20 May 2004 EUV interferometric testing and alignment of the 0.3-NA MET optic
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Abstract
Extreme ultraviolet (EUV) interferometry has been successfully performed for the first time at 0.3 numerical aperture (NA). Extensive EUV “at-wavelength” testing including alignment, was performed on a newly created Micro Exposure Tool (MET) optic designed for sub-50-nm EUV lithographic imaging experiments. The two-mirror, 0.3 NA MET is ar-guably the highest resolution light-projection lithography tool ever made. Using both lateral shearing and phase-shifting point-diffraction interferometry, the wavefront was measured across the field of view, and the alignment was optimized in preparation for imaging. The wavefront quality reached 0.55 nm RMS (lambda[EUV]/24.5) in a 37-term annular Zernike poly-nomial series, dominated by higher-order spherical aberration. Measurements included calibrations of the interferometer accuracy, assessment of repeatability, and cross-comparisons of visible and EUV interferometric measurements. The comparisons and the final, measured wavefront quality were affected by an apparent alignment drift, several tenths of a nm in magnitude. Significant unresolved differences between testing strategies shows that continued work is needed to improve the measurement accuracy to levels required for EUV lithography.
© (2004) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Kenneth A. Goldberg, Kenneth A. Goldberg, Patrick Naulleau, Patrick Naulleau, Paul Denham, Paul Denham, Senajith B. Rekawa, Senajith B. Rekawa, Keith Jackson, Keith Jackson, James Alexander Liddle, James Alexander Liddle, Erik H. Anderson, Erik H. Anderson, } "EUV interferometric testing and alignment of the 0.3-NA MET optic", Proc. SPIE 5374, Emerging Lithographic Technologies VIII, (20 May 2004); doi: 10.1117/12.546199; https://doi.org/10.1117/12.546199
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