Insulated-gate semiconductor device and method of manufacturing the same

An insulated-gate semiconductor comprising:

• a first trench having a first sidewall surface;
• a second trench having a second sidewall surface facing the first sidewall surface;
• a first conductivity type main-electrode region being in contact with the first sidewall surface;
• a second conductivity type base region being in contact with a bottom surface of the main-electrode region and the first sidewall surface;
• a first conductivity type drift layer being in contact with the first sidewall surface and a bottom surface of the base region and having an impurity concentration lower than the main-electrode region;
• and
• a second conductivity type trench below region provided below the second trench,
• wherein the first trench and the second trench are in striped shape and extend parallel to each other, and
• a boundary between an end of the trench below region on the second sidewall surface side and the drift layer is formed in a stepwise manner, in a cross section perpendicular to an extending direction of the first trench and the second trench.

A method for manufacturing an insulated-gate semiconductor device, the insulated gate semiconductor device comprising:

• a first trench having a first sidewall surface;
• a second trench having a second sidewall surface facing the first sidewall surface;
• a first conductivity type main-electrode region being in contact with the first sidewall surface;
• a second conductivity type base region being in contact with a bottom surface of the main-electrode region and the first sidewall surface;
• a second conductivity type gate protection-region being in contact with a bottom surface of the second trench;
• and
• a second conductivity type bottom region being in contact with a bottom surface of the gate protection-region,
• wherein the bottom surface of the gate protection-region is formed shallower than the bottom surface of the bottom region.