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Title: Ion velocities in the presheath of electronegative, radio-frequency plasmas measured by low-energy cutoff

Abstract

Simple kinematic considerations indicate that, under certain conditions in radio-frequency (rf) plasmas, the amplitude of the low-energy peak in ion energy distributions (IEDs) measured at an electrode depends sensitively on ion velocities upstream, at the presheath/sheath boundary. By measuring this amplitude, the velocities at which ions exit the presheath can be determined and long-standing controversies regarding presheath transport can be resolved. Here, IEDs measured in rf-biased, inductively coupled plasmas in CF{sub 4} gas determined the presheath exit velocities of all significant positive ions: CF{sub 3}{sup +}, CF{sub 2}{sup +}, CF{sup +}, and F{sup +}. At higher bias voltages, we detected essentially the same velocity for all four ions. For all ions, measured velocities were significantly lower than the Bohm velocity and the electropositive ion sound speed. Neither is an accurate boundary condition for rf sheaths in electronegative gases: under certain low-frequency, high-voltage criteria defined here, either yields large errors in predicted IEDs. These results indicate that many widely used sheath models will need to be revised.

Authors:
; ;  [1]
  1. National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)
Publication Date:
OSTI Identifier:
22590616
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 109; Journal Issue: 2; Other Information: (c) 2016 U.S. Government; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; AMPLITUDES; BOUNDARY CONDITIONS; CARBON TETRAFLUORIDE; CATIONS; ELECTRIC POTENTIAL; ELECTRODES; ENERGY SPECTRA; ERRORS; GASES; PEAKS; PLASMA; RADIOWAVE RADIATION; SOUND WAVES; VELOCITY

Citation Formats

Sobolewski, Mark A., Wang, Yicheng, and Goyette, Amanda. Ion velocities in the presheath of electronegative, radio-frequency plasmas measured by low-energy cutoff. United States: N. p., 2016. Web. doi:10.1063/1.4958836.
Sobolewski, Mark A., Wang, Yicheng, & Goyette, Amanda. Ion velocities in the presheath of electronegative, radio-frequency plasmas measured by low-energy cutoff. United States. doi:10.1063/1.4958836.
Sobolewski, Mark A., Wang, Yicheng, and Goyette, Amanda. Mon . "Ion velocities in the presheath of electronegative, radio-frequency plasmas measured by low-energy cutoff". United States. doi:10.1063/1.4958836.
@article{osti_22590616,
title = {Ion velocities in the presheath of electronegative, radio-frequency plasmas measured by low-energy cutoff},
author = {Sobolewski, Mark A. and Wang, Yicheng and Goyette, Amanda},
abstractNote = {Simple kinematic considerations indicate that, under certain conditions in radio-frequency (rf) plasmas, the amplitude of the low-energy peak in ion energy distributions (IEDs) measured at an electrode depends sensitively on ion velocities upstream, at the presheath/sheath boundary. By measuring this amplitude, the velocities at which ions exit the presheath can be determined and long-standing controversies regarding presheath transport can be resolved. Here, IEDs measured in rf-biased, inductively coupled plasmas in CF{sub 4} gas determined the presheath exit velocities of all significant positive ions: CF{sub 3}{sup +}, CF{sub 2}{sup +}, CF{sup +}, and F{sup +}. At higher bias voltages, we detected essentially the same velocity for all four ions. For all ions, measured velocities were significantly lower than the Bohm velocity and the electropositive ion sound speed. Neither is an accurate boundary condition for rf sheaths in electronegative gases: under certain low-frequency, high-voltage criteria defined here, either yields large errors in predicted IEDs. These results indicate that many widely used sheath models will need to be revised.},
doi = {10.1063/1.4958836},
journal = {Applied Physics Letters},
number = 2,
volume = 109,
place = {United States},
year = {Mon Jul 11 00:00:00 EDT 2016},
month = {Mon Jul 11 00:00:00 EDT 2016}
}