Method for manufacturing a vertical semiconductor device

A method of manufacturing a semiconductor device, comprising:

• forming a base layer of a second conductivity type in an upper part of a substrate of a first conductivity type so that the base layer has a thickness smaller than a thickness of the substrate, while allowing a remaining region of the substrate to remain as a drain region of the first conductivity type;
• forming a trench which reaches the drain region from the front surface of the substrate;
• forming a gate insulating film on an inner bottom surface and an inner side surface of the trench;
• embedding a gate electrode into the trench via the gate insulating film;
• etching the gate electrode so that an upper surface of the gate electrode locates a first height from the bottom of the trench;
• forming a source region by implanting impurities from an inner side of the trench, the source region being in contact with a part of an outer side surface of the trench and at least having a depth from the front surface of the substrate to the first height;
• etching the gate insulating film so that an upper end portion of the gate insulating film locates the first height;
• forming a first insulating film on the gate insulating film and the gate electrode in the trench to a second height which is higher than the first height;
• forming a base contact region of the second conductivity type having a depth from the front surface of the substrate to a third height which is higher than the second height and lower than an opening end of the trench;
• forming a second insulating film directly on the base layer,
• wherein the base contact region is in contact with another part of the outer side surface of the trench, an upper part of the base layer, an upper part of the source region, a side surface in contact with the base layer, and having an upper surface in contact with the second insulating layer, and having a higher impurity concentration than the base layer;
• and
• forming a source electrode on the first insulating film so that the source electrode is embedded in a remaining part of the trench, the source electrode being in contact with the source region and the base contact region.