Method of manufacturing a transistor

A transistor comprising:

• a semiconductor substrate having a semiconductor layer, a drain layer of a first conductivity type disposed on the semiconductor layer and an opposite conductive region of a second conductivity type disposed on the drain layer;
• a semiconductor material disposed in part of the drain layer and constituted so that a depletion layer can be formed therein;
• a gate trench disposed from a surface of the opposite conductive region to the semiconductor material;
• a source region of the first conductivity type formed on the surface of the opposite conductive region at a position adjacent to the gate trench;
• a gate insulating film positioned on the inner surface of the gate trench and disposed over the drain layer, the opposite conductive region and the source region;
• and
• a gate electrode film disposed in the gate trench in tight contact with the gate insulating film and insulated from the semiconductor material, wherein the semiconductor material is filled at the bottom of a deep trench disposed from the surface of the opposite conductive region to the inside of the drain layer;
• and
• the gate trench is formed by the surface of the semiconductor material and the inner peripheral surface of the deep trench.

A method of manufacturing a transistor, comprising the steps of:

• forming a deep trench in a semiconductor substrate having a drain layer of a first conductivity type and an opposite conductive region of a second conductivity type disposed on the drain layer from a surface of the opposite conductive region to the drain layer;
• filling a semiconductor material in the deep trench from the bottom surface of the deep trench to a depth not reaching the opposite conductive region to be constituted so that a depletion layer can be formed therein;
• forming a gate insulating film from the surface of the semiconductor material over the inner surface of the gate trench constituted by the surface of the semiconductor material and the deep trench;
• forming a gate electrode film in which impurities of the first conductivity type are diffused in the gate trench so as to come into tight contact with the gate insulating film, and
• forming a source region of the first conductivity type in the semiconductor substrate surface surrounding the gate trench.