EUV interferometric testing and alignment of the 0.3-NA MET optic

Kenneth A. Goldberg; Patrick Naulleau; Paul Denham; Senajith B. Rekawa; Keith Jackson; James Alexander Liddle; Erik H. Anderson

doi:10.1117/12.546199

20 May 2004 EUV interferometric testing and alignment of the 0.3-NA MET optic

Kenneth A. Goldberg, Patrick Naulleau, Paul Denham, Senajith B. Rekawa, Keith Jackson, James Alexander Liddle, Erik H. Anderson

Author Affiliations +

Proceedings Volume 5374, Emerging Lithographic Technologies VIII; (2004) https://doi.org/10.1117/12.546199
Event: Microlithography 2004, 2004, Santa Clara, California, United States

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.

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Kenneth A. Goldberg, Patrick Naulleau, Paul Denham, Senajith B. Rekawa, Keith Jackson, James Alexander Liddle, and 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); https://doi.org/10.1117/12.546199

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