Patent ID: 7556997

Claim:
A method of manufacturing a semiconductor device comprising the steps of: (a) preparing an SOI substrate formed by a semiconductor substrate, an insulating layer on said semiconductor substrate and a silicon layer on said insulating layer and said silicon layer has a first conductivity type in first, second and third regions; (b) forming a first oxide film having said silicon layer between said first oxide film and said insulating layer in a surface of said silicon layer in said second region between said first and third regions wherein the step (b) comprising the steps of: (b-1) depositing an oxide film and a nitride film for forming a trench on said SOI substrate; (b-2) forming said trench having said silicon layer between bottom of said trench and said insulating layer in a surface of said silicon layer in said second region between said first and third regions; (b-3) filling said trench by another oxide film; (b-4) forming said first another oxide film by polishing said oxide film; (c) forming a gate electrode by a gate oxide film on said surface of said silicon layer in said first region, said gate electrode extending on said first oxide film in said second region; (d) introducing a first impurity of a second conductivity type into both ends of said gate electrode in said first region using a first mask layer covering said third region and exposing said first region; and (e) introducing a second impurity of said first conductivity type into said third region using a second mask layer covering said first region and exposing said third region, wherein said first mask layer covers said third and second regions and a part of said gate electrode in said second region.