Manufacturing method of semiconductor device

A manufacturing method of a semiconductor device, the device including a semiconductor substrate made from silicon carbide and including a first conductivity type drain layer, a first conductivity type drift layer making contact with a front face of the drain layer, a second conductivity type body layer making contact with a front face of the drift layer, a first conductivity type source layer provided in part of a front face of the body layer, and a second conductivity type floating layer surrounded by the drift layer, and a trench gate which includes a gate insulating film formed on an inner wall of a trench and a gate electrode disposed inside the gate insulating film and which has a bottom portion making contact with the floating layer, the floating layer covering the bottom portion of the gate electrode, the manufacturing method comprising:

• forming the trench in a semiconductor wafer so as to have a bottom portion in which an end portion in a short direction perpendicular to a longitudinal direction thereof is deeper than a central portion;
• forming the floating layer by injecting second conductivity type impurity ions into the bottom portion of the trench after forming the trench;
• and
• forming the central portion of the trench in the short direction to be deeper than a depth of the end portion so as not to penetrate the floating layer to the drift layer after forming the floating layer, wherein
• the central portion of the trench in the short direction is deepened within an area defined by the diffusion of the second conductivity type impurity ions.