Silicon carbide semiconductor device and method for manufacturing same

Abstract

A silicon carbide semiconductor device includes: a substrate; a drift layer over the substrate; a base region over the drift layer; multiple source regions over an upper layer portion of the base region; a contact region over the upper layer portion of the base region between opposing source regions; multiple trenches from a surface of each source region to a depth deeper than the base region; a gate electrode on a gate insulating film in each trench; a source electrode electrically connected to the source regions and the contact region; a drain electrode over a rear surface of the substrate; and multiple electric field relaxation layers in the drift layer between adjacent trenches. Each electric field relaxation layer includes: a first region at a position deeper than the trenches; and a second region from a surface of the drift layer to the first region.

1 . A silicon carbide semiconductor device comprising:
 a substrate having a first conductivity type or a second conductivity type and made of silicon carbide;   a drift layer disposed over the substrate, made of silicon carbide, and having the first conductivity type with an impurity concentration lower than the substrate;   a base region disposed over the drift layer, made of silicon carbide, and having the second conductivity type;   a plurality of source regions disposed over an upper layer portion of the base region, made of silicon carbide, and having the first conductivity type with an impurity concentration higher than the drift layer;   a contact region disposed over the upper layer portion of the base region between opposing source regions, made of silicon carbide, and having the second conductivity type with an impurity concentration higher than the base layer;   a plurality of trenches disposed from a surface of each source region to a depth deeper than the base region, and arranged in parallel to each other along one direction as a longitudinal direction;   a gate insulating film arranged on an inner wall of each trench;   a gate electrode arranged on the gate insulating film in each trench;   a source electrode electrically connected to the source regions and the contact region;   a drain electrode arranged over a rear surface of the substrate; and   a plurality of electric field relaxation layers disposed in the drift layer located below the base region, spaced apart from a side of each trench, arranged between adjacent trenches along a direction as a longitudinal direction parallel to the longitudinal direction of the trenches, made of silicon carbide, and having the second conductivity type, wherein:   each of the plurality of electric field relaxation layers includes: a first region that is arranged at a position deeper than the trenches; and a second region that is arranged from a surface of the drift layer to the first region, has an impurity concentration lower than the first region, and has a uniform impurity concentration.   
     
     
         2 . The silicon carbide semiconductor device according to  claim 1 , wherein:
 the drift layer has a concave portion at a position corresponding to the second region; and   the second region is an embedded region made of silicon carbide, having the second conductivity type, and embedded in the concave portion.   
     
     
         3 . The silicon carbide semiconductor device according to  claim 2 , wherein:
 the first region is an ion implantation region of an impurity having the second conductivity type under a bottom of the concave portion.   
     
     
         4 . The silicon carbide semiconductor device according to  claim 1 , wherein:
 each of the first region and the second region is an ion implantation region of an impurity having the second conductivity type in the drift layer; and   the ion implantation region is provided in a box profile.   
     
     
         5 . The silicon carbide semiconductor device according to  claim 1 , wherein:
 a distance between adjacent second regions in the plurality of electric field relaxation layers is defined as W 1 ;   a distance between adjacent first regions in the plurality of electric field relaxation layers is defined as W 2 ; and   a relationship of “W 1 >W 2 ” is satisfied.   
     
     
         6 . The silicon carbide semiconductor device according to  claim 1 , wherein:
 a distance between adjacent first regions in the plurality of electric field relaxation layers is defined as W 2 ;   a width of a trench gate structure, in which the gate insulating film and the gate electrode are disposed in each of the trenches, is defined as W 3 ; and   a relationship of “W 2 >W 3 ” is satisfied.   
     
     
         7 . The silicon carbide semiconductor device according to  claim 1 , wherein:
 a portion of the drift layer that is located above the first region and surrounds at least a bottom of a trench gate structure, in which the gate insulating film and the gate electrode are disposed in each of the trenches, is a high impurity concentration layer having the impurity concentration of the first conductivity type impurity higher than a remaining portion of the drift layer.   
     
