Comparison of Electron Density Measurements in Planar Inductively Coupled Plasmas by Means of the Plasma Oscillation Method and Lanqmuir Probes

Published

January 1, 1998

Author(s)

A Schwabedissen, Eric C. Benck, J R. Roberts

Abstract

The absolute, spatially resolved electron densities in planar inductively coupled plasmas have been measured by two different plasma diagnostic techniques, the plasma diagnostic techniques, the plasma oscillation method and Langmuir probes. In the plasma oscillation method a weak electron beam injected into the plasma excites electrostatic electron waves oscillating at the electron plasma frequency, which is proportional to the square root of the electron density. The plasma source is a modified Gaseous Electronics Conference RF Reference Cell . The results for both methods in electropositive, pure rare gas and molecular gas discahrges (Ar, Ne, Kr and N₂) and in electronegative gases and gas mixtures like O₂, Cl₂, CF₄, BCl₃, Ar:CF₄, Ar:O₂ and Ar:Cl₂ are presented and analysed. Over a wide parameter range (gas type, input power and gas pressure), the two techniques yield charge densites which agree within the experimental uncertainty. The electron densities inferred from the plasma oscillation method are generally between the electron and positive-ion density obtained from Langmuir probe measurements. Disagreement between the two techniques is found in molecular gases at higher pressures (p > 3 Pa), where the plasma oscillation method yields electron densities of up to a factor of two higher than the Langmuir probe results.

Citation

Plasma Sources Science & Technology

Volume

7

Pub Type

Journals

Keywords

beam-plasma interaction, electron density, electron plasma frequency, electronegative gases, inductively coupled plasma, ion density, Langmuir probe, plasma diagnostics, plasma oscillation

Citation

Schwabedissen, A. , Benck, E. and Roberts, J. (1998), Comparison of Electron Density Measurements in Planar Inductively Coupled Plasmas by Means of the Plasma Oscillation Method and Lanqmuir Probes, Plasma Sources Science & Technology (Accessed April 19, 2024)