Patent ID: 6514775
Filing Date: 2003-02-04
Classification: B24B

Abstract:
A method for determining a process end point during a semiconductor wafer polishing process, using a measurement system having multiple pairs of lasers and sensors, the method comprising:scanning a beam of radiation to be incident upon each of a plurality of measurement positions on the semiconductor wafer in sequential order, the beam of radiation causing radiation to reflect off of the semiconductor wafer at each of the measurement positions; measuring a reflectance value of the radiation reflecting off each of the measurement positions on the semiconductor wafer with each of the sensors; recording the frequency of the reflectance values obtained by each of the sensors at each of the measurement positions; determining an average reflectance value representing the reflectance value that was most frequently measured by the sensors wherein a sequential execution of the scanning, measuring, recording, and determining operations is referred to a monitoring cycle; repeating the monitoring cycle to obtain additional average reflectance values, each of the additional average reflectance values obtained at a later time during the semiconductor wafer polishing process, the average reflectance values falling within an initial range of reflectance values during at least a beginning period of the polishing process; and identifying the process end point to be approximately at the time when the average reflectance values substantially begin to deviate from the initial range of reflectance values, whereby the polishing of the semiconductor wafer is terminated when the process end point has been identified.