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Title: The transition from symmetric to asymmetric discharges in pulsed 13.56 MHz capacitively coupled plasmas

Abstract

The behavior of a rapidly pulsed radio-frequency capacitively coupled parallel plate reactor has been investigated using time-resolved voltage probe, microwave interferometer, and optical emission techniques. The reactor was operated with 50 mTorr of argon and 100 W rf power (measured at the generator) at 13.56 MHz supplied to the 100-mm-diam powered electrode, with pulse durations of 25 and 100 {mu}s. For low repetition rates (50 Hz) the voltage envelope has a characteristic form which has been entitled the Bird`s Head. There is no plasma present at the beginning of the pulse, so that an initial breakdown phase occurs. This phase lasts about 600 ns, after which time the plasma density is sufficiently high for the Debye length to enter the gap between the electrodes and for sheaths to form on the electrodes. In asymmetric parallel plate reactors the blocking capacitor in the matching circuit charges such that the powered electrode acquires a continuous negative voltage offset (the so-called dc bias). In this system the charging time of the capacitor is longer than the rise time of the rf voltage. Consequently, for the first few {mu}s of the pulse the discharge is symmetric (no dc bias) and confined between the rfmore » and the adjacent earthed electrode. As the bias voltage increases the discharge fills more of the reactor and becomes asymmetric. The rate at which the blocking capacitor charges (due to net electron current from the plasma to the powered electrode) is controlled by the Bohm-criterion limited flux of ions to the earthed walls of the reactor, as shown by particle-in-cell simulations in H. B. Smith, C. Charles, and R. W. Boswell, J. Appl. Phys. {bold 82}, 561 (1997). At high repetition rates (20 kHz) the plasma density is hardly modulated, there is no breakdown or symmetric phase, and only the electron temperature and dc bias are modulated. The conditions which lead to a symmetric discharge phase are defined. (Abstract Truncated)« less

Authors:
; ;  [1];  [2]
  1. Laboratoire de Spectrometrie Physique, Universite Joseph Fourier, 38402 Saint Martin-d`Heres Cedex, Grenoble (France)
  2. PRL, Australian National University, ACT. 200 (Australia)
Publication Date:
OSTI Identifier:
549282
Resource Type:
Journal Article
Journal Name:
Journal of Applied Physics
Additional Journal Information:
Journal Volume: 82; Journal Issue: 2; Other Information: PBD: Jul 1997
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION; HIGH-FREQUENCY DISCHARGES; PLASMA DIAGNOSTICS; CAPACITANCE; INTERFEROMETRY; EMISSION SPECTRA; PLASMA DENSITY; IONS; PLASMA SIMULATION; ELECTRODES; ELECTRON TEMPERATURE

Citation Formats

Booth, J P, Cunge, G, Sadeghi, N, and Boswell, R W. The transition from symmetric to asymmetric discharges in pulsed 13.56 MHz capacitively coupled plasmas. United States: N. p., 1997. Web. doi:10.1063/1.365614.
Booth, J P, Cunge, G, Sadeghi, N, & Boswell, R W. The transition from symmetric to asymmetric discharges in pulsed 13.56 MHz capacitively coupled plasmas. United States. doi:10.1063/1.365614.
Booth, J P, Cunge, G, Sadeghi, N, and Boswell, R W. Tue . "The transition from symmetric to asymmetric discharges in pulsed 13.56 MHz capacitively coupled plasmas". United States. doi:10.1063/1.365614.
@article{osti_549282,
title = {The transition from symmetric to asymmetric discharges in pulsed 13.56 MHz capacitively coupled plasmas},
author = {Booth, J P and Cunge, G and Sadeghi, N and Boswell, R W},
abstractNote = {The behavior of a rapidly pulsed radio-frequency capacitively coupled parallel plate reactor has been investigated using time-resolved voltage probe, microwave interferometer, and optical emission techniques. The reactor was operated with 50 mTorr of argon and 100 W rf power (measured at the generator) at 13.56 MHz supplied to the 100-mm-diam powered electrode, with pulse durations of 25 and 100 {mu}s. For low repetition rates (50 Hz) the voltage envelope has a characteristic form which has been entitled the Bird`s Head. There is no plasma present at the beginning of the pulse, so that an initial breakdown phase occurs. This phase lasts about 600 ns, after which time the plasma density is sufficiently high for the Debye length to enter the gap between the electrodes and for sheaths to form on the electrodes. In asymmetric parallel plate reactors the blocking capacitor in the matching circuit charges such that the powered electrode acquires a continuous negative voltage offset (the so-called dc bias). In this system the charging time of the capacitor is longer than the rise time of the rf voltage. Consequently, for the first few {mu}s of the pulse the discharge is symmetric (no dc bias) and confined between the rf and the adjacent earthed electrode. As the bias voltage increases the discharge fills more of the reactor and becomes asymmetric. The rate at which the blocking capacitor charges (due to net electron current from the plasma to the powered electrode) is controlled by the Bohm-criterion limited flux of ions to the earthed walls of the reactor, as shown by particle-in-cell simulations in H. B. Smith, C. Charles, and R. W. Boswell, J. Appl. Phys. {bold 82}, 561 (1997). At high repetition rates (20 kHz) the plasma density is hardly modulated, there is no breakdown or symmetric phase, and only the electron temperature and dc bias are modulated. The conditions which lead to a symmetric discharge phase are defined. (Abstract Truncated)},
doi = {10.1063/1.365614},
journal = {Journal of Applied Physics},
number = 2,
volume = 82,
place = {United States},
year = {1997},
month = {7}
}