Disclosed is a method of removing resist preventing increase of dielectric constant of low permittivity insulating films and preventing remains of resist. Using a resist mask, a protection insulating film, a MSQ film, and a silicon oxide film composing an ILD are RIE dry etched sequentially, and a via is formed on the surface of a substrate for processing reaching the diffusion layer on the substrate for processing. Subsequent process consists of; removing a modified layer formed on the substrate for processing surface because of prior etching using plasma gas by plasma excitation of NH.sub.3 gas, and another etching for complete removal of the resist mask by irradiation of hydrogen active species created by hydrogen gas and inert gas, of which example is helium gas or argon gas.
