Patent ID: 6405101
Filing Date: 2002-06-11
Classification: H01L

Abstract:
A method of detecting the position of a substrate on a robot comprising:providing a plurality of sensors, each of said sensors being adapted to detect a passage of at least one of a leading and a trailing edge of a substrate; mounting a calibration substrate at a desired position on said robot; controlling said robot to cause said calibration substrate to make n passes over said detectors, wherein n is an integer greater than or equal to one; recording the position of said robot when at least one of a leading edge and a trailing edge of said calibration substrate, respectively, pass over each of said sensors during each of said n passes, thereby providing at least one recorded position for each pass of said robot; using the recorded positions to calculate a distance RCTR between a location of a reference point of said calibration substrate and a reference axis of said robot; averaging recorded positions of said robot when said leading edge of said calibration substrate passes over a first one of said sensors during said n passes and subtracting RCTR therefrom to yield a first calibration position RCA; averaging recorded positions of said robot when said leading edge of said calibration substrate passes over a second one of said sensors during said n passes and subtracting RCTR therefrom to yield a second calibration position RCB; averaging recorded positions of said robot when said trailing edge of said calibration substrate passes over said second one of said sensors during said n passes and subtracting RCTR therefrom to yield a third calibration position RCC; averaging recorded positions of said robot when said trailing edge of said calibration substrate passes over said first one of said sensors during said n passes and subtracting RCTR therefrom to yield a fourth calibration position RCD; using said robot to transport an operational substrate along a path with respect to said sensors; using each of said sensors to detect the passage of at least one of a leading and a trailing edge of said operational substrate, thereby providing a number of transition readings; using a first selected combination of said transition readings to calculate a first location of said operational substrate, said first location of said operational substrate corresponding to a first calculated reference point on said substrate; using second and successive selected combinations of said transition readings to calculate second and successive locations, respectively, of said operational substrate, said second and successive locations of said operational substrate corresponding to second and successive calculated reference points, respectively, on said operational substrate; determining physical relationships between said calculated reference points; discarding certain of said calculated reference points on the basis of said physical relationships, leaving a number of remaining calculated reference points; and using the remaining calculated reference points to compute a location of a net reference point on said operational substrate.