22 March 2010 Iterative procedure for in-situ optical testing with an incoherent source
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Abstract
Interferometry, the long-standing method for optical characterization, is difficult to perform at EUV wavelengths due to the lack of high power coherent EUV sources and difficult experimental setup. These problems are exacerbated by systematic errors from geometrical effects as EUV tools move to higher numerical apertures (NA) which require stricter tolerances for the optical elements involved in interferometry. In this paper we propose an iterative, image-based, in-situ method for optical characterization that is independent of the operating wavelength of light, illumination coherence, and NA of the system. In this method, a known pattern is imaged through focus, and matched to an experimental model with a trial set of pupil aberrations. The aberrations are then changed iteratively until the modeled images match the ones from the experiment. The Reduced Optical Coherent Sum (ROCS) decomposition for partially coherent aerial image calculation greatly reduces the computation time of each iteration which makes this method more computationally tractable.
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Ryan Miyakawa, Ryan Miyakawa, Patrick Naulleau, Patrick Naulleau, Avideh Zakhor, Avideh Zakhor, Ken Goldberg, Ken Goldberg, } "Iterative procedure for in-situ optical testing with an incoherent source", Proc. SPIE 7636, Extreme Ultraviolet (EUV) Lithography, 76361K (22 March 2010); doi: 10.1117/12.846235; https://doi.org/10.1117/12.846235
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