Quantitative determination of mass-resolved ion densities in H2-Ar inductively coupled radio frequency plasmas

Abstract

Inductively coupled H2-Ar plasmas are characterized by an energy-dispersive mass spectrometer (plasma monitor), a retarding field analyzer, optical emission spectroscopy, and a Langmuir probe. A procedure is presented that allows determining quantitatively the absolute ion densities of Ar+, H+, H2+, H3+, and ArH+ from the plasma monitor raw signals. The calibration procedure considers the energy and mass-dependent transmission of the plasma monitor. It is shown that an additional diagnostic like a Langmuir probe or a retarding field analyzer is necessary to derive absolute fluxes with the plasma monitor. The conversion from fluxes into densities is based on a sheath and density profile model. Measurements were conducted for a total gas pressure of 1.0 Pa. For pure H2 plasmas, the dominant ion is H3+. For mixed H2-Ar plasmas, the ArH+ molecular ion is the most dominant ion species in a wide parameter range. The electron density, ne, is around 3×1016 m−3 and the electron temperature, Te, decreases from 5 to 3 eV with increasing Ar content. The dissociation degree was measured by actinometry. It is around 1.7% nearly independent on Ar content. The gas temperature, estimated by the rotational distribution of the Q-branch lines of the H2 Fulcher-α diagonal band (v′=v″=2) is estimated to (540 ± 50) K.