Plasma Parameters and Etching Characteristics of SiO_xN_y Films in CF₄ + O₂ + X (X = C₄F₈ or CF₂Br₂) Gas Mixtures

In this work, we carried out the study of CF₄ + O₂ + X (X = C₄F₈ or CF₂Br₂) gas chemistries in respect to the SiO_xN_y reactive-ion etching process in a low power regime. The interest in the liquid CF₂Br₂ as an additive component is motivated by its generally unknown plasma etching performance. The combination of various diagnostic tools (double Langmuir probe, quadrupole mass-spectrometry, X-ray photoelectron spectroscopy) allowed us to compare the effects of CF₄/X mixing ratio, input power and gas pressure on gas-phase plasma characteristics as well as to analyze the SiO_xN_y etching kinetics in terms of process-condition-dependent effective reaction probability. It was found that the given gas systems are characterized by: (1) similar changes in plasma parameters (electron temperature, ion current density) and fluxes of active species with variations in processing conditions; (2) identical behaviors of SiO_xN_y etching rates, as determined by the neutral-flux-limited process regime; and (3) non-constant SiO_xN_y + F reaction probabilities due to changes in the polymer deposition/removal balance. The features of CF₄ + CF₂Br₂ + O₂ plasma are lower polymerization ability (due to the lower flux of CF_x radicals) and a bit more vertical etching profile (due to the lower neutral/charged ratio).