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Title: Electron and ion kinetics in magnetized capacitively coupled plasma source

Abstract

One-dimensional particle-in-cell Monte Carlo collision simulations of magnetized argon plasmas in an asymmetric capacitively coupled plasma reactor are presented. At low pressure (10 mTorr), electron kinetics are strongly affected by the magnetic field and transitions from nonlocal to local kinetic property occur with increasing magnetic field which are reflected in spatially resolved calculations of the electron-energy probability function. For high-energy electrons, the transition takes place when the energy-relaxation length is smaller than the system length. For low-energy electrons, however, the transition occurs when the electron-diffusion time scale in the energy space is shorter than the spatial-diffusion time scale in coordinate space. These observations are in agreement with experimental data and theoretical calculations deduced from the Boltzmann equation. The ion energy distribution function (IEDF) on the driven electrode changes from the ion-neutral collisional type to the ion-neutral collisionless type with increasing magnetic field strength. The maximum ion energy in the IEDF decreases and the angular spread in the ion angle distribution function slightly increases with increasing magnetic field strength. These changes are explained in terms of the ratio of the ion-transit time to rf frequency, the sheath length, and the mean potential difference between the driven electrode and the plasma. Atmore » high pressure (218 mTorr), electron-neutral collisions disrupt electron gyromotion so that the effects of the magnetic field on electron and ion kinetics are greatly reduced.« less

Authors:
; ; ;  [1]
  1. Department of Electronics and Electrical Engineering, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of)
Publication Date:
OSTI Identifier:
20979365
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Vacuum Science and Technology. A, International Journal Devoted to Vacuum, Surfaces, and Films; Journal Volume: 25; Journal Issue: 3; Other Information: DOI: 10.1116/1.2713408; (c) 2007 American Vacuum Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ARGON; BOLTZMANN EQUATION; DISTRIBUTION FUNCTIONS; ELECTRONS; IONS; KINETICS; MAGNETIC FIELDS; MONTE CARLO METHOD; ONE-DIMENSIONAL CALCULATIONS; PLASMA; PLASMA SHEATH; PLASMA SIMULATION; PRESSURE RANGE MEGA PA 10-100

