Precision creation of inter-gates insulator

Abstract

An ONO-type inter-poly insulator is formed by depositing intrinsic silicon on an oxidation stop layer. In one embodiment, the oxidation stop layer is a nitridated top surface of a lower, and conductively-doped, polysilicon layer. In one embodiment, atomic layer deposition (ALD) is used to precisely control the thickness of the deposited, intrinsic silicon. Heat and an oxidizing atmosphere are used to convert the deposited, intrinsic silicon into thermally-grown, silicon dioxide. The oxidation stop layer impedes deeper oxidation. A silicon nitride layer and an additional silicon oxide layer are further deposited to complete the ONO structure before an upper, and conductively-doped, polysilicon layer is formed. In one embodiment, the lower and upper polysilicon layers are patterned to respectively define a floating gate (FG) and a control gate (CG) of an electrically re-programmable memory cell. In an alternative embodiment, after the middle, silicon nitride of the ONO structure is defined, another layer of intrinsic silicon is deposited, by way of for example, ALD. Heat and an oxidizing atmosphere are used to convert the second deposited, intrinsic silicon into thermally-grown, silicon dioxide. An ONO structure with two thermally-grown, and spaced apart, silicon oxide layers is thereby provided.

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       22 . A method of forming insulation comprising: 
 (a) defining an oxidation stop layer in a top portion of a first conductively-doped semiconductor layer;    (b) providing an essentially undoped semiconductor layer on the first conductively-doped semiconductor layer and above the first oxidation stop layer;    (c) oxidizing the essentially undoped semiconductor layer so as to thereby create a corresponding, essentially undoped and thermally-grown, first oxide sublayer over the first conductively-doped semiconductor layer; and    (d) disposing a second conductively-doped semiconductor layer above the first oxide sublayer so that the first oxide sublayer provides electrical insulation between the first and second conductively-doped semiconductor layers.    
   
   
       23 . The insulation forming method of  claim 22  wherein: 
 (a.1) said defining of the oxidation stop layer includes introducing nitrogen into the top portion of a first conductively-doped semiconductor layer.    
   
   
       24 . The insulation forming method of  claim 23  wherein: 
 (a.1a) said introducing of the nitrogen into the top portion includes causing the introduced nitrogen to exhibit a concentration gradient.    
   
   
       25 . The insulation forming method of  claim 22  wherein: 
 (a.1) said defining of the oxidation stop layer includes defining an adhesion surface on the top portion of a first conductively-doped semiconductor layer for adhering to the essentially undoped semiconductor layer.    
   
   
       26 . A method of providing a high quality silicon dioxide layer atop a first conductively-doped semiconductor layer, the method comprising: 
 (a) introducing nitrogen into the first conductively-doped semiconductor layer through a top portion of the first conductively-doped semiconductor layer;    (b) adhering an essentially undoped silicon layer to the top portion of the first conductively-doped semiconductor layer;    (c) thermally oxidizing the adhered and essentially undoped silicon layer at least until a corresponding oxidation front of said thermal oxidizing step reaches the nitrogen introduced into the first conductively-doped semiconductor layer; and    (d) continuing said thermal oxidizing step beyond when the corresponding oxidation front reaches the introduced nitrogen.    
   
   
       27 . The providing method of  claim 26  and further comprising: 
 (e) disposing a second conductively-doped semiconductor layer above the thermally oxidized and essentially undoped silicon layer.    
   
   
       28 . The providing method of  claim 27  and further comprising: 
 (f) interposing a silicon nitride layer between the thermally oxidized and essentially undoped silicon layer and the second conductively-doped semiconductor layer.    
   
   
       29 . The providing method of  claim 28  and further comprising: 
 (g) interposing a silicon oxide layer between the silicon nitride layer and the second conductively-doped semiconductor layer.