Electrochemical Investigation of Cu Electroplating with Supercritical CO2 Emulsion Using a Rotating Disk Electrode under High Pressure

Abstract

The electrochemical properties of Cu deposition by plating solution with supercritical CO2 emulsion (Sc-CO2-E) were investigated using a specially constructed electrochemical measuring apparatus with a rotating disk electrode operable under high pressure. Polarization characteristics were examined with and without mixing Sc-CO2-E into the CuSO4-H2SO4 electroplating solution. Further, the relationship between the limiting current density and the rotation speed of the rotating electrode, that is, Levich plot, was obtained. As a result, a significant increase in the limiting current was observed by mixing Sc-CO2-E. In addition, as a result of estimating the diffusion coefficient D 0 of Cu ion and kinematic viscosity coefficient ν of the plating solution when Sc-CO2-E was mixed from gradients of the Levich plot, it was clarified that D 0 increased more than twice and ν decreased less than 1/2 compared to before mixing Sc-CO2-E. Therefore, it was suggested that mixing to emulsify the supercritical CO2 and the plating solution can greatly enhance the transfer of Cu ions by convection. Consequently, the use of Cu electrodeposition with Sc-CO2-E should enable plating in narrow spaces where convection cannot reach the level of supply of Cu ions, which was difficult with conventional plating.