SVC Topics Donald M. Mattox Technical Director Society of Vacuum Coaters 71 Pinon Hill Place, N.E. Alburquerque, NM 87122 505/856-7188 • FAX 505/856-6716 www.svc.org Applications Of Vacuum Coatings

Vacuum coatings are deposited in vacuum resistor materials. Non-transparent electri- ference-colored fi lms used for decorative by physical vapor deposition (PVD) proc- cally conductive oxides, such as Cr2O3, fi lms and, when pulverized, as pigments. esses where material is vaporized by evap- PbO and RuO, are used as electrodes in oration, physical sputtering, or arc vapor- high-temperature oxidizing atmospheres. Thermal Control Coatings ization, or by the decomposition of a chem- The composition of the thermal control ical vapor precursor (chemical vapor depo- Transparent Electrical coatings on windows differs with the end sition—CVD). Conductors result desired. If the object is to keep Transparent conductive oxide (TCO) fi lms, solar radiation from entering through the Electrically Conductive Films window, a multilayer fi lm of glass-TiO - such as In2O3, SnO2, ZnO, and an alloy 2 Metal fi lms are the most common electri- of indium oxide and tin oxide (ITO), have Cr-TiO2 may be used (solar control coat- cal conductor fi lms. The metal fi lms may numerous applications, such as heaters on ing). If the object is to keep heat in be used as blanket metallizations or can windows for defrosting, antistatic coatings the room, a thin fi lm of silver can be be formed into discrete conductor lines on display screens, electrodes on fl at-panel used to refl ect 85Ð95 percent of the low- (stripes) by masking the substrate during displays and electrochromic devices, and temperature infrared radiation back into deposition, or by subsequent photolytho- electrodes on both fl exible (resistive) and the room (low-E coating). One such dou- graphic etching processes. Conductor lines rigid (capacitive) touch screens. ble-E coating is glass-ZnO-Ag-(Ti)-ZnO- are used in hybrid microcircuit technology Ag-(Ti)-ZnO-TiO2. The ZnO provides an and in the manufacture of semiconductor Electrical Insulators antirefl ective coating. devices. Often, the electrical conductors are Other types of thermal-control coatings multilayer fi lms (stacks) where each layer Electrically insulating fi lms are used to are use to absorb solar radiation (solar has a function. For example, the conductor electrically isolate conducting components absorbers), selectively adsorb solar radia- fi lm stack might have the composition: in semiconductor devices, and as a dielec- tion and not emit infrared radiation (selec- glass-Ti-Pd-Cu-Au. The Ti is the glue layer, tric within capacitors. Common insulator tive solar absorbers), or to have a high the Pd provides corrosion resistance, the fi lm materials are SiO2, Al2O3, Ta2O5, Si3N4, emissivity to enhance cooling by radiation. Cu is an electrical conductor, and the Au and AlN. Insulating layers of SiO2, Si2N3, provides corrosion protection. Blanket met- and glass are deposited by plasma-enhanced Reflector Coatings allization is used to provide electromagnetic CVD (PECVD) for encapsulating conduc- Metal fi lms are widely used for refl ector interference (EMI) and radiofrequency tor stripes in semiconductor processing. surfaces. Silver is often used when corro- interference (RFI) shielding on structures sion is not a problem, such as for back- such as the plastic cases for cellular phones, Optical Films surface mirrors. Aluminum can be used as electrodes for rigid and fl exible capacitor Optical fi lms, usually multilayer fi lms, are a front-surface or back-surface refl ector. electrodes, and surfaces for radar chaff. fi lms that affect the optical transmission or Chromium is used on front-surface refl ec- Metal nitride, carbide, and silicide fi lms refl ection of a surface. They are generally tors when corrosion is a problem, even are generally electrically conductive (Si N 3 4 alternating layers of materials having high though its refl ectivity in the visible (60%) is and AlN are important exceptions). In some (Ge, Si, TiO2, ZrO2, SiO, CeO2) and low less than that of aluminum (>90%). In some applications, fi lms of these refractory mate- (MgF2, SiO2) indices of refraction. A major cases, multilayer fi lms, similar to multi- rials are used to provide diffusion barriers application is the antirefl ection (AR) coat- layer optical fi lms, are used to selectively between materials. For example, in semi- ings on lenses. Optical fi lm stacks can be refl ect certain wavelengths. Examples are conductor metallization, aluminum or gold used as optical fi lters. Neutral density or cold mirrors that refl ect the visible radia- electrode material will diffuse into the sil- gray fi lters reduce the light intensity equally tion but not the infrared wavelengths, and icon during high-temperature processing. for all wavelengths. Broadband fi lters affect heat mirrors that refl ect the infrared but not An electrically conductive titanium nitride the transmission of radiation over a wide the visible. Heat mirrors are used to raise fi lm deposited on the silicon surface before wavelength range, while narrow or mono- the internal temperature of halogen lamps. the metal electrode is deposited will pre- chromatic fi lters affect transmission over a Cold mirrors are used to reduce the heat vent the diffusion. Metal nitrides, such as very narrow wavelength region. produced by stage lighting. tantalum nitride (TaN), are used as thin-fi lm Some fi lm stacks are a special type of ______Reproduced with permission of the Society of optical fi lm that have a color related to Packaging Vacuum Coaters from the “SVC Educational Guides the angle of observation. They are used as to Vacuum Coating Processing.” For ordering infor- security devices to prevent counter feiting. Barrier coatings are used on fl exible poly- mation, contact SVC at the above address. These fi lms are an outgrowth of the inter- mer fi lms and paper for food packaging,

