Carrier Head Sweep Motor Current for In-Situ Monitoring

Abstract

A chemical mechanical polishing system includes a platen to support a polishing pad, two carrier heads configured to hold two substrates against the polishing pad at the same time, two actuators to sweep the two carrier heads laterally across the polishing pad, an in-situ polishing monitoring system including a two current sensors to sense two currents supplied to the two actuators and generate two signals, and a controller to receive the two signals and independently detect a two endpoints for the two substrates based on the two signals.

1 . A chemical mechanical polishing system, comprising:
 a platen to support a polishing pad;   a first rotatable carrier head configured to hold a first substrate against the polishing pad;   a second rotatable carrier head configured to hold a second substrate against the same polishing pad at the same time that the first carrier head holds the first substrate against the polishing pad;   a first actuator to sweep the first carrier head laterally across the polishing pad while the first substrate contacts the polishing pad;   a second actuator to sweep the second carrier head laterally across the polishing pad while the second substrate contacts the polishing pad; and   an in-situ polishing monitoring system comprising
 a first current sensor to sense a first current supplied to the first actuator and generate a first signal, 
 a second current sensor to sense a second current supplied to the second actuator and generate a second signal, and 
 a controller to receive the first signal and the second signal and independently detect a first endpoint and a second endpoint for the first substrate and the second substrate, respectively, based on the first signal and the second signal. 
   
     
     
         2 . The system of  claim 1 , further comprising a track, a first carriage supported by the track, and a second carriage supported by the track, wherein the first carrier head is suspended from the first carriage and the second carrier head is suspended from the second carriage. 
     
     
         3 . The system of  claim 2 , wherein the first actuator is configured to move the first carriage along the track to sweep the first carrier head and the second actuator is configured to move the second carriage along the track to sweep the second carrier head. 
     
     
         4 . The system of  claim 3 , wherein the track comprises a magnetic track, the first actuator comprises a first linear motor coil and the second actuator comprises a second linear motor coil. 
     
     
         5 . The system of  claim 1 , wherein the first signal comprises a first sequence of values and the second signal comprises a second sequence of values and the controller is configured to detect a first change in slope in the first sequence and to detect a second change in slope in the second sequence. 
     
     
         6 . The system of  claim 5 , wherein the controller is configured to detect a first endpoint by detecting a decrease in slope in the first sequence and to detect a second endpoint by detecting a decrease in slope in the second sequence. 
     
     
         7 . The system of  claim 6 , comprising the first substrate and the second substrate, wherein each of the first substrate and the second substrate include an overlying layer and an underlying layer having a lower coefficient of friction against the polishing pad than the overlying layer. 
     
     
         8 . The system of  claim 5 , wherein the controller is configured to detect a first endpoint by detecting an increase in slope in the first sequence and to detect a second endpoint by detecting a increase in slope in the second sequence. 
     
     
         9 . The system of  claim 8 , comprising the first substrate and the second substrate, wherein each of the first substrate and the second substrate include an overlying layer and an underlying layer having a higher coefficient of friction against the polishing pad than the overlying layer. 
     
     
         10 . The system of  claim 1 , comprising a first motor to rotate the first carrier head and a second motor to rotate the second carrier head. 
     
     
         11 . The system of  claim 10 , wherein the in-situ polishing monitoring system includes a third current sensor to sense a third current supplied to the first motor and generate a third signal, and a fourth current sensor to sense a fourth current supplied to the second motor and generate a fourth signal. 
     
     
         12 . The system of  claim 11 , wherein the controller is configured to receive the third signal and the fourth signal and independently detect the first endpoint based on the first signal and third signal, and detect the second endpoint based on the second signal and the fourth signal. 
     
     
         13 . The system of  claim 12 , wherein the controller is configured to add the first signal and the third signal to generate a first combined signal and to detect the first endpoint based on the first combined signal, and to add the second signal and the fourth signal to generate a second combined signal and to detect the second endpoint based on the second combined signal. 
     
     
         14 . The system of  claim 12 , wherein the controller is configured to detect the first endpoint based on detecting an endpoint in either the first signal or the third signal, and to detect the second endpoint based on detecting an endpoint in either the second signal or the fourth signal. 
     
     
         15 . The system of  claim 12 , wherein the controller is configured to detect the first endpoint based on detecting an endpoint in both the first signal and the third signal, and to detect the second endpoint based on detecting an endpoint in both the second signal and the fourth signal. 
     
     
         16 . A chemical mechanical polishing system, comprising:
 a platen to support a polishing pad;   a rotatable carrier head configured to hold a substrate against the polishing pad;   an actuator to sweep the carrier head laterally across the polishing pad while the substrate contacts the polishing pad; and   an in-situ polishing monitoring system comprising
 a current sensor to sense a current supplied to the actuator and generate a signal, and 
 a controller to receive the signal and detect an endpoint for the substrate based on the signal. 
   
     
     
         17 . The system of  claim 16 , further comprising a track, a carriage supported by the track, wherein the carrier head is suspended from the carriage, and wherein the actuator is configured to move the carriage along the track to sweep the carrier head. 
     
     
         18 . The system of  claim 16 , wherein the signal comprises a sequence of values and the controller is configured to detect a change in slope in the sequence. 
     
     
         19 . The system of  claim 16 , comprising a motor to rotate the carrier. 
     
     
         20 . The system of  claim 19 , wherein the in-situ polishing monitoring system includes a second current sensor to sense a second current supplied to the motor and generate a second signal, and wherein the controller is configured to receive the second signal and detect the endpoint based on the first signal and second signal.