Etching Characteristics and Mechanism of SiN_x films for nano-devices in CH₂F₂/O₂/Ar inductively coupled plasma: Effect of O₂ mixing ratio

Etching characteristics and mechanisms of low-temperature SiN_x thin films for nano-devices in CH₂F₂/O₂/Ar inductively-coupled plasmas were studied. The etching rates of SiN_x thin films as well as the etching selectivities over Si and photoresist were measured in the range of 25-75% O₂ in a feed gas at fixed CH₂F₂ content (25%), gas pressure (6 mTorr), input power (900 W), bias power (200 W), and total gas flow rate (40 sccm). Plasma parameters were analyzed using the Langmuir probe diagnostics and optical emission spectroscopy. The chemical states of the etched surfaces were examined by the X-ray photoelectron spectroscopy. It was found that the non-monotonic (with a maximum at about 50-60% O₂) SiN_x etching rate does not correlate with monotonically decreasing F atom flux and ion energy flux. It was proposed that, under the given set of experimental conditions, the SiN_x etching process is also controlled by the O and H atom fluxes through the destruction of the fluorocarbon polymer layer.