Patent ID: 8017482

Claim:
A method of manufacturing a semiconductor device, comprising: providing a semiconductor substrate comprising a first semiconductor layer of a first general conductive type and a second semiconductor layer of a second general conductive type disposed on the first semiconductor layer; forming a trench extending from a front surface of the second semiconductor layer into the first semiconductor layer; forming a gate insulation film on an inner sidewall of the trench and the front surface of the second semiconductor layer; forming a gate electrode in the trench after the formation of the gate insulation film; forming a gate electrode protection film on an upper surface of the gate electrode by thermally oxidizing the gate electrode; and forming an impurity region of the first general conductive type by ion-implanting impurity ions in the second semiconductor layer after the formation of the gate electrode protection film, wherein a thermal oxide film is formed on the upper surface of the second semiconductor layer so as to overlap the gate insulation film during the formation of the gate electrode protection film, a thickness of the gate electrode protection film is larger than a projected range of the impurity ions in the gate electrode protection film during the formation of the impurity region, and a total thickness of the overlapped gate insulation film and thermal oxide film is less than 70% of the projected range of the impurity ions in the gate electrode protection film.