ANALYSIS OF A CF4/O2 PLASMA USING EMISSION, LASER-INDUCED FLUORESCENCE, MASS, AND LANGMUIR SPECTROSCOPY

The behavior of CF2 radicals in CF4/O2 plasmas has been studied as a function of the oxygen partial pressure in an rf reactor with 13.56 MHz, 30 W, and 40 mTorr total pressure. The CF2 ground and excited states were detected by the CF2 (A-X) band spectra applying laser-induced fluorescence and optical emission spectroscopy, respectively. Adding oxygen to the CF4 feed gas, the intensity of the CF2 signals in both spectra showed similar decrease. No evidence is found for a simple correlation between the neutral CF2 densities and the CF+2 ions measured by quadrupole mass spectrometry. Electron densities and temperatures were evaluated to be slightly above 8×109 cm-3 and ∼5 eV, respectively. A simplified model, which takes into account different excitation paths, suggests that direct electron impact of the CF2 ground state species was the dominant mechanism for the population of the electronically excited state. Absolute CF2 and O concentrations depending on the oxygen feed could be estimated. We obtained CF2 densities between 2×10 13 and 2×1012 cm -3, when the oxygen concentration increases from 2% to 23%. The corresponding O densities varied from 1012 to 6×1013 cm-3.