A Scientist's Perspective on the Early Days of Mos Technology

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2 equation of the form xο + Axο = B(t + τ ), in subsequent investigations discussed A Scientist’s Perspective on the Early Days Table II. Fairchild Investigators Who indicated in Fig. 1, where xο = oxide below. It should be noted that MOS thickness, t = oxidation time, and A, layers of oxide thickness of 20 to 200 nm Studied Ambient Effects on Thermal of MOS Technology B, and τ are constants. The shift in could be reproducibly prepared using Oxidation. by Bruce E. Deal the time coordinate, τ, is an empirical the equation in Fig. 1. The model was correction factor related to the used in various modeling programs, P. Castro...... H2 (Nit)...... 1971 thickness of the initial oxide layer, including Stanford SUPREM. Below D. Hess...... O2/N2...... 1975 n September 1957, Frosch and Derick to be improved as well. It was soon Projects – General Detail (Kinetics) xi. Thermal oxidation proceeds by 20 nm, a different mechanism takes of Bell Telephone Laboratories obvious that considerable competition D. Hess...... O2/N2...... 1975 three consecutive reactions: (a) silicon over, which is still not understood (Oxide charges) published a seminal paper in the developed among the various oxide Silicon Thermal Oxidation I oxide surface oxidant adsorption, (b) completely. Generally, empirical data D. Hess...... O2/HCl...... 1977 groups established by other electronic Journal of The Electrochemical Society Kinetics.—Following the preliminary oxygen diffusion through the oxide, must be used in this range. B. Deal...... O /Cl ...... 1978 companies, as noted above. 2 2 concerning the use of silicon dioxide as a studies of silicon thermal oxidation and (c) Si-SiO interface reaction. The B. Deal...... Pyro/H O...... 1978 Members of the Fairchild oxide team 2 2 selective mask against dopant diffusion kinetics by Deal and coworkers at Rheem parabolic constant B includes the MOS Capacitance–Voltage (C–V) B. Deal...... O /HCl; H O/HCl.... 1978 had various backgrounds (physical 2 2 into silicon wafers. This oxide layer was Semiconductor in Mountain View, CA, effective oxidant diffusion coefficient Model for Investigating Thermally R. Razouk...... High Pressure H O... 1981 chemistry, chemical engineering, 2 soon shown to passivate the underlying and reported at the fall, 1962 ECS (D ), which includes the effect of space Oxidized Silicon Structures.—With the J. Rouse...... O /HCl...... 1981 physics, electrical engineering). These eff 2 p-n junctions. Subsequent Bell Labs work meeting, a more complete investigation charge on the rate of transport, C* is the development of the planar passivation R. Razouk...... H ...... 1982 diverse backgrounds provided a good 2 involved the fabrication of both bipolar was initiated in 1963 at Fairchild R&D equilibrium concentration of oxidant process at Fairchild and the MOS L. Lie...... High Pressure O ..... 1982 basis for the challenges soon encountered. 2 and the newly developed metal-oxide- by Deal and Grove. The so-called “Deal- in the oxide and is proportional to the transistor at Bell Labs in 1959-1960, J. Rouse...... O /HCl...... 1984 Assistance was provided by consultants 2 semiconductor, or MOS, transistors. At Grove” oxidation model, Thermal partial pressure of the oxidant in the gas investigators began to look for a simple J. de Larios..... Surface Clean...... 1987 previously at Bell Labs and Stanford about the same time, Jean Hoerni of Oxidation Kinetics Model, published in by Henry’s Law, and N is the number of method for characterizing the thermally University. Technical information was I Fairchild Semiconductor Corporation 1965 in the Journal of Applied Physics oxidant molecules incorporated into oxidized silicon structure. Earlier obtained from attendance at technical in Palo Alto, California, developed the (see Table I, Ref. 1), was one of the most a unit volume of the oxide layer. B/A techniques employed more complicated voltage (C–V) relationship was simpler to meetings and from technical papers. so-called planar process, in which the cited in semiconductor technology is a function of the surface reactions field-effect structures where the change obtain and monitor (See Table I, Ref. 2). Several Fairchild investigators had diffused junctions were left covered by and was the basis for numerous future and is referred to as