Patent ID: 7807537

Claim:
A method for forming silicon oxide films, comprising the steps of: (a) preparing a substrate; (b) forming a silicon nitride film or a silicon oxynitride film covering one main surface of the substrate; (c) forming an ion-doping mask on the silicon nitride film or the silicon oxynitride film in accordance with a predetermined pattern; (d) doping an impurity ion for changing oxidation speed to the silicon nitride film or the silicon oxynitride film by a selective ion doping process using the ion doping mask; (e) removing the ion-doping mask; and (f) performing a thermal oxidation process to the silicon nitride film or the silicon oxynitride film so as to form a first silicon oxide film in a part of the silicon nitride film or the silicon oxynitride film where the impurity ion is doped and to form a second silicon oxide film in a part of the silicon nitride film or the silicon oxynitride film where the impurity ion is not doped with a thickness different from a thickness of the first silicon oxide film.