Plasma electron temperatures and electron energy distributions measured by trace rare gases optical emission spectroscopy

Abstract

This article reviews a spectroscopic method for extracting plasma electron temperatures and electron energy distributions: trace rare gases optical emission spectroscopy. Specifically, traces of Ne, Ar, Kr, and Xe are added to the plasma and the intensities of emissions from the Paschen 2p levels are recorded. Intensities are also computed from a model that includes direct excitation from the ground state, as well as two-step excitation through the 3P2, and 3P0 metastable levels. A Maxwellian electron energy distribution function (EEDF), described by an electron temperature (Te), is assumed, and Te is extracted from the best match between the observed and calculated relative emission intensities. By choosing emission from specific sets of levels, the range of electron energies effective in exciting emission can be selected and various portions of the EEDF can be investigated. Accurate measurement of Te depends critically on accurate cross sections for electron impact excitation, and hence a large portion of this article is devoted to a critical review of this subject. Improving on previous treatments, the model for computing emission intensities and electron temperatures includes a complete analysis of the complex excitation and de-excitation of the metastable levels. Previous measurements of Te and EEDFs in chlorine and oxygen inductively coupled plasmas are re-evaluated with the current model. In general, the current version of the model yields similar results; specific differences are discussed.

Experimental and modeling study of O and Cl atoms surface recombination reactions in O2 and Cl2 plasmas

“…10 vs. axial distance. Considering that uncertainties on T e determination from TRG-OES exceed 1 eV at high electron temperatures [68], T e values deduced from the model are in very good agreement with measured values. In the range of experimental conditions investigated, γ Cl ranges from 0.02-0.04.…”

“…The plasma under investigation was produced in a 6-mm inside diameter fused silica tube by a propagating surface wave at 2.45 GHz [65,66]. The line-integrated electron density measured with phase-sensitive microwave interferometry [67], the percent dissociations of Cl 2 determined by actinometry on Cl 2 molecules using Xe as the actinometer [62] and the electron temperature, T e , obtained by trace-rare-gas optical emission spectroscopy (TRG-OES) [68] are shown in Fig. 10 as a function of axial distance with respect to the wave launcher for a 50 mTorr, Cl 2 plasma.…”

Application of a collisional radiative model to atomic hydrogen for diagnostic purposes

“…The noble gases added to the plasma are used as diagnostic gases to determine the line-of-sight averaged electron temperature: the temperature (4.4 eV − 2.1 eV) is deduced from the intensities of the Ar line at 750 nm and the He line at 728 nm [5,39]. The electron temperatures determined from these two lines are in good agreement.…”

Measurement of Argon emission spectral of ICP plasma using a diagnostic system based on photomultiplier tubes array

“…In our ICP rf Argon discharge process, the pressure is 20mTorr and the flow is 200sccm, hence the corona model is valid for analyzing the process. The reason is that other collisional processes are trivial and the density of metastables is too low to make a significant contribution to the excitation of the excited species under these conditions [9][10][11]. In a corona model for these levels, we have the electron-impact excitation from the ground-state atom, Ar(gs) + e Ar(2p1 ) + e (1) and the spontaneous radiation, Ar(2p 1 )Ar(1s 2 ) + hv…”