METHOD AND APPARATUS FOR INSPECTING A SEMICONDUCTOR WAFER USING A DYNAMIC THRESHOLD

A method and apparatus for inspecting the surface of an object such as a semiconductor wafer for contaminant particles. The apparatus includes a light source for illuminating an area on the surface of the object. A camera is positioned above the surface of the object and detects light scattered by any particles present on the surface at that area, the camera detecting light scattered from the area over a field of view, or window, which is defined by the camera, a focusing lens and the relative distance therebetween. A computer is coupled to the camera and serves to store, process, identify and/or analyze the light detected by the camera. The computer also serves to calculate a minimum light intensity threshold level which is dynamic to compensate for variances in the background light intensity of different portions of the object. The value of the threshold level is calculated for each window of the object defined by the apparatus using the equation: T.sub.W =.mu..sub.W +.eta.-.delta..sub.W, where T.sub.W represents the threshold value for the particular window, .mu..sub.W represents the mean light intensity for the particular window, .eta. is a floating point constant value and .delta..sub.W is the light intensity standard deviation for the particular window.