Method of fabricating a semiconductor device using plasma to form an insulating film

A fabrication method of a semiconductor device is disclosed by which damage to another film or exfoliation of a film is prevented and an insulating film having a dielectric constant of 2.5 or less can be formed while a film strength is maintained without deteriorating a wiring line characteristic. According to an embodiment, an insulating film is formed on a substrate by a plasma process, which uses film-forming gas having a ring structure of Si-O bonds, such that it maintains the ring structure of the Si-O bonds. According to another embodiment, an insulating film is formed on a substrate by a plasma process, which uses film-forming gas which contains silane-containing gas and oxygen gas or film-forming gas which contains Si-O bond-containing gas, such that it has a ring structure of the Si-O bonds.