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4904. Semiconducting behaviour in antimony-doped bismuth films
Clatsified abstracts 489B-4905 angular distributions of desorbed H, molecules from Si (111) surfaces.
(Japan)
M Kobayashi et al, J Vat Sci Technol, 18 (3), 1981, 1013-1016. 22
(USA) A system is described for the sampling ofchemically reactive species from a plasma reactor in a mass spectrometer integrated in a 20 K cryopump. The performance of this system is characterized by high detection sensitivity and low background interference. The application of the sampling method with appearance-potential discrimination measurements of chemically active species is demonstrated. (The Netherlands) J Visser, I Vat Sci Technol, 19 (I), 1981, 104-108. 489% Cryopumped beam mass spectrometry.
23. PLUMBING,
VACUUM VALVES, BAFFLES AND TRAPS
23 4899. Molecular and radiation transmissivities of chevron type baffles for cryopumping. (USA) In the design of cryopumps, intermediate temperature (e.g. 77 K) battles
are interposed between the cold pumping surfaces and ambient temperature walls of the vacuum system. This intermediate baffle serves to reduce the effects of thermal radiation on the pumping surfaces. The introduction of the baftle, however, decreases the pumping speed, and therefore its design has to be optimized with respect to both molecular and radiation transparencies. We have studied the transmission probabilities for molecules and photons, assuming diffuse and specular reflection, respectively, as a function of the geometry and surface reflectivity of chevron type baffles, using the Monte Carlo method. The calculated figures are in good agreement with experimental results. Using a black paint which provides a reflectivity of -0.10, a molecular transmissivity of about 0.24 and a radiation transmissivity of - 7 x 10e4 were achieved. (Switzerland) C Benvenuti et al, J Vat Sci Technol, 19 (1). 1981, 100-103. 23 4900. Selection and evahtation of an ultrahigh vacuum gate valve for ISABELLE beam line vacuum system. (USA) A minimum of 84 ultrahigh vacuum gate valves will be utilized in ISABELLE to protect proton beam lines from catastrophic vacuum failure and to provide sector isolation for maintenance requirements. The valve to beselected must function at less than 1 x 10-i’ torr (1.3 x 10m9Pa) and be bakeable to 300°C in its open or closed position. In the open position, the valve must have an rf shield to make the beam line walls appear continuous. Several proposed designs were built and evaluated. The evaluation consisted mainly of leak testing, life tests, thermal cycling, mass spectrometer analysis, and 10-i* torr operation. Problems with initial design and fabrication were resolved. Special requirements for design and construction were developed. This paper describes the tests on two final prototypes which appear to be the best candidates for ISABELLE operation. CL FoersterandDMcCafferty,J VacSci Technol, 18 (3), 1981,997-1000.
24. LEAK DETECTORS AND LEAK DETECTION
25. HEATING EQUIPMENT
III. Vacuum
AND THERMOMETERS
applications
30 EVAPORATION
AND DEPOSITION
IN VACUO 30
power measurements in thin tin films. (GB) Thermoelectric power (TEP) measurements in thin tin films over the thickness range 400-150 A are reported. The TEP is found to be thickness dependent and increases with film thickness. Thermopower reaches a constant value of about 4 pV “C-’ for a film thickness greater than 1200 A. (India) M A Angadi and L A Udachan, J Phys D: Appl Phys, 14 (7). 1981, L103-LlO5. 30 4992. Platinum silicide formation under ultrahigh vacuum and controlled impurity ambients. (USA) The thin-film Pt-Si silicide system has been investigated under clean, well controlled conditions. A (UHV) ultrahigh vacuum apparatus for this 4901. Thermoelectric
study is described which allows preparation of atomically clean Si surfaces and subsequent evaporation of Pt films in uncuo 10m9 torr. Samples are annealed and characterized with in situ (RBS) Rutherford backscattering and (AES) Auger electron spectroscopy and later examined with (TEM) transmission electron microscopy and (SEM) scanning electron microscopy techniques. Impurity-free Pt films deposited on clean, roomtemperature Si substrates react initially to form Pt,Si and then PtSi with diffusivities one to three orders of magnitude higher than previously reported in the 200-325°C temperature range. However, the observed activation energies of 1.3kO.2 eV and 1.5kO.2 eV are in reasonable agreement with previous reports. No differences in PtSi-Si interface width, PtSi surface character, growth rates, and phase growth progression are observed between extremely clean, well controlled UHV processed samples and samples prepared with normal wet and dry device processing cleanliness levels provided that the Pt films are impurity-free. The presence of oxygen in the deposited Pt film is crucial in determining reaction rates and the phase growth sequence. Increasing impurity concentrations in the initial metal film or at the Pt-Si interface cause macroscopically nonplanar PtSi-Si interfaces and PtSi surfaces. Diffusivities for both Pt,Si and PtSi formation are observed to be strongly dependent upon oxygen contamination in the initial Pt film over a wide range; excessive contamination alters the phase growth sequence. This behaviour would tend to indicate that Pt-silicide growth occurs by grain boundary diffusion at these temperatures. C A Crider et al, J Appl Phys, 52 (4), 1981, 2860-2868. 