PLASMA SURFACE INTERACTIONS IN FLUOROCARBON ETCHING OF SILICON DIOXIDE

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 CF(x) radicals in a CF4 plasma; the beams included F and CF2, with a beam of Ar+ to simulate energetic ion bombardment. Both CF2 and F enhance the etching yield of SiO2 under energetic Ar+ bombardment; however, the enhancement with F is twice that seen with CF2 at similar fluxes. When CF2 and F fluxes are used simultaneously, F dominates and the CF2 flux 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.