Method of manufacturing semiconductor device

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

• (a) preparing a semiconductor substrate of a first conductivity type having an upper surface and a bottom surface opposite to the upper surface;
• (b) after the step of (a), forming a first resist pattern on the upper surface of the semiconductor substrate;
• (c) after the step of (b), forming a first ion-implantation layer and a second ion-implantation layer in the semiconductor substrate by performing a first ion-implantation with a first ion-implantation energy by using the first resist pattern as a mask;
• (d) after the step of (c), forming a third ion-implantation layer at a position overlapping the first ion-implantation layer in the semiconductor substrate in plan view and forming a fourth ion-implantation layer at a position overlapping the second ion-implantation layer in the semiconductor substrate in plan view by performing a second ion-implantation with a second ion-implantation energy different of the first ion-implantation energy by using the first resist pattern as a mask;
• (e) after the step of (d), removing the first resist pattern;
• (f) after the step of (e), by performing a first heat treatment for the semiconductor substrate, forming a first impurity region of a second conductivity type opposite to the first conductivity type by diffusing impurities included in the first ion-implantation layer and the third ion-implantation layer and forming a second impurity region of the second conductivity type by diffusing impurities included in the second ion-implantation layer and the fourth ion-implantation layer;
• (g) after the step of (f), forming a first trench and a second trench on the upper surface of the semiconductor substrate;
• (h) after the step of (g), forming a first gate insulating film in the first trench and forming a second gate insulating film in the second trench;
• and
• (i) after the step of (h), forming a first gate electrode so as to fill in the first trench via the first gate insulating film and forming a second gate electrode so as to fill in the second trench via the second gate insulating film, wherein
• the first trench has a first side surface, a second side surface facing to the first side surface and a first bottom surface connecting the first side surface and the second side surface,
• the second trench has a third side surface, a fourth side surface facing to the third side surface and a second bottom surface connecting the third side surface and the fourth side surface,
• the first trench and the second trench are spaced apart such that the second side surface and the third side surface are adjacent each other,
• the first impurity region is formed in the semiconductor substrate close to the first side surface and covers the first bottom surface so as to pass under and not substantially contact the second side surface,
• the second impurity region is formed in the semiconductor substrate close to the fourth side surface and covers the second bottom surface so as to pass under and not substantially contact the third side surface,
• the first impurity region and the second impurity region are spaced apart from each other,
• the first ion-implantation energy is larger than the second ion-implantation energy, and
• in the step of (g), the first trench and the second trench are formed so that a position of each of the first bottom surface and the second bottom surface is shallower than peak positions of an impurity concentration of each of the first ion-implantation layer and the second ion-implantation layer.