Effect of substrate surface treatment on the nucleation and crystal growth of electrodeposited copper and copper–indium alloys

Abstract

Thin films of copper–indium alloy electroplated on molybdenum substrates show different morphologies related to the substrate treatment. An ammonia treatment of the molybdenum electrode can remove a thin oxide layer from the electrode surface, changing the morphological structure of the deposit. The nucleation kinetics of copper were investigated by potentiostatic current–time transients. The deposition process involves instantaneous nucleation for untreated substrates and progressive nucleation for ammonia treated substrates, with diffusion-controlled growth of the three-dimensional nuclei. A higher nucleation density is observed for ammonia-treated molybdenum substrates. The film morphology of the copper–indium alloys can be closely related to the copper nucleation mechanism. On the untreated substrates a low nucleation density together with high adatom mobility lead to the formation of a globular structure. However, when the nucleation density is high and the nuclei are formed continuously during crystal growth, the film evolves towards a porous structure. After the selenization step the film morphology appears related to the precursor structure. © 1997 Elsevier Science S.A. All rights reserved.