Mechanism for Polyethylene Glycol Suppression of Copper Electrodeposition Kinetics

Electrodeposition of copper, Cu, is a critical process for constructing copper interconnects used in the semiconductor industry. Additives such as suppressors, accelerators, and levelers are used to achieve uniform, void-free Cu deposits. While standard models describe the macroscopic mechanisms of suppressors and accelerators, the molecular details of how these additives modify Cu deposition kinetics are poorly understood. Here, we report the effects of long chain-length polyethylene glycol (a common suppressor for Cu plating) on underpotential-deposited monolayers of Cu at Au(111) surfaces, which provided a molecularly defined active site for interfacial ion transfer with a fixed number of sites available for adsorption. The relationship between chain length and concentrations of polyethylene glycol on copper adsorption kinetics was quantified and supported a model for interactions between polyethylene glycol, Cu ions, and the Au(111)/electrolyte interface. Polyethylene glycol chains >6000 g/mol were found to completely obstruct copper adsorption sites at concentrations <60 ppm. These findings could inform the design of powerful suppressors for copper plating acting with nanoscale specificity, which would support advanced semiconductor manufacturing processes.