the linear rate in conductance of an MOS device was Such was the case at Fairchild. Without worked at Rheem Semiconductor (first the masking oxide during subsequent publications by Fairchild and other constant, under appropriate conditions. determined as a function of gate bias. going into detail, the nature of the Si- device fabrication and operation. This spin-off of Fairchild), and Bruce Deal organizations. Typically, silicon thermal Several of these factors are involved It was soon found that the capacitance- SiO2 interface could be characterized by process quickly began to revolutionize had published preliminary results oxidation is accomplished by reacting the C–V method of analysis. Examples of obtained there in 1962 involving the semiconductor industry. silicon in oxygen (O2) and/or water C–V plots are shown in Fig. 2 (left-hand silicon oxidation kinetics. Some of Not too long after that, in the early vapor (H2O) at 800-1250° C. Based on side), with their corresponding charge 1960s, several industrial laboratories— those results were reported at the 1962 a combination linear-parabolic model, models on the right-hand side (see the RCA, Sprague Electric, Westinghouse, ECS fall meeting in Los Angeles by the relationship is summarized by an section below on “Charges in Thermally Texas Instruments, General Electric, Deal and Fairchild personnel. Many Oxidized Silicon”). The experimental IBM, and others—initiated research personnel in the field also presented curves can be compared with theory, programs involving investigation of their experimental findings at the newly and properties such as fixed and mobile thermally oxidized silicon structures. formed Silicon Interface Specialists Table I. Thermally Oxidized Silicon oxide charges, oxide thickness, average These programs were aimed at Conference (SISC) meetings sponsored References: Highlights of Fairchild doping density in the surface space eventually developing MOS devices, by the IEEE beginning in 1962. R&D (1965-1981). charge region, work function differences which made use of these metal-oxide- A list of highlighted Fairchild and other properties can be determined silicon sandwiches and their associated publications (mainly by Deal, Grove, 1. Thermal Oxidation Kinetics by observing the voltage dependence or structures. Fairchild Semiconductor was Snow, and Sah) published from 1965 Model, Deal, et al., J. Appl. Phys., shape of the C–V plot. The dependence no exception, in 1963 assembling a to 1981, which dealt with the oxidized 36, 3770 (1965). of interface characteristics as a function research team that began a series of silicon system, is presented in Table I. 2. MOS C-V Model, Grove et al., (a) Uniform drift of sodium ions originally at of surface doping concentration, oxide Al-SiO2 interface. MOS projects. Five of these publications are discussed Solid State Elect., 8, 145 (1965). thickness and measurement frequency The following section summarizes in more detail in subsequent sections. 3. Ion Transport in Thermal Oxides, can also be measured. Much of Fairchild’s the Fairchild oxide program during the The subjects of these projects serve to Snow, et al., J. Appl. Phys., 36, 1664 subsequent oxide research (as well as years 1963-1979. Related investigations identify the thrust of this early Fairchild (1965). that of other organizations) made use continued there well into the 1980s. silicon thermal oxide research. 4. Thermal Oxidation of Si in of the MOS C–V procedure for Si-SiO2 Numerous papers were presented and/ Various Ambients, Hess, at al., J. characterization. The parameters used in or published by the various Fairchild Electrochem. Soc., 122, 529 (1975). Fig. 2 represent terminology used in the investigators involved in subjects 5. Charges in Thermally Oxidized early days of MOS C–V characterization. related to thermal oxidation during the Si, Deal, et al., J. Electrochem. Soc., The term “Qss” originally intended to entire time. Even by 1970, more than 121, 198C (1974). describe what we now call “Qf”, became 25 technical papers on the oxidation of 6. Barrier Energies in Oxidized Si, so widely used for various effects that silicon had been published. Deal, et al., J. Phys. Chem. Solids, the new definitions to be described 27, 1873 (1966). (b) Distorted C-V plot after drift of spatially below became a necessity. 7. Polar Effects in Oxidized Films, non-uniform Na+ ions at Al-SiO2 interface.

