System for detecting a signal for aligning two bodies and signal processing method

摘要

Disclosed is a system to be used with a wafer provided with at least one first alignment mark and a mask provided with a plurality of second alignment marks and which is provided with a detecting device for sensing the first and second alignment marks and putting out detection signals, a signal producing circuit producing a comparison signal, and a signal comparing and producing circuit for comparing the pulse width of the comparison signal with the pulse width of the detection signals and producing a plurality of substitute signals when the pulse width of the detection signal is greater than the pulse width of the comparison signal and wherein when the first and second alignment marks have come close to each other or partly overlapped each other, the respective alignment marks are discriminated.