Unveiling the Molecular Mechanism of Action of 4,4′-Bipyridine as a Suppressor for Superconformal Cobalt Electrodeposition

Abstract Molecular-level understanding of additive-mediated regulation of cobalt (Co) electrodeposition remains elusive, although organic additives are essential for controlling interfacial deposition behavior in advanced interconnect technologies. Here, 4,4′-bipyridine (4BPY) is employed as a suppressor to elucidate its adsorption configuration and inhibition mechanism on Co electrodes through electrochemical measurements, in situ electrochemical surface-enhanced Raman spectroscopy (EC-SERS), and density function theory (DFT) calculations. Electrochemical studies demonstrate that 4BPY effectively suppresses both Co deposition and hydrogen evolution reaction at the interface between the Co electrode and the electrolyte. Crystallographic orientation analysis reveals that 4BPY preferentially adsorbs on Co (110) plane, altering the competitive growth behavior among Co (110), Co (100), and Co (002) planes and consequently modifying the deposition morphology. Combined experimental and theoretical results reveal that 4BPY anchors onto the Co surface through Co–N coordination with a perpendicular molecular configuration, which blocks active sites and regulates Co deposition kinetics. These findings provide molecular-level insights into the mechanism by which additive adsorption regulates Co electrodeposition and offer fundamental guidance for the rational design of suppressors for advanced interconnect metallization.