Inhibition of Copper Deposition by Polyethylene Glycol and Chloride

A physicochemical model for the effect of the additives polyethylene glycol (PEG) and on reduction onto a rotating-disk electrode in acidic sulfate solutions has been developed and fit to experimental potential scans to estimate kinetic parameters. The model, which applies to either transient or steady-state conditions, incorporates diffusion, convection, and a reaction mechanism that explicitly includes the effects of both additives. Very good agreement between the fitted model and experimental data is obtained. The model captures the range of voltammogram shapes experimentally observed over a wide range of additive levels (i.e., from the gradual loss of reduction inhibition with increasing overpotential at high PEG and concentrations to the sudden and complete breakdown of the inhibiting film at a critical potential when intermediate additive levels are used). An impedance model has also been derived and solved to generate impedance spectra using the previously obtained kinetic parameters. The predicted impedance spectra show good agreement with measured ones. Key aspects of the reaction mechanism are PEG desorption from the electrode, which occurs due to displacement by depositing copper, and the distinction made between the situations when the electrode is completely and partially covered by the inhibiting film.