AB-INITIO MOLECULAR-ORBITAL STUDY OF WATER-ABSORPTION AND HYDROLYSIS OF CHEMICAL-VAPOR-DEPOSITED SIOF FILMS .1.

We investigated the mechanism of water absorption and hydrolysis of F- doped SiO2 (SiOF) films using the ab initio molecular orbital (MO) met hod with small SiFn(OH)(4-n) (n = 0-3) tetrahedral model clusters. Mie focused on the dependence of the reactivity of these clusters with bo th OH- and H2O on the number of F atoms bonded with a Si atom. The rea ctivity of defect sites such as non bridging oxygens (NBOs) and free v olumes around Si-F bonding were also investigated. The calculations re vealed the following. SiOF films are more reactive with OH- than with H2O. Si atoms linked with multiple F atoms become more reactive with H 2O by reducing the activation barrier of the -OH coordination to Si, a nd with OH- by increasing the stabilization energy of the pentacoordin ated-Si formation. Multiple H2O attacks at sparse, i.e., sparsely pack ed, network sites increase the adsorption energy and reduce the activa tion barrier. NBO defects also promote successive H2O adsorption.