From Pinhole Density to Nucleation Onset: A Numerical Model for SAM Barrier Performance in Selective Atomic Layer Deposition

Self-assembled monolayers (SAMs) are widely used as blocking layers in area-selective atomic layer deposition (AS-ALD), yet the kinetics of their failure by pinhole nucleation remain poorly quantified. In this work, we develop a numerical model that represents pinhole filling with a sigmoid function, enabling high-accuracy fits to nucleation data across multiple material systems. The model shows that lower pinhole density D─produced by smoother substrates and stronger SAM–substrate binding─extends the nucleation delay, in agreement with experiments. Increased surface roughness or weaker chemical binding reduces the compactness and ordering of SAMs, increasing D and accelerating the onset of nucleation. The characteristic delay cycle, Cd, scales with the time needed to fill pinholes: longer SAM chains and bulky, less-reactive precursors lengthen Cd, whereas smaller, highly reactive precursors penetrate pinholes rapidly, shorten Cd, and reduce selectivity. By connecting measurable surface properties and precursor chemistry to nucleation behavior, the model offers clear guidelines for designing SAMs that maximize selectivity in AS-ALD.