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A study of thermal transpiration using ultrahigh-vacuum techniques
ABSTRACTS ON M I C R O E L E C T R O N I C S AND R E L I A B I L I T Y
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litre of hydrogen was sorbed by the time the speed had fallen to 15,000 1./sec. The initial pumping speeds are higher than the conductance limit of the pump. The curves of pumping speed vs time, moreover, show no sign of being conductance limited. This and other evidence indicates that adsorptiondesorption processes are taking place on the liquid-nitrogen cooled stainless steel, apart from the pumping action of the titanium film. Pressure fluctuations in systems evacuated by diffusion pumps. U. R. BANCEand E. H. HARDEN, Vacuum 15, No. 9, p. 437. The problem of pressure fluctuations occurring in systems pumped by diffusion pumps has been reported by several investigators, various conclusions having been reached. Such fluctuations can exhibit differing characteristic symptoms, one common mode taking the form of relatively high pressure (10 -5 tort or greater) repetitive pulses. In this paper experiments are described which prove that these repetitive fluctuations are due to gases released from the region of the pump top flange seal, and the theoretical considerations supporting the experiments, together with the simple modifications required to effect a complete and proven cure for such pressure pulses, are detailed. Practical aspects of v a c u u m leak detection and location. T. THORLEY,Vacuum 15, No. 9, p. 443. In common with the observations of other workers it had been realized during a lengthy testing experience at the author's establishment that the minimum sensitivities achieved in practice were often very much higher than the values normally quoted in the literature. Probe gas response times also were very long indeed in some cases. Explanations covering these effects had been advanced in the literature some years earlier but some of the results actually encountered appeared to be worse than would have been expected from those explanations. A series of minimum sensitivity values and probe gas response times were calculated taking into account the various relevant factors and these were found to confirm the results obtained in practice. The paper includes some comments on practical aspects of leak detection, particularly with reference to certain aspects of use of the mass spectrometer, and also discusses some of the relative features of leak up testing versus hooding and use of a probe gas. Hall-effect and resistivity measurements at room temperature and --165°C on c h r o m i u m nickel alloys. C. E. McCAIN and K. SCHRSDER,J. Phys. Chem. Solids 26, p. 1139 (1965). The Hallcoefficient RH and the electrical resistivity of Cr-Ni alloys was measured at room temperature and --165°C. An alloy with 3.6 at. per cent Ni showed at --165°C the highest RH value. It was found that the RH values of Cr-Ni alloys were similar to those found for Cr-Fe alloys, if plotted as a function of electron concentration. The production of precision masks for v a c u u m deposition of thin films. D. L. ATHERTONand A. A. PECK, SCP and Solid State Technology, p. 30 (July 1965). Precise masks used for vacuum deposition work require high resolution photographic masters covering larger areas than do semiconductors; photographic artwork reduction is therefore slightly different; problems and compromises are discussed and techniques described. Refined photo-resist techniques used for the production of metal masks are outlined. Materials and etches for metal masks are considered and the development and special advantages of composite double-etched masks of nickel-plated beryllium copper are described. Process steps for producing metal masks from photographic masters are enumerated. Cylindrical geometry sputtering apparatus. W. R. SINCLAIRand F. G. PETERS,J. Vacuum Science Technology 2, No. 4, p. 178 (July-August 1965). A cylindrical geometry sputtering apparatus and associated fixtures have been described which feature ease of construction and use. Because of the high symmetry of the apparatus, films can be deposited simultaneously on different substrates at different temperatures and meaningful comparisons made between results. Films can be deposited on to substrates that are electrically floating, and it is pointed out that this is valuable in reactive sputtering in oxygen as it minimizes damage to sensitive electronic structures which can be caused by anionic bombardment. The planarity of the sputtered films and the rate of deposition are discussed. A study of thermal transpiration using ultrahlgh-vacuum techniques. T. EDMONDSand J. P. HOBSON,J. Vacuum Science & Technology 2, No. 4, p. 182 (July-August 1965). The thermal transpiration ratio R = Pa/P~ was measured by the absolute method in helium and neon over the pressure range
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A B S T R A C T S ON M I C R O E I , E C T P , O N I C S AN[) R E I ~ I A B I L I T Y
10-° ~< P2 ~< 60 Torr. (;old temperatures were T~ :- 77.4°K and 232°K with warm temperature T 2 = 295°K. An aperture and various tubes were used at the temperature interface. For the aperture Rm = (Ta/T2)~/'~ was found, as expected, at low pressures but this value was not found, in general, for tubes. The latter case represents a departure from normal assumptions, which are examined in detail. A related conclusion is that the relative method for measuring R is unreliable for tubes at low pressures. It is concluded that a molecule has a greater probability of traversing a tube from the hot end to the cold end than in the opposite direction. It is found that several analytic expressions for R represent the data satisfactorily after suitable choice of constants.
