Thermal Atomic Layer Etching Mechanism of Amorphous Aluminum Oxide by Hydrogen Fluoride and Trimethylaluminum: First-Principles Study

We present a first-principles density functional theory (DFT) study of the mechanism of thermal atomic layer etching (ALE) of aluminum oxide (Al2O3). Using amorphous Al₂O₃ and aluminum fluoride (AlF3) slab models generated by ab initio molecular dynamics and optimized by DFT, we simulated the sequential surface reactions. The fluorination reactions with hydrogen fluoride (HF), leading to the formation of multilayer AlF3 and the release of H2O and CH4, were calculated to occur spontaneously at 250 °C with low activation energies ranging from 0.18 to 1.14 eV. The subsequent removal reactions with trimethylaluminum (TMA) were also spontaneous, with low activation energies of less than 1.08 eV, releasing the dimethylaluminum fluoride dimer. Our results indicate that the Al2O3 ALE is thermodynamically favorable and kinetically accessible at 250 °C, which agrees with experimental observations in the literature. In addition, the self-limiting nature of the removal step and the formation of multilayer AlF3 were also explained.