Method of manufacturing semiconductor device

Abstract

A semiconductor substrate exposed from an oxidation-resistant mask layer is thermally oxidized to form a field oxidation film. The mask layer has multiple mask parts with a first width and multiple mask parts with a second width smaller than the first width. In the thermal oxidation process, an oxidation film is formed integrally with the field oxidation film under the mask part, and an oxidation film is formed integrally with the field oxidation film under the mask part. After removing the mask layer, plurality of p-type semiconductor regions is formed by ion-implantation into the semiconductor substrate using the field oxidation film as a mask. The plurality of p-type semiconductor regions includes a first semiconductor region formed under the oxidation film and a second semiconductor region formed under the oxidation film, and the depth of the second semiconductor region is shallower than the depth of the first semiconductor region.