High-temperature kinetics of AlCl₃ decomposition in the presence of additives for chemical vapor deposition

A numerical study has been performed modeling the gas-phase reactions occurring during the chemical vapor deposition (CVD) of alumina from AlCl₃/CO₂/H₂ mixtures. The purpose is to answer whether and to what extent trends in the decomposition of AlCl₃ via gas-phase reactions can explain experimentally observed trends in CVD deposition of aluminum-containing films. The AlCl₃ decomposition is predicted to occur via a free-radical chain mechanism that, in the presence of H₂, has H atoms and the AlCl₂ radical as the primary chain carriers. We find that the present kinetic model predicts trends for the decomposition rate of AlCl₃ in the gas phase that are consistent with trends observed experimentally for the Al₂O₃ deposition rate. Based on these results, the chemical kinetics model is used to study the effects on AlCl₃ thermal decomposition of other additives (H₂O₂, H₂O, O₂, Cl₂) for which no experimental data are available in the literature. H₂O₂ is predicted to be a particularly efficient promoter for AlCl₃ thermal decomposition. The mechanism also predicts that the presence of AlCl₃ dramatically increases the rate of H₂O production compared to H₂O production from CO₂ and H₂ in the absence of AlCl₃.