Patent ID: 6081325
Filing Date: 2000-06-27
Classification: G01N

Abstract:
An optical scanning system for detection of anomalies, such as particles or pattern defects, on a surface comprising:means for directing a focused beam of light onto a sample surface to produce an illuminated spot thereon;means for scanning the spot across the surface along a first scan line in a first scan and then subsequently along at least a second scan line in at least a second scan, so that said spot illuminates a common area on the surface during the at least two scans;a detector positioned adjacent to said surface to collect scattered light from the spot, wherein the detector includes a group of sensors including a first and at least one second line of sensors, said sensors providing output signals in response to the collected scattered light from an array of surface portions defining a line of pixels in the common area so that during the at least two scans, scattered light from one of the pixels is collected by a corresponding sensor in the first line of sensors and by a corresponding sensor in the second line of sensors, said detector located away from a specular reflection direction of the beam;an optical element focusing scattered light from each of the pixels in the line of pixels during the first scan to the corresponding sensor in the first line of sensors, and scattered light from each of the pixels in the line of pixels during the at least one second scan to the corresponding sensor in the at least one second line of sensors;mean for synchronizing a transfer of signals from said first line of sensors to the at least one second line of sensors, thereby performing time delayed integration of signals at scattered by the line of pixels; andmeans for analyzing the outputs of the sensors to detect anomalies on the surface.