Abstract
We describe the application of a linear birefringence measurement system at the optical lithographic wavelengths (157, 193, and 248 nm). Using this instrument, we obtain linear birefringence maps of a variety of calcium fluoride samples with different crystal orientations and at different DUV (deep ultraviolet) wavelengths. Comparing the birefringence results measured at DUV and visible wavelengths, we find that some calcium fluoride samples show a strong correlation in birefringence measured at different wavelengths while others do not. Significant differences in birefringence patterns are observed at 157 and 633 nm for certain calcium fluoride samples when the light beam propagates along the [111] crystal axis. We explain the discrepancy in the birefringence patterns observed at 157 and 633 nm based on the crystalline structural quality of calcium fluoride samples.
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