On the etching characteristics and mechanisms of HfO₂ thin films in CF₄/O₂/Ar and CHF₃/O₂/Ar plasma for nano-devices

The study of etching characteristics and mechanisms for HfO₂ and Si in CF₄/O₂/Ar and CHF₃/O₂/Ar inductively-coupled plasmas was carried out. The etching rates of HfO₂ thin films as well as the HfO₂/Si etching selectivities were measured as functions of Ar content in a feed gas (0-50% Ar) at fixed fluorocarbon gas content (50%), gas pressure (6 mTorr), input power (700 W), bias power (200 W), and total gas flow rate (40 sccm). Plasma parameters as well as the differences in plasma chemistries for CF₄- and CHF₃-based plasmas were analyzed using Langmuir probe diagnostics and 0-dimensional plasma modeling. It was found that, in both gas systems, the non-monotonic (with a maximum at about 15-20% Ar) HfO₂ etching rate does not correlate with monotonic changes of F atom flux and ion energy flux. It was proposed that, under the given set of experimental conditions, the HfO₂ etching process is affected by the factors determining the formation and decomposition kinetics of the fluorocarbon polymer layer. These factor are the fluxes of CF_x (x = 1, 2) radicals, O atoms and H atoms.