| The physics and chemistry of low temperature, atmospheric pressure plasmas containing fluorine have been investigated with current, voltage, and power measurements, infrared absorption spectroscopy, and optical emission spectroscopy. The plasma source consisted of two closely spaced metal electrodes, supplied with radio-frequency power at 13.56 MHz. The fluorine atom concentration was measured in the downstream region of a carbon tetrafluoride and helium plasma using infrared spectroscopy. The gas discharge generated 1.2 × 10 15 cm−3 of F atoms, which is ∼100 times higher than that found in low-pressure plasmas. A numerical model of the plasma indicated that most of the F atoms were generated by the reaction of CF4 with metastable helium atoms.;It was discovered that the atmospheric pressure, radio-frequency plasma could be made to undergo sheath breakdown with conversion from an α- to a γ-mode discharge. With 0.4 vol% nitrogen in helium, this transition was accompanied by a 40% drop in voltage, a 12% decrease in current, and a surge in power density from 25 to 2083 W/cm3. The shift in intense plasma emission from the bulk gas to the surface of the electrodes was documented by optical techniques. When the plasma was operated in the α and γ modes, 5.2% and 15.2% of the N2 was dissociated into atoms, respectively. In the latter case, the low dissociation efficiency was ascribed to the nonuniform structure of the plasma across the gap.;In plasmas containing 1.0 vol% carbon tetrafluoride and sulfur hexafluoride, the α to γ transition occurred smoothly with no discharge contraction. The electron density in these plasmas equaled 6.0 × 1011 cm−3, compared to 1.9 × 1013 cm −3 in pure helium. The drop in plasma density was due to fast electron attachment processes caused by the electronegative molecules, which also resulted in a high density of negative ions, up to 1013 cm−3.;In addition, the non-equilibrium, atmospheric pressure plasma was used to etch uranium oxide. Etching rates up to 4.0 μm/min were achieved with 729.0 Torr He, 15.0 Torr CF4, 6.6 Torr O2, 300 W RF power, and a 200°C sample temperature. |
