Preparations for EUV Interferometry of the 0.3 NA MET Optic

摘要

An at-wavelength interferometer is being created for the measurement and alignment of the 0.3 numerical aperture Micro Exposure Tool projection optic at EUV wavelengths. The prototype MET system promises to provide early learning from EUV lithographic imaging down to 20-nm feature size. The threefold increase to 0.3 NA in the image-side numerical aperture presents several challenges for the extension of ultra-high-accuracy interferometry, including pinhole fabrication and the calibration and removal of systematic error sources.