Abstract
Vacuum ultraviolet (VUV) absorption spectra of resist materials for 157 nm lithography were calculated theoretically by the symmetry adapted cluster configuration interaction (SAC-CI) method. In this study, we investigated the excited states of several alkanes and fluorinated alkanes in the VUV region, and found that most of the transitions of the evaluated alkanes are Rydberg-like transitions. Furthermore, we found a good linear correlation between the lowest absorption energy of alkane and its highest occupied orbital (HOMO) energy. This suggests that consideration of these HOMO energies could be an effective way to explain the change in VUV spectra by fluorination. We also investigated the molecular structures of fluorinated norbornanes to improve their transparency at the VUV region. Through our SAC-CI spectroscopic calculations and evaluation of the HOMO energies for the norbornane derivatives, it was found that fluorination at positions 1, 2, 4 and 5 of norbornane is an efficient molecular method for improving transparency in the VUV region.
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