Cuprous Ion Mass Transport Limitations During Copper Electrodeposition

Abstract

Polarization experiments in sulfuric acid based copper plating electrolytes disclosed unique mass‐transport limitations at very small cathodic overpotentials. Determination of the bulk concentration of the species, which is correlated to the observed limiting current plateaus, by means of Levich plots indicated that these plateaus may be related to mass‐transport‐limited copper deposition from cuprous ions. This hypothesis was further supported by comparison of the equilibrium constant of the comproportionation of cupric ions and metallic copper to cuprous ions obtained from experiments with literature values. The results provide a simple technique to detect cuprous ions and support the view that cuprous ions are deposited at a diffusion‐limited rate, whereas cupric ions deposition is controlled by electrochemical kinetics. The method may be of relevance for superfilling, since the action of additives in industrial plating electrolytes involves interaction with cuprous ions.

Effects of Temperature on the Comproportionation of Metallic Copper and Cupric Ions to Cuprous Ions

“…where n denotes the number of transferred electrons, F the Faraday constant, D the diffusion coefficient, ν the kinematic viscosity of the electrolyte, and c the bulk concentration. By this means, the cuprous ion bulk concentration was determined to [Cu +1 ]=(2.29±0.03 M)×10 −4 M at 298 K. Noteworthy, this value is in very good agreement with results reported earlier . As mentioned previously, the curves in Figure b show apparently counterintuitive behavior at overpotentials slightly more negative than the plateaus and the expected order of the curves is reestablished at η ≈−30 to −50 mV .…”

“…By this means, the cuprous ion bulk concentration was determined to [Cu +1 ]=(2.29±0.03 M)×10 −4 M at 298 K. Noteworthy, this value is in very good agreement with results reported earlier . As mentioned previously, the curves in Figure b show apparently counterintuitive behavior at overpotentials slightly more negative than the plateaus and the expected order of the curves is reestablished at η ≈−30 to −50 mV . This behavior was ascribed to either transport phenomena of smallest residual amounts of dissolved oxygen or different sulfate surface coverages at different rotational speeds and corresponding different catalytic activities for copper deposition.…”

“…Recently, a simple electrochemical method for determination of the cuprous ion concentration based on a conventional rotating disc electrode (RDE) setup was described . Based on this procedure, the impact of temperature on the cuprous ion concentration and the equilibrium constant for the comproportionation reaction was studied.…”

“…In order to study the influence of temperature on K , determination of the cuprous ion bulk concentration at different temperatures is required. As described recently, the cuprous ion bulk concentration may be calculated from the slope of Levich plots of Cu +1 diffusion‐limited currents obtained from carefully performed linear sweep voltammetry (LSV) experiments . Currents, which are largely potential‐independent, were observed at very small cathodic overpotentials η and current densities i ( η ≈−3 to −10 mV).…”

“…Currents, which are largely potential‐independent, were observed at very small cathodic overpotentials η and current densities i ( η ≈−3 to −10 mV). This regime was ascribed to cuprous ion mass transport limitations . Diffusion‐limited currents i L at different rotational speeds (200–1600 rpm) were determined from plateaus of the η ‐ i curves at very small cathodic overpotentials by extracting the current at the respective inflection points.…”