The Kinetics of Epitaxial Silicon Deposition by the Hydrogen Reduction of Chlorosilanes†

Abstract

A model is proposed for the physical and chemical processes involved in the epitaxial deposition of silicon by the hydrogen reduction of chlorosilanes, in which it is assumed that there is a boundary-layer of relatively static gas adjacent to the silicon surface; that the chlorosilane and hydrogen diffuse across the boundary-layer and react at the silicon surface; and that the gaseous products of reaction diffuse back across the boundary-layer and are swept away in the main gas stream. By assuming that the gas in contact with the silicon surface is in equilibrium at the surface temperature, the transport equations are solved for the case where the equilibrium reactions are 2SiHCl₃ ½ SiCl₄ + SiCl₂ + H₂, SiCl₄ + H₂ ½ SiCl₂ + 2HC1 and Si + SiCl₄ ½ 2SiCl2, and an expression is derived for the deposition rate which involves only known terms. The predictions of the theory are compared with the experimental results, and it is shown that reasonable agreement obtains.