| 摘要 |
PURPOSE:To acquire detecting light having stable intensity even when the film thickness of a resist applied onto a wafer is dispersed partially by providing a means through which only lighting light having an incident angle that detecting light intensity has a peak in response to the film thickness of the resist is passed through the conjugate plane of an entrance pupil for a reducing glass in an optical path lighting the wafer. CONSTITUTION:An optical switching element is formed in such a manner that a liquid crystal 9 is sealed between two parallel glass plates 7, 7' by a seal 8, and AC voltage 11 can be applied to transference electrodes printed on glass plates 10, 10' by a switch 12. When P polarized light is irradiated, light passing through a liquid crystal element 13 is changed into S polarized light under the state in which the AC voltage 11 is at OFF by the switch 12, but it passes as it is as P polarized light under an ON state. Consequently, when an analyzer 14 is inserted and arranged on the backside of the liquid crystal element 13, only P polarized light is passed. A plurality of such optical switching elements are fitted, and only light having a specific illuminating angle is passed. |
