Plasma Oxidation of Patterned Mo Nanowires for Precise and Uniform Dry Etching

We demonstrate that a uniform recess of polycrystalline Mo can be achieved using a two-step method: metal oxidation with isotropic oxygen plasma that forms a layer of MoO 3 and selective etching of this oxide layer. The oxidation step fully defines the recess depth, and its uniformity is ensured by the low facet dependence of plasma oxidation. We have extensively studied the oxidation of patterned Mo nanowires (30 nm width) in isotropic oxygen plasma and achieved uniform oxide layers of predefined thickness by controlling radio-frequency (RF) power, gas pressure, and exposure time. We showed that using highly selective oxide etching, we can perform multiple etching cycles with a typical etch rate of 1-2 nm per cycle, depending on the RF power. Due to plasma isotropy, this approach can be implemented for a controlled uniform etching of large vertical stacks of metal nanostructures.