30 4903. Novel device structures by molecular beam epitaxy. (USA) This paper briefly reviews a few selected technologically important areas where Molecular Beam Epitaxy has been used to advantage. These include the use of MBE to study and improve ohmic and Schottky metallizations to GaAs and the invention of new types of variable barrier height diodes. The proven potential of MBE grown ternary alloy structures as materials for enhanced microwave and high speed digital devices and the use of selected area epitaxy for state of the art digital integrated circuit elements are also discussed. C E C Wood, J Vuc Sci Technol, 18 (3), 1981, 772-777. 30 4904. Semiconducting behaviour in antimony-doped bismuth films. (USA) The electric resistivity and Hall effect were studied for the vacuum evaporated and annealed _ 1 atm% Sb-doped bismuth alloy films of various thickness (350-3500 A) in the temperature range of 77-510 K. Contrary to the behaviour of bulk BiSb alloy, where the alloy becomes semiconducting only at about 4 atm% of Sb and above (A. L. Jain, 1959), it is found that thin films of 1% Sb-doped Bi alloy are semiconducting. Moreover, this semiconducting trend begins at about room temperature unlike in bulk BiSb alloys where it is observed only at temperatures below about 180 K. The present type of behaviour has been predicted and observed by some earlier workers (Ivanov et al. 1963. 1964). The intercrystalline barrier activation energies determined for various film thicknesses deposited at different substrate temperatures (257 K, 300 K, 373 K) were found to vary with thickness and substrate temperature, activation energy decreasing with increasing thickness and substrate temperature. These observations have been attributed to the film nature of the polycrystalline films (Slater 1956, Espevik 1971, Okuyama 1976, Bednarczyk 1976). (India) V Damodara Das and M S Jagadeesh, J Vat Sci Technol, 19 (I), 1981, 89-92. 30 4905. Structural aspects of tunnel-junction coupled granular lead films. (USA)
Granular lead films were deposited using the technique of reactive ion beam sputtering of a lead target with argon ions in the presence of an oxygen background. The superconducting properties of these films reveal that the primary means of electron transport is by tunnelling across insulating lead oxide barriers separating clusters of lead grains. Results of X-ray and TEM studies confirm this interpretation and show that the films consist of randomly-oriented lead grains, less than 500 A in diameter, embedded in an insulating matrix which contains at least two identifiable oxides of lead. These unique structural properties are most likely responsible for the excellent mechanical and electrical stability observed for these films. J M Vandenberg et al, J i’oc Sci Technol, 18 (2) 1981, 2688272. 211
(Japan)
M Kobayashi et al, J Vat Sci Technol, 18 (3), 1981, 1013-1016. 22
(USA) A system is described for the sampling ofchemically reactive species from a plasma reactor in a mass spectrometer integrated in a 20 K cryopump. The performance of this system is characterized by high detection sensitivity and low background interference. The application of the sampling method with appearance-potential discrimination measurements of chemically active species is demonstrated. (The Netherlands) J Visser, I Vat Sci Technol, 19 (I), 1981, 104-108. 489% Cryopumped beam mass spectrometry.
23. PLUMBING,
VACUUM VALVES, BAFFLES AND TRAPS
23 4899. Molecular and radiation transmissivities of chevron type baffles for cryopumping. (USA) In the design of cryopumps, intermediate temperature (e.g. 77 K) battles
are interposed between the cold pumping surfaces and ambient temperature walls of the vacuum system. This intermediate baffle serves to reduce the effects of thermal radiation on the pumping surfaces. The introduction of the baftle, however, decreases the pumping speed, and therefore its design has to be optimized with respect to both molecular and radiation transparencies. We have studied the transmission probabilities for molecules and photons, assuming diffuse and specular reflection, respectively, as a function of the geometry and surface reflectivity of chevron type baffles, using the Monte Carlo method. The calculated figures are in good agreement with experimental results. Using a black paint which provides a reflectivity of -0.10, a molecular transmissivity of about 0.24 and a radiation transmissivity of - 7 x 10e4 were achieved. (Switzerland) C Benvenuti et al, J Vat Sci Technol, 19 (1). 1981, 100-103. 23 4900. Selection and evahtation of an ultrahigh vacuum gate valve for ISABELLE beam line vacuum system. (USA) A minimum of 84 ultrahigh vacuum gate valves will be utilized in ISABELLE to protect proton beam lines from catastrophic vacuum failure and to provide sector isolation for maintenance requirements. The valve to beselected must function at less than 1 x 10-i’ torr (1.3 x 10m9Pa) and be bakeable to 300°C in its open or closed position. In the open position, the valve must have an rf shield to make the beam line walls appear continuous. Several proposed designs were built and evaluated. The evaluation consisted mainly of leak testing, life tests, thermal cycling, mass spectrometer analysis, and 10-i* torr operation. Problems with initial design and fabrication were resolved. Special requirements for design and construction were developed. This paper describes the tests on two final prototypes which appear to be the best candidates for ISABELLE operation. CL FoersterandDMcCafferty,J VacSci Technol, 18 (3), 1981,997-1000.
