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Molecular-beam study of oxygen and c2 hydrocarbon chemisorption and reactions on pt(111)
Classified abstracts 1674-1682 35 1674. Deep uv lithography. (USA) Using deep uv light ranging from 2000 to 2600 A, submicrometer patterns in photoresist with height-to-width aspect ratios as high as 15 can be achieved. The well known electron-beam positive resist, polymethyl methacrylate (PMMA), is used as the deep uv photoresist. Its optical absorption coefficient, dissolution rate, and sensitivity are given in the deep uv wavelength region. Its absorption coefficient being a factor of two lower than that of AZ 1350J, makes it suitable for deep penetration of submicrometer-wide beams. The negligible sensitivity at wavelengths longer than 2600 A eliminates the need for an expensive filter. Both Xe-Hg arc lamps and deuterium spectral lamrs have been used to expose the resist. Chrome or aluminum masks on quartz or sapphire substrates were found satisfactory. Chevron patterns of 1.6 tLm width and 0.4 p.m spacing and Y-I bars of 1.6 tJm width and 0.2 t~m gaps were printed in 3 t~m of PMMA 2041, as well as Y-I bars of 0.5/Jm width and 0.25 g.m gaps in 1.78 t~m of P M M A 2041. The exposure time in both cases was below l0 min. Burn Jeng Lin, J Vac Sci Technol, 12 (6), 1975, 1317-1320. 35 1675. Prospects for X-ray fabrication of Si IC devices. (USA) In this paper we report on low X-ray attenuation Si vacuum windows for use with AI K X-ray sources and the fabrication of 5.5 cm diam Si-membrane X-ray masks without supporting ribs. Also discussed are exposure configurations for achieving multilevel pattern superposition on 7.5 cm diam wafers, H I Smith and S E Bernacki, J Vac Sci Technol, 12 (6), 1975,1321-1323. 35 1676. Monte Carlo simulation of spatially distributed beams in electronbeam lithography. (LISA) The spatial distribution of energy deposited in a thin polymer film of polymethyl methacrylate (PMMA) by a laterally distributed electron beam is simulated with Monte Carlo calculations. The Monte Carlo simulation includes the significant contribution from electrons that are backscattered from the substrate (Si) into the film. Equienergy density contours (eV/cm a) are calculated for specific cases of beam voltage, film thickness, beam width, and beam-edge slope. A lime-dependent solubility model is also incorporated to simulate the time evolution of the developed contours. A size effect is el:served; i.e., the development time for a line depends on the line width. This intraproximity effect is ascribed to electrons backscattered from the substrate. D F Kyser and N S Viswnnathan, J Vac Sci Technol, 12 (6), 1975, 1305-1308. 35 1677. Distortion measurements in an electron image projector. (USA) Distortion measurements in an electron image projector for integrated-circuit fabrication are described. It is shown that the major cause of distortion which varies from exposure to exposure is due to slice bowing, and that this distortion is approximately 1/30 the height of the bow. This figure can be reduced by increasing the operating magnetic field strength. (GB). J P Scott, J Vac Sci Technol, 12 (6) 1975, 1309-1312. 35 1678. Experimental scanning electron-beam automatic registration system. (USA) An experimental automatic registration system is discussed that is capal:le of precisely overlaying two or more levels of a microcircuit pattern written by an electron-beam lithographic machine. Because positional information of the registration mark arrives at the detector in the form of random discrete quanta, it is subject to the statistical fluctuations inherent in all such systems. Achievement of a signal-tonoise ratio adequate for precise registrations with inherently noisy baekseattered electrons and without overexposure of the resist layers covering the registration mark is accomplished using digital signal enhancement techniques. Manual and computer methods have been developed to correct field size, shift, rotation, and orthogonality. Correlation between manual and automatic registrations and the pattern are excellent because the same basic deflection and electronics systems are used for all three modes of operation. The necessary software to control the registration subsystems and to perform registration computations and edge detection have also been developed. Registration overlays have been made automatically with 220