Fairchild Oxidation Concentration Investigations (1963-1979) Snow, et al., TMS-AIME, 242, 512 Ion Transport in Thermal Oxides.— (1968). As oxidized silicon structures suitable Distance from Surface 8. Heavily-Doped Si Effects for fabricating potential MOS devices Starting in 1963, the primary members on Oxidation, Deal, et al., J. of the Fairchild oxidation group were were characterized, it was soon found Electrochem. Soc., 112, 430 (1965). (at Fairchild and competitors) that they Gordon Moore and C. T. Sah. Bruce 9. Charge Terminology, Deal, at al., Deal, Andy Grove, and Ed Snow joined were very unstable electrically. Using J. Electrochem. Soc., 127, 979 C–V analysis, voltage biased, 200 nm Fairchild R&D in early 1963, with Frank (1980); Semiconductor Silicon/1977, thick oxide gate flat-band voltages (Vfb) Wanlass already on board. Several other H. R. Huff and E. Sirtl, Editors, PV support personnel joined the activity were found to “drift” 50 volts or more 77-2, p. 276, The Electrochemical at temperatures of 200°C or lower. These late in 1963. The overall goal at Fairchild Society proceedings Series, was to obtain a better understanding of results led to on-going speculation at Pennington, NJ (1977); IEEE technical meetings as to the source of the thermally oxidized silicon system Trans. Electron Devices, ED-27, 606 (c) Drift in both directions due + these instabilities. Some of the proposed with emphasis on developing stable and to Na ions in bulk of SiO2. (1980). sources were surface ion migration, reproducible MOS devices. Currently 10. Kinetics of High Pressure Silicon available bipolar devices were expected hetero-junctions, oxygen vacancies, slow Oxidation, Razouk, et al., J. oxide traps, protons, polar molecules, Fig. 1. Kinetics of silicon thermal oxidation. Fig. 2. C-V plots of three types of ion drift. Electrochem. Soc., 128, 2214 and other effects. It turned out that one (1981). of the Fairchild team members (Ed Snow)

42 The Electrochemical Society Interface • Fall 2007 The Electrochemical Society Interface • Fall 2007 43 2 equation of the form xο + Axο = B(t + τ ), in subsequent investigations discussed A Scientist’s Perspective on the Early Days Table II. Fairchild Investigators Who indicated in Fig. 1, where xο = oxide below. It should be noted that MOS thickness, t = oxidation time, and A, layers of oxide thickness of 20 to 200 nm Studied Ambient Effects on Thermal of MOS Technology B, and τ are constants. The shift in could be reproducibly prepared using Oxidation. by Bruce E. Deal the time coordinate, τ, is an empirical the equation in Fig. 1. The model was correction factor related to the used in various modeling programs, P. Castro...... H2 (Nit)...... 1971 thickness of the initial oxide layer, including Stanford SUPREM. Below D. Hess...... O2/N2...... 1975 n September 1957, Frosch and Derick to be improved as well. It was soon Projects – General Detail (Kinetics) xi. Thermal oxidation proceeds by 20 nm, a different mechanism takes of Bell Telephone Laboratories obvious that considerable competition D. Hess...... O2/N2...... 1975 three consecutive reactions: (a) silicon over, which is still not understood (Oxide charges) published a seminal paper in the developed among the various oxide Silicon Thermal Oxidation I oxide surface oxidant adsorption, (b) completely. Generally, empirical data D. Hess...... O2/HCl...... 1977 groups established by other electronic Journal of The Electrochemical Society Kinetics.—Following the preliminary oxygen diffusion through the oxide, must be used in this range. B. Deal...... O /Cl ...... 1978 companies, as noted above. 2 2 concerning the use of silicon dioxide as a studies of silicon thermal oxidation and (c) Si-SiO interface reaction. The B. Deal...... Pyro/H O...... 1978 Members of the Fairchild oxide team 2 2 selective mask against dopant diffusion kinetics by Deal and coworkers at Rheem parabolic constant B includes the MOS Capacitance–Voltage (C–V) B. Deal...... O /HCl; H O/HCl.... 1978 had various backgrounds (physical 2 2 into silicon wafers. This oxide layer was Semiconductor in Mountain View, CA, effective oxidant diffusion coefficient Model for Investigating Thermally R. Razouk...... High Pressure H O... 1981 chemistry, chemical engineering, 2 soon shown to passivate the underlying and reported at the fall, 1962 ECS (D ), which includes the effect of space Oxidized Silicon Structures.—With the J. Rouse...... O /HCl...... 1981 physics, electrical engineering). These eff 2 p-n junctions. Subsequent Bell Labs work meeting, a more complete investigation charge on the rate of transport, C* is the development of the planar passivation R. Razouk...... H ...... 1982 diverse backgrounds provided a good 2 involved the fabrication of both bipolar was initiated in 1963 at Fairchild R&D equilibrium concentration of oxidant process at Fairchild and the MOS L. Lie...... High Pressure O ..... 