| 摘要 |
A surface of a semiconductor substrate is selectively etched to form a first opening, which serves as the opening of a trench. A USG film is deposited on the first opening. A second opening, the width of which is smaller than that of the first opening, is formed in the USG film within the first opening. An inner section of the trench is formed by etching while using the USG film as a mask. The inner surface of the inner region is thermally oxidized to form a silicon oxide film, and a gate insulating film is made by the silicon oxide film and the USG film. A gate electrode is formed in the trench. The gate insulating film is relatively thick at the opening of the trench, so the breakdown voltage at the opening of the trench is increased.
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