absolute errors on the order to 100 ppm. For a 2 mm chip, this is a level-to-level error of about +0.1 t~m. Several samples of typical complex microcircuit patterns registered with this experimental automatic system are shown. A D Wilson et al, J Vac Sci Technol, 12 (6), 1975, 1240-1245. 36. VACUUM I N S T R U M E N T A T I O N FOR SURFACE SCIENCE 36 1679. Ultraviolet reflectivity and electron-energy-loss spectra of AgGaS, and CuGaS2. (USA) Ultraviolet reflectivity and reflection electron-energy-loss techniques have been used to determine the higher energy excitation spectra of the ternary compounds AgGaS2 and CuGaS2. The ultraviolet reflectivity spectra were obtained over the energy range of band gap to I l eV, whereas the energy-loss spectra covered the range of band gap to 40 eV. The energy-loss measurements were made on both clean cleaved surfaces of these materials and on selectively contaminated surfaces. This technique allows distinction to be made between surface and bulk plasmon excitations. Surface plasmon energies of 14.0 and 13.5 eV and bulk plasmon energies of 18.5 and 19.0 eV were found for AgGaS2 and CuGaS2, respectively. F L Hengehold and F L Pedrotti, J Appl Phys, 46 (12), 1975, 5202-5204. 36 1680. Potential profiling across semiconductor junctions by Auger electron spectroscopy in the scanning electron microscopy. (USA) Auger electron spectroscopy in an ultra-vacuum scanning electron microscope is shown capable of the direct and quantitative measurement of potential profiles across biased semiconductor junctions. Profiles are obtained with submicron spatial resolution and subvolt potential resolution by measuring shifts of an Auger electron peak across a semiconductor device as a function of surface potential and spatial position. Experimental results on a GaSs p+-n junction diode for values of reverse bias between 5 and 25 V are in agreement with the potential profiles predicted by the depletion approximation model of a p-n junction. J R Waldrop and J S Harris, J ApplPhys, 46 (12), 1975, 5214-5217. 36 1681. Thickness determination of ultrathin films by Auger electron spectroscopy. The feasibility of using Auger electron peak-height ratios for film thickness determination has been demonstrated for ultrathin films of chromium oxide on gold substrates. The range of equivalent film thicknesses determined was from 3 to 67 A, but the technique can measure thicknesses up to ,-~100 ,~. Using peak-height ratios from Auger electrons of different energies, the uniformity of the chromium oxide film was demonstrated. It was also demonstrated that argonion sputtering removed the chromium oxide in a nonuniform manner. The mean free path lengths of 70, 527, and 2024 eV electrons in chromium oxide were determined to be 4.3, 14, and 28 A, respectively. P H Holloway, J Vac Sci Technol, 12 (6), 1418-1422. 36 1682. Molecular-beam study of oxygen and C2 hydrocarbon chemisorption and reactions on P t ( l l l ) . (USA) The chemisorption and reactions of.oxygen and the Cz hydrocarbons (acetylene, ethylene, and ethane) on epitaxially grown P t ( l l l ) crystals have been studied using modulated molecular beam techniques. The sticking coefficient of ethylene is observed to I:e about half that for acetylene, which is near unity on oxygen covered P t ( l l l ) in the temperature range 550-1000 K. For ethane, S <0.05, under these same conditions. The results of this study are in agreement with other studies that show that the adsorption of the C2 hydrocarbons on platinum at elevated temperatures results in a surface acetylenic species. The first step in the oxidation process appears to be the removal of hydrogen atoms from this surface acetylene, either by molecular desorption or by reaction with surface oxygen atoms. Surface carbon then reacts with surface oxygen to form CO which either desorbs or reacts further to form CO2. At high oxygen pressures, the reaction rate is apparently limited by the mobility of surface oxygen atoms which have an activation barrier to diffusion on Pt(l 11) of about 16 kcal/mole. Some implications of this high surface mobility with regard to the gas-surface oxygen equilibrium are discussed. The observance here of two distinct
Classified abstracts 1 683-1684
components in the angular desorption distributions of CO and CO2 is discussed in terms of finer details of the reaction mechanism. R L Palmer, J Vac Sci Technol, 12 (6), 1975, 1403-1409. 36 1683. High-spatial-resolution scanning Auger spectroscopy applied to analysis of X-band diode burnout. (USA) Low-noise-figure Schottky-barrier mixer diodes for use at X-band and above have small active areas and are thus susceptible to burnout or degradation from high rf power levels. As part of a program to improve burnout resistance of mixer diodes for a Navy system, metal diffusion couples were studied and diodes were fabricated, burnedout, and analyzed. The microspot Auger analysis technique in the Auger-spot mode provided the required submicron identification of the interdiffusion phenomena in the failed regions of the mixer diodes. For cw-failed diodes, interdiffusion between the various diffusion couples found in both P t - T i - M o - A u and T i - M o - A u diodes has been identified as the primary failure mode. In the pulsed case the lack of interdiffusion as made evident in the analysis of edge-burned-out sites indicates the existence of an alternate failure mode. W H Weisenberger et al, J Vac Sci Technol, 12 (6), 1365-1368.
