| 摘要 |
PROBLEM TO BE SOLVED: To enable an SOI element to be lessened in well resistance and improved in punch-through propertie. SOLUTION: An SOI element comprises an SOI substrate of laminated structure composed of a base layer 21, a buried oxide film 22 formed on the base layer 21, and a semiconductor layer 23 formed on the buried oxide film 22. The SOI element comprises a first field oxide film 34a which is formed in the semiconductor layer 22 as deep as prescribed so as not to come into contact with the buried oxide film 22, a second field oxide film 34b narrower in didth than the first field oxide film 34a, and a transistor 40 formed in the active region of the semiconductor layer 23 demarcated by the field oxide films 34a and 34b, wherein the semiconductor layer 23 is set thicker in a region where the first field oxide film 34a is formed thicker than in the other region. A space between the first field oxide film 34a and the buried oxide film 22 is larger than that between the second field oxide film 34b and the buried oxide film 22.
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