Silicon carbide semiconductor device

Abstract

A gate insulating film is provided on a trench. The gate insulating film has a trench insulating film and a bottom insulating film. The trench insulating film covers each of a side wall and a bottom portion. The bottom insulating film is provided on the bottom portion with a trench insulating film being interposed therebetween. The bottom insulating film has a carbon atom concentration lower than that of the trench insulating film. The gate electrode is in contact with a portion of the trench insulating film on the side wall. Accordingly, a low threshold voltage and a large breakdown voltage can be attained.

What is claimed is: 
     
         1 . A silicon carbide semiconductor device comprising:
 a silicon carbide substrate including a first layer having first conductivity type, a second layer provided on said first layer and having second conductivity type, and a third layer provided on said second layer, separated from said first layer by said second layer, and having said first conductivity type, said silicon carbide substrate being provided with a trench having a side wall and a bottom portion, said side wall extending through said third layer and said second layer and reaching said first layer, said bottom portion being formed of said first layer;   a gate insulating film provided on said trench, said gate insulating film including a trench insulating film and a bottom insulating film, said trench insulating film covering each of said side wall and said bottom portion, said bottom insulating film being provided on said bottom portion with said trench insulating film being interposed therebetween, said bottom insulating film having a carbon atom concentration lower than that of said trench insulating film; and   a gate electrode provided in said trench, said gate electrode being in contact with a portion of said trench insulating film on said side wall.   
     
     
         2 . The silicon carbide semiconductor device according to  claim 1 , wherein a total of a thickness of said trench insulating film on said bottom portion and a thickness of said bottom insulating film is larger than a thickness of said trench insulating film on said side wall. 
     
     
         3 . The silicon carbide semiconductor device according to  claim 1 , wherein on said bottom portion, a thickness of said bottom insulating film is larger than that of said trench insulating film. 
     
     
         4 . The silicon carbide semiconductor device according to  claim 1 , wherein a thickness of said trench insulating film on said bottom portion is smaller than a thickness of said trench insulating film on said side wall. 
     
     
         5 . The silicon carbide semiconductor device according to  claim 1 , wherein the carbon atom concentration of said trench insulating film is more than 1×10 15  cm −3 , and the carbon atom concentration of said bottom insulating film is less than 1×10 15  cm −3 . 
     
     
         6 . The silicon carbide semiconductor device according to  claim 1 , wherein said bottom insulating film has a thickness of more than 100 nm. 
     
     
         7 . The silicon carbide semiconductor device according to  claim 1 , wherein said trench insulating film is a thermal oxidation film of silicon carbide. 
     
     
         8 . The silicon carbide semiconductor device according to  claim 1 , wherein said bottom insulating film is formed of at least any one of silicon oxide, silicon nitride, and phosphorus silicate glass. 
     
     
         9 . The silicon carbide semiconductor device according to  claim 1 , wherein said bottom insulating film is a thermal oxidation film of a film containing silicon and containing no carbon.