| 摘要 |
Before forming a trench in a silicon substrate through a patterned silicon nitride film serving as a mask, etching is executed until the main surface of the silicon substrate is exposed. Thereafter exposed side walls of a silicon dioxide film and a polysilicon film and the exposed surface of the silicon substrate are oxynitrided thereby forming an silicon oxynitride film. Thereafter the trench is formed, then a silicon dioxide film is formed on its inner wall, and thereafter the trench is filled with an insulation. In the process of forming the silicon dioxide film on the inner wall, a bird's beak is formed on the side walls of the silicon dioxide film and the polysilicon film. The silicon oxynitride film suppresses excessive growth of the bird's beak and prevents the bird's beak from formation of a depressed part. Thus, reduction of the area of an active region caused by the bird's beak is suppressed without no depression part formed on the upper end of an STI structure.
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