The influence of Exciting Frequency on N2 and N2+ Vibrational Temperature of Nitrogen Capacitively Coupled Plasma

By using optical emission spectroscopy (OES), N₂ and N₂⁺ vibrational temperatures in capacitively coupled plasma discharges with different exciting frequencies are investigated. The vibrational temperatures are acquired by comparing the measured and calculated spectra of selected transitions with a least-square procedure. It is found that N₂ and N₂⁺ vibrational temperatures almost increase linearly with increasing exciting frequency up to 23MHz, then increase slowly or even decrease. The pressure corresponding to the maximum point of N₂ vibrational temperature decreases with the increasing exciting frequency. These experimental phenomena are attributed to the increasing electron density, whereas the electron temperature decreases with exciting frequency rising.