Finding substrate notch on substrate between platens in chemical mechanical polishing

Abstract

A notch finding station includes a sensor to generate a signal that depends on an proportion of a sensing region of the sensor that is covered by the substrate, and a controller. The controller is configured to cause an actuator to position a carrier head relative to the sensor such that the sensing region of the sensor is at an edge of the substrate, cause the motor to generate rotational motion such that the sensing region of the sensor scans along a circumference of the substrate, and detect an angular position of a notch in the edge of the substrate based on a signal from the sensor, including compensating for a sinusoidal component of the signal resulting from an offset of the center of the substrate from the axis of rotation.

What is claimed is: 
     
         1 . A polishing apparatus, comprising:
 a plurality of stations including a first station that is a polishing station or a transfer station and a second station that is a polishing station;   a carrier head to hold a substrate, the carrier head movable by an actuator along a path from the first station to the second station;   a motor to rotate the carrier head about an axis of rotation;   a notch finding station positioned on the path between the first station and the second station, the notch finding station including a sensor to generate a signal that depends on an proportion of a sensing region of the sensor that is covered by the substrate; and   a controller configured to
 cause the actuator to position the carrier head such that the substrate is positioned at the notch finding station such that sensing region of the sensor is at an edge of the substrate, 
 cause the motor to rotate the carrier head such that the sensing region of the sensor scans along a circumference of the substrate, and 
 detect an angular position of a notch in an edge of the substrate based on a signal from the sensor, including compensating for a sinusoidal component of the signal resulting from an offset of the center of the substrate from the axis of rotation. 
   
     
     
         2 . The apparatus of  claim 1 , wherein the sensor comprises an optical sensor including a light source to generate a light beam that impinges a surface of the substrate and a detector to detect reflected light and generate a signal indicating an intensity of the reflected light. 
     
     
         3 . The apparatus of  claim 2 , wherein the optical sensor is configured to at an oblique angle. 
     
     
         4 . The apparatus of  claim 2 , wherein the optical sensor is configured to generate a light beam that impinges a surface the substrate normal to the surface. 
     
     
         5 . The apparatus of  claim 2 , wherein the light source comprises a laser. 
     
     
         6 . The apparatus of  claim 2 , wherein the light source comprises a plurality of light sources that generate light beams having different wavelengths. 
     
     
         7 . The apparatus of  claim 6 , wherein the controller is configured to select a light source from the plurality of light sources based on a pattern on the substrate. 
     
     
         8 . The apparatus of  claim 1 , wherein the sensor comprises a capacitive sensor. 
     
     
         9 . The apparatus of  claim 1 , wherein the sensor comprises a confocal microscope. 
     
     
         10 . The apparatus of  claim 1 , wherein the sensor comprises a laser displacement sensor. 
     
     
         11 . The apparatus of  claim 1 , wherein the first station is a polishing station. 
     
     
         12 . The apparatus of  claim 1 , wherein the first station is a transfer station. 
     
     
         13 . The apparatus of  claim 1 , wherein the controller is configured to compensate for the sinusoidal component of the signal by monitoring a first derivative of the signal and detecting a portion of the first derivative that exceeds a threshold value. 
     
     
         14 . The apparatus of  claim 1 , wherein the controller is configured to compensate for the sinusoidal component of the signal by monitoring a second derivative of the signal and detecting a portion of the second derivative that exceeds a threshold value. 
     
     
         15 . The apparatus of  claim 1 , wherein the controller is configured to compensate for the sinusoidal component of the signal by subtracting a sinusoidal function from the signal. 
     
     
         16 . The apparatus of  claim 15 , wherein the sinusoidal function is fit to the signal before being subtracted from the signal. 
     
     
         17 . The apparatus of  claim 1 , wherein the controller is configured to compensate for the sinusoidal component of the signal by applying a high-pass filter to the signal that removes the sinusoidal component. 
     
     
         18 . The apparatus of  claim 1 , wherein the sensing region has a radial width of 5-10 mm. 
     
     
         19 . The apparatus of  claim 1 , wherein the sensing region is substantially circular. 
     
     
         20 . The apparatus of  claim 1 , wherein the controller is configured cause the actuator to position the carrier head such that the substrate is positioned such that the sensing does not overlap a retaining ring of the carrier head. 
     
     
         21 . A method, comprising:
 holding a substrate in a carrier head with the substrate positioned such that a sensing region of a sensor of a notch finding station is at an edge of the substrate;   rotating the carrier head to rotate the substrate such that the sensing region of the sensor scans along a circumference of the substrate; and   detecting an angular position of a notch in an edge of the substrate based on a signal from the sensor, including compensating for a sinusoidal component of the signal resulting from an offset of the center of the substrate from the axis of rotation.   
     
     
         22 . A notch finding station, comprising:
 a sensor to generate a signal that depends on an proportion of a sensing region of the sensor that is covered by a substrate; and   a controller is configured to
 cause an actuator to position a carrier head relative to the substrate with the sensing region of the sensor at an edge of the substrate, 
 cause a motor to generate relative motion between the carrier head and the sensor such that the sensing region of the sensor scans along a circumference of the substrate, and 
 detect an angular position of a notch in the edge of the substrate based on a signal from the sensor, including compensating for a sinusoidal component of the signal resulting from an offset of the center of the substrate from the axis of rotation.