by increasing the pressure or extending the integration time

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Fundamentals of Vacuum Technology Leak Detection

• Indirect leaks: leaking supply lines in where R = 83.14 mbar · l/mol · K, T = tem- 5. Leaks and their vacuum systems or furnaces (water, perature in K; M = molar mass in g/mole; compressed air, brine) ∆m for the mass in g; ∆t is the time period detection in seconds. Equation 5.1 is then used • “Serial leaks”: this is the leak at the end a) to determine the mass flow ∆m / ∆t at a Apart from the vacuum systems them- of several “spaces connected in series”, known pV gas flow of ∆p · V/∆t (see in selves and the individual components used e.g. a leak in the oil-filled section of the this context the example at 5.4.1) or in their construction (vacuum chambers, oil pan in a rotary vane pump piping, valves, detachable [flange] connec- b) to determine the pV leak gas flow where • “One-way leaks”: these will allow gas to tions, measurement instruments, etc.), the mass flow is known (see the follo- there are large numbers of other systems pass in one direction but are tight in the wing example). and products found in industry and rese- other direction (very seldom) Example for case b) above: arch which must meet stringent require- An area which is not gas-tight but which is ments in regard to leaks or creating a so- not leaky in the sense that a defect is pre- A refrigeration system using Freon (R 12) called “hermetic” seal. Among these are sent would be the exhibits refrigerant loss of 1 g of Freon per many assemblies and processes in the year (at 25 °C). How large is the leak gas • Permeation (naturally permeability) of automotive and refrigeration industries in flow QL? According to equation 5.1 for particular but also in many other branches gas through materials such as rubber M(R12) = 121 g/mole: of industry. Working pressure in this case hoses, elastomer seals, etc. (unless these parts have become brittle and ∆(p ⋅V ) 83.14mbar ⋅ `⋅ 298K ⋅1g is often above ambient pressure. Here QL = = ∆t mol ⋅ K ⋅121g ⋅ mol –1⋅1year “hermetically sealed” is defined only as a thus “leaky”). relative “absence of leaks”. Generalized ⋅ ⋅ 2⋅ ⋅ = 83.14 2.98 10 1⋅ mbar ` statements often made, such as “no detec- 121⋅1 3.15⋅107s table leaks” or “leak rate zero”, do not 83.14⋅2.98⋅102 mbar ⋅ ` represent an adequate basis for accep- = ⋅10 –7⋅ tance testing. Every experienced engineer 5.2 Leak rate, leak 1.21⋅102⋅ 3.15 s knows that properly formulated accep- mbar ⋅ ` tance specifications will indicate a certain size, mass flow = 65 ⋅10–7⋅ s leak rate (see Section 5.2) under defined No vacuum device or system can ever be conditions. Which leak rate is acceptable is absolutely vacuum-tight and it does not Thus the Freon loss comes to also determined by the application itself. actually need to be. The simple essential is –6 -1 QL = 6.5 · 10 mbar·l·s . According to the that the leak rate be low enough that the “rule of thumb” for high vacuum systems required operating pressure, gas balance given below, the refrigeration system men- and ultimate pressure in the vacuum con- tioned in this example may be deemed to tainer are not influenced. It follows that the be very tight. Additional conversions for requirements in regard to the gas-tightn- 5.1 Types of leaks QL are shown in Tables VIIa and VIIb in ess of an apparatus are the more stringent Chapter 9. Differentiation is made among the follo- the lower the required pressure level is. In wing leaks, depending on the nature of the order to be able to register leaks quantita- The following rule of thumb for quantita- material or joining fault: tively, the concept of the “leak rate” with tive characterization of high vacuum the symbol Q was introduced; it is mea- equipment may be applied: • Leaks in detachable connections: Flan- L sured with mbar·l·s-1 or cm3/s (STP) as -6 -1 ges, ground mating surfaces, covers Total leak rate < 10 mbar·l·s : the unit of measure. A leak rate of Equipment is very tight • Q = 1 mbar·l·s-1 is present when in an Leaks in permanent connections:Solder L -5 -1 and welding seams, glued joints enclosed, evacuated vessel with a volume Total leak rate 10 mbar·l·s : of 1 l the pressure rises by 1 mbar per Equipment is sufficiently tight • Leaks due to porosity: particularly follo- second or, where there is positive pressu- Total leak rate > 10-4 mbar·l·s-1: wing mechanical deformation (ben- re in the container, pressure drops by 1 Equipment is leaky ding!) or thermal processing of poly- mbar. The leak rate QL defined as a mea- crystalline materials and cast compo- sure of leakiness is normally specified in A leak can in fact be “overcome” by a nents the unit of measure mbar·l·s-1. With the pump of sufficient capacity because it is true that (for example at ultimate pressure • Thermal leaks (reversible): opening up assistance of the status equation (1.7) one p and disregarding the gas liberated at extreme temperature loading (heat/ can calculate Q when giving the tempera- end L from the interior surfaces): cold), above all at solder joints ture T and the type of gas M, registering this quantitatively as mass flow, e.g. in the Q • Apparent (virtual) leaks: quantities of p = L g/s unit of measure. The appropriate end S (5.2) gas will be liberated from hollows and relationship is then: eff cavities inside cast parts, blind holes and joints (also due to the evaporation ∆(p ⋅V) R ⋅ T ∆m (QL Leak rate, Seff the effective pumping Q = = ⋅ (5.1) of liquids) L ∆t M ∆t speed at the pressure vessel)

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Where Seff is sufficiently great it is possible – regardless of the value for the leak ∆p = 1013 mbar, Hole diameter d = 1 cm rate Q – always to achieve a pre-determi- m L Gas speed = Speed of sound = 330 s ned ultimate pressure of pend. In practice, however, an infinite increase of Seff will run 2 3 m 1 · π 2 +3 cm ` up against economic and engineering limi- Volume/second: 330 · · cm = 25.95 · 10 = 25.95 s 4 s s tations (such as the space required by the ` +4 +4 mbar · ` system). Quantity/second: 1013 mbar · 25.95 s = 2.63 · 10 Ȃ 10 s Whenever it is not possible to achieve the mbar · ` desired ultimate pressure in an apparatus Diameter cm Leak rate s there are usually two causes which can be 10–2 m= 1.0 cm 10+4 cited: The presence of leaks and/or gas 10–3 m= 1.0 mm 10+2 being liberated from the container walls 10–4 m= 0.1 mm 10 0 (= 1) and sealants. 10–5 m= 0.01 mm 10–2 10–6 m= 1.0 µm 10–4 Partial pressure analysis using a mass 10–7 m= 0.1 µm 10–6 spectrometer or the pressure rise method 10–8 m= 0.01 µm 10–8 may be used to differentiate between these 10–9 m= 1.0 nm 10–10 two causes. Since the pressure rise 10–10 m= 1.0 Angstrom 10– 1 2 (Detection limit, He leak detector) method will only prove the presence of a leak without indicating its location in the Fig. 5.1 Correlation between leak rate and hole size apparatus, it is advisable to use a helium leak detector with which leaks can, in general, also be located much more quick- table shows that when the hole diameter is led to the development of calibrated refe- ly. reduced to 1 µm (= 0.001 mm) the leak rate rence leaks with very small leak rates (see will come to 10-4 mbar·l·s-1, a value which Section 5.5.2.3). This is a measurable “lack In order to achieve an overview of the cor- in vacuum technology already represents a of tightness” but not a “leak” in the sense relation between the geometric size of the major leak (see the rule of thumb above). A of being a defect in the material or joint. hole and the associated leak rate it is pos- leak rate of 10-12 mbar·l·s-1 corresponds to Estimates or measurements of the sizes of sible to operate on the basis of the follo- hole diameter of 1 Å; this is the lower atoms, molecules, viruses, bacteria, etc. wing, rough estimate: A circular hole 1 cm detection limit for modern helium leak have often given rise to everyday terms in diameter in the wall of a vacuum vessel detectors. Since the grid constants for such as “watertight” or “bacteria-tight”; is closed with a gate valve. Atmospheric many solids amount to several Å and the see Table 5.1. pressure prevails outside, a vacuum insi- diameter of smaller molecules and atoms Compiled in Figure 5.2 are the nature and de. When the valve is suddenly opened all (H , He) are about 1 Å, inherent permeati- 2 detection limits of frequently used leak the air molecules in a cylinder 1 cm in dia- on by solids can be registered metrologi- detection methods. meter and 330 m high would within a cally using helium leak detectors. This has 1-second period of time “fall into” the hole at the speed of sound (330 m/s). The Concept / criterion Comment QL [mbar · l/s] Relevant particle size quantity flowing into the vessel each Water-tight *) Droplets Q < 10–2 second will be 1013 mbar times the cylin- L –3 der volume (see Fig. 5.1). The result is that Vapor-tight “Sweating” QL < 10 for a hole 1 cm in diameter QL (air) will be Bacteria-tight *) 2.6 · 104 mbar·l·s-1. If all other conditions (cocci) Q < 10–4 Avg. ≈ 1 µm are kept identical and helium is allowed to L flow into the hole at its speed of sound of (rod-shaped) Avg. ≈ 0.5-1 µm, 2–10 µm long –5 970 m/s, then in analogous fashion the QL Oil-tight QL < 10 (helium) will come to 7.7 · 10+4 mbar·l·s-1, Virus-tight *) or a pV leaking gas current which is larger –6 ≈ –7 by a factor of 970 / 330 = 2.94. This grea- (vaccines such as pox) QL < 10 Ø 3 · 10 m ter “sensitivity” for helium is used in leak (smallest viruses, –8 –8 detection practice and has resulted in the bacteriophages) QL < 10 Ø 3 · 10 m development and mass production of hig- (viroids, RNA) Q < 10–10 Ø ª≈ 1 · 10–9 m (thread-like) hly sensitive helium-based leak detectors L –7 (see Section 5.5.2). Gas-tight QL < 10 –10 Shown in Figure 5.1 is the correlation bet- “Absolutely tight” Technical QL < 10 ween the leak rate and hole size for air, with *) As opposed to vapor, it is necessary to differentiate between hydrophilic and hydrophobic solids. This D00 also applies to bacteria and viruses since they are transported primarily in solutions. the approximation value of QL (air) of 10+4 mbar·l·s-1 for the “1 cm hole”. The Table 5.1 Estimating borderline leak rates

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Fundamentals of Vacuum Technology Leak Detection

Leak <----> Hole Substance quantity trhough hole per unit of time Helium standard leak rate: Helium leak detector ULTRATEST UL 200 dry/UL 500 ∆ Q ... Leak rate, ∆ (p · V) p1 = 1 bar, p2 < 1 mbar ( p = 1 bar) Definition: Q = In short: Leak ∆t Test gas = Helium

Contura Z ➔ ➔ ➔

Helium leak detector ULTRATEST UL 200/UL 500 dry/Modul 200/LDS 1000 Familiar leaks: Quantity escaping: Standard He leak rate: acuum method V mg mbar · ഞ mbar · ഞ Pressure rise Dripping water faucet 34 s Water ΂= 6.45 s Air ΃ 0.17 s He Std 4 mm diam., 1 Hz, ∆p = 4 bar

103...... 100 10-1 10-2 10-3 10-4 10-5 10-6 10-7 10-8 10-9 10-10 10-11 10-12 mbar · l · s-1 –2 mbar · ഞ –2 mbar · ഞ Hair on a gasket 10 s Air 0.9 · 10 s He Std

Ecotec II / Protec Bicycle tube in water (bubble test) Ncm 3 mbar · ഞ mbar · ഞ ∆ –3 –3 –2 2 mm diam., 1 Hz, p = 0.1 bar 4.19 · 10 s ΂= 4.24 · 10 s Air΃ 1.88 · 10 s He Std ULTRATEST with helium sniffer

Car tire loses air –5 mbar · ഞ Halogen sniffer HLD4000A –4 mbar · ഞ 4.3 · 10 s He Std 25 l, 6 Mo: 1.8 --> 1.6 bar 3.18 · 10 s Air

Bubble test pressure method

er Small refrigerant cylinder g mbar · ഞ mbar · ഞ empties in 1 year 430 Frigen = 2.8 · 10 –3 F12 4.33 · 10 –5 He Std Ov a ΂ s ΃ s Pressure drop test 430 g refrigerant R12, 25°C

Fig. 5.2 Leak rate ranges for various leak detection processes and devices Fig. 5.3 Examples for conversion into helium standard leak rates

5.2.1 The standard helium range the manufacturer (who is liable red to as the “inside-out leak”), where leak rate under the guarantee terms) must assume the fluid passes from inside the test values on the safe side. The equations are specimen outward (pressure inside the Required for unequivocal definition of a listed in Table 5.2. specimen being greater than ambient leak are, first, specifications for the Here indices “I” and “II” refer to the one or pressure). pressures prevailing on either side of the the other pressure ratio and indices “1” The specimens should wherever possible partition and, secondly, the nature of the and “2” reference the inside and outside of be examined in a configuration corre- medium passing through that partition the leak point, respectively. sponding to their later application – com- (viscosity) or its molar mass. The designa- ponents for vacuum applications using the tion “helium standard leak” (He Std) has vacuum method and using the positive become customary to designate a situati- pressure method for parts which will be on frequently found in practice, where pressurized on the inside. testing is carried out using helium at 1 bar differential between (external) atmosphe- 5.3 Terms and When measuring leak rates we differentia- ric pressure and the vacuum inside a definitions te between registering system (internal, p < 1 mbar), the designa- a. individual leaks (local measurement) – tion “helium standard leak rate” has beco- When searching for leaks one will general- sketches b and d in Figure 5.4, and regime customary. In order to indicate the ly have to distinguish between two tasks: stering rejection rate for a test using helium under 1. Locating leaks and standard helium conditions it is necessary b. the total of all leaks in the test specimen 2. Measuring the leak rate. first to convert the real conditions of use to (integral measurement) – sketches a helium standard conditions (see Section In addition, we distinguish, based on the and c in Figure 5.4. 5.2.2). Some examples of such conversi- direction of flow for the fluid, between the The leak rate which is no longer tolerable ons are shown in Figure 5.3. a. vacuum method (sometimes known as in accordance with the acceptance specifi- an “outside-in leak”), where the direc- cations is known as the rejection rate. Its tion of flow is into the test specimen calculation is based on the condition that (pressure inside the specimen being the test specimen may not fail during its 5.2.2 Conversion equations less than ambient pressure), and the planned utilization period due to faults caused by leaks, and this to a certain When calculating pressure relationships b. positive pressure method (often refer- and types of gas (viscosity) it is necessary to keep in mind that different equations are applicable to laminar and molecular flow; Range Laminar Molecular the boundary between these areas is very Q ⋅ (p2 − p2) = Q ⋅ (p2 − p2) Q ⋅ (p − p ) = Q ⋅ (p − p ) difficult to ascertain. As a guideline one Pressure I 1 2 II II 1 2 I I 1 2 II II 1 2 I may assume that laminar flow is present at η η Q ⋅ = Q ⋅ -5 Qgas A á gas A = Qgas B á gas B gas A Mgas A gas B Mgas B leak rates where QL > 10 mbar · l/s and Gas molecular flow at leak rates where -7 Table 5.2 Conversion formulae for changes of pressure and gas type QL < 10 mbar · l/s. In the intermediate

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5.4 Leak detection methods without a Helium leak detector unit The most sensible differentiation between the test methods used is differentiation as to whether or not special leak detection equipment is used. In the simplest case a leak can be determined qualitatively and, when using certain test techniques, quantitatively as well (this a: Integral leak detection; vacuum inside c: Integral leak detection (test gas enrichment being the leak rate) without the assistance specimen inside the enclosure); pressurized test gas inside of a special leak detector. Thus the quanti- specimen ty of water dripping from a leaking water faucet can be determined, through a certain period of time, using a graduated cylinder but one would hardly refer to this as a leak detector unit. In those cases Helium where the leak rate can be determined during the course of the search for the leak without using a leak detector (see, for example, Sect. 5.4.1), this will often be converted to the helium standard leak rate (Sect. 5.2.1). This standard leak rate value is frequently needed when issuing accept- Helium ance certificates but can also be of service when comparing leak rate values deter- b: Local leak detection; vacuum inside specimen d: Local leak detection; pressurized test gas mined by helium leak detector devices. inside the specimen In spite of careful inspection of the indivi- Fig. 5.4 Leak test techniques and terminology dual engineering components, leaks may also be present in an apparatus following its assembly – be it due to poorly seated degree of certainty. Often it is not the leak in parallel to the system’s pumps, then one seals or damaged sealing surfaces. The rate for the test specimen under normal refers to partial-flow mode. One also processes used to examine an apparatus operating conditions which is determined, refers to partial stream mode when a sepa- will depend on the size of the leaks and on but rather the throughput rate of a test gas rate auxiliary pump is used parallel to the the degree of tightness being targeted and – primarily helium – under test conditions. leak detector. also on whether the apparatus is made of The values thus found will have to be con- When using the positive pressure method metal or glass or other materials. Some verted to correspond to the actual applica- it is sometimes either impractical or in fact leak detection techniques are sketched out tion situation in regard to the pressures impossible to measure the leakage rate below. They will be selected for use in inside and outside the test specimen and directly while it could certainly be sensed accordance with the particular application the type of gas (or liquid) being handled. in an envelope which encloses the test situations; economic factors may play an Where a vacuum is present inside the test specimen. The measurement can be made important part here. specimen (p < 1 mbar), atmospheric pres- by connecting that envelope to the leak sure outside, and helium is used at the test detector or by accumulation (increasing gas, one refers to standard helium condi- the concentration) of the test gas inside tions. Standard helium conditions are the envelope. The “bombing test” is a always present during helium leak detec- special version of the accumulation test 5.4.1 Pressure rise test tion for a high vacuum system when the (see Section 5.7.4). In the so-called sniffer system is connected to a leak detector and technique, another variation of the of the This leak testing method capitalizes on the is sprayed with helium (spray technique). positive pressure technique, the (test) gas fact that a leak will allow a quantity of gas If the specimen is evacuated solely by the issuing from leaks is collected (extracted) – remaining uniform through a period of leak detector, then one would say that the by a special apparatus and fed to the leak time – to enter a sufficiently evacuated leak detector is operating in the direct- detector. This procedure can be carried out device (impeded gas flow, see Fig. 1.1). In D00 flow mode. If the specimen is itself a com- using either helium or refrigerants or SF6 contrast, the quantity of gas liberated from plete vacuum system with its own vacuum as the test gas. container walls and from the materials pump and if the leak detector is operated used for sealing (if these are not suffi-

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ally in Figure 5.5. Once it has become clear tus) the test gas which has passed through that the rise in pressure is due solely to a leaks and into the apparatus. Another opti- real leak, then the leak rate can be deter- on is to use the positive-pressure leak test. mined quantitatively from the pressure A test gas (helium) is used to fill the appa- rise, plotted against time, in accordance ratus being inspected and to build up a e with the following equation: slight positive pressure; the test gas will

essur pass to the outside through the leaks and ∆p⋅V Pr Q = (5.3) will be detected outside the device. The L ∆t leaks are located with leak sprays (or soap Example: Once the vacuum vessel with a suds, 5.4.5) or – when using He or H2 as volume of 20 l has been isolated from the the test gas – with a leak detector and snif- pump, the pressure in the apparatus rises fer unit (5.7.2). Time from 1·10-4 mbar to 1·10-3 mbar in 300 s. 1 Leak Thus, in accordance with equation 5.2, the 2 Gas evolved from the container walls leak rate will be 3 Leak + gas evolution    ⋅ – 3 − ⋅ – 4 ⋅ 5.4.2 Pressure drop test 1 10 1 10  20 Fig. 5.5 Pressure rise within a vessel after the pump is Q = switched off L 300 The thinking here is analogous to that for the pressure rise method (Section 5.4.1). 9⋅10– 4 ⋅ 20 mbar⋅ ` The method is, however, used only rarely ciently free of outgassing) will decline = = 6 ⋅10– 5 300 s to check for leaks in vacuum systems. If through time since these will practically this is nonetheless done, then gauge pres- always be condensable vapors for which The leak rate, expressed as mass flow sure should not exceed 1 bar since the an equilibrium pressure is reached at ∆m / ∆t, is derived from equation 5.1 at flange connectors used in vacuum techno- some time (see Fig. 5.5). The valve at the Q = 6 · 10-5 mbar · l/s, T = 20 °C and the logy will as a rule not tolerate higher pres- pump end of the evacuated vacuum vessel L molar mass for air (M = 29 g/mole) at sures. Positive pressure testing is, on the will be closed in preparation for pressure other hand, a technique commonly rise measurements. Then the time is mea- ∆m –5 mbar ⋅ ` g QL = = 6⋅10 ⋅ ⋅ 29 ⋅ employed in tank engineering. When dea- sured during which the pressure rises by a ∆t s mol ling with large containers and the long test certain amount (by one power of ten, for mol ⋅ K g ⋅ = 7⋅10–8 periods they require for the pressure drop example). The valve is opened again and 2 83.14mbar⋅ `⋅293 ⋅10 K s there it may under certain circumstances the pump is run again for some time, fol- be necessary to consider the effects of lowing which the process will be repeated. If the container is evacuated with a temperature changes. As a consequence it If the time noted for this same amount of TURBOVAC 50 turbomolecular pump, for may happen, for example, that the system pressure rise remains constant, then a leak example (S = 50 l/s), which is attached to cools to below the saturation pressure for is present, assuming that the waiting peri- the vacuum vessel by way of a shut-off water vapor, causing water to condense; od between the two pressure rise trials valve, then one may expect an effective this will have to be taken into account was long enough. The length of an appro- pumping speed of about S = 30 l/s. Thus when assessing the pressure decline. priate waiting period will depend on the eff the ultimate pressure will be nature and size of the device. If the pressure rise is more moderate during the Q 6⋅10– 5 mbar⋅`⋅s –1 p = L = second phase, then the rise may be assu- end –1 Seff 30` ⋅s med to result from gases liberated from 5.4.3 Leak test using the inner surfaces of the vessel. One may = 2⋅10– 6 mbar also attempt to differentiate between leaks vacuum gauges which and contamination by interpreting the Naturally it is possible to improve this ulti- are sensitive to the type curve depicting the rise in pressure. Plot- mate pressure, should it be insufficient, by of gas ted on a graph with linear scales, the curve using a larger-capacity pump (e.g. the The fact that the pressure reading at vacu- for the rise in pressure must be a straight TURBOVAC 151) and at the same time to line where a leak is present, even at higher um gauges (see Section 3.3) is sensitive to reduce the pump-down time required to the type of gas involved can, to a certain pressures. If the pressure rise is due to reach ultimate pressure. gas being liberated from the walls (owing extent, be utilized for leak detection purpo- ultimately to contamination), then the Today leak tests for vacuum systems are ses. Thus it is possible to brush or spray pressure rise will gradually taper off and usually carried out with helium leak detec- suspected leaks with alcohol. The alcohol will approach a final and stable value. In tors and the vacuum method (see Section vapors which flow into the device – the most cases both phenomena will occur 5.7.1). The apparatus is evacuated and a thermal conductivity and ionizablity of simultaneously so that separating the two test gas is sprayed around the outside. In which will vary greatly from the same pro- causes is often difficult if not impossible. this case it must be possible to detect (on perties for air – will affect and change These relationships are shown schematic- the basis of samplings inside the appara- pressure indication to a greater or lesser

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extent. The availability of more precise, Here, again, the detection of smaller leaks krypton 85, a gaseous, radioactive isotope, easy-to-use helium leak detectors has, is time-consuming and will depend greatly can first be forced into the device by app- however, rendered this method almost on the attentiveness of the inspector. The lying pressure from the outside. Once an completely obsolete. hydrogen gas cooling systems used in exactly measured holding period has elap- power plant generators represent a special sed the pressure will be relieved, the com- case. These are indeed sometimes tested ponent flushed and the activity of the “gas in the fashion described above but they charge” will be measured. In the same way can be examined much better and at much it is also possible to use helium as the test 5.4.4 Bubble immersion test higher sensitivity by “sniffing” the hydro- gas (see Section 5.7.4, bombing test). gen escaping at leaks using a helium leak The pressurized test specimen is sub- detector which has been adjusted to res- merged in a liquid bath. Rising gas bub- pond to H (see Section 5.7.2). bles indicate the leak. Leak detection will 2 depend greatly on the attentiveness of the 5.4.8 High-frequency vacuum person conducting the test and involves the temptation to increase the “sensitivity” test by using ever higher temperatures, wher- 5.4.6 Vacuum box check The so-called high-frequency vacuum ein the applicable safety regulations are tester can be used not only to check the sometimes disregarded. This method is bubble pressure in glass equipment but also to very time-consuming for smaller leaks, as As a variation on the spray technique men- locate porous areas in plastic or paint coa- Table 5.3 shows. It references leak testing tioned above, in which the escaping gas tings on metals. This comprises a hand- on a refrigeration system using type R12 causes the bubbles, it is possible to place held unit with a brush-like high-frequency refrigerant. Here the leak rate is specified a so-called “vacuum box” with a seal electrode and a power pack. The shape in grams of refrigerant loss per year (g/a). (something like a diver’s goggles) on the and color of the electrical gas discharge Water is used as a test liquid (which may surface being examined once it has been can serve as a rough indicator for the pres- be heated or to which a surfactant may be sprayed with a soap solution. This box is sure prevailing inside glass equipment. In added) or petroleum-based oils. The surfa- then evacuated with a vacuum pump. Air the case of the vacuum tester – which ce tension should not exceed 75 dyn/cm entering from the outside through leaks comprises primarily a tesla transformer (1 dyn = 10-5 N). will cause bubbles inside the box, which (which delivers a high-voltage, high-fre- can be observed through a glass window quency AC current) – the corona electrode in the box. In this way it is also possible, approaching the apparatus will trigger an for example, to examine flat sheet metal electrode-free discharge inside the apparatus. The intensity and color of this dischar- 5.4.5 Foam-spray test plates for leaks. Vacuum boxes are available for a variety of applications, made to ge will depend on the pressure and the In many cases pressurized containers or suit a wide range of surface contours. type of gas. The luminous discharge phe- gas lines (including the gas supply lines nomenon allows us to draw conclusions for vacuum systems) can be checked quite regarding the approximate value for the conveniently for leaks by brushing or pressure prevailing inside the apparatus. spraying a surfactant solution on them. The discharge luminosity will disappear at Corresponding leak detection sprays are 5.4.7 Krypton 85 test high and low pressures. also available commercially. Escaping gas When searching for leaks in glass equip- When dealing with small, hermetically sea- forms “soap bubbles” at the leak points. ment the suspect sections will be scanned led parts where the enclosure is leaky, or traced with the high-frequency vacuum tester electrode. Where there is a leak an Freon F12 loss Time taken to form Equivalent Detection time using arc will strike through to the pore in the per year a gas bubble leak rate helium leak detector glass wall, tracing a brightly lit discharge (g/a) (s) (cm3[STP]/s) (s) trail. Small pores can be enlarged by these 280 13.3 1.8 · 10–3 a few seconds sparks! The corona discharge of the vacuum tester can also penetrate thin areas in 84 40 5.4 · 10–4 a few seconds the glass particularly at weld points and 28 145 1.8 · 10–4 a few seconds transitional areas between intermediate components. Equipment which was ori- –5 14 290 9.0· 10 a few seconds ginally leak-free can become leaky in this 2.8 24 min 1.8 · 10–5 a few seconds fashion! In contrast to the actual leak detector units, the high-frequency vacuum 0.28 * 6 h 1.8 · 10–6 a few seconds tester is highly limited in its functioning. D00 *) This leak rate represents the detection limit for good halogen leak detectors (≈ 0,1 g/a).

Table 5.3 Comparison of bubble test method (immersion technique) wit helium leak detector

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5.4.9 Test with chemical lity of the surface of the solid and the capil- The function of most leak detectors is reactions and dye lary action; see also Table 5.1. Some wide- based on the fact that testing is conducted penetration ly used leak detection methods are shown – with a special test gas, i.e. with a medium together with the test gas, application range other than the one used in normal operati- Occasionally leaks can also be located or and their particular features – in Table 5.4. on. The leak test may, for example, be car- detected by means of chemical reactions ried out using helium, which is detected which result in a discoloration or by pene- using a mass spectrometer, even though tration of a dye solution into fine openings. the component being tested might, for The discoloration of a flame due to halo- example, be a cardiac pacemaker whose gen gas escaping through leaks was used 5.5 Leak detectors and interior components are to be protected earlier to locate leaks in solder joints for against the ingress of bodily fluids during refrigeration units. how they work normal operation. This example alone makes it clear that the varying flow pro- A less frequently employed example of a Most leak testing today is carried out using perties of the test and the working media chemical effect would be that of escaping special leak detection devices. These can need to be taken into consideration. ammonia when it makes contact with oza- detect far smaller leak rates than techni- lid paper (blueprint paper) or with other ques which do not use special equipment. materials suitably prepared and wrapped These methods are all based on using spe- around the outside of the specimen. Leaks cific gases for testing purposes. The diffe- are then detected based on the discolorati- rences in the physical properties of these 5.5.1 Halogen leak detectors on of the paper. test gases and the gases used in real-life (HLD4000, D-Tek) An example of a dye penetration test is the applications or those surrounding the test inspection of the tightness of rubber plugs configuration will be measured by the leak Gaseous chemical compounds whose or plungers in glass tubes, used for exam- detectors. This could, for example, be the molecules contain chlorine and/or fluorine ple in testing materials suitability for dis- differing thermal conductivity of the test – such as refrigerants R12, R22 and posable syringes or pharmaceutical packa- gas and surrounding air. The most widely R134a – will influence the emissions of ges. When evaluating tiny leaks for liquids used method today, however, is the detec- alkali ions from a surface impregnated it will be necessary to consider the wetabi- tion of helium used as the test gas. with a mixture of KOH and Iron(III)hydroxide and maintained at 800 °C to 900 °C by an external Pt heater. The released ions Method Test gas Smallest detectable Pressure range Quantitative flow to a cathode where the ion current is leak rate measurement measured and then amplified (halogen mbar `/s g/a R 134 a diode principle). This effect is so great that –4 –1 Foaming Air and others 10 7 · 10 Positive pressure No partial pressures for halogens can be mea- liquids sured down to 10-7 mbar. Ultrasonic Air and others 10–2 70 Positive pressure No microphone Whereas such devices were used in the past for leak testing in accordance with the –3 –5 –1 Thermal conducti- Gases other 10 – 10 10 – 7 Positive pressure No vacuum method, today – because of the vity leak detector than air and vacuum problems associated with the CFCs – more sniffer units are being built. The attainable Halogen Substances 10–6 7 · 10–3 Positive pressure With -6 –5 –1 detection limit is about 1 · 10 mbar · l/s leak detection containing (10 ) (10 ) (vacuum) limitations for all the devisces. Equipment operating in halogens accordance with the halogen diode princi- Universal Refrigerants, 10–5 7 · 10–3 Positive pressure Yes ple can also detect SF6. Consequently these sniffer helium and sniffer units are used to determine whether leak detector other gases refrigerants are escaping from a refrigera- Helium Helium 10–12 7 · 10–9 Vacuum, Yes tion unit or from an SF type switch box (fil- –7 –4 6 leak detection 10 7 · 10 positive pressure led with arc suppression gas). Bubble test Air and other 10–3 7 Positive pressure No gases

Water pressure Water 10–2 70 Positive pressure No test 5.5.2 Leak detectors with mass Pressure Air and other 10–4 7 · 10–1 Positive pressure Yes spectrometers (MSLD) drop test gases The detection of a test gas using mass Pressure Air 10–4 7 · 10–1 Vacuum Yes rise test spectrometers is far and away the most sensitive leak detection method and the one Table 5.4 Comparison of leak detection methods most widely used in industry. The MS leak

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detectors developed for this purpose make 5.5.2.1 The operating principle for a In this case the gas quantity per unit of possible quantitative measurement of leak MSLD time is the leak rate being sought; the total rates in a range extending across many pressure may not be used, but only the The basic function of a leak detector and powers of ten (see Section 5.2) whereby share for helium or the partial pressure for the difference between a leak detector and the lower limit ≈ 10-12 mbar · l/s, thus helium. This signal is delivered by the mass spectrometer can be explained using making it possible to demonstrate the inhe- mass spectrometer when it is set for ato- Figure 5.6. This sketch shows the most rent gas permeability of solids where heli- mic number 4 (helium). The value for S commonly found configuration for leak eff um is used as the test gas. It is actually is a constant for every series of leak detec- detection using the helium spray method possible in principle to detect all gases tors, making it possible to use a micropro- (see Section 5.7.1) at a vacuum compo- using mass spectrometry. Of all the availa- cessor to multiply the signal arriving from nent. When the sprayed helium is drawn ble options, the use of helium as a tracer the mass spectrometer by a numerical into the component through a leak it is gas has proved to be especially practical. constant and to have the leak rate dis- pumped thorough the interior of the leak The detection of helium using the mass played direct. detector to the exhaust, where it again lea- spectrometer is absolutely (!) unequivocal. ves the detector. Assuming that the detec- Helium is chemically inert, non-explosive, tor itself is free of leaks, the amount of gas non-toxic, is present in normal air in a con- 5.5.2.2 Detection limit, background, flowing through each pipe section (at any centration of only 5 ppm and is quite eco- gas storage in oil (gas desired point) per unit of time will remain nomical. Two types of mass spectrometer ballast), floating zero-point constant regardless of the cross section are used in commercially available MSLD’s: suppression and the routing of the piping. The follo- a) The quadrupole mass spectrometer, alt- wing applies for the entry into the pumping The smallest detectable leak rate is dicta- hough this is used less frequently due port at the vacuum pump: ted by the natural background level for the to the more elaborate and complex gas to be detected. Even with the test design (above all due to the electrical Q = p · S (5.4) connector at the leak detector closed, supply for the sensor), or At all other points every gas will pass – counter to the pumping direction – through the exhaust and b) the 180° magnetic sector field mass Q = p · Seff (5.4a) through the pumps (but will be reduced spectrometer, primarily due to the rela- accordingly by their compression) through tively simple design. applies, taking the line losses into account. to the spectrometer and will be detected Regardless of the functional principle The equation applies to all gases which are there if the electronic means are adequate employed, every mass spectrometer com- pumped through the piping and thus also to do so. The signal generated represents prises three physically important sub- for helium. the detection limit. The high vacuum systems: the ion source, separation system used to evacuate the mass spec- Q = p · S (5.4b) system and ion trap. The ions must be able He He eff, He to travel along the path from the ion source and through the separation system to Test gas the ion trap, to the greatest possible extent e.g. He without colliding with gas molecules. This path amounts to about 15 cm for all types of spectrometers and thus requires a medium free path length of at least 60 cm, Test specimen corresponding to pressure of about 1 · 10-4 mbar; in other words, a mass Test connection spectrometer will operate only in a vacuum. Due to the minimum vacuum level of 1 · 10-4 mbar, a high vacuum will be required. Turbomolecular pumps and suitable roughing pumps are used in modern leak detectors. Associated with the individual component groups are the required electrical- and electronic supply systems and Leak detector software which, via a microprocessor, allow for the greatest possible degree of automation in the operating sequence, QHe = pHe · Seff including all adjustment and calibration He routines and measured value display. Exhaust D00

Fig. 5.6 Basic operating principle for a leak detector

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Test connection tinued until all the oil from the pump’s oil pan has been recirculated several times. This period of time will usually be 20 to 30 minutes. Mass spectrometer In order to spare the user the trouble of always having to keep an eye on the background level, what has been dubbed floa- Turbomolecular pump ting zero-point suppression has been integrated into the automatic operating con- Venting cepts of all INFICON leak detectors (Sec- valve tion 5.5.2.5). Here the background level measured after the inlet valve has been Gas ballast closed is placed in storage; when the valve valve is then opened again this value will auto- Roughing pump matically be deducted from subsequent measurements. Only at a relatively high Exhaust threshold level will the display panel show a warning indicating that the background noise level is too high. Figure 5.8 is provi- Fig. 5.7 Correct set-up for a MSLD ded to illustrate the process followed in zero point suppression. Chart on the left. The signal is clearly larger than the back- trometer will normally comprise a turbo- detector, to increase the helium level in the ground. Center chart: the background has molecular pump and an oil-sealed rotary oil and the elastomer seals there and thus risen considerably; the signal can hardly vane pump. (Diffusion pumps were used to induce a background signal in the mass be discerned. Chart on the right: the back- earlier instead of the turbomolecular spectrometer which is well above the nor- ground is suppressed electrically; the sig- pumps.) Like every liquid, the sealing oil in mal detection limit. When the device is nal can again be clearly identified. the rotary vane pump has the capability of properly installed (see Fig. 5.7) the gas dissolving gases until equilibrium is rea- ballast valve and the airing valve will be Independent of this floating zero-point ched between the gas dissolved in the oil connected to fresh air and the discharge suppression, all the leak detectors offer and the gas outside the oil. When the line (oil filter!) should at least be routed to the capability for manual zero point shif- pump is warm (operating temperature) outside the room where the leak test takes ting. Here the display for the leak detector this equilibrium state represents the detec- place. at the particular moment will be “reset to tion limit for the leak detector. The helium zero” so that only rises in the leak rate An increased test gas (helium) background stored in the oil thus influences the detec- from that point on will be shown. This ser- level can be lowered by opening the gas tion limit for the leak detector. It is possi- ves only to facilitate the evaluation of a dis- ballast valve and introducing gas which is ble for test gas to enter not only through play but can, of course, not influence its free of the test gas (helium-free gas, fresh the test connection and into the leak detec- accuracy. air). The dissolved helium will be flushed tor; improper installation or inept handling out, so to speak. Since the effect always Modern leak detectors are being more fre- of the test gas can allow test gas to enter affects only the part of the oil present in quently equipped with oil-free vacuum through the exhaust and the airing or gas the pump body at the particular moment, systems, the so-called “dry leak detectors” ballast valve and into the interior of the the flushing procedure will have to be con- (UL 200 dry, UL 500 dry). Here the problem of gas being dissolved in oil does not occur but similar purging techniques will nonetheless be employed. 10–6

caution –7 10 5.5.2.3 Calibrating leak detectors; 10–8 test leaks fine 10–9 Calibrating a leak detector is to be under- prec 10–10 stood as matching the display at a leak detector unit, to which a test leak is atta- 10–11 ched, with the value shown on the “label” or calibration certificate. The prerequisite Equipment background level: < 2 · 10–10 1 · 10–8 1 · 10–10 (suppressed) Leak: 2 · 10–8 2 · 10–8 2 · 10–8 for this is correct adjustment of the ion Display: 2 · 10–8 3 · 10–8 2 · 10–8 paths in the spectrometer, also known as tuning. Often the distinction is not made Fig. 5.8 Example of zero-point suppression quite so carefully and both procedures

