LiCaAlF 6:Nd 3+ crystal as optical material for 157 nm photolithography

Abstract

The laser induced fluorescence spectrum (LIF) of the LiCaAlF 6:Nd 3+ single crystal, pumped by the molecular fluorine pulsed discharge laser at 157.6 nm, was obtained in the vacuum ultraviolet (VUV) region of the spectrum. The transitions originate from the edge of the 4f 25d electronic configuration and they were assigned to the 4f 25d→4f 3 interconfigurational dipole allowed transitions. The absorption spectrum of the crystal in the VUV was obtained as well. We observed twenty main dipole allowed transitions between the ground level 4 I 9/2 of the 4f 3 electronic configuration and the Stark components of the levels of the 4f 25d electronic configuration in the spectral range between 120 and 200 nm. The experimental results suggest that the LiCaAlF 6:Nd 3+ crystal can be used as wavelength selective optical filter and refractive element for 157 nm photolithography.