3976. The nitrogen pressure in a vacuum system. (USA)

Classified abstracts 3973-3981 The etch rate in a CC14 plasma at a power input of 0.6 W/cm 2 is as high as 5000 A./min. Variations in reaction rate with rf power, reactant concentration, reactant flow rate, temperature, gas pressure, batch size and residual gas contamination are discussed. Etch rate data for various materials found suitable for masking are also presented. P M Schaible et ai, J Vac Sci Technol, 15 (2), 1978, 334-337. 35 3973. Low-temperature interdiffusion in titaninm-permalioy thin-film diffusion couples. (USA) Interdiffusion in thin-film Ti-permalloy (nominally 81 at. % Ni + 19 at. % Fe) diffusion couples has been investigated in the temperature range 200°-350°C. These diffusion couples were isothermally annealed in vacuum for times up to 6 × l0 s s and their magnetic properties such as the coercivity, the anisotropy field, the saturation magnetization, and electrical properties such as the sheet resistance and the sheet magnetoresistance were monitored as functions of time. From the observed changes in these properties and from concurrent X-ray diffraction measurements, it may be concluded that the dominant mechanism in this interdiffusion process is the volume diffusion of Ti in permalloy; the activation energy for this process is estimated to be 1.9 eV. R J Miller and A Gangulee, J Vac Sci Technol, 15 (2), 1978, 244--247. 35 3974. Thirty cm ion milling source. (USA) A 30 cm beam diameter ion source has been designed and fabricated for micromachining and sputtering applications. An argon ion current density of 1 mA/cm 2 at 500 eV ion energy was selected as a design operating condition. The completed ion source met the design criteria at this operating condition with a uniform and wellcollimated beam having an average variation in current density of =[=5% over the centre of 20 cm of the beam. This ion source has a multipole magnetic field that employs permanent magnets between permeable pole pieces. Langmuir probe surveys of the source plasma support the design concepts of a multipole field and a circumferential cathode to enhance plasma uniformity. R S Robinoon, J Vac Sci Technol, 15 (2), 1978, 277-280. 35 3975. Advances in cleaning metal and glass surfaces to micron-level cleanliness. (USA) A high-pressure 6.9 MPa liquid spraying technique has been developed to remove small ( > 5/~m) contaminant particles from large (100 m z) surface areas. Chemically polished and etched 304 stainlesssteel components are solvent sprayed to achieve cleanliness levels of less than 10 particle/cm" > 5 /~m dia. The high-pressure and highliquid-velocity cleaning technique can remove 99.9 % of > 5/~m dia particles in 5-10 s compared to only 20-60% > 5 g.m particles by ultrasonic cleaning in 2-10 min. High levels of particulate cleanliness are required for large solid-state laser systems where contaminants may migrate to optical surfaces and cause severe pitting. The pitted glass must be removed and periodically repolished to maintain acceptable beam quality. Special Class 100 clean room procedures and equipment have been developed to determine the degree of cleanliness of laser components and to maintain cleanliness during installation and operation. Development of these cleaning procedures resulted in greatly reduced failure rates for solid-state disk amplifiers. Although developed specifically for cleaning optical components, the basic technique should find wide application in any field requiring particulate-free surfaces. I F Stowers, J Vac Sci Technol, 15 (2), 1978, 751-754. 35 3976. The nitrogen pressure in a vacuum system. (USA) Since the N , outgassing rate from walls of a vacuum system is generally recognized to be very small, the presence of a N2 pressure in the system is a useful indication of the presence of real leaks to the atmosphere. A technique of thermal desorption mass spectrometry is introduced which allows the Nz pressure in the background gas of a baked system to be separated from a C H - background to a minimum level of N2 detectability of ~ 1 ~, of the CO background pressure. In typical baked systems (of which an example is given), it is possible to determine the sum of all real N2 leaks from atmosphere at a level of ~ 1 0 - *x torr I/s. This feature makes the technique ideally suited to large complex systems since the leak rate can be evaluated before detailed leak finding procedures are initiated. D Edwards Jr, J Vac Sci Technol, 15 (2), 1978, 755-757.

