Patent ID: 7745303

Claim:
A method of manufacturing a semiconductor device, comprising: forming a first trench in a semiconductor substrate, the first trench having a first opening size; performing oxidation with anisotropy on an inner surface of the first trench to form a sacrifice oxide film, the sacrifice oxide film having a thickness that is different locally such that a thickness of the sacrifice oxide film in a shoulder portion of the first trench is thicker than a thickness of the sacrifice oxide film in a portion other than the shoulder portion of the first trench; removing the sacrifice oxide film to preferentially back off the shoulder portion of the trench while rounding a shape of the shoulder portion, the first trench being thereby converted into a second trench that has a second opening size that is larger than the first opening size of the first trench; performing isotropic oxidation on an inner surface of the second trench to form an oxide film on the inner surface of the second trench, a substantial entirety of the oxide film has substantially a uniform thickness so that an opening size defined by the oxide film is smaller than the second opening size of the second trench and larger than the first opening size of the first trench; and filling the second trench with an insulating film with an intervention of the oxide film.