Surface studies relevant to silicon carbide chemical vapor deposition

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Abstract
Experimental studies of C2 H4, C3 H8, and CH4 reactions on the Si(111) surface and C2 H4 reaction on the Si(100) surface have been performed for surface temperatures in the range of 1062–1495 K. These studies used x-ray photoelectron spectroscopy and related ultrahigh vacuum procedures to identify the reaction products, characterize the solid-state transport mechanisms, determine the surface nucleation mechanisms and growth kinetics, and assess the effects of surface orientation. The reaction product was found to be essentially carbidic throughout the course of the reaction, although the surface layer may contain partially hydrogenated C adspecies. The dominant transport process was shown to be Si out-diffusion rather than C in-diffusion. The Si adspecies produced by out-diffusion react at the gas-surface interface with C adspecies to form the SiC film via a two-dimensional nucleation and layer-by-layer growth mechanism. The reaction efficiency for C2 H4 on the Si(111) and Si(100) surfaces was shown to be ∼10−3. The reaction efficiency for C3 H8 and CH4 on the Si(111) surface was shown to be ∼10−5. For growth temperatures above 1395 K, Si diffusion limitations and sublimation from the SiC surface were found to limit the availability of Si for the SiC growth process. In the absence of Si adspecies, the adlayer formed by the reaction of C2 H4 on SiC appeared to passivate the surface with respect to further C2 H4 reaction. When combined with previously reported modeling studies of the associated gas phase chemistry, these results provide the basis for a mechanistic model of the β-SiC chemical vapor deposition process.