LiCaAlF6 : Nd3+ crystal as optical material for 157 nm photolithography

The laser induced fluorescence spectrum (LIF) of the LiCaAlF6:Nd3+ single c rystal, 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(2)5d electronic configuration and they were assigned to the 4f(2)5d --> 4f(3) interconfigurational dipol e allowed transitions. The absorption spectrum of the crystal in the VUV wa s obtained as well. We observed twenty main dipole allowed transitions betw een the ground level I-4(9/2) of the 4f(3) electronic configuration and the Stark components of the levels of the 4f(2)5d electronic configuration in the spectral range between 120 and 200 nm. The experimental results suggest that the LiCaAlF6:Nd3+ crystal can be used as wavelength selective optical filter and refractive element for 157 nm photolithography. (C) 2000 Elsevi er Science B.V. All rights reserved.