The effect of added acetylene on the rf discharge chemistry of C2F6was studied as a function of acetylene concentration. The principle products are HF, CF4, CHF3, C2F4, and CF2as determined by mass spectrometry. Under conditions typically used for etching SiO2, residence time and power density control the amount of conversion of feed gas to products. Large amounts of polymeric material, with composition (CF)n, are formed in the discharge zone. A chemical model for flourocarbon discharges is proposed, which assumes an equilibrium between dissociation and recombination of flourocarbon fragments and flourine atoms. Polymerization and selective etching of Si and SiO2in flourocarbon dishcarges containing oxygen or hydrogen additives is interpreted in terms of the proposed model.