Characterization of RF He-N2/Ar mixture plasma via Langmuir probe and optical emission spectroscopy techniques

Abstract

A Magnetic Pole Enhanced inductively coupled RF He- N2/ Ar plasma is characterized using a Langmuir probe and optical emission spectroscopy (OES) techniques. The effect of helium mixing on electron density (ne) and temperature (Te), electron energy probability functions (EEPFs), [N] atomic density, and N2 dissociation is investigated. A Langmuir probe and a zero slope method based on trace rare gas-optical emission spectroscopy (TRG-OES) are employed to measure the electron temperature. It is noted that the electron temperature shows an increasing trend for both methods. However, the temperature measured by a zero slope method Te(Z·S) approaches the temperature measured by a Langmuir probe; Te(L·P) at 56% and above helium concentration in the discharge. “Advance actinometry” is employed to monitor the variation in [N] atomic density with helium concentration and gas pressure. It is noted that [N] atomic density increases at 56% and above helium in the discharge, which is consistent with the trend of electron temperature and EEPFs. A drastic enhancement in N2 dissociation fraction D1 determined by “advance actinometry” is noted at 56% and above helium concentration in the mixture due to modifications in different population and depopulation mechanisms. However, it is also noted that the dissociation fraction D2 determined by intensity ratio method increases linearly with helium addition.