Methods and apparatus for chemical-mechanical polishing utilizing low suspended solids polishing compositions

Abstract

The present invention provides chemical-mechanical polishing (CMP) methods and apparatus suitable for polishing a substrate utilizing a low suspended solids slurry composition. The CMP methods of the invention comprise polishing a substrate with CMP slurry containing a low suspended solids level (e.g., about 0.01 percent by weight to about 1.0 percent by weight) of a particulate abrasive material in a CMP apparatus, while continuously monitoring and accurately maintaining a predetermined total suspended solids (TSS) level in the slurry. Preferably, maximum TSS variability of the slurry is less than about 20 percent (i.e., ±20% of the target TSS level), more preferably less than about 10 percent TSS variability (i.e., ±10% of the target TSS level) during the course of the polishing process.

1 . A chemical-mechanical polishing (CMP) method for polishing a substrate comprising: (a) contacting a surface of the substrate with an aqueous slurry comprising a low level of a suspended particulate abrasive material; (b) monitoring the TSS level in the slurry at one or more points in a CMP process using a suspended solids sensor; (c) maintaining a predetermined TSS level in the slurry by adjusting the level of the suspended particulate abrasive material in the slurry based upon the monitoring by the suspended solids sensor. 
   
   
       2 . The method of  claim 1  wherein the TSS level of the slurry is in the range of about 0.01 percent by weight to about 1.0 percent by weight. 
   
   
       3 . The method of  claim 1  wherein the TSS level of the slurry is in the range of about 0.05 percent by weight to about 0.6 percent by weight. 
   
   
       4 . The method of  claim 1  wherein the particulate abrasive material comprises a metal oxide. 
   
   
       5 . The method of  claim 4  wherein the metal oxide is cerium oxide. 
   
   
       6 . The method of  claim 1  wherein the TSS of the CMP slurry has a maximum TSS variability during the CMP process of less than about 20%. 
   
   
       7 . The method of  claim 1  wherein the TSS of the CMP slurry has a maximum TSS variability during the CMP process of less than about 10%. 
   
   
       8 . A CMP apparatus comprising a movable platen adapted to hold a polishing pad on the platen, and a movable carrier assembly adapted to hold a substrate and to urge a surface of the substrate against the polishing pad; the apparatus also including a slurry delivery system adapted to contact an aqueous slurry comprising a low level of a suspended particulate abrasive material with the surface of the substrate; wherein during use the platen and carrier assembly are disposed in an opposed, parallel relation to one another with the pad and substrate therebetween; the delivery system being adapted to deposit at least a portion of the slurry between the pad and the surface of the substrate; the CMP slurry delivery system including at least one suspended solids sensor for measuring the TSS of the slurry. 
   
   
       9 . The apparatus of  claim 8  wherein the at least one suspended solids sensor comprises an in-line TSS monitoring device disposed within the slurry delivery system near an outlet for depositing the slurry onto the polishing pad. 
   
   
       10 . A method of diluting a CMP slurry concentrate to a target TSS concentration comprising, monitoring the TSS of the slurry in real time using a suspended solids sensor and adding a diluents until the target TSS concentration is achieved. 
   
   
       11 . The method of  claim 10  wherein the target TSS concentration of the CMP slurry is in the range of about 0.01 percent by weight to about 1.0 percent by weight. 
   
   
       12 . The method of  claim 10  wherein the target TSS concentration of the CMP slurry is in the range of about 0.05 percent by weight to about 0.6 percent by weight. 
   
   
       13 . The method of  claim 10  wherein the particulate abrasive material comprises a metal oxide. 
   
   
       14 . The method of  claim 13  wherein the metal oxide is cerium oxide.