Patent ID: 7270763

Claim:
A wet etching method comprising: forming a silicon oxide film on one principal surface of a silicon substrate, and then forming a silicon nitride film on the silicon oxide film, a thickness T O of said silicon oxide film and a thickness T N of said silicon nitride film being set to have a film thickness ratio T O /T N of 1.25 or larger; selectively etching a lamination layer of said silicon oxide film and said silicon nitride film to form an etching mask with an aperture, said etching mask being made from the remaining region of said lamination layer; forming at least one stress relaxing groove partially in said silicon nitride film, before or after the formation of said etching mask, to relax film stress to be applied to said aperture; and selectively and anisotropically etching said silicon substrate with alkali etchant by using said etching mask.