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Properties of polycrystalline silicon grown on insulating subtrates by electron beam gun evaporation
Classified abstracts 6829-6835
W(110) surface is calculated for different distances. The calculations are based on a model Hamiltonian and allow for tip-surfaee interaction. At small surface-tip separations (~<6/~) a negative corrugation is found, i.e. Oad induces a dent in the constant current contours, in contrast to the contours of total charge density and that at Er. At larger distances they all exhibit a positive corrugation with maxima at the position of the Oad. G Doyen et ai, J Vac Sci Technol, A6, 1988, 327 330.
13. MATERIALS AND TECHNIQUES IN VACUUM 13 6829. Characterization and thermal desorption spectroscopy study on a new, low outgassing material surface for improved ultrahigh vacuum uses The surface of an austenitic stainless steel doped with N, B and Ce (SUS304-NBCe), which was covered with thin BN precipitated layers, has been characterized using Auger electron spectroscopy (AES), Fourier transform infrared, transmission electron microscopy, transmission electron diffraction (TED), and reflection high-energy electron diffraction (RHEED) techniques. Thermal desorption spectroscopy method was also applied for evaluating its outgassing nature. AES spectra obtained from the BN precipitated layers coincided well with those of a hexagonal BN even in fine structures of B(KLL) and N(KLL) Auger transitions. RHEED and TED patterns obtained from them showed that the structure of the BN layer was hexagonal and that the c axis preferred to be parallel to the surface normal. That is to say, the basal plane of the hexagonal BN, which is more inert to adsorption than other planes are preferred to cover the surface. The outgassing nature of the above surface has been measured and compared with two other types of stainless-steel surfaces such as an electropolished surface and a S segregated one. Among the three, the amount of desorbed gases from the BN covered surface was the lowest on heating up to 800°C. The potential of the BN precipitated surface for UHV vessels with low outgassing is pointed out. D Fnjita and T Homma, J Vac Sci Technol, A6, 1988, 23(~234. 13 6830. Tritium removal from noble gas streams A process loop to remove tritium from a flowing helium stream in a single pass has been constructed and commissioned. Inventories injected into the loop range from 1 GBq-28 TBq. Concentrations within the stream entering the loop range from 40 MBq/m 3 to 15 TBq/m ~. The tritium is removed from the stream by gettering on uranium beds. Residual concentrations leaving these beds are removed with zirconium-iron getter beds. Purification factors of 10 for the uranium beds and a minimum of 19400 for the zirconium iron bed have been measured. This paper describes the process loop and the performance of the getter beds during one 28-TBq injection. W T Shmayda et al, J Vac Sci Technol, A6, 1988, 1259 1262, 13 6831. Techniques for testing cryopump capacity Pneurop has proposed guidelines for measuring cryopump specifications (Minutes of Pneurop Committee-Vacuum Technology, "Acceptance Specifications, Part 5: Cryopumps", 1987). However, conditions used during capacity measurement are not specific for condensibles. Methods used for this measurement strongly affect the results, and the distinction between useful capacity and gross capacity is important to the end user of equipment affected by this specification. This paper describes various methods for measuring condensible and adsorbable gas capacity and compares their relative merits. Gases which are condensed on the pumping arrays required considerations different from those which are adsorbed. A cyclical test has been developed and standardized for inhouse use which provides information on pumping speed stability and condensation characteristics of cryopumps. John R Porter, J Vac Sci Technol, A6, 1988, 1214-1216. 13 6832. The influence of heavier gases in pumping helium and hydrogen in an ion pump Pumping mechanisms for hydrogen and helium in an ion pump are quite different from the usual mechanisms by which other gases are pumped. Their sputtering yield is much lower and their diffusion higher than for heavier gases. Hence the pumping effect at the cathode plays an important role in pumping these two gases, being comparable with or even larger than the standard pumping at the anode. The effect of the presence of heavier gases on the pumping mechanisms for helium and hydrogen has 972
been investigaed for various pressures, concentrations, and gas species. The pumping speed for helium is shown to decrease as a function of heavier gas pressure; such a decrease is strongly dependent on helium pressure and on the amount of previously pumped gas. Pumping speed for hydrogen shows very different behavior : both considerable increases and decreases have been observed, depending on hydrogen pressure, heavier gas concentration and species, and temperature. Pumping speed for a getterable gas such as nitrogen, whose pumping mechanisms are well known, has been reported as a function of concentration of xenon for comparison. The various and sometimes contrasting phenomena responsible for these effects are analyzed, and their relative importance is pointed out. M Andi and M DeSimou, J Vac Sci Technol, A6, 1988, 1205-1208. 