1 July 2002 ASET development of at-wavelength phase-shifting point diffraction interferometer
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We have been studying phase-shifting point diffraction interferometry (PSPDI) as a technique evaluating extreme-ultraviolet (EUV) lithographic optics at the working wavelengths. In the PSPDI, the wavefront error of the test optic affects the measurement itself. One of these effects is that flare of a spot focused onto a pinhole of a PSPDI mask is mixed with a test beam as an optical noise. To mitigate the flare effect, we changed the PSPDI mask design and replaced the convex mirror of a test optic. The other effect is reducing the contrast of the interference fringe. To reduce the misalignment of the test optic, we have improved the accuracy of the PSPDI using visible light. Since the residual wavefront error of the test optic is not small enough for at-wavelength PSPDI measurement, we obtained an at-wavelength wavefront using a rather large second pinhole. The obtained EUV wavefront qualitatively agreed with the visible one.
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Katsumi Sugisaki, Katsumi Sugisaki, Yucong Zhu, Yucong Zhu, Yoshio Gomei, Yoshio Gomei, Masahito Niibe, Masahito Niibe, } "ASET development of at-wavelength phase-shifting point diffraction interferometer", Proc. SPIE 4688, Emerging Lithographic Technologies VI, (1 July 2002); doi: 10.1117/12.472344; https://doi.org/10.1117/12.472344

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