1 April 2013 In-situ optical testing of exposure tools via localized wavefront curvature sensing
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Abstract
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, Xibin Zhou, Michael Goldstein, Dominic Ashworth, Kevin Cummings, Yu-Jen Fan, Yashesh Shroff, Gregory Denbeaux, Yudhi Kandel, 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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