Mechanism and Application of Imidazolium Derivatives as a Bifunctional Additive for Void-free Blind via Copper Filling

In conventional acidic copper electroplating, the accelerator and leveler are typically provided by different molecules, resulting in complex additive formulations and difficult-to-control intermolecular interactions. This study proposes an “intramolecular functional group division” strategy and designs a series of imidazolium salts bearing different substituents as bifunctional additives, integrating the leveling function of the imidazolium cation and the accelerating function of the pendant groups within a single molecule. Electrochemical measurements, electroplating of silicon-based micro blind vias, and multi-scale characterization demonstrate that a simplified binary system consisting solely of this additive and PEG8000 can achieve void-free superconformal filling. Systematic comparison of four imidazole derivatives containing sulfonate, cyano, and carboxyl substituents establishes a clear structure–activity relationship: the sulfonate group is the key moiety that confers the accelerating effect, Cl– bridging is a prerequisite for strong adsorption, and the structural basis for acceleration is that the sulfonate group remains exposed on the outer surface without participating in copper-surface adsorption. DFT calculations further elucidate this mechanism from the perspectives of electronic structure and adsorption configuration. This work elevates the integration of dual functions in copper electroplating additives from intermolecular synergy to the single-molecule level, providing a new paradigm for the design of multifunctional electroplating additives.