Semiconductor device and method for manufacturing the same

Abstract

A semiconductor device is provided in which a lowering in the breakdown voltage of a gate insulating film (nitrided silicon oxide film) in a boundary region between the upper-end corner portion of the side wall of an element isolating groove and a silicon substrate in the end portion of an element forming region which is formed in contact therewith can be suppressed without causing an increase in the number of steps (time for effecting the steps). An element isolation insulating film is filled into the internal portion of the element isolating groove to cover the end portion of the silicon substrate in the element forming region which is formed in contact with the upper-end portion of the side wall of the element isolating groove, nitrogen is selectively doped into the surface of the silicon substrate in a region of the element forming region other than the end portion thereof with the element isolation insulating film used as a mask, then a portion of the element isolation insulating film lying outside the element isolating groove is removed to expose the upper-end portion of the side wall, and a nitrided silicon oxide film used as the gate insulating film is formed by the heat treatment in an atmosphere containing an oxidizing agent.

1 . A semiconductor device comprising: 
 a silicon substrate including an element forming region, an element isolating region, and a boundary region including the boundary between the element forming region and the element isolating region; and    a gate insulating film formed on the surface of the silicon substrate to extend from the element forming region to the element isolating region across the boundary region,    wherein the gate insulating film includes either of a silicon nitride film or a silicon oxide film containing nitrogen and is formed in a self-alignment manner to make the thickness of the gate insulating film on the boundary region greater than the thickness of the gate insulating film in the regions other than the boundary region.    
     
     
         2 . The semiconductor device according to  claim 1 , wherein said gate insulating film is of laminated structure including said silicon nitride film.  
     
     
         3 . A method for manufacturing a semiconductor device according to  claim 1 , comprising the steps of: 
 dividing said silicon substrate into said element forming region and said element isolating region;    doping nitrogen into the surface of said silicon substrate in said element forming region; and    forming said gate insulating film on the surface of said silicon substrate so that said gate insulating film can extend from said element forming region to said element isolating region across said boundary region, by the heat treatment in an atmosphere containing an oxidizing agent.    
     
     
         4 . The method according to  claim 3 , wherein: 
 said step of dividing said silicon substrate into said element forming region and said element isolating region is conducted by forming an element isolating groove in the surface of said silicon substrate,    said step of doping nitrogen into the surface of said silicon substrate in said element forming region comprises the steps of: 
 filling an element isolation insulatingfilm into the internal portion of the element isolating groove to cover said silicon substrate at the upper-end corner portion of the side wall formed by said element isolating groove;  
 selectively doping nitrogen into the surface of the silicon substrate in a portion of the element forming region by using the element isolation insulating film as a mask, and  
 said step of forming said gate insulating film further comprises a step of removing a portion of said element isolation insulating film lying outside said element isolating groove so that the upper-end corner portion of the side wall can be exposed.  
   
     
     
         5 . The method according to  claim 4 , wherein a film of laminated structure having a nitrided silicon oxide film is used as said gate insulating film in said step of forming the gate insulating film.  
     
     
         6 . The method according to  claim 4 , wherein radical nitrogen is used for the doping of nitrogen in said step of selectively doping nitrogen.  
     
     
         7 . The method according to  claim 4 , wherein the doping of nitrogen is conducted by using an ion-implantation method.  
     
     
         8 . A method for manufacturing the semiconductor device according to  claim 1 , comprising the steps of: 
 dividing a silicon substrate into an element forming region and an element isolating region;    doping nitrogen into the surface of the silicon substrate in said boundary region; and    forming a silicon nitride film or a silicon oxide film containing nitrogen as said gate insulating film so that said gate insulating film can extend on the surface of said silicon substrate from the element forming region to said element isolating region across said boundary region.    
     
     
         9 . The method according to  claim 8 , wherein a deposition method is applied to said step of forming said silicon nitride film or said silicon oxide film containing nitrogen as said gate insulating film.  
     
     
         10 . The method according to  claim 8 , wherein a nitriding method is applied to said step of forming said silicon nitride film or said silicon oxide film containing nitrogen as said gate insulating film.  
     
     
         11 . The method according to  claim 8 , the method further comprising the step of forming an underlying silicon nitride film on the surface of said silicon substrate by using a nitriding method prior to the formation of said silicon nitride film or said silicon oxide film containing nitrogen as said gate insulating film, so that the underlying silicon nitride film can extend from said element forming region to said element isolating region across said boundary region.  
     
     
         12 . The method according to  claim 8 , wherein: 
 said step of dividing said silicon substrate into said element forming region and said element isolating region is implemented by forming a mask pattern on a silicon substrate and etching the silicon substrate with the mask pattern used as a mask to form an element isolating groove in the surface of the silicon substrate.    
     
     
         13 . The method according to  claim 12 , wherein a deposition method is used in forming said silicon nitride film or said silicon oxide film containing nitrogen as said gate insulating film.  
     
     
         14 . The method according to  claim 12 , wherein a nitriding method is used in forming said silicon nitride film or said silicon oxide film containing nitrogen as said gate insulating film.  
     
     
         15 . The method according to  claim 12 , wherein said gate insulating film is of laminated structure containing Ta 2 O 5 .  
     
     
         16 . A method for manufacturing the semiconductor device according to  claim 1 , wherein: 
 said silicon substrate is a crystalline silicon substrate, and    the method comprises the steps of: 
 dividing the crystalline silicon substrate into an element forming region and an element isolating region;  
 selectively forming the surface of the silicon substrate in said boundary region into an amorphous form; and  
 forming said silicon nitride film or said silicon oxide film containing nitrogen as said gate insulating film by use of a nitriding method, so that said gate insulating film can extend from said element forming region to said element isolating region across said boundary region.  
   
     
     
         17 . The method according to  claim 16 , further comprising the step of forming an underlying silicon nitride film on the surface of said silicon substrate by using a nitriding method, prior to the formation of said silicon nitride film or said silicon oxide film containing nitrogen as said gate insulating film, so that the underlying silicon nitride film can extend from said element forming region to said element isolating region across said boundary region.  
     
     
         18 . The method according to  claim 16 , wherein: 
 said step of dividing said crystalline silicon substrate into said element forming region and said element isolating region comprises the steps of;    forming a mask pattern on said crystalline silicon substrate; and    etching said crystalline silicon substrate with the mask pattern used as a mask to form an element isolating groove in the surface of said crystalline silicon substrate,    said step of selectively forming the surface of the silicon substrate in said boundary region into an amorphous form comprises the steps of: 
 removing an end portion of the mask pattern which is formed in contact with the upper-end corner portion of the side wall of the element isolating groove; and  
 implanting ions into the surface of the silicon substrate with the remaining portion of the mask pattern used as a mask to selectively form the surface of the silicon substrate into an amorphous form, and  
 said step of forming said silicon nitride film or said silicon oxide film containing nitrogen as said gate insulating film is carried out after the removal of the remaining portion of the mask pattern.  
   
     
     
         19 . The method according to  claim 16 , wherein a deposition method is applied to said step of forming said silicon nitride film or said silicon oxide film containing nitrogen as said gate insulating film.  
     
     
         20 . The method according to  claim 16 , wherein a nitriding method is applied to said step of forming said silicon nitride film or said silicon oxide film containing nitrogen as said gate insulating film.