Patent ID: 6841440

Claim:
A method of manufacturing a semiconductor device, comprising the steps of: (a) preparing a substrate including a predetermined semiconductor material and having a predetermined conductivity type; (b) forming an oxide film including an oxide of said predetermined semiconductor material on said substrate to have a predetermined film thickness; (c) forming a semiconductor film including said predetermined semiconductor material on said oxide film; (d) partially etching said semiconductor film, said oxide film and said substrate in this order, to form a trench which extends from said semiconductor film towards the inside of said substrate; (e) oxidizing surfaces of said substrate and said semiconductor film which are exposed in said trench to make an edge portion of said oxide film along said trench thicker than said predetermined film thickness; and (f) implanting an impurity of the same conductivity type as said predetermined conductivity type into said substrate through said oxide film after said step (e), thereby forming an impurity layer, wherein a first portion of the impurity layer adjacent to said trench is formed shallower than a second portion of the impurity layer.