Direct Cu-on-Ta electroplating from ionic liquids in high vacuum

Smooth layers of 20 nm of copper have been deposited on a tantalum substrate from ionic liquids under high vacuum conditions. By electrochemical vacuum deposition (EVD) it is possible to achieve extremely low concentrations of oxygen and water, so that the tantalum electrode does not oxidize. Due to the low vapor pressure of ionic liquids, no evaporation of the electrolyte was observed in high vacuum. The wide electrochemical windows of the ionic liquids are advantageous to obtain nucleation densities up to 8x10^14 m-2 of copper on the tantalum electrode by applying a very large overpotential. Copper was deposited at potentials as negative as -3 V versus a Cu pseudoreference electrode.