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together are referred to as calibration. Test leaks (also known as standard leaks 5.5.2.4 Leak detectors with or reference leaks) normally comprise a quadrupole mass In the calibration process proper the gas supply, a choke with a defined con- spectrometer (Ecotec II) straight-line curve representing the nume- ductance value, and a valve. The configu- rically correct, linear correlation between INFICON builds leak detectors with qua- ration will be in accordance with the test the gas flow per unit of time and the leak drupole mass spectrometers to register leak rate required. Figure 5.9 shows rate is defined by two points: the zero point masses greater than helium. Apart from various test leaks. Permeation leaks are (no display where no emissions are detec- special cases, these will be refrigerants. usually used for leak rates of ted) and the value shown with the test leak These devices thus serve to examine the 10-10 < Q < 10-7, capillaries, between (correct display for a known leak). L tightness of refrigeration units, particular- 10-8 and 10-4 and, for very large leak rates ly those for refrigerators and air conditio- In vacuum operations (spray technique, in a range from 10 to 1000 mbar · l/s, pipe ning equipment. see Section 5.7.1) one must differentiate sections or orifice plates with exactly between two types of calibration: with an defined conductance values (dimensions). Figure 4.2 shows a functional diagram for internal or external test leak. When using a Test leaks used with a refrigerant charge a quadrupole mass spectrometer. Of the test leak built into the leak detector the unit represent a special situation since the ref- four rods in the separation system, the two can itself be calibrated but it can only cali- rigerants are liquid at room temperature. pairs of opposing rods will have identical brate itself. When using an external test Such test leaks have a supply space for potential and excite the ions passing leak not just the device but also a comple- liquid from which, through a shut-off through along the center line so that they te configuration, such as a partial flow valve, the space filled only with the refrige- oscillate transversely. Only when the arrangement, can be included. Internal test rant vapor (saturation vapor pressure) can amplitude of these oscillations remains leaks are permanently installed and cannot be reached, ahead of the capillary leak. smaller than the distance between the rods be misplaced. At present all the leak detec- One technological problem which is diffi- can the appropriate ion pass through the tors being distributed by INFICON are fit- cult to solve is posed by the fact that all system of rods and ultimately reach the ted with an automatic calibration routine. refrigerants are also very good solvents for ion trap, where it will discharge and thus be counted. The flow of electrons thus Sniffer units or configurations will as a rule oil and grease and thus are often seriously created in the line forms the measurement have to be calibrated with special, external contaminated so that it is difficult to fill the signal proper. The other ions come into test leaks in which there is a guarantee that test leaks with pure refrigerant. Decisive contact with one of the rods and will be on the one hand all the test gas issuing here is not only the chemical composition neutralized there. from the test leak reaches the tip of the but above all dissolved particles which can probe and on the other hand that the gas repeatedly clog the fine capillaries. Figure 5.10 shows the vacuum schematic flow in the sniffer unit is not hindered by for an Ecotec II. The mass spectrometer calibration. When making measurements using the sniffer technique (see Section 5.7.2) it is also necessary to take into 1 Diaphragm pump 5 2 Piezo-resistive account the distance from the probe tip to pressure sensor the surface of the specimen and the scan- 3 Turbomolecular external flow internal ning speed; these must be included as a particle limiter 1 particle pump part of the calibration. In the special case filter filter 4 Quadrupole mass spectrometer where helium concentration is being mea- 5 Sniffer line sured, calibration can be made using the 6 Gas flow limiter helium content in the air, which is a uni- 6 7 Gas flow limiter form 5 ppm world-wide. QMA 200 flow divider 1 8 Gas flow meter flow limiter 2 4

5 flow divider 2 flow 7 3 limiter 3 flow meter

a b c d e 1 8 2

a Reference leak without gas supply, TL4, TL6 b Reference leak for sniffer and vacuum 1 2 applications, TL4-6 c (Internal) capillary test leak TL7 d Permeation (diffusion) reference leak, TL8 D00 e Refrigerant calibrated leak

Fig. 5.9 Examples for the construction of test leaks Fig. 5.10 Vacuum schematic for the Ecotec II

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(4) only operates under high vacuum con- is possible to switch directly from one gas 1. the mass spectrometer ditions, i.e. the pressure here must always to another. 2. the high vacuum pump and remain below 10-4 mbar. This vacuum is generated by the turbomolecular pump (3) 3. the auxiliary roughing pump system in with the support of the diaphragm pump 5.5.2.5 Helium leak detectors with stationary units. (1). The pressure PV between the two 180° sector mass The mass spectrometer (see Fig. 5.11) pumps is measured with a piezo resistive spectrometer (UL 200, UL 500) comprises the ion source (1–4) and the measuring system (2) and this pressure These units are the most sensitive and also deflection system (5–9). The ion beam is lies in the range between 1 to 4 mbar while provide the greatest degree of certainty. extracted through the orifice plate (5) and in the measurement mode. This pressure Here “certain” is intended to mean that enters the magnetic field (8) at a certain must not exceed a value of 10 mbar as there is no other method with which one energy level. Inside the magnetic field the otherwise the turbomolecular pump will can, with greater reliability and better sta- ions move along circular paths whereby not be capable of maintaining the vacuum bility, locate leaks and measure them the radius for a low mass is smaller than in the mass spectrometer. The unit can quantitatively. For this reason helium leak that for higher masses. With the correct easily be switched over at the control unit detectors, even though the purchase price setting of the acceleration voltage during from helium to any of various refrigerants, is relatively high, are often far more eco- tuning one can achieve a situation in which some of which may be selected as desired. nomical in the long run since much less the ions describe a circular arc with a defi- Naturally the unit must be calibrated sepa- time is required for the leak detection pro- ned curvature radius. Where mass 4 (heli- rately for each of these masses. Once set, cedure itself. um) is involved, they pass thorough the however, the values remain available in aperture (9) to the ion trap (13). In some storage so that after calibration has been A helium leak detector comprises basically devices the discharge current for the ions effected for all the gases (and a separate two sub-systems in portable units and impinging upon the total pressure electro- reference leak is required for each gas!) it three in stationary units. These are: des will be measured and evaluated as a total pressure signal. Ions with masses which are too small or too great should not be allowed to reach the ion trap (13) at all, but some of these ions will do so in spite of this, either because they are deflected by collisions with neutral gas particles or 14 because their initial energy deviates too far 1 from the required energy level. These ions are then sorted out by the suppressor (11) so that only ions exhibiting a mass of 4 13 (helium) can reach the ion detector (13). 2 The electron energy at the ion source is 80 12 3 eV. It is kept this low so that components with a specific mass of 4 and higher – 4 such as multi-ionized carbon or quadruply 11 ionized oxygen – cannot be created. The 5 ion sources for the mass spectrometer are simple, rugged and easy to replace. They 6 are heated continuously during operation and are thus sensitive to contamination. The two selectable yttrium oxide coated iri- 10 dium cathodes have a long service life. These cathodes are largely insensitive to 7 air ingress, i.e. the quick-acting safety cut- out will keep them from burning out even if air enters. However, prolonged use of the 9 8 ion source may eventually lead to cathode embrittlement and can cause the cathode 1 Ion source flange 5 Extractor 10 Magnetic field 2 Cathode 6 Ion traces for M > 4 11 Suppressor to splinter if exposed to vibrations or (2 cathodes, Ir + Y2O3) 7 Total pressure electrode 12 Shielding of the ion trap shock. 3 Anode 8 Ion traces for M = 4 13 Ion trap 4 Shielding of the ion 9 Intermediate orifice 14 Flange for ion trap with Depending on the way in which the inlet is source with discharge plate preamplifier connected to the mass spectrometer, one orifice can differentiate between two types of MSLD. Fig. 5.11 Configuration of the 180° sector mass spectrometer

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Leak Detection Fundamentals of Vacuum Technology

5.5.2.6 Direct-flow and counter-flow for helium is QHe = pHe · Seff · K (5.5b) leak detectors p = 1 · 10-12 mbar. The pumping min,He S = effective pumping speed at the speed for helium would be S = 10 l/s. eff Figure 5.12 shows the vacuum schematic He rotary vane pump at the Then the smallest detectable leak rate is for the two leak detector types. In both branching point Q = 1 · 10-12 mbar · 10 l/s cases the mass spectrometer is evacuated min K = Helium compression factor at = 1 · 10-11 mbar · l/s. If the pumping speed by the high vacuum pumping system com- the turbomolecular pump is now reduced to 1/s, then one will achie- prising a turbomolecular pump and a ve the smallest detectable leak rate of The counter-flow leak detector is a particu- rotary vane pump. The diagram on the left 1 · 10-12 mbar · l/s. One must keep in lar benefit for automatic vacuum units shows a direct-flow leak detector. Gas mind, however, that with the increase in since there is a clearly measurable pressu- from the inlet port is admitted to the spec- the sensitivity the time constant for achie- re at which the valve can be opened, name- trometer via a cold trap. It is actually equi- ving a stable test gas pressure in the test ly the roughing vacuum pressure at the valent to a cryopump in which all the specimen will be correspondingly larger turbomolecular pump. Since the turbo- vapors and other contaminants condense. (see Section 5.5.2.9). molecular pump has a very large compres- (The cold trap in the past also provided sion capacity for high masses, heavy mo- effective protection against the oil vapors In Figure 5.12 the right hand diagram lecules in comparison to the light test gas, of the diffusion pumps used at that time). shows the schematic for the counter-flow helium (M = 4), can in practice not reach The auxiliary roughing pump system ser- leak detector. The mass spectrometer, the the mass spectrometer. The turbomolecu- ves to pre-evacuate the components to be high vacuum system and also the auxiliary lar pump thus provides ideal protection for tested or the connector line between the roughing pump system correspond exact- the mass spectrometer and thus elimina- leak detector and the system to be tested. ly to the configuration for the direct-flow tes the need for an LN cold tap, which is Once the relatively low inlet pressure arrangement. The feed of the gas to be 2 certainly the greatest advantage for the (pumping time!) has been reached, the examined is however connected between user. Historically, counter-flow leak detec- valve between the auxiliary pumping the roughing pump and the turbomolecu- tors were developed later. This was due in system and the cold trap will be opened for lar pump. Helium which reaches this part to inadequate pumping speed stabili- the measurement. The Seff used in equati- branch point after the valve is opened will ty, which for a long time was not sufficient on 5.4b is the pumping speed of the tur- cause an increase in the helium pressure with the rotary vane pumps used here. For bomolecular pump at the ion source loca- in the turbomolecular pump and in the both types of leak detector, stationary tion: mass spectrometer. The pumping speed units use a built-in auxiliary pump to assist S inserted in equation 5.4b is the pum- Q = p · S eff in the evacuation of the test port. With por- He He eff,turbomolecular pump ion source ping speed for the rotary vane pump at the table leak detectors, it may be necessary to (5.5a) branch point. The partial helium pressure provide a separate, external pump, this established there, reduced by the helium In the case of direct-flow leak detectors, an being for weight reasons. increase in the sensitivity can be achieved compression factor for the turbomolecular by reducing the pumping speed, for exam- pump, is measured at the mass spectro- ple by installing a throttle between the tur- meter. The speed of the turbomolecular 5.5.2.7 Partial flow operation bomolecular pump and the cold trap. This pump in the counter-flow leak detectors is Where the size of the vacuum vessel or the is also employed to achieve maximum regulated so that pump compression also leak makes it impossible to evacuate the sensitivity. To take an example: remains constant. Equation 5.5b is derived from equation 5.5a: test specimen to the necessary inlet pres- The smallest detectable partial pressure sure, or where this would simply take too long, then supplementary pumps will have to be used. In this case the helium leak Solution 1: Direct-flow leak detector Solution 2: Counter-flow leak detector detector is operated in accordance with the so-called “partial flow” concept. This means that usually the larger part of the Test specimen Test specimen gas extracted from the test object will be Test gas stream Test gas stream removed by an additional, suitably dimen- sioned pump system, so that only a part of

–4 the gas stream reaches the helium leak pTOT < 10 mbar detector (see Fig. 5.13). The splitting of LN 2 pHe pHe MS MS the gas flow is effected in accordance with

–4 pTOT < 10 mbar High vacuum pump the pumping speed prevailing at the bran- High vacuum pump ching point. The following then applies:

Auxiliary pump Roughing pump Auxiliary pump Roughing pump γ QVacuum vessel = · DisplayLeak detector (5.6) Cold trap: S = 6.1 `/s · cm2 Fl ≈ 1000 cm2 where g is characterized as the partial flow D00 S = 6,100 `/s ratio, i.e. that fraction of the overall leak current which is displayed at the detector. Fig. 5.12 Full-flow and counter-flow leak detector

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Fundamentals of Vacuum Technology Leak Detection

Where the partial flow ratio is unknown, g the partial flow ratio to be expected vis à valve. In order to avoid this valve being can be determined with a reference leak vis a diffusion pump with pumping speed opened inadvertently, it should be sealed attached at the vacuum vessel: of 12000 l/s, for example – which leak off with a blank flange during normal vacu- rates can be detected at all. In systems um system operation. Display at the leak detector γ with high vacuum- and Roots pumps, the = ——————————— (5.7) A second method for coupling to larger Q for the reference leak surest option is to connect the leak detec- L systems, for example, those used for tor between the rotary vane pump and the removing the air from the turbines in po- roots pump or between the roots pump wer generating stations, is to couple at the and the high vacuum pump. If the pressu- 5.5.2.8 Connection to vacuum systems discharge. A sniffer unit is inserted in the re there is greater than the permissible system where it discharges to atmosphe- The partial flow concept is usually used in inlet pressure for the leak detector, then re. One then sniffs the increase in the heli- making the connection of a helium leak the leak detector will have to be connected um concentration in the exhaust. Without detector to vacuum systems with multi- by way of a metering (variable leak) valve. a tight coupling to the exhaust, however, stage vacuum pump sets. When conside- Naturally one will have to have a suitable the detection limit for this application will ring where to best make the connection, it connector flange available. It is also advis- be limited to 5 ppm, the natural helium must be kept in mind that these are usual- able to install a valve at this point from the content in the air. In power plants it is suf- ly small, portable units which have only a outset so that, when needed, the leak ficient to insert the tip of the probe at an low pumping speed at the connection flan- detector can quickly be coupled (with the angle of about 45° from the top into the ge (often less than 1 l/s). This makes it all system running) and leak detection can discharge line (usually pointing upward) of the more important to estimate – based on commence immediately after opening the the (water ring) pump.

Partial flow principle (example) 5.5.2.9 Time constants The time constant for a vacuum system is Q = 3 · 10– 5 mbar · ` (Leak rate) V = 150 ` He s set by V τ = (5.8) Seff S = S + S → S = 8 ` Leak detector (LD) eff PFP LD LD s τ = Time constant m3 ` S = 60 = 16.66 Partial flow pump (PFP) V = Volume of the container PFP s s S = Effective pumping speed, at the A) Signal amplitude: eff Splitting of the gas flow (also of the test test object gas!) in accordance with the effective pumping Figure 5.14 shows the course of the signal speed at the partial flow branch point after spraying a leak in a test specimen ` attached to a leak detector, for three diffe- Overal pumping speed: Seff = SLD + SPFP = 8 + 16.66 = 24.66 s rent configurations: γ ... Partial flow ratio 1. Center: The specimen with volume of V ͭ is joined directly with the leak detector

` –5 mbar · ` 8 s –6 mbar · ` LD (effective pumping speed of S). Signal to Leak detector: 3 · 10 s · ` = 9.73 · 10 s (8 + 16.66) s ` 2. Left: In addition to 1, a partial flow –5 mbar · ` 16,668s –5 mbar · ` Signal to partial flow pump: 3 · 10 s · ` = 2.02 · 10 s pump with the same effective pumping (8 + 16.66) s speed, S’ = S, is attached to the test

–5 mbar · ` Check: Overall signal QHe = QLD + QPFP = 3.00 · 10 s specimen.

3. Right: As at 1, but S is throttled down to Partial flow ratio = Fraction of the overall flow to the leak detector 0.5 · S. QLD QLD 1 ͭ γ = = = The signals can be interpreted as follow: QPFP QHe QLD + QPFP 1 + nnn QLD Q = γ · Q LD He 1: Following a “dead period” (or “delay S Display Leak rate or γ = LD = 1 time”) up to a discernible signal level, the SPFP SLD + SPFP 1 + nnn S signal, which is proportional to the partial LD pressure for helium, will rise to its full B) Response time: t = 3 · V = 3 · 150 ` = 18.25 s value of pHe = Q/Seff in accordance with 95% S 24.66 `m eff s equation 5.9: Estimate: Value for S, V and γ are uncertain → certain: calibrate with reference leak  – t  Q ⋅ − τ  pHe = 1 e (5.9 ) Seff   Fig. 5.13 Partial flow principle

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5.7 Leak detection

ᕄ Q ᕃ Q ᕅ Q techniques using V V V S S’ S S/2 helium leak MS MS MS Throttle detectors

Q ա LD LD LD Signal S amplitude Faster, less sensitive normal Slower, more sensitive 5.7.1 Spray technique 100% Q = 2p 2,0 (local leak test) S/2 95% The test specimen, connected to the heli- ᕅ um leak detector, is slowly traced with a very fine stream of helium from the spray Signal rise pistol, aimed at likely leakage points (wel- 100% Q = p 1,0 S ding seams, flange connectors, fused 95% ᕃ joints), bearing in mind the time constant of the system as per Equation 5.8 (see Fig. Q P 100% τ V = /2 0,5 Compensation period, e.g. t95% = 3 · = 3 · S + S’ 95% S 5.14). The volume sprayed must be adju- V ᕄ (τ = ... Time constant) sted to suit the leak rate to be detected and S Time 0 the size and accessibility of the object to 3 · V = 1 (3 · V) 3 · V 3 · V = 2 (3 · V ) being tested. Although helium is lighter Dead time S + S’ 2 S S S/2 S than air and therefore will collect beneath the ceiling of the room, it will be so well distributed by drafts and turbulence indu- Fig. 5.14 Signal responses and pumping speed ced by movements within the room that one need not assume that helium will be The signal will attain a prortion of its ulti- 5.6 Limit values / found primarily (or only) at the top of the mate value after room during search for leaks. In spite of Specifications for this, it is advisable, particularly when dea- t = 1 τ . . 63.3 % t = 2 τ . . 86.5 % ling with larger components, to start the t = 3 τ . . 95.0 % t = 4 τ . . 98.2 % the leak detector search for leaks at the top. t = 5 τ . . 99.3 % t = 6 τ . . 99.8 % 1. The smallest detectable leak rate. In order to avoid a surge of helium when The period required to reach 95 % of the the spray valve is opened (as this would ultimate value is normally referred to as 2. The effective pumping speed at the “contaminate” the entire environment) it is the response time. test connection. advisable to install a choke valve to adjust 2: With the installation of the partial flow 3. The maximum permissible pressure the helium quantity, directly before or after pump both the time constant and the sig- inside the test specimen (also the the spray pistol (see Fig. 5.15). The correct nal amplitude will be reduced by a factor of maximum permissible inlet pressure). quantity can be determined easiest by sub- -1 2; that means a quicker rise but a signal This pressure pmax will be about 10 merging the outlet opening in a container which is only half as great. A small time for LDs with classical PFPs and about 2 of water and setting the valve on the basis constant means quick changes and thus to 10 mbar for LDs with compound of the rising bubbles. Variable-area flow- quick display and, in turn, short leak detec- PFPs. The product of this maximum meters are indeed available for the requi- tion times. permissible operating pressure and the red small flow quantities but are actually pumping speed S of the pump system too expensive. In addition, it is easy to use 3: The throttling of the pumping speed to at the detector’s test connection is the the water-filled container at any time to 0.5 S, increases both the time constant maximum permissible throughput: determine whether helium is still flowing. and the signal amplitude by a factor of 2. A Q = p · S (5.10) large value for t thus increases the time max max eff, connector The helium content of the air can also be required appropriately. Great sensitivity, This equation shows that it is by no means detected with helium leak detectors where achieved by reducing the pumping speed, advantageous to attain high sensitivity by large leaks allow so much air to enter the is always associated with greater time throttling down the pumping speed. The vessel that the 5 ppm share of helium in requirements and thus by no means is maximum permissible throughput would the air is sufficient for detection purposes. always of advantage. otherwise be too small. The unit is not fun- The leak rate is then: An estimate of the overall time constants ctional when – either due to one large leak Display (pure He) Display (atmosph. He) or several smaller leaks – more gas flows ———————– = —————————— for several volumes connected one behind 1 5 · 10-6 to another and to the associated pumps into the unit than the maximum permissi- D00 can be made in an initial approximation by ble throughput rate for the leak detector. QL = Display (pure He) (5.11) adding the individual time constants. = 2 · 10+5 · Display (atmospheric He)

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5.7.3.1 Envelope test – test specimen pressurized with helium

a) Envelope test with concentration measurement and subsequent leak rate calculation To determine overall leakiness of a test object pressurized with helium the object shall be enclosed in an envelope which is either rigid or deformable (plastic). The test gas leaving the leaks accumulates so that the helium concentration in the envelope rises. Following an enrichment period to be determined (operating period) the change in concentration inside the envelope will be measured with a sniffer connected to the helium detection unit. The overall leak rate (integral leak rate) can be calculated following calibration of the test Avoiding the “helium surge” when the pistol valve is opened configuration with a reference concen- a) Throttle hose or tration, e.g. atmospheric air. This method b) Adjustable throttle valve ahead of the spray pistol makes it possible to detect even the smal- Minimum helium quantity for correct display: Changing the setting for the throttle shall not affect lest overall leakiness and is suitable in par- indication. The minimum quantity is always much smaller than one would set without a flowmeter (e.g. by ticular for automated industrial leak listening for flow or letting the helium flow across moistened lips). The simplest check without a testing. Due to gas accumulation, the flowmeter: Letting gas bubble through water. limits for normal sniffer techniques are shifted toward lower leak rates and the Fig. 5.15 Helium spray equipment ambient conditions such as temperature, air flow and sniffer tracing speed lose 5.7.2 Sniffer technology detector and sniffer unit will have to be influence. When using plastic envelopes it (local leak test using the calibrated together. Here the distance from is necessary to take into account helium the specimen and the tracing speed will permeation through the plastic envelope positive pressure have to be included in calibration, too. method) during long enrichment periods. Here the points suspected of leaking at the b) Direct measurement of the leak rate pressurized test specimen (see Fig. 5.4, d) with the leak detector (rigid envelope) are carefully traced with a test gas probe When the test specimen, pressurized with which is connected with the leak detector 5.7.3 Vacuum envelope test helium, is placed in a rigid vacuum cham- by way of a hose. Either helium or hydro- (integral leak test) ber, connected to a helium leak detector, gen can be detected with the INFICON heli- the integral leak rate can be read directly at Vacuum envelope tests are integral leak um leak detectors. The sensitivity of the the leak detector. tests using helium as the test gas, in which method and the accuracy of locating leaky the test specimen is enclosed either in a points will depend on the nature of the rigid (usually metal) enclosure or in a light sniffer used and the response time for the 5.7.3.2 Envelope test with test plastic envelope. The helium which enters leak detector to which it is connected. In specimen evacuated or leaves (depending on the nature of the addition, it will depend on the speed at test) the test specimen is passed to a heli- a) Envelope = “plastic tent” which the probe is passed by the leak um leak detector, where it is measured. The evacuated test specimen is surroun- points and the distance between the tip of Envelope tests are made either with the ded by a light-weight (plastic) enclosure the probe and the surface of the test spe- test specimen pressurized with helium and this is then filled with helium once the cimen. The many parameters which play a (Fig. 5.4c) or with the test specimen eva- atmospheric air has been removed. When part here make it more difficult to determi- cuated (Fig. 5.4a). In both cases it may be using a plastic bag as the envelope, the ne the leak rates quantitatively. Using snif- necessary to convert the helium enrich- bag should be pressed against the test fer processes it is possible, virtually inde- ment figure (accumulation) to the helium specimen before filling it with helium in pendent of the type of gas, to detect leak standard leak rate. order to expel as much air as possible and rates of about 10-7 mbar · l/s. The limitati- to make the measurement with the purest on of sensitivity in the detection of helium helium charge possible. The entire outside is due primarily to the helium in the atmos- surface of the test object is in contact with phere (see Chapter 9, Table VIII). In regard the test gas. If test gas passes through to quantitative measurements, the leak leaks and into the test specimen, then the

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integral leak rate will be indicated, regard- 5.8 Industrial leak less of the number of leaks. In addition, it is necessary to observe when repeating testing testing in enclosed areas that the helium content of the room will rise quite rapidly Industrial leak testing using helium as the when the envelope is removed. Using pla- test gas is characterized above all by the fact stic bags is thus more advisable for “one- that the leak detection equipment is fully off” testing of large plants. The plastic integrated into the manufacturing line. The envelope used here is often referred to as design and construction of such test units a “tent”. will naturally take into account the task to be carried out in each case (e.g. leak testing b) Rigid envelope vehicle rims made of aluminum or leak The use of a solid vacuum vessel as the testing for metal drums). Mass-produced, rigid envelope, on the other hand, is better standardized component modules will be for repetitive testing where an integral test used wherever possible. The parts to be is to be made. When solid envelopes are examined are fed to the leak testing system used it is also possible to recover the heli- (envelope test with rigid envelope and positi- um once the test has been completed. ve pressure [5.7.3.1b] or vacuum [5.7.3.2b] inside the specimen) by way of a conveyor system. There they will be examined individually using the integral methods and automatically moved on. Specimens found to be 5.7.4 “Bombing” test, leaking will be shunted to the side. “Storage under pressure” The advantages of the helium test method, seen from the industrial point of view, may The “bombing” test is use to check the be summarized as follows: tightness of components which are already hermetically sealed and which exhibit a • The leak rates which can be detected gas-filled, internal cavity. The components with this process go far beyond all prac- to be examined (e.g. transistors, IC hou- tical requirements. sings, dry-reed relays, reed contact swit- • The integral leak test, i.e. the total leak ches, quartz oscillators, laser diodes and rate for all individual leaks, facilitates the like) are placed in a pressure vessel the detection of microscopic and spon- which is filled with helium. Operating with ge-like distributed leaks which alto- the test gas at relatively high pressure (5 gether result in leakage losses similar to 10 bar) and leaving the system standing to those for a larger individual leak. over several hours the test gas (helium) will collect inside the leaking specimens. • The testing procedure and sequence This procedure is the actual “bombing”. To can be fully automated. make the leak test, then, the specimens are • The cyclical, automatic test system placed in a vacuum chamber following check (self-monitoring) of the device “bombing”, in the same way as described ensures great testing reliability. for the vacuum envelope test. The overall leak rate is then determined. Specimens • Helium is non-toxic and non-hazardous with large leaks will, however, lose their (no maximum allowable concentrations test gas concentration even as the vacuum need be observed). chamber is being evacuated, so that they • Testing can be easily documented, indi- will not be recognized as leaky during the cating the parameters and results, on a actual leak test using the detector. It is for printer. this reason that another test to register very large leaks will have to be made prior Use of the helium test method will result in to the leak test in the vacuum chamber. considerable increases in efficiency (cycling times being only a matter of seconds in length) and lead to a considerable increase in testing reliability. As a result of this and due to the EN/ISO 9000 requirements, traditional industrial test methods D00 (water bath, soap bubble test, etc.) will now largely be abandoned.

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Fundamentals of Vacuum Technology Thin Film Controllers / Control Units

oscillates reliably) despite refined techno- of less than one atomic layer can be detec- 6 Thin film logy, a number of approaches have been ted. developed to expand this capacity: controllers and In the late 1950s Sauerbrey and Lostis dis- 1. The use of several crystals, one behind covered that the frequency shift connected control units the other, in a multiple crystal holder with the coating of the quartz crystal is a with automatic change and data upda- function of the change in mass due to the with quartz ting in the event of imminent failure of a coating material in the following way: quartz: CrystalSix. M ∆ ∆ f = F = F oscillators or Mf Mq · with (6.1) 2. The RateWatcher function, in which the Mq Fq Fq quartz is alternately exposed to the coating beam for a short time until all mea- Mf mass of the coating 6.1 Introduction surements and regulation have been Mq mass of the quartz prior to coating carried out and then remains covered Fq frequency prior to coating It took a long time to go from the coating by a shutter for a longer period of time. Fc frequency after coating of quartz crystals for frequency fine ∆F = Ff – Fc ... frequency shift due to coa- The selection of the “right” crystal holder tuning, which has long been in practice, to ting utilization of frequency change to determi- thus plays an important role in all measurements with quartz oscillators. Various If the following are now applied: ne the mass per unit area as a microbalan- M = (M – M ) = D · ρ · A and ce with the present-day degree of precisi- crystal holder designs are recommended f c q f f for the different applications: with or with- on. In 1880 two brothers, J. and P. Curie, Mq = Dq · rq · A, where T = the coating out shutter, bakeable for UHV, double discovered the piezoelectric effect. Under thickness, ρ = density and A stands for crystal holder or crystal six as well as spe- mechanical loads on certain quartz crystal area while the index q stands for the state cial versions for sputter applications. In surfaces, electrical charges occur that are of the “uncoated quartz” and c for the state addition to these important and more caused by the asymmetrical crystalline after “frequency shift due to coating”, the “mechanical” aspects, the advances in structure of SiO . Conversely, in a piezo- following results are obtained for the coa- 2 measuring and control technology and crystal deformations appear in an electri- ting thickness: cal field and mechanical oscillations occur equipment features will be discussed in the following. F ∆F ∆F in an alternating field. A distinction is D = q · D · ρ · = K · f q q ρ ρ with made between bending oscillations, thick- Fq Fq · f f ness shear mode and thickness shear oscillations. Depending on the orientation D · F · ρ N · ρ of the cut plane to the crystal lattice, a q q q AT q K = = where number of different cuts are distinguished, 2 2 6.2 Basic principles of Fq Fq of which only the so-called AT cut with a coating thickness cut angle of 35°10" is used in thin film con- N = Fq · Dq is the frequency constant (for trollers because the frequency has a very measurement with the AT cut NAT = 166100 Hz · cm) and low temperature dependence in the range ρ 3 q = 2.649 g/cm is the density of the between 0 and 50 °C with this cut. Accor- quartz oscillators quartz. The coating thickness is thus pro- dingly, an attempt must be made not to ∆ The quartz oscillator coating thickness portional to the frequency shift F and exceed this temperature range during coa- inversely proportional to the density ρf of ting (water cooling of crystal holder). gauge (thin film controller) utilizes the piezoelectric sensitivity of a quartz oscillator the coating material. The equation Since there is still a problem with “quartz (monitor crystal) to the supplied mass. ∆F capacity” (i.e. the maximum possible coa- D f = K · ρ This property is utilized to monitor the f ting thickness of the quartz at which it still coating rate and final thickness during vacuum coating. for the coating thickness was used in the A very sharp electromechanical resonance first coating thickness measuring units occurs at certain discrete frequencies of with “frequency measurement” ever used. the voltage applied. If mass is added to the According to this equation, a crystal with a surface of the quartz crystal oscillating in starting frequency of 6.0 MHz displays a resonance, this resonance frequency is decline in frequency of 2.27 Hz after coa- diminished. This frequency shift is very ting with 1Å of aluminum 3 reproducible and is now understood preci- (de = 2.77 g/cm ). In this way the growth equency change (ppm) sely for various oscillation modes of of a fixed coating due to evaporation or

el. fr sputtering can be monitored through pre- r quartz. Today this phenomenon, which is Temperature (°C) easy to understand in heuristic terms, is cise measurement of the frequency shift of an indispensable measuring and process the crystal. It was only when knowledge of Fig. 6.1 Natural frequency as a function of temperature the quantitative interrelationship of this in an AT cut quartz crystal control tool, with which a coating increase

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→

↔ E Node

Fig. 6.2 Thickness shear oscillations Fig. 6.3 Shape of INFICON quartz crystals

effect was acquired that it became possible The characteristic motions of the thickness The two together ensure that the acoustic to determine precisely the quantity of shear oscillation are parallel to the main energy is recorded. Reducing the electrode material that is deposited on a substrate in crystal boundary surfaces. In other words: diameter limits the excitation to the midd- a vacuum. Previously this had been prac- the surfaces are shift antinodes, see Fig. le area. The surface contour consumes the tically impossible. 6.2. The resonance frequencies slightly energy of the moving acoustic waves befo- above the basic frequency are called re they reach the crystal edge. It is not “anharmonic” and are a combination of reflected into the center where it could thickness shear and thickness rotation interfere with new incoming waves. oscillation forms. The resonance frequen- Such a small crystal behaves like an infini- cy at around three times the value for the 6.3 The shape of tely expanded crystal. However, if the fundamental wave is called “quasi-harmo- crystal vibrations remain restricted to the quartz oscillator nic”. Near the quasi-harmonic there are center, one can clamp the outer edge to a also a number of anharmonics with a crystals crystal holder, without engendering unde- slightly higher frequency. sired side effects. Moreover, contouring Regardless of how sophisticated the elec- The design of the monitor crystals used reduces the resonance intensity of undesi- tronic environment is, the main compo- nowadays (see Fig. 6.3) displays a number red anharmonics. This limits the capacity nent for coating measurement remains the of significant improvements over the origi- of the resonator to maintain these oscilla- monitor quartz crystal. Originally monitor nal square crystals. The first improvement tions considerably. quartzes had a square shape. Fig. 6.4 was the use of round crystals. The enlar- shows the resonance spectrum of a quartz Use of an adhesive coating has enhanced ged symmetry greatly reduced the number resonator with the design used today (Fig. the adhesion of the quartz electrode. Even of possible oscillation modes. A second 6.3). The lowest resonance frequency is the rate spikes occurring with increasing group of improvements involved providing initially given by a thickness shear oscilla- film stress (strain) and caused by micro- one of the surfaces with a contour and tion, which is called the fundamental wave. tears in the coating were reduced. Coating making the excitation electrode smaller. material remains at these micro-tears without adhesion and therefore cannot oscillate. These open areas are not registered and thus an incorrect thickness is indicated. Fig. 6.4 shows the frequency behavior of a quartz crystal shaped as in Fig. 6.3. The ordinate represents the amplitude of the oscillation or also the current flowing through the crystal as a function of the frequency on the abscissa.

log Relative intensy Usually an AT cut is chosen for the coating thickness measurement because through the selection of the cut angle the frequency has a very small temperature coefficient D00 at room temperature. Frequency (MHz) Fig. 6.4 Frequency resonance spectrum Since one cannot distinguish between

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• coating: frequency reduction = negati- multaneously with the first and counts the 6.5 The Z match ve influence oscillations of the reference crystal during m oscillations of the monitor crystal. technique • temperature change: Because the reference frequency F is negative or positive influence r known and stable, the time for m monitor Miller and Bolef (1968) treated the quartz • temperature gradients on the crystal, oscillations can be determined accurately oscillator and coating system as a single- positive or negative to ± 2/Fr. The monitor oscillation period is dimensional, coherent acoustic resonator. then Lu and Lewis (1972) developed the simpli- • stresses caused by the coating fied Z match equation on that basis. Simul- n taneous advances in electronics, particu- it is important to minimize the temperatu- · Fr m larly the microprocessor, made it possible re influence. This is the only way to mea- to solve the Z match equation in real time. sure small differences in mass. where n is the reading of the reference Most coating process control units sold counter. The accuracy of the measurement today use this sophisticated equation, is determined by the frequency of the refe- which takes into account the acoustic pro- rence oscillator and the length of the coun- perties of the quartz oscillator/coating ting time that is specified through the size system: 6.4 Period of m.  N ⋅ d   π ⋅(F − F ) T =  AT q  ⋅ arctg Z ⋅ tg q c  For low coating rates, small densities of f π ⋅ ⋅ ⋅    measurement  df Fc Z   Fq  (6.4) the coating material and fast measure- Although the instruments that functioned ments (that require short counting times), according to equation 6.2 were very use- it is important to have a reference oscilla- ful, it soon became obvious that for the d ⋅U tor with a high frequency. All of this requi- Z = q q acoustic impedance ratio desired accuracy their area of application ⋅ res great time precision so that the small df U f was typically limited to ∆F < 0.02 F . Even q coating-related frequency shifts can be U = shear module, quartz at a relative frequency change of resolved. If the frequency shift of the mo- q U = shear module, film (Fq – Fc) / Fq < 2 %, errors of around 2 % nitor crystal decreases between two mea- f occurred in the coating thickness measu- surements on the order of magnitude of This led to basic understanding of the con- rement so that the "usable service life" of the frequency measurement accuracy, version of frequency shift into thickness the coating in the case of a 6-MHz monitor good rate regulation becomes impossible which enabled correct results in a practical crystal was about 120 kHz. (rate regulation: regulation of the energy time frame for process control. To achieve In 1961 Behrndt discovered that: supply to the coating source so that a spe- this high degree of accuracy, the user cified coating thickness growth per time must only enter an additional material Mf (Tc − Tq) ∆F = = with (6.3) unit is maintained). The great measure- parameter Z for the coating material. The Mq Tq Fc f ment uncertainty then causes more noise validity of the equation was confirmed for T = 1 / F ... oscillation period, coated in the closed loop, which can only be many materials and it applies to frequency c c countered with longer time constants. This ∆ T = 1 / F ... oscillation period, uncoated shifts up to F < 0.4 Fq! Note that equati- q q ∆ in turn makes the corrections due to on 6.2 was only valid up to F < 0.02 Fq. The period measurement (measurement of ∆ system deviation slow so that relatively And equation 6.3 only up to F < 0.05 Fq. the oscillation duration) was the result of long deviations from the desired rate the introduction of digital time measure- result. This may not be important for sim- ment and the discovery of the proportiona- ple coatings, but for critical coatings, as in lity of crystal thickness Dq and oscillation the case of optical filters or very thin, duration Tq. The necessary precision of slowly growing single-crystal coatings, 6.6 The active thickness measurement permits applicati- errors may result. In many cases, the desi- on of equation 6.3 up to about red properties of such coatings are lost if oscillator ∆ F < 0.05 Fq. the rate deviations are more than one or two percent. Finally, frequency and stabili- All units developed up to now are based on In period measurement a second crystal use of an active oscillator, as shown sche- oscillator is essentially used as a reference ty of the reference oscillator determine the precision of the measurement. matically in Fig. 6.5. This circuit keeps the oscillator that is not coated and usually crystal actively in resonance so that any oscillates at a much higher frequency than type of oscillation duration or frequency the monitor crystal. The reference oscilla- measurement can be carried out. In this tor generates small precision time inter- type of circuit the oscillation is maintained vals, with which the oscillation duration of as long as sufficient energy is provided by the monitor crystal is determined. This is the amplifier to compensate for losses in done by means of two pulse counters: the the crystal oscillation circuit and the first counts a fixed number of monitor crystal can effect the necessary phase oscillations m. The second is started si- shift. The basic stability of the crystal