1982 basis for the challenges soon encountered. 2 and the newly developed metal-oxide- by Deal and Grove. The so-called “Deal- in the oxide and is proportional to the transistor at Bell Labs in 1959-1960, J. Rouse...... O /HCl...... 1984 Assistance was provided by consultants 2 semiconductor, or MOS, transistors. At Grove” oxidation model, Thermal partial pressure of the oxidant in the gas investigators began to look for a simple J. de Larios..... Surface Clean...... 1987 previously at Bell Labs and Stanford about the same time, Jean Hoerni of Oxidation Kinetics Model, published in by Henry’s Law, and N is the number of method for characterizing the thermally University. Technical information was I Fairchild Semiconductor Corporation 1965 in the Journal of Applied Physics oxidant molecules incorporated into oxidized silicon structure. Earlier obtained from attendance at technical in Palo Alto, California, developed the (see Table I, Ref. 1), was one of the most a unit volume of the oxide layer. B/A techniques employed more complicated voltage (C–V) relationship was simpler to meetings and from technical papers. so-called planar process, in which the cited in semiconductor technology is a function of the surface reactions field-effect structures where the change obtain and monitor (See Table I, Ref. 2). Several Fairchild investigators had diffused junctions were left covered by and was the basis for numerous future and is referred to as the linear rate in conductance of an MOS device was Such was the case at Fairchild. Without worked at Rheem Semiconductor (first the masking oxide during subsequent publications by Fairchild and other constant, under appropriate conditions. determined as a function of gate bias. going into detail, the nature of the Si- device fabrication and operation. This spin-off of Fairchild), and Bruce Deal organizations. Typically, silicon thermal Several of these factors are involved It was soon found that the capacitance- SiO2 interface could be characterized by process quickly began to revolutionize had published preliminary results oxidation is accomplished by reacting the C–V method of analysis. Examples of obtained there in 1962 involving the semiconductor industry. silicon in oxygen (O2) and/or water C–V plots are shown in Fig. 2 (left-hand silicon oxidation kinetics. Some of Not too long after that, in the early vapor (H2O) at 800-1250° C. Based on side), with their corresponding charge 1960s, several industrial laboratories— those results were reported at the 1962 a combination linear-parabolic model, models on the right-hand side (see the RCA, Sprague Electric, Westinghouse, ECS fall meeting in Los Angeles by the relationship is summarized by an section below on “Charges in Thermally Texas Instruments, General Electric, Deal and Fairchild personnel. Many Oxidized Silicon”). The experimental IBM, and others—initiated research personnel in the field also presented curves can be compared with theory, programs involving investigation of their experimental findings at the newly and properties such as fixed and mobile thermally oxidized silicon structures. formed Silicon Interface Specialists Table I. Thermally Oxidized Silicon oxide charges, oxide thickness, average These programs were aimed at Conference (SISC) meetings sponsored References: Highlights of Fairchild doping density in the surface space eventually developing MOS devices, by the IEEE beginning in 1962. R&D (1965-1981). charge region, work function differences which made use of these metal-oxide- A list of highlighted Fairchild and other properties can be determined silicon sandwiches and their associated publications (mainly by Deal, Grove, 1. Thermal Oxidation Kinetics by observing the voltage dependence or structures. Fairchild Semiconductor was Snow, and Sah) published from 1965 Model, Deal, et al., J. Appl. Phys., shape of the C–V plot. The dependence no exception, in 1963 assembling a to 1981, which dealt with the oxidized 36, 3770 (1965). of interface characteristics as a function research team that began a series of silicon system, is presented in Table I. 2. MOS C-V Model, Grove et al., (a) Uniform drift of sodium ions originally at of surface doping concentration, oxide Al-SiO2 interface. MOS projects. Five of these publications are discussed Solid State Elect., 8, 145 (1965). thickness and measurement frequency The following section summarizes in more detail in subsequent sections. 3. Ion Transport in Thermal Oxides, can also be measured. Much of Fairchild’s the Fairchild oxide program during the The subjects of these projects serve to Snow, et al., J. Appl. Phys., 36, 1664 subsequent oxide research (as well as years 1963-1979. Related investigations identify the thrust of this early Fairchild (1965). that of other organizations) made use continued there well into the 1980s. silicon thermal oxide research. 