the method for fabricating the semiconductor device comprises the step of forming an insulating film 14 having an opening 18 ; the step of forming an organic resist film 20 a ; the step of forming over the organic resist film 20 a a mask film 20 b having etching characteristics different from those of the organic resist film 20 a ; the step of forming an opening in the mask film 20 b ; and the step of etching the organic resist film 20 a with the mask film 20 b as the mask . in the step of etching the organic resist film , the organic resist film 20 a is etched with a mixed gas of nitrogen gas and oxygen gas .