Halogen exchange reactions of silicon tetrachloride with fluorine and fluorine-containing substances

Abstract

SiCl 4 is the final reaction product generated by laser-induced dry chemical etching of silicon in a chlorine atmosphere. During our experiments on laser photochemical etching with chlorine, infrared spectra were taken. The main reaction product was SiCl 4, in addition to which traces of HCl, SiF 4 and SiF 2Cl 2 were found. These traces were assumed to originate from a secondary halogen exchange reaction between SiCl 4 and unknown fluorine containing compounds. For this reason systematic investigations were carried out with the pure substances in the absence of laser light. The reactions of SiCl 4 with gaseous and adsorbed fluorine or HF were studied intensively. It was found that a small amount of moisture entered the reaction vessel each time the sample was changed. In the presence of residual fluorine-containing substances on the inner walls, adsorbed HF was formed which reacted with SiCl 4 to form SiF 4 via the intermediates (SiF x Cl y ).