Reaction Mechanism of Area-Selective Atomic Layer Deposition for Al₂O₃ Nanopatterns

The reaction mechanism of area-selective atomic layer deposition (AS-ALD) of Al₂O₃ thin films using self-assembled monolayers (SAMs) was systematically investigated by theoretical and experimental studies. Trimethylaluminum (TMA) and H₂O were used as the precursor and oxidant, respectively, with octadecylphosphonic acid (ODPA) as an SAM to block Al₂O₃ film formation. However, Al₂O₃ layers began to form on the ODPA SAMs after several cycles, despite reports that CH₃-terminated SAMs cannot react with TMA. We showed that TMA does not react chemically with the SAM but is physically adsorbed, acting as a nucleation site for Al₂O₃ film growth. Moreover, the amount of physisorbed TMA was affected by the partial pressure. By controlling it, we developed a new AS-ALD Al₂O₃ process with high selectivity, which produces films of ∼60 nm thickness over 370 cycles. The successful deposition of Al₂O₃ thin film patterns using this process is a breakthrough technique in the field of nanotechnology.