- Email: [email protected]
Discharge cleaning experiment in the JFT-2 tokamak with surface observation by AES. (USA)
Classified abstracts 3762-3769 36. VACUUM STUDIES
INSTRUMENTATION
FOR SURFACE
36 3762. Utilization of backscattering of medium energy ions for the determination of the composition and crystalline structure of surfaces. (France) The principles of the analysis by MeV Rutherford backscattering are presented. The application of the technique to the study of the composition and structure of monocrystalline surfaces are described. The advantages (quantitativity, high sensitivity to surface atomic displacements) and limits of the method are indicated. C Cohen, Vide, 32 (189). 1978, 135-l 38 (in french). 36 3763. Time dependence of the chemical composition of the surface film on the metastable tin-nickel alloy studied with X-ray photoelectron spectroscopy. (USA) X-ray photoelectron spectroscopy is used to study the change in the chemical composition of the surface film of the metastable tin-nickel alloy as a function of age. As-plated samples as well as HCI-etched samples are studied from very young (6 h and 2 min old, respectively) to about 60 days old. The change in the spectra caused by heating in vacuum is also shown. The film which exists on the As-plated samples which are reasonably young (e.g. 14 days old) is significantly different from the film which grows after this native film has been removed. In all samples studied, the film contains primarily tin components. A small amount of nickel hydroxide forms as the samples age. The change of the film on the etched sample would be described as growth. For the As-plated sample some change in thickness probably occurs over very long times, but the major change is in the chemical composition. H G Tompkins et al, J Vuc Sci Techno!, 15 (I), 1978, 20-23. 36 3764. Characterization of anodic barrier films on tantalum and 1100 aluminium by ISS/SIMS. (USA) Ion scattering spectrometry (ISS) and concurrent secondary ion mass spectrometry (SIMS) were used to determine the depth profiles of anodic barrier oxide films grown on tantalum and type 1100 aluminium. The sputter rate in each case was determined from the film thickness measured by the anodic overvoltage and the penetration time determined by the decrease in intensity of the metal oxide fragment observed using SIMS. A mixture of helium and neon ions was used to sputter aluminium oxide films in order to observe ion scattering of helium by oxygen, while taking advantage of the higher sputtering rate available with neon. A comparison of sputter rates for helium and neon on tantalum oxide indicated that neon sputtered the film at a rate eight times that of helium. SIMS depth profiling of the residual boron in the anodic aluminium oxide indicated a mixing effect which did not permit adequate resolution of the interface between the oxide film and the underlying metal. R C McCune, J Vat Sci Technol, 15 (I), 1978,31-34. 36 3765. Depth profiles of sodium and calcium in glasses: A comparison of secondary ion mass analysis and Auger spectrometry. (USA) Depth profiles of sodium and calcium in soda-lime glasses have been measured by both Auger electron spectrometry and secondary ion mass spectrometry. Profiles by the two techniques agree closely and can be influenced by experimental conditions. In particular, radiation heating from a charge neutralization filament in the SIMS system is shown to alter the sodium depth profile in specimens, which have a surface depletion of sodium. D L Maim et al, J Vat Sci Technof, 15 (I), 1978,35-38. 36 3766. Convolution and deconvolution in Auger electron spectroscopy, with application to silicon. (USA) Auger electrons emitted from the valence band in solids carry information on the local density of states in this band in the surface region. The emitted Auger electron intensity distribution is a convolution product of the transition densities of the two valence-band electrons involved in the Auger process in the ionized solid, multiplied with the probability of escape of the outgoing electron. In a first-order approximation the transition density is proportional to the density of states. A comparison between a theoretical or a directly measured, density of states and Auger spectra must rely on mathematical convolution/ deconvolution techniques. Here it is proposed to.use splinefunctions 380
to represent the densities of states to be convolved. This method is unconstrained with respect to form of the density of states. The same representation is used to deconvolve experimental kinetic energy distributions of Auger electrons, in a nonlinear least-squares fitting of a convolution square of a trial density-of-states function. As an example, the Auger spectrum of Si is considered and compared with a calculated density of states. (Denmark) J H Onsgaard et al, J Vat Sci Technol, 15 (I), 1978, 44-49. 36 3767. Auger depth profiling of thick insulating films by angle lapping. (USA) It is demonstrated that the chemical composition of thick and multilayer insulating films can be easily depth profiled by Auger electron spectroscopy by laterally scanning an angle-lapped region that reveals the entire depth to be profiled. Conventional depth profiling of such structures is often difficult because of unstable sample charge-up conditions that occur when Auger measurements are made during ion milling. The angle-lap technique is nondestructive, in that it allows one to reexamine the entire profile whenever desired. It is thus particularly suitable for investigation of samples with initially unknown or trace impurities. Also, this technique is free of depthresolution degradation and differential sputter yield effects usually associated with long-term ion milling of thick films. The absolute depth resolution