| 摘要 |
PURPOSE:To obtain a more precise means of measuring the amount of misalignment of a mask and a wafer by a method wherein a mark interval measurement error caused by a magnification error of an optical system for observing an identification mark is corrected by adjusting the scanning speed of a laser beam. CONSTITUTION:A speed control driver 18 provided with a driver capable of finely adjusting the speed of rotation of a motor 6 for driving a polygon mirror 7, according to an outside signal, and with a control circuit is attached to said motor 6, and an instruction from CPU17 is given to this driver 18 to set the speed of rotation of the motor. On the occasion of assembly and adjustment, the magnitication error of an optical system for measuring (observing) positions is measured, and it is stored in a memory of CPU17. This CPU17 computes, from the value of the magnification error, a speed of rotation appropriate for correcting said magnification error, and gives a computed value to the driver 18. Thereby the speed of rotation of the motor 6, and that of the polygon mirror 7 consequently, is controlled, and thus a scanning distance per one period (e.g. 1muS) of clock by a laser beam shows a prescribed value, e.g. 0.1mum, constantly irrespective of the magnification error of an optical system for observation. |
