| 摘要 |
PURPOSE:To increase Vt of a transistor corresponding to the sidewall of an element region larger than that of a transistor at the top of the element region by forming a semiconductor film which contains in high concentration the same impurity as that of a substrate only at the sidewall of the region, and increasing the thickness of the oxide film of the sidewall of the region. CONSTITUTION:A polysilicon film 6 on a surface is etched to retain the film 6 diffused in high concentration with boron only on the sidewall of a silicon film 3, and the films 3, 6 are partly thermally oxidized. An Si3N4 film 4 prevents the top of an element region from being oxidized at this time. As a result, a thick oxide film 2' is formed only on the sidewall of the region. Thus, the film 6 in which boron is diffused in high concentration and the film 2' are formed on the sidewall of the region of an MOS semiconductor device of SOI structure. Thus, Vt of the transistor of second channel region corresponding to the sidewall of the region is increased larger than that of a transistor of a first channel region to remove the influence of the transistor of the sidewall.
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