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output phase amplifier

| impedance | ees) phase (degr log .Z. (Ohm) series resonance

crystal Frequency (MHz)

Fig. 6.5 Circuit of the active oscillator Fig. 6.6 Crystal frequencies near the series resonance point

oscillator is created through the sudden noise in the oscillator circuit leads to a lar- cantly smaller, i.e. by the amount of the phase change that takes place near the ger frequency shift than would be the case frequency difference between the funda- series resonance point even with a small with a new crystal. In extreme cases, the mental wave and the anharmonic adopted change in crystal frequency, see Fig. 6.6. original phase/frequency curve shape is by the oscillation. not retained; the crystal is not able to carry Normally an oscillator circuit is designed out a full 90° phase shift. such that the crystal requires a phase shift of 0 degrees to permit work at the series The impedance “Z” can increase to very resonance point. Long- and short-term high values. If this happens, the oscillator frequency stability are properties of crystal prefers to oscillate in resonance with an 6.7 The mode-lock oscillators because very small frequency anharmonic frequency. Sometimes this oscillator differences are needed to maintain the condition is met for only a short time and phase shift necessary for the oscillation. the oscillator oscillation jumps back and INFICON has developed a new technology The frequency stability is ensured through forth between a basic and an anharmonic for overcoming these constraints on the the quartz crystal, even if there are long- oscillation or it remains as an anharmonic active oscillator. The new system con- term shifts in the electrical values that are oscillation. This phenomenon is well stantly analyzes the response of the crystal caused by “phase jitter” due to temperatu- known as “mode hopping”. In addition to to an applied frequency: not only to deter- re, ageing or short-term noise. If mass is the noise of the rate signal created, this mine the (series) resonance frequency, but added to the crystal, its electrical pro- may also lead to incorrect termination of a also to ensure that the quartz oscillates in perties change. coating because of the phase jump. It is the desired mode. The new system is important here that, nevertheless, the con- Fig. 6.7 shows the same graph as Fig 6.6, insensitive to mode hopping and the resul- troller frequently continues to work under but for a thickly coated crystal. It has lost tant inaccuracy. It is fast and precise. The these conditions. Whether this has occur- the steep slope displayed in Fig. 6.6. crystal frequency is determined 10 times a red can only be ascertained by noting that Because the phase rise is less steep, any second with an accuracy to less than the coating thickness is suddenly signifi- 0.0005 Hz. The ability of the system to initially identify and then measure a certain mode opens up new opportunities thanks to the advantages of the additional information content of these modes. This new, “intelligent” measuring device makes use of the

phase ess) phase/frequency properties of the quartz crystal to determine the resonance fre- | impedance | quency. It works by applying a synthesized log .Z. (Ohm) sinus wave of a certain frequency to the phase (degr crystal and measuring the phase differen- series resonance ce between the applied signal voltage and the current flowing through the crystal. In the case of series resonance, this difference is exactly zero degrees; then the crystal D00 Frequency (MHz) behaves like an ohmic resistance. By dis- connecting the applied voltage and the Fig. 6.7 Oscillations of a thickly coated crystal current that returns from the crystal, one

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can determine with a phase comparator 1) The Z values of the solid material often cut on the position of the anharmonic in whether the applied frequency is higher or deviate from those of a coating. Thin relation to the fundamental oscillation. lower than the crystal resonance point. coatings are very sensitive to process If one side of the quartz is coated with parameters, especially in a sputter envi- The crystal impedance is capacitive at fre- material, the spectrum of the resonances ronment. As a result, the existing values quencies below the fundamental wave and is shifted to lower frequencies. It has been for solid material are not adequate. inductive at frequencies above the reso- observed that the three above mentioned nance. This information is useful if the 2) For many exotic substances, including modes have a somewhat differing mass resonance frequency of a crystal is unkno- alloys, the Z value is not known and not sensitivity and thus experience somewhat wn. A brief frequency sweep is carried out easy to determine. different frequency shifts. This difference until the phase comparator changes over is utilized to determine the Z value of the 3) It is repeatedly necessary to carry out a and thus marks the resonance. For AT material. By using the equations for the precise coating thickness measurement quartzes we know that the lowest usable individual modes and observing the fre- for multiple coating with the same frequency is the fundamental wave. The quencies for the (100) and the (102) crystal sensor. This applies in particular anharmonics are slightly above that. This mode, one can calculate the ratio of the to optical multiple and semi-conductor information is not only important for the two elastic constants C60 and C55. These coatings with a high temperature coeffi- beginning, but also in the rare case that the two elastic constants are based on the cient T . However, the effective Z value instrument loses “track” of the fundamen- C shear motion. The key element in Wajid’s of the mixture of multiple coatings is tal wave. Once the frequency spectrum of theory is the following equation: unknown. the crystal is determined, the instrument In such a case, therefore, the only effective (C55 /C66)coated 1 must track the shift in resonance frequen- ≈ (6.5) cy, constantly carry out frequency measu- method is to assume a Z value of 1, i.e. to (C55 /C66)uncoated (1+ M⋅ Z ) rements and then convert them into ignore reality with respect to wave propa- thickness. gation in multi-substance systems. This with incorrect assumption causes errors in the Use of the “intelligent” measuring system M ... area mass/density ratio (ratio of coa- prediction of thickness and rate. The ting mass to quartz mass per area has a number of obvious advantages over magnitude of the error depends on the the earlier generation of active oscillators, unit) coating thickness and the amount of devia- Z ... Z value primarily insensitivity to mode hopping as tion from the actual Z value. well as speed and accuracy of measure- It is a fortunate coincidence that the pro- ment. This technique also enables the In 1989 A. Wajid invented the mode-lock duct M π Z also appears in the Lu-Lewis introduction of sophisticated properties oscillator. He presumed that a connection equation (equation 6.4). It can be used to which were not even conceivable with an existed between the fundamental wave and assess the effective Z value from the follo- active oscillator setup. The same device one of the anharmonics, similar to that wing equations: that permits the new technology to identify ascertained by Benes between the funda-     the fundamental wave with one sweep can mental oscillation and the third quasi-har- Fc Fc tg M⋅ Z ⋅π ⋅  + Z ⋅ tg π ⋅  = 0 (6.6) also be used to identify other oscillation monic oscillation. The frequencies of the  Fq  Fq modes, such as the anharmonics or quasi- fundamental and the anharmonic oscillati- harmonics. The unit not only has a device ons are very similar and they solve the or for constantly tracking the fundamental problem of the capacity of long cables. He   Fc found the necessary considerations for tg  M⋅ Z ⋅π ⋅  wave, but can also be employed to jump  F  establishing this connection in works by Z = − q back and forth between two or more   Wilson (1954) as well as Tiersten and Fc modes. This query of different modes can tg π ⋅  take place for two modes with 10 Hz on the Smythe (1979).  Fq same crystal. The contour of the crystal, i.e. the spheri- cal shape of one side, has the effect of Here Fq and Fc are the frequencies of the separating the individual modes further non-coated or coated quartz in the (100) from each other and preventing energy mode of the fundamental wave. Because of transfer from one mode to another. The the ambiguity of the mathematical func- 6.8 Auto Z match usual method of identification is to desig- tions used, the Z value calculated in this nate the fundamental oscillation as (100), way is not always a positively defined technique the lowest anharmonic frequency as (102) variable. This has no consequences of any and the next higher anharmonic as (120). significance because M is determined in The only catch in the use of equation 6.4 is These three indices of the mode nomen- another way by assessing Z and measuring that the acoustic impedance must be clature are based on the number of phase the frequency shift. Therefore, the thickn- known. There are a number of cases where reversals in the wave motion along the ess and rate of the coating are calculated a compromise has to be made with accu- three crystal axes. The above mentioned one after the other from the known M. racy due to incomplete or restricted know- works by Wilson, Tiersten and Smythe One must be aware of the limits of this ledge of the material constants of the coa- examine the properties of the modes by technique. Since the assessment of Z ting material: studying the influence of the radius of the depends on frequency shifts of two mo-

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des, any minimal shift leads to errors due The most widespread type of controller is used for the setting, a distinction is made to substantial mechanical or thermal stres- the PID controller. Here P stands for pro- between the closed loop, open loop and ses. It is not necessary to mention that portional, I for integral and D for differen- resonance response method. under such circumstances the Z match tial control function. In the following some Due to the simplicity with which the expe- technique, too, leads to similar errors. of the properties of this controller are rimental data can be obtained, we prefer- Nevertheless, the automatic Z value deter- described in detail. Information on the red the open loop method. Moreover, mination of the Z match technique is system behavior is gained through a step application of this technique permits somewhat more reliable regarding occur- response to a control fault in certain con- extensive elimination of the trial and error rence of errors because the amplitude dis- troller settings. method. tribution of the (102) mode is asymmetric This response is recorded, and then over the active crystal surface and that of The Auto Control Tune function developed improved control parameters for a new the (100) mode is symmetric. by Inficon characterizes a process on the test are estimated. This procedure is con- basis of its step responses. After a step-by- According to our experience, coating-rela- tinued until a satisfactory result is achie- step change in the power the resulting ted stresses have the most unfavorable ved. At the end the controller is optimized changes in the rate as a function of time are effect on the crystal. This effect is particu- so that its parameters exactly match the smoothed and stored. The important step larly pronounced in the presence of gas, characteristics of the evaporator source. responses are determined, see Fig. 6.8. e.g. in sputter processes or reactive vacu- It is a long and frustrating process to um coating or sputter processes. If the Z In general, it is not possible to characteri- adjust a controller to an evaporation sour- value for solid material is known, it is bet- ze all processes exactly, so several appro- ce, requiring several minutes for stabiliza- ter to use it than to carry out automatic ximations have to be made. Normally one tion and hours to obtain satisfactory determination of the “auto Z ratio”. In assumes that the dynamic characteristic results. Often the parameters selected for cases of parallel coating and coating can be reproduced by a process of the first a certain rate are not suitable for an altered sequences, however, automatic Z determi- order plus dead time. The Laplace trans- rate. Thus, a controller should ideally nation is significantly better. formation for this assumption (transfer to adjust itself, as the new controllers in the s plane) is approximated: INFICON coating measuring units do. At the beginning of installation and connec- −L Output K ⋅10 s tion the user has the unit measure the cha- = p with (6.8) racteristics of the evaporation source. Input τ ⋅ s +1 6.9 Coating thickness Either a PID controller is used as the basis regulation for slow sources or another type of con- Kp = amplification in stationary state troller for fast sources without significant L = dead time τ The last point to be treated here is the dead time. = time constant theory of the closed loop for coating In relevant literature a distinction is made These three parameters are determined thickness measuring units to effect coating between three different ways of setting through the response curve of the pro- growth at a controlled (constant) growth controllers. Depending on which data are cess. An attempt has been made by means rate. The measuring advantages of the instruments, such as speed, precision and reliability, would not be completely exploi- ted if this information were not inputted into an improved process monitoring 1.00 Kp system. For a coating process this means the coating rate should be kept as close and stable as possible to a setpoint. The purpose of the closed loop is to make use 0.0632 Kp of the information flow of the measuring point of system in order to regulate the capacity for maximum rise a special evaporation source in an appropriately adapted way. When the system functions correctly, the controller transla- tes small deviations of the controlled para- 0 t(0.632) Time t meter (the rate) from the setpoint into cor- L rection values of the re-adjusted evaporation capacity parameter. The ability of the

controller to measure quickly and precise- T 1 = t(0.632) – L ly keeps the process from deviating signi- K = (change in output signal)/(change in control signal) p D00 ficantly from the setpoint.

Fig. 6.8 Process response to a step change with t = 0 (open loop, control signal amplified)

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amplification Kp, time constant T1 and setpoint deviation –L precipitation rate dead time L) are used to generate the most R(s) + E(s) K · eaaas C(s) s p appropriate PID control parameters. (Σ) Kc (1 + + T d * s) T T1s + 1 – i The best results in evaluating coating control units are achieved with ITAE. There are [process] [controller] overshoots, but the reaction is fast and the ripple time short. Controller setting condi- Fig. 6.9 Block diagram of the PID controller tions have been worked up for all integral evaluation criteria just mentioned so as to of several methods to calculate the requi- setpoint minus measured rate. ISE is rela- minimize the related deviations. With a red parameters of the system response tively insensitive to small deviations, but manual input as well as with experimental from curves, as shown in Fig. 6.8. This large deviations contribute substantially to determination of the process response results in a 1-point accordance at 63.2 % the value of the integral. The result is small coefficients, the ideal PID coefficients for of the transition (a time constant), an “overshoots”, but long ripple times becau- the ITAE evaluation can easily be calcula- exponential accordance at two points and se deviations occurring late contribute litt- ted from equations 6.13, 6.14 and 6.15: an exponential accordance weighted le to the integral.    –0.947 according to the method of the smallest 1.36 L The integral of the absolute value of the Kc =   ⋅  (6.13) squares. A process is sufficiently characte-  K   T  deviation IAE (Integral Absolute Error) p 1 rized by this information so that the con- was also proposed as a measure for controller algorithm can be applied. Equation 0.738 trol quality: 1.19  L 6.9 shows the Laplace transformation for T =   ⋅  i     (6.14) the very often used PID controller: T1 T1 IAE = ∫ e(t) ⋅ dt (6.11)  S  0.995 M(s) = Kc· 1+ +T · S · E(s) (6.9)  L  T d  This is more sensitive for small deviations, T = (0.381⋅T )⋅  i d 1  T  (6.15) but less sensitive for large deviations than 1 with ISE. For slow systems the time interval bet- M(s)= controlled variable or power Graham and Lanthrop introduced the inte- ween the forced changes in control voltage Kc = Control amplification gral over time, multiplied by the absolute is extended to avoid “hanging” the control- (the proportional term) error ITAE (Integral Time Absolute Error), ler (hanging = rapid growth of the control Ti = integration time as a measure for control quality: signal without the system being able to respond to the altered signal). This makes Td = differentiation time ITAE = ∫ t ⋅ e(t) ⋅dt (6.12) a response to the previous change in the E(s) = process deviation controller setting and “powerful” control- Fig. 6.9 shows the control algorithm and a The ITAE is sensitive to initial and, to a ler settings possible. Another advantage is process with a phase shift of the first order certain extent, unavoidable deviations. the greater insensitivity to process noise and a dead time. The dynamics of the mea- Optimum control responses defined because the data used for control do not suring device and the control elements (in through ITAE consequently have short come from merely one measurement, but our case the evaporator and the power response times and larger “overshoots” from several, so that the mass-integrating supply) are implicitly contained in the pro- than in the case of the other two criteria. nature of the quartz crystal is utilized. cess block. R(s) represents the rate set- However, ITAE has proven to be very use- In processes with short response times point. The return mechanism is the devia- ful for evaluating the regulation of coating (short time constants) and small to tion created between the measured preci- processes. unmeasurable dead times, the PID control- pitation rate C(s) and the rate setpoint INFICON’S Auto Control Tune is based on ler often has difficulties with the noise of R(s). measurements of the system response the coating process (beam deflection, The key to use of any control system is to with an open loop. The characteristic of rapid thermal short-circuits between melt select the correct values for Kc, Td and Ti. the system response is calculated on the and evaporator, etc.). In these cases a con- The “optimum control” is a somewhat basis of a step change in the control sig- trol algorithm of the integral reset type is subjective term that is made clear by the nal. It is determined experimentally used with success. This controller always presence of different mathematical defini- through two kinds of curve accordance at integrates the deviation and presses the tions: two points. This can be done either quick- system towards zero deviation. This tech- Usually the smallest square error ISE ly with a random rate or more precisely nique works well with small or completely (Integral Square Error) is used as a mea- with a rate close to the desired setpoint. imperceptible dead times. However, if it is sure of the quality of the control: Since the process response depends on used with a noticeable phase shift or dead the position of the system (in our case the time, the controller tends to generate 2 ISE = ∫e (t)⋅ dt (6.10) coating growth rate), it is best measured oscillations because it overcompensates near the desired work point. The process the controller signal before the system has Here e is the error (the deviation): e = rate information measured in this way (process a chance to respond. Auto Control Tune

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recognizes the properties of these fast systems during the measurement of a step response and utilizes the information to calculate the control amplification for a non-PID control algorithm.

6.10 INFICON instrument variants The instrument models available differ both in hardware and software equipment: the simplest unit, the XTM/2, is purely a measuring or display device that cannot control vacuum coating. The XTC/2 and XTC/C group can control vacuum coating sources and up to three different coatings of a process (not to be confused with nine different coating programs). In the case of XTM/2, XTC/2 and XTC/C units, the AutoZero and AutoTune functions are not available, and measurement with several sensors simultaneously as well as simultaneous control of two vacuum coating sources are not possible. However, the IC/5 offers all comfort functions available today: measurement with up to eight sensors with AutoZero and AutoTune as well as capability of simultaneous control of two evaporator sources. Moreover, it offers 24 material programs, with which 250 coatings in 50 processes can be programmed. To simplify operation and avoid errors, the unit also has a dis- kette drive. All types of crystal holders can be connected here. The thickness resolution is around 1 Å, the rate resolution for rates between 0 and 99.9 Å/s around 0.1 Å/s and for rates between 100 and 999 Å/s around 1 Å/s. A particularly attractive option offered by the IC/5 is a microbalance board with a highly stable reference quartz. This oscillator is 50 times more stable than the standard oscillator; long- term stability and accuracy are then 2 ppm over the entire temperature range. This option is specially designed for coatings of material with low density and at low coating rates. This is important for space contamination and sorption studies, for example. D00

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produce conductive coatings for film capa- 7.2 Coating sources 7. Application of citors. Polymer layers on metals enhance vacuum the corrosion resistance of the substrate. In all vacuum coating methods layers are Through the use of vacuum it is possible formed by deposition of material from the technology for to create coatings with a high degree of gas phase. The coating material may be uniform thickness ranging from several formed by physical processes such as eva- coating nanometers to more than 100 mm while poration and sputtering, or by chemical still achieving very good reproducibility of reaction. Therefore, a distinction is made techniques the coating properties. Flat substrates, between physical and chemical vapor web and strip, as well as complex molded- deposition: plastic parts can be coated with virtually • physical vapor deposition = PVD no restrictions as to the substrate materi- • 7.1 Vacuum coating al. For example, metals, alloys, glass, cera- chemical vapor deposition = CVD. technique mics, plastics and paper can be coated. The variety of coating materials is also Vacuum technology has been increasingly very large. In addition to metal and alloy used in industrial production processes coatings, layers may be produced from during the last two decades. Some of various chemical compounds or layers of 7.2.1 Thermal evaporators these processes and their typical working different materials applied in sandwich (boats, wires etc.) form. A significant advantage of vacuum pressure ranges are shown in Fig. 7.1. In the evaporation process the material to coating over other methods is that many be deposited is heated to a temperature Since a discussion of all processes is special coating properties desired, such as high enough to reach a sufficiently high beyond the scope of this brochure, this structure, hardness, electrical conductivity vapor pressure and the desired evaporati- section will be restricted to a discussion of or refractive index, are obtained merely by on or condensation rate is set. The sim- several examples of applications in the selecting a specific coating method and plest sources used in evaporation consist important field of coating technology. the process paramaters for a certain coa- of wire filaments, boats of sheet metal or ting material. Deposition of thin films is used to change electrically conductive ceramics that are the surface properties of the base material, heated by passing an electrical current the substrate. For example, optical pro- through them (Fig. 7.2). However, there perties such as transmission or reflection are restrictions regarding the type of mate- of lenses and other glass products, can be rial to be heated. In some cases it is not adjusted by applying suitable coating layer possible to achieve the necessary evapora- systems. Metal coatings on plastic web

Ultrahigh vacuum High vacuum Medium vacuum Rough vacuum

Annealing of metals

Degassing of melts

Electron beam melting

Electron beam welding

Evaporation

Sputtering of metals

Casting of resins and lacquers

Drying of plastics

Drying of insulating papers

Freeze-drying of bulk goods

Freeze-drying of pharmaceutical products

10–10 10–7 10–3 100 103

Pressure [mbar]

Fig. 7.1 Pressure ranges for various industrial processes

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Hairpin-shaped evaporator made of Evaporator made of twisted tungsten wire electrically conductive 6 ceramics 5 7 4 Spiral evaporator made of twisted tung- Boat-shaped sten wire 8 evaporator 3

Trough-shaped Evaporator evaporator 1 9 with ceramic insert

1 Substrates 6 Cathode 2 Sputtered 7 Magnetic atoms field lines 3 Anode 8 Argon ions Trough-shaped 4 Electrons 9 Substrate evaporator with Basket-shaped 5 Target ceramic coating evaporator

Fig. 7.2 Various thermal evaporators Fig. 7.3 Schematic diagram of a high-performance cathode sputter arrangement

tor temperatures without significantly eva- 7.2.3 Cathode sputtering 7.2.4 Chemical vapor porating the source holder and thus con- deposition taminating the coating. Furthermore che- In the cathode sputtering process, the tar- mical reactions between the holder and the get, a solid, is bombarded with high ener- In contrast to PVD methods, where the material to be evaporated can occur resul- gy ions in a gas discharge (Fig. 7.3). The substance to be deposited is either solid or ting in either a reduction of the lifetime of impinging ions transfer their momentum liquid, in chemical vapor deposition the the evaporator or contamination of the to the atoms in the target material, substance is already in the vapor phase coating. knocking them off. These displaced atoms when admitted to the vacuum system. To – the sputtered particles – condense on deposit it, the substance must be thermal- the substrate facing the target. Compared ly excited, i.e. by means of appropriate to evaporated particles, sputtered particles high temperatures or with a plasma. Gene- 7.2.2 Electron beam have considerably higher kinetic energy. rally, in this type of process, a large num- Therefore, the conditions for condensation evaporators ber of chemical reactions take place, some and layer growth are very different in the of which are taken advantage of to control (electron guns) two processes. Sputtered layers usually the desired composition and properties of have higher adhesive strength and a den- To evaporate coating material using an the coating. For example, using silicon- ser coating structure than evaporated electron beam gun, the material, which is hydrogen monomers, soft Si-H polymer ones. Sputter cathodes are available in kept in a water-cooled crucible, is bombar- coatings, hard silicon coatings or – by many different geometric shapes and sizes ded by a focused electron beam and there- addition of oxygen – quartz coatings can as well as electrical circuits configurations. by heated. Since the crucible remains cold, be created by controlling process parame- What all sputter cathodes have in common in principle, contamination of the coating ters. is a large particle source area compared to by crucible material is avoided and a high evaporators and the capability to coat large degree of coating purity is achieved. With substrates with a high degree of uniformi- the focused electron beam, very high tem- ty. In this type of process metals, alloys of peratures of the material to be evaporated any composition as well as oxides can be can be obtained and thus very high evapo- used as coating materials. ration rates. Consequently, high-melting point compounds such as oxides can be evaporated in addition to metals and alloys. By changing the power of the elec- D00 tron beam the evaporation rate is easily and rapidly controlled.

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7.3 Vacuum coating in the plasma and deposits on the substra- turbomolecular pumps and backing pump tes as a polymer coating. In this type of sets consisting of Roots and rotary vane technology/ system there may be plastic substrates pumps. with a surface area of several 10 m2 on the coating systems cage, causing a correspondingly high desorption gas flow. The vacuum system must be able to attain the required pressu- 7.3.2 Web coating 7.3.1 Coating of parts res reliably despite these high gas loads. In the example shown, the system is eva- Metal-coated plastic webs and papers play For molded-plastic parts, vacuum coating cuated with a combination of a backing an important role in food packaging. They techniques are increasingly replacing con- and Roots pump. A diffusion pump along preserve food longer according to storage ventional coating methods, such as elec- with a cold surface forms the high vacuum and transport logistics requirements and troplating. For example, using vacuum pump system. The cold surfaces pump a give packaging an attractive appearence. coating methods, automobile reflectors large portion of the vapor and volatile sub- Another important area of application of obtain a mirror-like surface, plastic articles stances emitted by the plastic parts while metal-coated web is the production of film in the furniture, decoration, clock and the diffusion pump basically removes the capacitors for electrical and electronics watch as well as electronics industry are non-condensable gases as well as the applications. Metal-coating is carried out metal-coated and optical effects are crea- noble gas required for the sputter process. in vacuum web coating systems. Fig. 7.6 ted on articles in the decoration industry. shows a typical scheme. The unit consists A completely different concept for the of two chambers, the winding chamber Fig. 7.4 shows a type of vacuum system in same process steps is shown in Fig. 7.5. with the roll of web to be coated and the which large batches of molded-plastic The system consists of four separate stati- winding system, as well as the coating parts can be coated simultaneously. The ons made up of a drum rotating around the chamber, where the evaporators are loca- substrates are placed on a cage that rota- vertical axis with four substrate chambers ted. The two chambers are sealed from tes past the coating source, a sputter and process stations mounted in the vacu- each other, except for two slits through cathode in this example. In some applica- um chamber. During rotation, a substrate which the web runs. This makes it possible tions, by using a glow discharge treat- chamber moves from the loading and to pump high gas loads from the web roll ment, the substrates are cleaned and the unloading station to the pretreatment sta- using a relatively small pumping set. The surface is activated prior to the coating tion, to the metallization station, to the pressure in the winding chamber may be process. This enhances the adhesive protective coating station and then back to more than a factor of 100 higher than the strength and reproducibility of the coating the initial position. Since each station has pressure simultaneously established in the properties. A corrosion protection coating its own pumping system, all four proces- coating chamber. The pump set for the can be applied after sputtering. In this ses can run simultaneously with entirely winding chamber usually consists of a case, a monomer vapor is admitted into independent adjustable process parame- combination of Roots and rotary vane the system and a high-frequency plasma ters. The vacuum system comprises of discharge ignited. The monomer is actived pumps.

1 Vacuum chamber 7 Rotary piston pump 2 High-performance cathode 8 Cold trap 3 Substrate holder 9 High vacuum valve 4 Substrates 10 Valve for bypass line 5 Diffusion pump 11 Foreline valve 6 Roots pump 12 Venting valve Fig. 7.5 Multi-chamber parts-coating unit (rotationally symmetric in-line system Fig. 7.4 Diagramm of a batch system for coating parts DynaMet 4V)

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With strongly degassing rolls of paper, it 7.3.3 Optical coatings periods of time. This requires to produce may be necessary to install a cold surface the densest coatings possible, into which in the winding chamber to act as a water Vacuum coatings have a broad range of neither oxygen nor water can penetrate. vapor pump. The rolls of the plastic web or applications in production of ophthalmic Using glass lenses, this is achieved by paper typically have diameters between optics, lenses for cameras and other opti- keeping the substrates at temperatures up 400 and 1000 mm and a width of 400 to cal instruments as well as a wide variety of to 300 °C during coating by means of 3000 mm. A precise, electronically con- optical filters and special mirrors. To radiation heaters. However, plastic lenses, trolled winding system is required for win- obtain the desired transmission or reflec- as those used in eyeglass optics, are not ding and unwinding as well as web gui- tion properties, at least three, but someti- allowed to be heated above 80 °C. To dance. mes up to 50 coatings are applied to the obtain dense, stable coatings these sub- glass or plastic substrates. The coating strates are bombarded with Ar ions from During the coating process the web, at a properties, such as thickness and refrac- an ion source during coating. Through the speed of more than 10 m/s, passes a group tive index of the individual coatings, must ion bombardement the right amount of of evaporators consisting of ceramic boats, be controlled very precisely and matched energy is applied to the growing layer so from which aluminium is evaporated. To to each other. Most of these coatings are that the coated particles are arranged on achieve the necessary Al-coating thickness produced using electron beam evapora- the energetically most favorable lattice at these high web speeds, very high evapo- tors in single-chamber units (Fig. 7.7). The sites, without the substrate temperature ration rates are required. The evaporators evaporators are installed at the bottom of reaching unacceptably high values. At the must be run at temperatures in excess of the chamber, usually with automatically same time oxygen can be added to the 1400 °C. The thermal radiation of the eva- operated crucibles, in which there are argon. The resulting oxygen ions are very porators, together with the heat of conden- several different materials. The substrates reactive and ensure that the oxygen is sation of the growing layer, yields a consi- are mounted on a rotating calotte above included in the growing layer as desired. derable thermal load for the web. With the the evaporators. Application of suitable help of cooled rollers, the foil is cooled shieldings combined with relative move- The vacuum system of such a coating unit during and after coating so that it is not ment between evaporators and substrates, usually consists of a backing pump set damaged during coating and has cooled results in a very high degree of coating comprising a rotary vane pump and Roots down sufficiently prior to winding. uniformity. With the help of quartz coating pump as well as a high vacuum pumping system. Depending on the requirements, During the entire coating process the coa- thickness monitors (see Section 6) and diffusion pumps, cryo pumps or turbo- ting thickness is continuously monitored direct measurement of the attained optical molecular pumps are used here, in most with an optical measuring system or by properties of the coating system during cases in connection with large refrigerator- means of electrical resistance measure- coating, the coating process is fully con- cooled cold surfaces. The pumps must be ment devices. The measured values are trolled automatically. installed and protected by shieldings in a compared with the coating thickness set- One of the key requirements of coatings is way that no coating material can enter the points in the system and the evaporator that they retain their properties under pumps and the heaters in the system do power is thus automatically controlled. usual ambient conditions over long

High-performance plasma source Electron beam evaporator

1 Unwinder 4 Drawing roller Monomer O 2 Coating source 5 Take-up reel 2 D00 3 Coating roller Ar Fig. 7.6 Schematic diagram of a vacuum web coating system Fig. 7.7 Coating unit for optical coating systems

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not thermally overload them. Since shiel- with oxygen, the individual process stati- required. It is provided by combinations of ding always reduces the effective pumping ons have to be vacuum-isolated from each rotary vane pumps and Roots pumps. For speed, the system manufacturer must find other and from the transfer stations. Uti- particularly short cycle times gas cooled a suitable compromise between shielding lization of valves for separating process Roots pumps are also used. effect and reduction of pumping speed. chambers is unsatisfactory because it All major functions of a plant, such as increases plant dimensions. To avoid fre- glass transport, control of the sputter pro- quent and undesirable starting and stop- cesses and pump control, are carried out ping of the glass panes, the process cham- fully automatically. This is the only way to bers are vacuum-separated through so- ensure high productivity along with high called “slit locks”, i.e. constantly open slits 7.3.4 Glass coating product quality. combined with an intermediate chamber Coated glass plays a major role in a num- with its own vacuum pump (Fig. 7.9). The ber of applications: window panes in gaps in the slits are kept as small as tech- moderate and cold climate zones are pro- nically possible to minimize clearance and vided with heat-reflecting coating systems therefore conductance as the glass panes to lower heating costs; in countries with are transported through them. The pum- 7.3.5 Systems for producing high intensity solar radiation, solar protec- ping speed at the intermediate chamber is data storage disks tion coatings are used that reduce air kept as high as possible in order to achie- Coatings for magnetic- or magneto-optic conditioning costs; coated car windows ve a considerably lower pressure in the reduce the heating-up of the interior and data storage media usually consist of intermediate chamber than in the process several functional coatings that are applied mirrors are used both in the furniture and chambers. This lower pressure greatly the automobile industry. Most of these to mechanically finished disks. If several reduces the gas flow from a process plates are placed on one common carrier, coatings are produced in large in-line chamber via the intermediate chamber to vacuum systems. Fig. 7.8 shows a typical the coating processes can be carried out in the adjacent process chamber. For very a system using a similar principle to that system. The individual glass panes are stringent separation requirements it may transported into a entrance chamber at used for glass coating. However, most be necessary to place several intermediate disks must be coated on both sides and atmospheric pressure. After the entrance chambers between two process chambers. valve is closed, the chamber is evacuated there are substantially greater low particle with a forepump set. As soon as the pres- The glass coating process requires high contamination requirements as compared sure is low enough, the valve to the eva- gas flows for the sputter processes as well to glass coating. Therefore, in-line cuated transfer chamber can be opened. as low hydrocarbon concentration. The systems for data memories use a vertical The glass pane is moved into the transfer only vacuum pump which satisfies these carrier that runs through the system (Fig. chamber and from there at constant speed requirements as well as high pumping 7.10). The sputter cathodes in the process to the process chambers, where coating is speed stability over time are turbo-mole- stations are mounted on both sides of the carried out by means of sputter cathodes. cular pumps which are used almost exclu- carrier so that the front and back side of On the exit side there is, in analogy to the sively. the disk can be coated simultaneously. entrance side, a transfer chamber in which While the transfer and process chambers An entirely different concept is applied for the pane is parked until it can be transfer- are constantly evacuated, the entrance and coating of single disks. In this case the dif- red out through the exit chamber. exit chambers must be periodically vented ferent process stations are arranged in a Most of the coatings consist of a stack of and then evacuated again. Due to the large circle in a vacuum chamber (Fig. 7.11). alternative layers of metal and oxide. Since volumes of these chambers and the short The disks are transferred individually from the metal layers may not be contaminated cycle times, a high pumping speed is a magazine to a star-shaped transport arm.

Process chamber Intermediate chamber Process chamber 1 2

L1Z LZ2 ← Slits →

to backing pumps

S1 SZ S2

Entrance chamber Transfer chamber 2 Exit chamber Transfer chamber 1 Sputter chambers

L1Z, LZ2 = conductance between intermediate chamber and process chamber 1 or 2 SZ = pumping speed at intermediate chamber S , S = pumping speed at process chamber 1 or 2 Fig. 7.8 Plant for coating glass panes – 3-chamber in-line system, throughput up to 1 2 3,600,000 m2 / year Fig. 7.9 Principle of chamber separation through pressure stages

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The transport arm cycles one station furt- rated from each other by closing seals. dual processes can be achieved. However, her after each process step and in this way Each station is pumped by means of its since the slowest process step determines transports the substrates from one pro- own turbomolecular pump and the indivi- the cycle interval, two process stations cess station to the next. During cycling all dual processes are started. As many pro- may have to be dedicated for particularly processes are switched off and the stati- cess stations as there are in the system as timeconsuming processes. ons are vacuum-linked to each other. As many processes can be performed in par- soon as the arm has reached the process allel. By sealing off the process stations, position, the individual stations are sepe- excellent vacuum separation of the indivi-

Fig. 7.10 Plant for coating data storage disks with carrier transport system

Fig. 7.11 Plant for individual coating of data storage disks D00

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Fundamentals of Vacuum Technology Instruction for Equipment Operation

8.2 Contamination of unsuitable in all cases) will have to be used 8. Instructions for for cleaning. Maximum cleanliness can be vacuum vessels achieved with vapor baths such as those vacuum equip- commonly found in industry. If one desires and eliminating to get down to extremely low pressure ran- ment operation contamination ges (< 10-7 mbar), then – after cleaning – the metal components will have to be baked In addition to the pressure rise method out at temperatures of up to 200 °C. 8.1 Causes of faults (Section 6.1) there is a further method for Seriously contaminated metal components detecting contamination, based on the fact will first have to be cleaned by cutting away where the desired that condensable vapors will generally or sandblasting the top surface. These account for the major share of the gas mix methods suffer the disadvantage that the ultimate pressure in dirty vessels: here the pressure reading surface area for the surface thus treated is not achieved or at a compression vacuum gauge (partial will be increased through roughening and pressure for the non-condensable gases) is active centers may potentially be formed is achieved too compared with that at an electrical vacuum which would readily adsorb vapor molecu- slowly gauge, e.g. a thermal conductivity or les. Supplementary cleaning in the vapor ionization vacuum gauge (measuring total bath (see above) is advisable. In some If the desired ultimate pressure is not rea- pressure). These two vacuum gauges cases electrolytic pickling of the surface ched at all in vacuum equipment or if it is must, however, be clean themselves. may be beneficial. In the case of high vacu- attained only after an excessively long Where vapors are present the compression um components it is necessary to pay pumping period, then the following pro- vacuum gauge will indicate much better attention to ensuring that the pickling does blems may be the reason: pressure than the electrical vacuum gauge. not turn into etching, which would serious- If the desired ultimate pressure is not reached, This is a sure sign that the vessel walls are ly increase the surface area. Polishing sur- then contaminated, usually with oil. Another faces which have been sandblasted is not commonly used procedure is to compare necessary when working in the rough and • the apparatus may be leaky or dirty, the pressure indication of one and the medium vacuum ranges since the surface same vacuum gauge (not a compression • the pump may dirty or damaged, plays only a subordinate role in these pres- vacuum gauge) with and without a cold sure regimes. • the vacuum gauge may be defective. trap inserted in the line: Filling the cold trap with liquid nitrogen will cause the pressure If the desired ultimate pressure is reached to drop abruptly, by one power of ten or only after a very long running time, then more, if the container is contaminated 8.3 General operating • since the vapors will freeze out in the trap. the apparatus may be dirty, information for • the pumping line may be restricted, Eliminating contamination for glass vacuum pumps • the pump may be dirty or of too small a equipment capacity, If the contaminants exhibit a high vapor If no defects are found in the vacuum ves- pressure, then they can be pumped out sels and at the measurement tubes or if • the pumping speed may be restricted relatively quickly. If this is not successful, the apparatus still does not operate satis- due to other causes. then the apparatus will have to be cleaned. factorily after the faults have been rec- In order to locate the fault, one normally Contaminated glass components will first tified, then one should first check the flan- proceeds by separating the evacuated ves- be cleaned with chromic-sulfuric acid mix- ge seals at the pump end of the system sel from the pump system (where this is ture or – if this is necessary – with dilute and possibly the shut-off valve. Flange possible) and checking the vessel alone for hydrofluoric acid (1:30). They are then rin- seals are known to be places at which leaks and contamination using the pressu- sed with distilled water. If this does not leaks can appear the most easily, resulting re rise method, for example. If it has been bring about the desired results, then an from slight scratches and mechanical found that the vessel is free of defects in organic solvent can be tried. Then the damage which initially appears insignifi- this regard, then the measurement system glass components will again have to be cant. If no defect can be discerned here, will be checked for cleanliness (see Sec- rinsed with methanol and distilled water. either, then it is advisable to check to see tion 8.38) and ultimately – if required – the (Do not use denatured alcohol!) whether the pumps have been maintained pump or the pumping system itself will be in accordance with the operating instruc- examined. Eliminating contamination at metallic tions. equipment Metal components will usually exhibit Given initially in this section are general traces of contamination by oil and greases. instructions on pump maintenance, to be If these cannot be readily removed by pum- followed in order to avoid such defects ping down the vessel, then an appropriate from the very outset. In addition, potential organic solvent (denatured alcohol is errors and their causes are discussed.

