Patent ID: 8027088

Claim:
A projection objective having an object surface and an image surface, the projection objective comprising: a plurality of optical elements arranged along an optical axis and configured so that during operation the projection objective images a pattern arranged in the object surface onto the image surface, the optical elements comprising: a concave mirror; a first deflecting mirror tilted relative to the optical axis by a first tilt angle, t 1 , about a first tilt axis so that during operation the first deflecting mirror deflects light at a wavelength λ from the object surface towards the concave mirror or deflects light at λ from the concave mirror towards the image surface, the first deflecting mirror comprising a first reflective coating with reflectivity R s 1 (α 1 ) for s-polarized light at λ and a reflectivity R p 1 (α 1 ) for p-polarized light at λ incident on the first deflecting mirror at first angles of incidence α 1 for at least a first range of angles of incidence according to (t 1 −Δα 1 )≦α 1 ≦(t 1 +Δα 1 ); and a second deflecting mirror tilted relative to the optical axis by a second tilt angle, t 2 , about a second tilt axis, the second deflecting mirror comprising a second reflective coating with a reflectivity R s 2 (α 2 ) for s-polarized light at λ and a reflectivity R p 2 (α 2 ) for p-polarized light at λ incident on the second deflecting mirror at second angles of incidence α 2 for at least a second range of angles of incidence according to (t 2 −Δα 2 )≦α 2 ≦(t 2 +Δα 2 ), wherein: a first reflectivity sum, R s PE , for s-polarized light at λ of polar edge rays accumulated upon reflection on the first and second deflecting mirrors is substantially equal to a second reflectivity sum, R p E for p-polarized light of equatorial edge rays accumulated upon reflection on the first and second deflecting mirrors; Δα 1 is an angular difference between a center value of a range of angles of incidence on the first deflecting mirror and an angle selected from the group consisting of a maximum angle of incidence on the first deflecting mirror and a minimum angle of incidence on the first deflecting mirror; Δα 2 is an angular difference between a center value of a range of angles of incidence on the second deflecting mirror and an angle selected from the group consisting of a maximum angle of incidence on the second deflecting mirror and a minimum angle of incidence on the second deflecting mirror; and the projection objective is a catadioptric projection objective.