Electrochemical Nucleation and Growth of Copper-Tin Alloys from Ammonia-Free Citrate-Based Electrolyte

The cyclic voltammetry and chronoamperometry methods are used in the present work for the purpose of investigating the electrodeposition mechanism of Cu-Sn alloys onto Pt and Mo substrates from a slightly acidic aqueous electrolyte (pH asymptotic to 4.2) containing CuCl2 and SnCl2 as metal sources, and tri-sodium citrate as a complexing agent. The structural properties of the deposits were characterized by means of the X-ray diffraction (XRD) technique, whereas the surface morphology and composition were examined using the field-emission scanning electron microscopy (FESEM) and energy-dispersive spectroscopy (EDS). The resulting crystalline films were mainly composed of Cu, Sn, and intermetallic Cu6Sn5 phases with spherical grains, at the early stages of nucleation, and a mixture of spherical grains and dendrites with hierarchical secondary branches after long electrolysis duration. The analysis of potentiostatic current transients, using the Scharifker-Hills model, showed that the electroplating of Cu-Sn alloy followed the instantaneous nucleation mode on platinum substrate and the progressive nucleation mode on the molybdenum substrate.