Semiconductor device

Abstract

A semiconductor device includes: a silicon substrate, having a main surface, in which trenches are formed; element isolation oxide films filling in trenches; a tunnel oxide film, formed on main surface located between element isolation oxide film and element isolation oxide film, having birds beak portions in birds beak forms that bring into contact with element isolation oxide film and element isolation oxide film, respectively; and a polysilicon film, formed on tunnel oxide film, having a thickness exceeding 0 and being less than 50 nm in an intermediate portion between element isolation oxide film and element isolation oxide film, and being thinner than the above thickness on birds beak portions. Thereby, it is possible to provide a semiconductor device wherein birds beaks are formed in the gate insulating film so as to have the desired dimensions and wherein the gate insulating film has excellent electrical characteristics.

1 . A semiconductor device comprising: 
 a semiconductor substrate, having a main surface, in which first and second trenches are formed in said main surface at a distance away from each other;    first and second isolation insulating films filling in said first and second trenches;    a gate insulating film, formed on said main surface located between said first isolation insulating film and said second isolation insulating film, including silicon, having an end portion in a birds beak form which brings into contact with said first isolation insulating film and said second isolation insulating film, respectively; and    a silicon film formed on said gate insulating film, having a thickness exceeding 0 and being less than 50 nm in an intermediate portion between said first isolation insulating film and said second isolation insulating film, and being thinner than said thickness on said end portion.    
   
   
       2 - 9 . (canceled)  
   
   
       10 . A manufacturing method for a semiconductor device, comprising the steps of: 
 forming a gate insulating film including silicon on a main surface of a semiconductor substrate;    forming a silicon film having a thickness exceeding 0 and being less than 50 nm on said gate insulating film;    forming a mask film for exposing said silicon film at positions, respectively, located at a distance away from each other, on said silicon film;    sequentially etching said silicon film, said gate insulating film and said semiconductor substrate using said mask film as a mask, thereby exposing sidewalls of said silicon film while forming first and second trenches in said semiconductor substrate; and    oxidizing the sidewalls of said silicon film, thereby forming birds beak portions at positions adjacent to said gate insulating film.    
   
   
       11 . The manufacturing method for a semiconductor device according to  claim 10 , further comprising the steps of: 
 forming first and second isolation insulating films filling in said first and second trenches after said step of forming said birds beak portions;    removing said mask film; and    forming a conductive film, including silicon, so as to cover said silicon film as well as said fist and second isolation insulating films.    
   
   
       12 . The manufacturing method for a semiconductor device according to  claim 11 , wherein 
 each of said first and second isolation insulating films has a second top surface, and the distance from said main surface to said second top surface is at least 20 nm.    
   
   
       13 . The manufacturing method for a semiconductor device according to  claim 11 , wherein 
 each of said first and second isolation insulating films has a second top surface, and the distance from said main surface to said second top surface is at least the sum of the thickness of said gate insulating film and said silicon film.    
   
   
       14 . The manufacturing method for a semiconductor device according to  claim 11 , wherein 
 the thickness of said conductive film is at least 50 nm and at most 200 nm.    
   
   
       15 . The manufacturing method for a semiconductor device according to  claim 11 , wherein 
 each of said first and second isolation insulating films has a second top surface, and said conductive film is formed to cover at least part of said second top surface.    
   
   
       16 . The manufacturing method for a semiconductor device according to  claim 11 , further comprising the step of 
 removing said silicon film after said step of removing said mask film.    
   
   
       17 . The manufacturing method for a semiconductor device according to  claim 11 , further comprising the step of 
 forming a well region by implanting an impurity into said semiconductor substrate before said step of forming said gate insulating film.    
   
   
       18 . The manufacturing method for a semiconductor device according to  claim 11 , further comprising the step of 
 forming a well region by implanting an impurity into said semiconductor substrate after said step of removing said mask film.    
   
   
       19 . The manufacturing method for a semiconductor device according to  claim 10 , wherein 
 said step of forming said first and second trenches includes the steps of:    forming recesses, whose bottoms are defined by said semiconductor substrate, by sequentially etching said silicon film, said gate insulating film and said semiconductor substrate using said mask film as a mask;    forming sidewall insulating films that make contact with sides of said silicon films and said gate insulating films, and that cover portions of bottoms of said recesses so that remaining portion of the bottoms of said recesses are exposed; and    forming said first and second trenches by etching portions of semiconductor substrate that are exposed from said sidewall insulating films using said sidewall insulating films as a mask.    
   
   
       20 . The manufacturing method for a semiconductor device according to  claim 19 , further comprising the step of 
 removing said sidewall insulating films before said step of forming said birds beak portions.