Patent ID: 7387743

Claim:
An etching method for etching a silicon nitride film in a laminated body wherein the silicon nitride film is laminated on a silicon oxide film and is covered with a hard mask whose principal component is a silicon oxide, and a patterned resist film is formed on the hard mask, the method comprising: (a) an etching step of etching the hard mask by using the resist film as a mask to form a mask pattern in the hard mask; (b) an ashing step of ashing the resist film; (c) an oxidizing step of oxidizing the surface of the hard mask under a different condition from that in the ashing; (d) a main etching step of etching the silicon nitride film by using the patterned hard mask as a mask; and (e) an overetching step of overetching the silicon nitride film under a selectivity condition of the silicon nitride film to the silicon oxide film that an etching of the silicon oxide film exposed under the silicon nitride film is suppressed, wherein the main etching step (d) is performed after the step (a) and before the overetching step (e) at a selectivity of the silicon nitride film to the silicon oxide film smaller than the selectivity in the overetching step (e).