Patent ID: 7081956

Claim:
A device for determining reflection lens pupil transmission distribution in a photolithographic reflective imaging system, the device comprising: an illumination source; a reticle supporting a reflective mask layer having a plurality of light-reflecting areas and non-reflective areas thereon; a diffuser removably mounted with respect to the reflective mask layer; a lens system comprising one or more reflective elements; and an image plane, wherein a pupil image corresponding to one or more the plurality of light-reflecting areas in the reflective mask layer is formed at or near the image plane when light from the illumination source passes through the diffuser to the reflective mask layer, reflects from the light-reflecting areas and passes through the lens system, the pupil image having a reflection lens pupil transmission distribution, wherein the diffuser is removably mounted for normal operation with the diffuser in place and the diffuser is removed for determination of reflection lens pupil transmission distribution.