Planarizing a semiconductor structure to form replacement metal gates

Abstract

A sacrificial gate structure, including nitride and fill layers, may be replaced with a metal gate electrode. The metal gate electrode may again be covered with a nitride layer covered by a fill layer. The replacement of the nitride and fill layers may reintroduce strain and provide an etch stop.

1 . a semiconductor structure comprising: 
 a substrate;    a metal gate electrode formed over said substrate;    a nitride layer over said metal gate electrode; and    an interlayer dielectric layer over said nitride layer.    
     
     
         2 . The structure of  claim 1  wherein said interlayer dielectric has a dielectric constant less than five.  
     
     
         3 . The structure of  claim 1  wherein said structure includes a pair of metal gate electrodes, one for an NMOS transistor and one for a PMOS transistor.  
     
     
         4 . The structure of  claim 1  wherein said nitride layer is in direct contact with said gate electrode.  
     
     
         5 . The structure of  claim 1  wherein said interlayer dielectric fills the region between metal gate electrodes.  
     
     
         6 . The structure of  claim 1  wherein said interlayer dielectric is carbon-doped oxide.