of the angle-lap-Auger profiling method is independent of the film thickness and is equal to the electron beam diameter plus sample manipulator resolution divided by the angle-lap lateral magnification. An ultimate depth resolution of -35 8, would be possible using a 0.5 pm dia beam, a 0.2” lap, and a 0.5 pm manipulator resolution. This is approaching the depth resolution associated with the finite escape depth of Auger electrons. Using a IO pm electron beam and a 0.5” angle lap in the present study, a depth resolution of about 1000 A was obtained, as predicted. The oxygen concentration in oxygen-rich polysilicon films measured by this technique agrees with that measured by an Electron Probe Microanalyzer. The Auger data also suggest that all oxygen atoms in the films are bonded to silicon in the form of Si02. M L Tarng and D G Fisher, J Vat Sci Technol, 15 (I), 1978,50-53. 36 3768. Surface cleaning by low-temperature bombardment with hydrogen particles: An AES investigation on copper and Fe-Cr-Ni steel surfaces. (USA) Hydrogen has been used at a pressure of 5 x low5 torr (6.6 x 10e3 Pa) and at room temperature in an ‘ion-etching beam mode’ for cleaning solid surfaces. Two systems, viz. solvent-cleaned and atmosphere-exposed copper and heat-resistant Fe-Cr-Ni steel, were analysed in Auger spectroscopy before and after bombardment with hydrogen particles produced in a conventional ion gun. Copper is almost completely cleaned of carbon, sulfur and oxygen within 30 min. A bulk-carbon-containing steel is completely freed from surface carbon while the bulk carbon is preserved in the subsurface zone at a satisfactory level. The proposed cleaning method seems to be very surface specific and nondestructive to subsurface layers. (Netherlands) R Bouwman et al, J Vat Sci Technol, 15 (I), 1978, 91-94. 36 3769. Discharge cleaning experiment in the JFT-2 tokamak with surface observation by AES. (USA) The effects of wall conditioning by tokamak discharges with low toroidal magnetic field have been studied by observing the concomitant changes in discharge characteristics, wall conditions and residual gases. After 2500 shots of discharge cleaning, stable reproducible plasmas with Zcrr = 4.5 were obtained with the equilibrium surface composition of vacuum wall samples, which consists of the limiter and wall materials (molybdenum and 304 stainless steel, respectively), carbon and oxygen. Depth profiling by Auger/sputter techniques shows that the mixed layers composed of the same elements as the surfaces were formed on the samples. The layers are thicker by 5-10 times on the sample located at’the minimum inner radius of vacuum chamber than on the one located 3.4 cm further away from the plasma. The results indicate that the wall condition is determined by deposition of the metallic particles during the discharge and adsorption of the residual gases during the interval between discharges. (Japan) Y Gomay et al, J Vat Sci Technof, 15 (I), 1978, 103-l IO.
INSTRUMENTATION
FOR SURFACE
36 3762. Utilization of backscattering of medium energy ions for the determination of the composition and crystalline structure of surfaces. (France) The principles of the analysis by MeV Rutherford backscattering are presented. The application of the technique to the study of the composition and structure of monocrystalline surfaces are described. The advantages (quantitativity, high sensitivity to surface atomic displacements) and limits of the method are indicated. C Cohen, Vide, 32 (189). 1978, 135-l 38 (in french). 36 3763. Time dependence of the chemical composition of the surface film on the metastable tin-nickel alloy studied with X-ray photoelectron spectroscopy. (USA) X-ray photoelectron spectroscopy is used to study the change in the chemical composition of the surface film of the metastable tin-nickel alloy as a function of age. As-plated samples as well as HCI-etched samples are studied from very young (6 h and 2 min old, respectively) to about 60 days old. The change in the spectra caused by heating in vacuum is also shown. The film which exists on the As-plated samples which are reasonably young (e.g. 14 days old) is significantly different from the film which grows after this native film has been removed. In all samples studied, the film contains primarily tin components. A small amount of nickel hydroxide forms as the samples age. The change of the film on the etched sample would be described as growth. For the As-plated sample some change in thickness probably occurs over very long times, but the major change is in the chemical composition. H G Tompkins et al, J Vuc Sci Techno!, 15 (I), 1978, 20-23. 36 3764. Characterization of anodic barrier films on tantalum and 1100 aluminium by ISS/SIMS. (USA) Ion scattering spectrometry (ISS) and concurrent secondary ion mass spectrometry (SIMS) were used to determine the depth profiles of anodic barrier oxide films grown on tantalum and type 1100 aluminium. The sputter rate in each case was determined from the film thickness measured by the anodic overvoltage and the penetration time determined by the decrease in intensity of the metal oxide fragment observed using SIMS. A mixture of helium and neon ions was used to sputter aluminium oxide films in order to observe ion scattering of helium by oxygen, while taking advantage of the higher sputtering rate available with neon. A comparison of sputter rates for helium and neon on tantalum oxide indicated that neon sputtered the film at a rate eight times that of helium. SIMS depth profiling of the residual boron in the anodic aluminium oxide indicated a mixing effect which did not permit adequate resolution of the interface between the oxide film and the underlying metal. R C McCune, J Vat Sci Technol, 15 (I), 1978,31-34. 