Steric Barriers in Area-Selective Atomic Layer Deposition: Theoretical Insights into Al Precursors on Octadecanethiol-Covered Cu Substrates

Self-assembled monolayers (SAMs) have emerged as pivotal coatings to achieve area-selective atomic layer deposition (ALD) in high-precision semiconductor manufacturing. In this work, we employ first-principles calculations to elucidate the steric interactions among three aluminum precursors─trimethylaluminum (TMA), dimethylaluminum isopropoxide (DMAI), and triethylaluminum (TEA)─and octadecanethiol (ODT) SAMs on Cu substrates. Our results reveal that with loosely packed ODT coverage the three precursors could access the pinholes between the SAMs, which does not exhibit effective resistance of the AlOx deposition. For closely packed ODT chains (with the nearest distance of 4.50 Å on Cu substrates), the steric effect causes strong repulsion between the precursors (DMAI and TEA), effectively preventing their penetration into the SAM’s interstitial space. However, the smaller TMA molecule and coreactant water can diffuse through the ODT layer with favorable binding energies, allowing access to the underlying Cu. The ALD reaction of TMA with the hydroxyl on the Cu in the interstitial space of SAMs is exothermic with a low energy barrier, indicating the failure of ODT to block TMA-based ALD. These findings demonstrate that steric effects between SAM chains and precursors play a decisive role in controlling area-selective ALD.