Articles you may be interested inComparison of atmospheric-pressure helium and argon plasmas generated by capacitively coupled radiofrequency discharge Phys. Plasmas 13, 093503 (2006); 10.1063/1.2355428 Modeling of microcrystalline silicon film deposition in a capacitively coupled radio-frequency plasma reactor J. Appl. Phys. 97, 023308 (2005); 10.1063/1.1821639Electrostatic probe diagnostics of a planar-type radio-frequency inductively coupled oxygen plasma
A reproducible instability, which appears similar to those reported previously, has been observed and studied in a low-pressure 13.56 MHz inductively coupled gaseous electronics conference rf cell operating in oxygen. The instability has been observed in the form of periodic modulations in the light output, floating potential, electron and positive and negative ion densities. The magnitude and frequency of the modulations is sensitive to the plasma operating conditions and the modulation amplitude has been observed to be as high as 40%. The instability is observed in a pressure and power regime where both the capacitive and inductive modes can exist. The frequency of the oscillations increases with increase in gas pressure from 3 to 21 kHz. This pressure window coincides with the pressure regime where there exists a significant fraction of negative ions in both modes. Time-resolved measurements of the electron energy distribution functions and charged particle densities indicate that at all phases of the instability, the plasma parameters remain close to those of the inductive mode. A global model has been modified for an oxygen discharge and this provides a qualitative description of the instability. The global model predicts a smaller power and pressure window for the instability but it can provide a framework for the discussion of instabilities in weakly electronegative discharges.
Optical emission spectra from a low-pressure Ar plasma were studied with high spatial resolution. It has been shown that the intensity ratios of Ar lines excited through metastable levels to those excited directly from the ground state are sensitive to the shape of electron energy distribution function. From these measurements, important information on the spatial variation of plasma parameters can be obtained.
Reproducible modulations in low-pressure, inductively coupled discharges operating in chlorine and argon-chlorine mixtures have been observed and studied. Changes in the light output, floating potential, negative ion fraction, and charged particle densities were observed. Here we report two types of unstable operational modes in an inductively coupled discharge. On the one hand, when the discharge was matched, to minimize reflected power, instabilities were observed in argon-chlorine plasmas over limited operating conditions of input power and gas pressure. The instability window decreased with increasing chlorine content and was observed for chlorine concentrations between 30% and 60% only. However, when operating at pressures below 5 mTorr and the discharge circuit detuned to increase the reflected power, modulations were observed in a pure chlorine discharge. These modulations varied in nature from a series of sharp bursts to a very periodic behavior and can be controlled, by variation of the matching conditions, to produce an apparent pulsed plasma environment.
Electron energy probability functions measured with a passively compensated Langmuir probe in asymmetric capacitively coupled hydrogen and deuterium plasmas exhibit structure. The otherwise relatively continuous distribution appears to have an abrupt peak in electron density near 5 eV. This structure occurs at a higher energy in deuterium than hydrogen and there is a correlation between floating potential and the voltage at which the structure is observed in the second derivative of the I(V) characteristic. While the cause of the structure has yet to be clarified, spectroscopic observations and computer-based hydrogen models indicate that the high energy tail of the distribution is strongly modulated during the radio frequency cycle. The effect of this modulation on plasma properties and probe measurements has yet to be explored.
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