Semiconductor devices and processes for making them

Abstract

A semiconductor device such as a flash EEPROM has oxide/nitride/oxide sandwich structure deposited on a semiconductor substrate. Optical lithography and plasma-assisted etching are used to remove portions of the structure that extend over active regions. Since the nitride layer of the etched sandwich structure has oxidation proof, oxygen radical is prevented from reaching the substrate. Thus, the bird's beak is prevented from appearing.

What is claimed is:  
     
         1 . A semiconductor device including adjacent elements separated by an electrically insulating layer, wherein said insulating layer has a portion that has an oxidation proof property.  
     
     
         2 . The semiconductor device as claimed in  claim 1 , wherein said insulating layer is a sandwich structure resulting from laminating a first oxide layer, a nitride layer, and a second oxide layer.  
     
     
         3 . The semiconductor device as claimed in  claim 1 , wherein said insulating layer includes an oxide layer, portions of which have been removed to define openings exposing active regions of the semiconductor substrate, and spacers of a nitride layer extending along the sidewall of the openings within said oxide layer.  
     
     
         4 . A process of making a semiconductor device, comprising the steps of: 
 forming a sandwich structure on a semiconductor substrate by laminating a first oxide layer, a nitride layer and a second oxide layer;    depositing, by optical lithography, a photo resist extending over each neighboring elements separating region; and    removing, by dry etching using said photo resist as a mask, portions of said sandwich structure that extend over active regions.    
     
     
         5 . A process of making a semiconductor device comprising the steps of: 
 forming an oxide layer on a semiconductor substrate;    depositing, by optical lithography, a photo resist extending over each neighboring elements separating region;    removing, by dry etching using said photo resist as a mask, portions of said oxide layer that extend over active regions to define openings; and    depositing, by CVD, a nitride layer over said etched oxide layer and the exposed semiconductor substrate; and    removing, by anisotropically etching, said nitride layer leaving portions extending along the sidewall of the openings in said etched oxide layer.