| 摘要 |
PURPOSE:To discriminate a small defect of a work by comparing the circular- arc of a wafer with a radius of a true circle reversely calculated from the area of the two-dimensional profile of the wafer, and comparing the chord of the wafer with a linear line calculated from the least square method. CONSTITUTION:A computer first writes a video signal in an image memory 15 to display the profile 13A of a wafer 12 on a display unit 18, counts the picture elements on the wafer 12 to calculate the area S of the profile of the wafer 12 and a histogram, calculates the position (GX, GY) of the centroid of the profile of the wafer 12, measures the distance to the outer edge of the profile, and detects the minimum of the distance. It then obtains dot positions P1-P5 of the suitable number near the minimum portion to obtain a formula y=ax+b for approximating the linear line corresponding to the chord of the profile of the wafer 12 by the least square method. Then, it compares the circle of a radius (r) with the position (SX, SY) calculated from the centroid position, y=ax+b, d as a center with the circular arc of the outer edge of the profile along the circumference to obtain the displacement. It also compares the linear line of the linear approximate equation y=ax+b wit the chord of the outer edge of the profile to obtain the displacement.
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