Competitive-adsorption-resistant interfacial regulation by 2-mercaptopyridine enables selective copper microvia superfilling.

Selective copper superfilling in microvias is governed by how co-additives compete for Cu surface sites under confined mass-transfer conditions, yet the interfacial characteristics that allow a leveler to remain effective in accelerator-containing electrolytes are not well understood. Here, we show that 2-mercaptopyridine (2-MP), a small N,S-containing heterocycle, enables selective bottom-up copper filling by stabilizing an inhibitory interfacial state against bis-(3-sulfopropyl) disulfide (SPS)-induced displacement. Galvanostatic measurements (GMs), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), microvia filling tests, surface characterization, X-ray photoelectron spectroscopy (XPS), density functional theory (DFT) calculations, and molecular dynamics simulations collectively reveal that 2-MP adsorbs on Cu through dual-site chemisorption via pyridinic N and thiol S atoms. This adsorption mode suppresses SPS-induced depolarization and preserves interfacial inhibition under polyethylene glycol (PEG)/SPS co-additive conditions. Under practical plating conditions, reinforced 2-MP/PEG adsorption near the via mouth and partial SPS activity at the via bottom generate the deposition-rate gradient required for nearly void-free superfilling, with a relatively thin overburden of 23-36 μm. Compared with the conventional leveler Janus Green B (JGB), 2-MP provides stronger control over SPS occupation and more stable filling selectivity. These results identify competitive-adsorption resistance as an interfacial descriptor for evaluating small-molecule levelers and provide mechanistic insight into competition-regulated copper electrodeposition in confined geometries.