8 November 2000 Present status of the ASET at-wavelength phase-shifting point diffraction interferometer
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The precise alignment of Extreme Ultra-Violet Lithography (EUVL) imaging system is necessary in order to achieve diffraction-limited performance. Interferometric testing at the exposure wavelength is needed to ensure proper alignment and to achieve an acceptable final wavefront. We have built a prototype at-wavelength interferometer at the NewSUBARU facility. This interferometer is a phase-shifting point diffraction interferometer (PS/PDI) testing specially constructed Schwarzschild optics. Preliminary experiments using visible light were performed in order to learn this PS/PDI. The Schwarzschild optics were aligned using visible wavefront measurements with the interferometer. The precision of the visible measurements was evaluated. Experiments using EUV radiation have been started.
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Katsumi Sugisaki, Katsumi Sugisaki, Yucong Zhu, Yucong Zhu, Yoshio Gomei, Yoshio Gomei, Masahito Niibe, Masahito Niibe, Takeo Watanabe, Takeo Watanabe, Hiroo Kinoshita, Hiroo Kinoshita, } "Present status of the ASET at-wavelength phase-shifting point diffraction interferometer", Proc. SPIE 4146, Soft X-Ray and EUV Imaging Systems, (8 November 2000); doi: 10.1117/12.406675; https://doi.org/10.1117/12.406675

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