Edge and hot spot compensation techniques in chemical mechanical polishing

Abstract

A polishing pad has a polishing layer having a polishing surface that has a circular central region and an annular outer region surrounding the central region. The polishing surface can include slurry distribution grooves formed with uniformity spacing across the central region and the annular outer region, and slurry discharge grooves that start at an outer perimeter of the circular central region and extend radially outward to an edge of the polishing pad so as to preferentially discharge the polishing liquid from the annular outer region. The central region can be formed of a first polishing material and the annular outer region can be formed of a second polishing material that is softer than the first polishing material.

What is claimed is: 
     
         1 . A method for chemical mechanical polishing, the method comprising:
 rotating a polishing pad about an axis of rotation, the polishing pad having an annular outer region that surrounds a circular central region, the annular outer region having a plurality of polishing liquid discharge grooves that start at an outer perimeter of the circular central region and extend radially outward to an edge of the polishing pad so as to preferentially discharge a polishing liquid from the annular outer region;   positioning a substrate against the polishing pad;   dispensing the polishing liquid onto the polishing pad; and   oscillating the substrate laterally across the polishing pad such that
 for a first duration a central portion of the substrate and an edge portion of the substrate are positioned over the central region of the polishing pad such that the central portion of the substrate and the edge portion of the substrate are polished for the first duration by the central region of the polishing pad, and 
 for a second duration holding the central portion of the substrate is positioned over the central region of the polishing pad and an angularly extending section of the edge portion of the substrate is positioned over the annular outer region such that the central portion of the substrate is polished for the second duration by the central region of the polishing pad and the edge portion of the substrate is polished for the second duration by both the central region of the polishing pad and the annular outer region so as to reduce a polishing rate of the edge portion. 
   
     
     
         2 . The method of  claim 1 , comprising holding the substate in a laterally fixed position for the second duration. 
     
     
         3 . The method of  claim 2 , wherein the polishing pad further comprises polishing liquid distribution grooves that are uniformly spaced across the central region of the polishing pad. 
     
     
         4 . A polishing system, comprising:
 a rotatable platen;   a polishing pad on the platen, the polishing pad having an annular outer region that surrounds a circular central region, the annular outer region having a plurality of polishing liquid discharge grooves that start at an outer perimeter of the circular central region and extend radially outward to an edge of the polishing pad so as to preferentially discharge polishing liquid from the annular outer region;   a dispenser to deliver the polishing liquid onto the polishing pad;   a carrier head to hold a substrate against the polishing pad, the carrier head laterally movable across the polishing pad;   an actuator to move the carrier head; and   a controller coupled to the actuator and configured to cause the actuator to oscillate the carrier head and substrate laterally across the polishing pad such that
 for a first duration cause the actuator to position a central portion of the substrate and an edge portion of the substrate over the central region of the polishing pad such that the central portion of the substrate and the edge portion of the substrate are polished for the first duration by the central region of the polishing pad, and 
 for a second duration cause the actuator to position the central portion of the substrate over the central region of the polishing pad and an angularly extending section of the edge portion of the substrate over the outer annular region such that the central portion of the substrate is polished for the second duration by the central region of the polishing pad and the edge portion of the substrate is polished for the second duration by both the central region of the polishing pad and the annular outer region so as to reduce a polishing rate of the edge portion. 
   
     
     
         5 . The system of  claim 4 , wherein the controller is configured to cause the actuator to hold the substate in a laterally fixed position for the second duration. 
     
     
         6 . The system of  claim 5 , wherein the polishing pad further comprises polishing liquid distribution grooves. 
     
     
         7 . The system of  claim 6 , wherein the polishing liquid distribution grooves are uniformly spaced across the central portion of the polishing pad. 
     
     
         8 . The system of  claim 7 , wherein the polishing liquid distribution grooves are uniformly spaced across the central portion and annular outer portion of the polishing pad. 
     
     
         9 . The system of claim  65 , wherein the polishing liquid distribution grooves are narrower than the polishing liquid discharge grooves. 
     
     
         10 . A polishing pad, comprising:
 a polishing layer having a polishing surface that has a circular central region and an annular outer region surrounding the central region, wherein the polishing surface includes a plurality of polishing liquid distribution grooves formed with uniformity spacing across the central region and the annular outer region, and wherein the polishing surface further includes a plurality of polishing liquid discharge grooves that start at an outer perimeter of the circular central region and extend radially outward to an edge of the polishing pad so as to preferentially discharge the polishing liquid from the annular outer region.   
     
     
         11 . The polishing pad of  claim 10 , wherein the polishing liquid distribution grooves comprise a plurality of concentric circular grooves. 
     
