The impact of branched polyethyleneimine (PEI) on Cu electrodeposition from an acidified cupric sulfate electtrolyte containing a combination of superfilling additives, specifically polyethylene glycol, bis(3-sulfopropyl)disulfide, and chloride (PEG-Cl-SPS), is examined. Electroanalytical measurements reveal that adsorption of cationic PEI leads to inhibition of the metal deposition reaction to an extent similar to that provided by PEG-Cl adsorption. However, unlike the PEG-Cl suppressor, PEI is shown to deactivate adsorbed SPS accelerator. As a result, addition of PEI quenches the hysteretic voltammetric response that is a signature of competitive adsorption in the PEG-Cl-SPS additive system. Trench-filling experiments in a PEI-PEG-Cl-SPS electrolyte demonstrate that the deactivating interaction between PEI adsorption and adsorbed SPS can be optimized to prevent overfill bump formation without substantial detrimental impact on bottom-up, void-free feature filling. (c) 2006 The Electrochemical Society.