Substrate holder to reduce substrate edge stress during chemical mechanical polishing

Abstract

Embodiments of the present invention generally relate to methods for chemical mechanical polishing a substrate. The methods generally include coupling a first substrate to be polished to a dummy substrate, and removing a portion of the backside of the first substrate to reduce the thickness of the first substrate. The first substrate and the dummy substrate are positioned in a carrier head assembly comprising an inflatable membrane and a support ring. The first substrate is placed in contact with a polishing pad to reduce the surface roughness of the backside of the first substrate. The support ring restricts lateral movement of the inflatable membrane to prevent the first substrate from contacting an interior surface of the carrier head assembly. The support ring is sized to allow vertical movement of the inflatable membrane within the carrier head assembly.

1 . A method, comprising:
 coupling a first substrate to a second substrate, the first substrate having a first surface in contact with the second substrate and the first surface opposite a second surface;   positioning the second substrate and the first substrate in a carrier head assembly, the carrier head assembly comprising:
 an inflatable membrane in contact with the second substrate; and 
 a support ring disposed circumferentially around the inflatable membrane; and 
   contacting the second surface of the first substrate to a polishing pad to reduce the surface roughness of the second surface of the first substrate.   
     
     
         2 . The method of  claim 1 , wherein the support ring is sized to restrict substantially all lateral movement of the inflatable membrane, but allow the inflatable membrane to travel in a vertical direction. 
     
     
         3 . The method of  claim 1 , wherein the average distance between the support ring and an interior surface of the carrier head assembly is less than about ten-thousandths of an inch. 
     
     
         4 . The method of  claim 3 , wherein the interior surface of the carrier head assembly consists essentially of a planar surface. 
     
     
         5 . The method of  claim 4 , wherein the first substrate is coupled to the second substrate using an epoxy. 
     
     
         6 . The method of  claim 5 , wherein the first substrate comprises a through-silicon via, and a device feature formed on the first surface. 
     
     
         7 . The method of  claim 6 , further comprising removing a portion of the second surface of the first substrate to decrease the thickness of the first substrate prior to the contacting the second surface of the first substrate to a polishing pad. 
     
     
         8 . A method, comprising:
 coupling a first surface of a first substrate to a second substrate;   positioning the second substrate and the first substrate in a carrier head assembly, the carrier head assembly comprising:
 an inflatable membrane in contact with the second substrate, the inflatable membrane comprising a textured surface; and 
 a support ring disposed circumferentially around the inflatable membrane and the second substrate, the support ring positioned to reduce lateral movement of the inflatable membrane and the second substrate such that the first substrate does not contact an interior surface of the carrier head assembly during polishing; and 
   contacting a second surface of the first substrate to a polishing pad to reduce the surface roughness of the second surface of the first substrate.   
     
     
         9 . The method of  claim 8 , wherein there is substantially no lateral movement of the inflatable membrane in the carrier head. 
     
     
         10 . The method of  claim 9 , wherein the average distance between the support ring and an interior surface of the carrier head assembly is less that about ten-thousandths of an inch. 
     
     
         11 . The method of  claim 10 , wherein the interior surface of the carrier head assembly consists essentially of a planar surface. 
     
     
         12 . The method of  claim 11 , further comprising removing a portion of the second surface of the first substrate to decrease the thickness of the first substrate prior to the contacting a second surface of the first substrate to a polishing pad. 
     
     
         13 . The method of  claim 12 , wherein first substrate is coupled to the second substrate using an epoxy. 
     
     
         14 . The method of  claim 8 , wherein the support ring contacts at least about 25 percent of the sidewall of the second substrate. 
     
     
         15 . The method of  claim 14 , wherein the support ring contacts at least about 50 percent of the sidewall of the second substrate. 
     
     
         16 . The method of  claim 15 , wherein the first substrate comprises a through-silicon via, and a device feature formed on the first surface. 
     
     
         17 . A method, comprising:
 coupling a first surface of a first substrate to a second substrate using an epoxy, the first surface of the first substrate opposite a second surface, the first surface having a device feature formed thereon;   positioning the second substrate and the first substrate in a carrier head assembly, the carrier head assembly comprising:
 an inflatable membrane in contact with the second substrate; and 
 a support ring disposed circumferentially around the inflatable membrane and the second substrate, the support ring sized to restrict substantially all lateral movement of the inflatable membrane, but allow the inflatable membrane to travel in a vertical direction; and 
   contacting the first substrate to a polishing pad to reduce a surface roughness of the second surface of the first substrate.   
     
     
         18 . The method of  claim 17 , wherein the thickness of the first substrate is about 100 microns. 
     
     
         19 . The method of  claim 18 , wherein the support ring contacts at least about 25 percent of the sidewall of the second substrate. 
     
     
         20 . The method of  claim 19 , wherein the inflatable membrane comprises a textured surface in contact with the second substrate.