     
         12 . The polishing pad of  claim 10 , wherein the polishing liquid distribution grooves are narrower than the polishing liquid discharge grooves. 
     
     
         13 . The polishing pad of  claim 10 , wherein the polishing liquid distribution grooves are distributed at equal angular intervals around the circumference of the polishing pad. 
     
     
         14 . A method for chemical mechanical polishing, the method comprising:
 rotating a polishing pad about an axis of rotation;   positioning a substrate against the polishing pad that has a polishing layer with a polishing surface, wherein the polishing pad has a circular central region formed of a first polishing material and an annular outer region that surrounds the circular central region and that is formed of a second polishing material that is softer than the first polishing material;   dispensing a polishing liquid onto the polishing pad; and   oscillating the substrate laterally across the polishing pad such that
 for a first duration a central portion of the substrate and an edge portion of the substrate are positioned over the central region of the polishing pad such that the central portion of the substrate and the edge portion of the substrate are polished for the first duration by the central region of the polishing pad, and 
 for a second duration holding the central portion of the substrate is positioned over the central region of the polishing pad and an angularly extending section of the edge portion of the substrate is positioned over the annular outer region such that the central portion of the substrate is polished for the second duration by the central region of the polishing pad and the edge portion of the substrate is polished for the second duration by both the central region of the polishing pad and the annular outer region so as to reduce a polishing rate of the edge portion. 
   
     
     
         15 . The method of  claim 14 , wherein the first polishing material has a hardness of 50-80 Shore D. 
     
     
         16 . The method of  claim 15 , wherein the first polishing material has a hardness of 20-50 Shore D. 
     
     
         17 . A polishing pad, comprising:
 a polishing layer having a polishing surface, wherein the polishing pad has a circular central region formed of a first polishing material having a hardness of 50-80 Shore D and an annular outer region that surrounds the circular central region and that is formed of a second polishing material that is softer than the first polishing material and has a hardness of 20-50 Shore D, wherein a polishing surface of the central region and a polishing surface of the annular outer region are coplanar.   
     
     
         18 . The polishing pad of  claim 17 , wherein the first polishing material and second polishing material have the same material composition but different porosity. 
     
     
         19 . The polishing pad of  claim 18 , wherein the first polishing material and second polishing material are a poromeric polyurethane. 
     
     
         20 . The polishing pad of  claim 18 , wherein the second polishing material extends entirely through the polishing layer. 
     
     
         21 . The polishing pad of  claim 18 , wherein the second polishing material extends partially through the polishing layer and is supported on a thin section of pad formed of the first polishing material. 
     
     
         22 . The polishing pad of  claim 18 , wherein the polishing pad further comprises polishing liquid distribution grooves. 
     
     
         23 . The polishing pad of  claim 22 , wherein the polishing liquid distribution grooves are uniformly spaced across the central portion of the polishing pad. 
     
     
         23 . The polishing pad of  claim 22 , wherein the polishing liquid distribution grooves are uniformly spaced across the central portion and the annular outer portion of the polishing pad. 
     
     
         24 . The polishing pad of  claim 22 , wherein the polishing liquid distribution grooves comprise a plurality of concentric circular grooves. 
     
     
         25 . The method of claim  35 , wherein the polishing layer has a thickness of 40-100 mils. 
     
     
         26 . A polishing system, comprising:
 a rotatable platen to support a polishing pad that has a polishing layer with a polishing surface, wherein the polishing pad has a circular central region formed of a first polishing material and an annular outer region that surrounds the circular central region and that is formed of a second polishing material that is softer than the first polishing material;   a dispenser to deliver a polishing liquid onto the polishing pad;   a carrier head to hold a substrate against the polishing pad, the carrier head laterally movable across the polishing pad;   an actuator to move the carrier head; and   a controller coupled to the actuator and configured to cause the actuator to oscillate the carrier head and substrate laterally across the polishing pad such that
 for a first duration cause the actuator to position a central portion of the substrate and an edge portion of the substrate over the central region of the polishing pad such that the central portion of the substrate and the edge portion of the substrate are polished for the first duration by the central region of the polishing pad, and 
 for a second duration cause the actuator to position the central portion of the substrate over the central region of the polishing pad and an angularly extending section of the edge portion of the substrate over the outer annular region such that the central portion of the substrate is polished for the second duration by the central region of the polishing pad and the edge portion of the substrate is polished for the second duration by both the central region of the polishing pad and the annular outer region so as to reduce a polishing rate of the edge portion. 
   
     
     
         27 . The system of  claim 26 , wherein the controller is configured to cause the actuator to hold the substate in a laterally fixed position for the second duration.