Decoupling PEG and chloride co-adsorption kinetics at copper/electrolyte interface during pattern-dependent electrodeposition

Abstract

During the electrodeposition of copper for high-density interconnects, achieving uniform bottom-up filling across dissimilar pattern densities remains challenging due to the complex interplay of localized mass transport and surface adsorption kinetics. This study elucidates the molecular-level spatiotemporal dynamics of an accelerator-free, suppressor (polyethylene glycol)/chloride ion (PEG–Cl⁻) co-adsorption system at the copper/electrolyte interface. We define the pattern-density-dependent filling effect (PDFE) as the variation in bottom deposition thickness between isolated and dense via patterns. To decouple the individual kinetic contributions of PEG and Cl⁻, we employed a combined computational and experimental surface approach. A comprehensive multiphysics model, integrating Nernst–Planck species transport, dynamic surface adsorption–desorption kinetics, and Butler–Volmer electrode reactions, was constructed to track the suppressor coverage evolution. The spatiotemporal simulations, validated by specific surface electrochemical analysis (linear sweep voltammetry) and patterned electroplating, quantitatively revealed a distinct surface kinetic hierarchy. We demonstrate that while Cl⁻ acts as an essential molecular anchor to establish the co-adsorption operating window, the rate of surface coverage formation and subsequent deposition thickness are overwhelmingly governed by the PEG concentration. Notably, the suppression layer exhibits an over 70-fold higher electrochemical sensitivity to PEG than to Cl⁻. Ultimately, this work provides fundamental insights into the interfacial mechanisms dictating pattern-dependent electrodeposition.