| 摘要 |
A position detecting apparatus (Fig. 1) usable for aligning a mask (15) and a semiconductor wafer (16), wherein a laser beam (14) produced by a semiconductor laser (1) is projected through a predetermined optical system to alignment marks (15a,16a) formed on the mask (15) and the wafer (16), and the light (17) reflected by the marks is detected by an accumulation type sensor (4) to produce an electric signal, from which the relative positional relation between the mask (15) and the wafer (16) is detected on the basis of the electric signal. To obtain proper mark signals, the quantity of light incident on the accumulation sensor (4) is controlled. In this apparatus, the beam emitting strength of the semiconductor laser (1) is made constant, and the control of the amount of light incident on the accumulation sensor (4) is effected by controlling (2) the operation period of the semiconductor laser (1). In addition, the actuation timing (7) of the semiconductor laser (1) is advanced from the accumulation start of the accumulation type sensor (4) by the time (Ts) required for the semiconductor laser (1) to be thermally stabilized after its actuation. The mark detection signal produced by the accumulation sensor (4) is precise. |
