The major species present in a fluorocarbon plasma environment were simulated and independently controlled using radical and ion beams in an ultrahigh‐vacuum apparatus. The beams used in this study were chosen to determine the importance of CFxradicals in a CF4plasma; the beams included F and CF2, with a beam of Ar+to simulate energetic ion bombardment. Both CF2and F enhance the etching yield of SiO2under energetic Ar+bombardment; however, the enhancement with F is twice that seen with CF2at similar fluxes. When CF2and F fluxes are used simultaneously, F dominates and the CF2flux has little effect on the overall etching yield. Combined with previous work on Si substrates, these results are consistent with qualitative theories for SiO2/Si selectivity in fluorocarbon plasmas. Possible elementary steps in the ion‐enhanced etching process are proposed and reduced to a two‐parameter model which represents the process as ion‐enhanced neutral adsorption followed by ion‐induced reaction to form volatile products.