     
         8 . A method of manufacturing a silicon carbide semiconductor device comprising:
 forming a drift layer, made of silicon carbide and having a first conductivity type with an impurity concentration lower than a substrate, over the substrate made of silicon carbide and having the first conductivity type or a second conductivity type;   forming a plurality of electric field relaxation layers, having the second conductivity type in the drift layer and arranged in parallel to each other along one direction as a longitudinal direction, in the drift layer;   forming a base region, made of silicon carbide and having the second conductivity type, over the electric field relaxation layers and the drift layer;   forming a plurality of source regions, made of silicon carbide and having the first conductivity type with an impurity concentration higher than the drift layer, over an upper layer portion of the base region in the base region;   forming a contact region, made of silicon carbide and having the second conductivity type with an impurity concentration higher than the base layer, over the upper layer portion of the base region between opposing source regions;   forming a plurality of trenches disposed from a surface of each source region, penetrating the base region, reaching the drift layer, having a bottom shallower than a bottom of each electric field relaxation layer, spaced apart from the electric field relaxation layers, and arranged along a direction as a longitudinal direction parallel to the longitudinal direction of the electric field relaxation layers;   forming a gate insulating film on a surface of each trench;   forming a gate electrode on the gate insulating film in each trench;   forming a source electrode electrically connected to the source regions and the contact region; and   forming a drain electrode over a rear surface of the substrate, wherein:   the forming of the electric field relaxation layers includes:
 forming a first region at a position deeper than the trenches; and 
 forming a second region arranged from a surface of the drift layer to the first region, having an impurity concentration lower than the first region, and having a uniform impurity concentration. 
   
     
     
         9 . The method of manufacturing the silicon carbide semiconductor device according to  claim 8 , wherein:
 the forming of the electric field relaxation layers includes:
 forming a concave portion at a position of the drift layer corresponding to the second region; 
 forming the first region by ion-implanting an impurity having the second conductivity type below a bottom of the concave portion in the drift layer; and 
 forming the second region in the concave portion by an epitaxial growth after the forming of the first region. 
   
     
     
         10 . The method of manufacturing the silicon carbide semiconductor device according to  claim 9 , wherein:
 the forming of the second region includes:
 forming the second region in the concave portion by an epitaxial growth; and 
 simultaneously forming the base region over the drift layer by an epitaxial growth as the forming of the base region. 
   
     
     
         11 . The method of manufacturing the silicon carbide semiconductor device according to  claim 8 , wherein:
 the forming of the electric field relaxation layers includes:
 forming the first region and the second region by ion-implanting 
   an impurity having the second conductivity type on the surface of the drift layer with different acceleration voltages after the forming of the drift layer; and
 performing the ion-implanting by a box profile when forming the second region. 
   
     
     
         12 . The method of manufacturing the silicon carbide semiconductor device according to  claim 8 , wherein:
 the forming of the drift layer includes:
 increasing an impurity concentration of the second conductivity type in a portion of the drift layer located above the first region to be higher than a remaining portion of the drift layer. 
   
     
     
         13 . The method of manufacturing the silicon carbide semiconductor device according to  claim 8 , wherein:
 the forming of the drift layer includes:
 increasing the impurity concentration of the first conductivity type in a portion of the drift layer, located above the first region and surrounding at least a bottom of a trench gate structure in which the gate insulating film and the gate electrode are disposed in each trench, to be higher than a remaining portion of the drift layer; 
   the forming of the first region includes:
 forming the first region by ion-implanting an impurity having the second conductivity type after the forming of the remaining portion of the drift layer; and 
 forming a portion of the drift layer located above the first region after the forming of the first region; and 
   the forming of the second region includes:
 forming a concave portion at a position of the drift layer corresponding to the second region and located above the first region; and 
 then, forming the second region in the concave portion by an epitaxial growth. 
   
     
     
         14 - 18 . (canceled)