Optical apparatus, measurement method, and semiconductor device manufacturing method

摘要

An optical apparatus includes an optical device arranged on the optical path of EUV light which extends from a plasma light source to a predetermined position, an optical sensor, and a measuring device which measures the optical characteristic or its change of the optical device on the basis of an output from the optical sensor. The optical sensor measures in situ the optical characteristic or its change of the optical device arranged on the optical path by the optical apparatus arranged outside the optical path.