Analysis of Mixed Composition Cold Plasmas by Optical Emission Diagnostics and Simulations

Abstract

The behavior of mixed composition cold non-equilibrium plasmas was investigated in a low-pressure capacitively coupled reactor using optical emission spectroscopy (OES). By fitting experimental data to simulations of the Second Positive System () of N2, rotational and vibrational temperatures were determined for various Ar/N2 mixtures as a function of plasma input power (40–100 W) and pressure (300–700 mTorr). Simulations of the plasma were performed for comparison. For pure N2, the observed trends revealed that both the rotational and vibrational temperatures increased with input power, (of increased from 369 to 396 K and from 5938 to 6542 K, at 40–100 W, 100 SCCM and 293 mTorr) but both temperatures showed minimal response to the applied changes in pressure. The rotational and vibrational temperatures for the mixed composition Ar/N2 plasmas were significantly higher compared to the pure N2 plasmas (e.g. of 1308 K and of 7279 K for 1.8% of N2 in Ar; at 50 W, 4 SCCM of N2, 220 SCCM of Ar for a total pressure of 587 mTorr). Moreover, the addition of Ar caused a larger separation between the rotational and vibrational temperatures compared to the pure N2 case. These phenomena illustrate the effects of Ar on the non-equilibrium energy distribution and more generally the influence that the gas mixture composition may have on the plasma reactivity.