Dual nanoscale roughness on plasma-etched Si surfaces: Role of etch inhibitors

The nanoroughness formation and evolution during fluorine-based plasma etching of Si surfaces is investigated both experimentally and theoretically. Dual nanoscale morphology, as well as, almost linear increase of both root mean square roughness and correlation length versus etching time is observed in the experiment. The effect of etch inhibitors from the plasma environment is modeled. Two kinds of etch inhibitors can explain and predict the nanoroughness formation and evolution. Key factors in the nanoroughness formation is the angular distribution of etch inhibitors versus that of ions and their sticking probability compared to that of reactive neutral species.