The discharge characteristics of capacitively coupled nitrogen plasma driven by 6∼50 MHz by optical emission spectra

Abstract

The discharge characteristics of capacitively coupled nitrogen plasma driven by four different exciting radio frequencies (RF) of 6 MHz, 15 MHz, 35 MHz and 50 MHz are investigated by optical emission spectra (OES). The RF power change from 20 to 70 W and pressure change from 20 to 90 mTorr. The vibrational temperature Tv and rotational temperature Tr of N2 second positive system (C3Пu−B3Пg) and N2+ in the first negative band system (B2∑u+—X2∑g+state) are studied by comparing the experimental emission spectra with the calculated results. When the pressure is fixed at 40 mTorr, the spectral line intensity increases with the increase of RF power, and the vibrational temperature and rotational temperature of N2 and N2+ both increase. The vibrational temperature and rotational temperature of N2 and N2+ are the highest at 6 MHz and are the lowest at 15 MHz. When the RF power is fixed at 30 W, the vibrational temperature of N2 and N2+ both decrease and the rotational temperature of N2 and N2+ both increase with the increase of pressure. The vibration and rotational temperatures of N2 and N2+ are also the highest at 6 MHz. The influence of the driving frequency on the N2+ is greater than the influence on the N2, which may also be caused by the different response of the nitrogen ions to the driving frequency.