Textural characteristics and electrical properties of v a c u u m evaporated silicon films. A. J. MOUNTVALA and G. ABOWITZ,Vacuum 15, No. 7, p. 359. The textural characteristics and electrical properties of silicon fihns have been studied. The films were formed by vacuum evaporation on to heated polished quartz substrates. The substrate temperature strongly influences the preferred orientation in the films. The most significant low-energy texture is of the (110) variety. At higher substrate temperatures the (111) tends to become significant. All films were p-type, regardless of evaporation parameters, starting materials and doping. This invariable p-type behaviour is probably associated with contamination from the source container as well as from boron transfer during pump down of the glass vacuum system. Special technological equipment for manufacturing thin-film components. M. VON ARDENNE, S. SCHILLERand U. HEism, Nachrichtentechnik 15, No. 8, p. 306 (1965). Problems of the technological processes operating in vacuum, above all vapour depositions, dusting and uses of the electron beam as a tool, are discussed. Various methods of vapour deposition are described including their special possibilities of application, and their limits. Problems of additional equipment are also mentioned. Microelectronics based on the thin-film technique. K. KRAHL,E. SCHLEICHERand W. PERTSCH, Nachrichtentechnik 15, No. 8, p. 287 (1965). A system of miniaturization of electronic circuits has been developed by VEB Keramische Werke Hermsdorf which makes possible an economic manufacture of most modern integrated components by way of constantly enlarging technological equipment according to the latest scientific progress. Mass filter studies of gases in a 90-1itre getter-ion v a c u u m system. M. C. PAUL, Vacuum 15, No. 5, p. 239. The basic residual gases present in a 90-1itre titanium getter-ion vacuum system operating under different conditions are determined with the aid of a quadrupole-field mass filter. Mass spectra of gases in the system during successive temperature increases of molybdenum and tungsten filament heaters over a temperature range from 25°C to 1050°C for molybdenum and 25°C to 1250°C for tungsten are presented. Possible sources of the gases are discussed primarily in terms of outgassing characteristics of materials and interaction between gases and the surfaces on which they impinge. Fragments resulting from the introduction of solvents commonly used in cleaning vacuum hardware (acetone and isopropyl alcohol) are presented. Results show that major residual gases present in the getter-ion system are carbon monoxide, nitrogen, argon, hydrogen, methane and water vapour, with their order of prominence variable depending upon conditions. The introduction of hot tungsten or molybdenum filament heaters does not alter the gas profile appreciably until their surface temperatures reach about 1000°C, at which point outgassing from surrounding surfaces becomes appreciable. Carbon dioxide, carbon and a host of hydrocarbons then play increasingly important roles. When acetone and isopropyl alcohol are introduced into the vacuum system, they dissociate quite readily and completely into several smaller components, in particular CH +, CHa +, C~Ha+, C2H.~+ and C3Ha ~. The m e a s u r e m e n t of the speed of pumps. W. STECKELMACHER,Vacuum 15, No. 5, p. 249. It is proposed to specify an "intrinsic" speed of a pump as well as an "intrinsic" conductance of components as obtained when these are connected to a large chamber or between large chambers. It is shown that by separating out an aperture conductance, both for the case of a component and a pump, the reciprocals of conductances and of pump speeds in composite systems are additive in the usual way, provided that the number of aperture conductances have been correctly accounted for. On the other hand Dayton suggested that the pump speed should be specific as measured with a test dome of the same diameter
93
litre of hydrogen was sorbed by the time the speed had fallen to 15,000 1./sec. The initial pumping speeds are higher than the conductance limit of the pump. The curves of pumping speed vs time, moreover, show no sign of being conductance limited. This and other evidence indicates that adsorptiondesorption processes are taking place on the liquid-nitrogen cooled stainless steel, apart from the pumping action of the titanium film. Pressure fluctuations in systems evacuated by diffusion pumps. U. R. BANCEand E. H. HARDEN, Vacuum 15, No. 9, p. 437. The problem of pressure fluctuations occurring in systems pumped by diffusion pumps has been reported by several investigators, various conclusions having been reached. Such fluctuations can exhibit differing characteristic