Polishing pad with built-in optical sensor

Abstract

An optical sensor that includes a light source and a detector is located within a cavity in a polishing pad so as to face the surface that is being polished. Light from the light source is reflected from the surface being polished and the detector detects the reflected light. The electrical signal produced by the detector is conducted to a hub located at the central aperture of the polishing pad. The disposable polishing pad is removably connected, both mechanically and electrically to the hub. The hub contains electronic circuitry that is concerned with supplying power to the optical sensor and with transmitting the electrical signal to a non-rotating station. Several techniques are described for accomplishing these tasks. The system permits continuous monitoring of an optical characteristic of a surface that is being polished, even while the polishing machine is in operation, and permits the end point of the polishing process to be determined.

1 . A polishing pad assembly for use in a CMP process, said polishing pad assembly comprising: 
 a polishing pad sized and dimension for use on a CMP system;    an optical sensor disposed within the polishing pad; and    a means for transferring a signal indicative of an optical characteristic of a surface of a wafer from the optical sensor.    
   
   
       2 . The polishing pad assembly of  claim 1  wherein the means for transferring the signal is selected from the group consisting of a radio link, an optical link and an acoustic link.  
   
   
       3 . The polishing pad assembly of  claim 1  further comprising a means for supplying electrical power to the optical sensor.  
   
   
       4 . The polishing pad assembly of  claim 3  wherein the means for supplying electrical power to the optical sensor is selected from the group consisting of a battery, a solar cell, a photo voltaic array, a magneto and a transformer.  
   
   
       5 . The polishing pad assembly of  claim 1  wherein the optical sensor is adapted to detect an optical quality in the wafer selected from the group consisting of reflectivity, polarization, absorptivity and photoluminescence.