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.