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8.3.1 Oil-sealed rotary vacuum the minimum level. During a pumping pro- extent of which will depend on the size of pumps cess oil-sealed rotary pumps will emit oil the pump and the nature of the operations. (Rotary vane pumps and vapors from the discharge port, this being In the worst case this can amount to about due to the high operating temperature. 2 cm3 for every cubic meter of air pumped rotary piston pumps) This leads to oil loss to an extent which (at STP and including the gas ballast also will depend on the quantity of gas or vapor drawn in). Figure 8.1 makes it possible to which is drawn into the pump. Larger oil predict the amount of oil loss to be expec- 8.3.1.1 Oil consumption, oil droplets can be retained by installing a ted in practical situations. The example contamination, oil change coarse separator in the discharge line. This demonstrates that greater oil losses must The oil serves to: will reduce oil loss considerably. The fine be expected when operating the pump with • lubricate moving parts, oil mist filter installed in some pumps will gas ballast. This situation, which is gene- • seal moving parts against atmospheric also retain the finest oil droplets (fine rally valid, is always to be taken into pressure, separation) so that no oil at all will leave account in practice. • seal the valve, the outlet of the pump and oil loss is redu- If the pump oil has become unusabledue • fill the dead space below the valve, ced practically to zero since – as in coarse to exposure to the vapors or contaminants separation – the oil which is separated out • to seal the various operational spaces which are encountered in the process, is returned to the pump. With pumps with- one from another. then the oil will have to be replaced. It is out an integral fine separator this device is impossible to formulate any hard-and-fast In all pumps it is possible to check the oil offered as an optional extra. rules as to when an oil change will be charge during operation using the built-in If an oil-filled rotary pump is operated required since the nature of the operations oil level sight glass. During continuous without an oil separation and return devi- will determine how long the oil will remain operation in particular it is necessary to ce, then it will be necessary to expect a good. Under clean conditions (e.g. backing ensure that the oil charge never falls below certain amount of oil consumption, the pumps for diffusion pumps in electro- nuclear accelerators) rotary vacuum pumps can run for years without an oil change. Under extremely “dirty” conditions (e.g. during impregnation) it may be necessary to change the oil daily. The oil will have to be replaced when its original light brown color, has turned dark brown or black due to ageing or has become cloudy because liquid (such as water) has entered the pump. An oil change is also necessary when flakes form in corrosion ∏

] protection oil, indicating that the corrosion –1 protection agent is exhausted. · h 3 Changing the oil The oil change should always be carried out with the pump switched off but at operating temperature. The oil drain (or fill)

Pumping speed [m opening provided for each pump is to be used for this purpose. Where the pump is more seriously contaminated, then it should be cleaned. The applicable operating instructions are to be observed in this case.

Intake pressure [mbar] 8.3.1.2 Selection of the pump oil Example: Oil losses for a TRIVAC S 16 A at pressure of 1 mbar: when handling aggressive a) Without gas ballast: in accordance with the pumping speed curve S = 15 m3 / h; according to diagram: vapors oil loss = 0.03 cm3 / h (line a) b) With gas ballast: S = 9 m3/h at 1 mbar; oil loss = 0.018 cm3 / h (line b1), plus additional loss due to If corrosive vapors (e.g. the vapors formed gas ballast quantity (0.1 times the 1.6 m3 / h rated pumping speed); that is: Chart on the horizontal by acids) are to be pumped, then a 3 line b2 up to atmospheric pressure: additional loss: 3 cm / h (diagonal line). Overall loss during gas PROTELEN® corrosion protection oil ballast operation 0.018 + 3 = 3.018 cm3 / h should be used in place of the normal D00 pump oil (N 62). These types of vapors will 3 Fig. 8.1 Oil loss for oil-sealed pumps (referenced to an approximate maximum value of 2 cm oil loss per cubic meter then react with the basic (alkaline) corrosi- of air drawn in [STP]) on protection agent in the oil. The conti-

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nuous neutralization reactions will exhaust Protection against condensation cing agent. When CO is being pumped it is the corrosion protection agent at a rate LEYBOLD pumps offer three options for therefore important that air not be used as depending on the quantity and acidity of keeping vapors from condensing in the the gas ballast but rather that inert gases the vapors. The oil will have to be changed pumps: be used at the very outside (e.g. Ar or N2). more frequently, in accordance with these Inert gas ballast should also be used when • The gas ballast principle (See Fig. 2.14). factors. Corrosion protection oils are eit- pumping SO , SO , and H S. A corrosion This increases considerably the amount 2 3 2 her very hygroscopic or they easily form inhibiting oil is also to be used when hand- of vapor which the pump can tolerate. emulsions with water. Consequently a ling these three anhydrides. Carbon dioxi- • Increased pump temperature. The rug- pump which is filled with corrosion pro- de (CO ) can be pumped without making ged design of our pumps makes it pos- 2 tection oil will absorb moisture from the any special arrangements. sible to run them at temperatures of up air if it is out of service for an extended to 120 °C. Thus the tolerance for pure period of time. In no case should one ever c) Alkaline solutions water vapor, for example, will rise by a use a pump filled with corrosion protection Normal N 62 pump oil is to be used to factor of five when compared with nor- oil in order to pump water vapor since the pump basic (alkaline) solutions. Sodium mal gas ballast operation. lubricating and corrosion inhibition pro- hydroxide and caustic potash solutions • Using vacuum condensers (see Section perties of the oil would be adversely affec- should not be pumped in their concen- ted. Once the oil has absorbed water it will 2.15). These act as selective pumps and trated form. Ammonia is highly amenable no longer be possible for such pumps to should be sized so that the downstream to pumping with the gas ballast valve clo- achieve the ultimate pressures which gas ballast pump will not receive more sed. Alkaline organic media such as would be the case with fresh corrosion vapor than the amount corresponding methylamine and dimethylamine can also protection oil or standard pump oil (N 62). to the appropriate vapor tolerance. be pumped satisfactorily, but with the gas Oil-filled pumps should, under normal ballast valve open. Corrosion protection operating con-ditions, not be filled with Oil-sealed pumps are already quite satis- corrosion protection oil. N 62 oil is prefer- d) Elementary gases factorily protected against corrosion due red when pumping air, water vapor and Pumping nitrogen and inert gases requires to the oil film which will be present on all non-corrosive organic vapors in so far as no special measures. the component surfaces. Corrosion is defi- there is positive protection against the ned here as the electrochemical dis- When handling hydrogen it is necessary to vapors condensing inside the pump. solution of metals, i.e. the release of elec- make note of the hazard of creating an trons by the metal atom and their accep- explosive mixture. The gas ballast valve may in no case be opened when dealing 8.3.1.3 Measures when pumping tance by the oxidation agent (corrosive with hydrogen. The motors driving the various chemical substances gas). A metal atom which is susceptible to corrosion must therefore be exposed to an pumps must be of explosion-proof design. This discussion cannot provide exhaustive active atom of the oxidation agent. Oxygen: Particular caution is required coverage of the many and varied applicati- when pumping pure oxygen! Specially on fields for oil-filled vacuum pumps in the This makes clear how the oil-sealed pump formulated pump oils must be used for chemicals industry. Our many years of is protected against corrosion; the concen- this purpose. We can supply these, experience with the most difficult of che- tration of the oxidation agent in the oil is accompanied by an approval certificate micals applications can be used to solve negligible and thus the opportunity for the issued by the German Federal Materials your particular problems. Three aspects metal to release electrons is equally small. Testing Authority (BAM), following consul- should, however, be mentioned briefly: This also makes it clear that the use of so- tation. pumping explosive gas mixes, condensab- called “non-rusting” or “stainless” steels le vapors, and corrosive vapors and gases. does not make sense since oxidation is necessary for the passivation of these e) Alkanes The low molecular weight alkanes such as Explosion protection steels, in order to reach the so-called passive region for these steel compounds. methane and butane can be pumped with Applicable safety and environmental pro- the gas ballast valve closed or using inert tection regulations shall be observed when The critical passivation current density will normally not appear in oil-sealed pumps. gas as the gas ballast and/or at increased planning and engineering vacuum temperature of the pump. But important – systems. The operator must be familiar Increased explosion hazard! with the substances which the system will a) Acids Our pumps are fundamentally suited to be pumping and take into account not only f) Alcohols pumping acids. In special situations normal operating conditions but also Once operating temperature has been rea- problems with the oil and with auxiliary abnormal situations, operating outside ched, methanol and ethanol can be extrac- equipment attached at the intake and/or normal parameters. The most important ted without using gas ballast (N 62 pump discharge end may occur. Our engineers in aids to avoiding explosive mixtures are – oil). To pump higher molecular weight Cologne are available to assist in solving in addition to inertization by adding pro- alcohols (e.g. butanol) the gas ballast such problems. tective gases – maintaining the explosion valve will have to be opened or other pro- limit values with the aid of condensers, tective measures will have to be imple- b) Anhydrides adsorption traps and gas scrubbers. mented to prevent condensation. CO (carbon monoxide) is a strong redu-

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g) Solvents c) The measurement instrument is soiled vacuum vessel down to the cut-in pressu- Acetone: Can be extracted without difficul- (see Section 8.4.2). re. ty; wait until normal operating temperatu- Permissible cut-in pressure P will depend re is reached. Potential sources of error when the pump E on the reduction ratios of the roots pump no longer turns Benzene: Caution – vapors are highly as against the roughing pump and is cal- • Check the pump electrical supply. flammable. Ultimate pressure is degraded culated by dividing the permissible pressu- • The pump has stood for a long time by dilution of the pump oil. Mixtures of air re differential ∆p by the compression containing contaminated or resinous max and benzene are explosive and flammable. ratio, reduced by the value of 1: oil. Work without a gas ballast! Inert gases • The pump is colder than 10°C and the ∆p may possibly be used as ballast gas. p = max where oil is stiff. Heat the pump. E kth – 1 Carbon tetrachloride and trichlorethy- • There is a mechanical error. Please con- lene: Amenable to pumping; non-flam- tact our customer service department. Theoretical pumping speed for the roots pump k = mable and non-explosive but will be dis- th Nominal pumping speed for the roughing pump solved in oil and thus increase the ultima- Oil exits at the shaft te pressure; wait until normal operating If oil is discharged at the shaft, then the If the pump is protected using a dia- temperature is achieved. Keep the gas bal- Seeger rotary shaft circlip in the drive bea- phragm-type pressure switch, then the last open when pumping carbon tet and ring will have to be inspected and possibly pump will be switched on automatically. If other non-flammable solvents. Use N 62 replaced. The design of the pumps makes a combination of roots pump and roughing pump oil. it possible to replace this ring easily, follo- pump is to convey highly volatile substances such as liquids with a low boiling Toluene: Pump through the low-temper- wing the operating instructions provided with the unit. point, then it is advisable to use a roots ature baffle and without gas ballast. Use pump which is equipped with an integral inert gas, not air, as the gas ballast. bypass line and a valve which will respond to a pre-set pressure. Example: Roots vacuum pumps RUVAC WAU/WSU. 8.3.1.4 Operating defects while pumping with gas ballast – 8.3.2 Roots pumps Roots pumps from the RUVAC WAU/WSU Potential sources of error series, being equipped with bypass lines, where the required ultimate 8.3.2.1 General operating instruc- can generally be switched on together with pressure is not achieved tions, installation and com- the forepump. The bypass protects these missioning roots pumps against overloading. a) The pump oil is contaminated (particularly with dissolved vapors). Check Roots pumps must be exactly level. When attaching the pump it is necessary to ensu- the color and properties. Remedy: 8.3.2.2 Oil change, maintenance work Allow the pump to run for an extended re that the pump is not under any tension period of time with the vacuum vessel or strain whatsoever. Any strains in the Under clean operating conditions the oil in isolated and the gas ballast valve open. pump casing caused by the connection the roots pump will be loaded only as a In case of heavy contamination an oil lines shall be avoided. Any strain to which result of the natural wear in the bearings change is advisable. The pump should the pump is subjected will endanger the and in the gearing. We nevertheless never be allowed to stand for a longer pump since the clearances inside the roots recommend making the first oil change period of time when it contains conta- pump are very small. after about 500 hours in service in order to remove any metal particles which might minated oil. Roots pumps are connected to the line have been created by abrasion during the power supply via the motor terminal strip; b) The sliding components in the pump run-in period. Otherwise it will be suffi- a motor protection switch (overload/ are worn or damaged. Under clean con- cient to change the oil every 3000 hours in overheating) shall be provided as required ditions our pumps can run for many operation. When extracting gases contai- by local codes. years without any particular mainte- ning dust or where other contaminants are nance effort. Where the pump has been The direction of motor rotation shall be present, it will be necessary to change the allowed to run for a longer period of checked with the intake and outlet ports oil more frequently. If the pumps have to time with dirty oil, however, the bea- open prior to installing the pump. The run at high ambient temperatures, then the rings and the gate valves may exhibit drive shaft, seen from the motor end, must oil in the sealing ring chamber shall also mechanical damage. This must always rotate counter-clockwise. Note the arrow be replaced at each oil change. be assumed when the pump no longer on the motor indicating the direction of We recommend using our specially formu- achieves the ultimate pressure specified rotation! If the roots pump runs in the lated N 62 oil. in the catalog even though the oil has wrong direction, then it is reversed by been changed. In this case the pump interchanging two of the phases at the Under “dirty” operating conditions it is should be sent in for repair or our motor connection cord. possible for dust deposits to form a D00 customer service department should be “crust” in the pump chamber. These conta- The roots pump may be switched on only contacted. minants will deposit in part in the pumping after the roughing pump has evacuated the

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chamber and in part on the pump’s impel- 2. Excessive power consumption: All the The turbomolecular pump may, for exam- lers. They may be removed, once the two factors which can lead to elevated tem- ple, be used unprotected inside magnetic connection lines have been detached, eit- peratures can also cause excessisve fields if the magnetic induction at the sur- her by blowing out the system with dry amounts of power to be drawn. The face of the pump casing does not exceed compressed air or by rinsing with a suita- motor is defective if excessive power B = 3 · 10-3 T when radially impinging and ble cleaning agent, such as petroleum requirements are not accompanied by a B = 15 · 10-3 T at axial impingement. ether (naphtha). rise in the temperature at the pump. In a radioactive environment standard tur- The oil in the roots pump will then have to 3. Oiling at the pump chamber: bomolecular pumps can be used without be changed. The rotor may be turned only hazard at dose rates of from 104 to 105 by hand during cleaning since, due to the Possible causes: rad. If higher dose rates are encountered, high speed when the motor is running, the • Oil level too high: Oil is subjected to then certain materials in the pump can be deposits could damage the pump as they modified in order to withstand the greater excessive thermal loading. Oil foam is dislodge from the surfaces. loading. The electronic frequency conver- swept along. ters in such cases are to be set up outside Grime which cannot be eliminated by • Oil mixed with the product: Azeotropic the radioactive areas since the semicon- washing can be removed mechanically degasification of the oil. ductors used inside them can tolerate a using a wire brush, metallic scrubber or • Pump leaking: Air ingress through the dose rate of only about 103 rad. The use of scraper. oil drain or filler screw will cause a large motor-driven frequency converters which stream of air and conveyance of oil into can withstand up to 108 rad represents Important! the pumping chamber. another option. The dislodged residues may not remain in the pump chamber. After cleaning is com- 4. Abnormal running noises: Roughing (backing) pumps are required pleted check the pump for operability by Possible causes: for the operation of turbomolecular slowly turning the impellers by hand. pumps. Depending on the size of the ves- There may be no resistance to rotation. It • Grime at the impeller sel to be evacuated, the turbomolecular is generally not necessary to dismantle the • Bearing or gearing damage pumps and forepumps may be switched roots pump. If this should nevertheless be • Impellers are touching the housing on simultaneously. If the time required to required due to heavy soiling, then it is pump the vessel down to about 1 mbar In the case of bearing or gearing damage highly advisable to have this done by the using the particular fore-pump is longer or where the impeller scrapes the housing manufacturer. than the run-up time for the pump (see the pump should be repaired only by the operating instructions), then it is advisab- manufacturer. le to delay switching on the turbomolecu- 8.3.2.3 Actions in case of operational lar pump. Bypass lines are advisable when disturbances using turbomolecular pumps in systems set up for batch (cyclical) operations in 1. Pump becomes too warm: (maximum order to save the run-up time for the operating temperature 100 to 115 °C) 8.3.3 Turbomolecular pumps pump. Opening the high vacuum valve is Possible causes: not dangerous at pressures of about 8.3.3.1 General operating instructions 10-1 mbar. • Overloading: Excessive heat of compression due to an excessively high In spite of the relatively large gap between the pump rotor and the stator, the turbo- pressure ratio. Check the pressure 8.3.3.2 Maintenance value adjustments and the tightness of molecular pumps should be protected the vacuum chamber! against foreign objects entering through Turbomolecular pumps and frequency • Incorrect clearances: The distances the intake port. It is for this reason that the converters are nearly maintenance-free. In between the rotors and the housings pump should never be operated without the case of oil-lubricated pumps it is have been narrowed due to dirt or the supplied wire-mesh splinter guard. In necessary to replace the bearing lubricant mechanical strain. addition, sharp shock to the pump when at certain intervals (between 1500 and • Soiled bearings: Excessive friction in running and sudden changes in attitude 2500 hours in operation, depending on the the bearings are to be avoided. type). This is not required in the case of grease-lubricated pumps (lifetime lubri- • Improper oil level: If the oil level is too Over and above this, and particularly for cation). If it should become necessary to high, the gears will touch the oil, the larger types with long rotor blades, clean the pump’s turbine unit, then this causing friction resistance. Where the airing the pump to atmospheric pressure can easily be done by the customer, obser- oil level is too low the system will not be while the impellers are rotating may be ving the procedures described in the ope- lubricated. done only when observing exactly the rating instructions. • Incorrect oil type: An SAE 30 grade oil rules given in the operating instructions. must be used for the pump. Under certain circumstances it is possible to operate turbomolecular pumps under exceptional conditions.

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8.3.4 Diffusion and vapor-jet the contaminated pump fluid poured out. should not exceed 10-2 mbar when vacuum pumps The interior section and the pump body are DIFFELEN is being used. then cleaned with pure petroleum ether • Measurement system old or soiled (see 8.3.4.1 Changing the pump fluid and (naphtha). The interior section and pump Section 8.4.2). cleaning the pump body of mercury pumps should have been cleaned beforehand with a clean brush; Potential sources of error where there is Changing the pump fluid is always ne- use a bottle brush for the nozzle bores. insufficient pumping speed: cessary whenever the pump no longer Ensure that all the nozzle orifices are pro- • Forevacuum pressure is too high: achieves the required ultimate vacuum or perly cleaned. It is advantageous to evapo- Check the forevacuum; allow the gas when its pumping speed falls off. The ser- rate all solvent residues in a drying kiln. ballast pump to run for a longer period vice life of the pump fluid will as a rule Then the inside section is inserted once of time with the gas ballast valve open. come to several weeks or months – or again and the fresh pump fluid is installed It may be necessary to change the oil in even years – and will depend largely on the through the forevacuum port. It is neces- the forepump. operating conditions for the pump. It is sary to ensure that the upper nozzle cover • The pump fluid in the diffusion pump reduced by frequent pumping at high pres- is not moistened with pump fluid! Do not has become unserviceable: Driving sures, by exposure to aggressive vapors install too much pump fluid! medium will have to be replaced. and by air ingress of longer duration (this • Nozzles at the diffusion pump are clog- does not apply to silicone oil and merged: Clean the diffusion pump. cury). 8.3.4.2 Operating errors with diffusion • Heating is too weak: Check heating out- In the case of oil diffusion and vapor-jet and vapor-jet pumps put; examine heating plate for good pumps the danger presented to the pump Potential sources of defects when the thermal contact with the bottom of the fluid where there is air ingress with the desired ultimate pressure is not reached boiler chamber. pump hot is often overestimated. Where • Coolant temperature is too high; inade- • Substances are present in the vacuum air ingress (up to atmospheric pressure) is quate water throughput. The coolant vessel which have a higher vapor pres- encountered only occasionally and for flow should always be monitored by a sure than the driving medium being short periods of time then silicone oil will water flowmeter in order to protect the used: among these are, for example, not be attacked at all and the DIFFELEN pump from damage. Remedy: Measure mercury, which is particularly hazard- pump fluid will only barely be affected. The the exit temperature of the coolant ous because the mercury vapors will products with considerably higher vapor water (it should not exceed 30 °C). form amalgams with the nonferrous pressures which can be created through Increase the coolant flow-through rate. metals in the oil diffusion pump and oxidation are removed again in a short The cooling coils at the pump may have thus make it impossible to achieve per- period of time by the fractionation and to be decalcified. fect vacuums. degassing equipment in the pump (see • Forevacuum pressure too high: This is Section 2.1.6.1). Even though the pump possible particularly where vapors fluid which was originally light in color has which are either evacuated from the been turned brown by air ingress, this vessel or are created as cracking pro- need not necessarily mean that the medi- ducts from the driving medium (e.g. 8.3.5 Adsorption pumps um has become unusable. If, on the other following air ingress) get into the roug- hand, the pump fluid has turned cloudy hing pump. Check the forevacuum 8.3.5.1 Reduction of adsorption and has become more viscous, as well pressure with the oil diffusion pump capacity (which may be the case following periods disconnected. Remedy: Run the fore- A considerable reduction in pumping of air ingress lasting for several minutes) vacuum pump for an extended period of speed and failure to reach the ultimate then the medium will have to be replaced. time with gas ballast. If this is not suffi- pressure which is normally attainable in It is possible that under certain circum- cient, then the oil in the forepump will spite of thermal regeneration having been stances cracking products from the pump have to be changed. carried out indicates that the zeolite being fluid may make the oil in the forepump • Pump fluid at the diffusion pump spent used has become contaminated by outside unserviceable so that here, too, an oil or unserviceable: Replace the driving substances. It does not make good sense change will have to be made. medium. to attempt to rejuvenate the contaminated • Heating is incorrect: Check the heating Mercury diffusion and vapor-jet pumps are zeolite with special thermal processes. The output and check for good thermal less sensitive to air ingress than oil diffusi- zeolite should simply be replaced. on pumps. The oxidation of the hot mer- contact between the heating plate and cury caused by the air ingress is negligible the bottom of the boiler section. Repla- ce the heating unit if necessary. in regard to the operating characteristics 8.3.5.2 Changing the molecular sieve • of the pump when compared with the mer- Leaks, contamination: Remedy: if the cury loss in the forepump line. pump has been contaminated by vapors It will be necessary to rinse the adsorption it may help to use a metering valve to pump thoroughly with solvents before D00 Changing the pump fluid: The interior sec- pass air through the apparatus for installing the new zeolite charge. Before tion will be extracted from the pump and some period of time; here the pressure putting the adsorption pump which has

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been charged with fresh zeolite into servi- 8.3.7 Sputter-ion pumps pump itself will have to be baked out for a ce it is also necessary to bake out the new few hours at 250 to 300 °C (but not higher zeolite charge, under vacuum and using Sputter-ion pumps use high-voltage cur- than 350 °C!). The pump should without the heating element associated with the rent. Installation and connection should be fail remain in operation throughout this pump, for a period of several hours so that carried out only under the supervision of a period! If the pressure rises above contaminants which might have collected qualified specialist. The operating instruc- 5 · 10-5 mbar it will be necessary either to during the storage period can dissipate. tions shall be observed! heat more slowly or to connect an auxiliary The service life of sputter-ion pumps pump. Before airing one should allow the depends linearly on the pump’s operating hot sputter-ion pump enough time to cool pressure. In the case of pumps manufac- down at least to 150 °C. tured by LEYBOLD, the following applies: 8.3.6 Titanium sublimation -3 pumps p · T = 45 · 10 mbar · h (p = operating pressure, T = service life) Each of the turns in the titanium sublimati- This means that for operating pressure of 8.4 Information on on pump contains approximately 1.2 g of -3 useable titanium supply. At a heating cur- 10 mbar working with rent of 50 A the surface temperature comes the service life is 45 hours to about 1850 K, the sublimation rate 10-6 mbar vacuum gauges approximately 0.12 g/h, i.e. a turn can be the service life is 45,000 hours operated continuously for about 10 hours. 10-9 mbar 8.4.1 Information on installing Since at pressures below 1 · 10-6 mbar sub- the service life is 45,000,000 hours vacuum sensors limation is not continuous but rather only at If a triode pump is not needed over an intervals which – at low pressures (below Here both the external situation in the extended period of time it can either be 5 · 10-8 mbar) and low gas volumes – are immediate vicinity of the vacuum appara- operated continuously at low pressure – already more than ten times the actual sub- tus and the operating conditions within the with practically no influence on the service limation period, one may assume a pum- apparatus (e.g. working pressure, compo- life – or it can be aired, removed from the ping period of almost one month at a wor- sition of the gas content) will be important. pump and packed in a dust-tight container. king pressure of 10-10 mbar per turn. It is initially necessary to ascertain whether The starting properties of the sputter-ion the measurement system being installed is The effective pumping speed of a titanium (triode) pumps manufactured by sensitive in regard to its physical attitude. sublimation pump will depend on the get- LEYBOLD are so good that no problems Sensors should only be installed vertically ter screen surface and the geometry of the will be encountered when returning the with the vacuum flange at the bottom to suction opening. The pumping speed, refe- units to service, even after a longer period keep condensates, metal flakes and filings renced to the surface area of the getter in storage. from collecting in the sensor or even small surface, will be dependent on the type of When the sputter-ion pumps are installed components such as tiny screws and the gas and the getter screen temperature. one should ensure that the magnetic fields like from falling into the sensorand the Since inert gases, for example, cannot be will not interfere with the operation of measurement system. The hot incandes- pumped at all, titanium sublimation pumps other devices (ionization vacuum gauges, cent filaments could also bend and deform should always be used only with an auxili- partial pressure measurement units, etc.). improperly and cause electrical shorts ary pump (sputter-ion pump, turbomole- Mounting devices for the sputter-ion inside the measurement system. This is cular pump) used to pump these gas com- pumps may not short circuit the induc- the reason behind the following general ponents. The supplementary pump can be tance flow and thus weaken the air gap rule: If at all possible, install sensors much smaller than the titanium sublimati- inductance and pumping speed. vertically and open to the bottom. It is on pump. Only in a few special cases can also very important to install measurement one do without the additional pump. If the ultimate pressure which can be attai- systems if at all possible at those points in ned is not satisfactory even though the The selection of the coolant is dictated by the vacuum system which will remain free apparatus is properly sealed, then it will the working conditions and the require- of vibration during operation. usually be sufficient to bake out the atta- ments in terms of ultimate pressure. At ched equipment at about 200 to 250 °C. If The outside temperature must be taken high pressures, above 1 · 10-6 mbar, more the pressure here rises to about into account and above all it is necessary thermal energy is applied to the getter 1 · 10-5 mbar when this is done, then the to avoid hot kilns, furnaces or stoves or screen by frequent sublimation cycles. It is sputter ion pump will become so hot after other sources of intense radiation which for this reason that cooling with liquid evacuating the gases for two hours that it generate an ambient temperature around nitrogen is more favorable. At low pressu- will not be necessary to heat it any further the measurement system which lies above res water cooling may be sufficient. The in addition. It is also possible to heat the the specific acceptable value. Excessive getter screen should if at all possible be pump by allowing air to enter for 2 hours ambient temperatures will result in false heated to room temperature before airing at 10-5 mbar before the other apparatus is pressure indications in thermal conductivi- the pump as otherwise the humidity in the then subsequently baked out. If the ultima- ty vacuum sensors. air would condense out on the surface. te pressure is still not satisfactory, then the

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8.4.2 Contamination at the des, electrodes and the tube walls can be used the pressure indication, depending measurement system and soiled which, under certain circumstances, on the cleanliness of the measurement its removal will result in a reduction of dielectric sensors and the connector line, may be strengths. Here, however, the measure- either too high or too low. Here measurement systems can usually be baked out ment errors by more than one complete The vacuum gauges used in vacuum tech- and degassed by passing a current order of magnitude are possible! Where nology for pressure measurement will cer- through or by electron bombardment, systems can be baked out it is necessary tainly work under “dirty” conditions. This quite aside from the fact that ionization to ensure that the connector line can also is quite understandable since a vacuum vacuum gauges are often used in the ultra- be heated. device or system does not serve simply to high vacuum range where it is necessary produce low pressures but rather and pri- to ensure clean operating conditions for marily have to run processes in chemistry, other reasons. metallurgy or nuclear physics at low pressures. Here, depending on the nature of 8.4.4 Connectors, power pack, the process, considerable quantities of measurement systems gases or vapors will be liberated either continuously or intermittently; these can 8.4.3 The influence of The measurement cables (connector pass into the measurement systems provi- magnetic and electrical cables between the sensor and the vacuum ded for pressure measurement and instal- gauge control unit) are normally 2 m long. led in the vacuum system and – due to fields If longer measurement cables must be surface reactions or through simple depo- In all those measurement instruments used – for installation in control panels, for sits – can falsify the pressure measure- which use the ionization of gas molecules example – then it will be necessary to ments considerably. This is true for all as the measurement principle (cold-catho- examine the situation to determine types of vacuum gauges whereby, of cour- de and hot-cathode ionization vacuum whether the pressure reading might be false, high-sensitivity, high-accuracy measu- gauges), strong magnetic leakage fields or sified. Information on the options for using rement systems are particularly suscep- electrical potentials can have a major influ- over-length cables can be obtained from tible to soiling resulting from the causes ence on the pressure indication. At low our technical consulting department. named. One can attempt to protect the pressures it is also possible for wall poten- measurement systems against contam- tials which deviate from the cathode ination by providing suitable shielding. potential to influence the ion trap current. This, however, will often lead to the pressure registered by the measurement In vacuum measurement systems used in system – which is indeed clean – deviating the high and ultrahigh regimes it is neces- considerably from the pressure actually sary to ensure in particular that the requi- prevailing in the system. red high insulation values for the high-voltage electrodes and ion traps also be main- It is not fundamentally possible to keep the tained during operation and sometimes measurement system in a vacuum gauge even during bake-out procedures. Insulati- from becoming soiled. Thus it is necessary on defects may occur both in the external to ensure that feed line and inside the measurement • the influence of the contamination on system itself. Insufficient insulation at the pressure measurement remains as trap (detector) lead may allow creep cur- small as possible and that rents – at low pressures – to stimulate overly high pressure value readings. The • the measurement system can readily be very low ion trap currents make it neces- cleaned. sary for this lead to be particularly well These two conditions are not easy to satis- insulated. Inside the measurement sen- fy by most vacuum gauges in practice. sors, too, creep currents can occur if the trap is not effectively shielded against the Dirt in a compression vacuum gauge will other electrodes. cause an incorrect and uncontrollable pressure indication. Dirty THERMOVAC An error frequently made when connecting sensors will show a pressure which is too measurement sensors to the vacuum high in the lower measurement range system is the use of connector piping since the surface of the hot wire has chan- which is unacceptably long and narrow. ged. In Penning vacuum gauges contami- The conductance value must in all cases nation will induce pressure readings which be kept as large as possible. The most D00 are far too low since the discharge cur- favorable solution is to use integrated rents will become smaller. In the case of measurement systems. Whenever connec- ionization vacuum gauges with hot catho- tor lines of lower conductance values are

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Fundamentals of Vacuum Technology Tables, Formulas, Diagrams

9. Tables, formulas, nomograms and symbols

Unit N · m–2, Pa 2) mbar bar Torr Abbrev. Gas C* = λ · p [cm · mbar] 1 N · m–2 (= 1 Pa) 1 1 · 10–2 1 · 10–5 7.5 · 10–3 –3 1 mbar 100 1 1 · 10–3 0.75 H2 Hydrogen 12.00 · 10 –3 1 bar 1 · 105 1 · 103 1 750 He Helium 18.00 · 10 Ne Neon 12.30 · 10–3 1 Torr 3) 133 1.33 1.33 · 10–3 1 Ar Argon 6.40 · 10–3 1) The torr is included in the table only to facilitate the transition from Kr Krypton 4.80 · 10–3 -2 this familiar unit to the statutory units N · m , mbar and bar. In futu- Xe Xenon 3.60 · 10–3 re the pressure units torr, mm water column, mm mercury column –3 (mm Hg), % vacuum, technical atmosphere (at), physicalatmosphe- Hg Mercury 3.05 · 10 –3 re (atm), atmosphere absolute (ata), pressure above atmospheric O2 Oxygen 6.50 · 10 and pressure below atmospheric may no longer be used. Reference –3 N2 Nitrogen 6.10 · 10 is made to DIN 1314 in this context. HCl Hydrochloric acid 4.35 · 10–3 -2 2) The unit Newton divided by square meters (N · m ) is also –3 designated as CO2 Carbon dioxide 3.95 · 10 -2 –3 Pascal (Pa): 1 N · m = 1 Pa. H2O Water vapor 3.95 · 10 Newton divided by square meters or Pascal is the SI unit for the pres- –3 NH3 Ammonia 4.60 · 10 sure of fluids. C H OH Ethanol 2.10 · 10–3 3) 1 torr = 4/3 mbar; ﬂ torr = 1 mbar. 2 5 –3 Cl2 Chlorine 3.05 · 10 Air Air 6.67 · 10–3

Table III: Mean free path l Values of the product c* of the mean free path λ ( and pressure p for various Table I: Permissible pressure units including the torr 1) and its conversion gases at 20 °C (see also Fig. 9.1)

1 ↓ = → mbar Pa dyn · cm–2 atm Torr inch Micron cm kp · cm–2 lb · in–2 lb · ft–2 3 µ µ (N/m ) ( bar) (phys.) (mm Hg) Hg ( ) H2O (at tech.) (psi) mbar 1 102 103 9.87 · 10–4 0.75 2.953 · 10–2 7.5 · 102 1.02 1.02 · 10–3 1.45 · 10–2 2.089 Pa 10–2 1 10 9.87 · 10–6 7.5 · 10–3 2.953 · 10–4 7.5 1.02 · 10–2 1.02 · 10–5 1.45 · 10–4 2.089 · 10–2 µbar 10–3 0.1 1 9.87 · 10–7 7.5 · 10–4 2.953 · 10–5 7.5 · 10–1 1.02 · 10–3 1.02 · 10–6 1.45 · 10–5 2.089 · 10–3 atm 1013 1.01 · 105 1.01 · 106 1 760 29.92 7.6 · 105 1.03 · 103 1.033 14.697 2116.4 Torr 1.33 1.33 · 102 1.33 · 103 1.316 · 10–3 1 3.937 · 10–2 103 1.3595 1.36 · 10–3 1.934 · 10–2 2.7847 in Hg 33.86 33.9 · 102 33.9 · 103 3.342 · 10–2 25.4 1 2.54 · 104 34.53 3.453 · 10–2 0.48115 70.731 µ 1.33 · 10–3 1.33 · 10–1 1.333 1.316 · 10–6 10–3 3.937 · 10–5 1 1.36 · 10–3 1.36 · 10–6 1.934 · 10–5 2.785 · 10–3 –4 –2 2 –3 –2 cm H2O 0.9807 98.07 980.7 9.678 · 10 0.7356 2.896 · 10 7.36 · 10 1 10 1.422 · 10 2.0483 at 9.81 · 102 9.81 · 104 9.81 · 105 0.968 7.36 · 102 28.96 7.36 · 105 103 1 14.22 2048.3 psi 68.95 68.95 · 102 68.95 · 103 6.804 · 10–2 51.71 2.036 51.71 · 103 70.31 7.03 · 10–2 1 1.44 · 102 lb · ft–2 0.4788 47.88 478.8 4.725 · 10–4 0. 3591 1.414 · 10–2 359.1 0.488 4.88 · 10–4 6.94 · 10–3 1

Normal conditions: 0 °C and sea level, i.e. p = 1013 mbar = 760 mm Hg = 760 torr = 1 atm in Hg = inches of mercury; 1 mtorr (millitorr) = 10-3 torr = 1 µ (micron … µm Hg column) Pounds per square inch = lb · in-2 = lb / sqin = psi (psig = psi gauge … pressure above atmospheric, pressure gauge reading; psia = psi absolute … absolute pressure) Pounds per square foot = lb / sqft = lb / ft2; kgf/sqcm2 = kg force per square cm = kp / cm2 = at; analogously also: lbf / squin = psi 1 dyn · cm-2 (cgs) = 1 µbar (microbar) = 1 barye; 1 bar = 0.1 Mpa; 1 cm water column (cm water column = g / cm2 at 4 °C) = 1 Ger (Geryk) atm … physical atmosphere – at … technical atmosphere; 100 - (x mbar / 10.13) = y % vacuum

Table II: Conversion of pressure units

D00.142 LEYBOLD VACUUM PRODUCTS AND REFERENCE BOOK 2001/2002 D00 E 19.06.2001 21:40 Uhr Seite 143

Tables, Formulas, Diagrams Fundamentals of Vacuum Technology

VARIABLE General formula For easy calculation Value for air at 20 °C Most probable speed 2 ⋅ R ⋅ T T cm cw = ⋅ 4 cw = 410 [m/s] ͱ⒓⒓⒓M⒓ cw = 1.29 10 ͱM⒓ [ s ] of particles cw – 8 ⋅ R ⋅ T T cm – Mean velocity c = –c = 1.46 ⋅ 104 c = 464 [m/s] – ͱ⒓π⒓⋅⒓M⒓ ͱM⒓ [ s ] of particles c 2 –2 3 ⋅ R ⋅ T – T cm cm2 Mean square of velocity c = c2= 2.49 ⋅ 108 –2 ⋅ 4 – M M [ s2 ] c = 25.16 10 s2 of particles c2 [ ] p = n ⋅ k ⋅ T p = 13.80 ⋅ 10–20 ⋅ n ⋅ T [mbar] p = 4.04 ⋅ 10–17 ⋅ n [mbar] (applies to all gases) Gas pressure p of particles 1 – p = ⋅ n ⋅ m ⋅ c2 3 T 1 – p = ⋅ % ⋅ c2 3

p p = 2.5 ⋅ 1016 ⋅ p [cm–3] (applies to all gases) Number density of particles n n = p/kT n = 7.25 ⋅ 1018 ⋅ [cm–3] T

