Pad conditioning force modeling to achieve constant removal rate

Abstract

A method and apparatus for conditioning a polishing pad in a CMP system is provided. In one embodiment, a method for conditioning a polishing pad includes applying a down force to the conditioning disk that urges the conditioning disk against the polishing pad, measuring a torque required to sweep the conditioning disk across the polishing pad, determining a change in down force by comparing the measured torque to a model force profile (MFP), and adjusting the down force that the conditioning disk applies against the polishing pad in response to the determined change.

What is claimed is: 
     
         1 . A method for conditioning a polishing pad, comprising:
 applying a down force to a conditioning disk that urges the conditioning disk against the polishing pad;   measuring a torque required to sweep the conditioning disk across the polishing pad;   determining a change in down force by comparing the measured torque to a model force profile (MFP); and   adjusting the down force that the conditioning disk applies against the polishing pad in response to the determined change.   
     
     
         2 . The method of  claim 1 , wherein the MFP comprises an estimated relationship between the down force, the torque, and a rate of removal of material from a substrate by the polishing pad. 
     
     
         3 . The method of  claim 1 , wherein the determining comprises:
 determining the change in down force necessary to maintain a rate of material removal from a substrate by the polishing pad.   
     
     
         4 . The method of  claim 1 , wherein the determining comprises:
 determining a decrease in down force necessary to achieve a target torque of the MFP.   
     
     
         5 . The method of  claim 1 , wherein the determining comprises:
 determining an increase in down force necessary to maintain a constant removal rate of the polishing pad in response to the measured torque being less than the MFP.   
     
     
         6 . The method of  claim 1 , wherein the adjusting the down force comprises modifying a conditioning recipe for the polishing pad. 
     
     
         7 . The method of  claim 1 , wherein the adjusting the down force comprises adjusting the down force in-situ during conditioning of the polishing pad. 
     
     
         8 . A method for conditioning a polishing pad, comprising:
 applying a down force to urge a conditioning disk against the polishing pad;   measuring a frictional force generated by the conditioning disk contacting the polishing pad;   comparing the measured frictional force to a model force profile (MFP) to determine a change in down force; and   adjusting the applied down force in response to the comparison between the measured frictional force and the MFP.   
     
     
         9 . The method of  claim 8 , wherein the MFP further comprises:
 an estimated relationship between the down force, the frictional force, and a rate of removal of material from a substrate by the polishing pad.   
     
     
         10 . The method of  claim 9 , wherein the frictional force comprises a rotational torque required to rotate at least one of a conditioning head, a platen, or a polishing head. 
     
     
         11 . An apparatus for conditioning a polishing pad with a conditioning disk, comprising:
 a platen adapted to support the polishing pad;   a conditioning head adapted to retain the conditioning disk;   a down force actuator operable to move the conditioning head in a manner that the conditioning head applies a down force against the polishing pad with;   an arm coupled to the conditioning head to support the conditioning head above the platen; and   a sweep actuator coupled to the arm and operable to sweep the conditioning head across the platen; and   a sweep torque sensor operable to measure a torque required to sweep the conditioning head across the platen when the conditioning disk is in contact with the polishing pad.   
     
     
         12 . The apparatus of  claim 11 , further comprising:
 a controller coupled to the down force actuator and operable to instruct the down force actuator to apply the down force at a value selected in response to a model force profile (MFP)   
     
     
         13 . The apparatus of  claim 12 , wherein the controller is operable to provide a closed loop control of down force applied by the down force actuator based on the torque measured by the sweep torque sensor to maintain a substantially constant removal rate of material from a substrate by the polishing pad. 
     
     
         14 . The apparatus of  claim 11 , further comprising:
 a pad thickness sensor coupled to the conditioning head.