35 3977. Enhanced etching of ion-implanted silicon nitride in buffered hydrofluoric acid. (USA) The preferential etching of ion-implanted pyrolytic silicon nitride (Si3N4) and plasma-deposited silicon nitride in buffered hydrofluoric acid has been studied as a function of ion mass, energy and dose. The dose dependence of etching enhancement produced by light ions (H and He) shows that the relevant concentration parameter is the density of displaced atoms rather than the concentration of the implanted impurity. In addition to the atomic displacement mechanism, a species-dependent contribution is seen. For Si3N4 the enhancement produced by most ions is 7, whereas P gives 15. For plasma-deposited nitride, the average enhancement is 3, with values of 8 observed for P and 1.5 for B. These enhancement values can be reduced by in situ annealing due to localized ion beam heating. This annealing occurs at bulk sample temperatures which are several hundred degrees Centrigrade lower than the temperatures required to produce the same result in a furnace anneal. P D Parry and S P Bristol, J Vac Sci Technol, 15 (2), 1978, 664-667.

36. V A C U U M

INSTRUMENTATION

FOR SURFACE

STUDIES

36 3978. Auger study of surface carbon and oxygen on thorium following ion bombardment. (USA) The composition of a thorium metal surface has been monitored using Auger electron spectroscopy following Ar + bombardment at different temperatures. After extended Ar + bombardment, enough contaminated overlayers were removed to expose a surface region containing only thorium, bulk impurities and imbedded argon. The main impurities, carbon and oxygen, differed in their behaviour where the sample was annealed following bombardment. The amount of surface carbon either increased or remained constant during annealing depending upon the temperature of the sample during bombardment. The amount of surface oxygen decreased rapidly when the sample was heated above 500°C regardless of the sample temperature during bombardment. These experiments indicate that preparation of clean, annealed thorium surfaces requires ion bombardment at temperatures >400°C. R Bastusz and C Colmenares, ] Vac Sci Techno/, 15 (2), 1978, 791-793. 36 3979. Some performance tests of a micro-area AES. (USA) A micro-area Auger analysis system that has submicron Auger analysis capability is described. Capabilities of this versatile surface research system include secondary electron imaging, micro-area Auger analysis in both EdN/dE and EN(E) modes, macro-area AES, sputter ion cleaning and a multiple specimen handling facility. A thermal field emission Zr/W(100) source is used for micro-area AES. A spatial resolution of 1000 A in the secondary electron image is demonstrated. Auger line scans in both EdN/dE and EN(E) modes show submicron edge resolution under nonideal specimen conditions. G Todd and H Poppa, J Vac Sci Technol, 15 (2), 1978, 672-674. 36 3980. Application of a double-pass CMA to ion scattering from some actinide materials. (USA) Surfaces of polycrystalline U, Th and single-crystalline U O 2 ( l l l ) have been examined with He +, Ne + and Ar + at incident beam energies E~ < 650 eV. For this study we used a double-pass cylindrical mirror analyser in a custom vacuum system intended primarily for UPS chemisorption studies. The incident ion beam was perpendicular to the axis of the analyser. Our approach was to determine if the instrument could serve in a complementary ISS capacity and, if so, what the ion scattering conditions are for detecting both surface oxygen and the actinides. Data are presented illustrating definitive results. But severe limitations in resolution are evident, the energies do not correspond exactly to a simple binary-collision model and with He + the scattering intensities from actinide materials are quite low by comparison with a Au reference. W P Ellis and T N Taylor, J Vac Sci Technol, 15 (2), 1978, 679-683.

36 3981. Energy distributions of sputtered copper neutrals and ions. (USA) Direct quantitative analysis of surfaces by secondary ion mass spectrometry (SIMS) will depend on an understanding of the yield ratio of 199