Method of manufacturing semiconductor device having oxide films with different thickness

Abstract

After a first gate oxide film is formed on a substrate, a nitride layer is formed by a first oxynitriding process. The first gate oxide film is selectively removed from a thinner film part area of the substrate. A second gate oxide film forming process forms a second gate oxide film in the thinner film part area and a third gate oxide film in a thicker film part area. By executing second oxynitriding process, nitride layers are formed at the thinner and the thicker part areas.

1 . A semiconductor device, comprising: 
 a semiconductor substrate; and    two gate insulating films having different thicknesses on said semiconductor substrate,    wherein each of said gate insulating films includes a two-layer structure comprising an oxide layer and a nitride layer disposed on said oxide layer.    
   
   
       2 . A semiconductor device as claimed in  claim 1 , wherein said gate insulating films are different from each other in number of nitrogen atoms per unit area.  
   
   
       3 . A semiconductor device as claimed in  claim 1 , wherein said nitride layer is thinner than said oxide layer in one of said gate insulating films.  
   
   
       4 . A semiconductor device, comprising: 
 a semiconductor substrate; and    two gate insulating films having different thicknesses on said semiconductor substrate,    wherein each of said gate insulating films includes a three layer structure including lower and upper oxide layers and a nitride layer disposed between said lower and said upper oxide layers.    
   
   
       5 . A semiconductor device as claimed in  claim 4 , wherein one of said lower and said upper oxide layers includes nitrogen atoms whose density is lower than that of said nitride layer.  
   
   
       6 . A semiconductor device as claimed in  claim 4 , wherein said gate insulating films are different from each other in number of nitrogen atoms per unit area.  
   
   
       7 . A semiconductor device as claimed in  claim 4 , wherein said lower and said upper oxide layers have different thicknesses in one of said gate insulating films.  
   
   
       8 . A semiconductor device as claimed in  claim 4 , wherein said lower oxide layer is thinner than said upper oxide layer in one of said gate insulating films, and said lower oxide layer is thicker than said upper oxide layer in the other of said gate insulating films.  
   
   
       9 . A semiconductor device, comprising: 
 a semiconductor substrate; and    two gate insulating films having different thicknesses on said semiconductor substrate,    wherein each of said gate insulating films includes a two-layer structure comprising a nitride layer and an oxide layer disposed on said nitride layer.    
   
   
       10 . A semiconductor device as claimed in  claim 9 , wherein said oxide layer includes nitrogen atoms whose density is lower than that of said nitride layer.  
   
   
       11 . A semiconductor device as claimed in  claim 9 , wherein one of said gate insulating films is different from the other in number of nitrogen atoms per unit area.  
   
   
       12 . A semiconductor device as claimed in  claim 9 , wherein said nitride layer is thinner than said oxide layer in one of said gate insulating films.  
   
   
       13 . A semiconductor device, comprising: 
 a semiconductor substrate; and    two gate insulating films having different thicknesses on said semiconductor substrate,    wherein one of said gate insulating films includes a two layer structure comprising a first nitride layer and a first oxide layer, and    wherein the other of said gate insulating films includes a three layer structure comprising second and third oxide layers and a second nitride layer disposed between said second and said third oxide layers.    
   
   
       14 . A semiconductor device as claimed in  claim 13 , wherein each of said first, said second and said third oxide layers includes nitrogen atoms whose density is lower than that of an adjacent one of said first and said second nitride layers.  
   
   
       15 . A semiconductor device as claimed in  claim 13 , wherein one of said gate insulating films is different from the other in number of nitrogen atoms per unit area.  
   
   
       16 . A semiconductor device as claimed in  claim 13 , wherein said first oxide layer is disposed on said first nitride layer.  
   
   
       17 . A semiconductor device, comprising: 
 a semiconductor substrate; and    two gate insulating films having different thicknesses on said semiconductor substrate,    wherein one of said gate insulating films includes a three layer structure comprising first and second nitride layers and an oxide layer disposed between said first and said second nitride layers.    
   
   
       18 . A semiconductor device as claimed in  claim 17 , wherein said oxide layer includes nitrogen atoms whose density is lower than that of each of said first and said second nitride layers.  
   
   
       19 . A semiconductor device as claimed in  claim 17 , wherein the other of said gate insulating films includes at least one nitride layer, and 
 wherein said gate insulating films are different from each other in number of nitrogen atoms per unit area.    
   
   
       20 . A semiconductor device, comprising: 
 a semiconductor substrate; and    two gate insulating films having different thicknesses on said semiconductor substrate,    wherein one of said gate insulating films includes a four layer structure comprises a lower nitride layer, a lower oxide layer disposed on said lower nitride layer, an upper nitride layer disposed on said lower oxide layer and an upper oxide layer disposed on said upper nitride layer.    
   
   
       21 . A semiconductor device as claimed in  claim 20 , wherein each of said lower and said upper oxide layers includes nitrogen atoms whose density is lower than that of each of said lower and said upper nitride layers.  
   
   
       22 . A semiconductor device as claimed in  claim 20 , wherein the other of said gate insulating films includes a nitride layer, and 
 wherein said gate insulating films are different from each other in number of nitrogen atoms per unit area.    
   
   
       23 . A semiconductor device, comprising: 
 a semiconductor substrate; and    two gate insulating films having different thicknesses on said semiconductor substrate,    wherein one of said gate insulating films includes a four layer structure comprising a lower oxide layer, a lower nitride layer disposed on said lower oxide layer, an upper oxide layer disposed on said lower nitride layer and an upper nitride layer disposed on said upper oxide layer.    
   
   
       24 . A semiconductor device as claimed in  claim 23 , wherein each of said lower and said upper oxide layers includes nitrogen atoms whose density is lower than that of each of said lower and said upper nitride layers.  
   
   
       25 . A semiconductor device as claimed in  claim 23 , wherein the other of said gate insulating films includes a nitride layer, and 
 wherein said gate insulating films are different from each other in number of nitrogen atoms per unit area.    
   
   
       26 . A semiconductor device, comprising: 
 a semiconductor substrate; and    two gate insulating films having different thicknesses on said semiconductor substrate,    wherein one of said gate insulating films includes a five-layer structure comprising three nitride layers and two oxide layers which are alternately disposed.    
   
   
       27 . A semiconductor device as claimed in  claim 26 , wherein each of said oxide layers includes nitrogen atoms whose density is lower than that of each of said nitride layers.  
   
   
       28 . A semiconductor device as claimed in  claim 26 , wherein the other of said gate insulating films includes a nitride layer, and 
 wherein said gate insulating films are different from each other in number of nitrogen atoms per unit area.    
   
   
       29 . A semiconductor device as claimed in  claim 26 , wherein the other of said gate insulating films includes a nitride layer, and 
 wherein said gate insulating films are different from each other in number of nitrogen layers.    
   
   
       30 . A semiconductor device having two gate insulating film different from each other in thickness, produced by a process comprising: 
 executing a first oxide process for forming a first oxide layer;    executing a nitriding process for forming a nitride layer;    executing an etching process for partially etching the first oxide layer; and    executing a second oxide process for forming a second oxide layer.