System and method of defect optimization for chemical mechanical planarization of polysilicon

Abstract

A system and method of reducing defects in chemical mechanical planarization of polysilicon is disclosed. The system includes first and second polishing stations each having a different hardness polishing pad and a different slurry. A cleaning station using a dilute SC1 chemistry is also included. The process includes polishing a polysilicon wafer on a first polishing station using a hard polishing pad and then polishing the polysilicon wafer on a second polishing station having a soft pad. The polysilicon wafer may then be directly placed in a scrubber using a dilute SC1 chemistry.

We claim:  
     
         1 . A system for minimizing a defect level of a polysilicon workpiece, the system comprising: 
 A first chemical mechanical planarization polishing station including a first polishing pad having a first polishing surface for receiving the workpiece and a first chemical slurry applied to the first polishing surface;    A second chemical mechanical planarization polishing station including a second polishing pad having a second polishing surface for receiving the workpiece and a second chemical slurry applied to the second polishing surface; and    wherein the first polishing pad has a hardness different than a hardness of the second polishing pad and the first chemical slurry is different from the second chemical slurry.    
     
     
         2 . The system of  claim 1 , wherein the first chemical mechanical planarization polishing station is a linear polishing station and the second chemical mechanical planarization polishing station is a rotary polishing station.  
     
     
         3 . The system of  claim 1 , wherein the first and second chemical mechanical planarization polishing stations are each linear polishing stations.  
     
     
         4 . The system of  claim 1 , wherein the first polishing pad comprises a hard pad and the second polishing pad comprises a soft pad, and wherein the hardness of the first polishing pad is greater than the hardness of the second polishing pad.  
     
     
         5 . The system of  claim 4 , wherein the hardness of the first polishing pad is in the range of 45 to 75 on the Shore “D” scale.  
     
     
         6 . The system of  claim 1 , wherein the second polishing pad comprises a cast polyurethane material having a plurality of fibers extending above the second polishing surface and the first polishing pad comprises a cast polyurethane material having an absence of fibers extending above the first polishing surface.  
     
     
         7 . The system of  claim 1 , wherein the first chemical slurry and the second chemical slurry each comprise a basic solution containing colloidal silica particles, wherein the first chemical slurry contains a higher percentage of colloidal silica particles than the second chemical slurry.  
     
     
         8 . The system of  claim 7 , wherein the first chemical slurry comprises a basic solution containing at least a 50 percent concentration of colloidal silica particles that is diluted in the range of 18:1 to 22:1 with deionized water.  
     
     
         9 . The system of  claim 8 , further comprising a mechanical scrubber configured to receive the workpiece from the second polishing station and clean the workpiece utilizing a standard clean 1 (SC-1) chemistry.  
     
     
         10 . A method for minimizing a defect level of a polysilicon workpiece comprising: 
 providing a first chemical mechanical planarization polishing station including a first polishing pad having a first polishing surface for receiving the workpiece;    moving the first polishing surface relative to the workpiece and applying a first chemical slurry to the first polishing surface;    pressing a surface of the workpiece against the first polishing surface;    providing a second chemical mechanical planarization polishing station including a second polishing pad having a second polishing surface for receiving the workpiece, the second polishing pad having a lower hardness than the first polishing pad;    moving the second polishing surface relative to the workpiece and applying a second chemical slurry to the second polishing surface, the second chemical slurry having a lower concentration of colloidal silica particles than the first chemical slurry; and    pressing the surface of the workpiece against the second polishing surface.    
     
     
         11 . The method of  claim 10 , wherein the first chemical mechanical planarization polishing station is a linear polisher and moving the first polishing surface comprises moving the first polishing surface in a linear direction.  
     
     
         12 . The method of  claim 11 , wherein the second chemical mechanical planarization polishing station is a rotary polishing station and moving the second polishing surface further comprises rotating the second polishing surface relative to the surface of the workpiece.  
     
     
         13 . The method of  claim 11 , wherein the first polishing pad is a hard pad and the second polishing pad is a soft pad.  
     
     
         14 . The method of  claim 13 , wherein the first chemical slurry and the second chemical slurry each comprise a basic solution containing colloidal silica particles and wherein the first chemical slurry contains a higher percentage of colloidal silica particles than the second chemical slurry.  
     
     
         15 . The method of  claim 14 , wherein pressing the surface of the workpiece against the first polishing surface comprises applying a pressure in a range of 3 to 8 pounds per square inch to the workpiece while the first polishing surface moves at a rate in a range of 300 to 600 feet per minute.  
     
     
         16 . The method of  claim 15 , wherein pressing the surface of the workpiece against the second polishing surface comprises applying a pressure in a range of 2 to 5 pounds per square inch to the workpiece while the second polishing surface rotates at a speed in a range of 15 to 45 revolutions per minute.  
     
     
         17 . The method of  claim 16 , wherein applying a first chemical slurry to the first polishing surface comprises applying the first chemical slurry at a rate in a range of 100 to 500 milliliters per minute.  
     
     
         18 . The method of  claim 10 , further comprising receiving and cleaning the workpiece in a chemical mechanical scrubber directly after pressing the workpiece against the second polishing surface, wherein a buffing step is unnecessary between pressing the workpiece against the second polishing surface and receiving and cleaning the workpiece.  
     
     
         19 . A method for minimizing a defect level of a polysilicon workpiece comprising: 
 applying a first chemical slurry to a polishing surface of a first polishing pad moving relative to the workpiece, wherein the first polishing pad is constructed of a material having an absence of fibers extending from the polishing surface;    pressing the workpiece against the first polishing pad for a first time period;    applying a second chemical slurry to a polishing surface of a second polishing pad moving relative to the workpiece, wherein the second polishing pad is constructed of a material having a plurality of fibers extending from the polishing surface and wherein the second chemical slurry has a lower percentage of colloidal silica particles than the first chemical slurry;    pressing the workpiece against the second polishing pad for a second time period; and    receiving and cleaning the workpiece in a chemical mechanical scrubber directly after pressing the workpiece against the second polishing pad, wherein a buffing step is avoided between pressing the workpiece against the second polishing pad and receiving and cleaning the workpiece.