4. Thermal Oxidation of Si in of the MOS C–V procedure for Si-SiO2 Numerous papers were presented and/ Various Ambients, Hess, at al., J. characterization. The parameters used in or published by the various Fairchild Electrochem. Soc., 122, 529 (1975). Fig. 2 represent terminology used in the investigators involved in subjects 5. Charges in Thermally Oxidized early days of MOS C–V characterization. related to thermal oxidation during the Si, Deal, et al., J. Electrochem. Soc., The term “Qss” originally intended to entire time. Even by 1970, more than 121, 198C (1974). describe what we now call “Qf”, became 25 technical papers on the oxidation of 6. Barrier Energies in Oxidized Si, so widely used for various effects that silicon had been published. Deal, et al., J. Phys. Chem. Solids, the new definitions to be described 27, 1873 (1966). (b) Distorted C-V plot after drift of spatially below became a necessity. 7. Polar Effects in Oxidized Films, non-uniform Na+ ions at Al-SiO2 interface.

42 The Electrochemical Society Interface • Fall 2007 The Electrochemical Society Interface • Fall 2007 43 Deal (continued from previous page) Development. Advantage developed vapor phase wafer cleaning equipment. Charges in Thermally Oxidized Deal retired when the company closed Silicon.—The mobile ionic charges (Na+, in 1992. Deal was a consulting professor Li+) were shown to cause instabilities at Stanford and Santa Clara Universities in the as-prepared test structures, as for more than twenty five years. Dr. well as MOS device operation in the Deal was the recipient of several of the early 1960s. These mobile ionic charges most prestigious ECS awards: ECS Fellow were found to be only one of four (1991), the ECS Gordon E. Moore Medal types of charges present in thermally for Outstanding Achievement in Solid oxidized silicon films (see Fig. 4). Two State Science and Technology (1993), of these were fixed oxide charge (Qf) and the ECS Edward Goodrich Acheson and interface trapped charge (Qit). They Award (2002). were both more stable than mobile ions (Qm), but also adversely affected Concentration A Note from the Guest Editors MOS device characteristics. They also both appeared to be associated with We expected that Bruce’s article for the final temperature treatment, and this issue of Interface would be his were either in the oxide near the Si– last. It was quite clear that this was a SiO interface (Q ), or directly at the 2 f somewhat difficult task for Bruce; not interface (Q ). These are depicted in Fig. it the thoughts, per se, which indeed 5, along with the proposed diffusion Bruce had introduced to the integrated and interface reaction of the oxidant in Distance of Charge Species from Surface circuit (IC) community over the past 45 an MOS structure. Their density could years, but the physical effort at writing be varied by the final oxidation and/ them. Ever the scientist, Bruce sent to or annealing temperature conditions. one of us (HRH) a typed copy of the A direct correlation between Q and Q f it Fig. 5. Distribution of charges in thermally oxidized silicon. manuscript, which I dutifully critiqued. was observed, and both were proposed I advised his wife, Rachel Deal, of this to be due to missing Si-O bonds in the and annealed by higher temperature A summary of the silicon dioxide plan to submit the “reviewed” version Fig. 3. H2O and dry O2 silicon oxidation kinetics. interface region. A number of these and processing, interface traps could also be technologies discussed herein, “Thermal back for Bruce’s assessment, whereupon related investigations were conducted complexed by hydrogen or hydrogen Silicon Dioxide—A Unique Dielectric in Bruce, ever the clever wit, told Rachel to had just completed his PhD research, anneal at low temperatures (interface and reported by Fairchild researchers bearing species treatment at tempera- Semiconductor Technology,” was also “write deceased on the manuscript” and which was concerned with impurity ion trap anneal). These published papers over several years in the 1960s and tures as low as 300°C and were presented at the ECS Symposium let me handle it. With the introduction migration through thin oxide layers. primarily reported oxidation data in 1970s (see Table I, Ref. 5). subsequently made ineffective. This on “Progress and Opportunities in of the Frosch/Derrick paper fifty years Subsequent analysis demonstrated that addition to passivation results. Certain One other charge type, oxide trapped the main instability was due to alkali observations were noted, such as the latter process has also been referred to Dielectric Science and