Influence of exciting frequency on gas and ion rotational temperatures of nitrogen capacitively coupled plasma

Abstract

By using optical emission spectroscopy, the nitrogen gas and ion rotational temperatures in capacitively coupled plasma discharges with different exciting frequencies are investigated. The rotational temperatures are acquired by comparing the measured and calculated spectra of selected transitions with a least-square procedure. It is found that N2 gas rotational temperature minimum around 13MHz is the combined effect of ion-dominated heating and electron-dominated heating in the plasma. The influence of exciting frequency on N2+ rotational temperature is much more than that of the N2 molecule, the lower frequency, the higher N2+ rotational temperature. Also, N2+ rotational temperature is much higher than the corresponding N2 gas rotational temperature in the plasma driven by low frequencies. These experimental phenomena may be attributed to the effective ion heating and/or possible resonant heating in the bulk plasma under the low-frequency field.