Microstructural and chemical properties of Cu-In alloys formed using co-electrodeposition

We investigated the microstructural and chemical properties of Cu-In alloys formed on Au-coated Si substrates using co-electrodeposition. The co-electrodeposition was performed using electrolytic solutions with various molar ratios of CuCl₂ and InCl₃ (1 mM/5 mM, 2 mM/4 mM, and 5 mM/5 mM) at room temperature. With increased electrodeposition current, the concentrations of Cu and In atoms in the Cu-In alloys decreased and increased, respectively. Because of the preferential growth of Cu, a decrease in themolar ratio of CuCl₂ and InCl₃ led to a reduction in the minimumelectrodeposition current that is required to obtain Cu-In alloys with the same concentration of Cu and In atoms. The increases in electrodeposition current and the molar ratio of CuCl₂ and InCl₃ facilitated the formation of Cu-In dendrites with long central trunks and secondary branches. The dendrites could be associated with autocatalytical alloy growth driven by a concentric diffusion field of metal ions on a thermodynamically unstable surface. During co-electrodeposition using electrolytic solution (CuCl₂ = 1 mM and InCl₃ = 5 mM) under an electrodeposition current of 20 mA, the increase in the cathodic overpotential caused by surface irregularity led to the formation of Au-In, which could be a main cause of the observed hillock formation.