1 – 22 p –2 –1 Z = 2.85 ⋅ 1020 ⋅ p [cm–2 s–1] (see Fig. 78.2) Area-related impingement ZA ZA = · n · c Z = 2.63 · 10 · · p [cm s ] A 4 A ͱ⒓M⒓⒓· ⒓T N Z = A · p A ͱ⒓2⒓⋅ π⒓⋅⒓M ⋅ k ⋅ T

1 n ⋅ –c 2 Volume collision rate Z Z = ⋅ 22 p –3 –1 Z = 8.6 ⋅ 1022 ⋅ p2 [cm–3 s–1] (see Fig. 78.2) V V λ ZV = 5.27 · 10 · [cm s ] V 2 c*· ͱ⒓M⒓⒓⒓·⒓T 1 2 ⋅ N Z = A ⋅p2 A c* ͱ⒓π⒓⋅ ⒓M⒓⋅ k ⋅ T

⋅ ν ⋅ ⋅ 4 Equation of state of ideal gas p V = R T p ⋅ V = 83.14 ⋅ ν ⋅ T [mbar ⋅ `] p ⋅ V = 2.44 ⋅ 10 ν [mbar ⋅ `] (for all gases) M Area-related mass flow rate qm, A ⋅ M ⋅ Q = 4.377 ⋅ 10–2 ⋅ p [g cm–2 s–1] q = 1.38 ⋅ 10–2 ⋅ p g [cm–2 s–1] qm, A = ZA mT =ͱ⒓⒓⋅ π⒓⋅⒓⋅ ⋅ p m, A ͱ⒓ m, A 2 k T NA T

λ c* = · p in cm · mbar (see Tab. III) mT particle mass in g p gas pressure in mbar –1 –1 –1 –1 k Boltzmann constant in mbar · l · K NA Avogadro constant in mol R molar gas constant in mbar · l · mol K λ mean free path in cm n number density of particles in cm–3 T thermodynamic temperature in K M molar mass in g · mol–1 υ amount of substance in mol V volume in l

Table IV: Compilation of important formulas pertaining to the kinetic theory of gases

Designation, Symbol Value and Remarks alphabetically unit

–27 Atomic mass unit mu 1.6605 · 10 kg 23 –1 Avogadro constant NA 6.0225 · 10 mol Number of particles per mol, formerly: Loschmidt number Boltzmann constant k 1.3805 · 10–23 J · K–1 mbar · l 13.805 · 10–23 K –31 Electron rest mass me 9.1091 · 10 kg Elementary charge e 1.6021 · 10–19 A · s Molar gas constant R 8.314 J · mol–1 K–1 mbar · l = 83.14 R = N · k mol · K A Molar volume of 22.414 m3 kmol–1 DIN 1343; formerly: molar volume –1 the ideal gas Vo 22.414 l · mol at 0 °C and 1013 mbar –2 Standard acceleration of free fall gn 9.8066 m · s Planck constant h 6.6256 · 10–34 J · s W Stefan-Boltzmann constant s 5.669 · 10–8 also: unit conductance, radiation constant m2 K4 – e A · s Specific electron charge – 1.7588 · 1011 me kg Speed of light in vacuum c 2.9979 · 108 m · s–1 –3 ϑ Standard reference density ln kg · m Density at = 0 °C and pn = 1013 mbar of a gas Standard reference pressure pn 101.325 Pa = 1013 mbar DIN 1343 (Nov. 75) D00 Standard reference temperature Tn Tn = 273.15 K, J = 0 °C DIN 1343 (Nov. 75)

Table V: Important values

LEYBOLD VACUUM PRODUCTS AND REFERENCE BOOK 2001/2002 D00.143 D00 E 19.06.2001 21:40 Uhr Seite 144

Fundamentals of Vacuum Technology Tables, Formulas, Diagrams

Unit l · s–1 m3 · h–1 cm3 · s–1 cuft · min–1 1 l · s–1 1 3.6 1000 2.12 1 m3 · h–1 0.2778 1 277.8 0.589 1 cm3 · s–1 10–3 3.6 · 10–3 1 2.1 · 10–3 1 cuft · min–1 0.4719 1.699 471.95 1 Table VI: Conversion of pumping speed (volume flow rate) units

1↓ = ... → mbar · l/s kg · h–1 (20°C) kg · h–1 (0°C) cm3/h (NTP) cm3/s (NTP) Torr · l/s g/a (F12. 20 °C) g/a (F12. 25 °C) µ · cfm lusec Pa · l/s slpm mbar · l/s 1 4.28 · 10–3 4.59 · 10–3 3554 0.987 0.75 1.56 · 105 1.54 · 105 1593 7.52 · 102 100 59.2 · 10–3 kg · h–1 (20 °C) 234 1 1.073 8.31 · 105 231 175 – – 37.2 · 104 1.75 · 105 23.4 · 103 13.86 kg · h–1 (0 °C) 218 0.932 1 7.74 · 105 215 163 – – 34.6 · 104 1.63 · 105 21.8 · 103 12.91 cm3/h (NTP) 2.81 · 10–4 1.20 · 10–6 1.29 · 10–6 1 2.78 · 10–4 2.11 · 10–4 44 – 44.7 · 10–2 2.11 · 10–1 2.81 · 10–2 1.66 · 10–5 cm3/s (NTP) 1.013 4.33 · 10–3 4.65 · 10–3 3600 1 0.760 1.58 · 105 – 1611 760 101 6 · 10–2 Torr · l/s 1.33 5.70 · 10–3 6.12 · 10–3 4727 1.32 1 2.08 · 105 2.05 · 105 2119 1 · 103 133 78.8 · 10–3 g/a (F12. 20 °C) 6.39 · 10–6 – – 2.27 · 10–2 6.31 · 10–6 4.80 · 10–6 1 – 10.2 · 10–3 4.8 · 10–3 6.39 · 10–4 37.9 · 10–8 g/a (F12. 25 °C) 6.50 · 10–6 – – – – 4.88 · 10–6 – 1 10.4 · 10–3 4.89 · 10–3 6.5 · 10–4 38.5 · 10–8 µ · cfm 6.28 · 10–4 2.69 · 10–6 2.89 · 10–6 2.24 6.21 · 10–4 4.72 · 10–4 98.16 96.58 1 0.472 6.28 · 10–2 37.2 · 10–6 lusec 1.33 · 10–3 5.70 · 10–6 6.12 · 10–6 4.737 1.32 · 10–3 1 · 10–3 208 205 2.12 1 13.3 · 10–2 78.8 · 10–6 Pa · l/s 1 · 10–2 4.28 · 10–5 4.59 · 10–5 35.54 9.87 · 10–3 7.5 · 10–3 1.56 · 103 1.54 · 103 15.93 7.50 1 59.2 · 10–5 slpm 16.88 72.15 · 10–3 77.45 · 10–3 60.08 · 103 16.67 12.69 2.64 · 106 2.60 · 106 26.9 · 103 12.7 · 103 16.9 · 102 1

1 cm3 (NTP) = 1 cm3 under normal conditions (T = 273.15 K; p = 1013.25 mbar) NTP = normal temperature and pressure (1 atm; 0 °C) R = 83.14 mbar · l · mol–1 · K–1 1 cm3 (NTP) · h–1 = 1 atm · cm3 · h–1 = 1 Ncm3 · h–1 = 1 std cch 1 sccm = 10–3 slpm = 10–3 N · l · min–1 = 60 sccs SI coherent: 1 Pa · m3 · s–1 = 10 mbar · l · s–1; R = 8.314 Pa · m3 · mol–1 · K–1; M in kg / mol 1 cm3 (NTP) · s–1 = 1 sccs = 60 cm3 (NTP) · min–1 60 sccm = 60 std ccm = 60 Ncm3 · min–1 1 lusec = 1 l · µ · s–1 1 · µ = 1 micron = 10–3 Torr 1 lusec = 10–3 Torr · l · s–1 –1 –1 Freon F 12 (CCl2F2) M = 120.92 g · mol ; air M = 28.96 g · mol Note: Anglo-American units are not abbreviated nonuniformly! Example: Standard cubic centimeter per minute → sccm = sccpm = std ccm = std ccpm

Table VIIa: Conversion of throughput (QpV) units; (leak rate) units

1↓= ... → mbar · l/s cm3/s **) Torr · l/s Pa · m3/s g/a *) oz/yr *) lb/yr *) atm · ft3/min µ · l/s µ · ft3/h µ · ft3/min mbar · l/s 1 0.987 0.75 10–1 1.56 · 105 5.5 · 103 3.4 · 102 2.10 · 10–3 7.52 · 102 9.56 · 104 1593 cm3/s **) 1.013 1 0.76 1.01 · 10–1 1.58 · 105 5.6 · 103 3.44 · 102 2.12 · 10–3 760 96.6 · 103 1614 Torr · l/s 1.33 1.32 1 1.33 · 10–1 2.08 · 105 7.3 · 103 4.52 · 102 2.79 · 10–3 103 1.27 · 105 2119 Pa · m3/s 10 9.9 7.5 1 1.56 · 106 5.51 · 104 3.4 · 103 2.09 · 10–2 7.5 · 103 9.54 · 105 15.9 · 103 g/a *) 6.39 · 10–6 6.31 · 10–6 4.80 · 10–6 6.41 · 10–7 1 3.5 · 10–2 2.17 · 10–3 1.34 · 10–8 4.8 · 10–3 0.612 10.2 · 10–3 oz/yr *) 1.82 · 10–4 1.79 · 10–4 1.36 · 10–4 1.82 · 10–5 28.33 1 6.18 ·· 10–2 3.80 · 10–7 0.136 17.34 0.289 lb/yr *) 2.94 · 10–3 2.86 · 10–3 2.17 · 10–3 2.94 · 10–4 4.57 · 102 16 1 6.17 · 10–6 2.18 280 4.68 atm · ft3/min 4.77 · 102 4.72 · 102 3.58 · 102 47.7 7.46 · 107 2.63 · 106 1.62 · 105 1 3.58 · 105 4.55 · 107 7.60 · 105 µ · l/s 1.33 · 10–3 1.32 · 10–3 10–3 1.33 · 10–4 208 7.34 4.52 · 10–1 2.79 · 10–6 1 127 2.12 µ · ft3/h 1.05 · 10–5 1.04 · 10–5 7.87 · 10–6 1.05 · 10–6 1.63 5.77 · 10–2 3.57 · 10–3 2.20 · 10–8 7.86 · 10–3 1 1.67 · 10–2 µ · ft3/min 6.28 · 10–4 6.20 · 10–4 4.72 · 10–4 6.28 · 10–5 98 3.46 2.14 · 10–1 1.32 · 10–6 0.472 60 1

1 · µ · ft3 · h–1 = 1.04 · 10–5 stsd cc per second 1 micron cubic foot per hour = 0.0079 micron liter per second 1 kg = 2.2046 pounds (lb) 1 cm3 · s–1 (NTP) = 1 atm · cm3 · s–1 = 1 scc · s–1 = 1 sccss 1 micron liter per second = 0.0013 std cc per second = 1 lusec 1 cubic foot (cfut. cf) = 28.3168 dm3 1 atm · ft3 · min–1 = 1 cfm (NTP) 1 micron cubic foot per minute = 1 µ · ft3 · min–1 = 1 µ · cuft · min–1 = 1 µ · cfm 1 lb = 16 ounces (oz) 1 Pa · m3/s = 1 Pa · m3/s (anglo-am.) = 103 Pa · l/s 1 standard cc per second = 96.600 micron cubic feet per hour 1 lusec = 1 µ · l · s–1 1 µ · l · s–1 = 127 µ · ft3 · h–1 = 0.0013 std cc per second = 1 lusec 1 std cc/sec = 760 µ · l · s–1

*) F12 (20 °C) C.Cl2F2 M = 120.92 h/mol **) (NTP) normal temperature and pressure 1 atm und 0 °C

Table VII b: Conversion of throughput (QpV) units; (leak rate) units

D00.144 LEYBOLD VACUUM PRODUCTS AND REFERENCE BOOK 2001/2002 D00 E 19.06.2001 21:40 Uhr Seite 145

Tables, Formulas, Diagrams Fundamentals of Vacuum Technology

% by weight % by volume Partial pressure mbar

N2 75.51 78.1 792 O2 23.01 20.93 212 Ar 1.29 0.93 9.47 CO2 0.04 0.03 0.31 Ne 1.2 · 10–3 1.8 · 10–3 1.9 · 10–2 He 7 · 10–5 7 · 10–5 5.3 · 10–3 –4 –4 –3 CH4 2 · 10 2 · 10 2 · 10 Kr 3 · 10–4 1.1 · 10–4 1.1 · 10–3 –5 –5 –4 N2O 6 · 10 5 · 10 5 · 10 –6 –5 –4 H2 5 · 10 5 · 10 5 · 10 Xe 4 · 10–5 8.7 · 10–6 9 · 10–5 –6 –6 –5 O3 9 · 10 7 · 10 7 · 10 Σ 100 % Σ 100 % Σ 1013 50 % RH at 20 °C 1.6 1.15 11.7

Note: In the composition of atmospheric air the relative humidity (RH) is indicated separately along with the temperature. At the given relative humidity, therefore, the air pressure read on the barometer is 1024 mbar Table VIII: Composition of atmospheric air

Rough vacuum Medium vacuum High vacuum Ultrahigh vacuum Pressure p [mbar] 1013 – 1 1 – 10–3 10–3 – 10–7 < 10–7 Particle number density n [cm–3] 1019 – 1016 1016 – 1013 1013 – 109 < 109 Mean free path λ [cm] < 10–2 10–2 – 10 10 – 105 > 105 –2 –1 23 20 20 17 17 13 13 Impingement rate Za [cm · s ] 10 – 10 10 – 10 10 – 10 < 10 –3 –1 29 23 23 17 17 9 9 Vol.-related collision rate ZV [cm · s ] 10 – 10 10 – 10 10 – 10 < 10 Monolayer time τ [s] < 10–5 10–5 – 10–2 10–2 – 100 > 100 Type of gas flow Viscous flow Knudsen flow Molecular flow Molecular flow

Other special features Convection dependent Significant change in Significant reduction- Particles on the on pressure thermal conductivity in volume surfaces dominate of a gas related collision rate to a great extend in relation to particles in gaseous space

Table IX: Pressure ranges used in vacuum technology and their characteristics (numbers rounded off to whole power of ten)

At room temperature Standard values1 Metals Nonmetals (mbar · l · s–1 · cm–2) 10–9 ... · 10–7 10–7 ... · 10–5 Outgassing rates (standard values) as a function of time Examples: 1/2 hr. 1 hr. 3 hr. 5 hr. Examples: 1/2 hr. 1 hr. 3 hr. 5 hr. Ag 1.5 · 10–8 1.1 · 10–8 2 · 10–9 Silicone 1.5 · 10–5 8 · 10–6 3.5 · 10–6 1.5 · 10–6 Al 2 · 10–8 6 · 10–9 NBR 4 · 10–6 3 · 10–6 1.5 · 10–6 1 · 10–6 Cu 4 · 10–8 2 · 10–8 6 · 10–9 3.5 · 10–9 Acrylic glass 1.5 · 10–6 1.2 · 10–6 8 · 10–7 5 · 10–7 Stainless steel 9 · 10–8 3.5 · 10–8 2.5 · 10–8 FPM, FKM 7 · 10–7 4 · 10–7 2 · 10–7 1.5 · 10–7 1 All values depend largely on pretreatment!

Table X: Outgassing rate of materials in mbar · l · s–1 · cm–2 D00

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Fundamentals of Vacuum Technology Tables, Formulas, Diagrams

Nominal width (DN) Internal diam. (mm) Series R5 R10 10 10 16 16 20 21 25 24 32 34 40 41 50 51 63 70 80 83 100 102 125 127 160 153 200 213 250 261 320 318 400 400 500 501 630 651 800 800 1000 1000

The nominal internal diameters correspond approximately to the internal diameters of the pipeline components” (DIN 2402 - Feb. 1976). The left-hand column of the nominal internal diameter series is preferred in practice.

Table XI: Nominal internal diameters (DN) and internal diameters of tubes, pipes and apertures with circular cross-section (according to PNEUROP)

Solvent Relative Density Melting Boiling Maximum admissible molecular g / cm3 point point concentration (MAC) mass (20 °C) °C °C cm3 / m3

Acetone 58 0.798 56 Benzene (solution) 78 0.8788 5.49 80.2 25 Petrol (light) 0.68 ... 0.72 > 100 Carbon tetrachloride 153.8 1.592 – 22.9 76.7 25 Chloroform 119.4 1.48 – 63.5 61 50 Diethyl ether 46 0.7967 –114.5 78 1000 Ethyl alcohol 74 0.713 – 116.4 34.6 400 Hexane 86 0.66 – 93.5 71 500 Isopropanol 60.1 0.785 – 89.5 82.4 400 Methanol 32 0.795 – 97.9 64.7 200 (toxic!) Methylene chloride 85 1.328 41 Nitromethane 61 1.138 – 29.2 101.75 100 Petroleum ether mixture 0.64 – 40 ... 60 Trichlorethylene (“Tri”) 131.4 1.47 55 Water 18.02 0.998 0.00 100.0 –

Table XII: Important data (characteristic figures) for common solvents

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Tables, Formulas, Diagrams Fundamentals of Vacuum Technology

t ps %D t ps %D t ps %D t ps %D °C mbar g/m3 °C mbar g/m3 °C mbar g/m3 °C mbar g/m3 – 100 1.403 · 10–5 1.756 · 10–5 – 35 0.2233 0.2032 30 42.43 30.38 95 845.3 504.5 – 99 1.719 2.139 – 34 0.2488 0.2254 31 44.93 32.07 96 876.9 522.1 – 98 2.101 2.599 – 33 0.2769 0.2498 32 47.55 33.83 97 909.4 540.3 – 97 2.561 3.150 – 32 0.3079 0.2767 33 50.31 35.68 98 943.0 558.9 – 96 3.117 3.812 – 31 0.3421 0.3061 34 53.20 37.61 99 977.6 578.1 – 95 3.784 · 10–5 4.602 · 10–5 – 30 0.3798 0.3385 35 56.24 39.63 100 1013.2 597.8 – 94 4.584 5.544 – 29 0.4213 0.3739 36 59.42 41.75 101 1050 618.0 – 93 5.542 6.665 – 28 0.4669 0.4127 37 62.76 43.96 102 1088 638.8 – 92 6.685 7.996 – 27 0.5170 0.4551 38 66.26 46.26 103 1127 660.2 – 91 8.049 9.574 – 26 0.5720 0.5015 39 69.93 48.67 104 1167 682.2 – 90 9.672 · 10–5 11.44 · 10–5 – 25 0.6323 0.5521 40 73.78 51.19 105 1208 704.7 – 89 11.60 13.65 – 24 0.6985 0.6075 41 77.80 53.82 106 1250 727.8 – 88 13.88 16.24 – 23 0.7709 0.6678 42 82.02 56.56 107 1294 751.6 – 87 16.58 19.30 – 22 0.8502 0.7336 43 86.42 59.41 108 1339 776.0 – 86 19.77 22.89 – 21 0.9370 0.8053 44 91.03 62.39 109 1385 801.0 – 85 23.53 · 10–5 27.10 · 10–5 – 20 1.032 0.8835 45 95.86 65.50 110 1433 826.7 – 84 27.96 32.03 – 19 1.135 0.9678 46 100.9 68.73 111 1481 853.0 – 83 33.16 37.78 – 18 1.248 1.060 47 106.2 72.10 112 1532 880.0 – 82 39.25 44.49 – 17 1.371 1.160 48 111.7 75.61 113 1583 907.7 – 81 46.38 52.30 – 16 1.506 1.269 49 117.4 79.26 114 1636 936.1 – 80 0.5473 · 10–3 0.6138 · 10–3 – 15 1.652 1.387 50 123.4 83.06 115 1691 965.2 – 79 0.6444 0.7191 – 14 1.811 1.515 51 129.7 87.01 116 1746 995.0 – 78 0.7577 0.8413 – 13 1.984 1.653 52 136.2 91.12 117 1804 1026 – 77 0.8894 0.9824 – 12 2.172 1.803 53 143.0 95.39 118 1863 1057 – 76 1.042 1.145 – 11 2.376 1.964 54 150.1 99.83 119 1923 1089 – 75 1.220 · 10–3 1.334 · 10–3 – 10 2.597 2.139 55 157.5 104.4 120 1985 1122 – 74 1.425 1.550 – 9 2.837 2.328 56 165.2 109.2 121 2049 1156 – 73 1.662 1.799 – 8 3.097 2.532 57 173.2 114.2 122 2114 1190 – 72 1.936 2.085 – 7 3.379 2.752 58 181.5 119.4 123 2182 1225 – 71 2.252 2.414 – 6 3.685 2.990 59 190.2 124.7 124 2250 1262 – 70 2.615 · 10–3 2.789 · 10–3 – 5 4.015 3.246 60 199.2 130.2 125 2321 1299 – 69 3.032 3.218 – 4 4.372 3.521 61 208.6 135.9 126 2393 1337 – 68 3.511 3.708 – 3 4.757 3.817 62 218.4 141.9 127 2467 1375 – 67 4.060 4.267 – 2 5.173 4.136 63 228.5 148.1 128 2543 1415 – 66 4.688 4.903 – 1 5.623 4.479 64 293.1 154.5 129 2621 1456 – 65 5.406 · 10–3 5.627 · 10–3 0 6.108 4.847 65 250.1 161.2 130 2701 1497 – 64 6.225 6.449 1 6.566 5.192 66 261.5 168.1 131 2783 1540 – 63 7.159 7.381 2 7.055 5.559 67 273.3 175.2 132 2867 1583 – 62 8.223 8.438 3 7.575 5.947 68 285.6 182.6 133 2953 1627 – 61 9.432 9.633 4 8.129 6.360 69 298.4 190.2 134 3041 1673 – 60 10.80 · 10–3 10.98 · 10–3 5 8.719 6.797 70 311.6 198.1 135 3131 1719 – 59 12.36 12.51 6 9.347 7.260 71 325.3 206.3 136 3223 1767 – 58 14.13 14.23 7 10.01 7.750 72 339.6 214.7 137 3317 1815 – 57 16.12 16.16 8 10.72 8.270 73 354.3 223.5 138 3414 1865 – 56 18.38 18.34 9 11.47 8.819 74 369.6 232.5 139 3512 1915 – 55 20.92 · 10–3 20.78 · 10–3 10 12.27 9.399 75 385.5 241.8 140 3614 1967 – 54 23.80 23.53 11 13.12 10.01 76 401.9 251.5 – 53 27.03 26.60 12 14.02 10.66 77 418.9 261.4 – 52 30.67 30.05 13 14.97 11.35 78 436.5 271.7 – 51 34.76 33.90 14 15.98 12.07 79 454.7 282.3 – 50 39.35 · 10–3 38.21 · 10–3 15 17.04 12.83 80 473.6 293.3 – 49 44.49 43.01 16 18.17 13.63 81 493.1 304.6 – 48 50.26 48.37 17 19.37 14.48 82 513.3 316.3 – 47 56.71 54.33 18 20.63 15.37 83 534.2 328.3 – 46 63.93 60.98 19 21.96 16.31 84 555.7 340.7 – 45 71.98 · 10–3 68.36 · 10–3 20 23.37 17.30 85 578.0 353.5 – 44 80.97 76.56 21 24.86 18.34 86 601.0 366.6 – 43 90.98 85.65 22 26.43 19.43 87 624.9 380.2 – 42 102.1 95.70 23 28.09 20.58 88 649.5 394.2 – 41 114.5 · 10–3 106.9 · 10–3 24 29.83 21.78 89 674.9 408.6 – 40 0.1283 0.1192 25 31.67 23.05 90 701.1 423.5 – 39 0.1436 0.1329 26 33.61 24.38 91 728.2 438.8 – 38 0.1606 0.1480 27 35.65 25.78 92 756.1 454.5 – 37 0.1794 0.1646 28 37.80 27.24 93 784.9 470.7 – 36 0.2002 0.1829 29 40.06 28.78 94 814.6 487.4 D00 Sources: Smithsonian Meteorological Tables 6th. ed. (1971) and VDI vapor tables 6th ed (1963).

Table XIII: Saturation pressure ps and vapor density % D of water in a temperature range from –100 °C to +140 °C

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Fundamentals of Vacuum Technology Tables, Formulas, Diagrams

Group A 3) Group B 3) Group C 3)

Methane c Ethylene c Hydrogen c

Ethane c Buta-1,3-diene c Acetylene (ethyne) c

Propane c Acrylonitrile c Carbon bisulfide c

Butane c hydrogen cyanide a

Pentane c Dethyl ether (s) c

Hexane c Ethylene oxide (oxiran) c

Heptane c 1.4 Dioxan a

Octane a Tetrahydrofuran a

Cyclohexane c Tetrafluoroethylene a

Propylene (propene) a

Styrene (s) b

Benzene (s) c

Toluene (s) –

Xylene a Legend Group A Group B Group C

Naphthalene – MESG 1) > 0.9 mm 0.5 ... 0.9 mm < 0.5 mm

Methanol (s) c MIC 2) ratio > 0.8 mm 0.45 ... 0.8 mm < 0.45 mm Ethanol (s) c 1) Minimum Electrical Spark Gap Propyl alcohol (propanol) c 2) Minimum Ignition Current The ratio is based on the MIC value for laboratory methane Butyl alcohol (butanol) a 3) Group allocation: Phenol – a – according to MESG value b – according to MIC ratio Acetaldehyde (ethanal) a c – according to both MESG value and MIC ratio (s) – solvent Acetone (s) (propanone) c

Methyl ethyl ketone (s) (propan-2-one) c

Ethyl acetate (s) a

Butyl acetate (s) c

Amyl acetate (s) –

Ethyl methacrylate –

Acetic acid (ethanoic acid) b

Methyl chloride (s) a

Methylene chloride (s) (dichlormethane) –

Ammonia a

acetonitrile a

Aniline –

Pyridine –

Table XIV: Hazard classification of fluids according to their MESG1 and/or MIC2 values. (Extract from European Standard EN 50.014)

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Tables, Formulas, Diagrams Fundamentals of Vacuum Technology ene Medium Medium ene iton iton

x = resistant x = resistant ubber (NBR) Perbunan – = conditionally resistant ubber (NBR) Perbunan – = conditionally resistant o = not resistant o = not resistant ubber (CR) Neopr ubber (CR) Neopr ubber ubber ene r ene r ubber (FPM, FKM) V ubber (FPM, FKM) V opr opr o r o r eflon (PTFE) eflon (PTFE) T EPDM Nitrile-butadiene r Chlor Silicone r Fluor Nitrile-butadiene r Chlor Silicone r Fluor T EPDM Acetaldehyde o o o o x x Carbon dioxide, dry x x x x x Acetic acid (crystalline), pure – o – o x – Carbon dioxide, wet x x x x Acetic acid, industrial x x Carbon tetrachloride o o o x x o Acetic acid vapors x x – x Chloracetic acid o o o x x Acetic acid, 20 % x x x Chlorinated solvents o x

Acetic acid, 50 % o x x x Clorine, dry x x Acetic acid, 80 % o o x Chlorine water – x o x x Acetic anhydride – x x x Chlorine, wet o o x x x Aceto-acetic ester o x – Chlorobromomethane o x – Acetone o – o x x Chlorobenzene o o o x o

Acetophenone o x x Chloroform o o x x o Acetylene x – x x Chloromethyl o – x x o Acrylnitrile – o x Citrus oils o o x Air, clean x x x x x x Coke furnace gas o o x o Air, oily x x x x x o Copra oil acid – o – x

Ammonia liquid x x – – x x Cottonseed oil x – x x – Ammonia gas x x o x Cresol x x o Amyl acetate o o o x x Crude petroleum – x x o Amyl alcohol – – o o x x Cyclohexane x x x o Aniline o o x x x Cyclohexanone o o o x o

Anthracene oil o o x x Cyclohexylamine x o ASTM oil No. 1 x x x x x o Decahydronaphtalene x x o ASTM oil No. 2 x x x x x o Desmodur T o o x o ASTM oil No. 3 – – – o x o Desmophene 2000 x x Benzaldehyde 100 % x x Dibutylphthalate o o x o x x

Benzene o o x x o Dichlorethylene x Benzene bromide o o x o Dichlorethane x x x o Benzoic acid x x Diethylamine – o x x Bitumen x Diethylene glycol x x x x Blast furnace gas x x x x – Diethyl ether o – o x o

Boron trifluoride x x x Diethyl ether o o x – Bromine o o x x Diethyl sebazate o o x – Butadiene x o Dichlorbenzene o o x o Butane x – x x o Dichlorbutylene x x o Butyl acetate o o o x – Diesel oil o – x x o

Butyl alcohol – x – o x x Di-isopropyl ketone o x x Butyl glykol x x x Dimethyl ether o x x Butyraldehyde o o x x – Dimethylaniline o o x Carbolineum o o x x x o Dimethyl formamide o o o x – Carbon bisulfide o o – x x o Dioctylphthalate o o x x – D00

Table XV: Chemical resistance of commonly used elastomer gaskets and sealing Table XV: Chemical resistance of commonly used elastomer gaskets and sealing materials materials

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Fundamentals of Vacuum Technology Tables, Formulas, Diagrams

Medium ene Medium ene iton iton

x = resistant x = resistant

– = conditionally resistant ubber (NBR) Perbunan – = conditionally resistant ubber (NBR) Perbunan o = not resistant o = not resistant ubber (CR) Neopr ubber (CR) Neopr ubber ubber ene r ene r ubber (FPM, FKM) V ubber (FPM, FKM) V opr opr o r o r eflon (PTFE) eflon (PTFE) T EPDM T EPDM Silicone r Fluor Silicone r Fluor Nitrile-butadiene r Chlor Nitrile-butadiene r Chlor

Dioxan o o x – Heating fuel oil (coal base) o o x x Diphenyl o o – x x o Heating fuel oil (petroleum crude base) x – x x o Diphenyloxyd o x x Heptane x – o x x o Edenol 888 x x Hexaldehyde o o x x Essential oils o o – x o Hexane x – o x x o

Ethyl acetate (acetic ether) o o x x Hydraulic fluids Ethane x – o x x o Hydraulic oils DIN 51524 x – – x x o Ethyl acetate o o o o x o Phosphoric ester HFD o o o x Ethyl acrylate o x Polyglycol water HFC x – x x x x Ethyl alcohol, denatured – – – x Hydrobromic acid o o x x

Ethyl alcohol, pure – – – x x Hydrobromic crystalline acid x x Ethyl cloride x – o x – Hydrocyanic acid – – x x Ethylene bromide o o x Hydrogen bromide x Ethylene chloride x – Hydrogen gas 20 x x – x Ethylene dichloride o o – x Hydrogen sulfide x x x x

Ethylene glycol x x o x x x Isobutyl alcohol – x x x Ethyl ether o o o x – Isopropyl acetate o o x – Ethyl silicate x x x Isopropyl alcohol – x x x Ethyl acrylate x Isopropyl chloride o o x o Fatty acids – – x Isopropyl ether o x

Fatty alcohol x x x x – Kerosene – – x x Fir leaf oil x o x Kerosine x – x x o Fluorbenzene x o x o Lighting gas – – x x o Hydrofluoric acid, cold, 5 % x x x Maleic anhydride x Hydrofluoric acid, cold, pure – x Mercury x x x x

Formaldehyde x – x x x Methane x – x – Formalin, 55 % x x x x Methane (pit gas) x x x x – Formic acid – – x – Methylene chloride o o o x o Formic acid methyl ester o – – x Methyl acrylate o x o Freon 11 x x o x Methyl alcohol (methanol) – – x o x x

Freon 12 x x – x – Methyl ethyl ketone o o o x – Freon 22 o x o x x Methyl isobutyl ketone o o x – Freon 113 x x x x Methyl methacrylate o o o x o Furane o o x o Methyl salicylate o o x – Furfurol o o o o x Naphtalene o o x o

Gas oill x – x x o Natural gas – x – x x – Generator gas x – x x Nitrobenzene o o o x o Glycerine x x x x x x Nitrous oxide x x x Glycol x x x x x x Oleic acid x x x o Halowax oil o o x Orange oil o o x x Table XV: Chemical resistance of commonly used elastomer gaskets and sealing Table XV: Chemical resistance of commonly used elastomer gaskets and sealing materials materials

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Tables, Formulas, Diagrams Fundamentals of Vacuum Technology ene Medium Medium ene iton iton

Oxygen x x x x Tar oil o x o Ozone o – x x x x Tetrachlorethylene x x o Palmitic acid x x x o Tetrahydrofurane o o x o Palm oil acid – o x x Tetraline o o o x o Paraffin x x x x o Toluene o o o x x o

Paraffin oil x x x o Transformer oil x x x x o Pentachlordiphenyl o x x o Train oil o x x – Pentane x x o x x o Triethanolamine o o x – Perchloroethylene o o x x o Tributoxyethyl phosphate o o x o Petrol x – o x o Tributyl phosphate o o o x o

Petrol alcohol 3:1 – o x x Trichloroethane o o x x Petrol benzene 4:1 x o o x x o Trichloroethylene o o x x o Petrol benzene 7:3 o o o x x o Trichloroethyl phosphate 20 – x x Petrol benzene 3:2 o o o x x o Trichloroethyl phosphate 80 o x x Petrol benzene 1:1 o o o x x o Trichloracetic acid 60 x x –

Petrol benzene 3:7 o o o x x Tricresyl phosphate o x x x – Petrol benzene spirit 5:3:2 o o o x o Turpentine – – x x o Phenol o o x x x o Turpentine oil, pure x x x o Phenyl ethyl ether o o x o Vinyl acetate o o x Phenylic acid (phenol) o o – – x – Vinylaceto-acetic acid 3:2 o – o o x

Phosphorous chloride o – x x Vinyl chloride, liquid x x x Phthalic anhydride x x x x Water 50 x x x x x Piperidine o o x Water 100 x – x x x Polyglycol x x Wood oil – x Propane, gas x x x x x Xylamon o o x x o

Propylene oxyde o x – Xylene o o o x x o Propyl alcohol x x x x Pydraul F-9 o o x x x Pydraul AC o x x x Pydraul A 150 o x x

Pydraul A 200 o x x x Pyridine o x – Salicylic acid x x x x Skydrol 500 x o x x Skydrol 7000 x x x

Stearic acid – x x Styrene o o x x o Sulfur – x x x x x Sulfur dioxide o o x x x Sulfur trioxide, dry o – x x – D00 Table XV: Chemical resistance of commonly used elastomer gaskets and sealing Table XV: Chemical resistance of commonly used elastomer gaskets and sealing materials materials

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Fundamentals of Vacuum Technology Tables, Formulas, Diagrams

Vacuum symbols Ejector vacuum pump *) Vacuum chambers All symbols with the exception of those marked with *) do not depend on the posi- Diffusion pump *) Vacuum chamber tion. *) These symbols may only be used in the position shown here (tip of the angle Adsorption pump *) Vacuum bell jar pointing down)

The symbols for vacuum pumps should Getter pump always be arranged such that the side with Shut-off devices the constriction is allocated to the higher pressure Sputter-ion pump

Shut-off device, general Vacuum pumps Cryopump Shut-off valve, straight- through valve Scroll pump *) Vacuum pump, general Right-angle valve Evaporation pump Piston vacuum pump Stop cock Diaphragm vacuum pump Accessories Three-way stop cock Rotary positive Condensate trap, general displacement pump *) Right-angle stop cock

Rotary plunger Condensate trap with heat vacuum pump *) exchanger (e.g. cooled) Gate valve Sliding vane rotary Gas filter, general vacuum pump *) Butterfly valve

Rotary piston vacuum pump *) Filtering apparatus, general Nonreturn valve

Liquid ring vacuum pump *) Baffle, general Safety shut-off valve

Roots vacuum pump *) Cooled baffle

Turbine vacuum pump, general Cold trap, general Modes of operation

Radial flow vacuum pump Cold trap with coolant reservoir Manual operation

Axial flow vacuum pump Sorption trap Variable leak valve

Turbomolecular pump Throttling Electromagnetic operation

Table XVI: Symbols used in vacuum technology (extract from DIN 28401)

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Tables, Formulas, Diagrams Fundamentals of Vacuum Technology

Hydraulic or pneumatic Linear-motion leadthrough, operation flange-mounted

Electric motor drive Linear-motion leadthrough, without flange

Leadthrough for transmission Weight-operated of rotary and linear motion

Rotary transmission leadthrough

Connections and Electric current leadthrough piping Measurement and Flange connection, general gauges

Bolted flange connection

General symbol for Small flange connection vacuum *)

Vacuum measurement, vacu- Clamped flange connection um gauge head *

Vacuum gauge, operating and display unit for vacuum gauge Threaded tube connection head *)

) Ball-and-socket joint Vacuum gauge, recording *

Vacuum gauge with analog Spigot-and-socket joint measured-value display *)

Vacuum gauge with digital Taper ground joint connection measured-value display *)

Intersection of two lines with Measurement of throughput connection

Intersection of two lines without connection

Branch-off point

Combination of ducts

Flexible connection (e.g. bellows, flexible tubing) D00

Table XVI: Symbols used in vacuum technology (extract from DIN 28401)

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Fundamentals of Vacuum Technology Tables, Formulas, Diagrams

Kelvin Celsius Réaumur Fahrenheit Rankine

Boiling point H2O 373 100 80 212 672 Body temperature 37 °C 310 37 30 99 559 Room temperature 293 20 16 68 527

Freezing point H2O 273 0 0 32 492

NaCl/H2O 50:50 255 –18 –14 0 460 Freezing point Hg 34 –39 –31 –39 422

CO2 (dry ice) 195 –78 –63 –109 352

Boiling point LN2 77 –196 –157 –321 170 Absolute zero point 0 –273 –219 –460 0

Conversion in K °C °R °F °R Kelvin Celsius Réaumur Fahrenheit Rankine K 4 9 9 1 K – 273 (K – 273) (K – 273) + 32 K = 1,8 K Kelvin 5 5 5

°C 4 9 9 °C + 273 1 · °C · °C + 32 (°C + 273) Celsius 5 5 5

°C 5 5 9 5 5 · °R + 273 · °R 1 · °R + 32 (°R + 273) Réaumur 4 4 4 9 [ 4 ]

°F 5 (°F – 32) + 273 5 (°F – 32) 4 (°F – 32) 1 °F + 460 Fahrenheit 9 9 9

°R 5 5 (°R) 5 (°R – 273) 4 (°R – 273) °R – 460 1 Rankine 9 9 5 [ 9 ]

Table XVII: Temperature comparison and conversion table (rounded off to whole degrees)

– p

V 2 Z – p Z A [cm] λ

λ ee path ∼ 1 p Mean fr

Pressure p [mbar] Pressure p [mbar] λ : mean free path in cm (λ ~ 1/p) n : particle number density in cm–3 (n ~ p) –3 –1 2 ZA : area-related impingement rate in cm · s (ZA ~ p ) –3 –1 2 ZV : volume-related collision rate in cm · s (ZV ~ p ) Fig. 9.1: Variation of mean free path λ (cm) with pressure for various gases Fig. 9.2: Diagram of kinetics of gases for air at 20 °C

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Tables, Formulas, Diagrams Fundamentals of Vacuum Technology

106

105

104 e (K) e [mbar] ] –1 essur

Pr 3 emperatur 10 T

2 conductance [l · cm 10

1 10 8 Altitude [km] 6 4

2 Fig. 9.3: Decrease in air pressure (1) and change in temperature (2) as a function of altitude 100 101 2 4 6 8 102 103 104 Pipe length l [cm]

Fig. 9.5: Conductance values for piping of commonly used nominal width with circular cross-section for laminar flow (p = 1 mbar) according to equation 53a. (Thick lines refer to preferred DN) Flow medium: air (d, l in cm!) ] –1 Altitude (km) conductance [l · s

Pipe length l [cm] Molecules/atoms [cm–3] D00 Fig. 9.6: Conductance values for piping of commonly used nominal width with circular cross-section for molecular flow according to equation 53b. (Thick Fig. 9.4: Change in gas composition of the atmosphere as a function of altitude lines refer to preferred DN) Flow medium: air (d, l in cm!)

