Etching method and apparatus, computer program and computer readable storage medium

摘要

An etching method, for etching a silicon nitride film on an underlying silicon oxide film by using a hard mask whose principal component is a silicon oxide, includes a step of etching the hard mask by using the resist film as a mask to form a mask pattern therein; a step of ashing the resist film; a step of oxidizing the hard mask; a main etching step of etching the silicon nitride film by using the patterned hard mask as a mask; and a step of overetching the silicon nitride film at a high selectivity of the silicon nitride film to the silicon oxide film. The main etching step is performed after the step of forming the mask pattern in the hard mask and before the overetching step at a selectivity of the silicon nitride film to the silicon oxide film smaller than that in the overetching step.