N2, O2, and NF3 Dissociation in a Low Frequency, High Density Plasma Source
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Radical densities and gas dissociation fractions were measured by optical emission spectroscopy (OES), combined with Ar actinometry for various mixes of N2, O2, and NF3 feed gases with Ar at 400 sccm total flow rate in a low frequency (400 kHz), high pressure (4.0 Torr), inductively-coupled toroidal remote plasma source from MKS Instruments, operating at a power density of 5 – 50 W/cm3. The dissociation of O2 drops from 60% to 10% with an increase of O2 percentage. For NF3, the dissociation to form F rises with an increase of NF3 percentage from 20% at 1% NF3 to 100% at 10% NF3, while about 65% of the nitrogen is present as N2, with presumably some or all of the remaining nitrogen present as N atoms, which are detected in optical emission. For N2 the dissociation based on N emission drops from 25% to 3% with an increase of N2 percentage, while the dissociation rate using N2 emission appears to increase with N2 percentage. Possible reasons for this discrepancy and the favoring of the results from N emission are discussed.