Mechanisms of surface roughness induced in silicon by fluorine containing plasmas

Abstract

Deep trenches were etched in silicon with SF 6 plasmas in a simple RIE system. Two process factors influence directly the silicon surface roughness generated by these processes: the dc bias voltage and the presence of oxygen. In general, the roughness increases when the dc bias voltage becomes more negative. Small traces of oxygen increase the roughness substantially. We show that this oxygen does not necessarily have to be introduced as a gas, but its origin could also be oxygen containing materials, such as glass, which are etched during the process. Processes with low dc bias voltage and without any oxygen result in smooth bottom and wall profiles.