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1990
Journal Article
Title
Analysis of a CF4/O2 plasma using emission, laser-induced fluorescence, mass, and Langmuir spectroscopy
Abstract
The behavior of CF sub 2 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 m Torr 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 sub 2 high plus ions measured by quadrupole mass spectrometry. Electron densities and temperatures were evaluated to be slightly above 8 x 10 high 9 cm high minus 3 and about 5 eV, respectively. A simplified model, which takes into account different excitation paths, suggests that direct electron impact of the CF sub 2 ground state species was the dominant mechanism for the population of the electronically excited state. Absolute CF2 and O concentrat ions depending on the oxygen feed could be estimated. We obtained CF2 densities between 2 x 10 high 13 and 2 x 10 high 12 cm high minus 3, when the oxygen concentration increases from 2% to 23%. The corresponding O densities varied from 10 high 12 to 6 x 10 high 13 cm high minus 3.