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

Experiment and density functional theory (DFT) are combinedtostudy the selective growth of Al2O3 with methanesulfonicacid (MSA) as a small molecule inhibitor (SMI) for Cu. Two metalorganicaluminum 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 goniometryresults suggest facile uptake of MSA on Cu, compared to more limitedchemisorption on Ru, SiO2, and TiO2, a phenomenonfurther confirmed with Auger electron spectroscopy (AES) elementalmapping. X-ray photoelectron spectroscopy (XPS) shows a reductionprocess that occurs between MSA and the native oxide of Cu, suggestinga mechanism in which MSA more favorably interacts with metallic overoxidic surfaces such as SiO2 or TiO2. DFT furtherelucidates this hypothesis by revealing reaction barriers for MSAand SiO2 that are an order of magnitude higher than thosefor the reaction between MSA and Cu. Selective chemisorption of MSAon Cu, confirmed by XPS and AES, protects the Cu while allowing growthof up to 3.5 nm of Al2O3 with greater than 97%selectivity on SiO2, TiO2, and Ru using DMAIas the aluminum precursor; TMA as a precursor produces much less selectivegrowth of Al2O3. Together, these results indicatethat selective adsorption of MSA allows for the inhibition of Al2O3 ALD on Cu substrates. Furthermore, we show thatarea-selective atomic layer deposition (AS-ALD) is strongly influencedby precursor selection, revealing that process optimization is a keyrequirement for producing AS-ALD with SMIs.