First Principles Investigation of HCl, H2, and Chlorosilane Adsorption on Cu3Si Surfaces with Applications for Polysilicon Production

Abstract

The hydrochlorination reaction used in polysilicon production is often catalyzed through copper-based materials which have been found to form the Cu3Si intermetallic under reaction conditions. The structure and composition of the η″ phase, present in the reaction temperature range, has been only recently derived. We conduct the first study of Cu3Si surfaces and their interaction with molecules. Two surfaces of the η″ phase were examined through density functional theory, a silicon-rich Si termination in hexagonal geometry and an equal-parts copper and silicon CuSi termination in honeycomb geometry. The adsorption of H2, HCl, SiCl2, dichlorosilane (SiH2Cl2 or DCS), trichlorosilane (SiHCl3 or TCS), and silicon tetrachloride (SiCl4 or STC) was tested on multiple sites. The SiCu termination favorably adsorbed only the SiCl2 molecule, where a bridge position between a Cu and Si atom produced the strongest adsorption. The Si-terminated surface dissociatively adsorbed HCl at all sites with almost equal adsorption energies. The SiCl2 adsorbed at all sites but greatly preferred a Cu–Si bridge site, where it produced the strongest adsorption of this study. The H2 molecule moved away from the surface for all sites. The STC molecule was unfavorable at sites with closely spaced Cu and Si atoms but dissociatively adsorbed at the other sites with more isolated Si atoms. The TCS molecule underwent dissociative chemisorption on all sites while the DCS molecule moved away from the surface for all site types. Therefore, the Si-terminated surface is preferred for molecular adsorption and appears to provide promising starting sites for surface hydrochlorination reactions.