| 摘要 |
<p>PURPOSE:To improve the positioning accuracy of the title device by providing an optical-path forming optical member, which leads parallel beams coming from a light emitting member through a rotating wafer after intersecting the peripheral section of the wafer at two or more points to a light receiving member. CONSTITUTION:Nearly parallel beams from a light emitting member 1-D are made incident to a light receiving member 2D after the beams are bent in the direction parallel to, but opposite to, the direction from the member 1-D by means of optical-path forming optical members 7-A and 7-B. The beams are made to intersect the peripheral section including the OF section of a rotating wafer at two points before passing through the member 7-A and after passing through the member 7-B. Accordingly, even when the rotating center of the wafer deviates slightly, measurement errors hardly occur due to the unevenness in illuminance, because the unevenness in illuminance of the two beams in Y-direction can be regarded as equal to each other. Therefore, highly accurate positioning can easily be performed.</p> |
