Area-Selective Atomic Layer Deposition of Al2O3 with a Methanesulfonic Acid Inhibitor

Experiment and density functional theory (DFT) are combined to study the selective growth of Al2O3 with methanesulfonic acid (MSA) as a small molecule inhibitor (SMI) for Cu. Two metalorganic aluminum precursors for Al2O3 atomic layer deposition (ALD), trimethylaluminum (TMA) and dimethylaluminum isopropoxide (DMAI), are compared in the presence of Cu, Ru, SiO2, and TiO2 substrates treated with MSA. Water contact angle goniometry results suggest facile uptake of MSA on Cu, compared to more limited chemisorption on Ru, SiO2, and TiO2, a phenomenon further confirmed with Auger electron spectroscopy (AES) elemental mapping. X-ray photoelectron spectroscopy (XPS) shows a reduction process that occurs between MSA and the native oxide of Cu, suggesting a mechanism in which MSA more favorably interacts with metallic over oxidic surfaces such as SiO2 or TiO2. DFT further elucidates this hypothesis by revealing reaction barriers for MSA and SiO2 that are an order of magnitude higher than those for the reaction between MSA and Cu. Selective chemisorption of MSA on Cu, confirmed by XPS and AES, protects the Cu while allowing growth of up to 3.5 nm of Al2O3 with greater than 97% selectivity on SiO2, TiO2, and Ru using DMAI as the aluminum precursor; TMA as a precursor produces much less selective growth of Al2O3. Together, these results indicate that selective adsorption of MSA allows for the inhibition of Al2O3 ALD on Cu substrates. Furthermore, we show that area-selective atomic layer deposition (AS-ALD) is strongly influenced by precursor selection, revealing that process optimization is a key requirement for producing AS-ALD with SMIs.