Patent ID: 8004756

Claim:
A catadioptric objective comprising: a plurality of optical elements arranged along an optical axis to image a pattern from an object field in an object surface of the objective to an image field in an image surface region of the objective at an image-side numerical aperture NA with electromagnetic radiation from a wavelength band around a central wavelength λ<300 nm, the optical elements including: a concave mirror; and a plurality of lenses; wherein the projection objective forms an image of the pattern in a respective Petzval surface for each wavelength λ of a wavelength band, the Petzval surfaces deviating from each other for different wavelengths; wherein the plurality of lenses include lenses made from different materials having substantially different Abbe numbers; and wherein a longitudinal departure p of the Petzval surface at a given wavelength from a planar reference surface at an edge field point of the image field, at maximum image height y′, measured parallel to the optical axis in the image surface region, varies with the wavelength λ according to dp/d λ<(15 λ/NA 2 )/nm.