Adhesion of electroless deposited Cu on ZnO-coated glass substrates: The effect of the ZnO surface morphology

ZnO thin films with various surface morphologies were prepared on glass substrates by spray pyrolysis, and the influence of the morphology on the adhesion of the electroless deposited Cu films was investigated. Results showed that the adhesive strength of the electroless Cu deposits was greatly affected by the surface morphology of the ZnO thin films, which can be controlled by changing the preparation parameters, e.g., substrate temperature, precursor solution composition, and spray time. Cu deposits with high adhesion (>2.5 kg/mm(2)) were achieved on ZnO thin films with rougher, more porous morphologies. The latter were mainly composed of small ball-like structures, with diameters on the order of 0.2 - 1.0 mu m Upon electroless Cu deposition on these ZnO films, in addition to the strong van der Waals force acting at the Cu/ZnO interface caused by the large surface area on a rough, porous surface, the Cu penetrates deeply into the film, giving rise to a strong mechanical, anchoring effect ("dovetail" or ball-and-socket joint effect), which also greatly improves adhesive strength. Such porous structures, which are difficult to obtain by chemical etching of the substrate in the conventional electroless metal deposition process, were obtained by spraying 0.05 M zinc acetate/ethanol solution onto glass substrates at temperatures above 380 degrees C. (C) 1999 The Electrochemical Society. S0013-4651(98)08-074-4. All rights reserved.