37. I N O R G A N I C CHEMISTRY, ANALYTICAL CHEMISTRY, DISTILLATION 37 1684. Size characterisation of small metal particles. (France) Small tin and vanadium particles were prepared by evaporation in helium at pressures between 0.I and 50 torr. As a function of preparation conditions the average diameter of the tin particles could be varied from tens to thousands of,~ and that o f the vanadium particles from tens to hundreds of,~. Size distributions and average diameters of the samples were determined by means of electron micrographs. The temperature dependence of the diamagnetic susceptibility Z at low temperatures was measured for some of the Sn samples and showed a size dependent enhancement of the superconducting transition temperature T=. From the features of the Z = X (To)-curves informations about the particle size could be drawn which reasonably compare with the data obtained from electron micrographs. (Germany) G-H Comsa et al, Vide, 30 (177-178), 1975, 113-I16.
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absolute errors on the order to 100 ppm. For a 2 mm chip, this is a level-to-level error of about +0.1 t~m. Several samples of typical complex microcircuit patterns registered with this experimental automatic system are shown. A D Wilson et al, J Vac Sci Technol, 12 (6), 1975, 1240-1245. 36. VACUUM I N S T R U M E N T A T I O N FOR SURFACE SCIENCE 36 1679. Ultraviolet reflectivity and electron-energy-loss spectra of AgGaS, and CuGaS2. (USA) Ultraviolet reflectivity and reflection electron-energy-loss techniques have been used to determine the higher energy excitation spectra of the ternary compounds AgGaS2 and CuGaS2. The ultraviolet reflectivity spectra were obtained over the energy range of band gap to I l eV, whereas the energy-loss spectra covered the range of band gap to 40 eV. The energy-loss measurements were made on both clean cleaved surfaces of these materials and on selectively contaminated surfaces. This technique allows distinction to be made between surface and bulk plasmon excitations. Surface plasmon energies of 14.0 and 13.5 eV and bulk plasmon energies of 18.5 and 19.0 eV were found for AgGaS2 and CuGaS2, respectively. F L Hengehold and F L Pedrotti, J Appl Phys, 46 (12), 1975, 5202-5204. 36 1680. Potential profiling across semiconductor junctions by Auger electron spectroscopy in the scanning electron microscopy. (USA) Auger electron spectroscopy in an ultra-vacuum scanning electron microscope is shown capable of the direct and quantitative measurement of potential profiles across biased semiconductor junctions. Profiles are obtained with submicron spatial resolution and subvolt potential resolution by measuring shifts of an Auger electron peak across a semiconductor device as a function of surface potential and spatial position. Experimental results on a GaSs p+-n junction diode for values of reverse bias between 5 and 25 V are in agreement with the potential profiles predicted by the depletion approximation model of a p-n junction. J R Waldrop and J S Harris, J ApplPhys, 46 (12), 1975, 5214-5217. 36 1681. Thickness determination of ultrathin films by Auger electron spectroscopy. The feasibility of using Auger electron peak-height ratios for film thickness determination has been demonstrated for ultrathin films of chromium oxide on gold substrates. The range of equivalent film thicknesses determined was from 3 to 67 A, but the technique can measure thicknesses up to ,-~100 ,~. Using peak-height ratios from Auger electrons of different energies, the uniformity of the chromium oxide film was demonstrated. It was also demonstrated that argonion sputtering removed the chromium oxide in a nonuniform manner. The mean free path lengths of 70, 527, and 2024 eV electrons in chromium oxide were determined to be 4.3, 14, and 28 A, respectively. P H Holloway, J Vac Sci Technol, 12 (6), 1418-1422. 