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Very high-vacuum heat treatment facility
Classified abstracts 646645475
12. G A S E O U S I N T E R A C T I O N S W I T H SOLIDS 12 6466. Calculation of desorption energy distribution applied to temperature programmed H 2 0 desorption from silicate glass surface A method of calculating the desorption energy distribution from temperature programmed desorption data based on an iteration process is proposed, checked by model calculations, and applied to H 20 desorption spectra from silicate glass surfaces. H Wittkopf, Vacuum, 37, 1987, 819-823. 12 6467. Adsorption and reaction of oxygen on Cu(ll0) in O2]H 2 and O2/CO gas mixtures Gas mixtures of CO and O2, and H2 and 02 were admitted to a Cu(110) crystal at 475 775 K and 675-775 K respectively. Except for the CO/O2 mixture at 775 K it was observed that the crystal was either clean or oxidized up to 00 = 0.5. F r o m the oxidation and reduction rates it appeared that the reactivity o f CO and H2 towards adsorbed oxygen was not influenced by the presence of oxygen in gas phase. However the adsorption of oxygen was enhanced for CO/O2 at T > 550 K and even more strongly for H2/O2 gas mixtures. An explanation of this effect is given. O P van Pruissen et al, Vacuum, 38, 1988, 247 250. 12 6468. Analytical relationship for the oxidation of silicon in dry oxygen in the thin-film regime The oxidation of silicon in dry oxygen is characterized by an initial stage where the growth rate is larger than predicted by the Deal-Grove linearparabolic general oxidation relationship. This growth-rate enhancement has been studied in the 8 0 ~ 1 0 0 0 ° C range by using in situ ellipsometry, and its dependence on the oxidation parameters has been analyzed. In this paper, the rate enhancement in the thin-film regime is analyzed as a function of oxidation time and is found to fit two terms which decay exponentially with time. These results yield an analytical relationship between the oxide thickness and the oxidation time that describes SiO2 growth beyond the native oxide. The nature of the additional oxidation mechanisms and their decay with time is discussed. Hisham Z Massoud and James D Hummer, J appl Phys, 62, 1987, 34163423. 12 6469. Gases released by surface llashover of insulators The gases released by surface flashovers on alumina ceramics, glass, and quartz, using 20-#s voltage pulses, were investigated using an ion-pumped metal vacuum system. Appreciable quantities of gas were measured (approximately 10 6 Torr liter or 1013 molecules). The composition of this gas differed significantly from the background gas. The dominant species in the surface flashover gases were CO2, CO, and H2 ; a modest a m o u n t of CH 4 was observed, along with lesser quantities of N2 and H20. The dominant gas in the system background was nitrogen, accompanied by (in decreasing amounts) H2, H20, CO/CO2, Ar, CH4, and He. We concluded that the gas released by flashovers on the surface of the insulators was not adsorbed system background gas, but was gas absorbed during the handling and processing o f the insulator. H Craig Miller and Robert J Ney, J appl Phys, 63, 1988, 668 673.
13. M A T E R I A L S A N D T E C H N I Q U E S IN V A C U U M 13 6470. Chemical cleaning of metal surfaces in vacuum systems by exposure to reactive gases Chemical surface cleaning procedures for metals using oxidation/ reduction cycles by exposure to oxidizing (02, NO) and reducing (H2, NH3) gases are summarized and an update of the original compilation for chemical cleaning procedures published by Musket et al. [Appl. Surf. Sci. 10, 143 (1982)] is given. Examples discussed in this paper are cleaning procedures for iron, nickel, palladium, copper, and silver surfaces. We also present data on the reduction of gaseous contaminants in a stainless-steel U H V system by flowing nitric oxide through the system during bakeout. M Grunze et al, J Vac Sci Technol, A6, 1988, 1266-1275.
