Manufacturing method of semiconductor device

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

• (a) preparing a substrate that includes a semiconductor substrate, an insulating layer on the semiconductor substrate, a semiconductor layer on the insulating layer, a first insulating film on the semiconductor layer, a trench penetrating the first insulating film, the semiconductor layer and the insulating layer so as to reach the semiconductor substrate, and a second insulating film embedded in the trench,
• the insulating layer, the first insulating film and the second insulating film being made of the same material as one another;
• (b) after the step (a), forming a first mask layer that covers the first insulating film in a first region of the substrate and exposes the first insulating film in a second region different from the first region of the substrate;
• (c) after the step (b), removing the first insulating film in the second region by etching using the first mask layer as an etching mask, thereby exposing the semiconductor layer in the second region;
• (d) after the step (c), removing the semiconductor layer in the second region by isotropic dry etching using the first mask layer as an etching mask, thereby exposing the insulating layer in the second region;
• (e) after the step (d), performing etching for the insulating layer in the second region using the first mask layer as an etching mask, thereby reducing a thickness of the insulating layer in the second region;
• (f) after the step (e), removing the first mask layer;
• (g) after the step (f), forming a first semiconductor region by ion-implanting an impurity to the semiconductor substrate in the first region, and forming a second semiconductor region by ion-implanting an impurity to the semiconductor substrate in the second region;
• (h) after the step (g), removing the first insulating film in the first region and the insulating layer in the second region by wet etching, thereby exposing the semiconductor layer in the first region and the semiconductor substrate in the second region;
• and
• (i) after the step (h), forming a first transistor on the semiconductor layer in the first region, and forming a second transistor on the semiconductor substrate in the second region.