Theoretical Analysis for Thermal Chemical Vapor Deposition from Tetraethoxysilane Using a Semi-Empirical Molecular Orbital Method
1999 Volume 63 Issue 7 Pages 931-937
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1999 Volume 63 Issue 7 Pages 931-937
In order to elucidate the reaction mechanism for the Tetraethoxysilane(TEOS) thermal decomposition at atmospheric pressure, its pertinent elemental reactions involving the SiO(OC2H5)2 reaction intermediate were first proposed. For respective species formed in these elemental reactions, the total energy and the electronic state were calculated using a semi-empirical molecular method. The adsorption process which involves adsorbent species formation and surface reaction mechanism were then analyzed from the standpoint of molecular orbital formation and charge transfer mechanism, and the results are summarized as follows:
(1) A reaction intermediate, SiO(OC2H5)2(1A1), is probably formed through the following β-elimination reaction route:
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(2) The adsorption of SiO(OC2H5)2(1A1) on SiO2 occurs with charge transfer from the dangling bond of silicon atom at an active site of the SiO2 surface to the π∗-LUMO unoccupied orbital of SiO(OC2H5)2(1A1).
(3) The sequence of surface reactions is considered as follows:
\ding172 First, a dissociation reaction of C2H5(2A′) takes place, whereby producing a double bond between silicon atom and oxygen atom of the intermediate, since they possess unpaired electrons.
\ding173 Si-O bond is successively formed following the mechanism similar to the one operating in the adsorption of SiO(OC2H5)2(1A1) on SiO2.
\ding173 Electronic state of the reactant finally formed is in the 1A1 state, which has a σ-orbital to be fully occupied with electrons.
