Absolute Refractive Indices and Thermal Coefficients of CaF2, SrF2, BaF2, and LiF Near 157 nm

Published

May 1, 2002

Author(s)

John H. Burnett, R Gupta, Ulf Griesmann

Abstract

We present accurate measurements near 157 nm of the absolute index of refraction, the index dispersion, and the temperature dependence of the index, for the cubic-symmetry, ultraviolet optical materials CaF₂, SrF₂, BaF₂, and LiF. Accurate values of these quantities for these materials are needed for designs of the lens systems for F₂ excimer-laser-based exposure tools for 157 nm photolithography. These are expected to use CaF₂ as the primary optical material and possibly one of the others for correcting chromatic aberrations. These optical properties were measured using the minimum deviation method in a nitrogen atmosphere. Using the known index of refraction of nitrogen gas, the absolute refractive indices were obtained with an absolute accuracy of 5-6 x 10-6. Measurements on CaF₂ and BaF₂ samples from different suppliers showed sample variations outside the measurement uncertainty

Citation

Applied Optics

Volume

41

Issue

No. 13

Pub Type

Journals

Keywords

BaF₂, barium fluoride, CaF₂, calcium fluoride, index of refraction, lithium fluoride, refractive index, SrF₂, strontium fluoride

Citation

Burnett, J. , Gupta, R. and Griesmann, U. (2002), Absolute Refractive Indices and Thermal Coefficients of CaF₂, SrF₂, BaF₂, and LiF Near 157 nm, Applied Optics (Accessed October 13, 2024)