Method for manufacturing a forming method and a semiconductor device of the insulating film

Method for forming the insulating film includes the steps of: preparing a substrate to be processed silicon surface is exposed, subjected to oxidation treatment to the silicon surface, forming a thin film of silicon oxide film on the silicon surface, a silicon oxide film and silicon of the foundation to performing the first nitriding treatment, and forming a silicon oxynitride film, the silicon oxynitride film and a step of performing first heat treatment in N The method, after the first heat treatment may be further comprises applying a second nitriding process on a silicon oxynitride film, the silicon oxynitride film after the second nitriding process in addition to it may further comprises applying a second heat treatment for.