Method of forming a semiconductor device

Abstract

In one embodiment, a transistor has a drift region that is formed to have a plurality of zones having different vertical doping profiles across the zones. At least one of the zones has a vertical doping profile that has a first peak near a top surface of the zone and a second peak near a bottom surface. An embodiment may have a lower doping in a region that is between the two peaks.

1 . A method of forming a semiconductor device, the method comprising:
 forming a first doped region of a first conductivity type having a first active doping concentration, the first doped region having a first surface and a first depth;   forming a drift region of a second conductivity type within the first doped region, the drift region having a first lateral distance across the first doped region;   forming within the drift region a second doped region of the second conductivity type and having a second active doping concentration, positioning the second doped region a second depth from the first surface in a first portion of the drift region, positioned a third depth from the first surface in a second portion of the drift region that is adjacent the first portion of the drift region, and positioned substantially the third depth in a third portion of the drift region wherein the second portion of the drift region is in-between the first portion and the third portion; and   forming within the third portion of the drift region a third doped region of the second conductivity type and a third active doping concentration,   wherein the third doped region is substantially not in the first portion of the drift region and substantially not in the second portion of the drift region,   wherein the third depth is greater than the second depth,   wherein the drift region has a fourth active doping concentration extending from the second doped region to the third doped region, and   wherein the fourth active doping concentration is less than the second active doping concentration and less than the third active doping concentration.   
     
     
         2 . The method of  claim 1 , further including forming the third active doping concentration to be substantially the same as the second active doping concentration. 
     
     
         3 . The method of  claim 1 , further including forming an opening extending into the drift region and overlying the second portion of the drift region and the third portion of the drift region but not overlying the first portion of the drift region,
 wherein the second doped region that is within the second portion of the drift region and the third portion of the drift region underlies the opening.   
     
     
         4 . The method of  claim 1 , further including forming a fourth doped region of the first conductivity type and a fourth active doping concentration, forming the fourth doped region in the second portion of the drift region and the third portion of the drift region and overlying the second doped region. 
     
     
         5 . The method of  claim 1 , further including forming a fourth doped region of the first conductivity type and a fourth active doping concentration within the second portion of the drift region and positioned substantially the third depth from the first surface. 
     
     
         6 . A method of forming a semiconductor device, the method comprising:
 forming an opening in a first doped region of a first conductivity type and a first doping concentration;   forming a second doped region of a second conductivity type in the first doped region, wherein forming the second doped region includes doping a first portion of the first doped region that underlies the opening and doping a second portion of the first doped region that is adjacent the opening; and   forming a third doped region of the first conductivity type and a second doping concentration,   wherein a first portion of the third doped region is outside of and adjacent the opening,   wherein a second portion of the third doped region underlies a portion of the opening that is adjacent the first portion of the third doped region, and   wherein the second doping concentration is different from the first doping concentration.   
     
     
         7 . The method of  claim 6 , wherein forming the second doped region further includes applying a first mask that exposes the opening and exposes the second portion of the first doped region. 
     
     
         8 . The method of  claim 7 , wherein forming the third doped region includes forming a second mask. 
     
     
         9 . The method of  claim 6 , further comprising forming the first doped region on a substrate. 
     
     
         10 . The method of  claim 9 , wherein the first doped region comprises an epitaxial layer. 
     
     
         11 . The method of  claim 6 ,
 wherein a lower portion of the second doped region has a third doping concentration,   wherein an upper portion of the second doped region that is adjacent a bottom of the opening has the third doping concentration, and   wherein a region that is between the upper and lower portions of the second doped region has a fourth doping concentration that is lower than the third doping concentration.   
     
     
         12 . The method of  claim 6 ,
 wherein forming the second doped region includes using a series of chain implants to form the second doped region with a third doping concentration adjacent a bottom of the second doped region, a fourth doping concentration adjacent a bottom of the opening, and a fifth doping concentration in a region between the bottom of the opening and the bottom of the second doped region, and   wherein the fifth doping concentration is less than the third doping concentration and less than the fourth doping concentration.   
     
     
         13 . The method of  claim 6 , further including forming the third doped region prior to forming the second doped region. 
     
     
         14 . The method of  claim 6 , wherein the second doping concentration is higher than the first doping concentration. 
     
     
         15 . A method of forming a semiconductor device, the method comprising:
 forming an opening in a first doped region of a first conductivity type and a first doping concentration;   doping a first section of the first doped region with a first dopant of a second conductivity type, wherein the first section includes a first portion that underlies the opening and second portions that are outside, and adjacent opposite sides of, the opening; and   doping a second section of the first doped region with a second dopant of the first conductivity type, wherein the second section has a first part that is outside of the opening and on one side of the opening and has a second part that underlies a portion of the opening that is adjacent the first part.   
     
     
         16 . The method of  claim 15 , wherein doping the second section is performed after doping the first section. 
     
     
         17 . The method of  claim 15 , wherein doping the second section is performed before doping the first section. 
     
     
         18 . The method of  claim 15 , wherein doping the first section of the first doped region includes varying dopant concentrations of the second conductivity type at different depths to form a second doped region having a second doping concentration adjacent a bottom of the second doped region, a third doping concentration adjacent a bottom of the opening, and a fourth doping concentration in a region between the bottom of the opening and the bottom of the second doped region, wherein the fourth doping concentration is less than the second doping concentration and less than the third doping concentration. 
     
     
         19 . The method of  claim 15 ,
 wherein doping the first section comprises forming a second doped region of the second conductivity type, and   wherein doping the second section comprises counter-doping the second doped region.   
     
     
         20 . The method of  claim 15 ,
 wherein doping the first section forms a drift region of the semiconductor device, and   wherein doping the second section provides the second dopant along a bottom of the drift region.