Continuous ultraviolet emissions produced by electron impact on SF ₆ and NF₃

We studied the continuous emissions in the wavelength range 2000 to 3400 Å produced by low energy electron impact on SF₆ and NF ₃. In both cases two different features contribute to the emission spectrum. In NF₃, we found a structured emission with maxima at 2880, 3005, and 3130 Å and an onset energy of 8.5±2 eV superimposed on a continuous feature from 2500 to 3500 Å with an onset at about 30 eV. We attribute the structured emission, which has an emission cross section of 2.2×10^-19 cm² at 25 eV, to the NF₂ fragment. In SF₆, we observed a broad emission feature from 2000 to 3300 Å with maximum intensity at 3010 and 3145 Å with a comparatively weak shoulder at 3160 Å. The 3160 Å feature, which has an emission cross section of about 2×10^-20 cm² at 25 eV, has a single onset at 13.5±1.5 eV, whereas at least two different processes with onsets at 28±2 eV and 42±3 eV, respectively, contribute to the main SF6 emission. The potential relevance of these continuous emissions for diagnostic purposes of NF₃ and SF₆ processing plasmas utilizing plasma-induced emission spectroscopy and laser-induced fluorescence techniques is discussed.