Monitoring a metal layer during 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 polishing system, comprising: 
 a platen having a top surface configured to support a polishing pad having a polishing surface;    a carrier configured to hold a substrate against the polishing surface; and    an eddy current monitoring system including a core supported by the platen, the core extending above the top surface of the platen.    
   
   
       2 . The polishing system of  claim 1 , further comprising a recess formed within the platen and configured to house the core body.  
   
   
       3 . The system of  claim 1 , wherein the core comprises a ferromagnetic body.  
   
   
       4 . The system of  claim 1 , further comprising a coil wound around the core.  
   
   
       5 . The system of  claim 1 , wherein the eddy current monitoring system includes a first coil wound around a first portion of the core, an oscillator electrically coupled to the first coil to induce an alternating current in the first coil and generate an alternating magnetic field in proximity to the substrate, a second coil wound around a second portion of the core, a capacitor electrically coupled to the second coil, and an amplifier electrically coupled to the second coil and the capacitor to generate an output signal.  
   
   
       6 . The system of  claim 5 , wherein the oscillator is configured to induce an alternating current with a substantially constant frequency selected to provide a resonant frequency when the substrate is not in proximity to the core.  
   
   
       7 . The system of  claim 5 , wherein the core includes two prongs and a connecting portion between the two prongs.  
   
   
       8 . The system of  claim 7 , wherein the first coil is wound around the connecting portion and the second coil is wound around at least one of the two prongs.  
   
   
       9 . The system of  claim 5 , wherein the second coil and the capacitor are connected in parallel.  
   
   
       10 . The system of  claim 1 , wherein the core is U shaped.  
   
   
       11 . The system of  claim 1 , further comprising a motor to cause relative motion between the platen and the carrier.  
   
   
       12 . The system of  claim 1 , wherein the core consists essentially of ferrite.  
   
   
       13 . The system of  claim 1 , wherein the platen is rotatable.  
   
   
       14 . The system of  claim 1 , further comprising an endpoint detection system to receive an output signal from the eddy current monitoring system and determine a polishing endpoint.