Kinetics of SiHCl<SUB>3</SUB> and SiCl<SUB>4</SUB> Evolution in Si(s)–HCl(g) System Simulated by Ab-initio MO

Abstract

A reaction model for a HCl(g)-Si(s) system is proposed in this study as follows: first, SiCl 2 (g) and H 2 (g) are produced by a heterogeneous surface reaction, and then SiHCl 3 (g) and SiH 2 Cl 2 (g) are produced by the homogeneous reaction between SiCl 2 (g) and HCl(g) and between SiCl 2 (g) and H 2 (g), respectively; finally, SiCl 4 (g) and SiHCl 3 (g) are produced by the homogeneous reaction between SiHCl 3 (g) and HCl(g) and between SiH 2 Cl 2 (g) and HCl(g), respectively. The mechanism in the first heterogeneous surface reaction step has been studied extensively in the past. However, the detail of the subsequent homogeneous reactions has not yet been understood. It is important to get information of the chemical kinetics of the reactions derived from the reaction intermediate of SiCl 2 (g) in the SiCl 2 (g)-HCl(g)-H 2 (g) system, so the most plausible elementary reactions of reversible unimolecular fission and chain reaction are proposed here. The structures of the molecules formed in these reactions are optimized using the minimization principle of energy calculated by ab-initio molecular orbital method and also their rate constants are calculated by conventional transition state theory. Using these rate constants, the ordinary differential equations are solved on mass balance, and the time dependent concentration profile of respective chemical species and the prior reaction paths are discussed in this study.