Optical endpoint detection for buff module on CMP tool

Abstract

The invention includes a polishing station and a buffing station for chemically mechanically polishing a wafer. The buffing station preferably includes a pair of rotating opposing buffing pads that receive a portion of the wafer. In the buffing station, a measurement instrument may be positioned adjacent an exposed portion of the wafer for detecting an endpoint of the buffing process. A first slurry may be used in the polishing station and a second slurry may be used in the buffing station. For planarizing a wafer with a metal layer over a barrier layer, the metal layer may be removed at the polishing station while the barrier layer is removed at the buffing station. For planarizing a dielectric layer, the top portion of the dielectric layer may be removed at the polishing station with an additional amount removed at the buffing station thereby leaving a dielectric layer with a desired thickness.

We claim:  
     
         1 . A buffing station for removing material from a front surface of a wafer comprising: 
 a) a pair of adjacent buff pads for receiving a first portion of the wafer;    b) at least one motor for rotating the buff pads; and    c) an end point detection system comprising a probe and a measurement instrument for taking measurements on the front surface of the wafer.    
     
     
         2 . The buffing station of  claim 1  wherein the probe is positioned adjacent a second portion of the wafer that is different than the first portion of the wafer.  
     
     
         3 . The buffing station of  claim 1  wherein the buff pads are disk shaped.  
     
     
         4 . The buffing station of  claim 3  wherein the diameter of the buff pads is smaller than the diameter of the wafer.  
     
     
         5 . The buffing station of  claim 1  wherein the measurement instrument comprises a spectrometer.  
     
     
         6 . The buffing station of  claim 1  wherein the measurement instrument comprises an interferometer.  
     
     
         7 . An apparatus for removing material from a front surface of a wafer comprising: 
 a) a polishing station; and    b) a buff station, wherein the buff station comprises a dual opposing buff pad system and an endpoint detection system.    
     
     
         8 . The apparatus of  claim 7 , wherein the polishing station comprises an orbital motion generator and a polishing pad connected to the orbital motion generator.  
     
     
         9 . The apparatus of  claim 7  further comprising: 
 c) a cleaning station wherein the wafer is cleaned and dried.  
 
     
     
         10 . A method of planarizing a front surface of a wafer with a deposited barrier and metal layer comprising the steps of: 
 a) removing substantially the entire metal layer on a polishing station; and    b) removing substantially the entire barrier layer on a buffing station wherein the buffing station comprises a dual opposing buff pad system and an endpoint detection system.    
     
     
         11 . The method of  claim 10  further comprising the steps of: 
 c) delivering a first slurry to the polishing station that that has a first level of chemically reactivity with the metal layer; and  
 d) delivering a second slurry to the buffing station that has a second level of chemically reactivity with the metal layer, wherein the first level of chemical reactivity is greater than the second level of chemical reactivity.  
 
     
     
         12 . The method of  claim 10  further comprising the step of: 
 c) orbiting a polishing pad during the removal of the metal layer on the polishing station.  
 
     
     
         13 . The method of  claim 10  further comprising the steps of: 
 c) cleaning the wafer in a cleaning station; and  
 d) drying the wafer in the cleaning station.  
 
     
     
         14 . A method of planarizing a front surface of a wafer with a deposited dielectric layer comprising the steps of: 
 a) removing a desired thickness of the dielectric layer on a polishing station; and    b) removing microscratches caused by the polishing station on a buffing station wherein the buffing station comprises a dual opposing buff pad system and an endpoint detection system.    
     
     
         15 . The method of  claim 14  further comprising the steps of: 
 c) delivering a first slurry to the polishing station that that has a first level of chemically reactivity with the dielectric layer; and  
 d) delivering a second slurry to the buffing station that has a second level of chemically reactivity with the dielectric layer, wherein the first level of chemical reactivity is greater than the second level of chemical reactivity.  
 
     
     
         16 . The method of  claim 14  further comprising the step of: 
 c) orbiting a polishing pad during the removal of the metal layer on the polishing station.  
 
     
     
         17 . The method of  claim 14  further comprising the steps of: 
 c) cleaning the wafer in a cleaning station; and  
 d) drying the wafer in the cleaning station.