16 June 2003 Development of illumination optics and projection optics for high-NA EUV exposure tool (HiNA)
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We have developed a high numerical aperture (NA) small-field exposure system (HiNA) for EUV exposure process development. NA of projection optics of EUV exposure tools for 45-nm node lithography is expected to be around 0.25, which is higher than that previously expected (0.1). HiNA has compatible illumination system, which can be switched to partial coherent illumination and coherent illumination by changing some optical elements. Coherent illumination system was prepared for a high contrast imaging but the uniformity of intensity is less than that of partial coherent illumination. A reflected-type fly*fs-eye element was adopted for partial coherent illumination, which can provide uniformity of both coherency and intensity simultaneously. The coherency of the partial coherent illumination is 0.8. HiNA projection optics consists of two aspheric mirrors, with the NA and the imaging field of 0.3 and 0.3×0.5mm2, respectively. We fabricated two sets of projection-optics. Although the wavefront error of set-1 optics was 7nmRMS, that of set-2 optics was improved to 1.9nmRMS, which was measured with a point diffraction interferometer (PDI) using He-Ne laser. The wavefront error of the set-2 optics was improved by using a new mirror mount mechanism. The mount system consists of several board springs made of super invar in order to minimize the deformation of mirrors by mounting stress. The projection optics of the set-2 has a remote controlled mirror adjustment mechanism which has five degrees of freedom (X,Y,Z,X-Tilt and Y-Tilt). The position of the concave secondary mirror was adjusted precisely with measuring the wavefront error using PDI.
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Tetsuya Oshino, Masayuki Shiraishi, Noriaki Kandaka, Katsumi Sugisaki, Hiroyuki Kondo, Kazuya Ota, K. Mashima, Katsuhiko Murakami, Hiroaki Oizumi, Iwao Nishiyama, Shinji Okazaki, "Development of illumination optics and projection optics for high-NA EUV exposure tool (HiNA)", Proc. SPIE 5037, Emerging Lithographic Technologies VII, (16 June 2003); doi: 10.1117/12.484936; https://doi.org/10.1117/12.484936

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