13 6833. Lubricating of mechanisms for vacuum service Seizure of metal parts which occurs during sliding or rolling in a vacuum environment can be prevented by use of appropriate lubricants. Fluid lubricants, having low evaporation rates, dry solid film lubricants, soft, low shear strength metals, and composite materials are customarily used, but ion implanted metals and ceramics are available for extremely harsh environments. Bearings, bushings, gears, cams, guides and slides, solenoids, commutators, motor brushes, and sliprings can be lubricated to yield vacuum service lives comparable to those achieved in normal atmospheric pressure applications, or even longer due to the absence of 02 and H20. The use of fluid and dry lubricants may require the incorporation of seals to prevent molecular or particulate contamination of test or production hardware within the vacuum system. The most important parameter to be considered in selecting the appropriate lubricant is the operating temperature, which drastically affects the evaporation and contamination rates. Fluid based lubricants are available having evaporation rates of 10 -9 to I0 - u g c m 2 s-J and metals, composites, and dry lubricants having 10-1°~10-14 g c m -2 s -1 loss rates at room temperature. K G Roller, J Vac Sci Technol, A6, 1988, 1161-1165. 13 6834. A generalized approach to vacuum system automation Computer automation of vacuum equipment has traditionally been dominated by custom hardware and software solutions, requiring long and expensive development periods. On-going modification and support of the installed computer equipment often requires an appreciable portion of a computer specialist's time. In order to achieve a more cost effective approach, the authors have analyzed a variety of vacuum deposition and etching processes running on equipment supplied by numerous manufacturers. The following observations have led to the development of a generalized vacuum equipment automation system which requires minimal custom engineering time to install and support: (1) In spite of the high marketing profile given to RS-232, IEEE-488 and SECS II interfaces, by far the most common and easy to use interfaces provided by vacuum equipment vendors are simple digital and analog. (2) Most processes involve between 50 and 300 discrete or continuous parameters ; however, few of these parameters vary at rates appreciably higher than 1 Hz. (3) The inter-relationships between these many parameters are often complex and/or difficult to specify in a fixed manner. The computer must therefore be capable of operating according to process logic entered and modified in the field by a process engineer, who may not be a computer specialist. (4) The skill level of vacuum operators varies from doctorate to grade school; uses of vacuum equipment vary from pure research to highvolume production. The user interface must therefore be highly adaptable yet easy to use. R W MeMahon et al, J Vac Sci Technol, A6, 1988, 1158 1160.
II. Thin film t e c h n o l o g y 20. EVAPORATION 20 6835. Properties of polycrystailine silicon grown on insulating substrates hy electron beam gun evaporation Growth of polycrystalline silicon on insulating substrates such as glass, silicon dioxide and fused quartz was studied using an electron beam gun evaporation technique. Growth characteristics were studied as a function of substrate temperature. The results of scanning electron microscopy,
W(110) surface is calculated for different distances. The calculations are based on a model Hamiltonian and allow for tip-surfaee interaction. At small surface-tip separations (~<6/~) a negative corrugation is found, i.e. Oad induces a dent in the constant current contours, in contrast to the contours of total charge density and that at Er. At larger distances they all exhibit a positive corrugation with maxima at the position of the Oad. G Doyen et ai, J Vac Sci Technol, A6, 1988, 327 330.
13. MATERIALS AND TECHNIQUES IN VACUUM 13 6829. Characterization and thermal desorption spectroscopy study on a new, low outgassing material surface for improved ultrahigh vacuum uses The surface of an austenitic stainless steel doped with N, B and Ce (SUS304-NBCe), which was covered with thin BN precipitated layers, has been characterized using Auger electron spectroscopy (AES), Fourier transform infrared, transmission electron microscopy, transmission electron diffraction (TED), and reflection high-energy electron diffraction (RHEED) techniques. Thermal desorption spectroscopy method was also applied for evaluating its outgassing nature. AES spectra obtained from the BN precipitated layers coincided well with those of a hexagonal BN even in fine structures of B(KLL) and N(KLL) Auger transitions. RHEED and TED patterns obtained from them showed that the structure of the BN layer was hexagonal and that the c axis preferred to be parallel to the surface normal. That is to say, the basal plane of the hexagonal BN, which is more inert to adsorption than other planes are preferred to cover the surface. The outgassing nature of the above surface has been measured and compared with two other types of stainless-steel surfaces such as an electropolished surface and a S segregated one. Among the three, the amount of desorbed gases from the BN covered surface was the lowest on heating up to 800°C. The potential of the BN precipitated surface for UHV vessels with low outgassing is pointed out. D Fnjita and T Homma, J Vac Sci Technol, A6, 1988, 23(~234. 