2012 Volume 4 Issue 3 Pages 71-80
CaF2 single crystal is expected being used as high performance optical elements for semiconductor lithography technology. When the wavelength of the light becomes down to the vacuum ultraviolet region such as in the lithography, this single crystal shows intrinsic birefringence phenomenon. Therefore we developed an analysis system for simulating birefringence of CaF2 single crystal, which is used as a chamber window of an ArF excimer laser light source, with consideration of intrinsic birefringence. The analysis system consists of a stress analysis and a birefringence analysis. In the stress analysis, the finite element method was applied to obtain the mechanical stress caused by a window holder and gas pressure. In the birefringence analysis, we treated the wave vector dependence of dielectric constant in order to consider the intrinsic birefringence, in addition to the photo-elastic effect. The crystal anisotropy of CaF2 single crystal was taken into account. We performed the analyses of two crystals with a surface vertical to the ⟨111⟩ direction under the Brewster's angle of incidence and several rotation angles. From these analyses, we obtained reasonable results of the optical path difference in comparison with experimental results. Then we evaluated the optical performance and optimum condition of single crystal window.