Technology Over ago, perhaps it is fitting, though charge (Qot), was identified in thermally + + as the “Alneal,” the low-temperature the Last 25 Years: A Retrospective,” certainly an ironic if not cruel trick, ions (Na , Li , etc.) which were common fact that while the O2 diffusion in silicon oxidized silicon. These were also due to nitrogen annealing of aluminum-gate in celebration of the ECS Centennial that the endpoint be placed on this processing impurities (see Table I, Ref. 3). oxide is greater than for H2O, the latter broken Si-O bonds, but could be located MOS structures. In this process, the Meeting (spring 2002). It has been noted heroic “silicon oxide technology era” Various techniques were developed to has a solubility three times greater than throughout the oxide. They were often nascent hydrogen thermally released by many personnel that the replacement with the passing of Bruce Deal as this address this problem, such as electron for O2. This results in a much higher caused by ionizing radiation effects, from the aluminum gate/moisture- of silicon dioxide by a high-k dielectric, issue was being prepared. The editors beam aluminum gate deposition, choice oxidation rate for H2O as seen in Fig. and could be annealed out or otherwise contaminated SiO interface migrates a major currently proposed (and wish to acknowledge the fine assistance of aluminum gate material, improved 3. Table II provides a list of Fairchild minimized at temperatures as low 200- 2 to the silicon dioxide-silicon interface, implemented in some cases) change in of George Brown in the conversion cleaning, phosphorus gettering, proper investigators who studied and reported 300°C. resulting in the annealing of N . MOSFET device and process technology, of original draft manuscript into its analysis, and so on. These improvements combination effects of various ambients. One other effect to be mentioned it A final note is that when various has a significant progeny to emulate. present form. resulted in stable and reproducible Certainly, this list may be significantly regarding silicon oxide charge in general MOS device characteristics, which have expanded considering the research of research groups were investigating was that while Qf and Qit were formed continued to be effective until the others in the field. charge effects related to MOS structures, present time. It has also been found considerable confusion arose concerning About the Author that similar material and process control symbols used to designate their name and nomenclature. This confusion was has resulted in improved bipolar devices Bruce E. Deal died on April 17, 2007, as well. C–V analysis has continued reasonably well resolved, however, by in Palo Alto, California. (See the summer to be a key monitoring method for committees and publications provided 2007 issue of Interface for the complete the semiconductor industry in general by both the ECS Electronics & Photonics obituary notice.) Dr. Deal received an (see Fig. 2). Division and the IEEE Electron Device AB degree from Nebraska Wesleyan Society (see Table I, Ref. 9). University in 1950, and MS and PhD Ambient Effects on Thermal degrees in physical chemistry from Iowa Oxidation Kinetics.—As described Summary State University in Ames, Iowa in 1953 above, silicon thermal oxidation kinetics and 1955 respectively. In 1959, Deal were first investigated in the early 1960s. The contributions of scientists and moved to Palo Alto, CA and spent During subsequent years, modifications of engineers at the Fairchild Research the rest of his career in Silicon Valley. the dry O2 oxidation ambient were found Laboratory regarding thermally oxidized He first conducted semiconductor to provide certain device advantages (see silicon properties in the 1963-1979 time research at Rheem Semiconductor in Table I, Ref. 4). These modifications (see period have been summarized. The Mountain View, the first spin-off of Fig. 3) included dry O2/H2O (increased results of these investigations helped to Fairchild Semiconductor. In 1963, he formation rate in H2O as can be seen by advance the understanding, and thus joined Fairchild’s R&D Laboratory in comparing the time scales for H2O and the successful fabrication of stable metal- Palo Alto, initially as a Member of dry O2). Additional ambients included: oxide-semiconductor (MOS) devices and Technical Staff and later as a Research O2/N2 (dilution of O2 with N2 is done to their implementation into the industry. Manager/Department Director. After permit higher oxidation temperatures to Fairchild’s efforts included numerous Moore and Noyce founded Intel in enhance dopant diffusion in conjunction publications and presentations in 1968, Deal remained at Fairchild until with a smaller growth of oxide); O2/HC1 oxidation kinetics, oxide charge the company was sold to National (alkali contaminate gettering); understanding and control, device Semiconductor in 1977. He spent a year O2/pyrogenic (flame) H2O, high-pressure yield and stability, and other improved at National as Principal Technologist, O2 or H2O (increased oxidation rate/ electrical and physical properties of and then joined Advantage Production decreased process temperature); and H2 Fig. 4. Charges in thermally oxidized silicon. virtually all types of device structures. Technology as Vice-President of

