Semiconductor device

Abstract

A semiconductor device including: a source region formed at one main face of a semiconductor substrate; a drain region formed at the one main face and connected to the source region through a channel region; a gate electrode formed above the channel region; a drift layer formed at the one main face at a position between a lower portion of the gate electrode and the drain region; a trench including an opening in which one end is at the lower portion of the gate electrode and another end is at a position adjacent to the drain region, the trench being formed in the semiconductor substrate at a predetermined depth from the one main face to cut vertically across the drift layer; and an electrical field weakening portion, provided at vicinity of the one end, that weaken an electrical field generated between the source region and the drain region.

What is claimed is: 
     
         1 . A semiconductor device comprising:
 a semiconductor substrate;   a source region having a first conductivity type formed at one main face of the semiconductor substrate;   a drain region having the first conductivity type formed at the one main face and connected to the source region through a channel region;   a gate electrode formed above the channel region with an insulating film therebetween;   a drift layer having the first conductivity type formed at the one main face at a position between a lower portion of the gate electrode and the drain region;   a trench including an opening in which one end is at the lower portion of the gate electrode and another end is at a position adjacent to the drain region, the trench being formed in the semiconductor substrate at a predetermined depth from the one main face to cut vertically across the drift layer; and   an electrical field weakening portion provided at vicinity of the one end, the electrical field weakening section weaken an electrical field generated between the source region and the drain region.   
     
     
         2 . The semiconductor device of  claim 1 , further comprising:
 a first region having a second conductivity type formed at the one main face to include the source region; and   a second region having the first conductivity type formed at the one main face to include the drain region, and having a lower impurity concentration than the drift layer,   wherein an interface between the first region and the second region is positioned below the gate electrode.   
     
     
         3 . The semiconductor device of  claim 1 , wherein the drift layer includes a plurality of diffusion layers having the first conductivity type and are formed at different distances from the one main face. 
     
     
         4 . The semiconductor device of  claim 1 , wherein an interior of the trench is filled with an insulator. 
     
     
         5 . The semiconductor device of  claim 1 , wherein the electrical field weakening portion is an electrical field weakening electrode provided in the interior of the trench. 
     
     
         6 . The semiconductor device of  claim 5 , wherein the electrical field weakening electrode is an enlarged gate electrode formed by extending the gate electrode from the gate electrode, vertically across the insulating film, and into the interior of the trench. 
     
     
         7 . The semiconductor device of  claim 5 , wherein the electrical field weakening electrode is a second gate electrode different from the gate electrode and is formed in the interior of the trench. 
     
     
         8 . The semiconductor device of  claim 1 , wherein the electrical field weakening portion includes one or more corners opposing a side face of the trench that is connected to the one end of the opening. 
     
     
         9 . The semiconductor device of  claim 1 , wherein the electrical field weakening portion is formed of polysilicon. 
     
     
         10 . The semiconductor device of  claim 1 , further comprising sidewalls formed at two sides of the gate electrode and the insulating film,
 wherein the one end of the opening is disposed below the sidewall at the drain region side.   
     
     
         11 . The semiconductor device of  claim 1 , wherein the electrical field weakening portion is a thickened film portion at which the insulating film is formed thicker above the one end of the opening. 
     
     
         12 . The semiconductor device of  claim 1 , wherein the electrical field weakening portion is an implantation region having a second conductivity type implanted in the drift layer in the vicinity of the one end of the opening. 
     
     
         13 . The semiconductor device of  claim 12 , wherein:
 the drift layer includes a plurality of diffusion layers that have the first conductivity type and are formed with different distances from the one main face; and   the implantation region is implanted in a diffusion layer closest to the one main face among the plurality of diffusion layers.