Synergistic effect of additives on the surface roughness and throwing power of copper deposited from electrorefining solution

To elucidate the synergistic effect of gelatin, thiourea and chloride ions on the surface roughness, throwing power and polarization curves for Cu deposition from electrorefining solution, Cu electrodeposition was performed at a current density of 200 A•m^-2 and 5×10⁵ C•m^-2 of charge in an unagitated sulfate solution containing 0.708 mol•dm^-3 of CuSO₄ and 2.04 mol•dm^-3 of H₂SO₄ at a temperature of 60°C. In solutions containing three kinds of additives such as gelatin, thiourea and chloride ions, the surface roughness of deposited Cu decreased with increasing the concentration of thiouea and gelatin and decreasing the chloride ions. On the other hand, the throwing power of deposited Cu was improved with decrease in thiourea and increase in gelatin in solutions containing three kinds of additives. The throwing power of deposited Cu was significantly improved in solution containing both gelatin and chloride ions. The polarization resistance dE/di for Cu deposition increased in solution containing both gelatin and chloride ions, which resulting in improvement of throwing power of Cu deposition. As small amounts of thiourea have a depolarization effect on Cu deposition, a leveling effect is expected owing to the promotion of deposition at recesses.