Patent ID: 6869849

Claim:
A manufacturing method of a semiconductor device, comprising the steps of: forming a first oxide film on a surface of a semiconductor substrate; depositing a stacked film including a first conductive layer in contact with the first oxide film; etching the stacked film and the first oxide film to form a plurality of stacked film patterns arranged on the semiconductor substrate; oxidizing the semiconductor substrate to form a second oxide film on a surface of the semiconductor substrate sandwiched between adjacent said stacked film patterns and a surface of the semiconductor substrate below end portions of the stacked film patterns wherein the second oxide film has a film thickness thicker than the first oxide film; forming a side wall mask film on a side of the stacked film patterns to form mask patterns including the stacked film patterns; removing the portion of the second oxide film sandwiched between the mask patterns and a portion of the underlying semiconductor substrate using the mask patterns as a mask to form a trench in the semiconductor substrate; and filling the trench with an insulating film wherein the stacked film includes a stopper film that provides a stopper for a chemical mechanical polishing step.