Apparatus and method of determining an endpoint during a chemical-mechanical polishing process

Abstract

The present invention provides a polishing apparatus for use in polishing a substrate, including: (1) A polishing platen, and (2) a rotational strain sensor coupled to the polishing platen configured to detect a change in a rotational strain of the polishing platen during a polishing process. In addition, the present invention provides an accompanying method of detecting an endpoint during the polishing process by detecting a change between a first rotational strain and a second rotational strain with the rotational strain sensor.

What is claimed is:  
     
         1 . A polishing apparatus, comprising: 
 a polishing platen; and    a rotational strain sensor coupled to the polishing platen and configured to detect a change in a rotational strain of the polishing platen during a polishing process.    
     
     
         2 . The polishing apparatus as recited in  claim 1  wherein the polishing apparatus further includes a polishing pad coupled to an outer surface of the polishing platen and the rotational strain sensor is a piezoelectric sensor located between the outer surface and the polishing pad.  
     
     
         3 . The polishing apparatus as recited in  claim 1  wherein the polishing platen includes a base plate having a backing block projecting therefrom and an upper plate having a cavity formed therein and configured to receive the backing block therein, the rotational strain sensor being located between a face of the backing block and a face of the cavity.  
     
     
         4 . The polishing apparatus as recited in  claim 1  wherein the polishing platen includes a backing block projecting from a surface thereof and the polishing apparatus further includes a polishing pad having a cavity formed therein and configured to receive the backing block therein, the rotational strain sensor being located between a face of the backing block and a face of the cavity.  
     
     
         5 . The polishing apparatus as recited in  claim 1  wherein the polishing platen includes a base plate and the rotational strain sensor extends from the base plate and the polishing platen further includes an upper plate having a cavity formed therein and configured to receive the rotational strain sensor therein.  
     
     
         6 . The polishing apparatus as recited in  claim 5  wherein the rotational strain sensor includes a flexible stud member having adjacent, spaced-apart conductors located within the flexible stud member.  
     
     
         7 . The polishing apparatus as recited in  claim 5  wherein the rotational strain sensor includes a rigid stud member supported on a flexible base having adjacent, spaced-apart conductors.  
     
     
         8 . The polishing apparatus as recited in  claim 1  wherein the rotational strain sensor extends from a surface of the polishing platen and the polishing platen further includes a polishing pad having a cavity formed therein and configured to receive the rotational strain sensor therein.  
     
     
         9 . The polishing apparatus as recited in  claim 8  wherein the rotational strain sensor includes a flexible stud member having adjacent, spaced-apart conductors located within the flexible stud member.  
     
     
         10 . The polishing apparatus as recited in  claim 8  wherein the rotational strain sensor includes a rigid stud member supported on a flexible base having adjacent, spaced-apart conductors.  
     
     
         11 . The polishing apparatus as recited in  claim 1  further including a motor driven shaft coupled to the polishing platen, the rotational strain sensor coupled to the motor driven shaft.  
     
     
         12 . A method of detecting an endpoint during polishing of a substrate, comprising: 
 pressing a substrate having a first layer composed of a first material and a second layer composed of a second material against a polishing pad coupled to a polishing platen;    producing a first rotational strain of the polishing platen by polishing the first layer of the substrate with the polishing pad;    producing a second rotational strain of the polishing platen by polishing the second layer of the substrate with the polishing pad; and    detecting a change between the first rotational strain and the second rotational strain with a rotational strain sensor coupled to the polishing platen.    
     
     
         13 . The method as recited in  claim 12  wherein detecting the change includes detecting a change with a piezoelectric sensor located between the polishing platen and the polishing pad.  
     
     
         14 . The method as recited in  claim 12  wherein detecting the change includes detecting a change with a rotational strain sensor located between a face of a backing block projecting from a base plate of the polishing platen and a face of a cavity formed in an upper plate of the polishing platen.  
     
     
         15 . The method as recited in  claim 12  wherein detecting the change includes detecting a change with a rotational strain sensor located between a face of a backing block projecting from the polishing platen and a face of a cavity formed in the polishing pad.  
     
     
         16 . The method as recited in  claim 12  wherein detecting the change includes detecting a change with a rotational strain sensor that extends from a base plate of the polishing platen and is received in a cavity formed in an upper plate of the polishing platen.  
     
     
         17 . The method as recited in  claim 16  wherein detecting the change includes detecting a change with a rotational strain sensor that includes a flexible stud member having adjacent, spaced-apart conductors located within the flexible stud member.  
     
     
         18 . The method as recited in  claim 16  wherein detecting the change includes detecting a change with a rotational strain sensor that includes a rigid stud member supported on a flexible base having adjacent, spaced-apart conductors.  
     
     
         19 . The method as recited in  claim 12  wherein detecting the change includes detecting a change with a rotational strain sensor that extends from the polishing platen and is received in a cavity formed in the polishing pad.  
     
     
         20 . The method as recited in  claim 19  wherein detecting the change includes detecting a change with a rotational strain sensor that includes a flexible stud member having adjacent, spaced-apart conductors located within the flexible stud member.  
     
     
         21 . The method as recited in  claim 19  wherein detecting the change includes detecting a change with a rotational strain sensor that includes a rigid stud member supported on a flexible base having adjacent, spaced-apart conductors.  
     
     
         22 . The method as recited in  claim 12  wherein detecting the change includes detecting a change with a rotational strain sensor coupled to a motor driven shaft that is coupled to the polishing platen.  
     
     
         23 . The method as recited in  claim 12  wherein pressing a substrate includes pressing a substrate located over a semiconductor wafer.  
     
     
         24 . The method as recited in  claim 23  wherein pressing a substrate includes pressing a first layer comprising a dielectric and pressing a second layer comprising a metal.  
     
     
         25 . The method as recited in  claim 24  further including forming transistors on the semiconductor wafer, forming a plurality of alternating first and second layers over the transistors and interconnecting the transistors to form an operative integrated circuit.  
     
     
         26 . A method of polishing a substrate comprising: 
 detecting a change in a rotational strain during a polishing process of the substrate.    
     
     
         27 . The method as recited in  claim 26  further comprising: 
 changing the polishing process when a change in the rotational strain is detected.  
 
     
     
         28 . The method as recited in  claim 26  further comprising: 
 providing a strain gauge to measure the rotational strain.