PROGRESS TOWARDS LAMBDA 20 EXTREME-ULTRAVIOLET INTERFEROMETRY/

Diffraction-limited optical imaging systems for extreme ultraviolet (E UV) lithography require wave front aberrations to be limited to a frac tion of the EUV wavelength. Surface figure metrology and wave front me asurement at this level: of accuracy represent key challenges in the d evelopment of EUV lithography. We have constructed and operated a wave front measuring interferometer at 12-13 nm wavelength. This interfero meter is being used to measure the aberrations in 0.1 numerical apertu re Fresnel zone plate lenses. Factors limiting the resolution and accu racy of the interferometer were studied. Substantial progress toward l ambda/20 wave front measurement accuracy has been made. (C) 1995 Ameri can Vacuum Society.