Method for forming a floating gate using chemical mechanical planarization

Abstract

An improved process forming a floating gate region of a semiconductor memory device. The process includes using a ceria slurry for chemical mechanical planarization to provide “stop on polysilicon” capabilities, allowing a thin nitride layer, or in the alternative no nitride layer, to be used and reducing the number of processing steps required to form the floating gate region.

1 - 33 . (canceled) 
     
     
         34 . A method of forming a memory cell structure comprising the acts of:
 providing a first oxide layer over a substrate;   providing a polysilicon layer over the first oxide layer;   providing an insulating layer over the polysilicon layer;   forming a plurality of trenches extending through the insulating layer, the polysilicon layer, the first oxide layer and into the substrate;   providing a second oxide layer over the insulating layer and within the plurality of trenches;   removing the second oxide layer above the plurality of trenches and the insulating layer by planarization which stops at the polysilicon layer;   providing a third oxide layer over the polysilicon layer and the second oxide layer; and   providing a control gate over the third oxide layer.   
     
     
         35 . The method of  claim 34 , wherein the insulating layer is a nitride layer. 
     
     
         36 . The method of  claim 35 , wherein the nitride layer has a thickness of approximately 50 Å to 150 Å. 
     
     
         37 . The method of  claim 34 , wherein the polysilicon layer has a thickness of approximately 400 Å to 1000 Å. 
     
     
         38 . The method of  claim 34 , wherein the removing act utilizes a chemical mechanical planarization process which utilizes a slurry comprising CeO 2  particles and chosen to selectively remove only the second oxide and insulating layers. 
     
     
         39 . The method of  claim 38 , wherein the slurry has a solids percent within a range of about 1% and about 7%. 
     
     
         40 . The method of  claim 38 , wherein the slurry is mixed with an additive. 
     
     
         41 . The method of  claim 40 , wherein the additive is at least one of a cationic additive and an anionic additive. 
     
     
         42 . The method of  claim 40 , wherein the additive is cetyl trimethyl ammonium bromide. 
     
     
         43 . The method of  claim 40 , wherein the slurry has a pH within a range of about 5 and about 8. 
     
     
         44 . The method of  claim 38 , wherein the CeO 2  particles have a mean particle size of between approximately 0.1 μm and 1.5 μm.