Measurements of the plasma potential, electron density, effective electron temperature, and electron energy distribution function ͑EEDF͒ have been performed with Langmuir probes in planar, electrostatically shielded, low-pressure inductively coupled plasmas. The plasma source is a modification of the Gaseous Electronics Conference RF Reference Cell ͓P. J. Hargis et al., Rev. Sci. Instrum. 65, 140 ͑1994͔͒ with the upper electrode replaced by a five-turn planar coil and a quartz vacuum interface. Four different rare gases ͑Ar, Kr, Xe, and Ne͒, a He:Ar ͑96:4͒ mixture, and O 2 and N 2 were investigated. We found that with increasing ionization potential of the rare gas the electron density decreases, while the effective electron temperature and the plasma potential increase. Non-Maxwellian EEDFs were observed for all energies for O 2 and N 2 discharges as well as for the rare gases above the energy range for elastic collisions. Spatially resolved measurements confirm that the EEDF is determined by spatially averaged quantities instead of the local electric field.

The absolute, spatially resolved electron densities in planar inductively coupled plasmas have been measured by two different plasma diagnostic techniques, the plasma oscillation method and Langmuir probes. In the plasma oscillation method a weak electron beam injected into the plasma excites electrostatic electron waves oscillating at the electron plasma frequency, which is proportional to the square root of the electron density. The plasma source is a modified Gaseous Electronics Conference RF Reference Cell. The results for both methods in electropositive, pure rare gas and molecular gas discharges (Ar, Ne, Kr and N 2 ) and in electronegative gases and gas mixtures like O 2 , Cl 2 , CF 4 , BCl 3 , Ar:CF 4 , Ar:O 2 and Ar:Cl 2 are presented and analysed. Over a wide parameter range (gas type, input power and gas pressure), the two techniques yield charge densities which agree within the experimental uncertainty. The electron densities inferred from the plasma oscillation method are generally between the electron and positive-ion density obtained from Langmuir probe measurements. Disagreement between the two techniques is found in molecular gases at higher pressures (p > 3 Pa), where the plasma oscillation method yields electron densities of up to a factor of two higher than the Langmuir probe results.

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Laser-collision induced fluorescence (LCIF) is the emission of light from states that have been populated by laser excitation and a subsequent collision. By simultaneously measuring the LCIF from two different states, it is possible to determine both the electron density and temperature of the low energy bulk electrons within a plasma. This method is described in detail and has been applied in the determination of the total, temporally averaged, and spatially resolved electron density in a rf (13.56 MHz) helium discharge in the Gaseous Electronics Conference reference cell. The rf discharge was operated at pressures P=33.3–133.3 Pa (0.25–1.0 Torr) and peak-to-peak voltages of Vpp=75–300 V were applied. We found the total electron density varied from 1.8×108 cm−3 at P=33.3 Pa and Vpp=75 V to 4.0×1010 cm−3 at P=133.3 Pa and Vpp=300 V. A comparison of results from different experiments has been made.