13 6830. Tritium removal from noble gas streams A process loop to remove tritium from a flowing helium stream in a single pass has been constructed and commissioned. Inventories injected into the loop range from 1 GBq-28 TBq. Concentrations within the stream entering the loop range from 40 MBq/m 3 to 15 TBq/m ~. The tritium is removed from the stream by gettering on uranium beds. Residual concentrations leaving these beds are removed with zirconium-iron getter beds. Purification factors of 10 for the uranium beds and a minimum of 19400 for the zirconium iron bed have been measured. This paper describes the process loop and the performance of the getter beds during one 28-TBq injection. W T Shmayda et al, J Vac Sci Technol, A6, 1988, 1259 1262, 13 6831. Techniques for testing cryopump capacity Pneurop has proposed guidelines for measuring cryopump specifications (Minutes of Pneurop Committee-Vacuum Technology, "Acceptance Specifications, Part 5: Cryopumps", 1987). However, conditions used during capacity measurement are not specific for condensibles. Methods used for this measurement strongly affect the results, and the distinction between useful capacity and gross capacity is important to the end user of equipment affected by this specification. This paper describes various methods for measuring condensible and adsorbable gas capacity and compares their relative merits. Gases which are condensed on the pumping arrays required considerations different from those which are adsorbed. A cyclical test has been developed and standardized for inhouse use which provides information on pumping speed stability and condensation characteristics of cryopumps. John R Porter, J Vac Sci Technol, A6, 1988, 1214-1216. 13 6832. The influence of heavier gases in pumping helium and hydrogen in an ion pump Pumping mechanisms for hydrogen and helium in an ion pump are quite different from the usual mechanisms by which other gases are pumped. Their sputtering yield is much lower and their diffusion higher than for heavier gases. Hence the pumping effect at the cathode plays an important role in pumping these two gases, being comparable with or even larger than the standard pumping at the anode. The effect of the presence of heavier gases on the pumping mechanisms for helium and hydrogen has 972
been investigaed for various pressures, concentrations, and gas species. The pumping speed for helium is shown to decrease as a function of heavier gas pressure; such a decrease is strongly dependent on helium pressure and on the amount of previously pumped gas. Pumping speed for hydrogen shows very different behavior : both considerable increases and decreases have been observed, depending on hydrogen pressure, heavier gas concentration and species, and temperature. Pumping speed for a getterable gas such as nitrogen, whose pumping mechanisms are well known, has been reported as a function of concentration of xenon for comparison. The various and sometimes contrasting phenomena responsible for these effects are analyzed, and their relative importance is pointed out. M Andi and M DeSimou, J Vac Sci Technol, A6, 1988, 1205-1208. 13 6833. Lubricating of mechanisms for vacuum service Seizure of metal parts which occurs during sliding or rolling in a vacuum environment can be prevented by use of appropriate lubricants. Fluid lubricants, having low evaporation rates, dry solid film lubricants, soft, low shear strength metals, and composite materials are customarily used, but ion implanted metals and ceramics are available for extremely harsh environments. Bearings, bushings, gears, cams, guides and slides, solenoids, commutators, motor brushes, and sliprings can be lubricated to yield vacuum service lives comparable to those achieved in normal atmospheric pressure applications, or even longer due to the absence of 02 and H20. The use of fluid and dry lubricants may require the incorporation of seals to prevent molecular or particulate contamination of test or production hardware within the vacuum system. The most important parameter to be considered in selecting the appropriate lubricant is the operating temperature, which drastically affects the evaporation and contamination rates. Fluid based lubricants are available having evaporation rates of 10 -9 to I0 - u g c m 2 s-J and metals, composites, and dry lubricants having 10-1°~10-14 g c m -2 s -1 loss rates at room temperature. K G Roller, J Vac Sci Technol, A6, 1988, 1161-1165. 13 6834. A generalized approach to vacuum system automation Computer automation of vacuum equipment has traditionally been dominated by custom hardware and software solutions, requiring long and expensive development periods. On-going modification and support of the installed computer equipment often requires an appreciable portion of a computer specialist's time. In order to achieve a more cost effective approach, the authors have analyzed a variety of vacuum deposition and etching processes running on equipment supplied by numerous manufacturers. The following observations have led to the development of a generalized vacuum equipment automation system which requires minimal custom engineering time to install and support: (1) In spite of the high marketing profile given to RS-232, IEEE-488 and SECS II interfaces, by far the most common and easy to use interfaces provided by vacuum equipment vendors are simple digital and analog. (2) Most processes involve between 50 and 300 discrete or continuous parameters ; however, few of these parameters vary at rates appreciably higher than 1 Hz. (3) The inter-relationships between these many parameters are often complex and/or difficult to specify in a fixed manner. The computer must therefore be capable of operating according to process logic entered and modified in the field by a process engineer, who may not be a computer specialist. (4) The skill level of vacuum operators varies from doctorate to grade school; uses of vacuum equipment vary from pure research to highvolume production. The user interface must therefore be highly adaptable yet easy to use. R W MeMahon et al, J Vac Sci Technol, A6, 1988, 1158 1160.
II. Thin film t e c h n o l o g y 20. EVAPORATION 20 6835. Properties of polycrystailine silicon grown on insulating substrates hy electron beam gun evaporation Growth of polycrystalline silicon on insulating substrates such as glass, silicon dioxide and fused quartz was studied using an electron beam gun evaporation technique. Growth characteristics were studied as a function of substrate temperature. The results of scanning electron microscopy,