Charged particle densities and kinetics in a radio-frequency SF6 plasma

Abstract

Electron, negative ion, and positive ion densities in a capacitively-coupled radio-frequency (rf, 13.56 MHz) SF, plasma have been investigated as functions of the pressure (30-700 mTorr) and rf power. The decay of the charged particle densities in the afterglow has also been studied to obtain information about their kinetics. The electron density was determined by using a microwave cavity resonance technique. Negative ions were detected by measuring the density of photodetached electrons produced by pulsed laser irradiation of the plasma. The positive ion density was obtained from Langmuir probe measurements. At a rf power of 0.13 W/cm* and at low pressures (5100 mTorr) the positive ion density, which is virtually equal to the negative ion density, is found to be larger than the electron density by a factor of a few hundred; the ion/electron density ratio increases with increasing pressure to reach a value of a few thousand at high pressures. Wavelength-dependent photodetachment measurements indicate that the dominant contribution to the photodetachment signal at 266 nm comes from F-, but F-is a minor negative-ion species with respect to the density; that is, the photodetachment efficiency for the dominant negative ion species (supposed to be SF;) is low. The recombination rate constant for F-(supposedly with SF;) is suggested to be an order of magnitude larger than that for the dominant ion species, the latter being estimated to be slightly smaller than 10m7 cm3 s-l. 0 I994 American Institute of Physics.136.165.238.131 On

Negative ion measurements and etching in a pulsed-power inductively coupled plasma in chlorine

“…The excess electron density created by the photodetachment in the saturation regime is equal to the absolute density of negative ions. The detached electrons can be monitored either by a positively biased Langmuir probe or by a microwave cavity resonance technique [11,12]. In comparison to the former, the latter technique gives the absolute density.…”

Electrostatic probe measurement of the negative ion fraction in an SF6helicon discharge

“…A number of diagnostics have been used to characterize electronegative discharges. Laser-induced photodetachment has been studied extensively [10][11][12][13] and has demonstrated its utility. Mass spectrometric measurements have also been used [5,6,14], and allow the identification of negative ion species.…”

Negative Ions in Low Pressure Discharges

“…However, in very fast attaching gases, like CC12F2 or SF, a deconvolution method may be necessary [16, 791. Photodetachment in combination with a microwave cavity has been used to measure negative ion densities in various electronegative gases, including hydrogen [80], oxygen [ 171, SF, [79], halocarbons [81,18,19,161 and SiH,[16]. In some gases several different negative ions have been detected, e.g.…”