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Fundamentals of Vacuum Technology Tables, Formulas, Diagrams

pSTART – pend, P R = p – p pEND – pend, p END end, P mbar pSTART < 1013 mbar pSTART = 1013 mbar

Column ➀: Vessel volume V in liters Example 1 with regard to nomogram 9.7: Example 2 with regard to nomogram 9.7: ➁ A clean and dry vacuum system (q = 0) with Column : Maximum effective pumping speed Seff,max pV,in at the vessel in (left) liters per second or A vessel with the volume V = 2000 l is to be pumped V = 2000 l (as in example 1) is to be pumped down -2 (right) cubic meters per hour. down from a pressure of pSTART = 1000 mbar to a pressure of pEND = 10 mbar. Since this pres- -2 Column ➂: Pump-down time t in (top right) seconds (atmospheric pressure) to a pressure of pEND = 10 sure is smaller than the ultimate pressure of the p mbar by means of a rotary plunger pump with an 3 or (center left) minutes or (bottom right) rotary piston pump (Seff,max = 60 m /h = 16.7 l -1 -2 hours. effective pumping speed at the vessel of ( s = 3 · 10 mbar), a Roots pump must be used S = 60 m3/h = 16.7 l · s-1. The pump-down time in connection with a rotary piston pump. The former Column ➃: Right: eff,max can be obtained from the nomogram in two steps: has a starting pressure of p = 20 mbar, a pumping Pressure p in millibar at the END of the 1 END speed of S = 200 m3/h – 55 l · s-1 as well as pump-down time if the atmospheric eff,max 1) Determination of τ: A straight line is drawn p – 4 · 10-3 mbar. From p = 1000 mbar to p = pressure p ( p = 1013 prevailed at the ult,p start START n through V = 2000 l (column ➀) and S = 60 m3/h-1 20 mbar one works with the rotary piston pump and START of the pump-down time. The desired eff = 16.7 l · s-1 (column ➁) and the value t = 120 s then connects the Roots pump from p = 20 mbar to pressure p is to be reduced by the 1 END = 2 min is read off at the intersection of these straight p = 10-2 mbar, where the rotary piston pump acts ultimate pressure of the pump p and the END ult,p lines with column ➂ (note that the uncertainty of this as a backing pump. For the first pumping step one differential value is to be used in the co- procedure is around ∆τ = ± 10 s so that the relative obtains the time constant τ = 120 s = 2 min from the lumns. If there is inflow q , the value pV,in uncertainty is about 10 %). nomogram as in example 1 (straight line through pend – pult,p – qpV,in / Seff,max is to be used -1 V = 2000 l, Seff = 16.7 l · s ). If this point in in the columns. ➂ 2) Determination of tp: The ultimate pressure of the column is connected with the point -2 -2 Left: rotary pump is pult,p = 3 · 10 mbar, the apparatus is p1 - pult,p = 20 mbar – 3 · 10 mbar = 20 mbar (pult,p Pressure reduction ratio R = (pSTART – pult,p clean and leakage negligible (set qpV,in = 0); this is is ignored here, i.e. the rotary piston pump has a -1 -2 -2 – qpV,in / Seff,max)/(pend – pult,p – qpV,in / pSTART – pult,p = 10 mbar – 3 · 10 mbar = 7 · 10 constant pumping speed over the entire range from Seff,max), if the pressure pSTART prevails at mbar. Now a straight line is drawn through the point 1000 mbar to 20 mbar) in column 5, one obtains tp,1 the beginning of the pumping operation found under 1) t = 120 s (column ➂) and the point = 7.7 min. The Roots pump must reduce the -2 ➄ -2 and the pressure is to be lowered to pEND pEND – pult,p = 7 · 10 mbar (column ) and the pressure from p1 = 20 mbar to pEND = 10 mbar, i.e. by pumping down. intersection of these straight lines with column ➃ the pressure reduction ratio R = (20 mbar – 4 · 10-3 -2 -3 -3 The pressure dependence of the pumping tp = 1100 s = 18.5 min is read off. (Again the relative mbar) / (10 mbar-4 · 10 ) = 20/6 · 10 mbar = speed is taken into account in the nomo- uncertainty of the procedure is around 10 % so that 3300. gram and is expressed in column ➄ by the relative uncertainty of tp is about 15 %.) Taking The time constant is obtained (straight line V = 2000 ➀ –1 ➁ p . If the pump pressure p is small in into account an additional safety factor of 20 %, l in column , Seff = 55 l · s in column ) at = 37 ult,p ult,p ➂ ➂ relation to the pressure p which is one can assume a pump-down time of s (in column ). If this point in column is end ➄ desired at the end of the pump-down tp = 18.5 min · (1 + 15 % + 20 %) connected to R = 3300 in column , then one ➃ operation, this corresponds to a constant = 18.5 min · 1.35 = 25 min. obtains in column tp, 2 = 290 s = 4.8 min. If one takes into account t = 1 minfor the changeover pumping speed S or Seff during the entire u pumping process. time, this results in a pump-down time of t = t + t + t = 7.7 min + 1 min + 4.8 min = 13.5 min. Fig. 9.7: Nomogram for determination of pump-down time tp of a vessel in the rough vacuum pressure range p p1 u p2

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Tables, Formulas, Diagrams Fundamentals of Vacuum Technology

C t tubes ube length T ube diameter T ection factor for shor r Conductance for molecular flow Cor

Example: What diameter d must a 1.5-m-long pipe have so tubes, is taken into account by means of a correction factor that it has a conductance of about C = 1000 l / sec in the α. For d / l < 0.1, α can be set equal to 1. In our example region of molecular flow? The points l = 1.5 m and C = 1000 d/l = 0.16 and α = 0.83 (intersection point of the straight line l/sec are joined by a straight line which is extended to inters- with the a scale). Hence, the effective conductance of the ect the scale for the diameter d. The value d = 24 cm is obtai- pipeline is reduced to C · α = 1000 · 0.83 = 830 l/sec. If d ned. The input conductance of the tube, which depends on is increased to 25 cm, one obtains a conductance of the ratio d / l and must not be neglected in the case of short 1200 · 0.82 = 985 l / sec (dashed straight line). D00 Fig. 9.8: Nomogram for determination of the conductance of tubes with a circular cross-section for air at 20 °C in the region of molecular flow (according to J. DELAFOSSE and G. MONGODIN: Les calculs de la Technique du Vide, special issue “Le Vide”, 1961)

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Fundamentals of Vacuum Technology Tables, Formulas, Diagrams

Air 20 °C es ] ] essur –1 e [mbar] –1 e [mbar] · h 3 essur essur Pr Pr Laminar flow nal diameter [cm] conductance [ l · s ection factor for higher pr ube length [meters] r Clausing factor ube inter T T Cor ected conductance for mol. flow [m r Uncor Knudsen flow Mol. flow

Procedure: For a given length (l) and internal dia- Example: A tube with a length of 1 m and an internal In a tube with a length of 1 m and an internal diameter (d), the conductance Cm, which is indepen- diameter of 5 cm has an (uncorrected) conductance meter of 5 cm a molecular flow prevails if the mean dent of pressure, must be determined in the mole- C of around 17 l/s in the molecular flow region, as pressure p in the tube is < 2.7 · 10-3 mbar. cular flow region. To find the conductance C* in determined using the appropriate connecting lines To determine the conductance C* at higher the laminar flow or Knudsen flow region with a between the “l” scale and the “d” scale. The conduc- pressures than 2.7 · 10-3 mbar, at 8 · 10-2 mbar given mean pressure of p in the tube, the conductance C found in this manner must be multiplied (= 6 · 10-2 torr), for example, the corresponding tance value previously calculated for Cm has to be by the clausing factor γ = 0.963 (intersection of point on the p scale is connected with the point multiplied by the correction factor a determined in connecting line with the γ scale) to obtain the true d = 5 cm on the “d” scale. This connecting line α α the nomogram: C* = Cm · . conductance Cm in the molecular flow region: intersects the “a“ scale at the point = 5.5. γ -2 Cm · = 17 · 0.963 = 16.37 l/s. The conductance C* at p = 8 · 10 mbar is: α C* = Cm · = 16.37 · 5.5 = 90 l/s. Fig. 9.9: Nomogram for determination of conductance of tubes (air, 20 °C) in the entire pressure range

D00.158 LEYBOLD VACUUM PRODUCTS AND REFERENCE BOOK 2001/2002 D00 E 19.06.2001 21:41 Uhr Seite 159

Tables, Formulas, Diagrams Fundamentals of Vacuum Technology ] 3 ] Pumping speed –1 olume V [min V · h 3 [m

Example 2 Pump-down time t [min]

Example 1 ] –2 · m –1 weak

normal

strong Gas evolution [mbar · l s

Area F [m2]

The nomogram indicates the relationship between the surface area concerned of 100 m2 and a gas evo- 70 m3 (C) on the volume scale: the extension results the nominal pumping speed of the pump, the cham- lution of 2 · 10-3 mbar · l · s-1 · m-2 result in an inters- in the intersection point at 30 min (E) on the time ber volume, size and nature of the inner surface as ection point A, which is joined to point B by an scale. well as the time required to reduce the pressure upward sloping line and then connected via a vertical from 10 mbar to 10-3 mbar. line to the curve that is based on the pumping speed In example 2 one has to determine what of the pump of 1300 m3/h (D). If the projection to the pumping speed the pump must have if the vessel Example 1: A given chamber has a volume of 70 m3 curve is within the marked curve area (F), the pum- (volume = approx. 3 m3) with a surface area and an inner surface area of 100 m2; a substantial ping speed of the pump is adequate for gas evoluti- of 16 m2 and a low gas evolution of gas evolution of 2 · 10-3 mbar · l · s-1 · m-2 is assu- on. The relevant pump-down time (reduction of pres- 8 · 10-5 mbar · l · s-1 · m-2 is to be evacuated from med. The first question is to decide whether a pump sure from 10 mbar to 10-3 mbar) is then given as 10 mbar to 10-3 mbar within a time of 10 min. The with a nominal pumping speed of 1300 m3/h is 30 min on the basis of the line connecting the point nomogram shows that in this case a pump with a generally suitable in this case. The coordinates for 1300 m3/h on the pumping speed scale to the point nominal pumping speed of 150 m3/h is appropriate. D00

Fig. 9.10: Determination of pump-down time in the medium vacuum range taking into account the outgasing from the walls

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Fundamentals of Vacuum Technology Tables, Formulas, Diagrams

1,00E+031000

Mercury 1,00E+02100

Halocarbon 11 1,00E+0110 Halocarbon 12

1,00E+001 Halocarbon 13 Santovac 5 (similar to Ultralen) Halocarbon 22 -1 e [mbar] 1,00E-0110 Aziepon 201

-2 1,00E-0210 essur Trichorethylene

-3 Acetone 1,00E-0310 DC 704 Diffelen ultr a apor pr

V -4 1,00E-0410 apor pressure (mbar) V -5 1,00E-0510

-6 DC 705 1,00E-0610

-7 1,00E-0710 Diffelen Temperature [°C] light -8 1,00E-0810 Diffelen normal

-9 Fig. 9.11: Saturation vapor pressure of various substances 1,00E-0910

1,00E-1010-10

-11 1,00E-1110

-12 1,00E-1210 0 25 50 75 100 150 200 250 Temperature (°C)

Fig. 9.12: Saturation vapor pressure of pump fluids for oil and mercury fluid entrainment pumps C] ° e [K] e [ emperatur emperatur T T

Vapor pressure

Fig. 9.13: Saturation vapor pressure of major metals used in vacuum technology

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Tables, Formulas, Diagrams Fundamentals of Vacuum Technology e [mbar] ć critical point b melting point essur apor pr V

Temperature [°C] 1 NBR (Perbunan) 2 Silicone rubber 3 Teflon

Fig. 9.14: Vapor pressure of nonmetallic sealing materials (the vapor pressure curve Fig. 9.15: Saturation vapor pressure ps of various substances relevant for for fluoro rubber lies between the curves for silicone rubber and Teflon) cryogenic technology in a temperaturerange of T = 2 – 80 K

Ultrahigh vacuum High vacuum Medium vacuum Rough vacuum <10–7 mbar 10–7 to 10–3 mbar 10–3 to 1 mbar 1 to approx. 103 mbar <10–5 Pa 10–5 to 10–1 Pa 10–1 to 102 Pa 102 to approx. 105 Pa

Piston vacuum pump

Diaphragm vacuum pump

Liquid-ring vacuum pump

Sliding-vane rotary vacuum pump

Multiple-vane rotary vacuum pump

Trochoide vacuum pump

Rotary plunger vacuum pump

Roots vacuum pump

Turbine vacuum pump

Gaseous-ring vacuum pump

Turbomolecular pump Liquid jet vacuum pump

Vapor jet vacuum pump

Diffusion pump

Diffusion ejector pump

Adsorption pump

Submilation pump

Sputter-ion pump

Cryopump

10–14 10–13 10–12 10–11 10–10 10–9 10–8 10–7 10–6 10–5 10–4 10–3 10–2 10–1 100 101 102 103 p in mbar → D00 Working range for special model or special operating data Normal working range

Fig. 9.16: Common working ranges of vacuum pumps

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Fundamentals of Vacuum Technology Tables, Formulas, Diagrams

Ultrahigh vacuum High vacuum Medium vacuum Rough vacuum <10–7 mbar 10–7 to 10–3 mbar 10–3 to 1 mbar 1 to approx. 103 mbar <10–5 Pa 10–5 to 10–1 Pa 10–1 to 102 Pa 102 to approx. 105 Pa

Pressure balance

Spring element vacuum gauge

Bourdon vacuum gauge

Diaphragm vacuum gauge

Capacitance diaphragm vacuum gauge

Piezoelectric vacuum gauge

Liquid level vacuum gauge

U-tube vacuum gauge

Compression vacuum gauge

(McLeod vacuum gauge)

Decrement vacuum gauge

Thermal conductivity vacuum gauge

Pirani vacuum gauge

Thermocouple vacuum gauge

Bimetallic vacuum gauge

Thermistor vacuum gauge

Cold-cathode ionization vacuum gauge

Penning ionization vacuum gauge

Magnetron gauge

Hot-cathode ionization vacuum gauge

Triode ionization vacuum gauge for medium vacuum

Triode ionization vacuum gauge for high vacuum

Bayard-Alpert ionization vacuum gauge

Bayard-Alpert ionization vacuum gauge with modulator

Extractor vacuum gauge

Partial pressure vacuum gauge

10–14 10–13 10–12 10–11 10–10 10–9 10–8 10–7 10–6 10–5 10–4 10–3 10–2 10–1 100 101 102 103 p in mbar → The customary limits are indicated in the diagram.

Working range for special models or special operating data

Fig. 9.16a: Measurement ranges of common vacuum gauges

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Tables, Formulas, Diagrams Fundamentals of Vacuum Technology

Saturated vapor

3 Fig. 9.17: Specific volume Vsp of saturated water vapor in m /kg within a range of 0.013 to 133 mbar

D00 Fig. 9.18: Breakdown voltage U between parallel electrodes in a homogeneous electrical field as a function of gas pressure p distance between electrodes d (in mm) (Paschen curve), for air

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Fundamentals of Vacuum Technology Tables, Formulas, Diagrams

SOLID liquid

Evaporation

Melting

Triple point (0.01°C, 6.09 mbar)

Sublimation e [mbar] essur

GASEOUS ater vapor pr W

Temperature [°C]

Fig. 9.19: Phase diagram of water

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Statutory Units Fundamentals of Vacuum Technology

the units now to be used, including the SI Detailed descriptions are provided in publi- 10. The statutory units (see below) and legally permissible cations by W. Haeder and E. Gärtner (DIN), units derived from them. The list is follo- by IUPAP 1987 and by S. German, P. Draht units used in wed by a number of remarks in Section (PTB). These should always be referred to 10.3. The purpose of the remarks is, on the if the present summary tailored to vacuum vacuum one hand, to establish a connection with technology leaves any questions open. previous practice wherever this is neces- technology sary and, on the other hand, to provide explanations on practical use of the con- 10.1 Introduction tent of the alphabetical list. The statutory units for measurements are Two federal German laws and the related based on the seven basic SI units of the 10.2 Alphabetical list 1) implementing provisions stipulate which Système International (SI). units must be used for measurements of variables, today (generally since January 1, 1978) in Statutory units are: symbols and units business and official documents and com- a) the basic SI units (Table 10.4.1) munications. The provisions resulted in a frequently used in number of fundamental changes that also b) units derived from the basic SI units, in have to be taken into account in vacuum some cases with special names and unit vacuum technology technology. Many of the units commonly symbols (Tables 10.4.2 and 10.4.4) and its used in the past, such as torr, gauss, stan- c) units used in atomic physics (Table dard cubic meter, atmosphere, poise, kilo- 10.4.3) applications (see calorie, kilogram-force, etc., are no longer permissible. Instead, other units are to be d) decimal multiples and decimal parts of also DIN 28 402) used, some of which are new while others units, some with special names 1) were previously used in other fields. The 5 -2 The list is based on work done by Prof. Dr. I. Examples: 10 N ( m = 1 bar) Lückert, for which we would like to express our alphabetical list in Section 10.2 contains 3 1 dm = 1 l (liter) gratitude the major variables relevant for vacuum 103 kg = 1 t (ton) technology along with their symbols and

No. Variable Symbol SI- Preferred statutory No. of remark Notes unit units in Section 10.3 –1 –1 1 Activity (of a radioactive substance) A s (Bq) s 3/1 2 (General gas constant) – see no. 73 3 Work W J J, kJ, kWh, Ws

4 Atomic mass mu kg kg, mg see Table V in Sect. 9 –1 –1 5 Avogadro constant NA mol mol 6 Acceleration a m · s–2 m · s–2, cm · s–2 7 Boltzmann constant k J · K–1 j · K–1, mbar · l · K–1 see Table V in Sect. 9 8 Celsius temperature ϑ (theta) – °C 3/2 –2 9 Vapor pressure pv N · m , Pa mbar, bar 3/3 Pa = Pascal 10 Time t s s, min, h see Table 10.4.4 11 Density (gas density) ρ (ro) kg · m–3 kg · m–3, g · cm–3 3/6 12 Dielectric constant ε (epsilon) F · m–1 F · m–1, As · V–1 · m–1 F = Farad 13 Diffusion coefficient D m2 · s–1 m2 · s–1, cm2 · s–1 14 Moment of momentum L N · s · m N · s · m 15 Torque M N · m N · m, kN · m 16 Rotational speed, rotational frequency n, f s–1 s–1, min–1 17 Pressure in fluids p N · m–2, Pa bar, mbar 3/3 Pa = Pascal 18 Pressure as mechanical stress p N · m–2, Pa N · mm–2 3/4 19 Diameter d m cm, mm 20 Dynamic viscosity η (eta) Pa · s mPa · s 3/5 –2 21 Effective pressure pe N · m , Pa mbar 3/3 see also no. 126 22 Electric field strength E V · m–1 V · m–1 D00 23 Electrical capacitance C F F, µF, pF F = Farad 24 Electrical conductivity σ (sigma) S · m–1 S · m–1

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Fundamentals of Vacuum Technology Statutory Units

No. Variable Symbol SI unit Preferred statutory No. of remark Notes units in Section 10.3 25 Electrical conductance G S S S = Siemens 26 Electrical voltage U V V, mV, kV 27 Electric current density S A · m–2 a · m–2, A · cm–2 28 Electric current intensity I A A, mA, µA 29 Electrical resistance R Ω (ohm) Ω , kΩ , MΩ 30 Quantity of electricity (electric charge) Q C C, As C = Coulomb 31 Electron rest mass me kg kg, g see Table V in Sect. 9 32 Elementary charge e C C, As –2 33 Ultimate pressure pult N · m , Pa mbar 34 Energy E J J, kJ, kWh, eV J = Joule 35 Energy dose D J · k–1 3/5 a 36 Acceleration of free fall g m · s–2 m · s–2 see Table V in Sect. 9 37 Area A m2 m2, cm2 –2 –1 –2 –1 –2 –1 38 Area-related impingement rate ZA m · s m · s ; cm · s 39 Frequency f Hz Hz, kHz, MHz 40 Gas permeability Q m3 (NTP) cm3 (NTP) 3/19 d =day (see Tab. 10.4.4 perm –––––––––– –––––––––– m2 · s · Pa m2 · d · bar see no. 73 and no. 103) 41 Gas constant R 42 Velocity v m · s–1 m · s–1, mm · s–1, km · h–1 43 Weight (mass) m kg kg, g, mg 3/6 44 Weight (force) G N N, kN 3/7 45 Height h m m, cm, mm 46 Lift s m cm see also no. 139 47 Ion dose J C · kg–1 c · kg–1, C · g–1 3/8 48 Pulse p^ (b) N · s N · s 49 Inductance L H H, mH H = Henry κ κ –1 50 Isentropic exponent (kappa) – – = cp · cv –1 –1 –1 –1 51 Isobaric molar heat capacity Cmp J · mol · K J · mol · K –1 –1 –1 –1 52 Isobaric specific heat capacity cp J · kg · K J · kg · K –1 –1 53 Isochore molar heat capacity Cmv J · mol · K –1 –1 –1 –1 54 Isochore specific heat capacity cv J · kg · K J · kg · K 55 Kinematic viscosity ν (nü) m2 · s–1 mm2 · s–1, cm2 · s–1 3/9

56 Kinetic energy EK J J 57 Force F N N, kN, mN 3/10 N = Newton 58 Length l m m, cm, mm 3/11 59 Linear expansion coefficient α (alpha) m m ––––– –––––––– ; K–1 m · K m · K 60 Leak rate Q N · m · s–1 mbar · l ; cm3 3/12 L ––––––– –––– (NTP) s s 61 Power P W W, kW, mW 62 Magnetic field strength H A · m–1 A · m–1 3/13 63 Magnetic flux density B T T 3/14 T = Tesla 64 Magnetic flux Φ (phi) Wb, V · s V · s 3/15 Wb = Weber 65 Magnetic induction B T T see no. 63 66 Mass m kg kg, g, mg 3/6 –1 –1 –1 –1 67 Mass flow rate qm kg · s kg · s , kg · h , g · s –1 o 68 Mass content wi kg · kg %, /oo, ppm ppm = parts per million ρ –3 –3 –3 –3 69 Mass concentration i (ro-i) kg · m kg · m , g · m , g · cm 70 Moment of inertia J kg · m2 kg · m2 71 Mean free path λ m m, cm –1 –1 72 Molality bi mol · kg mol · kg 73 Molar gas constant R J mbar · l see Table V in Sect. 9 –––––––––– –––––––––– mol · K mol · K 74 Molar mass (quantity-related mass) M kg mol–1 kg · kmol–1, g · mol–1

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Statutory Units Fundamentals of Vacuum Technology

No. Variable Symbol SI unit Preferred statutory No. of remark Notes units in Section 10.3 3 –1 3 –1 –1 75 Molar volume Vm m · mol m · mol , l · mol 3 –1 3 –1 76 Molar volume, standard Vmn m · mol m · mol (NTP) see Table V in Sect. 9 l · mol–1 (NTP) 77 Molecular mass m kg g 78 Normal stress (mech.) σ (sigma) N · m–2 N · mm–2 ρ –3 –3 –3 79 Standard density of a gas n (ro-en) kg · m kg · m , g · cm –2 80 Standard pressure pn N · m , Pa mbar see Table V in Sect. 9 3 3 3 81 Standard volume Vn m m (NTP), cm (NTP) 3/16 –2 82 Partial pressure pi N · m , Pa mbar 3/17 83 Period T s s, ms, µs 84 Permeation coefficient P m3 · m cm2 3/18 ––––––––– –––––––– s · m2 · bar s · mbar 85 Planck constant h J · s J · s see Table V in Sect. 9 –1 –1 86 pV throughput qpV N · m · s mbar · l · s 3/19 87 pV value pV N · m mbar · l 3/19 88 Radius (also molecular radius) r m cm, mm, µm 89 Space charge density ρ (ro) C · m–3 C · m–3, As · m–3 90 Solid angle Ω (omega) sr sr sr = steradian

91 Relative atomic mass AT – – 3/20 nondimensional variab. 92 Relative molecular mass Mr – – 3/21 nondimensional variab. 93 Relative particle mass Mr – – nondimensional variab. –2 94 Residual vapor pressure prd N · m , Pa mbar –2 95 Residual gas pressure prg N · m , Pa mbar –2 96 Residual (total) pressure pr N · m , Pa mbar 97 Reynold number nondimensional Re – – nondimensional variab. variable –2 98 Saturation vapor pressure ps N · m , Pa mbar –1 –1 99 Throughput (of a pump) qpV, Q N · m · s mbar · l · s 100 Pumping speed S m3 · s–1 m3 · h–1, l · s–1 see no. 132 101 Stress (mech.) ρ, σ, τ N · m–2 N · m–2, N · mm–2 3/4 see no. 18 (ro, sigma, tau) –1 –1 –1 –1 102 Specific electron charge –e · me C · kg C · kg , As · kg see Table V in Sect. 9 103 Specific gas constant R J · kg–1 · K–1 mbar · l 3/22 i –––––––– kg · K 104 Specific ion charge e · m–1 C · kg–1 C · kg–1, As · kg–1 105 Specific electrical resistance ρ (ro) Ω · m Ω · cm, Ω · mm2 · m–1 106 Specific volume v m3 · kg–1 m3 · kg–1; cm3 · g–1 107 Specific heat capacity c J · kg–1 · K–1 J · kg–1 · K–1, J · g–1 · K–1 3/23 108 Stefan-Boltzmann constant s (sigma) W W see Table V in Sect. 9 –––––– –––––– m2 · K4 m2 · K4 109 Quantity of substance ν (nü) mol mol, kmol –1 –1 110 Throughput of substance qv mol · s mol · s –3 –3 –1 111 Concentration of substance ci mol · m mol · m , mol · l for substance “i” 112 Collision rate Z s–1 s–1 113 Conductance C, German: L m3 · s–1 m3 · s–1, l · s–1 114 Flow resistance R s · m–3 s · m–3, s · l–1 115 Number of particles N – – nondimensional variab. 116 Particle number density (volume-related) n m–3 cm–3 –1 –1 117 Particle number density (time-related) qN s s see no. 120 –2 –1 –2 –1 –2 –1 118 Particle throughput density jN m · s m · s , cm · s see no. 121 119 Particle mass m kg kg, g D00 –1 –1 120 Particle flux qN s s see no. 117

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Fundamentals of Vacuum Technology Statutory Units

No. Variable Symbol SI unit Preferred statutory No. of remark Notes units in Section 10.3 –2 –1 –2 –1 –2 –1 121 Particle flux density jN m · s m · s , cm · s see no. 118 122 Thermodyn. temperature T K K, mK 123 Temperature difference ∆T, ∆ϑ K K, °C 3/24 2 –1 λ ρ–1 124 Temperature conductivity a m · s a = · · cp –2 125 Total pressure pt N · m , Pa mbar 3/3 –2 126 Overpressure pe N · m , Pa mbar 3/3 –2 127 Ambient pressure Pamb N · m , Pa mbar, bar 3/3 128 Speed of light in vacuum c m · s–1 m · s–1, km · s–1 see Table V in Sect. 9

129 Evaporation heat Ld J kJ 130 Viscosity, dynamic η (eta) Pa · s mPa · s see no. 20 131 Volume V m3 m3, l, cm3 3 –1 3 –1 –1 132 Volume throughput (volumetric flow) qv m · s m · h , l · s σ 3 –3 –1 o 133 Volume concentration i m · m l · l , %, /oo, ppm ppm = parts per million (sigma-i) –1 –3 –1 –3 –1 –3 134 Volume-related collision rate Zv s · m s · m , s · cm 135 Quantity of heat Q J J, kJ, kWh, Ws 3/25 136 Heat capacity C J · K–1 J · K–1, kJ · K–1 137 Thermal conductivity λ W W ––––– –––––– (lambda) K · m K · m 138 Heat transfer coefficient α (alpha) W –––––– K · m2 139 Path length s m m, cm 140 Wave length λ (lambda) m nm 3/11 141 Angle (plane) α, β, γ rad rad rad, °, ‘, ‘’ 3/26 rad = radian (alpha, beta, gamma) 142 Angular acceleration α (alpha) rad · s–2 rad · s–2 143 Angular velocity ω (omega) rad · s–1 rad · s–1 144 Efficiency η (eta) – – nondimensional variab. 145 Time t s s, min, h, nn, mn see Table 10.44 146 Period of time t, ∆t s s, min, h see Table 10.44

5 10.3 Remarks on bar (1 bar = 0.1 MPA = 10 Pa) is stated gnated as overpressure pe: pe = p – pamb. in addition to the (derived) SI unit, The overpressure can have positive or alphabetical list 1 Pa = 1 N · m-2, as a special name for one negative values. tenth of a megapascal (Mpa). This is in in Section 10.2 Conversions accordance with ISO/1000 (11/92), p. 7. -2 3/1: Activity Accordingly the millibar (mbar), a very 1 kg · cm = 980.665 mbar = 981 mbar The unit previously used was curie (Ci). useful unit for vacuum technology, is also 1 at (technical atmosphere) = permissible: 1 mbar = 102 Pa = 0.75 torr. 10 -1 -1 980.665 mbar = 981 mbar 1 Ci = 3.7 · 10 · s = 37 ns The unit “torr” is no longer permissible. 1 atm (physical atmosphere) = 3/2: (°C) Celsius temperature Special note 1013.25 mbar = 1013 mbar The term degrees Celsius is a special name Exclusively absolute pressures are measu- 1 atmosphere above atmospheric pressure for the SI unit kelvin (K) [see no. 122] for red and used for calculations in vacuum (atmospheric overpressure) = indicating Celsius temperatures. The term technology. 2026.50 mbar = 2 bar degrees Celsius is legally approved. In applications involving high pressures, 1 atm frequently pressures are used that are 1 torr = 1 mm Hg = –––––– = 1 3/3: Pressure 760 The revised version of DIN 1314 must based on the respective atmospheric pres- be complied with. The specifications of sure (ambient pressure) pamb. According 33.322 Pa= 1.333 mbar this standard primarily apply to fluids to DIN 1314, the difference between a 1 meter head of water = 9806.65 Pa = (liquids, gases, vapors). In DIN 1314, pressure p and the respective atmospheric pressure (ambient pressure) pamb is desi- 98 mbar

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1 mm Hg = 133.332 Pa = 1.333 mbar = 3/10: Force 3/18: Gas permeability 4/3 mbar The dyne, the CGS unit for force, is no lon- The permeation coefficient is defined as ger used. the gas flow m3 · s-1 (volumetric flow p ) The pressure as mechanical stress V that goes through a fixed test unit of a (strength) is generally given in pascal (Pa) 1 dyne = 10-5 N given area (m2) and thickness (m) at a –2 and in N · nm . given pressure difference (bar). 3/11: Length/wavelength According to DIN 53.380 and DIN 7740, Conversions: The unit Ångström (Å) (e.g. for wave- Sheet 1, supplement, the gas permeability 1 Pa = 1 N · m–2 = 10–6 N · mm–2 length) will no longer be used in future (see no. 40) is defined as “the volume of a (see Table 4.6). gas, converted to 0 °C and 760 torr, which 1 kg · cm–2 = 98,100 Pa = 0.981 N · mm–2 -8 goes through 1 m2 of the product to be –2 1 Å = 10 cm = 0.1 nm = 0,1 N mm tested at a certain temperature and a cer- 1 kg · mm–2 = 9,810,000 Pa = tain pressure differential during a day 9.81 N · mm–2 = 10 N · mm–2 3/12: Leak rate (= 24 hours)”. In DIN 40.046 sheet 102 (draft of August 1973 issue), the unit mbar · dm3 · s-1 3/5: Dynamic viscosity (= mbar · l · s-1) is used for the leak rate. 3/19: pV throughput/pV value The unit previously used was poise (P). Note that the leak rate corresponding DIN 28.400, Sheet 1 is to be taken into -1 account here. No. 86 and no. 87 have a 1 P = 0.1 Pa · s = 1 g · cm–1 · s–1 to the unit 1 mbar · l · s at 20 °C is practically the same as the leak rate quantitative physical significance only if 1 cm3 · s-1 (NTP). (See also 3/17) the temperature is indicated in each case. 3/5a: Energy dose Rad (rd) is no longer permissible. 3/13: Magnetic field strength 3/20: Relative atomic mass 1 The previously used unit was the oersted Misleadingly called “atomic weight” in the 1 rd = –––– J · kg–1 100 (Oe). past! 1 Oe = 79.577 A · m-1 3/6: Weight DIN 1305 is to be complied with in this 3/21: Relative molecular mass context. Because of its previous ambiva- 3/14: Magnetic flux density Misleadingly called “molecular weight” in lence, the word weight should only be The previously used unit was the gauss the past! used to designate a variable of the nature (G). of a mass as a weighing result for indica- -4 -2 -4 ting quantities of goods. 1 G = 10 Vs · m = 10 T (T = Tesla) 3/22: Specific gas constant As mass-related gas constant of the The designations “specific weight” and substance “i”. Ri = Rm ( Mi-1; Mi molar “specific gravity” should no longer be 3/15: Magnetic flux mass (no. 74) of the substance “i”. See used. Instead, one should say density. The previously used unit was the maxwell also DIN 1345. (M). 1 M = 10-8 Wb (Weber) 3/7: Weight force 3/23: Specific heat capacity See DIN 1305. The previous units pond (p) Also called specific heat: and kilopond, i.e. kilogram-force, (kp) as 3/16: Standard volume Specific heat (capacity) at constant well as other decimal multiples of p are no DIN 1343 must be complied with. longer used. pressure: cp. The designation m3 (NTP) or m3 (p , T ) 1 kp = 9.81 N n n Specific heat (capacity) at constant is proposed, though the expression in volume: c . parentheses does not belong to the unit V symbol m3 but points out that it refers to 3/8: Ion dose the volume of a gas in its normal state 3/24: Temperature difference The previously used unit was the Röntgen (T = 273 K, p = 1013 mbar). (R). 1 R = 2,58 · 10–4 C · kg–1 n n Temperature differences are given in K, but can also be expressed in °C. The designation degrees (deg) is no longer 3/17: Partial pressure 3/9: Kinematic viscosity permissible. The index “i” indicates that it is the partial The previously used unit was stokes (St). pressure of the “i-th” gas that is contained 1 St = 1 cm2 · s–1; 1 cSt = 1 mm2 · s–1 in a gas mixture. D00

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3/25: Quantity of heat 10.4.2 Derived coherent 1) SI 10.4.3 Atomic units The units calorie (cal) and kilocalorie (kcal) units with special names are no longer be used. and symbols Basic unit Symbol Vartiable 1 kcal = 4.2 kJ ———————————————— (alphabetical) Atomic Mass for indication of Name Symbol Variable Relationship mass mu particle mass; 3/26: Angle of unit 1 radian (rad) is equal to the plane angle ———————————————————— unit 1 mu = 1/12 mass which, as the central angle of a circle, cuts coulomb C quantity of of 12C out an arc having a length of 1 m from the electricity also amu circle. See also DIN 1315 (8/82). or electric (atomic mass charge 1 C = 1 A · s π unit). farad F electrical Electron eV energy 1° = ––––– rad: 1’ = 1°/60; 1’’ = 1’/60. –1 180 capacitance 1 F = 1 A · s · V volt henry H inductance 1 H = 1 V · s · A–1 360° hertz Hz frequency 1 Hz = 1 · s–1 1 rad = ––––– · 60° 2π joule J energy, work, 1 J = 1 N · m quantity = Ws of heat 10.4.4 Derived noncoherent lumen lm luminous flux 1 lm = cd · sr SI units with special lux lx illuminance 1 lx = 1 lm · m–2 names and symbols newton N force 1 N = 1 kgm · s–2 10.4 Tables ohm Ω electrical 1 Ω = 1 V · A–1 Basic unit Symbol Definition resistance ———————————————— pascal Pa pressure, 1 Pa = 1 N · m–2 Day d 1 d = 86.400 s 10.4.1 Basic SI units mechanical stress Hour h 1 h = 3.600 s radian rad 2) angle, 1 rad = 1 m · m–1 Minute min 1 min = 60 s Basic unit Symbol Variable plane angle Round angle – 2 p rad ———————————————— siemens S electrical meter m length conductance 1 S = 1 · Ω–1 π Degree (°) –––– rad kilogramm kg mass steradian sr 2) solid angle 1 sr = 1 m2 · m–2 180 second s time, period; –2 π duration tesla T magnetic 1 T = 1 Wb · m flux density or Minute (‘) –––––– rad ampere A electric current induction 10.800 kelvin K thermodyn. volt V electrical 1 V = 1 W · A–1 1 temperature (= ––– grad) voltage 60 mole mol quantity of or potential substance difference p Second (‘’) ––––––– rad candela cd luminous watt W power, 1 W = 1 J · s–1 648.000 intensity energy flux, heat 1 (= –––– minute) flux 60 weber Wb magnetic 1 Wb = 1 V · s flux 1 Wb = 1 V · s

