| 摘要 |
PURPOSE:To perform positioning accurately by providing movable mirrors on four sides of an XY stage, measuring the position in coordinates of mirrors in a pair by means of an optical system, processing electrically an information obtained through measurement, and thus finding the position of the center of the XY stage. CONSTITUTION:A beam light emitted from a laser head 18 is separated into beams for measuring the right and left sides of a slightly-moving stage 29 by a beam splitter 19. One of the beams falls on a right-side movable mirror 22 and a fixed mirror 23 through the intermediary of a mirror 20 and a beam splitter 21, and the reflected lights thereof enter a photoreceptor 24. Likewise, the reflected lights from a left-side movable mirror 26 and a fixed mirror 27 enter a photoreceptor 28. Information signals from the right and left photoreceptors enter counters 36 and 37. The signal of the counter 36 inverted by a phase inverter 38 and the signal of the conter 37 are added by an adder 39, while a value multiplied by 1/2 in a frequency-divider 40 and the value of the counter 36 are added by an adder 41, and thus the amount of transfer of the center of the slightly-moving stage in the direction X is calculated. The amount of transfer in the direction Y is found in the same way and thus the positioning is performed accurately. |
