Patent ID: 8399361

Claim:
A method of manufacturing a semiconductor device, comprising: forming a compound semiconductor layer over a substrate; forming a first layer silicon nitride film constituting a protective insulating film over a surface of the compound semiconductor layer by a plasma CVD method; and forming a second layer silicon nitride film constituting the protective insulating film over the first layer silicon nitride film by a plasma CVD method under a film-forming condition where the second layer silicon nitride film is formed with a lower film density than the first silicon nitride film, as a film-forming condition of the second layer silicon nitride film, any one of the following conditions is employed: (i) a frequency of a high-frequency power applied to a film-forming atmosphere is set higher than a frequency of a high-frequency power applied at the time of forming the first layer silicon nitride film; (ii) a power of a high-frequency power applied to a film-forming atmosphere is set lower than a power of a high-frequency power applied at the time of forming the first layer silicon nitride film; (iii) a pressure of a film-forming atmosphere is set higher than a pressure at the time of forming the first layer silicon nitride film; (iv) ammonia is used as a source gas for nitrogen of the second layer silicon nitride film, and nitrogen is used as a source gas for nitrogen of the first layer silicon nitride film; (v) a substrate temperature is set lower than the substrate temperature at the time of forming the first layer silicon nitride film; and (vi) a film-forming speed is set faster than the film-forming speed at the time of forming the first layer silicon nitride film.