| 摘要 |
PURPOSE:To make it possible to automatically and properly set the sensitivity of a light receiving element corresponding to the state of a surface to be inspected, by controlling applied voltage on the basis of the average level of the detection signal of a light receiving element. CONSTITUTION:A microprocessor PU131 calculates the average value of four distance codes in the vicinity of the outer periphery of a wafer and control information for moving a Z-stage so as to take the distance and direction negating the average displacement thereof is applied to a motor controller 116 and the focus matching of an objective lens with respect to the entire surface region of the wafer is performed. Next, PU131 outputs a start pulse ST and a variable voltage applying circuit 120 applies the min. or max. voltage to a light receiving element 9. The detection output of the element 90 is integrated by an integrating circuit 124 and the voltage signal corresponding to the average level thereof is compared with a reference level by a comparator 125 and, when said signal is higher than the reference level, the output voltage of the circuit 120 is fixed and the light receiving element 90 is operated with sensitivity optimum to the wafer. |