1) Formed with numeric factor 1; e.g. 1 C = 1 As, 1 Pa = 1 N · m–2 2) Additional SI unit

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Vacuum Technology Standards Fundamentals of Vacuum Technology

11. National and with German participation (also by DIN Title Issue LEYBOLD), has been extensively incorpo- 1319 Basic definitions for rated into DIN standards, as reflected in measurement technology international designations such as DIN / ISO or DIN / Part 1 – Basic definitions 1/95 EN. Part 2 – Definitions for the standards and use of gauges 1/80 The most important standards to be com- Part 3 – Definitions for measurement recommendati- plied with are listed in Table 11.1 below. uncertainty and Abbreviations used: evaluation of gauges ons particular- and measuring D = draft equipment 8/83 CD = Committee Draft Part 4 – Treatment of use ly relevant to of measurements 12/85 vacuum A) National agreements, Part 1: DIN technology 11.1 National and (cont.) international DIN Title Issue 1343 Normal state, reference state 1/90 For around 20 years now, numerous stan- standards and dards and recommendations have been 1345 Thermodynamics; basic recommendations definitions drawn up at national and international level 12/93 and revised, whenever necessary, in of special accordance with the state of the art. These 1952 Flow measurement with relevance to screens, nozzles, etc. 7/82 standards and recommendations must be observed whenever use is made of vacu- vacuum technology 2402 Pipelines; nominal internal diameters, definitions, um equipment (pumps, gauges, valves, classification 2/76 etc.) and vacuum apparatus, systems and A) National agreements, Part 1: DIN plants are assembled. They not only con- 3535 Seals for gas supply – Part 6 4/94 tain specifications applying specially to DIN Title Issue 8964 Circuit parts for refrigeration vacuum technology, but also go beyond 1301-8 E Units systems with hermetic and semi-hermetic compressors this specific field and involve, for example, Part 1 – Names of units, symbols 1993 Part 1: Tests 3/96 physical units, formulas, noise protection Part 2 – Parts and multiples Part 2: Requirements 9/86 regulations, etc. generally used 2/78 (E 12/95) Part 3 – Conversions for units National standards are primarily DIN stan- 16005 Overpressure gauges with no longer used 6/79 elastic measuring element for dards, particularly those relating to the 1304 General symbols general use Requirements area of vacuum technology in the DIN Part 1 – General symbols 3/94 and testing 2/87 Standards Committee on Mechanical Part 2 – Symbols for 16006 Overpressure gauges with Engineering (NAM). International stand- meteorology and Bourdon tube Safety-related ards and recommendations are drawn up geophysics 9/89 requirements and testing 2/87 Part 3 – Symbols for electrical and issued energy supply 3/89 19226 – 1 Control and a) by the International Standardization Part 5 – Symbols for flow instrumentation mechanics 9/89 technology; Organization (ISO), in particular by ISO Part 6 – Symbols for electrical control and regulation Committee TC 112 (vacuum technolo- communications technology; definitions – gy) technology 5/92 general principles 2/94 Part 7 – Symbols for – 4 Control and b) by the European Committee of Manu- meteorology and instrumentation facturers of Compressors, vacuum geophysics technology; Part 7 – Symbols for control and regulation pumps and compressed air tools electric machines 1/91 technology; (PNEUROP), in particular by PNEUROP definitions for control Subcommittee C5 (vacuum technology) 1305 Mass; weighed value, force, and regulation systems 2/94 weight force, weight – 5 Control and c) by the European Committee for Stan- load, definitions 1/88 instrumentation dardization (CEN), in particular by Tech- 1306 Density; definitions 6/84 technology; control and nical Committee TC 138 (nondestruc- regulation technology; 1313 Physical variables and functional definitions 2/94 tive testing) and Technical Committee equations, definitions, spelling 4/78 TC 318. 25436 Integral leak rate test of safety 1314 Pressure; basic definitions, vessel with absolute pressure D00 The content of the documents drawn up by units 2/77 method 7/80 the international organizations in a) to c),

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Fundamentals of Vacuum Technology Vacuum Technology Standards

DIN Title Issue DIN Title Issue A) European/national agreements, EN, 28090 Static seals for flange 28426 Vacuum technology; DIN/EN, CEN connections acceptance specifications or DIN/EN Title Issue Part 1 - Characteristic values frotary piston vacuum pumps for seals and Part 1 – Rotary piston and EN 473 Training and certification of testing methods 9/95 vane type rotary personnel for nondestructive Part 2 - Seals made of vacuum pumps in testing (including leak test) 7/93 sealing plate; special rough and medium testing methods for vacuum range 837-1 Pressure gauges, Part 1: quality assurance 9/95 Part 2 – Roots vacuum pumps Pressure gauges with in medium Bourdon tubes, dimensions, 28400 Vacuum technology; vacuum range measurement designations and definitions technology, requirements Part 1 - Basic definitions, units, 28427 Vacuum technology; and testing 2/97 ranges, characteristic acceptance specifications variables and basic for diffusion pumps and 837-2 Pressure gauges, Part 2: principles 5/90 ejector vacuum pumps for Selection and installation Part 2 - Vacuum pumps 10/80 pump fluid vapor pressures of recommendations for Part 3 - Vacuum plants; less than 1 mbar 2/83 pressure gauges 1/95 characteristic 28428 Vacuum technology; 837-3 Pressure gauges, Part 3: variables and gauges 6/92 Pressure gauges with Part 4 - Vacuum coating acceptance specifications for turbo-molecular pumps 11/78 plate and capsule elements, technology 3/76 dimensions, measurement Part 5 - Vacuum drying and 28429 Vacuum technology; technology, requirements vacuum freeze-drying 3/81 acceptance specifications and testing 2/97 Part 6 - Analytical techniques for getter-ion pumps 8/85 for surface technology 10/80 1330-8 E Nondestructive testing - Part 7 - Vacuum metallurgy 7/78 28430 Vacuum technology; definitions for leak test – Part 8 - Vacuum systems, measuring specifications for terminology 6/94 components and ejector vacuum pumps and accessories 10/80 ejector compressors. 1779 E Nondestructive (E 7/91) Pump fluid: water vapor 11/84 testing – leak test. Instructions for selection of a testing 28401 Vacuum technology; 28431 Acceptance specifications method 3/95 symbols – overview 11/76 for liquid ring vacuum pumps 1/87 1338-8 E Nondestructive 28402 Vacuum technology: variables, 28432 Acceptance specifications for testing – leak test. symbols, units - overview 12/76 diaphragm vacuum pumps E 5/95 Terminology on leak test 1994 28403 Vacuum technology; quick 53380 Testing of plastic foils, 1518 E Nondestructive connections, small flange determination of gas testing – determination of connections 9/86 permeability 6/69 characteristic variables for (E 10/83) mass spectrometer 28404 Vacuum technology: flanges, leak detectors dimensions 10/86 45635 Noise measurement at machines: measurement 1593 E Nondestructive 28410 Vacuum technology; mass of airborne noise, enveloping testing – bubble type spectrometer partial pressure surface methods. testing method 12/94 gauges, definitions, Part 13 – Compressors, characteristic variables, including vacuum NMP 826 Calibration of gaseous operating conditions 11/86 pumps, positive reference leaks, CD 9/95 Nr. 09–95 28411 Vacuum technology; displacement, turbo acceptance specifications and steam ejectors 2/77 for mass spectrometer leak 55350 Definitions of quality detection devices, definitions 3/76 assurance and statistics B) International agreements, ISO, EN/ISO Part 11 – Basic definitions of 28416 Vacuum technology; DIN Title Issue quality assurance 8/95 calibration of vacuum gauges in Part 18 – Definitions regarding a range from 10-3 to 10-7 mbar. 1000 SI units and recommendations certification of General methods; pressure for the use of their multiples results of quality and of certain other units 11/92 reduction through constant flow 3/76 tests/quality test 28417 Vacuum technology; measuring certificates 7/87 1607 / 1 Positive displacement vacuum pV mass flow according to pumps. Measurement of volumetric method at constant 66038 Torr – millibar; millibar – torr performance characteristics. 12/93 pressure 3/76 conversion tables 4/71 Part 1 - Measurement of volume rate of flow – Thesaurus Vacui 28418 Vacuum technology; standard (pumping speed) method for calibrating vacuum (definition of terms) 1969 gauges through direct compa- 1607 / 2 Positive displacement vacuum rison with a reference device pumps. Measurement of Part 1 – General principles 5/76 performance characteristics. 11/89 Part 2 – Ionization vacuum Part 2 - Measurement of gauges 9/78 ultimate pressure Part 3 – Thermal conductivity vacuum gauges 8/80

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DIN Title Issue DIN Title Issue 1608 / 1 Vapor vacuum pumps. DIN/ISO Requirements placed on quality Part 1 Measurement of volume 10012 assurance for measuring rate of flow 12/93 equipment 8/92 Part 1 – Confirmation system 1608 / 2 Vapor vacuum pumps. for measuring Part 2: Measurement of critical equipment backing pressure 12/89 1609 Vacuum technology. Flange dimensions 3/86 C) PNEUROP/C5 (6.93) DIN/ISO Standard atmosphere 12/79 Number Title/remark identical Issue 2533 to DIN 2861 / 1 Quick release couplings. 5607 Vacuum pumps; Dimensions 8/74 acceptance specifications 28427 1972 Part 1 - Clamped Type Part II: (Fluid 2861 / 2 Quick release couplings. entrainment pumps) Dimensions 8/80 5608 Vacuum pumps; Part 2 - Screwed type acceptance specifications 28428 1973 3529 / 1 Vacuum Technology Part III: (Turbomolecular Vocabulary 12/81 pumps) Part 1 - General terms 5615 Vacuum pumps; 3529 / 2 Vacuum Technology acceptance specifications 28429 1976 Vocabulary 12/81 Part IV: (Getter-ion Part 2 - Vacuum pumps and pumps) related terms 6601 Measurement of per 3529 / 3 Vacuum Technology formance of ejector Vocabulary 12/81 vacuum pumps and Part 3 - Vacuum gauges ejector compressors 28430 5/78 3556 / 1 Measurement of performance 6602 Vacuum pumps; characteristics. 1992 acceptance specifications Part 1 - Sputter ion pumps (E) Part I: (Oil-sealed rotary pumps and 3567 Vacuum gauges. Calibration by Roots pumps) 28426 1979 direct comparison with a reference gauge (CD) 2/91 6606 Vacuum flanges and connections; 28403 1985 3568 Ionisation vacuum gauge. dimensions and Calibration by direct 28404 comparison with a reference gauge (CD) 2/91 PN5ASR Vacuum pumps, CC/5 acceptance specifications 3570 / 1 Vacuum gauges – standard refrigerator cooled methods for calibration 2/91 cryopumps 7/89 Part 1 - Pressure reduction by continuous flow in the pressure range 10–1 ... 10–5 Pa 3669 Vacuum Technology. Bakable flanges, dimensions. 2/86 Part 1: Clamped Type EN/ISO Rubber and plastic hoses and 4080 hose lines – determination of gas permeability 4/95 5167 Measurement of fluid flow by means of orifice plates, nozzles etc. 1980 5300 Vacuum gauges of the thermal conductivity type. 2/91 Calibration by direct comparison with a reference gauge (CD) 9803 Pipeline fittings-mounting, dimensions (E) 2/93 D00

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Fundamentals of Vacuum Technology References

C. M. van Atta L. Fabel 12. References Vacuum Science and Engineering Physik in der 2. Hälfte des 19. Jahr 459 pages, 1965, McGraw-Hill hunderts und die vakuumtechnische 1. Overview, New York/San Francisco/Toronto/ Entwicklung bis Gaede London/Sydney Pages 128-138 definitions and J. M. Lafferty et. al. H.-B. Bürger: Foundations of Vacuum Science and G. Ch. Lichtenberg und die Vakuum history Technology technik 704 pages, 1998, Wiley 1998 Pages 124-127 K. Diels, R. Jaekel Leybold Vacuum Handbook A. Schubert G. Reich: Pergamon Press Normen und Empfehlungen für die Gaede und seine Zeit 1st Ed. 1966 Vakuum-Technik Pages 139-145 Vakuum in der Praxis, W. Haeder, E. Gärtner Vol. 3, 1991, 211-217 H. Adam Die gesetzlichen Einheiten in der Technik Vakuum-Technik in der Zeit nach Beuth-Vertrieb GmbH, 5. Aufl. 1980, H. Scharmann Gaede (1945 to the present); Berlin 30, Köln, Frankfurt (Main) Vakuum – Gestern und Heute Pages 146-147 Vakuum in der Praxis, H. Ebert Vol. 2, 1990, 276-281 G. Reich Vakuum-Chronik, A documentation on Die Entwicklung der Gasreibungspumpen works concerning vacuum that were M. Auwärter von Gaede, über Holweck, Siegbahn bis published before 1928 Das Vakuum und W. Gaede zu Pfleiderer und Becker (mit zahlreichen PTB-Bericht ATWD-11, September 1977 Vakuum-Technik, Vol. 32, 1983, 234-247 Literaturangaben) Vakuum-Technik in der Praxis, Vol. 4, M. Dunkel J. F. O’Hanlon 1992, 206-213 „Gedenken an Wolfgang Gaede“ A User’s Guide to Vacuum Technology Physikalische Blätter Nr. 34 (1978), 3nd Ed., 402 pages, Wiley 1989, G. Reich Heft 5, Pages 228-232 as well as New York Carl Hoffman (1844-1910), der Erfinder Vakuum-Technik, 27. Jahrgang, No. 4, der Drehschieberpumpe Pages 99-101 G. Reich Vakuum in der Praxis, 1994, 205-208 Wolfgang Gaede – Einige Gedanken zu IUPAP (SUNANCO Commission) seinem 50. Todestag aus heutiger Sicht Th. Mulder Symbols, Units etc. Vakuum in der Praxis, Blaise Pascal und der Puy de Dôme – Document 25, 1987 7th year, 1995, 136-140 Große Männer der Vakuum-Technik Vakuum in der Praxis, 1994, 283-289 Leybold AG S. German, P. Draht Vademekum, 93 pages, 1988 Handbuch SI Einheiten W. Pupp und H. K. Hartmann Vieweg Braunschweig/Wiesbaden, Vakuum-Technik, Grundlagen und Anwen- M. Wutz, H. Adam, W. Walcher 1979, 460 pages dungen Theory and Practice of C. Hanser, München, 1991, Wien, Vacuum Technology “Gesetz über Einheiten im Meßwesen” 5. Aufl., 696 pages, 1992, vom 2. Juli 1969 Friedrich Vieweg u. Sohn, “Gesetz zur Änderung des Gesetzes über Braunschweig/ Wiesbaden Einheiten im Meßwesen” vom 6. Juli 1973 A. Guthrie and R. K. Wakerling “Ausführungsverordnungen” vom 26. 2. Vacuum pumps Vakuum Equipment and Techniques Juni 1970 264 pages, 1949, McGraw-Hill, New York/London/Toronto In Vakuum-Technik Vol. 35, 1986: 2.1 Positive displacement Th. Mulder pumps, condensers D. J. Hucknall Otto von Guericke Vacuum Technology and Applications Pages 101-110 W. Gaede 1st Ed., 319 pages, 1991 Demonstration einer rotierenden Butterworth-Heinemann, Oxford P. Schneider Quecksilberpumpe Zur Entwicklung der Luftpumpen- Physikalische Zeitschrift, 6, 1905, 758-760 Initiationen und erste Reife bis 1730 Pages 111-123

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References Fundamentals of Vacuum Technology

W. Gaede H. Lang K. P. Müller Gasballastpumpen Vakuumpumpen in der chemischen Indu- Trockenlaufende Drehschiebervakuum- Zeitschrift für Naturforschung, strie – Wälzkolbenpumpen pumpen in einer Vielzweck-Produktions- 2a, 1947, 233-238 Vakuum-Technik, 1980, 72-82 anlage Vakuum in der Praxis, 1994, 109-112 W. Armbruster und A. Lorenz H. F. Weber Das maximale Kompressionsverhältnis Vakuumpumpen in der chemischen F. J. Eckle, W. Jorisch, R. Lachenmann und der volumetrische Wirkungsgrad von Industrie – ölgedichtete Vakuum-Technik im Chemielabor Vakuumpumpen nach dem Rootsprinzip Rotationsvakuumpumpen Vakuum in der Praxis, 1991, 126-133 Vakuum-Technik, 7, 1958, 81-85 Vakuum-Technik, 1980, 98-104 P. Bachmann und M. Kuhn W. Armbruster und A. Lorenz D. Bartels Einsatz von Vorpumpen im Al-Ätzprozeß. Die Kombination Rootspumpe-Wasser- Vakuumpumpen in der chemischen Erprobung trockenverdichtender Klauen- ringpumpe Industrie pumpen und ölgedichteter Drehschieber- Vakuum-Technik, 7, 1958, 85-88 Flüssigkeitsring-Vakuumpumpen – A Vakuumpumpen im Vergleich Vakuum-Technik, 1980, 131-140 Vakuum in der Praxis, 1990, 15 – 21 H. Reylander Über die Wasserdampfverträglichkeit von R. W. Adam und C. Dahmlos U. Gottschlich Gasballastpumpen Flüssigkeitsring-Vakuumpumpen – B Vakuumpumpen im Chemielabor Vakuum-Technik, 7, 1958, 78-81 Vakuum-Technik, 1980, 141-148 Vakuum in der Praxis, 1990, 257-260

F. Fauser U. Seegebrecht M. H. Hablanian Charakteristik von Pumpsystemen für Förderung trockener Luft und von Aufbau und Eigenschaften verschiedener größere Wasserdampfmengen unter gesättigtem Luft-Wasserdampfgemisch ölfreier Vakuumpumpen für den Grob- Vakuum und unter Anwendung von Kon- mit Flüssigkeitsring-Vakuumpumpen und Feinvakuumbereich (wichtige densation und Kompression des Vakuum-Technik, 1980, 246-252 Literaturangaben) Wasserdampfes Vakuum in der Praxis, 1990, 96-102 1965 Transactions of the Third Internatio- H.-D. Bürger nal Vacuum Congress, Stuttgart, Bd. 2/II, Fortschritte beim Betrieb von B. W. Wenkebach und J. A. Wickhold 393-395, Pergamon Press, Oxford 1966 Wälzkolbenpumpen Vakuumerzeugung mit Flüssigkeitsring- Vakuum-Technik 1983, 140-147 Vakuumpumpen M. Wutz Vakuum in der Praxis, 1989, 303-310 Das Abpumpen von Dämpfen mit gekühl- U. Seegebrecht ten Kondensatoren Einfluß der Temperatur des Fördermittels U. Gottschlich und W. Jorisch Vakuum-Technik, 16, 1967, 53-56 auf das Saugvermögen von Flüssigkeits- Mechanische Vakuumpumpen im ring-Vakuumpumpen bei der Förderung Chemieeinsatz H. Hamacher von trockener Luft Vakuum in Forschung und Praxis, 1989, Kennfeldberechnung für Rootspumpen Vakuum-Technik, 1985, 10-14 113-116 DLR FB 69-88, 1969 P. Bachmann und H.-P. Berger W. Jorisch H. Hamacher Sicherheitsaspekte beim Einsatz von Neue Wege bei der Vakuumerzeugung in Beitrag zur Berechnung des ölgedichteten Drehschiebervakuumpum- der chemischen Verfahrenstechnik Saugvermögens von Rootspumpen pen in CVD-Anwendungen Vakuum in der Praxis, 1995, 115-118 Vakuum-Technik, 19, 1970, 215-221 Vakuum-Technik, 1987, 41-47 D. Lamprecht H. Hamacher U. Fussel Trockenlaufende Vakuumpumpen Experimentelle Untersuchungen an Trockenlaufende Vakuumpumpen in der Vakuum in der Praxis, 1993, 255-259 Nachkühlern von Rootspumpen chemischen Industrie Vakuum-Technik, 23, 1974, 129-135 Vakuum in der Praxis, 1994, 85-88 P. Deckert et al. Die Membranvakuumpumpe – Entwick- M. Rannow L. Ripper lung und technischer Stand Ölgedichtete Vakuumpumpen in der Explosionsschutz-Maßnahmen an Vaku- Vakuum in der Praxis, 1993, 165-171 Chemie umpumpen (with numerous references to Chemie-Technik, No. 7, 1978, 39-41 relevant literature) W. Jorisch und U. Gottschlich Vakuum in der Praxis, 1994, 91-100 Frischölschmierung – Umlaufschmierung, H. P. Berges et al. Gegensätze oder Ergänzung? TRIVAC-B, ein neues Vakuumpumpen- Vakuum in der Praxis, 1992, 115-118 D00 Konzept für universelle Anwendungen Vakuum-Technik, 31, 1982, 168-171

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W. Jitschin et al. W. Armbruster J. Henning Das Saugvermögen von Pumpen: Unter- Vakuumpumpenkombinationen für Labor, 30 Jahre Turbo-Molekularpumpe suchung verschiedener Meßverfahren im Technikum und Produktion Vakuum-Technik, 1988, 134-141 Grobvakuumbereich Chemiker-Zeitung / Chemische Apparatur, Vakuum in Forschung und Praxis, 7, 88, 1964, 895-899 P. Duval et. al. (1995) 183 -193 Die Spiromolekularpumpe W. Becker Vakuum-Technik, 1988, 142-148 H.P. Berges and M. Kuhn Die Turbo-Molekularpumpe Handling of Particles in Forevacuum Vakuum-Technik, 15, 1966, 211-218 and G. Reich pumps 254-260 Berechnung und Messung der Abhängig- Vacuum, Vol. 41, 1990, 1828-1832 keit des Saugvermögens von Turbo-Mole- R. Frank et al. kularpumpen von der Gasart M. H. Hablanian Leistungsdaten von Turbo-Molekularpum- Vakuum-Technik, 1989, 3-8 The emerging technologies of oil-free pen des Typs TURBOVAC mit senkrecht vacuum pumps angeordnetem Axialkompressor J. Henning J. Vac. Sci. Technol. Vakuum-Technik, 24, 1975, 78 -85 Die Entwicklung der Turbo-Molekular- A6 (3), 1988, 1177-1182 pumpe W. Becker Vakuum in der Praxis, 1991, 28-30 E. Zakrzewski, P. L. May and B. S. Emslie Eine gegenüberstellende Betrachtung von Developments in vacuum Pumping Diffusionspumpen und Molekularpumpen D. Urban systems based on mechanical pumps Ergebnisse europäischer Ultrahochvaku- Moderne Bildröhrenfertigung mit with an oil free swept volume umforschung Turbo-Molekularpumpen Vacuum, 38, 968, 757-760 Leybold-Heraeus GmbH u. Co., in its own Vakuum in der Praxis, 1991, 196-198 publishing house, Cologne 1968, 41-48 H. Wycliffe O. Ganschow et al. Mechanical high-vacuum pumps with an R. Frank, E. Usselmann Zuverlässigkeit von Turbo-Molekular- oil-free swept volume Kohlenwasserstoffreier Betrieb mit Turbo- pumpen J. Vac. Sci. Technol. Molekularpumpen des Typs TURBOVAC Vakuum in der Praxis, 1993, 90-96 A5 (4) 1987, 2608-2611 Vakuum-Technik, 25, 1976, 48-51 M. H. Hablanian A. P. Troup and D. Turell R. Frank, E. Usselmann Konstruktion und Eigenschaften von Dry pumps operating under harsh Magnetgelagerte Turbo-Molekularpumpen turbinenartigen Hochvakuumpumpen condictions in the semiconductor industry des Typs TURBOVAC Vakuum in der Praxis, 1994, 20-26 J. Vac. Sci. Technol. A7 (3), Vakuum-Technik, 25, 1976, 141-145 1989, 2381-2386 J. H. Fremerey und H.-P. Kabelitz H.-H. Henning und G. Knorr Turbo-Molekularpumpe mit einer P. Bachmann and M. Kuhn Neue luftgekühlte, lageunabhängige neuartigen Magnetlagerung Evaluation of dry pumps vs rotary vane Turbo-Molekularpumpen für Industrie und Vakuum-Technik, 1989, 18-22 pumps in aluminium etching Forschung Vacuum 41, 1990, 1825-1827 Vakuum-Technik, 30, 1981, 98-101 H. P. Kabelitz and J.K. Fremerey Turbomolecular vacuum pumps with a H. P. Berges and D. Götz H.-H. Henning und H. P. Caspar new magnetic bearing concept Oil-free vacuum pumps of compact Wälzlagerungen in Turbo-Molekularpum- Vacuum 38, 1988, 673-676 design pen Vacuum, Vol. 38, 1988, 761-763 Vakuum-Technik, 1982, 109-113 E. Tazioukow et al. Theoretical and experimental investigation E. Kellner et al. of rarefied gas flow in molecular pumps Einsatz von Turbo-Molekularpumpen bei Vakuum in Forschung und Praxis, 7, Auspumpvorgängen im Grob- und 1995, 53-56 2.2 Turbomolecular pumps Feinvakuumbereich Vakuum-Technik, 1983, 136-139 W. Gaede Die Molekularluftpumpe D. E. Götz und H.-H. Henning Annalen der Physik, 41, 1913, 337-380 Neue Turbo-Molekularpumpe für überwiegend industrielle Anwendungen W. Becker Vakuum-Technik, 1988, 130-135 Eine neue Molekularpumpe Vakuum-Technik, 7, 1958, 149-152

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2.3 Fluid entrainment pumps R. Gösling W. Bächler und H. Henning Treibmittelpumpen Neuere Untersuchungen über den W. Gaede Vakuum-Technik, 1980, 163-168 Edelgas-Pumpmechnismus von Die Diffusion der Gase durch Quecksilber- Ionenzerstäuberpumpen des Diodentyps dampf bei niederen Drücken und die Dif- M. Wutz Proc. of the Forth Intern. Vacuum fusionspumpe Grundlagen zur Bestimmung der Congress 1968, I. 365-368, Annalen der Physik, 46, 1915, 357-392 charakteristischen Daten von Inst. of Physics, Conference Series No. 5, Dampfstrahl-Ejektorpumpen London W. Gaede Vakuum-Technik, 1982, 146-153 Die Öldiffusionspumpe H. Henning Z. techn. Physik, 13, 1932, 210-212 H. Bayer Der Erinnerungseffekt für Argon bei R. Jaeckel, H. G. Nöller und H. Kutscher Dampfstrahlpumpen Trioden-Ionenzerstäuberpumpen Die physikalischen Vorgänge in Diffusi- Vakuum-Technik, 1980, 169-178 Vakuum-Technik, 24, 1975, 37-43 ons- und Dampfstrahlpumpen Vakuum-Technik, 3, 1954, 1-15 H. Bayer Vakuumerzeugung durch W. Bächler und H. G. Nöller Dampfstrahl-Vakuumpumpen Fraktionierung und Entgasung in Vakuum in der Praxis, 1989, 127-135 2.5 Cryopumps and Öl-Diffusionspumpen cryoengineering Z. angew. Physik einschl. Nukleonik, 9, F. Hinrichs 1957, 612-616 Aufbau, Betriebsverhalten und R. A. Haefer Regelbarkeit von Cryo-Pumping H. G. Nöller Dampfstrahl-Vakuumpumpen 456 pages, 1989 Oxford University Press, Weshalb sind systematische Fehler bei Vakuum in der Praxis, 1991, 102-108 Oxford Saugvermögensmessungen besonders groß für Hochvakuumpumpen großer H. Frey und R-A. Haefer Leistung ? Tieftemperaturtechnologie, 560 pages, Vakuum-Technik, 12, 1963, 291-293 VDI-Verlag, Düsseldorf, 1981 2.4 Sorption pumps W. Bächler und H.-J. Forth G. Klipping und W. Mascher Die wichtigsten Einflußgrößen bei der G. Kienel Vakuumerzeugung durch Kondensation Entwicklung von Diffusionspumpen Zur Desorption von Gasen in Getter- an tiefgekühlten Flächen, I. Kryopumpen Vakuum-Technik, 13, 1964, 71-75 Ionenpumpen in „Physik und Technik von Vakuum-Technik, 11, 1962, 81-85 Sorptions- und Desorptionsvorgängen bei W. Reichelt niederen Drücken“ W. Bächler, G. Klipping und W. Mascher Bemerkungen zur Arbeitsweise moderner Rudolf A. Lange Verlag, 1963, Esch/Tau- Cryopump System operating down to 2,5 Diffusionpumpen nus, 266-270 K, 1962 Trans. Ninth National Vacuum Vakuum-Technik, 13, 1964, 148-152 Symposium, American Vacuum Society, W. Bächler 216-219, The Macmillan Company, H. G. Nöller Ionen-Zerstäuberpumen, ihre New York Theory of Vacuum Diffusion Pumps Wirkungsweise und Anwendung Handbook of Physics, Vol.1, Part 6, Leybold-Heraeus GmbH u. Co., in its own G. Klipping (pp. 323...419) Ed. A. H. Beck, Pergamon publishing house, Cologne 1966 Kryotechnik – Experimentieren bei tiefen Press Ltd., London, W.I. (1966) W. Espe Temperaturen Zur Adsorption von Gasen und Dämpfen Chemie-Ingenieur-Technik, 36, G. Herklotz an Molekularsieben 1964, 430-441 Enddruckversuche mit Diffusionspumpen Feinwerktechnik, 70, 1966, 269-273 hohen Saugvermögens und M. Schinkmann Restgasspektren G. Kienel Messsen und Regeln tiefer Temperaturen, Vakuum-Technik, 20, 1971, 11 – 14 Vakuumerzeugung durch Kondensation Teil I: Thermodynamische Verfahren und durch Sorption Meßtechnik, 81, 1973, 175-181 H. G. Nöller Chemikerzeitung / Chem. Apparatur 91, Die Bedeutung von Knudsenzahlen und 1967, 83-89 und 155-161 G. Schäfer, M. Schinkmann Ähnlichkeitsgesetzen in Diffusions- und Messsen und Regeln tiefer Temperaturen, Dampfstrahlpumpen H. Hoch Teil II: Elektrische Verfahren, Vakuum-Technik, 26, 1977, 72-78 Erzeugung von kohlenwasserstoffreiem Meßtechnik, 82, 1974, 31-38 D00 Ultrahochvakuum Vakuum-Technik, 16, 1967, 156-158

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R. Frank et al. J. P. Deville, L. Holland and L. Laurenson M. H. Hablanian Entwicklung von Refrigeratoren für den Measurement of the rate of evaporation of Backstreaming Measurements above Einbau in Kryopumpen Pump oils using a crystal vibrator Liquid-Nitrogen Traps Vakuum-Technik, 30, 1981, 134-137 3rd. Internat. Vac. Congr Stuttgart 153- Vac. Sci. Tech., Vol. 6, 265-268, 1969 160, Pergamon Press, Oxford, 1965 J. J. Scheer und J. Visser Z. Hulek, Z. Cespiro, R. Salomonovic, Anwendungen von Kryopumpen in der L. Laurenson, S. Hickman and M. Setvak and J. Voltr industriellen Vakuumtechnik R. G. Livesey Measurement of oil deposit resulting from Vakuum-Technik, 31, 1982, 34-45 Rotary pump backstreaming: An backstreaming in a diffusion pump analytical appriasal of practical results system by proton elastic scattering P. Duval and the factors affecting them Vacuum, Vol. 41 (7-9), 1853-1855, 1990 Diffusionspumpen, Turbo-Molekularpum- J. Vac. Sci. Technol. A 6 (2), pen oder Kryopumpen ? – Auswahlkriteri- 238-242, 1988 M. H. Hablanian en für Hochvakuumpumpen Elimination of backstreaming from Vakuum-Technik, 31, 1982, 99-105 B. D. Power, A. M. I. Mech, E. Crawley mechanical vacuum pumps and D. J. Crawley J. Vac. Sci. Technol. A5 (4), 1987, H. Henning und H.-H. Klein Sources, Measurement and Control of 2612-2615 Pumpen von Helium mit Backstreaming in Oil Vapour Vacuum Refrigerator-Kryopumpen Pumps Vakuum-Technik, 34, 1985, 181-184 Vacuum, Vol. 4 (4), 415-437, 1957 H.-H. Klein et al. M. A. Baker 3. Ultrahigh vacuum Einsatz von Kryopumpen in A cooled quartz crystal microbalance Produktionsanlagen methode for measuring diffusion pump technology Vakuum-Technik, 34, 1986, 203-211 backstreaming Journal of Scientific Instruments (Journal G. Kienel D. Müller und M. Sydow of Physics E), Series 2, Volume 1, Probleme und neuere Entwicklungen auf Kryopumpen im Vergleich mit anderen 774-776, 1968 dem Ultrahochvakuum-Gebiet Hochvakuumpumpen VDI-Zeitschrift, 106, 1964, 777-786 Vakuum in der Praxis, 2, 1990, 270-274 N. S. Harris Diffusion pump back-streaming G. Kienel und E. Wanetzky G. Kiese und G. Voß Vacuum, Vol. 27 (9), 519-530, 1977 Eine mehrmals verwendbare Kryopumpen mit neuartiger Metalldichtung für ausheizbare Regenerationstechnik M. A. Baker Uktrahochvakuum-Ventile und Vakuum in der Praxis, 4, 1992, 189-192 Vapour and Gas Measurements in Vacu- Flanschdichtungen um with the Quartz Crystal Microbalance Vakuum-Technik, 15, 1966, 59-61 in Vol.1, Proceedings of the ninth Confe- rence on Vacuum Microbalance Techni- H. G. Nöller ques, „Progress in Vacuum Microbalance Physikalische und technische Vorausset- 2.6 Oil backstreaming Techniques“ zungen für die Herstellung und Anwen- dung von UHV-Geräten. G. Levin Th. Gast and E. Robens ed., “Ergebnisse europäischer Ultrahochvaku- A quantitativ appraisal of the Heyden & Son Ldt., London, New York, um Forschung” backstreaming of forepump oil vapor Rheine, 1970 LEYBOLD-HERAEUS GmbH u. Co., in its J. Vac. Sci. Technol. A 3 (6), 1985, own publishing house, 2212-2213 M. A. Baker and L. Laurenson Cologne 1968, 49-58 The use of a quartz crystal microbalance M. A. Baker and L. Laurenson for measuring vapour backstreaming W. Bächler A quartz crystal microbalance holder for from mechanical pumps Probleme bei der Erzeugung von low Temperature use in vacuum Vacuum, Volume 16 (11), 633-637, 1966 Ultrahochvakuum mit modernen Vacuum Vol. 17, (12), 647-648, 1967 Vakuumpumpen. „Ergebnisse (Letters to the Editor) R. D. Oswald and D. J. Crawley europäischer Ultrahochvakuum A method of measuring back migration of Forschung“ M. A. Baker and W. Steckelmacher oil through a baffle The Measurement of Contamination in Vacuum, Vol. 16 (11), 623-624, 1966 Leybold-Heraeus GmbH u. Co., in its own Vacuum Systems publishing house, Cologne 1968, 139-148 Vuoto, scienza e technologia, Bd.3 , (1/2), 3-17, 1970

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P. Readhead, J. P. Hobson und W. Röllinger 5. Measurement of E. V. Kornelsen Die Verwendung von Klammerflanschen in The Physical Basis of Ultrahigh Vacuum der Vakuumtechnik low pressures Chapman and Hall, London, 1968 Vakuum-Technik, 13, 1964, 42-45 C. Meinke und G. Reich E. Bergandt und H. Henning H. Hoch Vermeidung von Fehlmessungen mit dem Methoden zur Erzeugung von Ausheizbare Verbindungen an Hoch- System McLeod-Kühlfalle Ultrahochvakuum vakuum-Apparaturen Vakuum-Technik, 12, 1963, 79-82 Vakuum-Technik, 25,1970, 131-140 Vakuum-Technik, 10, 1961, 235-238 P. A. Readhead and J. P. Hobson H. Wahl W. Bächler und I. Wikberg Total Pressure Measurem. below 10–10 Das Hochvakuumsystem der CERN am Dual Seal Bakable Section Valves of the Torr with Nonmagnetic Ionisation Gauge 450 GeV Supersynchrotron und CERN Intersection Storage Ring Brit. J. Appl. Phys., 16, 1965, 1555-1556 Speichering (SPS) Vacuum, 21, 1971, 457-459 Vakuum in der Praxis, 1989, 43-51 C. Meinke und G. Reich K. Teutenberg Comparison of Static and Dymanic F. Grotelüschen UHV-Ganzmetallventile großer Nennweite Calibration Methods for Ionisation Gauges Das UHV-System bei DESY. 1. Teil Vakuum-Technik, 21, 1972, 169-174 J. Vac. Sci. Techn., 4, 1967, 356-359 Vakuum in der Praxis, 4, 1991, 266-273 H. Henning G. Reich und W. Schulz D. Trines The approximate calculation of Probleme bei der Verwendung von Das Strahlrohrvakuumsystem des Hera- transmission probabilities Ionisations-Vakuummetern im Druck- Protonenringes Vacuum, 28, 1978, No. 3, Seite 151 bereich oberhalb 10–2 Torr Vakuum in der Praxis, 2, 1992, 91-99 Proc. of the Fourth Intern. Vacuum G. Kühn Congress, 1968, G. Schröder et al. Gasströme durch Spalte im Grobvakuum II. Inst. of Physics Conference Series No. COSV- eine neue Forschungsanlage mit Vakuum-Technik, 33, 1984, 171-175 6, London, 661-665 UHV-Technologie Vakuum in der Praxis, 5, 1993, 229-235 G. Reich Probleme bei der Messung sehr niedriger W. Jacobi Total- und Partialdrücke Das Vakuumsystem der GSI-Beschleuni- R. Haberland und B. Vogt „Ergebnisse europäischer Ultrahoch- geranlage UHV-Ventil für extrem viele Schließzyklen vakuum Forschung“ Vakuum in der Praxis, 6, 1994, 273-281 Vakuum-Technik, 34, 1985, 184-185 Leybold-Heraeus GmbH u. Co., in its own publishing house, Cologne 1968, 99-106 A. Sele Vakuum-Ventile (VAT) A. Barz and P. Kocian Vakuum in der Praxis, 1, 1989, 206-212 Extractor Gauge as a Nude System 4. Conductances, J. Vac. Sci Techn. 7, 1970, 1, 200-203 L. Fikes flanges, valves, Berechnung von Auspumpkurven mit U. Beeck and G. Reich Hilfe der Analogie von Gasstrom und Comparison of the Pressure Indication of a etc. elektrischem Strom Bayard-Alpert and an Extractor Gauge Vakuum in der Praxis, 4, 1992, 265-268 J. Vac. Sci. and Techn. 9, 1972, 1,126-128 M. Knudsen Gesetze der Molekularströmung und der W. Herz U. Beeck inneren Reibungsströmung der Gase Zuverlässige Flanschverbindung im Untersuchungen über die Druckmessun- durch Röhren Anwendungsgebiet der Tieftemperatur- gen mit Glühkathoden-Inisations-Vakuum- Annalen der Physik, 4th issue, 28, 1909, und Vakuumtechnik metern im Bereich größer als 10–3 Torr 75-130 Vakuum-Technik, 29, 1980, 67-68 Vakuum-Technik, 22, 1973, 16-20

