A Quantum Chemical Study of the Atomic Layer Deposition of Al₂O₃ Using AlCl₃ and H₂O as Precursors

Abstract

Atomic layer deposition (ALD) of alumina (Al2O3) using water and aluminum trichloride (AlCl3) is studied using density functional theory (DFT). The atomistic mechanisms of the two deposition half-cycles on Al2O3−OH* and Al2O3−Cl* surface sites include the formation of stable intermediates and result in high barriers for HCl formation. Increasing the temperature reduces the stability of the intermediates but also increases the desorption rate of adsorbed precursors. Both half-reactions are qualitatively similar to the corresponding reactions of ALD of HfO2 and ZrO2 from H2O and HfCl4 and ZrCl4, respectively, but differ significantly from the reactions of ALD of Al2O3 from Al(CH3)3 and H2O. Although the high electronegativity of Cl increases the stability of the dative-bonded trapped intermediates in the Zr and Hf chloride cases, the inductive effect is stronger for AlCl3, increasing the stability of adsorbed AlCl3 by 29 kcal/mol relative to the adsorption energy of Al(CH3)3. Furthermore, the ligand-exchange barrier is 26 kcal/mol higher for AlCl3 than for Al(CH3)3, thus reducing the reaction kinetics and increasing the ALD temperature for the AlCl3/H2O system. We have also found a new reaction pathway which involves ligand-exchange without metal deposition which we call nongrowth ligand-exchange. This pathway is more competitive in ALD using AlCl3 as the metal precursor than when using Al(CH3)3 and reduces the ALD growth rate. These results provide additional physical insight into the nature of these reaction mechanisms and demonstrate that the Cl ligands have a larger impact on the reaction energetics than the metal atom for the ALD of these high-κ oxides.

Modeling Mechanism and Growth Reactions for New Nanofabrication Processes by Atomic Layer Deposition

“…[ 16 ] Heyman and Musgrave also explore the AlCl 3 +H 2 O half reactions for alumina ALD with DFT, comparing the computed reaction mechanisms to those obtained for the TMA+water process. [ 17 ] Both half reactions are predicted to have similar reaction kinetics at T = 0 K involving only a single transition state for each discrete reaction step. At higher temperatures, non-ALD side-reactions of the chloro ligands compete with the ALD reactions through the deactivation of surface sites, leading to lower growth rates per cycle, as seen in experiment.…”

Formation of Metal Oxide Particles in Atomic Layer Deposition During the Chemisorption of Metal Chlorides: A Review

“…The possibility of this type of a ªnon-growth exchange reactionº has recently been indicated by quantum chemical calculations. [64,65] The second type of elementary step (2-*) is a ligand exchange reaction, typical in ALD. There is one difference between the proposed reaction and the ªnormalº ligand exchange reaction, however: the locations of the hydroxyl group and chlorine are switched.…”

Atomic-scale simulation of ALD chemistry

“…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.…”

“…The next mechanism to be computed with DFT was the prototypical ALD consideration of a non-growth side-reaction [12]. Hydroxychloride side-products are also computed [13].…”