Catadioptric objective for scatterometry

摘要

A system and method is described for correcting aberrations caused by field curvature with a catadioptric objective. In one example, a catadioptric optical system includes a first catadioptric element and a second catadioptric element. The first catadioptric element includes a first surface positioned to reflect a beam and a second surface positioned to focus the beam reflected by the first surface. The second catadioptric element is configured to receive the beam reflected by the second surface of the first catadioptric element. The second catadioptric element includes a third surface positioned to reflect the beam, and a fourth reflective surface positioned to focus the beam reflected by the third reflective surface. A curvature of the third or fourth surfaces of the second catadioptric element is chosen to apply a positive contribution to a field curvature associated with the first catadioptric element.