| 摘要 |
PROBLEM TO BE SOLVED: To planarize the surface of an element region by suppressing breaking into of bird's beak into the element region, when an isolation region is formed by dividing LOCOS method into two stages. SOLUTION: In the method for fabricating a semiconductor device, the isolation region forming region 4 of a substrate 1 is masked by a first antioxidation film (silicon nitride film 3) having a first opening 7 and then first field oxidation is carried out to form a first field oxide film 9. Subsequently, the first field oxide film 9 is masked by a second antioxidation film (silicon nitride film 20), having a second opening 22 of smaller width dimension than the first opening 7 and then a second field oxidation is carried out, to form a deep second field oxide film 15 locally in the center of the first field oxide film 9.
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