In one embodiment of the invention, a method for finishing or treating a silicon-containing surface is provided which includes removing contaminants and/or smoothing the surface contained on the surface by a slow etch process (e.g., about <100 .ANG./min). The silicon-containing surface is exposed to an etching gas that contains an etchant, a silicon source and a carrier gas. Preferably, the etchant is chlorine gas so that a relatively low temperature (e.g., <800.degree. C.) is used during etching or smoothing processes. In another embodiment of the invention, a method for etching a silicon-containing surface during a fast etch process (e.g., about >100 .ANG./min) is provided which includes removing silicon-containing material to form a recess in a source/drain (S/D) area on the substrate. The silicon-containing surface is exposed to an etching gas that contains an etchant, preferably chlorine, a carrier gas and an optional silicon source.