EQCM study of the effect of ligands on the rate of CuII reduction by formaldehyde

An increase in the stability of copper(II) complexes (ligands: HEDTA, EDTA, DTPA, CDTA, TTHA) has been found to decrease their cathodic reduction rate in most cases, with considerable specific effects with some ligands (DTPA, CDTA). Similar dependences of the Cu deposition kinetics on Cu-II complex stability were also found for the electroless Cu plating process at open-circuit potential. A potential dependence of the Cu-II reduction partial current on the electrode potential has been extracted from the EQCM data in the complete electroless plating bath. An increase in Cu-II reduction rate has been found to occur in electroless plating solution compared with that in formaldehyde-free solutions. Possible reasons for the acceleration of the partial Cu-II reduction reaction and the overall process kinetics are discussed using a reaction sequence involving intermediate copper oxy-species and active Cu* formation as well as development of the preferred Cu surface structure.