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) l evels of theory were performed to provide a mechanism of Ta2O5 CVD from TaC l5 and H2O. The geometries and vibrational frequencies of reactants, produc ts and transition states of the reactions modeling initial steps of the CVD process were calculated using effective core-potentials for Ta and Cl atom s. The reaction between TaCl5 and H2O proceeds via formation of a strongly bonded six-coordinated tantalum complex (25 kcal/mol at CCSD(T)//B3LYP). Th e correlated methods show the transition state energy to be close to the en ergy of the initial reagents while HF overestimates the reaction barrier. A similar trend shows up in the investigation of dehydration reaction of TaC l3(OH)(2), which was calculated in the presence of catalytical water molecu le. The data obtained in our study are applied for modeling the film growth and optimization of CVD conditions. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.