Electrochemical Investigation of Cu Electroplating with Supercritical CO 2 Emulsion Using a Rotating Disk Electrode under High Pressure

Abstract

The electrochemical properties of Cu deposition by plating solution with supercritical CO 2 emulsion (Sc-CO 2 -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-CO 2 -E into the CuSO 4 -H 2 SO 4 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-CO 2 -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-CO 2 -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-CO 2 -E. Therefore, it was suggested that mixing to emulsify the supercritical CO 2 and the plating solution can greatly enhance the transfer of Cu ions by convection. Consequently, the use of Cu electrodeposition with Sc-CO 2 -E should enable plating in narrow spaces where convection cannot reach the level of supply of Cu ions, which was difficult with conventional plating.