Morphology of silicon carbide formed by chemical vapour deposition

Abstract

Abstract Silicon carbide polycrystalline layers and particulate crystals were obtained in a modified van Arkel-de Boer apparatus on SiC-covered graphite and molybdenum susceptors. Gaseous SiCl4 + CCl4 + H2 reactive mixtures with Si C mole ratios varying between 0.9 and 1.4 and with Cl/Cl+H ratios varying between 2.10−3 and 1.10−3 were used. The morphology and structure of SiC products obtained at temperatures between 1400 and 1900°C and input gas flow rates between 5.10−4 and 6.10−2 moles per hour have been systematically investigated by scanning electronmicrographs, X-rays (using the Laue, Weissenberg, and rotation photographs), IR-spectra, and under the polarising microscope. The ranges of temperature and input gas flow rates in which the given habits and forms of the SiC products are formed have been assessed. The habits of the particulate crystals as function of temperature have been interpreted in terms of the existing theories of heterogeneous nucleation assuming layer growth of the crystals by two-dimensional nucleation. The influence of the composition of the gaseous mixtures upon the formation of the 2H polytype as well as the probable reasons for the common occurrence of stroking fault twins in the 3C polytype have been discussed.