Surface modelling of reactive ion etching of silicon-germanium alloys in a SF6 plasma

Reactive ion etching (RIE) of amorphous SixGe1-x alloys (0 less than or equal to x less than or equal to 100%) in a low-pressure SF6 plasma has been investigated by means of quasi in situ X-ray photoelectron spectroscopy. The reactive layer on the etched alloys mainly consists of SiF, GeF, SiS and GeS2 species. The sulfur and fluorine coverages on both Ge and Si atoms depend on the SiGe alloy stoichiometry in agreement with the nonlinear evolution of the alloy etch rates. A simple etching model where the etch rate is assumed to be proportional to the fluorine coverages has been developed for the description of the SixGe1-x etching mechanism. (C) 1997 Elsevier Science S.A.