Chemical Etching of Thermally Oxidized Silicon Nitride: Comparison of Wet and Dry Etching Methods

Abstract

The ability to etch silicon nitride changes after this material is exposed to a wet oxygen ambient, as a result of the partial oxidation of the silicon nitride to form a silicon oxynitride. We have measured the etch rate of silicon nitride exposed to different oxidation temperatures and pressures, to determine how these parameters affect the mask removal step needed in the local oxidation of silicon‐based processing sequence. Both wet (hydrofluoric acid and phosphoric acid) and dry ( remote plasma) isotropic etch methods are described, and correlated to Rutherford backscattering and ellipsometric measurements. Our results show the presence of an oxidized layer which increased in thickness with oxidation temperature and pressure. Process modifications must comprehend the altered silicon nitride surface in order to adequately strip this film.