Citation Formats

Lee, S. H., You, S. J., Chang, H. Y., and Lee, J. K. Electron and ion kinetics in magnetized capacitively coupled plasma source. United States: N. p., 2007. Web. doi:10.1116/1.2713408.
Lee, S. H., You, S. J., Chang, H. Y., & Lee, J. K. Electron and ion kinetics in magnetized capacitively coupled plasma source. United States. doi:10.1116/1.2713408.
Lee, S. H., You, S. J., Chang, H. Y., and Lee, J. K. Tue . "Electron and ion kinetics in magnetized capacitively coupled plasma source". United States. doi:10.1116/1.2713408.
@article{osti_20979365,
title = {Electron and ion kinetics in magnetized capacitively coupled plasma source},
author = {Lee, S. H. and You, S. J. and Chang, H. Y. and Lee, J. K.},
abstractNote = {One-dimensional particle-in-cell Monte Carlo collision simulations of magnetized argon plasmas in an asymmetric capacitively coupled plasma reactor are presented. At low pressure (10 mTorr), electron kinetics are strongly affected by the magnetic field and transitions from nonlocal to local kinetic property occur with increasing magnetic field which are reflected in spatially resolved calculations of the electron-energy probability function. For high-energy electrons, the transition takes place when the energy-relaxation length is smaller than the system length. For low-energy electrons, however, the transition occurs when the electron-diffusion time scale in the energy space is shorter than the spatial-diffusion time scale in coordinate space. These observations are in agreement with experimental data and theoretical calculations deduced from the Boltzmann equation. The ion energy distribution function (IEDF) on the driven electrode changes from the ion-neutral collisional type to the ion-neutral collisionless type with increasing magnetic field strength. The maximum ion energy in the IEDF decreases and the angular spread in the ion angle distribution function slightly increases with increasing magnetic field strength. These changes are explained in terms of the ratio of the ion-transit time to rf frequency, the sheath length, and the mean potential difference between the driven electrode and the plasma. At high pressure (218 mTorr), electron-neutral collisions disrupt electron gyromotion so that the effects of the magnetic field on electron and ion kinetics are greatly reduced.},
doi = {10.1116/1.2713408},
journal = {Journal of Vacuum Science and Technology. A, International Journal Devoted to Vacuum, Surfaces, and Films},
number = 3,
volume = 25,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}
  • With the energy resolved quadrupole mass spectrometer and hybrid simulation, the influence of low-frequency (LF) source parameters on the ion energy distributions (IEDs) of argon ions impinging on the grounded electrode was studied, both experimentally and numerically, in a dual frequency capacitively coupled plasma. It was shown that for decreasing LF or increasing LF power, the high energy peak in IEDs shifts toward the high energy region significantly. The simulation results were in general agreement with the experimental data.
  • We investigated the change in electron density using the plasma frequency by the wave cutoff method, and the behavior of ion species with a quadrupole mass spectrometer (QMS) in pure Ar and O{sub 2} and mixed O{sub 2}/Ar plasmas. The change in electron and ion density in pure Ar and O{sub 2} plasmas was evaluated while varying such process conditions as rf power and pressure. We found that electron density in a pure Ar and O{sub 2} discharge is closely correlated to loss and generation of ions. The electron densities in both pure Ar and O{sub 2} plasmas increase withmore » rf plasma power but show different dependence on pressure due to different loss mechanism for each type of gas. The addition of Ar to an O{sub 2} plasma significantly enhances the electron density due to the rapid increase of Ar{sup +} ions regardless of the pressure. Also, Ar addition results in more dissociation of O{sub 2}, which gives more atomic O. These results indicate that the electron density calculated from the plasma frequency, measured by the wave cutoff method, is well explained by the ion behavior, as characterized by QMS.« less
  • Spatially resolved measurements of the ion density and electron temperature in a dual-frequency capacitively coupled Ar discharge plasma are performed with a newly developed complete floating double probe. Axial and radial distributions of the ion density and electron temperature under various high-frequency (HF) power and gas pressure were studied in detail. Both the ion density and the electron temperature increased with increasing HF power. With increasing gas pressure from 1.3 to 9.3 Pa, the radial profile of ion density below the driven electrode experienced a change from ''bimodal'' to ''unimodal'' shape, with better uniformity being achieved at the optimal pressuremore » of about 5 Pa. In addition, changing the axial profile of ion density was also observed with the peak shift toward the powered electrode at higher pressures. The measured results showed satisfying consistency with that of improved two dimensional fluid simulations.« less
  • We present a 1D(r)2D(v) particle code for capacitively coupled radio frequency discharge plasmas in hydrogen, which includes a rigorous kinetic modeling of ion transport and several solutions to speed up the convergence. In a test case the effect of surface atom recombination and molecule vibrational deactivation on H- concentration is investigated.
  • A one-dimensional hybrid model is developed to study the characteristics of energy and angular distributions of the ions and fast neutrals impinging on the rf-biased electrode in a dual-frequency capacitively coupled Ar discharge. The hybrid model consists of a fluid model that determines the spatiotemporal evolution of the discharge, and a Monte-Carlo model that, including the electron-neutral, ion-neutral, and fast neutral-neutral collisions, predicts the energy and angular distributions of the ions and fast neutrals on the rf-biased electrode. The influence of pressure, voltage amplitude, and frequencies of the two rf sources on the energy and angular distributions is discussed. Themore » ion energy distributions (IEDs) appear to have multiple peaks in the dual-frequency capacitively coupled rf discharge rather than bimodal shape in a conventional single-frequency rf discharge. The ion angle distributions (IADs) have a significant peak at a small angle, and most ions strike to the process surface with the angle less than 4 deg. With the increase of the pressure, the maximum energy of IEDs and the peaks of IADs decrease. The structures of IEDs are controlled mainly by the voltage and frequency applied to the two rf sources. By decreasing the frequency or adding the voltage applied to the low-frequency (LF) source, the width of IEDs and the maximum energy increase. More ions strike to the electrode with a small angle by increasing either the voltage of LF source or the frequency of high-frequency source. The energy and angular distributions of the fast neutrals are correlative with those of the ions. Compared with the ions, the fast neutrals have a much lower energy and the scattering effect becomes more prominent.« less