The Systems Si-C-H and Si-C-H+Ar

Abstract

The gaseous Si-C-H and Si-C-Cl-H (see p. 534) systems are generally similar, but the most exhaustive theoretical investigation [1, 8], which considers ten gaseous species at 1000 to 2000 K, shows them to differ substantially. Results computed by [1, 3] for the Si-C-H gaseous species are combined in Table 28, p. 520. The thermodynamic calculations concentrate on SiC deposition from the mixtures SiH₄-CH₄ [1], SiH₄-C₂H₄ [1, 7], and SiH₄-C₃H₈ [1 to 4] with hydrogen as both reactant and carrier gas. Because of the lower free energy values of β-SiC, no α-SiC was predicted to occur. For SiH₄-CH₄ mixtures it was found that at the highest pressure of 10⁶ Pa the β-SiC single phase field is small at low H₂ carrier gas concentrations but increases markedly as the H₂ concentration increases. At a pressure of 10⁴ Pa the necessity for SiC deposition of high H₂ concentrations becomes very apparent, and two β-SiC single phase fields exist at low and high temperatures, respectively. At 10² Pa only the field at higher temperatures and at Si/(Si + C)> 0.5 remains [1]. For phase diagrams computed using various parameters see Fig. 9, p. 84. The SiH₄-C₂H₄-H₂ system is thermodynamically similar. Differences become only significant at low H₂ carrier gas concentrations [1]. The equilibrium calculations for the SiH₄-C₃H₈-H₂ system predict that it is also similar to the SiH₄-CH4 H₂ system, with the boundaries falling between those for the CH₄- and the C₂H₄-containing systems. The deposition of α-SiC on α-SiC substrates was predicted in [2 to 4]. A vapor pressure diagram between 1700 and 2100 K for nine important species out of thirty gaseous species considered is given [2]. Fourteen species gaseous between 1300 and 2000°C were considered in [3]. Gas mixtures of SiH₄-C₂H2 H₂ with or without additional N₂ were investigated experimentally in the temperature range from 700 to 1080°C, pressures between 10² and 10⁶ Pa [5]. For a thermodynamic analysis of equilibria between SiC and H₂ from 1500 to 3000 K at constant H₂ pressures of 1.5×10^-1, 10^-1, and 10^-2 atm, see [6].