13 6471. Scrubbing characteristics of CCI4 and C2F 6 with a titanium sublimation trap A quadrupole mass spectrometer with a mass range from 1 to 200 a m u gives m u c h useful information about scrubbing of contaminated effluent gases with a titanium sublimation trap. The gases investigated are CC14 and C2F6, which have been used to etch semiconductor materials in a glow discharge. The total pressure of test gases was measured with a capacitance manometer. The detailed experimental results of C C l 4 for both continuous and intermittent titanium evaporation under various conditions are presented. It is shown that the major constituents in the residual atmosphere are always H2, CH4, and C2H 6. The toxic gas, comprised of mostly chlorine rather than the parent CC14, w a s of the order of 0.1% of the total pressure. The efficiency of the trap was demonstrated even though the stainless-steel trap was not cleaned over one month. However, the titanium surface was almost inert for C2F6. Yao-Zhi Hu, J Vac Sci Technol, A6, 1988, 1255 1258. 13 6472. American Vacuum Society recommended practices for pumping hazardous gases The purpose of this recommended practice is to familiarize users with the issues involved with processes using toxic, flammable, or corrosive gases for the deposition or etching of semiconducting, metallic, or insulating films. We examine the general concerns for handling these gases, discuss the nature of several processes, their effluents, reactivit~¢ with p u m p fluids, and how to scrub noxious gases from the exhaust. We describe some specific concerns that relate to materials, components, and facilities layout which result from technical, safety, and regulatory obligations. As an aid in making these concerns clear, we have considered the design of seven different systems that use corrosive, flammable, pyrophoric, or toxic gases. We give examples of a plasma etch system, deposition systems for tungsten silicide, borophosphosilicate glass, a m o r p h o u s silicon, and silicon nitride, an organometallic deposition system, and finally an ion implantation system. We are keenly aware that design, process, and safety considerations vary throughout the industry. We ae not attempting to standardize or claim that the techniques presented here are the only techniques which are acceptable. We are trying to point out some wellknown hazards and recommend procedures which, to the best of our knowledge, are reliable, and to urge people to think through the entire process of design, construction, and operation very carefully. The final decision on how a facility is to be designed, constructed, and operated can only be made by the responsible management and facility safety officers. John F O'Hanlon and David B Fraser, J Vac Sci Technol, A6, 1988, 12261254. 13 6473. Very high-vacuum heat treatment facility We have designed and constructed a vacuum heat treatment facility, with hot zone dimensions of 12 x 19 x 19 cm, at a cost substantially below that of a commercial unit. The design incorporates efficient water cooling and a resistive heating element. A vacuum pressure of 1.5 x 10- 8 Tort at room temperature has been obtained after baking. The temperature limit is approximately 1900°C. This limit results from our choice of niobium as the hot zone material. W M Folkner et al, Rev Sci Instrum, 58, 1987, 2288-2291. 13 6474. Novel high-pressure isolation cell capable of reaching 120 atm mounted in an ultrahigh-vacuum chamber A high-pressure cell and manipulator mounted inside an U H V surface analysis chamber has been built which can reach 1800 psi. With this apparatus, catalytic reactions on small surface area ( ~ 1 cm 2) single crystals and polycrystalline surfaces are monitored, and the effect of reactant pressure, surface composition, and surface structure are correlated with catalytic activity. This article describes in detail the apparatus and typical experimental procedure. T G Rucker et al, Rev Sci Instrum, 58, 1987, 2292-2294. 13 6475. Channel electron multiplier compatibility with Viton and Apiezon-L vacuum grease Clean Viton and Viton coated with Apiezon-L vacuum grease were tested for their noncontaminating compatibility with channel electron multipliers (CEMs). The test setup and procedure were the same as those 491
12. G A S E O U S I N T E R A C T I O N S W I T H SOLIDS 12 6466. Calculation of desorption energy distribution applied to temperature programmed H 2 0 desorption from silicate glass surface A method of calculating the desorption energy distribution from temperature programmed desorption data based on an iteration process is proposed, checked by model calculations, and applied to H 20 desorption spectra from silicate glass surfaces. H Wittkopf, Vacuum, 37, 1987, 819-823. 12 6467. Adsorption and reaction of oxygen on Cu(ll0) in O2]H 2 and O2/CO gas mixtures Gas mixtures of CO and O2, and H2 and 02 were admitted to a Cu(110) crystal at 475 775 K and 675-775 K respectively. Except for the CO/O2 mixture at 775 K it was observed that the crystal was either clean or oxidized up to 00 = 0.5. F r o m the oxidation and reduction rates it appeared that the reactivity o f CO and H2 towards adsorbed oxygen was not influenced by the presence of oxygen in gas phase. However the adsorption of oxygen was enhanced for CO/O2 at T > 550 K and even more strongly for H2/O2 gas mixtures. An explanation of this effect is given. O P van Pruissen et al, Vacuum, 38, 1988, 247 250. 12 6468. Analytical relationship for the oxidation of silicon in dry oxygen in the thin-film regime The oxidation of silicon in dry oxygen is characterized by an initial stage where the growth rate is larger than predicted by the Deal-Grove linearparabolic general oxidation relationship. This growth-rate enhancement has been studied in the 8 0 ~ 1 0 0 0 ° C range by using in situ ellipsometry, and its dependence on the oxidation parameters has been analyzed. In this paper, the rate enhancement in the thin-film regime is analyzed as a function of oxidation time and is found to fit two terms which decay exponentially with time. These results yield an analytical relationship between the oxide thickness and the oxidation time that describes SiO2 growth beyond the native oxide. The nature of the additional oxidation mechanisms and their decay with time is discussed. Hisham Z Massoud and James D Hummer, J appl Phys, 62, 1987, 34163423. 12 6469. Gases released by surface llashover of insulators The gases released by surface flashovers on alumina ceramics, glass, and quartz, using 20-#s voltage pulses, were investigated using an ion-pumped metal vacuum system. Appreciable quantities of gas were measured (approximately 10 6 Torr liter or 1013 molecules). The composition of this gas differed significantly from the background gas. The dominant species in the surface flashover gases were CO2, CO, and H2 ; a modest a m o u n t of CH 4 was observed, along with lesser quantities of N2 and H20. The dominant gas in the system background was nitrogen, accompanied by (in decreasing amounts) H2, H20, CO/CO2, Ar, CH4, and He. We concluded that the gas released by flashovers on the surface of the insulators was not adsorbed system background gas, but was gas absorbed during the handling and processing o f the insulator. H Craig Miller and Robert J Ney, J appl Phys, 63, 1988, 668 673.
