Controlled Stepwise Wet Etching of Polycrystalline Mo Nanowires

With the persistent downscaling of integrated circuits, molybdenum (Mo) is currently considered a potential replacement for copper (Cu) as a material for metal interconnects. However, fabricating metal nanostructures with critical dimensions of the order of 10 nm and below is challenging. This is because the very high density of grain boundaries (GBs) results in highly non-uniform surface profiles during direct wet etching. Moreover, wet etching of Mo with conventional aqueous solutions is problematic, as products of Mo oxidation have different solubility in water, which leads to increased surface roughness. Here, a process is shown for achieving a stable and uniform soluble surface layer of Mo oxide by wet oxidation with H2O2 dissolved in IPA at -20 degrees C. The oxide layer is then selectively dissolved, and by repeating the oxidation and dissolution multiple times, a uniform etch profile is demonstrated with a fine control over the metal recess. Ultimately, this presents a method of precise and uniform wet etching for Mo and other metals needed to fabricate complex nanostructures that are critical in developing next-generation electronic devices. Wet chemical etching of polycrystalline metals produces non-uniform etch profiles, which poses a major challenge in nanofabrication of metal interconnects in future microelectronics components. A new approach that combines multiple cycles of cryo-oxidation of the surface of nanoscale metal followed by selective oxide dissolution overcomes this challenge and produces desired smooth and uniform nanostructures.image