Effect of Cu(II) ligands on electroless copper deposition rate in formaldehyde solutions: An EQCM study

Abstract

The electroless copper deposition rate for 6 CuII complexes decreases in the ligand sequence: nitrilotriacetic acid (NTA) > N,N,N′,N′-tetrakis-(2-hydroxypropyl)-ethylenediamine (Quadrol) > glycerol > L(+)-tartrate ~ sucrose > \(\hbox{\sc {DL}}(_+^-)\)-tartrate. Both CuII complex stability and specific ligand effects were found to influence the Cu deposition process. The specific ligand effects are most obvious in the case of Quadrol (high kinetic activity at a high CuII complex stability), glycerol and sucrose (additional reaction of Cu2O formation by interaction of CuII with ligand). According to the EQCM data for 11 CuII complexes (including data from the former study) the higher kinetic activity is demonstrated by complexes with ligands containing amino groups; this factor is more important for Cu deposition rate than copper complex stability. A potential dependence of the Cu 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 was found to occur in electroless plating solution for CuII complexes with NTA and Quadrol 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 hypothetical reaction sequence involving intermediate copper oxy-species and active Cu* formation as well as development of the preferred Cu surface structure.