Patent ID: 8062979

Claim:
A semiconductor device manufacturing method comprising: preparing a semiconductor substrate; forming a thermally oxidized film on the semiconductor substrate by thermally-oxidizing the surface of the semiconductor substrate; forming a polishing stopper layer on the thermally oxidized film; forming a hard mask A by patterning a hard mask material after forming the hard mask material on the polishing stopper layer; forming a trench in the polishing stopper layer, the thermally oxidized film and the semiconductor substrate, by etching the polishing stopper layer, the thermally oxidized film and the semiconductor substrate using the hard mask A; wherein at least a portion of the hard mask A remains on the polishing stopper layer after the trench is formed in the semiconductor substrate; removing the hard mask A; forming a thermally oxidized film in a part where the semiconductor substrate is exposed, by thermally-oxidizing the semiconductor substrate; forming an insulating film on the whole surface; removing the insulating film by CMP using the polishing stopper layer as a stopper; and removing the polishing stopper layer.