CODEPOSITION OF FREE SILICON - DURING CVD OF SILICON-CARBIDE

Factors influencing the concentration and distribution of elemental silicon codeposited during chemical vapor deposition (CVD) of SLC from MTS (CH3SiCl3) and hydrogen diluted by argon are reported, The experiments were carried out in both hot- and cold-wall reactors at 1383-1473 K at atmospheric pressure, Codeposition of free silicon was detected even at very low excess hydrogen, contrary to the prediction of thermochemical calculations, In the hot-wall reactor, under conditions of high exchange rate of the feed gases, deposits of uniform composition were obtained, containing 0%-90% free silicon, depending upon feed gas composition, The deposits of pure silicon carbide consisted of beta-SiC with a microhardness of 2400 kg/mm(2) at a typical formation rate of 30 mu m/h. Microhardness decreased to 800 kg/mm(2) with increasing silicon concentration. In the cold-wall reactor, under impinging gas flow conditions, nonuniform deposition occurred: a local gradient of Si/SiC was obtained with free silicon concentrations varying gradually between 0% and 35%. Si/SiC ratios in the deposits were determined by a combination of XRD, scanning AES, and SMP.