Underpotential-Mediated Co-Deposition of Copper-Manganese from an Alkaline Electrolyte for Application in Semiconductor Interconnects

Manganese (Mn) doping is a promising route for enhancing the electromigration resistance of copper (Cu) interconnects. However, conventional electrodeposition of Cu-Mn is hindered by the large difference in the reduction potentials between Cu and Mn, as well as the parasitic hydrogen evolution reaction (HER) which leads to a porous deposit morphology. To circumvent these issues, we present here a novel electrochemical strategy leveraging Mn underpotential deposition (UPD) to co-deposit a Cu-Mn alloy from a shelf-stable citrate-based alkaline electrolyte. We demonstrate precise control over both the deposit morphology and its Mn content through modulation of the applied current density and electrolyte composition. Such underpotential-mediated co-deposition enables formation of compact Cu-Mn alloy films at electrode potentials where HER is suppressed, leading to high coulombic efficiency (>99%). The technique presented here offers an attractive electrochemical alternative to traditional chemical or physical vapor deposition as a means of incorporating Mn into Cu without comprising the deposit quality as required for semiconductor interconnect applications.