A selective dry etch process includes use of an etchant that includes C.sub.2H.sub.xF.sub.y, where x is an integer from three to five, inclusive, where y is an integer from one to three, inclusive, and where x plus y equals six. The etchant etches doped silicon dioxide with selectivity over both undoped silicon dioxide and silicon nitride. Thus, undoped silicon dioxide and silicon nitride may be employed as etch stops in dry etch processes which utilize the C.sub.2H.sub.xF.sub.y-containing etchant. C.sub.2H.sub.xF.sub.y may be employed as either a primary etchant or as an additive to another etchant or etchant mixture.