Role of Molecular Orientation: Comparison of Nitrogenous Aromatic Small Molecule Inhibitors for Area-Selective Atomic Layer Deposition

Area-selective atomic layer deposition (AS-ALD) shows great potential for meeting the stringent demands of the semiconductor industry for precision nanopatterning. Small molecule inhibitors (SMIs) have recently proven to be a promising, industry-compatible means of achieving AS-ALD. In this work, we compare three nitrogenous aromatic SMIs – aniline, pyrrole, and pyridine – for their ability to block Al₂O₃ ALD on copper with (CuO_x) and without (Cu) a native oxide. We find that pyrrole and aniline perform much better as inhibitors than pyridine does. Furthermore, when redosed on copper before every ALD cycle in an ABC scheme, pyrrole and aniline provide outstanding inhibition, facilitating the selective deposition of over 11 nm of Al₂O₃ on an SiO₂ growth surface in the presence of Cu with 99.9% selectivity. By combining both theory and experiment, we provide new understanding of the mechanisms by which selectivity is prolonged and lost. First, we show that whereas pyrrole and aniline adsorb in a planar bonding orientation, pyridine binds upright at the copper surface, and we propose that the upright molecular orientation is the origin of the ineffective inhibition of pyridine. Second, we find that the CuO_x surface is inherently more reactive than the Cu surface, leading to an eventual loss of selectivity, despite the redosing of the inhibitor. Finally, we observe that redosing of aniline protects the copper surface from undesired oxidation, whereas the redosing of pyridine does not. As such, we posit that a likely benefit of redosing is preventing oxidation and thus reducing reactive site formation during ALD. Through this work, we demonstrate the capability of nitrogenous aromatics to serve as SMIs for AS-ALD, and we contribute insights regarding the role of molecular orientation on inhibition and the impact of ALD process parameters on selectivity.