Investigation of E–H mode transition in magnetic-pole-enhanced inductively coupled neon–argon mixture plasma

Abstract

In this paper, E–H mode transition in magnetic-pole-enhanced inductively coupled neon–argon mixture plasma is investigated in terms of fundamental plasma parameters as a function of argon fraction (0%–100%), operating pressure (1 Pa, 5 Pa, 10 Pa and 50 Pa), and radio frequency (RF) power (5–100 W). An RF compensated Langmuir probe and optical emission spectroscopy are used for the diagnostics of the plasma under study. Owing to the lower ionization potential and higher collision cross-section of argon, when its fraction in the discharge is increased, the mode transition occurs at lower RF power; i.e. for 0% argon and 1 Pa pressure, the threshold power of the E–H mode transition is 65 W, which reduces to 20 W when the argon fraction is increased. The electron density increases with the argon fraction at a fixed pressure, whereas the temperature decreases with the argon fraction. The relaxation length of the low-energy electrons increases, and decreases for high-energy electrons with argon fraction, due to the Ramseur effect. However, the relaxation length of both groups of electrons decreases with pressure due to reduction in the mean free path. The electron energy probability function (EEPF) profiles are non-Maxwellian in E-mode, attributable to the non-local electron kinetics in this mode; however, they evolve to Maxwellian distribution when the discharge transforms to H-mode due to lower electron temperature and higher electron density in H-mode. The tail of the measured EEPFs is found to deplete in both E- and H-modes when the argon fraction in the discharge is increased, because argon has a much lower excitation potential (11.5 eV) than neon (16.6 eV).