Electrodeposition of Ordered Copper Germanide from an Alkaline Tartrate-Complexed Electrolyte
In the present work, the electrochemical deposition of ɛ-Cu3Ge thin films from an alkaline tartrate-complexed electrolyte [[iv]] was thoroughly investigated. Primarily, the partial (single element Cu and Ge deposition) and net (Cu-Ge alloy co-deposition) processes occurring in such electrolyte were studied by means of cyclic voltammetry (CV), electrochemical quartz crystal microbalance (EQCM) and electrochemical impedance spectroscopy (EIS) techniques. Subsequently, the electrodeposition of Cu-Ge thin films was realized in potentiostatic mode at various selected potentials. The morphology, composition and microstructure of as-deposited Cu-Ge thin films were characterized, and the results reveal that the Ge content in the deposits increases with decreasing applied potential in a sigmoidal manner, leading to a gradual disorder-order phase transformation of Cu-Ge alloy from a disordered face-centered-cubic solid solution (α-phase) to an ordered orthorhombic Cu3Ge intermetallic compound (ɛ-phase). Combining the morphological, compositional and structural characteristics of electrodeposited Cu-Ge thin films with the processes kinetics studies, a possible mechanism of Cu-Ge induced codeposition was postulated.
The dependence of resistivity of as-deposited Cu-Ge thin films on Ge content was also examined, which exhibits a non-monotonic behavior. A minimum value was found around stoichiometric Cu3Ge, which corresponds to the completion of the disorder-order transformation. The ɛ-Cu3Ge thin film displays a resistivity of 7.5 μΩ cm-1 (~50 nm) and 25 μΩ cm-1 (~1 μm), increasing with the deposition duration, which is believed due to the progressive incorporation of O into the films. In order to overcome this limitation, the effect of the bath temperature and pH on Cu-Ge electrodeposition kinetics, composition and microstructure were investigated, and optimal electrodeposition conditions for ɛ-Cu3Ge were identified.
[i] M.O. Aboelfotoh, H.M. Tawancy, L. Krusin-Elbaum, Correlation of electrical-resistivity anomalies and crystal structure in copper-germanium thin-film alloys, Appl. Phys. Lett. 63, 1622 (1993).
[ii] L. Krunsin-Elbaum, M.O. Aboelfotoh, Unusually low resistivity of copper germanide thin films formed at low temperatures, Appl. Phys. Lett. 58, 1341 (1991).
[iii] M.A. Borek, S. Oktyabrsky, M.O. Aboelfotoh, J. Narayan, Low resistivity copper germanide on (100) Si for contacts and interconnections, Appl. Phys. Lett. 69, 3560 (1996).
[iv] A. Joi, R. Akolkar, U. Landau, Pulse plating of copper germanide, Appl. Phys. Lett. 102, 134107 (2013).