| 摘要 |
PURPOSE:To obtain a more precise means of measuring the amount of mis- alignment 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 varying a frequency of a measuring clock. CONSTITUTION:A clock pulse from a clock generator 7 is once frequency-divided by a preset counter 9 and then inputted to a counter 3 for measuring the amount of mis-alignment, i.e. a pulse interval. The preset counter 9 delivers a carry in every one rotation of the counter, and this carry turns to be a clock of a counter 4 for measuring the amount of mis-alignment. Some value is set in a latch 8 beforehand by CPU6, and this value is re-preset in the preset counter 9 automatically in every rotation of the preset counter 9. |
