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

Abstract

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 CuII complex stability were also found for the electroless Cu plating process at open-circuit potential. A potential dependence of the CuII reduction partial current on the electrode potential has been extracted from the EQCM data in the complete electroless plating bath. An increase in CuII 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 CuII 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.