Changes of the Cu electrode real surface area during the process of electroless copper plating

The surface area (nanoscale roughness) of copper coatings deposited from electroless plating solutions containing Quadrol, L(+)- and DL(-/+)-tartrate as Cu(II) ion ligands was measured using underpotential deposition thallium monolayer formation. Surface roughness of Cu coatings depends on the plating solution pH and the Cu(II) ligand, and varies over a wide range. In L(+)-tartrate and Quadrol solutions (pH 12.5-13.3) the roughness factor R-f is low and is equal to 2-3 and 4-6, respectively (substrate: electrodeposited Cu; R-f = 2.2). Cu coatings of higher surface area are obtained in DL(-/+)-tartrate (pH 12.3-12.7) and Quadrol (pH 12.0) solutions: R-f reaches 20-30. The correlation between R-f and Cu deposition rate was found in L(+)tartrate solution. The Cu surface area changes are discussed in terms of partial electrochemical reactions of the autocatalytic Cu deposition process, and the decisive role of cathodic Cu(II) reduction from adsorbed Cu(II) complex species.