Polishing Pad and Multi-Head Polishing System

Abstract

A chemical mechanical polishing system includes a polishing pad, a platen to support the polishing pad, and two rotatable carrier heads configured to hold two substrates against the polishing pad at the same time. Each carrier head includes a retaining ring. Two actuators sweep the two carrier heads laterally across the polishing pad between positions closer to and farther from the center axis. A polishing surface of the polishing pad includes a center region with a first grooving pattern and an annular region with a second grooving pattern different than the first grooving pattern. A radius of the center region is equal to or less than a distance from a center axis of the platen to a closest outer edge of the two retaining rings when the carrier heads are in the closer positions.

What is claimed is: 
     
         1 . A chemical mechanical polishing system, comprising:
 a polishing pad;   a platen to support the polishing pad, the platen rotatable about a center axis;   a rotatable first carrier head configured to hold a first substrate against the polishing pad, the first carrier head including a first retaining ring;   a rotatable second carrier head configured to hold a second substrate against the same polishing pad at the same time that the first carrier head holds the first substrate against the polishing pad, the second carrier head including a second retaining ring;   a first actuator to sweep the first carrier head laterally across the polishing pad while the first substrate contacts the polishing pad;   a second actuator to sweep the second carrier head laterally across the polishing pad while the second substrate contacts the polishing pad; and   a controller configured to cause the first actuator to sweep the first carrier head between a first position closer to the center axis and a second position farther from the center axis and to cause the second actuator to sweep the carrier head between a third position closer to the center axis and a fourth position farther from the center axis;   wherein a polishing surface of the polishing pad includes a center region and an annular region surrounding the center region, the center region having a first grooving pattern and the annular region having a second grooving pattern different than the first grooving pattern, and wherein a radius of the center region is equal to or less than a distance from the center axis to a closest outer edge of the first retaining ring when the first carrier head is in the first position and the second retaining ring when the second carrier head is in the third position.   
     
     
         2 . The system of  claim 1 , wherein the first grooving pattern is configured to provide a lower resistance to outward slurry flow than the second grooving pattern. 
     
     
         3 . The system of  claim 1 , wherein the polishing surface in the center region has no grooves. 
     
     
         4 . The system of  claim 1 , wherein the polishing surface in the center region has at least one groove, and the first grooving pattern differs from the second grooving pattern. 
     
     
         5 . The system of  claim 4 , wherein the at least one groove comprises a spiral groove. 
     
     
         6 . The system of  claim 5 , wherein the spiral grove spirals in a first direction from outside inwardly, and wherein the controller is configured to cause the motor to rotate in the first direction while the first substrate and the second substrate are being polished. 
     
     
         7 . The system of  claim 1 , wherein the polishing surface in the center region comprises a first plurality of grooves having a first pitch and the polishing surface in the annular region comprises a second plurality of grooves having a second pitch that is less than the first pitch. 
     
     
         8 . The system of  claim 1 , wherein the annular region comprises a plurality of concentric circular grooves. 
     
     
         9 . The system of  claim 1 , wherein the annular region comprises a first plurality of linear grooves and a second plurality of linear grooves orthogonal to the first plurality of linear grooves. 
     
     
         10 . The system of  claim 1 , wherein the radius of the center region is equal to the distance from the center axis to the closest outer edge. 
     
     
         11 . The system of  claim 1 , wherein the radius of the center region is less than the distance from the center axis to the closest outer edge. 
     
     
         12 . The system of  claim 1 , wherein the first position and the third position are equidistant from the center axis. 
     
     
         13 . The system of  claim 1 , further comprising a track, a first carriage supported by the track, and a second carriage supported by the track, wherein the first carrier head is suspended from the first carriage and the second carrier head is suspended from the second carriage. 
     
     
         14 . The system of  claim 13 , wherein the track forms an arcuate path over the polishing pad.