Retainer ring for semiconductor manufacturing processes

Abstract

An embodiment retainer ring includes an outer ring encircling an opening and an inner ring attached to the outer ring. The inner ring is disposed between the opening and the outer ring. The inner ring includes a softer material than the outer ring and a plurality of voids within the softer material.

What is claimed is: 
     
         1 . A retainer ring comprising:
 an outer ring encircling an opening; and   an inner ring attached to the outer ring, wherein the inner ring is disposed between the opening and the outer ring, and wherein the inner ring comprises:
 a softer material than the outer ring; and 
 a plurality of voids within the softer material. 
   
     
     
         2 . The retainer ring of  claim 1 , wherein the inner ring is attached to the outer ring by an adhesive layer disposed between the inner ring and the outer ring. 
     
     
         3 . The retainer ring of  claim 1 , wherein the inner ring comprises polyurethane. 
     
     
         4 . The retainer ring of  claim 1 , wherein the outer ring comprises polyether ether ketone (PEEK), polyphenylene sulfide (PPS), or a combination thereof. 
     
     
         5 . The retainer ring of  claim 1 , wherein a specific gravity of the inner ring is less than about 1.0. 
     
     
         6 . The retainer ring of  claim 1 , wherein a hardness of the inner ring is less than about 55 in a Shore A hardness scale or about 20 in a Shore B hardness scale. 
     
     
         7 . The retainer ring of  claim 1 , wherein the inner ring comprises a top surface lower than a top surface of the outer ring. 
     
     
         8 . The retainer ring of  claim 1 , wherein the retainer ring is configured to secure a wafer in the opening, and wherein a height of the inner ring is at least a height of the wafer. 
     
     
         9 . A polishing apparatus comprising:
 a polishing head; and   a retainer ring attached to the polishing head, wherein the retainer ring comprises:
 an outer ring comprising a first material; and 
 an inner ring comprising a porous second material having a specific gravity less than about 1.0, wherein the porous second material is softer than the first material, and wherein the inner ring is disposed between edges of a wafer and the outer ring when the retainer ring secures a wafer. 
   
     
     
         10 . The polishing apparatus of  claim 9 , wherein the porous second material comprises polyurethane, and wherein the first material comprises polyether ether ketone (PEEK), polyphenylene sulfide (PPS), or a combination thereof. 
     
     
         11 . The polishing apparatus of  claim 9 , wherein the specific gravity of the porous second material is less than about 0.8. 
     
     
         12 . The polishing apparatus of  claim 9 , wherein the porous second material is less than about 55 in a Shore A hardness scale or less than about 20 in a Shore B hardness scale. 
     
     
         13 . The polishing apparatus of  claim 9 , wherein the polishing head further comprises a membrane configured to apply downward pressure on a wafer secured by the retainer ring. 
     
     
         14 . The polishing apparatus of  claim 9  further comprising a polishing pad, wherein the polishing head is configured to rotate a wafer secured by the retainer ring against the polishing pad. 
     
     
         15 . The polishing apparatus of  claim 9 , wherein the retainer ring is attached to the polishing head using mechanical screws. 
     
     
         16 . A method for processing a wafer comprising:
 providing a retainer ring comprising:
 an outer ring encircling an opening; and 
 an inner ring attached to the outer ring and encircling the opening, wherein the inner ring comprises a different material than the outer ring, and wherein the different material is porous; 
   positioning a wafer in the opening, wherein the inner ring is disposed between edges of the wafer and the outer ring; and   processing the wafer while the wafer is secured by the retainer ring.   
     
     
         17 . The method of  claim 16 , wherein the inner ring comprises a softer material than the outer ring. 
     
     
         18 . The method of  claim 16 , wherein the inner ring comprises polyurethane, and wherein the outer ring comprises polyether ether ketone (PEEK), polyphenylene sulfide (PPS), or a combination thereof. 
     
     
         19 . The method of  claim 16 , wherein a specific gravity of the inner ring is less than about 1.0. 
     
     
         20 . The method of  claim 16 , wherein processing the wafer comprises applying a chemical mechanical polish (CMP) process to the wafer.