Influence of birefringence on the image formation of high-resolution projection optics.
The influence of birefringence on high-resolution projection optics used for microlithography is investigated theoretically. A formula for partially coherent imaging that is based on the scalar diffraction theory is extended to include the birefringent properties of lens materials. By the determination of the birefringent properties of lens materials by use of random numbers, data on 200 lenses, each composed of 10 birefringent elements, are generated to estimate statistically the degree of imaging-performance degradation. As a result, it was found that the image contrast of a five-bar pattern decreases as a quadratic function of the maximum magnitude of the birefringence that was set in common for all elements in each lens data set.
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Optics Technology Research Center, Canon, Inc., 20-2, Kiyohara-Kogyo-Danchi, Utsunomiya-shi, Tochigi-ken 321-3292, Japan. unno@cnt.canon.co.jp