| 摘要 |
PURPOSE:To enable to perform the positioning of a mask and a wafer at the prescribed position in a highly accurate manner by a method wherein the driving amount of a fine adjustment means is controlled in a closed loop based on the output of a displacement amount detector, and also the fluctuations in output of the displacement amount detector is automatically corrected. CONSTITUTION:A piezoelectric element is discharged, and the initial correction value is set on a resistor 51. Then, the output voltage of a displacement voltage converting circuit 48 is corrected by a differential amplifier 53 in terms of the initial correction value of a DAC 52, and the corrected value is inputted to a microprocessor 40 through the intermediary of an ADC47. If the input voltage of the ADC47 is within the allowable value, the inputted value is memorized in a memory storage as the zero point of a position detector 22 and the displacement voltage converting circuit 48. The required driving quantity of the piezoelectric element 23 is computed by the microprocessor 40 using the zero point as the reference point, and the piezoelectric element 23 is driven. Also, when said input voltage is larger than the allowable value, a series of correcting procedures is performed repeatedly until the input voltage is brought down within the allowable value. When proper correction can not be made, an alarm is given, and if the number of loops exceeds the prescribed number, a position detector 22 or the displacement voltage converting circuit 48 are considered as out of order, and the measurement of displacement amount is stopped.
|