symptoms, one common mode taking the form of relatively high pressure (10 -5 tort or greater) repetitive pulses. In this paper experiments are described which prove that these repetitive fluctuations are due to gases released from the region of the pump top flange seal, and the theoretical considerations supporting the experiments, together with the simple modifications required to effect a complete and proven cure for such pressure pulses, are detailed. Practical aspects of v a c u u m leak detection and location. T. THORLEY,Vacuum 15, No. 9, p. 443. In common with the observations of other workers it had been realized during a lengthy testing experience at the author's establishment that the minimum sensitivities achieved in practice were often very much higher than the values normally quoted in the literature. Probe gas response times also were very long indeed in some cases. Explanations covering these effects had been advanced in the literature some years earlier but some of the results actually encountered appeared to be worse than would have been expected from those explanations. A series of minimum sensitivity values and probe gas response times were calculated taking into account the various relevant factors and these were found to confirm the results obtained in practice. The paper includes some comments on practical aspects of leak detection, particularly with reference to certain aspects of use of the mass spectrometer, and also discusses some of the relative features of leak up testing versus hooding and use of a probe gas. Hall-effect and resistivity measurements at room temperature and --165°C on c h r o m i u m nickel alloys. C. E. McCAIN and K. SCHRSDER,J. Phys. Chem. Solids 26, p. 1139 (1965). The Hallcoefficient RH and the electrical resistivity of Cr-Ni alloys was measured at room temperature and --165°C. An alloy with 3.6 at. per cent Ni showed at --165°C the highest RH value. It was found that the RH values of Cr-Ni alloys were similar to those found for Cr-Fe alloys, if plotted as a function of electron concentration. The production of precision masks for v a c u u m deposition of thin films. D. L. ATHERTONand A. A. PECK, SCP and Solid State Technology, p. 30 (July 1965). Precise masks used for vacuum deposition work require high resolution photographic masters covering larger areas than do semiconductors; photographic artwork reduction is therefore slightly different; problems and compromises are discussed and techniques described. Refined photo-resist techniques used for the production of metal masks are outlined. Materials and etches for metal masks are considered and the development and special advantages of composite double-etched masks of nickel-plated beryllium copper are described. Process steps for producing metal masks from photographic masters are enumerated. Cylindrical geometry sputtering apparatus. W. R. SINCLAIRand F. G. PETERS,J. Vacuum Science Technology 2, No. 4, p. 178 (July-August 1965). A cylindrical geometry sputtering apparatus and associated fixtures have been described which feature ease of construction and use. Because of the high symmetry of the apparatus, films can be deposited simultaneously on different substrates at different temperatures and meaningful comparisons made between results. Films can be deposited on to substrates that are electrically floating, and it is pointed out that this is valuable in reactive sputtering in oxygen as it minimizes damage to sensitive electronic structures which can be caused by anionic bombardment. The planarity of the sputtered films and the rate of deposition are discussed. A study of thermal transpiration using ultrahlgh-vacuum techniques. T. EDMONDSand J. P. HOBSON,J. Vacuum Science & Technology 2, No. 4, p. 182 (July-August 1965). The thermal transpiration ratio R = Pa/P~ was measured by the absolute method in helium and neon over the pressure range
94
A B S T R A C T S ON M I C R O E I , E C T P , O N I C S AN[) R E I ~ I A B I L I T Y
10-° ~< P2 ~< 60 Torr. (;old temperatures were T~ :- 77.4°K and 232°K with warm temperature T 2 = 295°K. An aperture and various tubes were used at the temperature interface. For the aperture Rm = (Ta/T2)~/'~ was found, as expected, at low pressures but this value was not found, in general, for tubes. The latter case represents a departure from normal assumptions, which are examined in detail. A related conclusion is that the relative method for measuring R is unreliable for tubes at low pressures. It is concluded that a molecule has a greater probability of traversing a tube from the hot end to the cold end than in the opposite direction. It is found that several analytic expressions for R represent the data satisfactorily after suitable choice of constants.
