1 April 2013 In-situ optical testing of exposure tools via localized wavefront curvature sensing
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We present a new form of optical testing for exposure tools based on measuring localized wavefront curvature. In this method, offset monopole illumination is used to probe localized regions of the test optic pupil. Variations in curvature manifest as focus shifts, which are measured using a photodiode-based grating-on-grating contrast monitor, and the wavefront aberrations are reconstructed using a least-squares approach. This technique is attractive as it is independent of the numerical aperture of the system and does not require a CCD or a separate interferometer branch.
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Ryan Miyakawa, Ryan Miyakawa, Xibin Zhou, Xibin Zhou, Michael Goldstein, Michael Goldstein, Dominic Ashworth, Dominic Ashworth, Kevin Cummings, Kevin Cummings, Yu-Jen Fan, Yu-Jen Fan, Yashesh Shroff, Yashesh Shroff, Gregory Denbeaux, Gregory Denbeaux, Yudhi Kandel, Yudhi Kandel, Patrick Naulleau, Patrick Naulleau, "In-situ optical testing of exposure tools via localized wavefront curvature sensing", Proc. SPIE 8679, Extreme Ultraviolet (EUV) Lithography IV, 86790Q (1 April 2013); doi: 10.1117/12.2013880; https://doi.org/10.1117/12.2013880

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