13. M A T E R I A L S A N D T E C H N I Q U E S IN V A C U U M 13 6470. Chemical cleaning of metal surfaces in vacuum systems by exposure to reactive gases Chemical surface cleaning procedures for metals using oxidation/ reduction cycles by exposure to oxidizing (02, NO) and reducing (H2, NH3) gases are summarized and an update of the original compilation for chemical cleaning procedures published by Musket et al. [Appl. Surf. Sci. 10, 143 (1982)] is given. Examples discussed in this paper are cleaning procedures for iron, nickel, palladium, copper, and silver surfaces. We also present data on the reduction of gaseous contaminants in a stainless-steel U H V system by flowing nitric oxide through the system during bakeout. M Grunze et al, J Vac Sci Technol, A6, 1988, 1266-1275.
13 6471. Scrubbing characteristics of CCI4 and C2F 6 with a titanium sublimation trap A quadrupole mass spectrometer with a mass range from 1 to 200 a m u gives m u c h useful information about scrubbing of contaminated effluent gases with a titanium sublimation trap. The gases investigated are CC14 and C2F6, which have been used to etch semiconductor materials in a glow discharge. The total pressure of test gases was measured with a capacitance manometer. The detailed experimental results of C C l 4 for both continuous and intermittent titanium evaporation under various conditions are presented. It is shown that the major constituents in the residual atmosphere are always H2, CH4, and C2H 6. The toxic gas, comprised of mostly chlorine rather than the parent CC14, w a s of the order of 0.1% of the total pressure. The efficiency of the trap was demonstrated even though the stainless-steel trap was not cleaned over one month. However, the titanium surface was almost inert for C2F6. Yao-Zhi Hu, J Vac Sci Technol, A6, 1988, 1255 1258. 13 6472. American Vacuum Society recommended practices for pumping hazardous gases The purpose of this recommended practice is to familiarize users with the issues involved with processes using toxic, flammable, or corrosive gases for the deposition or etching of semiconducting, metallic, or insulating films. We examine the general concerns for handling these gases, discuss the nature of several processes, their effluents, reactivit~¢ with p u m p fluids, and how to scrub noxious gases from the exhaust. We describe some specific concerns that relate to materials, components, and facilities layout which result from technical, safety, and regulatory obligations. As an aid in making these concerns clear, we have considered the design of seven different systems that use corrosive, flammable, pyrophoric, or toxic gases. We give examples of a plasma etch system, deposition systems for tungsten silicide, borophosphosilicate glass, a m o r p h o u s silicon, and silicon nitride, an organometallic deposition system, and finally an ion implantation system. We are keenly aware that design, process, and safety considerations vary throughout the industry. We ae not attempting to standardize or claim that the techniques presented here are the only techniques which are acceptable. We are trying to point out some wellknown hazards and recommend procedures which, to the best of our knowledge, are reliable, and to urge people to think through the entire process of design, construction, and operation very carefully. The final decision on how a facility is to be designed, constructed, and operated can only be made by the responsible management and facility safety officers. John F O'Hanlon and David B Fraser, J Vac Sci Technol, A6, 1988, 12261254. 13 6473. Very high-vacuum heat treatment facility We have designed and constructed a vacuum heat treatment facility, with hot zone dimensions of 12 x 19 x 19 cm, at a cost substantially below that of a commercial unit. The design incorporates efficient water cooling and a resistive heating element. A vacuum pressure of 1.5 x 10- 8 Tort at room temperature has been obtained after baking. The temperature limit is approximately 1900°C. This limit results from our choice of niobium as the hot zone material. W M Folkner et al, Rev Sci Instrum, 58, 1987, 2288-2291. 13 6474. Novel high-pressure isolation cell capable of reaching 120 atm mounted in an ultrahigh-vacuum chamber A high-pressure cell and manipulator mounted inside an U H V surface analysis chamber has been built which can reach 1800 psi. With this apparatus, catalytic reactions on small surface area ( ~ 1 cm 2) single crystals and polycrystalline surfaces are monitored, and the effect of reactant pressure, surface composition, and surface structure are correlated with catalytic activity. This article describes in detail the apparatus and typical experimental procedure. T G Rucker et al, Rev Sci Instrum, 58, 1987, 2292-2294. 13 6475. Channel electron multiplier compatibility with Viton and Apiezon-L vacuum grease Clean Viton and Viton coated with Apiezon-L vacuum grease were tested for their noncontaminating compatibility with channel electron multipliers (CEMs). The test setup and procedure were the same as those 491