Cu-Ni Thin Films Electrodeposited on Si: Composition and Current Efficiency

Abstract

Constantan/Cu bilayers were electrodeposited potentiostatically at room temperature from a citrate electrolyte containing both copper and nickel sulfates. RBS and EDS techniques were used to determine bath efficiency, growth rate and layer composition as a function of deposition voltage. It is shown that the layer composition can be controlled by the applied potential (relative to a saturated calomel electrode (SCE)), being very sensitive to it, and may range from pure copper (at —0.45 V/SCE) up to a solid solution of 20 wt % Cu in Ni (at —1.2 V/SCE). Current efficiencies were also dependent on the applied potential, decreasing continuously from around 80% at —0.45 V/SCE, down to less than 10% for potentials more negative than —1.45 V/SCE. For the compositions of interest, however, i.e. 45–50 wt % Ni, current efficiencies were around 70%. Growth rates of 1.8 and 3.7 Å/s for copper and constantan, respectively, were obtained.