New developments in the design of ring-field projection cameras for EUV lithography: passive pupil correction

The design of all-reflective cameras for EUV-lithography is an area of lens design that has received attention in the last few years. One important goal is to design a projection camera that meets first-order requirements, image quality requirements, packaging requirements, minimizes the number of mirrors to minimize reflection losses, and that can be successfully manufactured. From the optical design point of view it is desirable to use the best designing tools and concepts to maximize the performance of a projection camera. The optical requirements are so stringent that every little bit of design help is welcome. Examples of some useful optical design ideas are the annular field concept and the concept of annular surfaces. In this paper we discuss how the concept of passive pupil correction can be applied to improve the theoretical performance of an annular or ring field system.