36 3765. Depth profiles of sodium and calcium in glasses: A comparison of secondary ion mass analysis and Auger spectrometry. (USA) Depth profiles of sodium and calcium in soda-lime glasses have been measured by both Auger electron spectrometry and secondary ion mass spectrometry. Profiles by the two techniques agree closely and can be influenced by experimental conditions. In particular, radiation heating from a charge neutralization filament in the SIMS system is shown to alter the sodium depth profile in specimens, which have a surface depletion of sodium. D L Maim et al, J Vat Sci Technof, 15 (I), 1978,35-38. 36 3766. Convolution and deconvolution in Auger electron spectroscopy, with application to silicon. (USA) Auger electrons emitted from the valence band in solids carry information on the local density of states in this band in the surface region. The emitted Auger electron intensity distribution is a convolution product of the transition densities of the two valence-band electrons involved in the Auger process in the ionized solid, multiplied with the probability of escape of the outgoing electron. In a first-order approximation the transition density is proportional to the density of states. A comparison between a theoretical or a directly measured, density of states and Auger spectra must rely on mathematical convolution/ deconvolution techniques. Here it is proposed to.use splinefunctions 380
to represent the densities of states to be convolved. This method is unconstrained with respect to form of the density of states. The same representation is used to deconvolve experimental kinetic energy distributions of Auger electrons, in a nonlinear least-squares fitting of a convolution square of a trial density-of-states function. As an example, the Auger spectrum of Si is considered and compared with a calculated density of states. (Denmark) J H Onsgaard et al, J Vat Sci Technol, 15 (I), 1978, 44-49. 36 3767. Auger depth profiling of thick insulating films by angle lapping. (USA) It is demonstrated that the chemical composition of thick and multilayer insulating films can be easily depth profiled by Auger electron spectroscopy by laterally scanning an angle-lapped region that reveals the entire depth to be profiled. Conventional depth profiling of such structures is often difficult because of unstable sample charge-up conditions that occur when Auger measurements are made during ion milling. The angle-lap technique is nondestructive, in that it allows one to reexamine the entire profile whenever desired. It is thus particularly suitable for investigation of samples with initially unknown or trace impurities. Also, this technique is free of depthresolution degradation and differential sputter yield effects usually associated with long-term ion milling of thick films. The absolute depth resolution of the angle-lap-Auger profiling method is independent of the film thickness and is equal to the electron beam diameter plus sample manipulator resolution divided by the angle-lap lateral magnification. An ultimate depth resolution of -35 8, would be possible using a 0.5 pm dia beam, a 0.2” lap, and a 0.5 pm manipulator resolution. This is approaching the depth resolution associated with the finite escape depth of Auger electrons. Using a IO pm electron beam and a 0.5” angle lap in the present study, a depth resolution of about 1000 A was obtained, as predicted. The oxygen concentration in oxygen-rich polysilicon films measured by this technique agrees with that measured by an Electron Probe Microanalyzer. The Auger data also suggest that all oxygen atoms in the films are bonded to silicon in the form of Si02. M L Tarng and D G Fisher, J Vat Sci Technol, 15 (I), 1978,50-53. 36 3768. Surface cleaning by low-temperature bombardment with hydrogen particles: An AES investigation on copper and Fe-Cr-Ni steel surfaces. (USA) Hydrogen has been used at a pressure of 5 x low5 torr (6.6 x 10e3 Pa) and at room temperature in an ‘ion-etching beam mode’ for cleaning solid surfaces. Two systems, viz. solvent-cleaned and atmosphere-exposed copper and heat-resistant Fe-Cr-Ni steel, were analysed in Auger spectroscopy before and after bombardment with hydrogen particles produced in a conventional ion gun. Copper is almost completely cleaned of carbon, sulfur and oxygen within 30 min. A bulk-carbon-containing steel is completely freed from surface carbon while the bulk carbon is preserved in the subsurface zone at a satisfactory level. The proposed cleaning method seems to be very surface specific and nondestructive to subsurface layers. (Netherlands) R Bouwman et al, J Vat Sci Technol, 15 (I), 1978, 91-94. 36 3769. Discharge cleaning experiment in the JFT-2 tokamak with surface observation by AES. (USA) The effects of wall conditioning by tokamak discharges with low toroidal magnetic field have been studied by observing the concomitant changes in discharge characteristics, wall conditions and residual gases. After 2500 shots of discharge cleaning, stable reproducible plasmas with Zcrr = 4.5 were obtained with the equilibrium surface composition of vacuum wall samples, which consists of the limiter and wall materials (molybdenum and 304 stainless steel, respectively), carbon and oxygen. Depth profiling by Auger/sputter techniques shows that the mixed layers composed of the same elements as the surfaces were formed on the samples. The layers are thicker by 5-10 times on the sample located at’the minimum inner radius of vacuum chamber than on the one located 3.4 cm further away from the plasma. The results indicate that the wall condition is determined by deposition of the metallic particles during the discharge and adsorption of the residual gases during the interval between discharges. (Japan) Y Gomay et al, J Vat Sci Technof, 15 (I), 1978, 103-l IO.