Etching characteristics and mechanisms of Mo thin films in Cl₂/Ar and CF₄/Ar inductively coupled plasmas

The etching characteristics and mechanism of Mo thin films in Cl₂/Ar and CF₄/Ar inductively coupled plasmas under the same operating conditions (pressure, 6 mTorr; input power, 700 W; bias power, 200 W) were investigated. For both gas mixtures, an increase in the Ar fraction or gas pressure at a fixed gas mixing ratio was found to cause a non-monotonic change in the Mo etching rates. The X-ray photoelectron spectroscopy (XPS) diagnostics indicated contamination of the etched surfaces by reaction products. The Cl₂/Ar and CF₄/Ar plasma parameters were also investigated using a combination of a zero-dimensional plasma model and plasma diagnostics using Langmuir probes. An analysis of the etching kinetics with the model-predicted fluxes of the plasma active species suggests that: 1) the Mo etching process occurs in the transitional regime of the ion-assisted chemical reaction, and 2) the non-monotonic Mo etching rate is probably associated with opposing changes in the fluxes of the reactive neutral species and ion energy.