Control of surface oxide formation in plasma-enhanced quasiatomic layer etching of tantalum nitride

Surface oxide formation inhibiting the etch of a tantalum nitride (TaN) film was controlled through step pressure modulation and H₂ addition in a Cl₂/Ar based plasma-assisted cyclic etch process. Sources contributing to the oxidation of the film included the mask materials, specifically the silicon-containing antireflective coating, as measured by optical emission spectroscopy. Surface analysis of etched films by secondary ion mass spectroscopy showed the presence of a modified surface layer ∼2 nm thick with localized oxygen concentrations 0.02 and 0.003 that of the control sample (without and with H₂ addition, respectively). Reduced Ta–O bonding observed via x-ray photoelectron spectroscopy as a result of H₂ addition was found to enhance etch rate uniformity of both blanket and patterned films. Minimization of redeposited oxidized TaN on the mask sidewalls of patterned samples was achieved using this etch process and by controlling the lithographic stack composition.