AC phase measuring interferometer for measuring dn/dT of fused silica and calcium fluoride at 193 nm

Richard N. Shagam

doi:10.1117/12.326662

8 October 1998 AC phase measuring interferometer for measuring dn/dT of fused silica and calcium fluoride at 193 nm

Richard N. Shagam

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Proceedings Volume 3425, Optical Diagnostic Methods for Inorganic Transmissive Materials; (1998) https://doi.org/10.1117/12.326662
Event: SPIE's International Symposium on Optical Science, Engineering, and Instrumentation, 1998, San Diego, CA, United States

Abstract

A novel method for the measurement of the change in index of refraction vs. temperature (dn/dT) of fused silica and calcium fluoride at the 193 nm wavelength has been developed in support of thermal modeling efforts for the development of 193 nm-based photolithographic exposure tools. The method, based upon grating lateral shear interferometry, uses a transmissive linear grating to divide a 193 nm laser beam into several beam paths by diffraction which propagate through separate identical material samples. One diffracted order passing through one sample overlaps the undiffracted beam from a second sample and forms interference fringes dependent upon the optical path difference between the two samples. Optical phase delay due to an index change from heating one of the samples causes the interference fringes to change sinusoidally with phase. The interferometer also makes use of AC phase measurement techniques through lateral translation of the grating. Results for several samples of fused silica and calcium fluoride are demonstrated.

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Richard N. Shagam "AC phase measuring interferometer for measuring dn/dT of fused silica and calcium fluoride at 193 nm", Proc. SPIE 3425, Optical Diagnostic Methods for Inorganic Transmissive Materials, (8 October 1998); https://doi.org/10.1117/12.326662

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KEYWORDS

Interferometers

Diffraction gratings

Silica

Temperature metrology

Phase shifts

Calcium

Phase measurement

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