P. Clausing G. Reich Über die Strömung sehr verdünnter Gase Über die Möglichkeiten der Messung sehr durch Röhren von beliebiger Länge niedriger Drücke Annalen der Physik, 5th issue, 12, Meßtechnik, 2, 1973, 46-52 1932, 961-989 D00

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G. Reich Vakuum in der Praxis, 3, 1991, 290-296 H. Dohmen Spinning rotor viscosity gauge; a transfer Vakuumdruckmessung und -Regelung in standard for the laboratory or an accurate M. Ruschitzka and W. Jitschin der chemischen Verfahrenstechnik gauge for vacuum process control Physikalische Grundlagen des Vakuum in der Praxis, 6,1994, 113-115 J. Vac. Sci. Technol., 20 (4), Wärmeleitungsvakuummeters 1982, 1148-1152 Vakuum in der Praxis, 4, 1992, 37-43 N. Pöchheim Druckregelung in Vakuumsystemen G. Reich T. Koopmann Vakuum in Forschung und Praxis, 7, Das Gasreibungs-Vakuummeter Neue Trends in der Vakuum-Meßtechnik 1995, 39-46 VISCOVAC VM 210 Vakuum in der Praxis, 5, 1993, 249-254 Vakuum-Technik, 31, 1982, 172-178 R. Heinen und W. Schwarz Chr. Edelmann Druckregelung bei Vakuumprozessen G. Grosse and G. Messer Die Entwicklung der Totaldruckmessung durch umrichtergespeiste Rootspumpen Calibration of Vacuum Gauges at im UHV- und Extremvakuumbereich Vakuum-Technik, 35, 1986, 231-236 Pressures below 10–9 mbar with a Vakuum in der Praxis, 6, 1994, 213-219 molecular beam method Vakuum-Technik, 30, 1981, 226-231 W. Jitschin Kalibrierung, Abnahme und Zertifizierung Chr. Edelmann et al.: Möglichkeiten der (with numerous references to relevant li- 7. Mass spectrometer Meßbereichserweiterung bei Glühkatho- terature) den-Ionisationsmanometern (numerous Vakuum in der Praxis, 6, 1994, 193-204 gas analysis at low references to relevant literature) Vakuum-Technik, 31, 1982, 2-10 W. Jitschin pressures Obere Meßbereichsgrenze von Glühkato- Chr. Edelmann den-Ionisationsvakuummetern H. Hoch Stand und Entwicklungstendenzen der Vakuum in Forschung und Praxis, 7, Total- und Partialdruckmessungen bei –10 Totaldruckmessung in der Vakuum-Tech- 1995, 47-48 Drücken zwischen 2 · 10 und –2 nik 2 · 10 Torr Vakuum-Technik, 16, 1967, 8-13 Vakuum-Technik, 33, 1984, 162-180 F. Mertens et al. Einfluß von Gasadsorbaten auf die Eigen- H. Junge J. K. Fremerey schaften eines Glühkatoden-Ionisations- Partialdruckmessung und Partialdruck- Das Gasreibungsvakuummeter vakuummeters mit axialer Emission nach meßgeräte Vakuum-Technik, 36, 1987, 205-209 Chen und Suen G-I-T May 1967, 389-394 and Vakuum in der Praxis, 7, 1995, 145-149 June 1967, 533-538 G. Messer Kalibrierung von Vakuummetern A. Kluge Vakuum-Technik, 36, 1987, 185-192 Ein neues Quadrupolmassenspektrometer mit massenunabhängiger Empfindlichkeit G. Messer und W. Grosse 6. Pressure Vakuum-Technik, 23, 1974, 168-171 Entwicklung der Vakuum-Metrologie in der PTB (numerous references to relevant li- monitoring, control S. Burzynski terature) Microprocessor controlled quadrupole Vakuum-Technik, 36, 1987, 173-184 and regulation mass spectrometer Vacuum, 32, 1982, 163-168 G. Reich K. G. Müller Industrielle Vakuummeßtechnik Betriebsüberwachung, Steuerung und W. Große Bley Vakuum-Technik, 36, 1987, 193-197 Automatisierung von Vakuumanlagen Chemie-Ingenieur-Technik, 35, Quantitative Gasanalyse mit dem Quadrupol Massenspektrometer L. Schmidt und E. Eichler 1963, 73-77 Vakuum-Technik, 38, 1989, 9-17 Die Praxis einer DKD-Kalibrierstelle Vakuum-Technik, 36, 1987, 78-82 G. Kienel Elektrische Schaltgeräte der Vakuumtech- A. J. B. Robertson Mass Spectrometry C. Kündig nik Methuen & Co, Ltd., London, 1954 Vakuummeßgeräte für Totaldruck Elektro-Technik, 50, 1968, 5-6 Vakuum in der Praxis, 2, 1990, 167-176 A. Bolz, H. Dohmen und H.-J. Schubert C. Brunee und H. Voshage Massenspektrometrie Chr. Edelmann Prozeßdruckregelung in der Karl Thiemig Verlag, München, 1964 Glühkahtoden-Ionisationsmanometer für Vakuumtechnik hohe Drücke im Vakuumbereich Leybold Firmendruckschrift 179.54.01

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A. Cornu and R. Massot Chr. Falland 8.2 Leak detection with Compilation of Mass Spectral Data Ein neuer Universal-Lecksucher mit halogen leak detectors Heyden and Son Ltd., London, 1966 luftgekühlter Turbo-Molekularpumpe Vakuum-Technik, 29, 1980, 205-208 H. Moesta und P. Schuff P. Dawson Über den thermionischen Halogendetektor Quadrupole Mass Spectroscopy W. Jansen Berichte der Bunsengesellschaft für Elsevier, Amsterdam, 1976 Grundlagen der Dichtheitsprüfung mit physikaische Chemie, Hilfe von technischen Gasen Bd. 69, 895-900, 1965 J. Backus Vakuum-Technik, 29, 1980, 105-113 Verlag Chemie, GmbH, Weinheim, Chap. 11 in “Characteristics of Electrical Bergstraße Discharges in Magnetic Fields” H. Mennenga National Nuclear Energy Series, Div. I, Dichtheitsprüfung von Kleinteilen J. C. Leh and Chih-shun Lu Vol. 5, McGraw-Hill Book Company Inc., Vakuum-Technik, 29, 1980, 195-200 US Patent Nr. 3,751,968 New York, 1949 Solid State Sensor Chr. Falland J. Backus Entwicklung von He-Lecksuchtechniken University of California Radiation für UHV-Systeme großer Beschleuniger- Laboratory Report, RL 20.6.36, und Speicherringe Mar. 1945. Vakuum-Technik, 30, 1981, 41-44 9 Film thickness W. Engelhardt et al. measurement and Lecksuchanlagen in der Industrie Vakuum-Technik, 33, 1984, 238-241 control 8. Leaks and Leak G. Sänger et al. G. Z. Sauerbrey detection Über die Lecksuche bei Raumfahrzeugen Phys. Verhandl. 8, 113, 1957 Vakuum-Technik, 33, 1984, 42-47 8.1 Mass spectrometer leak G. Z. Sauerbrey detection W. Jitschin et al. Verwendung von Schwingquarzen zur He-Diffusionslecks als sekundäre Normale Wägung dünner Schichten und zur für den Gasdurchfluß Mikrowägung G. Kienel Vakuum-Technik, 36, 1987, 230-233 Lecksuche an Vakuumanlagen auf Zeitschrift für Physik 155, 206-222, 1959 L. Holland, L. Laurenson and J. P. Deville elektrischem Wege W. Große Bley Elektrotechnik, 49, 1967, 592-594 Use of a Quartz Crystal Vibrator in Vacu- Moderne He-Leckdetektoren um Destillation Invstigations unterschiedlicher Prinzipien im prakti- Nature, 206 (4987), 883-885, 1965 U. Beeck schen Einsatz Möglichkeiten und Grenzen der automati- Vakuum in der Praxis, 1, 1989, 201-205 schen Lecksuche im Bereich unter R. Bechmann 10–8 Torr. l/s Über die Temperaturabhängigkeit der H. D. Bürger Frequenz von AT- und Vakuum-Technik, 23, 1974, 77-80 Lecksucher (with references to relevant Lecksuche an Chemieanlagen BT-Quarzresonatoren literature) Archiv für Elektronik und Übertragungs- Dechema Monographien (Ed. H. E. Bühler Vakuum in der Praxis, 2, 1990, 56-58 and K. Steiger), Vol. 89, Verlag Chemie, technik, Bd. 9, 513-518, 1955 Weinheim / New York W. Fuhrmann K. H. Behrndt and R. W. Love W. Jansen Einführung in die industrielle Dichtheits- Automatic control of Film Deposition Rate Grundlagen der Dichtheitsprüfung mit prüftechnik with the crystal oscillator for preparation Hilfe von Testgasen Vakuum in der Praxis, 3, 1991, 188-195 of alloy films. Vakuum-Technik, 29, 1980, 105-113 Vacuum 12 ,1-9, 1962 W. Fuhrmann K. Paasche Industrielle Dichtheitsprüfung – ohne P. Lostis Lecksuche an Chemieanlagen Testgas nach dem Massenspektrometrie- Automatic Control of Film Deposition Rate Vakuum-Technik, 29, 1980, 227-231 verfahren with the Crystal Oscillator for Preparation Vakuum in Forschung und Praxis, 7, fo Alloy Films. H. B. Bürger 1995, 179 -182 Rev. Opt. 38, 1 (1959) Lecksuche an Chemieanlagen mit He- D00 Massenspektrometer-Lecksuchern Vakuum-Technik, 29, 1980, 232-245

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Fundamentals of Vacuum Technology References

K. H. Behrndt H. F. Tiersten and R. C. Smythe C. Lu and A. W. Czanderna Longterm operation of crystal oscillators An analysis of contowced crystal Application of Piezoelectric Quarz Crystal in thin film deposition resonators operating in overtones of Microbalances (Vol.7 of: Methodes and J. Vac. Sci. Technol. 8, 622 (1971) coupled thickness shear and thickness Phenomena, Their Applications in Sience twist. and Technology) L. Wimmer, S. Hertl, J. Hemetsberger and J. Acoustic Soc. Am. 65, (6) 1455, 1979 Elesvier, Amsterdam, Oxford, New York, E. Benes Tokio, 1984 New method of measuring vibration R. E. Bennett, C. Rutkoeski and amplitudes of quartz crystals. L. A. Taylor G. Simmons and H. Wang Rev. Sci. Instruments 55 (4) , 608, 1984 Proceedings of the Thirteenth Annual Single Crystal Elastic Constants and Symposium on Frequency Controll, Calculated Aggregate Properties – P. J. Cumpson and M. P. Seah 479, 1959 A Handbook Meas. Sci. Technol., 1, 548, 1990 The MIT Press, Cambridge, Massachu- Chih-shun Lu setts, 1971 J. G. Miller and D. I. Bolef Improving the accuracy of Quartz csystal Sensitivity Enhancement by the use of monitors C. D. Stockbridge Acoustic Resonators in cw Ultrasonic Research/Development, Vol. 25, 45-50, in Vol. 5 “Vacuum Microbalance Spectroscopy. 1974, Technical Publishing Company Techniques” K. Behrndt, editor, Plenum J. Appl. Phys. 39, 4589, (1968) Press, Inc., New York, 1966 A. Wajid J. G. Miller and D. I. Bolef Improving the accuracy of a quartz crystal S. Sotier Acoustic Wave Analysis of the Operation microbalance with automatic determinati- Schwingquarz-Schichtdickenmessung of Quartz Crystal Film Thickness Moni- on of acoustic impedance ratio. Vakuum in der Praxis 1992, 182-188 tors. Rev. Sci. Instruments, Vol. 62 (8), 2026- J. Appl. Phys. 39, 5815, (1968) 2033, 1991

C. Lu and O. Lewis D. Graham and R. C. Lanthrop Investigation of Film thickness The Synthesis fo Optimum Transient 10. Materials and determination by oscillating quartz Response: Criteria and Standard Forms resonators with large mass load. Transactions IEEE, Vol. 72 pt. II, material J. Appl. Phys. 43, 4385 (1972) Nov. 1953 processing C. Lu A. M. Lopez, J. A. Miller, C. L. Smith and Mas determination with piezoelectric P. W. Murrill W. Espe quartz crystal resonators. Tuning Controllers with Error-Integral Werkstoffkunde der Hochvakuumtechnik J. Vac. Sci. Technol. Vol. 12 (1), Criteria Vol. 1 1959, Vol. 2 1960, Vol. 3 1961, 581-582, 1975 Instrumentation Technology, Nov. 1969 VEB Deutscher Verlag der Wissenschaf- ten, Berlin A. Wajid C. L. Smith and P. W. Murril U.S. Patent No. 505,112,642 A More Precise Method for Tuning W. Espe (May 12, 1992) Controllers Werkstoffe für trennbare metallische Ver- ISA Journal, May 1966 bindungen der Ultrahochvakuumtechnik C. Hurd Feinwerktechnik, 68, 1964, 131-140 U.S. Patent No. 5,117,192 (May 26, G. H. Cohen and G. A. Coon 1992) Theoretical considerations of Retarded W. Espe Control Synthetische Zeolithe und ihre Verwen- E. Benes Taylor Technical Data Sheet Taylor dung in der Hochvakuumtechnik Improved Qartz Crystal Microbalance Instrument Companies, Rochester, Experimentelle Technik der Physik, XII, Technique New York 1964, 293-308 J. Appl. Phys. 56, (3), 608-626 (1984) J. G. Ziegler and N. B. Nichols H. Adam C. J. Wilson Optimum Settings for Automatic Allgemeiner Überblick über die Werkstoffe Vibration modes of AT-cut convex quartz Controllers der Vakuumtechnik und deren Auswahl resonators. Taylor Technical Data Sheet No. TDS Haus der Technik Vortragsveröffentlichun- J. Phys. d 7, 2449, (1974) 10A100, Taylor Instrument Companies, gen “Werkstoffe und Werkstoffverbindun- Rochester, New York gen in der Vakuumtechnik” H. 172, Vul- kan-Verlag, Dr. W. Classen, Essen, 1968, 4 – 13

D00.182 LEYBOLD VACUUM PRODUCTS AND REFERENCE BOOK 2001/2002 D00 E 19.06.2001 21:41 Uhr Seite 183

References Fundamentals of Vacuum Technology

K. Verfuß Bessere Oberflächenvergütung durch Elektropolieren – am Beispiel der Vaku- um-Technik VDI-Berichte, 183, 1972, 29-34

K. Verfuß Schweißen und Hartlöten Haus der Technik, Vortragsveröffentli- chungen “Werkstoffe und Werkstoffver- bindungen in der Vakuumtechnik”, H. 172 Vulkan-Verlag Dr. W. Classen, Essen, 1968, Seiten 39 -49

Chr. Edelmann Gasabgabe von Festkörpern im Vakuum Vakuum-Technik, 38, 1989, 223-243

R. Fritsch Besonderheiten vakuumdichrter Schweißverbindungen Vakuum-Technik, 38, 1989, 94-102

H. Henning Vakuumgerechte Werkstoffe und Verbindungstechnik, Part 1 Vakuum in der Praxis, 2, 1990, 30-34

R. Fritsch Vakuumgerechte Werkstoffe und Verbindungstechnik, Part 2 Vakuum in der Praxis, 2, 1990, 104-112

M. Mühlloff Vakuumgerechte Werkstoffe und Verbindungstechnik, Part 3 Vakuum in der Praxis, 2, 1990, 179-184

11. Dictionaries

F. Weber Elsevier’s Dictionary of High Vacuum Science and Technology (German, English, French, Spanish, Italian, Russian) Elsevier Verlag 1968

Hurrle / Jablonski / Roth Technical Dictionary of Vacuum Physics and Vacuum Technology (German, English, French, Russian) Pergamon Press Verlag, Oxford, 1972 D00

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Fundamentals of Vacuum Technology Index

Causes of faults if/when the desired Cryocondensation ...... 52 13. Index ultimate pressure Cryopumps ...... 49, 177 is not achieved ...... 134 Cryosorption ...... 52 Absolute pressure ...... 7 Ceramic ball bearings (hybrid ball Cryotrapping ...... 52 Absorption isotherms ...... 45 bearings) ...... 42 Crystal Six ...... 120 Absorption pumps ...... 45, 139 CF-flange (conflathflange) ...... 68 Cut in (start) pressure ...... 44, 54, 55 Absorption traps ...... 33 Changing the molecular sieve ...... 139 CVD (chemical vapor Accessories for rotary Charles' law (Gay-Lussac's law) . . . . .11 deposition) ...... 128, 129 displacement pumps ...... 33 Chemical resistance of elastomer Dalton's law ...... 11 Active oscillator ...... 122, 123 gaskets ...... 149, 150, 151 Danger classes of fluids ...... 148 Adjustment and calibration of Chemical vapor deposition (CVD) . . .129 Data storage coating ...... 132 vacuum gauges ...... 88 Choked flow, critical pressure DC 704, DC 705 (Silicone oils) ...... 39 Adsorption pumps, difference ...... 12 Degassing of the pump oil ...... 37 Instructions for operation . . . . .139, 140 CIS (closed ion source) ...... 93 Derived coherent and not coherent Aggressive vapors ...... 135 Clamp flange ...... 67 SI units with special AGM (aggressive gas monitor) . . . . .94 Classification of vacuum pumps . . . . .16 names and symbols ...... 170 Air, atmospheric ...... 10 Clausius-Clapeyron equation ...... 11 Detection limit (leak detectors) . . . . .111 ALL·ex pumps ...... 28, 30 Claw pump ...... 27 Determination of a suitable Ambient pressure ...... 7 Closed ion source, (CIS) ...... 93 backing pump ...... 64 Amonton's law ...... 11 Coating of parts ...... 130 Determination of pump down Anticreep barrier ...... 40 Coating thickness regulation ...... 125 time from Nomograms ...... 65 Anti-suckback valve ...... 19 Cold cap baffle ...... 39 Determination of pump sizes ...... 62 APIEZON AP 201 ...... 39, 160 Cold cathode ionization vacuum DI series diffusion pumps ...... 38 Atmospheric air ...... 10 gauge ...... 77 Diaphragm contoller, examples Atmospheric air, composition ...... 145 Cold head ...... 50 of application ...... 86, 87 Atmospheric pressure ...... 7 Cold surfaces, bonding of Diaphragm vacuum gauges ...... 72 Atomic units ...... 170 gases to ...... 51 Diaphragm vacuum pumps ...... 17 Autoc ontrol tune ...... 125, 126 Cold traps ...... 39 DIAVAC diaphragm vacuum gauge . . .72 Automatic protection, monitoring Collision frequency ...... 10 DIFFELEN, light, normal, ultra . . .39, 160 and control of vacuum systems . . . . .83 Collision rate ...... 10 Diffusion / vapor-jet pumps, Auto-Z match technique ...... 122 Common solvents ...... 146 Instructions for operation ...... 139 Avogadro's law ...... 11 Compression ...... 43 Diffusion pumps ...... 36 Avogadro's number (Loschmidt Compression vacuum gauges ...... 74 Diode-type sputter ion pumps ...... 46 number) ...... 12, 143 Condensate traps ...... 33 Direct-flow leak detector ...... 115 Backing line vessel ...... 64 Condensers ...... 33, 174 Discharge filters ...... 33 Baffle ...... 36 Conductance ...... 9, 13 Displacement pumps ...... 16, 174 Baffles (vapor barriers) ...... 36, 37, 39 Conductance of openings ...... 179 DIVAC vacuum pump ...... 17 Baking (degassing) ...... 61, 68, 141 Conductance of DKD (Deutscher Kalibrierdienst) Barrier gas operation ...... 44 piping ...... 14, 155, 161, 179 German calibration service ...... 81 Basis SI units ...... 170 Conductance, nomographic Dry compressing rotary Bath cryostats ...... 49 determination ...... 14 displacement pumps ...... 24 Bayard-Alpert gauge ...... 80 Conductances, calculation of ...... 13 Dry processes ...... 57 Boat (thermal evaporator) ...... 128 Connection of leak detectors to Drying of paper ...... 67 Boltzmann constant ...... 11, 143 vacuum systems ...... 116 Drying processes ...... 60 Bombing-Test (storing under Contamination of vacuum sensors . .139 Drying processes, selection of pressure) ...... 119 Contamination of vacuum vessels . . .134 pumps for ...... 66 Booster (oil-jet) pump ...... 38, 46 Continous flow ...... 12 DRYVAC-Pumps ...... 28 Bourdon vacuum gauge ...... 72 Continous flow cryopumps ...... 49 D-Tek ...... 110 Boyle-Mariotte law ...... 11 Continuum theory ...... 11 Duo seal (sealing passage) . . .17, 18, 19 Break down voltage Conversion of leak rate units ...... 106 Dust separator (dust filter) ...... 33 (Paschen curve for air) ...... 163 Conversion of leak rate units ...... 144 Dynamic expansion method ...... 82 Bubble (immersion) test ...... 109 Conversion of pressure units ...... 142 Ecotec II ...... 113 Calibration curves of Conversion of pV-throughput units . .144 Effective pumping speed ...... 33, 62 THERMOVAC gauges ...... 77 Corrosion protection ...... 135, 136 Elastomer gaskets . . . .69, 149, 150, 151 Calibration inspection ...... 81 Counter-flow leak detector ...... 115 Electrical break down voltage Coating sources ...... 128 Cracking pattern ...... 136 (Paschen curve air) ...... 163 Capacitance diaphragm gauges . . . . .73 Critical pressure difference Electron beam evaporators Capsule vacuum gauge ...... 772 (choked flow) ...... 12 (electron guns) ...... 129 Crossover value ...... 53 Envelope test ...... 118, 119

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Envelope test (concentration Hybrid ball bearings (Ceramic ball LN2 cold traps ...... 40 measurement) ...... 118 bearings) ...... 42 Local leak rate ...... 106 Evacuation in the rough / medium / Hydrocarbon-free vacuum ...... 39, 60 Loschmidt's number high vacuum region ...... 62, 63, 64 IC 5 ...... 127 (Avogadro constant) ...... 11, 143 Evacuation of gases / vapors ...... 66 Ideal gas law ...... 7, 11 Magnetic suspension (bearings) . . . . .42 Evaluating spectra ...... 96 Impingement rate ...... 10 Mass flow ...... 8, 104 Expansion method static / Industrial leak testing ...... 119 Mass flow (leak detection) ...... 104 dynamic ...... 81, 82 Influence of magnetic / Mass range ...... 195 Extractor ionization vacuum electrical fields ...... 141 Mass spectrometer, general, gauge ...... 80 Internal compression (claw pumps) . .28 historical ...... 89, 180 Fast regeneration (partial Inside-out leak ...... 107 Maximum backing pressure regeneration) ...... 54 Integral leak rate ...... 107 (critical forevacuum pressure) ...... 37 Fingerprint ...... 96 Internal reflow (roots pumps) ...... 24 McLeod vacuum gauge ...... 74 Flanges and their seals ...... 67, 179 Ion desorption effect ...... 79 Mean free path ...... 9, 142, 159 Floating zero-point suppression . . . .111 Ion sputter pumps ...... 45, 46 Measuring range of vacuum Fluid entrainment pumps ...... 35, 177 Ionization vacuum gauge for gauges ...... 161 Foam spray leak test ...... 109 higher pressures up to 1 mbar ...... 80 Measuring range, favorable ...... 70 Fractionation of pump fluids ...... 37 Ionization vacuum gauges ...... 77 Measuring ranges of vacuum Fragment distribution pattern ...... 98 Ionization, specific (gas analysis) . . . .96 gauges ...... 162 Fundamental pressure Isotopes ...... 96 Measuring vacuum, vacuum measurement methods ...... 81 Kammerer compression vacuum gauges ...... 70, 179 Gas analysis ...... 89, 100, 101, 180 gauge ...... 74 Medium vacuum adsorption trap . . . .33 Gas ballast ...... 21, 22, 111 Kinetic gas theory ...... 11 MEMBRANOVAC ...... 73 Gas composition as a function Kinetic of gases, diagram of ...... 154 Mercury (pump fluid) ...... 36, 39,160 of altitude ...... 155 Kinetic of gases, formulas ...... 143 Mode-lock oscillator ...... 123 Gas constant, general (molar) .7, 11, 143 Knudsen flow ...... 13 Molar gas constant ...... 7, 11, 143 Gas density ...... 7 Krypton 85 test ...... 109 Molar mass Gas dependent pressure reading, Laminar flow ...... 12 (molecular weight) ...... 7, 10, 11 vacuum gauges with ...... 75 Langmuir-Taylor-effect ...... 111 Molecular flow ...... 12, 13 Gas discharge ...... 46, 78 Laval nozzle ...... 38 Molecular sieve ...... 45, 139 Gas independent pressure reading, Leak detection ...... 104, 181 Monolayer ...... 10 vacuum gauges with ...... 72 Leak detection using Helium Monolayer formation time . . . .10, 13, 61 Gas laws ...... 11 leak detectors ...... 117 National standards, resetting to . . . . .81 Gas locks ...... 69 Leak detection without leak detector .107 NEG pumps (non evaporable Gas sorption (pumping) of Leak detection, leak test ...... 104 getter pumps) ...... 45, 48 vacuum gauges ...... 78, 79 Leak detectors with 180° sector Neoprene ...... 68, 149, 150, 151 Gas storage in the oil of rotary mass spectrometer ...... 114 Nitrogen equivalent ...... 71, 78 vane pumps ...... 111 Leak detectors with mass Nominal internal diameter and Gaskets ...... 68, 149, 150, 151 spectrometer ...... 110, 181 internal diameter of tubes ...... 146 Gay-Lussac's law ...... 11 Leak detectors with quadrupole Nomogram ...... 65 General gas constant mass spectrometer ...... 113 Nomogram: conductance of (Molar gas constant) ...... 7, 11, 143 Leak detectors, how they work . . . . .110 tubes / entire pressure range ...... 158 Getter pumps ...... 45 Leak rate, hole size, Nomogram: conductance of Glass coating ...... 132 conversion ...... 9, 104, 105, 106 tubes / laminar flow range ...... 155 Halogen leak detector ...... 110, 181 Leak test (chemical reactions, dye Nomogram: conductance of Helium leak detectors with 180° penetration) ...... 110 tubes / molecular flow range . . .155, 162 sector mass spectrometer ...... 114 Leak test, using vacuum gauges Nomogram: pump down time / Helium spray equipment ...... 118 sensitive to the type of gas ...... 108 medium vacuum, taking in Helium standard leak rate ...... 106 LEYBODIFF-Pumps ...... 37 account the outgasing from the High frequency vacuum test ...... 109 INFICON Quartz crystal walls ...... 159 High pressure ionization vacuum controllers ...... 127 Nomogram: pump down time / gauge ...... 80 Line width ...... 94 rough vacuum ...... 156 High vacuum range ...... 62, 63 Linearity range of quadrupole Non evaporable getter (NEG) HLD 4000 ...... 110 gauges ...... 102 pumps ...... 45, 48 HO-factor (diffusion pumps) ...... 37 Liquid ring pumps ...... 17 Non gas-tight area ...... 1104 Hot cathode ionization vacuum Liquid sealed rotary displacement Nude gauge (nude system) ...... 72 gauge ...... 78 pumps ...... 17 Oil backstreaming ...... 39, 178 D00 HY.CONE pumps ...... 44 Liquid-filled vacuum gauges ...... 74 Oil change ...... 137 Literature references ...... 174 – 183 Oil consumption . . . .135, 136, 137, 138

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Oil contamination ...... 135 Pressure ranges in vacuum Roots pumps ...... 24 Oil diffusion pumps ...... 36 technology ...... 12, 56, 57, 145 Roots pumps, Instructions for Oil sealed rotary displacement Pressure regulation / control . . .84, 180 operation ...... 137 pumps ...... 18 Pressure regulation / control rough Rotary displacement pumps ...... 18 Oil vapor ejector vacuum pumps . . . .36 and medium vacuum systems ...... 84 Rotary plunger pumps ...... 20 Oil-free (hydrocarbon-free) Pressure regulation in high and Rotary vane / piston pumps, vacuum ...... 39, 60 ultra high vacuum systems ...... 87 Instructions for operation ...... 135 Oils (pump fluids) ...... 39 Pressure regulation, continuous / Rotary vane pumps ...... 18 Open (normal) ion source ...... 90 discontinuous ...... 84, 86 Salt, drying of ...... 66 Optical coatings ...... 131 Pressure rise / drop (leak) test .107, 108 Saturation vapor pressure Oscillation displacement pumps . . . . .17 Pressure units ...... 7, 142 (nonmetallic gaskets) ...... 161 Oscillator, ( active, mode-lock) .122, 123 PTB (Federal physical-technical Saturation vapor pressure ...... 7, 22 Outgasing of materials ...... 145 institute) ...... 81 Saturation vapor pressure Outgasing rate (referred to Pumpdown time ...... 62 - 66 (cryogenic technology) ...... 161 surface area) ...... 9, 61 Pump fluid ...... 39 Saturation vapor pressure (metals) . .160 Outside-in leak ...... 107 Pump fluid backstreaming ...... 39 Saturation vapor pressure Overpressure ...... 7 Pump fluid change cleaning (pump fluids) ...... 160 Oxide-coated cathodes ...... 78, 90 (diffusion pumps) ...... 139 Saturation vapor pressure Partial final pressure ...... 74 Pump oil, selection when handling (solvents) ...... 160 Partial flow opeartion ...... 115 aggressive vapors ...... 135 Saturation vapor pressure and Partial flow ratio ...... 116 Pump throughput ...... 9 vapor density of water ...... 147, 164 Partial pressure ...... 7 Pumping (gas sorption) of Sealing passage ...... 18, 19 Partial pressure measurement . . . . .100 vacuum gauges ...... 77, 78 Seal-off fitting ...... 69 Partial pressure regulation ...... 101 Pumping chamber ...... 16 Selection of pumps ...... 56 Particle number density ...... 7 Pumping of gases ...... 57 Selection of pumps for drying Paschen curve ...... 163 Pumping of gases and processes ...... 66 Penning vacuum gauges ...... 77 vapors . . . . .20, 21, 34, 52, 57, 58, 135 Sensitivity of quadrupole sensors . . . .95 Perbunan ...... 68, 149 - 151, 161 Pumping speed ...... 8 Sensitivity of vacuum gauges ...... 78 Period measurement ...... 122 Pumping speed units, Separating system of Permissible pressure units ...... 142 conversion of ...... 144 mass spectrometers ...... 90 Phase diagram of water ...... 164 Pumping various chemical Shell baffle ...... 39 Photons ...... 79 substances ...... 136 Silicone oils, DC 704, DC 705 . .39, 160 PIEZOVAC ...... 73 Purge gas ...... 29 Small flange ...... 67 Pirani vacuum gauge ...... 76 PVD (physical vapor deposition) . . .128 Smallest detectable concentration . . . .95 Plastic tent (envelope) ...... 118 pV-flow ...... 9 Smallest detectable partial pressure . .95 Plate baffle ...... 39 pV-value ...... 8 Smallest detectable partial PNEUROP ...... 165 – 168 Quadrupole mass spectrometer . . . . .89 pressure ratio ...... 95 PNEUROP flanges ...... 68 Quadrupole, design of the sensor . . . .90 Sniffer technology ...... 118 Poiseuille flow ...... 12 Quadrupole, gas admission / Software for TRANSPECTOR ...... 102 Poisson's law ...... 11 pressure adaptation ...... 93 SOGEVAC pumps ...... 18 Positive pressure methode Quadrupole, measurement system Solvents ...... 146 (leak detection) ...... 106 (detector) ...... 92 Sorption pumps ...... 45, 177 Pre-admission cooling (roots Quadrupole, separating system . . . . .91 Specific volume of water vapor .147, 163 pumps) ...... 27 Quadrupole, specifications ...... 94 Spinning rotor gauge (SRG) ...... 75 Precision diaphragm vacuum gauge . .72 Qualitative gas analysis ...... 100 Spray technique (Helium) ...... 117 Pressure ...... 7, 168 Quantitative gas analysis ...... 101 Sputter ion pumps, Instructions Pressure and temperature as Quantity of gas (pV value) ...... 8 for operation ...... 140 function of altitude ...... 155 Quartz crystals, shape of ...... 121 Sputter pumps ...... 46 Pressure converter ...... 92 Rate watcher ...... 120 Sputtering ...... 129 Pressure dependence of the Reduction of adsorption capacity . . .139 Sputtering (cathode sputtering) . . . .129 mean free path ...... 145, 154 Reduction ratio ...... 24, 25, 137 Sputter-ion pumps ...... 46, 47 Pressure difference oil supply ...... 19 Refrigerator cryopump ...... 49, 51 SRG (spinning rotor gauge), Pressure lubrication by geared Regeneration time ...... 53 VISCOVAC ...... 75 oil pump ...... 19 Relative ionization probability (RIP) . .98 Stability for noble gases (sputter ion Pressure measurement Residual gas composition pumps) ...... 46, 47, 48 direct / indirect ...... 71, 179, 180 (spectrum) ...... 43, 44 Standard pressure ...... 7 Pressure measurement, depending on / Response time of leak detectors . . . .117 Standards in independent of the type of gas ...... 71 Reynold's number ...... 12 vacuum technology ...... 171 – 173 Rigid envelope ...... 118, 119 Static expansion method ...... 81, 82

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Steam ejector pumps ...... 40 Vacumm meters, instructions on Storage under pressure installing ...... 140 (bombing test) ...... 119 Vacuum coating techniques ...... 128 Stray magnetic field ...... 47 Vacuum control ...... 70 Stray magnetic field Vacuum equipment, Instructions for (sputter ion pumps) ...... 47 operation ...... 134 Sublimation pumps ...... 46, 47 Vacuum gauge contant ...... 78 Symbols and units, Vacuum method (leak detection) . . .107 alphabetical list ...... 165 – 170 Vacuum physics ...... 7 Symbols used in vacuum Vacuum pumps, literature technology ...... 1572, 153 references ...... 174 Temperature comparison and Vacuum pumps, survey, conversion table ...... 154 classification ...... 16, 17 Temperature in the atmosphere . . . .155 Vacuum ranges (Pressure ranges) Terms and definitions ...... 13, 56, 57, 145, 161, 162 (leak detection) ...... 106 Vacuum regulation ...... 70 Test gas accumulation ...... 119 Vacuum symbols ...... 152, 153 Test leaks ...... 113 Vacuum coating technology ...... 128 Thermal conductivity vacuum gauge, Values of important physical constant / variable resistance ...... 76 constants ...... 143 Thermal conductivity vacuum Valves ...... 67, 178 gauges ...... 76 Van der Waals' equation ...... 11 Thermal evaporator (boat) ...... 128 Vapor density of water ...... 147, 164 THERMOVAC ...... 75 Vapor pressure . . . .7, 39, 160, 161, 164 Thickness control with quartz Vapor-jet pumps . . . .38, 39, 40, 41, 139 oscillators ...... 120 Venturi nozzle ...... 38 Thickness measurement ...... 120 Viscous (continuum) flow ...... 12 Thin film controllers . . . . .120, 127, 181 VISCOVAC vacuum gauge ...... 775 Throtteling of pumping speed Vitilan, Viton ...... 68, 149, 161 when using condensers ...... 34, 35 Volume ...... 8 Time constant ...... 62, 116 Volumetric efficiency (roots pumps) . .24 Titanium sublimation pump ...... 46 Volumetric flow ...... 8 Titanium sublimation pumps, Water jet pumps ...... 40 Instructions for operation ...... 140 Water ring pumps ...... 18 Torr and its conversion ...... 142 Water vapor tolerance ...... 23 Total pressure ...... 7 Web coating ...... 130 Transfer standard ...... 81 Wet processes ...... 58 Transmitter ...... 75 Working pressure ...... 7 TRANSPECTOR ...... 89 Working ranges of vacuum pumps . .161 Triode sputter ion pumps ...... 47 X-ray effect ...... 78 TRIVAC pumps ...... 19 XTC, XTM ...... 127 Trochoid pumps ...... 21 Zeolith ...... 45 Tuning / adjustment and Z-Match technique ...... 122 calibration of leak detectors ...... 112 Turbomolecular pumps ...... 41, 176 Turbomolecular pumps, Instructions for operation ...... 138 TURBOVAC pumps ...... 43 Turbulent flow ...... 12 Types of leak ...... 104 Types pV flow ...... 12 UL 200, UL 500 ...... 114 Ultimate pressure ...... 7 Ultra high vacuum . .11, 13, 60, 61, 178 ULTRALEN ...... 39, 161 Units, symbols ...... 165 – 170 U-tube vacuum gauge ...... 74 D00

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