Dual-wavelength interferometer for testing projection lenses

Klaus R. Freischlad; Chunsheng Huang

doi:10.1117/12.209301

26 May 1995 Dual-wavelength interferometer for testing projection lenses

Klaus R. Freischlad, Chunsheng Huang

Proceedings Volume 2440, Optical/Laser Microlithography VIII; (1995) https://doi.org/10.1117/12.209301
Event: SPIE's 1995 Symposium on Microlithography, 1995, Santa Clara, CA, United States

Abstract

A custom-built phase shifting interferometer is described for measuring the wavefront quality of Ultratech Stepper 1X projection lenses over a field of 25 mm X 50 mm using wavelengths of 363.8 nm (for i-line systems) and 442.0 nm (for gh-systems). Over an N.A. of 0.42 the wavefront is determined at 240 X 240 points with a calibrated accuracy of (lambda) /20 peak-to-valley (at (lambda) equals 363.8 nm). The interferometer is an unequal path Twyman-Green interferometer with an Argon-laser and a HeCd-laser as light sources. The interferometer test system is integrated on a 10 ft X 4 ft vibration isolation table together with an xy-stage to position the projection lens at different field points. The safe handling of the projection lens is supported by a load/unload mechanism on the table. The measurement wavefront maps at various field points of the tested projection lens are used to optimize the state of alignment of the projection lens.

Citation Download Citation

Klaus R. Freischlad and Chunsheng Huang "Dual-wavelength interferometer for testing projection lenses", Proc. SPIE 2440, Optical/Laser Microlithography VIII, (26 May 1995); https://doi.org/10.1117/12.209301

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