6 May 2005 Evaluation of pattern fidelity in EUVL using a high-numerical-aperture small-field EUV exposure tool (HiNA)
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Abstract
Since extreme-ultraviolet lithography (EUVL) uses a much shorter wavelength than optical lithography, it should provide better pattern fidelity. In this study, various patterns were printed with a high-numerical-aperture (NA=0.3) small-field EUV exposure tool (HiNA) with new set-3 projection optics, and their fidelity to the mask patterns was evaluated. The set-3 optics have one-half the wavefront error and one-quarter the flare of the set-2 optics, and should thus provide much better image contrast. For EUVL mask fabrication, we used mask blanks with a TaGeN/Cr absorber stack and existing process tools for photomasks, which enable the fabrication of very accurate mask patterns. In the printing experiments, 80-nm line-and-space (L/S) and isolated-line patterns were successfully fabricated simultaneously without any optical proximity correction (OPC) of the mask pattern. For 60-70-nm line patterns, the printed patterns were still of good quality, but were slightly deformed. We speculate that this was caused by the low contrast of the aerial image, mainly due to wavefront error and flare. For 60-80-nm contact-hole (C/H) patterns, both dense and isolated holes were successfully fabricated without OPC or phase-shift mask (PSM). However, the printed patterns were almost circular, even though the mask patterns were square. This might be due to deformation of the aerial image and deformation produced by the resist process. For better pattern fidelity, it will probably be necessary to improve the characteristics of both the projection optics and the resist.
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Yuusuke Tanaka, Hiroaki Oizumi, Takeo Hashimoto, Fumiaki Kumasaka, Iwao Nishiyama, Tsukasa Abe, Hiroshi Mohri, Naoya Hayashi, "Evaluation of pattern fidelity in EUVL using a high-numerical-aperture small-field EUV exposure tool (HiNA)", Proc. SPIE 5751, Emerging Lithographic Technologies IX, (6 May 2005); doi: 10.1117/12.599050; https://doi.org/10.1117/12.599050
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