Manufacturing method of semiconductor device

A manufacturing method of a semiconductor device comprising the steps of:

• preparing a semiconductor substrate having a first main surface and a second main surface;
• forming a recess in the first main surface and embedding an insulating film in the recess;
• forming a polysilicon film on the insulating film;
• forming an interlayer insulating film on the first main surface so as to cover the insulating film and the polysilicon film;
• and
• forming a first contact hole and a second contact hole,
• wherein the semiconductor substrate has a first impurity diffusion region formed in the first main surface, and a second impurity diffusion region in contact with a portion of the first impurity diffusion region, the portion being closer to the second main surface,
• the first contact hole is formed so as to penetrate the interlayer insulating film and to expose the second impurity diffusion region from the first contact hole,
• the second contact hole is formed so as to penetrate the interlayer insulating film and to expose the polysilicon film from the second contact hole,
• first etching, second etching and third etching are performed in the step of forming the first contact hole and the second contact hole,
• the second etching is performed after the first etching,
• the third etching is performed after the second etching,
• after the first etching and before the second etching, the first main surface is exposed from the first contact hole while the interlayer insulating film remains in a bottom surface of the second contact hole,
• after the second etching and before the third etching, the second impurity diffusion region is exposed from the first contact hole while the interlayer insulating film remains in the bottom surface of the second contact hole, and
• after the third etching, the polysilicon film is exposed from the second contact hole.