| 摘要 |
PURPOSE:To prevent an image of a body to be detected from shifting or deviating on its image plane in focusing operation by aligning the optical axis of a focusing lens group almost with the main light beam of parallel luminous flux from a collimator lens group. CONSTITUTION:Oblique luminous flux (a) from an alignment mark A and an alignment reference mark B is image-formed at the rear-side focus position of a lens 6 through objectives 5 and 6. Luminous flux from a position B1 is converted by a positive collimator lens 7 into parallel luminous flux a1, which is image-formed again as an image B2 of both marks A and B on a screen 9 through an image forming lens 8. Therefore, the image B2 is observed through an image pickup device 12; and the image B2 is focused by moving the screen 9 and objective 10 in one body and a wafer 1 and a reticle 4 are positioned by moving either of the wafer 1 and reticle 4. At this time, the main light beam is made incident on the screen 9 at right angles, so the image B2 neither shifts nor deviates on the screen 9. |
