Methods for removing silicon nitride and other materials during fabrication of contacts

Abstract

Methods for removing silicon nitride and elemental silicon during contact preclean process involve converting these materials to materials that are more readily etched by fluoride-based etching methods, and subsequently removing the converted materials by a fluoride-based etch. Specifically, silicon nitride and elemental silicon may be treated with an oxidizing agent, e.g., with an oxygen-containing gas in a plasma, or with Oor Oin the absence of plasma to produce a material that is more rich in Si—O bonds and is more easily etched with a fluoride-based etch. Alternatively, silicon nitride or elemental silicon may be doped with a number of doping elements, e.g., hydrogen, to form materials which are more easily etched by fluoride based etches. The methods are particularly useful for pre-cleaning contact vias residing in a layer of silicon oxide based material because they minimize the unwanted increase of critical dimension of contact vias.