Plasma reactor with heated source of a polymer-hardening precursor material

A general method of the invention is to provide a polymer-hardening precursor piece (60) (such as silicon, carbon, silicon carbide or silicon nitride, but preferably silicon) within the reactor chamber (10) during an etch process with a fluoro-carbon or fluoro-hydrocarbon gas, and to heat the polymer-hardening precursor piece above the polymerization temperature sufficiently to achieve a desired increase in oxide-to-silicon etch selectivity. Generally, this polymer-hardening precursor or silicon piece may be an integral part of the reactor chamber walls and/or ceiling or a separate, expendable and quickly removable piece (60), and the heating/cooling apparatus (30, 32, 34, 36, 62) may be of any suitable type including apparatus which conductively or remotely heats the silicon piece.