| 摘要 |
A silicon oxide film and a silicon nitride film are formed on a silicon substrate. Then, isotropic etching is performed to the silicon nitride film by the total thickness of the silicon oxide film and a sacrifice oxide film after trenches for element isolation have been formed in the silicon substrate. Subsequently, a high-voltage operation section is covered with a resist film, and isotropic etching is performed to the silicon oxide film in a low-voltage operation section by a thickness of one gate oxide film.
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