Initial Reactions in Chemical Vapor Deposition of Ta₂O₅from TaCl₅and H₂O. An Ab Initio Study

Abstract

Quantum chemical calculations at the Hartree−Fock, B3LYP, MP2, and CCSD(T) levels of theory were performed in order to study the mechanism of Ta2O5 chemical vapor deposition (CVD) from TaCl5 and H2O. The geometries and vibrational frequencies of reactants, products and transition states of the reactions, which are used for modeling the 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. Formation of TaOCl3, in the unimolecular decomposition of TaCl4OH and TaCl3(OH)2, has similar barriers of ∼20 kcal/mol. The catalytic effect of an assisting water molecule opens a barrierless channel for TaOCl3 formation in the gas phase.

Theoretical ab initio Study of TiCl4 Ammonolysis: Gas Phase Reactions of TiN Chemical Vapor Deposition

“…An elongation of the equatorial bonds in 1-ax can be explained by hydrogen bonding between equatorial chlorine atoms and the hydrogen atoms of ammonia. We have previously observed a similar effect in pentacoordinated oxichlorides TaCl 4 (OH) and TaCl 3 (OH) 2 [37 ].…”

Molecular modelling of tantalum penta-halides during hydrolysis and oxidation reactions

“…This implies that the three [8] showed Ax and Eq bond length to be 2.337 Å and 2.287 Å respectively. The modelled bond lengths are closer to the experimentally observed values [6] than the values presented by Siodmiak et al [8].…”

“…Since single crystals of TaF 5 do not form readily, they exist as oligomeric penta-fluorides with three possible structure types [6], neither the experimentally determined molecular structure of TaF 5 is well known, nor have these properties been modelled. However, for TaCl 5 both the molecular structure [7] as well as its interaction in an aqueous environment have been modelled [8,9]. If it is assumed that TaF 5 has a similar symmetrical structure and behaviour in water than TaCl 5 , (an assumption that will be evaluated in this paper), then TaCl 5 could be used to validate the novel modelling approach before applying the modelling to a compound of which the structure and behaviour is unknown.…”

Atomic-scale simulation of ALD chemistry

“…Frenking and Korkin on TaCl 5 +H 2 O [10]. The model consists of complexes totalling ten atoms or less, and despite the model being so small, reasonable reaction energies are obtained for adsorption,…”

“…HF or approximate DFT), thereby limiting the system size to <1000 atoms on today's computer hardware. Even so, error cancellation is poor when the wavefunction changes strongly at the transition state, so that chemical accuracy can only reliably be achieved by post-HF methods such as coupled cluster [10], [11] or configuration interaction [12], tractable for fewer than 100 atoms.…”