Shearing Interferometry for at Wavelength Wavefront Measurement of Extreme-Ultraviolet Lithography Projection Optics

概要

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We present a type of lateral shearing interferometer (LSI) for at-wavelength characterization of the projection lens for use in extreme-ultraviolet lithography (EUVL). LSI is one of the potential candidates for high Numerical Aperture (NA) optics testing at the EUV region. To address the problem of multiple-beam interference, we propose a general approach for derivation of a phase-shift algorithm that is able to eliminate the undesired 0th order effect. The main error source effects including shear ratio estimate, hyperbolic calibration, and charge coupled device (CCD) size, etc. are characterized and the measurement accuracy of the LSI is estimated to be within 7 m$\lambda$ rms (0.1 nm rms at 13.5 nm wavelength) for testing the wavefront of EUVL projection optics.
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2003-09-15