Non-contact chemical mechanical polishing wafer edge control apparatus and method

Abstract

Methods and apparatus for controlling a material removal rate at an edge of a wafer during a chemical mechanical polishing (CMP) process are disclosed. According to one aspect of the present invention, a CMP apparatus includes a wafer, a polishing pad to polish a surface of the wafer, a polishing pad structure to rotate the polishing pad over the surface of the wafer, and a wafer chuck to support the wafer. The wafer chuck directly supports a first portion of the wafer that is in physical contact with the wafer chuck and indirectly supports a second portion of the wafer that is not in physical contact with the wafer chuck. The second portion of the wafer is supported by the wafer chuck using a bearing surface arranged between the second portion of the wafer and the wafer chuck.

1 . A chemical mechanical polishing (CMP) apparatus comprising: 
 a wafer;    a polishing pad to polish a surface of the wafer;    a polishing pad structure to rotate the polishing pad over the surface of the wafer; and    a wafer chuck to support the wafer, the wafer chuck being arranged to support a first portion of the wafer that is in physical contact with the wafer chuck and to indirectly support a second portion of the wafer that is not in physical contact with the wafer chuck, wherein the second portion of the wafer is supported by the wafer chuck using a bearing surface arranged between the second portion of the wafer and the wafer.    
     
     
         2 . The CMP apparatus of  claim 1  wherein the wafer chuck is arranged to support the first portion of the wafer using a vacuum pressure.  
     
     
         3 . The CMP apparatus of  claim 1  wherein the wafer chuck defines at least one opening, the CMP apparatus further including: 
 a first supply, the first supply being arranged to provide the wafer chuck with a supply through the at least one opening that is arranged to create a boundary layer between an edge surface of the wafer chuck and the second portion of the wafer, wherein the boundary layer forms the bearing surface.    
     
     
         4 . The CMP apparatus of  claim 3 , wherein the first supply is an air supply, and the bearing surface is an air bearing surface.  
     
     
         5 . The CMP apparatus of  claim 3 , wherein the first supply is a fluid supply, and the bearing surface is a fluid bearing surface.  
     
     
         6 . The CMP apparatus of  claim 1  wherein the second portion of the wafer is a bottom edge periphery of the wafer, and wherein a boundary layer is formed between the bottom edge periphery of the wafer and an outside edge surface of the wafer chuck.  
     
     
         7 . The CMP apparatus of  claim 6  wherein a distance between the bottom edge periphery of the wafer and the outside edge surface of the wafer chuck is approximately 10 micrometers.  
     
     
         8 . The CMP apparatus of  claim 1  wherein the bearing surface has an associated pressure, the associated pressure being arranged to support the second portion of the wafer.  
     
     
         9 . The CMP apparatus of  claim 8  wherein the associated pressure is adjustable to adjust an amount of support provided to the second portion of the wafer.  
     
     
         10 . A method for controlling a removal rate of material from a top surface of a wafer during chemical mechanical polishing (CMP), the wafer being supported on a wafer chuck such that a portion of the wafer is in direct contact with the wafer chuck, the method comprising: 
 applying a polishing pressure to the top surface of the wafer; and    applying a support pressure to an edge periphery of a bottom surface of the wafer, wherein the support pressure is applied through a gap between an edge surface of the wafer chuck and the edge periphery of the bottom surface of the wafer, the edge periphery of the bottom surface of the wafer not being in direct contact with the wafer chuck.    
     
     
         11 . A method for controlling a removal rate of material from a top surface of a wafer during chemical mechanical polishing (CMP) the wafer being supported on a wafer chuck the method comprising: 
 applying a polishing pressure to the top surface of the wafer; and    applying a support pressure to an edge periphery of a bottom surface of the wafer, wherein the support pressure is applied through a gap between an edge surface of the wafer chuck and the edge periphery of the bottom surface of the wafer, the edge periphery of the bottom surface of the wafer not being in direct contact with the wafer chuck wherein the support pressure is in the range of between approximately 0.3 Mega Pascal (MPa) and approximately 0.6 MPa.    
     
     
         12 . The method of  claim 10  wherein applying the support pressure to the edge periphery of the bottom surface of the wafer includes distributing an air pressure on the edge periphery of the bottom surface of the wafer, the air pressure being arranged to act as an air bearing in the gap.  
     
     
         13 . The method of  claim 10  wherein applying the support pressure to the edge periphery of the bottom surface of the wafer includes distributing a fluid pressure on the edge periphery of the bottom surface of the wafer, the fluid pressure being arranged to act as fluid bearing in the gap.  
     
     
         14 . The method of  claim 10  further including: 
 determining if the removal rate of material from the top surface of the wafer over the edge periphery is acceptable; and    adjusting the support pressure to the edge periphery of the bottom surface of the wafer if it is determined that the removal rate of material from the top surface of the wafer over the edge periphery is not acceptable.    
     
     
         15 . The method of  claim 14  wherein adjusting the support pressure includes one selected from the group including increasing the support pressure and decreasing the support pressure.  
     
     
         16 . The method of  claim 14  wherein determining if the removal rate of material from the top surface of the wafer over the edge periphery is acceptable includes identifying an amount of deflection associated with the edge periphery of the bottom surface of the wafer.  
     
     
         17 . A method for controlling a removal rate of material from a top surface of a wafer during chemical mechanical polishing (CMP), the wafer being supported on a wafer chuck the method comprising: 
 applying a polishing pressure to the top surface of the wafer;    applying a support pressure to an edge periphery of a bottom surface of the wafer, wherein the support pressure is applied through a gap between an edge surface of the wafer chuck and the edge periphery of the bottom surface of the wafer, the edge periphery of the bottom surface of the wafer not being in direct contact with the wafer chuck    applying a vacuum pressure to the bottom surface of the wafer, the vacuum pressure being arranged to secure a portion of the bottom surface of the wafer that is not the edge periphery against the wafer chuck; and    adjusting the vacuum pressure to control the removal rate of material from the top surface of the wafer over the edge periphery.    
     
     
         18 . An apparatus for controlling a removal rate of material from a top surface of a wafer supported on a wafer chuck during chemical mechanical polishing (CMP), the wafer being supported on the wafer chuck such that a portion of the wafer is in direct contact with the wafer chuck the apparatus comprising: 
 means for applying a polishing pressure to the top surface of the wafer; and    means applying a support pressure to an edge periphery of a bottom surface of the wafer, wherein the support pressure is applied through a gap between an edge surface of the wafer chuck and the edge periphery of the bottom surface of the wafer, the edge periphery of the bottom surface of the wafer not being in physical contact with the wafer chuck.    
     
     
         19 . The apparatus of  claim 18  wherein the means for applying the support pressure to the edge periphery of the bottom surface of the wafer includes means for distributing an air pressure on the edge periphery of the bottom surface of the wafer, the air pressure being arranged to act as an air bearing in the gap.  
     
     
         20 . The apparatus of  claim 18  wherein the means for applying the support pressure to the edge periphery of the bottom surface of the wafer includes means for distributing a fluid pressure on the edge periphery of the bottom surface of the wafer, the fluid pressure being arranged to act as fluid bearing in the gap.