| 摘要 |
PURPOSE:To quickly and accurately detect the alignment mark of a wafer having large pedestal ingredient by a method wherein the average value and the peak value of an electric signal are detected, and the amplification factor of the amplifying means with which the signal obtained by deducting the average value from the electric signal is controlled in proportion to the difference between the average value and the peak value. CONSTITUTION:The signal only sent from the alignment mark of a mask 1 is measured in the state wherein a wafer signal is not present, and the peak of the output signal Sig of a photoelectric detector is detected. The timing of detection of the peak at that time is performed in synchronization with the count up of a counter 23, the peak position is stored in a RAM24, and the peak value is stored in the RAM located in a peak value detecting circuit 27. An amplifier of variable gain is controlled by a CPU17, and the difference between the signal Sig sent from a photoelectric detector 12 and the output of a pedestal level setting circuit 33 is amplified. Then, the value of a slice level setting circuit 26 is properly set again based on the detected peak level, and the signal only of the alignment mark of the mask is measured again. After the peak has been detected using the slice level which is set again, the CPU17 reads out a memory 24 and the positions TM1 and TM2 of the alignment mark of the mask are detected. |
