Patent ID: 9594316
Date: 2017-03-14
CPC Classifications: G01B,G03F

Claim:
1. A position detecting apparatus which detects a position of a target surface in a direction crossing the target surface with a light beam which is projected onto the target surface from an oblique direction with respect to the target surface and is reflected on the target surface, the surface position detecting apparatus comprising; a prism member arranged in an optical path of the light beam, the prism member having a first reflection surface and a second reflection surface, the first reflection surface performing a total reflection of the light beam within the prism member, the second reflection surface performing a total reflection of the light beam from the first reflection surface within the prism member, the first and second reflection surfaces being arranged so that the light beam from the second reflection surface and the light beam on an incidence side of the first reflection surface are non-crossing each other, wherein one of incidence angles of the light beam to the first and second reflection surfaces is smaller than the other of the incidence angles so that, with respect to a relative positional deviation caused by total reflection between a first polarization component and a second polarization component which have orthogonal polarization directions relative to each other and constitute the light beam, at least a part of a first relative positional deviation amount caused at the first reflection surface and a second relative positional deviation amount caused at the second reflection surface substantially cancel each other.