19 March 2015 Extending shearing interferometry to high-NA for EUV optical testing
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Abstract
Characterizing and removing optical aberrations remains a key part of achieving ultimate resolution in EUV exposure tools. Common-path approaches such as lateral shearing interferometry (LSI) have had success at moderate numerical apertures (NA ≈ 0:3); however, these techniques run into several obstacles when applied at higher NA (NA > 0:4). Chief among these obstacles are systematic aberrations due to high incident angles on the diffraction grating and non-planar Talbot surfaces that create regions of low fringe contrast across the pupil. In this paper, we present strategies for addressing these obstacles to extend LSI to high numerical apertures. These strategies will be employed in the installation and alignment of the 0.5-NA SEMATECH Berkeley Microfield Exposure Tool (MET5).
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Ryan Miyakawa, Patrick Naulleau, "Extending shearing interferometry to high-NA for EUV optical testing", Proc. SPIE 9422, Extreme Ultraviolet (EUV) Lithography VI, 94221J (19 March 2015); doi: 10.1117/12.2087568; https://doi.org/10.1117/12.2087568
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