The performance of sulfur hexafluoride as an in situ etchant for silicon during epitaxial growth processes has been examined as a function of temperature and partial pressure. Below 1060°C etching was preferential, producing pitted substrates, while above 1060°C etching was smooth. However, above 1060°C, both the masking layers on the substrates and the quartz reactor walls were attacked during the etching of the silicon. This occurred in both helium and hydrogen ambients. High resistivity silicon substrates were etched in situ with . Silicon epitaxial layers were deposited subsequent to in situ etching with . Both etched substrates and etched substrates with epitaxial layers were examined optically for the presence of active sulfur donor sites. The concentration of active sulfur donor sites resulting from etching with was found to be less than in both the etched substrates and the silicon layers deposited subsequent to etching.