| 摘要 |
A trench ( 4 ) is formed in a semiconductor substrate ( 1 ), and then a plasma oxynitride film ( 5 ) is formed on a side wall surface and a bottom surface of the trench ( 4 ) at a temperature of approximately 300° C. to 650° C. At such a temperature, no outward diffusion of impurities from the semiconductor substrate ( 1 ) occurs. Therefore, any problems such as formation of a parasitic transistor hardly occur even when ions of impurities are not implanted thereafter. After the plasma oxynitride film ( 5 ) is formed, it is thermally oxidized, and a portion where the outermost surface of the semiconductor substrate ( 1 ) meets the wall surface of the trench ( 4 ) is turned into a curved surface. As a result, the outermost surface of the semiconductor substrate ( 1 ) and the wall surface of the trench ( 4 ) meet each other while forming a curved surface, and hence a parasitic transistor is hardly formed at this portion. Consequently, formation of a hump is prevented, thereby achieving favorable characteristics.
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