Wet-Chemical Etching of Metals for Advanced Semiconductor Technology Nodes: Cu Recess Etching and Electrochemistry of Nanopatterned Metal Electrodes

Nanopatterned electrodes (nominal trench width = 45 nm) have been generated to enable electrochemical measurements of metals in a damascene integration scheme. Fabrication is done at 300 mm wafer scale using standard semiconductor technology processes. A morphological characterization of a wet-chemical Cu digital etching process is performed using transmission electron microscopy and atomic force microscopy, both of which provide insights into the material properties and surface features. Results reveal that recess depth increases linearly with etching cycles and indicate pit formation on the Cu surface. To validate the backside contact approach, electrical and electrochemical measurements of both Cu-filled and Ru-coated nanopatterned electrodes are performed, which show the typical metal behavior. As an application, the surface coverage of self-assembled monolayer modified Cu in damascene trenches is investigated by measuring cyclic voltammograms in an alkaline solution, demonstrating the quality of passivation using a test structure for which all materials (conductor metal, barrier/liner, and low-k dielectric) relevant for the application area-selective deposition are present.