24. LEAK DETECTORS AND LEAK DETECTION
25. HEATING EQUIPMENT
III. Vacuum
AND THERMOMETERS
applications
30 EVAPORATION
AND DEPOSITION
IN VACUO 30
power measurements in thin tin films. (GB) Thermoelectric power (TEP) measurements in thin tin films over the thickness range 400-150 A are reported. The TEP is found to be thickness dependent and increases with film thickness. Thermopower reaches a constant value of about 4 pV “C-’ for a film thickness greater than 1200 A. (India) M A Angadi and L A Udachan, J Phys D: Appl Phys, 14 (7). 1981, L103-LlO5. 30 4992. Platinum silicide formation under ultrahigh vacuum and controlled impurity ambients. (USA) The thin-film Pt-Si silicide system has been investigated under clean, well controlled conditions. A (UHV) ultrahigh vacuum apparatus for this 4901. Thermoelectric
study is described which allows preparation of atomically clean Si surfaces and subsequent evaporation of Pt films in uncuo 10m9 torr. Samples are annealed and characterized with in situ (RBS) Rutherford backscattering and (AES) Auger electron spectroscopy and later examined with (TEM) transmission electron microscopy and (SEM) scanning electron microscopy techniques. Impurity-free Pt films deposited on clean, roomtemperature Si substrates react initially to form Pt,Si and then PtSi with diffusivities one to three orders of magnitude higher than previously reported in the 200-325°C temperature range. However, the observed activation energies of 1.3kO.2 eV and 1.5kO.2 eV are in reasonable agreement with previous reports. No differences in PtSi-Si interface width, PtSi surface character, growth rates, and phase growth progression are observed between extremely clean, well controlled UHV processed samples and samples prepared with normal wet and dry device processing cleanliness levels provided that the Pt films are impurity-free. The presence of oxygen in the deposited Pt film is crucial in determining reaction rates and the phase growth sequence. Increasing impurity concentrations in the initial metal film or at the Pt-Si interface cause macroscopically nonplanar PtSi-Si interfaces and PtSi surfaces. Diffusivities for both Pt,Si and PtSi formation are observed to be strongly dependent upon oxygen contamination in the initial Pt film over a wide range; excessive contamination alters the phase growth sequence. This behaviour would tend to indicate that Pt-silicide growth occurs by grain boundary diffusion at these temperatures. C A Crider et al, J Appl Phys, 52 (4), 1981, 2860-2868. 30 4903. Novel device structures by molecular beam epitaxy. (USA) This paper briefly reviews a few selected technologically important areas where Molecular Beam Epitaxy has been used to advantage. These include the use of MBE to study and improve ohmic and Schottky metallizations to GaAs and the invention of new types of variable barrier height diodes. The proven potential of MBE grown ternary alloy structures as materials for enhanced microwave and high speed digital devices and the use of selected area epitaxy for state of the art digital integrated circuit elements are also discussed. C E C Wood, J Vuc Sci Technol, 18 (3), 1981, 772-777. 30 4904. Semiconducting behaviour in antimony-doped bismuth films. (USA) The electric resistivity and Hall effect were studied for the vacuum evaporated and annealed _ 1 atm% Sb-doped bismuth alloy films of various thickness (350-3500 A) in the temperature range of 77-510 K. Contrary to the behaviour of bulk BiSb alloy, where the alloy becomes semiconducting only at about 4 atm% of Sb and above (A. L. Jain, 1959), it is found that thin films of 1% Sb-doped Bi alloy are semiconducting. Moreover, this semiconducting trend begins at about room temperature unlike in bulk BiSb alloys where it is observed only at temperatures below about 180 K. The present type of behaviour has been predicted and observed by some earlier workers (Ivanov et al. 1963. 1964). The intercrystalline barrier activation energies determined for various film thicknesses deposited at different substrate temperatures (257 K, 300 K, 373 K) were found to vary with thickness and substrate temperature, activation energy decreasing with increasing thickness and substrate temperature. These observations have been attributed to the film nature of the polycrystalline films (Slater 1956, Espevik 1971, Okuyama 1976, Bednarczyk 1976). (India) V Damodara Das and M S Jagadeesh, J Vat Sci Technol, 19 (I), 1981, 89-92. 30 4905. Structural aspects of tunnel-junction coupled granular lead films. (USA)
Granular lead films were deposited using the technique of reactive ion beam sputtering of a lead target with argon ions in the presence of an oxygen background. The superconducting properties of these films reveal that the primary means of electron transport is by tunnelling across insulating lead oxide barriers separating clusters of lead grains. Results of X-ray and TEM studies confirm this interpretation and show that the films consist of randomly-oriented lead grains, less than 500 A in diameter, embedded in an insulating matrix which contains at least two identifiable oxides of lead. These unique structural properties are most likely responsible for the excellent mechanical and electrical stability observed for these films. J M Vandenberg et al, J i’oc Sci Technol, 18 (2) 1981, 2688272. 211