Patent ID: 7495742

Claim:
A method for measuring optical performance of a projection optical system in an exposure apparatus, said method comprising: placing an illumination stop for oblique illumination, the illumination stop having a predetermined optimized shape in an illumination optical system, wherein the shape of the illumination stop is optimized in accordance with a specific Zernike term; determining an area of a pupil in a pupil plane of the projection optical system based on said predetermined optimized shape; scanning a test reticle or a reference plate; imaging a test pattern on the test reticle or the reference plate onto a photosensitive substrate during said scanning step via the area of said pupil which has been determined by said determining step, wherein light intensity distribution at the determined area of said pupil is substantially similar to the predetermined optimized shape of said illumination stop; and measuring a positional offset between a predetermined position of the test pattern and an image of the test pattern that has been imaged by said imaging step, wherein light that passes through the determined area of the pupil is restricted by the test pattern and the illumination stop so that the positional offset of the test pattern image with respect to the predetermined position has a 1:1 relationship with a coefficient of the specific Zernike term.