Comparison of plasma parameters determined with a Langmuir probe and with a retarding field energy analyzer

Abstract

A comparison is made between plasma parameters measured with a retarding field energy analyzer (RFEA), mounted at a grounded electrode in an inductive discharge, and a Langmuir probe located in bulk plasma close to the analyzer. Good agreement between measured plasma parameters is obtained for argon gas pressure in the range 2-10 mTorr. Parameters compared include time averaged plasma potential, the tail of the electron energy distribution function (EEDF), the electron temperature and the ion flux. This highlights the versatility of the RFEA for determining plasma parameters adjacent to the surface where probe measurements are not easily made. Combination of the probe and energy analyzer has enabled the measurement of the EEDF to a higher energy than otherwise possible.

RFEA Measurements of High-Energy Electrons in a Helicon Plasma Device with Expanding Magnetic Field

“…The derivative was found by applying a 151 point, 4 degree SavitzkyGolay filter [37] to the collector current. This derivative should be proportional to the EEDF for energies high enough to enter the probe [24]. In this case the plasma potential was around 40 V, so that the electron energies in the plasma would be about 40 eV higher than what the discriminator voltage shows.…”

“…D is the discriminator grid and was scanned from 0 to −120 V, R is the repeller grid biased at +100 V and C is the collector kept at +9 V. The innermost grid was not needed in this configuration and was therefore grounded. This grid configuration with the discriminator in front of the repeller is similar to the one used by Gahan et al [24,30]. Only the electrons with energies high enough to overcome the sheath potential in front of the probe will be recorded, so that the RFEA detects only the high-energy tail of the EEDF [30].…”

“…The derivative of the collector current is proportional to the EEDF for energies high enough to enter the probe [24]. An RF-compensated Langmuir probe [32] and a floating emissive probe were used to measure some of the background parameters of the plasma.…”

“…In this paper, we report the first measurements of energetic electrons in the downstream region of the CFDL in the Njord device, applying a Retarding Field Energy Analyzer (RFEA). By inverting the grids of an RFEA, the probe can be applied to measure the flux of the high-energy tail of electrons [23][24][25][26]. In Section 2, the experimental setup and diagnostics is explained, and the measured distributions of energetic electrons are reported and discussed in Section 3.…”

Plasma parameters of pulsed-dc discharges in methane used to deposit diamondlike carbon films

“…26,27 Used in parallel with film deposition, plasma diagnostics ensure process control and reproducibility of the process. Optical emission spectroscopy ͑OES͒, 28,29 quadrupole mass spectrometry ͑QMS͒, 30,31 and diagnostics by means of a retarding field energy analyzer ͑RFEA͒ 32 and a Langmuir probe [33][34][35] are the most common plasma characterization techniques. The last of these provides reliable monitoring of plasma parameters by means of recording I-V characteristics from an electrostatic tip in the glow discharge.…”