In a semiconductor device fabricating process, a copper-based metal film is formed on an insulating layer, and an insulating film is formed on the copper-based metal film. A patterned resist film is formed on the insulating film, and the insulating film is dry-etched using the patterned resist film as a mask to form a hole penetrating through the insulating film. Thereafter, a plasma treatment using an non-oxidizing gas is carried out, and furthermore, a wet treatment using a resist remover liquid is carried out, for removing the resist film and a resist surface hardened layer which was generated in the dry-etching.