Textural characteristics and electrical properties of v a c u u m evaporated silicon films. A. J. MOUNTVALA and G. ABOWITZ,Vacuum 15, No. 7, p. 359. The textural characteristics and electrical properties of silicon fihns have been studied. The films were formed by vacuum evaporation on to heated polished quartz substrates. The substrate temperature strongly influences the preferred orientation in the films. The most significant low-energy texture is of the (110) variety. At higher substrate temperatures the (111) tends to become significant. All films were p-type, regardless of evaporation parameters, starting materials and doping. This invariable p-type behaviour is probably associated with contamination from the source container as well as from boron transfer during pump down of the glass vacuum system. Special technological equipment for manufacturing thin-film components. M. VON ARDENNE, S. SCHILLERand U. HEism, Nachrichtentechnik 15, No. 8, p. 306 (1965). Problems of the technological processes operating in vacuum, above all vapour depositions, dusting and uses of the electron beam as a tool, are discussed. Various methods of vapour deposition are described including their special possibilities of application, and their limits. Problems of additional equipment are also mentioned. Microelectronics based on the thin-film technique. K. KRAHL,E. SCHLEICHERand W. PERTSCH, Nachrichtentechnik 15, No. 8, p. 287 (1965). A system of miniaturization of electronic circuits has been developed by VEB Keramische Werke Hermsdorf which makes possible an economic manufacture of most modern integrated components by way of constantly enlarging technological equipment according to the latest scientific progress. Mass filter studies of gases in a 90-1itre getter-ion v a c u u m system. M. C. PAUL, Vacuum 15, No. 5, p. 239. The basic residual gases present in a 90-1itre titanium getter-ion vacuum system operating under different conditions are determined with the aid of a quadrupole-field mass filter. Mass spectra of gases in the system during successive temperature increases of molybdenum and tungsten filament heaters over a temperature range from 25°C to 1050°C for molybdenum and 25°C to 1250°C for tungsten are presented. Possible sources of the gases are discussed primarily in terms of outgassing characteristics of materials and interaction between gases and the surfaces on which they impinge. Fragments resulting from the introduction of solvents commonly used in cleaning vacuum hardware (acetone and isopropyl alcohol) are presented. Results show that major residual gases present in the getter-ion system are carbon monoxide, nitrogen, argon, hydrogen, methane and water vapour, with their order of prominence variable depending upon conditions. The introduction of hot tungsten or molybdenum filament heaters does not alter the gas profile appreciably until their surface temperatures reach about 1000°C, at which point outgassing from surrounding surfaces becomes appreciable. Carbon dioxide, carbon and a host of hydrocarbons then play increasingly important roles. When acetone and isopropyl alcohol are introduced into the vacuum system, they dissociate quite readily and completely into several smaller components, in particular CH +, CHa +, C~Ha+, C2H.~+ and C3Ha ~. The m e a s u r e m e n t of the speed of pumps. W. STECKELMACHER,Vacuum 15, No. 5, p. 249. It is proposed to specify an "intrinsic" speed of a pump as well as an "intrinsic" conductance of components as obtained when these are connected to a large chamber or between large chambers. It is shown that by separating out an aperture conductance, both for the case of a component and a pump, the reciprocals of conductances and of pump speeds in composite systems are additive in the usual way, provided that the number of aperture conductances have been correctly accounted for. On the other hand Dayton suggested that the pump speed should be specific as measured with a test dome of the same diameter