Mode transition in magnetic pole enhanced inductively coupled argon plasmas

Abstract

The electrical probe (Langmuir probe) diagnostics of different plasma parameters and operation regimes (E/H modes) of magnetic pole enhanced, inductively coupled (MaPE-ICP) argon plasmas are investigated. It is shown that uniform, high density (ne ∼ 1012 cm-3) and low electron temperature (Te ∼ 1.5 eV) plasma can be produced in low pressure argon discharges at a low power (100 W). It is found that an MaPE-ICP reactor operates in two different modes; capacitive (E mode) and inductive (H mode). No density jump or hysteresis are reported between these modes. The effect of pressure on transition power, where the mode changes from E to H mode at 20 sccm gas flow rate are studied and it is found that for all pressures tested (∼7.5 mTorr to 75 mTorr) the transition power remains same. In the inductive mode, the above plasma parameters show a smooth variation with increasing filling gas pressure at fixed power. The intensity of the emission line at 750.4 nm due to 2p1 → 1s2 (Paschen’s notation) transition, closely follows the variation of ne with RF power and filling gas pressure. Measured electron energy probability function (EEPF) shows that electron occupation mostly changes in the high-energy tail, which enlightens close similarity of the 750.4 nm argon line to electron number density (ne). The behaviour of the electron energy probability function (EEPF) with regard to pressure and RF power in two operational modes is presented.