Building successive generations of state-of-the-art wide field, sub-micron microlithographic lens systems dictates ever-tightening material tolerances that challenge glass manufacturers. This paper discusses the optical material needs for microlithographic lens systems and Tropel's in-house material qualification program. Material qualification is divided into three successive stages: (1) fluorescence testing to qualitatively analyze color center characteristics of the material; (2) homogeneity testing to determine the relative volumetric variations in index; and (3) absolute index testing at multiple wavelengths to determine the material's dispersion characteristics.
The design and system performance of an infrared phase-stepping interferometer is reviewed. This instrument is capable of measuring rms surface roughness with a repeatability of 0.02 waves. The instrument uses a 4-bucket unwrapping algorithm. Calibration of the interferometer and removal of inherent system aberrations are discussed along with the system performance, including repeatability and accuracy. The interferometer is an all-reflective optics design to permit use at any wavelength, accommodating both far- (10.6 micron) and near- (5 micron) infrared sources. Testing applications include infrared windows and surface testing.
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