Copper electrodeposition from a copper acid baths in the presence of PEG and NaCl

Abstract

Copper electrodeposition from copper acid solutions containing PEG and NaCl has been investigated onto Cu(111), Cu(100) and polycrystalline copper electrodes using polarization and EIS measurements. The adsorption of sulphate and chloride anions, and PEG molecules, was investigated onto Cu(111) and Cu(100) by cyclic voltammetry and differential capacitance measurements. Differential capacitance vs. potential curves recorded onto Cu(100) in solutions containing 0.1 M H2SO4, 0.1 M H2SO4 + 10-3 M PEG and 0.1 M H2SO4 + 10-3 M PEG + 10-3 M NaCl confirm that “specific adsorption” of PEG molecules occurs in the absence of NaCl in the solution, in the potential region of copper electrodeposition, e.g., between –1.0 V and –0.5 V vs. SSE. In the presence of chloride ions, the adsorption of PEG molecules is suppressed and there is no evidence of adsorption of neutral PEG molecules. It is shown that hysteresis, appearing on the polarization curves of copper electrodeposition, is not a consequence of competition between inhibition provided by the Cl-PEG/Cu2+/Cu+/Cu interface and the catalytic effects of Cl-MPSA/Cu2+/Cu+/Cu interaction, because hysteresis is present in the solution containing only PEG and NaCl, e.g., in the absence of MPSA. EIS measurements confirm the simultaneous occurrence of two processes during copper electrodeposition: deposition of copper by discharge of Cu2+ ions and “specific adsorption” and discharge of some heavily charged species, most probably containing Cu, PEG and Cl.