44 The Electrochemical Society Interface • Fall 2007 The Electrochemical Society Interface • Fall 2007 45 Deal (continued from previous page) Development. Advantage developed vapor phase wafer cleaning equipment. Charges in Thermally Oxidized Deal retired when the company closed Silicon.—The mobile ionic charges (Na+, in 1992. Deal was a consulting professor Li+) were shown to cause instabilities at Stanford and Santa Clara Universities in the as-prepared test structures, as for more than twenty five years. Dr. well as MOS device operation in the Deal was the recipient of several of the early 1960s. These mobile ionic charges most prestigious ECS awards: ECS Fellow were found to be only one of four (1991), the ECS Gordon E. Moore Medal types of charges present in thermally for Outstanding Achievement in Solid oxidized silicon films (see Fig. 4). Two State Science and Technology (1993), of these were fixed oxide charge (Qf) and the ECS Edward Goodrich Acheson and interface trapped charge (Qit). They Award (2002). were both more stable than mobile ions (Qm), but also adversely affected Concentration A Note from the Guest Editors MOS device characteristics. They also both appeared to be associated with We expected that Bruce’s article for the final temperature treatment, and this issue of Interface would be his were either in the oxide near the Si– last. It was quite clear that this was a SiO interface (Q ), or directly at the 2 f somewhat difficult task for Bruce; not interface (Q ). These are depicted in Fig. it the thoughts, per se, which indeed 5, along with the proposed diffusion Bruce had introduced to the integrated and interface reaction of the oxidant in Distance of Charge Species from Surface circuit (IC) community over the past 45 an MOS structure. Their density could years, but the physical effort at writing be varied by the final oxidation and/ them. Ever the scientist, Bruce sent to or annealing temperature conditions. one of us (HRH) a typed copy of the A direct correlation between Q and Q f it Fig. 5. Distribution of charges in thermally oxidized silicon. manuscript, which I dutifully critiqued. was observed, and both were proposed I advised his wife, Rachel Deal, of this to be due to missing Si-O bonds in the and annealed by higher temperature A summary of the silicon dioxide plan to submit the “reviewed” version Fig. 3. H2O and dry O2 silicon oxidation kinetics. interface region. A number of these and processing, interface traps could also be technologies discussed herein, “Thermal back for Bruce’s assessment, whereupon related investigations were conducted complexed by hydrogen or hydrogen Silicon Dioxide—A Unique Dielectric in Bruce, ever the clever wit, told Rachel to had just completed his PhD research, anneal at low temperatures (interface and reported by Fairchild researchers bearing species treatment at tempera- Semiconductor Technology,” was also “write deceased on the manuscript” and which was concerned with impurity ion trap anneal). These published papers over several years in the 1960s and tures as low as 300°C and were presented at the ECS Symposium let me handle it. With the introduction migration through thin oxide layers. primarily reported oxidation data in 1970s (see Table I, Ref. 5). subsequently made ineffective. This on “Progress and Opportunities in of the Frosch/Derrick paper fifty years Subsequent analysis demonstrated that addition to passivation results. Certain One other charge type, oxide trapped the main instability was due to alkali observations were noted, such as the latter process has also been referred to Dielectric Science and Technology Over ago, perhaps it is fitting, though charge (Qot), was identified in thermally + + as the “Alneal,” the low-temperature the Last 25 Years: A Retrospective,” certainly an ironic if not cruel trick, ions (Na , Li , etc.) which were common fact that while the O2 diffusion in silicon oxidized silicon. These were also due to nitrogen annealing of aluminum-gate in celebration of the ECS Centennial that the endpoint be placed on this processing impurities (see Table I, Ref. 3). oxide is greater than for H2O, the latter broken Si-O bonds, but could be located MOS structures. In this process, the Meeting (spring 2002). It has been