On the mechanism of chemical vapor deposition of Ta₂O₅ from TaCl₅ and H₂O. An ab initio study of gas phase reactions

Quantum chemical calculations at the Hartree-Fock, B3LYP, MP₂ and CCSD(T) levels of theory were performed to provide a mechanism of Ta₂O₅ CVD from TaCl₅ and H₂O. The geometries and vibrational frequencies of reactants, products and transition states of the reactions modeling initial steps of the CVD process were calculated using effective core-potentials for Ta and Cl atoms. The reaction between TaCl₅ and H₂O proceeds via formation of a strongly bonded six-coordinated tantalum complex (25 kcal/mol at CCSD(T)//B3LYP). The correlated methods show the transition state energy to be close to the energy of the initial reagents while HF overestimates the reaction barrier. A similar trend shows up in the investigation of dehydration reaction of TaCl₃(OH)₂, which was calculated in the presence of catalytical water molecule. The data obtained in our study are applied for modeling the film growth and optimization of CVD conditions.