A method of performing microfabrication using a hard mask in the manufacture of a semiconductor device having an interlayer dielectric (ILD) film made of low-dielectric constant, K, insulating material is provided. When treating a low-K dielectric film for use in semiconductor integrated circuitry and its underlying etching stopper film, a patterned resist film is used as a mask to etch a hard mask film. Subsequently, the resist pattern is subjected to stripping or "ashing" in the atmosphere of a mixture gas of hydrogen (H.sub.2) and helium (He) at a temperature higher than 200.degree. C. under a pressure of about 1 Torr. With this procedure, microfabrication relying upon the hard mask less in facet is achievable during its subsequent etching of the low-K dielectric film, without damaging the hard mask film upon removal of the resist.