46 Plating & Surface Finishing • January 2002 to reduce the water vapor transmission rate anodes in X-ray tubes. The low-shear com- (WVTR) and the oxygen transmission rate Electrically Active Films pound materials are used in mechanical- (OTR) through the packaging. The most Doped silicon fi lms are used in semiconduc- bearing applications in vacuum, and where common barrier coating material is alumi- tor devices, and these fi lms are often depos- “lubricant creep” can be a problem. num, which is deposited on rolls of poly- ited by a very sophisticated PVD evap- mer fi lm (web), then supplied to “conver- oration technique called molecular beam Freestanding Structures tors” that fabricate the packaging. In some epitaxy (MBE), or the low-pressure CVD cases, the metal coatings are deposited on a technique of vapor phase epitaxy (VPE). Freestanding structures are made by depos- surface and then transferred to the packag- Amorphous silicon for solar cells is depos- iting a coating on a surface (mandrel), then separating the coating from the mandrel ing fi lm. Layers of SiO2-x, by reactive evap- ited by PECVD on webs and rigid sub- oration and PECVD, and composite coat- strates. Electochromic fi lms, which change surface or dissolving the mandrel. The tech- nique is useful for fabricating very thin ings of [SiO2:30% Al2O3] by e-beam co- optical transmission on the application of evaporation, are used to form transparent a voltage, depend on the diffusion of a structures, complex surfaces, or foils or barrier layers. mobile species in the fi lm under an elec- sheets of materials that are hard to deform trical fi eld. Films of a material such as by rolling. Examples are beryllium win- selenium can become electrically charged dows used for X-ray transmission, boron Decorative thin-wall cones for high-frequency audio & Decorative/Wear Coatings when exposed to light, and are used to hold the toner in photocopying machines. speakers, and Ti-V-Al metal alloy foils. Metallization for strictly decorative pur- poses is a large market. Applications vary Magnetic Storage Media Basecoats for Electroplating from coating polymer webs, which are then Materials that are diffi cult to electroplate converted to decorative use, such as bal- Magnetic materials are classifi ed as hard or soft, depending on how hard it is to mag- because of rapid oxide formation can have loons and labels, to metallization of 3-D an adherent basecoat applied by PVD proc- articles, such as sports trophies, zinc diecast netize, demagnetize or switch the magnetic fi eld. Soft magnetic materials, such as the esses, and then the coating built up by elec- or molded polymer decorative fi xtures, and trodeposition. Examples are plating on tita- cosmetic containers. Often, these coatings Permalloys (Fe:40-80%Ni) and Y2Fe5O12 (garnet) are used in memory storage devices nium, uranium, and zirconium, where a consist of a refl ective aluminum coating basecoat of a material such as nickel or that is deposited on a smooth basecoat, then where the data is changed often. Hard mag- netic materials such as Fe O , Co:Ni:W, copper is applied by a PVD process before overcoated with a dyed lacquer to give the 3 4 the electroplated coating is built up. coating the desired color and texture. Co:Re, Gd:Co, and Gd:Tb:Fe are used in In some applications, in addition to the more permanent recording media, such as decorative aspects of the coating, the coat- audiotapes. Polymer Films ing is required to withstand wear. For There is increasing interest in depositing example, titanium nitride (TiN) is gold col- Corrosion Protective Coatings polymer fi lms in vacuum. These fi lms can be ored, and titanium carbonitride (TiC N ) formed by condensation of a monomer (fol- x y Protection from an aggressive chemical can vary in color from gold to purple environment can be accomplished in several lowed by e-beam or UV curing to polymer- to black, depending on the composition. ways. The surface can be coated with an ize the monomer), or by plasma polymer- Zirconium nitride (ZrN) has the color of inert material, or with a material that forms ization of the monomer. The monomer pre- brass. Decorative/wear coatings are used a protective surface after reacting with the cursor can yield a carbon, silicon or boron- on door hardware, plumbing fi xtures, fash- environment, or with a material that will be based polymer material that often contains P&SF ion items, marine hardware, and other such sacrifi cially removed to protect the under- hydrogen, chlorine, or fl uorine. applications. lying material. Tantalum, platinum, and carbon are inert in many chemical environ- Hard Coatings ments. For example, carbon coatings are Hard coatings are often called metallurgical used on metals that are implanted in the coatings and are a type of tribological coat- human body to provide biocompatibility. ing. The hard coatings are used to increase Chromium, aluminum, silicon, and the the cutting effi ciency and operational life MCrAlY (where M is Ni, Co, Fe) alloys of cutting tools, and to maintain the dimen- will react with oxygen to form a coherent, sional tolerances of components used in protective oxide layer on the surface. The applications where wear can occur, such as MCrAlY alloy coatings are used as pro- injection molds. There are various classes tective coatings on aircraft engine turbine of hard coating materials. They include: blades. Cadmium, aluminum, and Al:Zn alloys are used as galvanic sacrifi cial coat- ionically bonded metal oxides (Al2O3, ZrO2, ings on steel. Vacuum Cd-plating has the and TiO2), covalently bonded materials advantage over electroplated cadmium, in (SiC, B4C, diamond, diamond-like-carbon [DLC], TiC, AlN, CrC, mixed carbide, that there is no possibility of hydrogen nitride and carbonitride compound alloys, embrittlement of high-strength steel. and cubic boron nitride), and some metal alloys (CoCrAlY, NiAl, NiCrBSi). Solid Film Lubricants Hard coatings are also used to minimize Thin-fi lm solid lubricant fi lms are of two fatigue-wear, such as is found in ball bear- types: the low-shear metal lubricants (e.g., ings. Coatings may be deposited on plastics silver and lead), and the laminar-shearing to improve scratch resistance. In some compound materials (e.g., MoS ). The low- cases, wear coatings (SiO or Al O ) may 2 2 2 3 shear metal lubricants are used in high- be applied to already hard surfaces, such as torque applications, such as the rotating glass, to increase the scratch resistance.

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