Mechanism of precursor blocking by acetylacetone inhibitor molecules during area-selective atomic layer deposition of SiO2

Area-selective atomic layer deposition (ALD) is currently attracting significant interest as a solution to the current challenges in alignment that limit the development of sub-5 nm technology nodes in nanoelectronics. Development of area-selective ALD processes with high selectivity requires understanding of the mechanisms involved in the loss of selectivity. In this work, the use of acetylacetone (Hacac) inhibitor molecules in ABC-type cycles for area-selective ALD of SiO2 is investigated as a model system to gain insights into precursor blocking. In situ infrared spectroscopy measurements show that at saturation, Hacac adsorbs in a mixture of chelate and monodentate bonding configurations. Hacac adsorbates in monodentate configuration were found to desorb as a result of purging or to be displaced by bis(diethylamino)silane (BDEAS) precursor dosing and therefore significantly contribute to the loss of selectivity during area-selective ALD. Density functional theory (DFT) calculations reveal that the observed displacement reactions originate from attractive interactions between BDEAS precursor molecules and Hacac adsorbates in monodentate configuration. Moreover, the DFT calculations show that the strength of this interaction is dependent on the chemical structure of the precursor molecule. The obtained insights indicate that careful selection of both inhibitor and precursor molecules is required to improve the selectivity of area-selective ALD.