Method for fabricating semiconductor device

After forming a resist pattern on an insulating film deposited on a semiconductor substrate, the insulating film is subjected to plasma etching using an etching gas including carbon and fluorine with the resist pattern used as a mask. A polymer film having been deposited on the resist pattern during the plasma etching is subjected to a first stage of ashing with a relatively low chamber pressure and relatively low plasma generation power by using an oxygen gas or a gas including oxygen as a principal constituent. A residual polymer present on the insulating film in completing the first stage of the ashing is subjected to a second stage of the ashing with a relatively high chamber pressure and relatively high plasma generation power by using an oxygen gas or a gas including oxygen as a principal constituent.