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Ab initio Molecular Orbital Study of Water Absorption and Hydrolysis of Chemical Vapor Deposited SiOF Films I

1997; Institute of Physics; Volume: 36; Issue: 4S Linguagem: Inglês

10.1143/jjap.36.2533

1347-4065

Yasushi Nakasaki, Hideshi Miyajima, Ryota Katsumata Hayasaka,

Silicon Nanostructures and Photoluminescence

We investigated the mechanism of water absorption and hydrolysis of F-doped SiO 2 (SiOF) films using the ab initio molecular orbital (MO) method with small SiF n (OH) 4- n ( n =0–3) tetrahedral model clusters. We focused on the dependence of the reactivity of these clusters with both OH - and H 2 O on the number of F atoms bonded with a Si atom. The reactivity of defect sites such as non bridging oxygens (NBOs) and free volumes around Si–F bonding were also investigated. The calculations revealed the following. SiOF films are more reactive with OH - than with H 2 O. Si atoms linked with multiple F atoms become more reactive with H 2 O by reducing the activation barrier of the –OH coordination to Si, and with OH - by increasing the stabilization energy of the pentacoordinated-Si formation. Multiple H 2 O attacks at sparse, i.e., sparsely packed, network sites increase the adsorption energy and reduce the activation barrier. NBO defects also promote successive H 2 O adsorption.