36 1682. Molecular-beam study of oxygen and C2 hydrocarbon chemisorption and reactions on P t ( l l l ) . (USA) The chemisorption and reactions of.oxygen and the Cz hydrocarbons (acetylene, ethylene, and ethane) on epitaxially grown P t ( l l l ) crystals have been studied using modulated molecular beam techniques. The sticking coefficient of ethylene is observed to I:e about half that for acetylene, which is near unity on oxygen covered P t ( l l l ) in the temperature range 550-1000 K. For ethane, S <0.05, under these same conditions. The results of this study are in agreement with other studies that show that the adsorption of the C2 hydrocarbons on platinum at elevated temperatures results in a surface acetylenic species. The first step in the oxidation process appears to be the removal of hydrogen atoms from this surface acetylene, either by molecular desorption or by reaction with surface oxygen atoms. Surface carbon then reacts with surface oxygen to form CO which either desorbs or reacts further to form CO2. At high oxygen pressures, the reaction rate is apparently limited by the mobility of surface oxygen atoms which have an activation barrier to diffusion on Pt(l 11) of about 16 kcal/mole. Some implications of this high surface mobility with regard to the gas-surface oxygen equilibrium are discussed. The observance here of two distinct
Classified abstracts 1 683-1684
components in the angular desorption distributions of CO and CO2 is discussed in terms of finer details of the reaction mechanism. R L Palmer, J Vac Sci Technol, 12 (6), 1975, 1403-1409. 36 1683. High-spatial-resolution scanning Auger spectroscopy applied to analysis of X-band diode burnout. (USA) Low-noise-figure Schottky-barrier mixer diodes for use at X-band and above have small active areas and are thus susceptible to burnout or degradation from high rf power levels. As part of a program to improve burnout resistance of mixer diodes for a Navy system, metal diffusion couples were studied and diodes were fabricated, burnedout, and analyzed. The microspot Auger analysis technique in the Auger-spot mode provided the required submicron identification of the interdiffusion phenomena in the failed regions of the mixer diodes. For cw-failed diodes, interdiffusion between the various diffusion couples found in both P t - T i - M o - A u and T i - M o - A u diodes has been identified as the primary failure mode. In the pulsed case the lack of interdiffusion as made evident in the analysis of edge-burned-out sites indicates the existence of an alternate failure mode. W H Weisenberger et al, J Vac Sci Technol, 12 (6), 1365-1368.
37. I N O R G A N I C CHEMISTRY, ANALYTICAL CHEMISTRY, DISTILLATION 37 1684. Size characterisation of small metal particles. (France) Small tin and vanadium particles were prepared by evaporation in helium at pressures between 0.I and 50 torr. As a function of preparation conditions the average diameter of the tin particles could be varied from tens to thousands of,~ and that o f the vanadium particles from tens to hundreds of,~. Size distributions and average diameters of the samples were determined by means of electron micrographs. The temperature dependence of the diamagnetic susceptibility Z at low temperatures was measured for some of the Sn samples and showed a size dependent enhancement of the superconducting transition temperature T=. From the features of the Z = X (To)-curves informations about the particle size could be drawn which reasonably compare with the data obtained from electron micrographs. (Germany) G-H Comsa et al, Vide, 30 (177-178), 1975, 113-I16.
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