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

Journal Article · Tue Jul 01 04:00:00 EDT 1997 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.365614· OSTI ID:549282

Booth, J P; Cunge, G; Sadeghi, N ^[1]; Boswell, R W ^[2]

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1. Laboratoire de Spectrometrie Physique, Universite Joseph Fourier, 38402 Saint Martin-d`Heres Cedex, Grenoble (France)
2. PRL, Australian National University, ACT. 200 (Australia)

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)

• OSTI ID: 549282
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 2 Vol. 82; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
CAPACITANCE
ELECTRODES
ELECTRON TEMPERATURE
EMISSION SPECTRA
HIGH-FREQUENCY DISCHARGES
INTERFEROMETRY
IONS
PLASMA DENSITY
PLASMA DIAGNOSTICS
PLASMA SIMULATION