Chemical Vapor Deposited Silicon Carbide Research Articles

Neutral ion figuring of chemical vapor deposited SiC

Ion figuring of optical components is a relatively new technology that can alleviate some of the problems associated with traditional contact polishing. Because the technique is noncontacting, edge distortions and rib structure print through do not occur. This investigation was aimed at determining the effect of ion figuring on surface roughness of previously polished or ductile ground ceramic optical samples. This is the first step in research directed toward the combination of a prefinishing process (ductile grinding or polishing) with ion figuring to produce finished ceramic mirrors. Multiple, chemical vapor deposited silicon carbide (CVD SiC) samples were polished or ductile ground to specular or near-specular roughness. These samples were then characterized to determine topographic surface information. The surface evaluation consisted of stylus profilometry, interferometry, and optical and scanning electron microscopy. The surfaces were then ion machined to depths from 0 to 5 micron. The finished surfaces were characterized to evaluate the effects of the ion-machining process with respect to the previous processing methods and the preexisting subsurface damage. This study provides some of the information required to effectively utilize a combined ductile grinding or polishing with ion machining as a procedure for figuring optical components.

The Decomposition of Methyltrichlorosilane: Studies in A High-Temperature Flow Reactor

AbstractExperimental measurements of the decomposition of methyltrichlorosilane (MTS), a common silicon carbide precursor, in a high-temperature flow reactor are presented. The results indicate that methane and hydrogen chloride are major products of the decomposition. No chlorinated silane products were observed. Hydrogen carrier gas was found to increase the rate of MTS decomposition. The observations suggest a radical-chain mechanism for the decomposition. The implications for silicon carbide chemical vapor deposition are discussed.

Growth and structure of chemical vapor deposited silicon carbide from methyltrichlorosilane and hydrogen in the temperature range of 1100 to 1400°C: Myoung Gi So and John S Chun, J Vac Sci Technol, A6, 1988, 5–8

Growth and structure of chemical vapor deposited silicon carbide from methyltrichlorosilane and hydrogen in the temperature range of 1100 to 1400°C: Myoung Gi So and John S Chun, J Vac Sci Technol, A6, 1988, 5–8

Chemical vapour deposition of silicon carbide: An X-ray diffraction study

Low-pressure chemical vapour deposition of siliconcarbide from tetramethyl silane pyrolysis was studied by X-ray diffractometry.In situ measurements at high temperature gave kinetic information. The crystallization state, grain size, microstrains and residual macrostresses were measured at room temperature.

Growth and structure of chemical vapor deposited silicon carbide from methyltrichlorosilane and hydrogen in the temperature range of 1100 to 1400 °C

Silicon carbide has been grown at 1100 to 1400 °C by chemical vapor deposition using CH3SiCl3 and H2 gaseous mixture onto a graphite substrate. The effect of deposition temperature, total system pressure, and the CH3SiCl3 input fraction on growth characteristics and structure of deposits has been studied. The experimental results show that the SiC deposition reaction is a thermally activated process with the deposition rate limited by surface reactions. The apparent activation energy is about 26 kcal/mol at a system pressure of 200 Torr and decreases with the increasing total system pressure. In this experiment, polycrystalline β-SiC always has been deposited. The preferred orientation of the deposited SiC films changes from 〈111〉 to 〈220〉 with increasing deposition temperature. The size of the polycrystalline β-SiC grains becomes coarser as the deposition temperature and the CH3SiCl3 input fraction are increased.

Reflectance spectra of extreme ultraviolet mirrors for synchrotron radiation

Reflectance spectra have been measured for many materials in the wavelength range from 90 Å to 400 Å. The angle of incidence ranged from 20° to 85°. The samples were chemical-vapor-deposited silicon carbide (CVD-SiC), a single crystal of silicon with (100) surface, fused quartz, zerodur, pyrex, gold, platinum, copper and two kinds of steel. To obtain reflectances for surfaces for practical use, measurements were made on surfaces sufficiently exposed to air. Reflectances for s-polarized light (Rs) were measured for all samples. On CVD-SiC, gold and platinum, reflectances for p-polarized light (RP) were also observed. At short wavelengths and large angles of incidence, the difference between Rs and RP is small, and RP happened to exceed Rs in contrast to the result from the Fresnel equation. This may be due to the deviation of the present surfaces of mirrors from an ideal plane. Reflectance spectra of surfaces prepared by some feasible techniques are also presented.

Erosion behaviour of physically vapour-deposited and chemically vapour-deposited SiC films coated on molybdenum during oxygenated argon beam thinning

The erosion behaviour during bombardment with a 5 keV argon beam at room temperature was studied for silicon carbide (SiC) films of thickness of about 10 μm coated on molybdenum by physical vapour deposition (PVD) and chemical vapour deposition (CVD). The PVD SiC (plasma-assisted ion plating) exhibited a greater thinning rate than the CVD SiC film. Electron probe X-ray microanalysis revealed that the chemical composition of PVD SiC was changed to a composition enriched in silicon by the bombardment, and there was a notable change in its surface morphology. The CVD SiC retained its initial chemical composition with only a small change in its surface morphology. Auger electron spectroscopy indicated that silicon oxide was formed on the surface of PVD SiC by the bombardment. The greater thinning rate and easier change in chemical composition in PVD SiC could be attributed to its readier chemical reaction with oxygen due to its more non-uniform structure and weaker chemical bonding. Oxygen was present as one of the impurities in the argon beam.

Evaluation of CVD silicon carbide for synchrotron radiation mirrors

Chemical vapor deposited silicon carbide (CVD SiC) is a recent addition to the list of materials suitable for use in the harsh environment of synchrotron radiation (SR) beam lines. SR mirrors for use at normal incidence must be ultrahigh vacuum compatible, must withstand intense X-ray irradiation without surface damage, must be capable of being polished to an extremely smooth surface finish, and must maintain surface figure under thermal loading. CVD SiC exceeds the performance of conventional optical materials in all these areas. It is, however, a relatively new optical material. Few manufacturers have experience in producing optical quality material, and few opticians have experience in figuring and polishing the material. The CVD material occurs in a variety of forms, sensitively dependent upon reaction chamber production conditions. We are evaluating samples of CVD SiC obtained commercially from various manufacturers, representing a range of deposition conditions, to determine which types of CVD material are most suitable for superpolishing. At the time of this writing, samples are being polished by several commercial vendors and surface finish characteristics are being evaluated by various analytical methods.