EFFECT OF SUBSTRATE SURFACE-TREATMENT ON THE NUCLEATION AND CRYSTAL-GROWTH OF ELECTRODEPOSITED COPPER AND COPPER-INDIUM ALLOYS

Thin films of copper-indium alloy electroplated on molybdenum substrat es 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 b y potentiostatic current-time transients. The deposition process invol ves instantaneous nucleation for untreated substrates and progressive nucleation for ammonia treated substrates, with diffusion-controlled g rowth of the three-dimensional nuclei. A higher nucleation density is observed for ammonia-treated molybdenum substrates. The film morpholog y of the copper-indium alloys can be closely related to the copper nuc leation mechanism. On the untreated substrates a low nucleation densit y together with high adatom mobility lead to the formation of a globul ar structure. However, when the nucleation density is high and the nuc lei are formed continuously during crystal growth, the film evolves to wards a porous structure. After the selenization step the film morphol ogy appears related to the precursor structure. (C) 1997 Elsevier Scie nce S.A.