Chemistry and physics of atmospheric pressure argon plasmas.

摘要

The chemistry and physics of low temperature, atmospheric pressure plasmas containing argon and helium were investigated with current, voltage, and power measurements and infrared spectroscopy. In contrast to helium, the atmospheric pressure argon discharge powered at 13.56MHz contained streamers and was unstable, and the addition of small amounts of a secondary gas caused the plasma to extinguish. It was found that the electron density in the argon plasma was 2.5 times that of helium. This was attributed to the lower ionization energy and electron mobility of argon compared to helium.;It was discovered that a much more stable argon plasma could be generated by confining the gas flow to a dielectric housing made of quartz. The quartz housing was a cylindrical tube, 2mm inner diameter, with two aluminum electrodes mounted along the length of the cylinder and supplied with radio-frequency power at 13.56MHz. With this new design, the discharge could be operated with up to ∼10 vol.% of a secondary gas and power densities of 150W/cm 3. Time-dependent current and voltage waveforms of the discharge did not exhibit any spikes due to the charging and discharging of the quartz, as in traditional dielectric barrier discharges.;The concentration of ground-state oxygen atoms produced by the discharge inside the quartz tube was measured by NO titration. It was found that this concentration equaled 1.2vol.%, or 1.2±0.4×1017cm -3, at 6.0vol.% O2 in argon, 300°C, and 150W/cm 3. This plasma source etched Kapton® at 5.0μm/s at 280°C and an electrode-to-sample spacing of 1.5cm. This fast etch rate is attributed to the high O atom flux generated by the plasma source.;The concentration of ground-state nitrogen atoms was determined using the new capacitive plasma source with the dielectric housing, and it reached a maximum of 2.3vol.% or 3.0±0.8×1017cm -3 at 6.0 vol.% N2 in argon, 250°C, and 150W/cm 3. A model was developed of the plasma and the afterglow, and it was determined that the amount of N atoms generated by the source is limited by three body recombination.;An atmospheric pressure helium and hydrogen plasma was used to deposit amorphous-hydrogenated silicon. It was found that this process produced films with a low hydrogen content, ∼3.0 atom%, less than half the amount in films grown by low-pressure PECVD. The reduced hydrogen content of the films attests to the high radical density achieved in the atmospheric pressure plasma.