Abstract

Optical emission spectroscopy has been widely used in low-temperature argon plasma diagnostics. A coronal model is usually used to analyze the measured line ratios for diagnostics with a single temperature and density. However, many plasma processing conditions deviate from single temperature and density, optically thin conditions, or even coronal plasma conditions due to cascades from high-lying states. In this paper, we present a collisional-radiative model to investigate the validity of coronal approximations over a range of plasma conditions of Te = 1–4 eV and Ne = 108–1013 cm−3. The commonly used line ratios are found to change from a coronal limit where they are independent of Ne to a collisional-radiative regime where they are not. The effects of multiple-temperature plasma, radiation trapping, wall neutralization, and quenching on the line ratios are investigated to identify the plasma conditions under which these effects are significant. This study demonstrates the importance of the completeness of atomic datasets in applying a collisional-radiative model to low-temperature plasma diagnostics. View Full-Text

Keywords: argon optical emission spectroscopy; plasma processing; coronal models; collisional-radiative model; nonlocal thermodynamic equilibrium plasmas; population kinetics; radiation transport; opacity effects; Non-Maxwellian plasmas

Academic Editor: Grzegorz Piotr Karwasz

Atoms 2021, 9(4), 100; https://doi.org/10.3390/atoms9040100

Received: 3 November 2021 / Revised: 19 November 2021 / Accepted: 19 November 2021 / Published: 24 November 2021

(This article belongs to the Special Issue Electron Scattering in Gases –from Cross Sections to Plasma Modeling)