noted heroic “silicon oxide technology era” Various techniques were developed to has a solubility three times greater than throughout the oxide. They were often nascent hydrogen thermally released by many personnel that the replacement with the passing of Bruce Deal as this address this problem, such as electron for O2. This results in a much higher caused by ionizing radiation effects, from the aluminum gate/moisture- of silicon dioxide by a high-k dielectric, issue was being prepared. The editors beam aluminum gate deposition, choice oxidation rate for H2O as seen in Fig. and could be annealed out or otherwise contaminated SiO interface migrates a major currently proposed (and wish to acknowledge the fine assistance of aluminum gate material, improved 3. Table II provides a list of Fairchild minimized at temperatures as low 200- 2 to the silicon dioxide-silicon interface, implemented in some cases) change in of George Brown in the conversion cleaning, phosphorus gettering, proper investigators who studied and reported 300°C. resulting in the annealing of N . MOSFET device and process technology, of original draft manuscript into its analysis, and so on. These improvements combination effects of various ambients. One other effect to be mentioned it A final note is that when various has a significant progeny to emulate. present form. resulted in stable and reproducible Certainly, this list may be significantly regarding silicon oxide charge in general MOS device characteristics, which have expanded considering the research of research groups were investigating was that while Qf and Qit were formed continued to be effective until the others in the field. charge effects related to MOS structures, present time. It has also been found considerable confusion arose concerning About the Author that similar material and process control symbols used to designate their name and nomenclature. This confusion was has resulted in improved bipolar devices Bruce E. Deal died on April 17, 2007, as well. C–V analysis has continued reasonably well resolved, however, by in Palo Alto, California. (See the summer to be a key monitoring method for committees and publications provided 2007 issue of Interface for the complete the semiconductor industry in general by both the ECS Electronics & Photonics obituary notice.) Dr. Deal received an (see Fig. 2). Division and the IEEE Electron Device AB degree from Nebraska Wesleyan Society (see Table I, Ref. 9). University in 1950, and MS and PhD Ambient Effects on Thermal degrees in physical chemistry from Iowa Oxidation Kinetics.—As described Summary State University in Ames, Iowa in 1953 above, silicon thermal oxidation kinetics and 1955 respectively. In 1959, Deal were first investigated in the early 1960s. The contributions of scientists and moved to Palo Alto, CA and spent During subsequent years, modifications of engineers at the Fairchild Research the rest of his career in Silicon Valley. the dry O2 oxidation ambient were found Laboratory regarding thermally oxidized He first conducted semiconductor to provide certain device advantages (see silicon properties in the 1963-1979 time research at Rheem Semiconductor in Table I, Ref. 4). These modifications (see period have been summarized. The Mountain View, the first spin-off of Fig. 3) included dry O2/H2O (increased results of these investigations helped to Fairchild Semiconductor. In 1963, he formation rate in H2O as can be seen by advance the understanding, and thus joined Fairchild’s R&D Laboratory in comparing the time scales for H2O and the successful fabrication of stable metal- Palo Alto, initially as a Member of dry O2). Additional ambients included: oxide-semiconductor (MOS) devices and Technical Staff and later as a Research O2/N2 (dilution of O2 with N2 is done to their implementation into the industry. Manager/Department Director. After permit higher oxidation temperatures to Fairchild’s efforts included numerous Moore and Noyce founded Intel in enhance dopant diffusion in conjunction publications and presentations in 1968, Deal remained at Fairchild until with a smaller growth of oxide); O2/HC1 oxidation kinetics, oxide charge the company was sold to National (alkali contaminate gettering); understanding and control, device Semiconductor in 1977. He spent a year O2/pyrogenic (flame) H2O, high-pressure yield and stability, and other improved at National as Principal Technologist, O2 or H2O (increased oxidation rate/ electrical and physical properties of and then joined Advantage Production decreased process temperature); and H2 Fig. 4. Charges in thermally oxidized silicon. virtually all types of device structures. Technology as Vice-President of

44 The Electrochemical Society Interface • Fall 2007 The Electrochemical Society Interface • Fall 2007 45