| 摘要 |
PROBLEM TO BE SOLVED: To uniform the thickness of a gate oxide film and to increase reliability of the gate oxide film by forming side walls on side walls of a first insulating film, forming a concave part in a separation area between devices on a substrate and filling the inside of the concave part with a second insulating film. SOLUTION: Photoresist having open patterns above a separation area between devices on a silicon substrate is formed on an oxide film 2 and a polysilicon film is formed on the whole surface. The polysilicon film is etched in the depthwise direction of the silicon substrate 1 and side walls 4 are formed on side walls of the oxide film 2. Then a trench 5 is formed in the silicon substrate 1 in the separation area between devices. The shape of the top of the side walls 6 of the silicon substrate 1 near the boundary between the silicon substrate 1 and the trench 5 is made round. Then an oxide film 7 filling the concave part is formed on the whole surface. After that, the oxide film 7 and the oxide film 2 are removed by polishing until the silicon substrate 1 under the oxide film 2 is exposed. In this way, a separation oxide film 8 whose surface is flattened and which fills the trench 5 is obtained.
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