Eddy current sensing of metal removal for chemical mechanical polishing

Abstract

A sensor for monitoring a conductive film in a substrate during chemical mechanical polishing generates an alternating magnetic field that impinges a substrate and induces eddy currents. The sensor can have a core, a first coil wound around a first portion of the core and a second coil wound around a second portion of the core. The sensor can be positioned on a side of the polishing surface opposite the substrate. The sensor can detect a phase difference between a drive signal and a measured signal.

1 . A chemical mechanical polishing apparatus, comprising: 
 a polishing pad support assembly configured to position a polishing pad proximate to a substrate during polishing;    a carrier assembly configured to position the substrate against the polishing pad during polishing; and    an eddy current sensing system configured to monitor a conductive film of the substrate, the sensor including a core positioned to be on a side of the polishing pad opposite the substrate, wherein the core includes a plurality of prongs.    
   
   
       2 . The apparatus of  claim 1 , wherein the eddy current sensing system includes one or more coils wrapped around the core.  
   
   
       3 . The apparatus of  claim 2 , wherein the eddy current sensing system includes a single coil wrapped around the core.  
   
   
       4 . The apparatus of  claim 3 , wherein a first coil from the one or more coils is wrapped around at least two of the plurality of prongs.  
   
   
       5 . The apparatus of  claim 3 , wherein the eddy current sensing system further comprises an oscillator, and wherein the oscillator is in communication with the single coil.  
   
   
       6 . The apparatus of  claim 3 , wherein the eddy current sensing system further comprises a capacitor, and wherein the capacitor is in communication with the single coil in a parallel configuration.  
   
   
       7 . The apparatus of  claim 1 , wherein the core has a generally U-shaped cross section.  
   
   
       8 . The apparatus of  claim 1 , wherein the polishing pad support assembly includes a platen rotatable about an axis and the core is supported by and rotates with the platen.  
   
   
       9 . The apparatus of  claim 8 , wherein the plurality of prongs includes a first prong and a second prong positioned farther from the axis than the first prong.  
   
   
       10 . The apparatus of  claim 8 , wherein the first prong and the second prong are positioned substantially along a radius of the platen.  
   
   
       11 . The apparatus of  claim 1 , wherein the core comprises ferrite.  
   
   
       12 . The apparatus of  claim 1 , further comprising a first motor coupled to the polishing pad support assembly to move the polishing pad support assembly and create relative motion between the polishing pad and the substrate.  
   
   
       13 . The apparatus of  claim 12 , wherein the first motor rotates the polishing pad support assembly.  
   
   
       14 . The apparatus of  claim 12 , further comprising a second motor coupled to the carrier assembly to move the carrier assembly and create relative motion between the polishing pad and the substrate.  
   
   
       15 . The apparatus of  claim 12 , wherein the core is supported by and moves with the polishing pad support assembly.  
   
   
       16 . The apparatus of  claim 1 , further comprising at least one of the substrate and the polishing pad.