Electrochemical Nucleation and Growth of Copper on Molybdenum Substrate: Effect of pH, Potential and Cleaning procedure

In this study, the early stages of copper electrodeposition on molybdenum substrate from slightly acidic electrolyte were studied by cyclic voltammetry (CV) and chronoamperometry. The electrochemical deposition of copper on molybdenum substrate was investigated from the view point of thermodynamic, kinetic, and nucleation and growth mechanism. According to the CV analysis, the electrodeposition of copper on molybdenum substrate was determined to be irreversible process with diffusion controlled and it was confirmed by Randles-Sevcik equation. Diffusion coefficient of copper species at pH=3 and 4 was determined by Randles-Sevcik and Cottrel equations and their results were in agreement with each other. Using Scharifker-Hills model, the current transients of copper were analyzed. The copper nucleation mechanisms were evaluated as a function of solution pH and deposition potential. It was found that at pH=3 and 4, the nucleation mechanism of copper on grounded substrate was mixed, while with increasing the pH and potential, the nucleation mechanism shifts toward 3D instantaneous. Soaking of substrate in NH3 and then HCl solution after grounding did not change the nucleation mechanism. Etching the substrate in solution containing H2SO4, HNO3 and HCl after grounding changed the nucleation mechanism from 3D instantaneous to 3D progressive.