Mark detector

Abstract

Abstract PURPOSE:To detect an intersection with high reliability from a mark detection signal obtained by one beam scanning in a mark detector by detecting all the intersections between the mark detection signals and reference voltage and averaging these data. CONSTITUTION:A mark detection signal 12 is inputted to a comparator 15. A signal is fed to the controller 16 of a beam deflecting D/A converter every time the signal 12 exceeds the reference voltage 13 to latch the input value of the D/A converter. Simultaneously, pulses of number that exceeds the reference voltage 13 by the signal 12 are fed to a counter 18 for counting the pulses. Then, the input values Di of the respective D/A converters and the counted number Ni are applied to an arithmetic unit 19, which calculates the average of D'=(SIGMANiXDi)/SIGMANi (where i=1, 2,...,n). Here, n represents the number of steps of the D/A converter required for scanning the beam. The D' thus obtained is averaged to suppress the adverse effect of the noise to give reliable mark edge position thereto.

Inventors

• 👤 Korehito Matsuda
• 👤 Akinori Shibayama

Bibliographic Details