Ab Initio Molecular Orbital Study of Suppression of Water Absorption and Hydrolysis (F-Removal) of Chemical-Vapor-Deposited SiOF Films by Nitrogen Doping

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Abstract
We investigated the mechanism of the nitrogen-doping effect on the suppression of water absorption and hydrolysis (F-removal) of fluorine-doped SiO2 (SiOF) films, using the ab initio molecular orbital method with model clusters of three-membered-rings of Si–O bonds with and without N atoms in the siloxane rings ( Si3O3- n (NH) n F(OH)5 ( n=0, 1)). We focused on the changes in the reactivity of these clusters with OH- in the presence of N in the rings. The calculations revealed the following. Three-membered SiOF rings of Si–O bonds are more stabilized by the OH- coordination and more easily form metastable pentacoordinated-Si intermediates than the unconstrained small SiOF clusters we examined elsewhere. The N-incorporated SiOF ring becomes less reactive with OH- due to the increase in the reaction barrier for HF formation. The incorporated N atoms suppressed the back-bond deformations by forming Si–N–Si linkages.