Semiconductor device and manufacturing method thereof

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

• (a) preparing a semiconductor substrate;
• (b) forming a projecting portion serving as a part of the semiconductor substrate, projected from a main surface of the semiconductor substrate, and extending in a first direction when seen in a plan view;
• (c) forming, over the projecting portion, a first gate electrode extending in a second direction intersecting with the first direction when seen in a plan view and forming a first gate insulating film between the first gate electrode and the projecting portion;
• (d) forming, on the projecting portion and on a front surface of the first gate electrode, an insulating film including a charge storage unit inside;
• (e) forming a conductive film on the insulating film;
• (f) etching back the conductive film to leave the conductive film on a first side of the first gate electrode in the first direction via the insulating film, thereby forming a second gate electrode, and forming a second gate insulating film including the insulating film between the second gate electrode and the projecting portion and between the second gate electrode and the first gate electrode when seen in a plan view,
• wherein, in the step (b), the projecting portion including a first region and a second region arranged on the first side with respect to the first region when seen in a plan view is formed,
• wherein, in the step (c), the first gate electrode covering a first upper surface of the first region, a first side surface of the first region on a second side in the second direction, and a second side surface of the first region on an opposite side of the second side in the second direction is formed,
• wherein the step (d) includes the steps of:
• (d1) etching the second region after the step (c), thereby making a second upper surface of the second region lower than the first upper surface, and making a third side surface of the second region on the second side recede to the opposite side of the second side with respect to the first side surface in the second direction;
• and
• (d2) forming the insulating film, after the step (d1), on the second upper surface, the third side surface, a fourth side surface on the opposite side of the second side of the second region in the second direction, and the front surface of the first gate electrode, and
• wherein, in the step (f), the second gate electrode covering the second upper surface, the third side surface, and the fourth side surface is formed.