Comparative In Situ Study of the Initial Growth Trends of Atomic Layer-Deposited Al₂O₃ Films

In this work, we compare the initial growth trends of atomic layer-deposited aluminum oxide (Al₂O₃) using three different Al precursors and H₂O as the oxygen source on hydroxyl-terminated silicon (Si-OH) and hydrogen-terminated silicon (Si-H) surfaces. Trimethylaluminum (TMA), triethylaluminum (TEA), and dimethylaluminum chloride (DMAC) are chosen as the Al precursors due to comparable variations between their structures. Thickness evolution obtained from in situ ellipsometry exhibits similar behavior for all three precursors with initially accelerated growth during the first cycle on the Si-OH starting surface, which then proceeds in a steady manner characteristic of atomic layer deposition (ALD). In situ Fourier transform infrared spectroscopy (FTIR) shows that at 200 °C both TEA and TMA react with above 85% of −OH ligands present on the initial Si-OH substrate and the subsequent H₂O dose reacts with only ∼50% of the surface C–H groups, indicating incomplete removal of the methyl or ethyl ligands on the surface. Al₂O₃ growth on the Si-H surface exhibits a delay due to the lack of surface hydroxyl groups, leading to formation of Si-Me or Si-Et groups. A lower reactivity of DMAC compared to TMA and TEA results in a lower initial selectivity fraction. The results provide vital insight into the importance of precursor selection for area-selective ALD applications and open a pathway for realizing selective Al₂O₃ deposition based on inherent substrate selectivity.