Tuning Molecular Inhibitors and Aluminum Precursors for the Area-Selective Atomic Layer Deposition of Al₂O₃

Using both experiment and density functional theory (DFT), we study a group of small molecule inhibitors (SMIs) and aluminum precursors to determine how the interplay between the inhibitor and precursor can affect the selectivity of atomic layer deposition (ALD) on different materials. We compare several polyfunctional alkoxysilanes as the SMIs and trimethylaluminum and triethylaluminum as the ALD precursors. Spectroscopic ellipsometry shows a direct correlation between blocking performance and the number of hydrolysable alkoxy groups on the SMI. DFT results suggest that SMI polymerization at the surface may play an important role in producing a saturated passivation layer, while also indicating that defects in this layer develop primarily due to interactions with the co-reactant rather than with the aluminum ALD precursors. X-ray photoelectron spectroscopy and Auger electron spectroscopy reveal that alkoxysilane SMIs can support the selective growth of up to 4 nm of Al2O3 on copper substrates when the optimal ALD precursor/SMI pair is selected: triethylaluminum as the ALD precursor, water as the co-reactant, and trimethoxypropylsilane as the inhibitor for SiO2 substrates. The blocking performance is much poorer with trimethylaluminum as the precursor, an effect further confirmed by in situ Fourier transform infrared spectroscopy. These differences suggest a strong effect of precursor ligand size in achieving AS-ALD with SMIs. In addition, we show that tuning both inhibitor and precursor functionality for the system of interest is required to optimize selective growth.