Symmetry of Spatial-Dispersion-Induced Birefringence and its Implications for CaF2 Ultraviolet Optics

Published

August 1, 2002

Author(s)

John H. Burnett, Zachary H. Levine, Eric L. Shirley, J H. Bruning

Abstract

The discovery of a large intrinsic birefringence in CaF₂ at ultraviolet wavelengths has had a major impact on the design of 157 nm lithography systems, requiring complete redesign of the optics to take account of the imaging aberrations resulting from the birefringence and the accompanying index anisotropy. The intrinsic birefringence phenomena results from a symmetry-breaking effect of the finite wavevector of the photon on the symmetry of the light-meter interaction in fluorite-structure cubic crystals. As a follow-up to our original concise report of measurements and theory of the effect in CaF₂ and BaF₂, we present here a more detailed analysis of the theory of the effect, focusing on the symmetry and its consequences. We also provide the full directional dependence of the effect in useful closed forms. We analyze the implications of the intrinsic birefringence for precision optical design with CaF₂ optical elements, and discuss qualitatively the approaches being considered to compensate for it.

Citation

Journal of Microlithography Microfabrication and Microsystems

Pub Type

Journals

Keywords

157nm lithography, birefringence, calcium flouride

Citation

Burnett, J. , Levine, Z. , Shirley, E. and Bruning, J. (2002), Symmetry of Spatial-Dispersion-Induced Birefringence and its Implications for CaF₂ Ultraviolet Optics, Journal of Microlithography Microfabrication and Microsystems (Accessed October 13, 2025)