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. Here, utilizing in-situ liquid phase transmission electron microscopy (LP-TEM), we track the etching of polycrystalline Mo nanowires (NWs) with a hydrogen peroxide solution in real-time [1]. 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. Next, we show a process for achieving a stable and uniform soluble surface layer of Mo oxide by wet oxidation with H₂O₂ dissolved in IPA at -20 °C. The oxide layer is then selectively dissolved, and by repeating the oxidation and dissolution multiple times, we demonstrate a uniform etch profile 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.<br/><br/>[1] K. Saidov, I. Erofeev, Z. Aabdin, A. Pacco, H. Philipsen, A. W. Hartanto, Y. Chen, H. Yan, W. W. Tjiu, F. Holsteyns, U. Mirsaidov, Controlled Stepwise Wet Etching of Polycrystalline Mo Nanowires. <i>Adv. Funct. Mater.</i> 2023, 2310838.