Catadioptric projection lens for 1.3 NA scanner

In the history of DUV (Deep Ultra Violet) microlithographic lens design, three kinds of leaps have occurred to maintain the progress of technology in the semiconductor industry. The first step is the application of aspherical elements. This allowed us to increase NA up to around 0.9. The second innovation is water immersion. Thanks to the 1.44 refractive index of water, and because the numerical aperture (NA) is defined as the product of the sine of the maximum ray angle on the image plane and the refractive index in the image space, even with a lower maximum ray angle on the imaging plane than dry with a lens, we can achieve NA of 1.07. The latest technological jump is the development of catadioptric lens systems, which are roughly defined as the combined usage of refractive element(s) and reflective element(s). The catadioptric system allows us to achieve a full field 1.3NA projection lens that is used in our scanner NSR-S610C. In this paper we discuss optical design concepts and some challenges for catadioptric lenses. In addition, current lens performance including wavefront, lens flare, and image vibration are shown.