Bulletin of the American Physical Society
63rd Annual Gaseous Electronics Conference and 7th International Conference on Reactive Plasmas
Volume 55, Number 7
Monday–Friday, October 4–8, 2010; Paris, France
Session PR2: Plasma Diagnostics II |
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Chair: Timo Gans, Queen's University Belfast, UK Room: 162 |
Thursday, October 7, 2010 2:00PM - 2:30PM |
PR2.00001: Optical Diagnostics using Spectroscopic Measurements of Argon Invited Speaker: Passive, non-invasive optical emission measurements provide a means of probing important plasma parameters without introducing any foreign contaminants into a plasma system. We investigate such parameters as the excited/metastable species concentration and electron energy distribution function (EEDF) in an argon inductively-coupled plasma by measuring the readily observed $3p^54p \to 3p^54s$ emissions in the 650-1150 nm wavelength range. We have also developed an optical emission model which uses our experimentally measured electron-impact excitation cross sections into the $3p^54p$ levels from both the ground state and metastable levels to calculate the $3p^54p \to 3p^54s$ emissions. Moreover, the model includes a number of often neglected but critical processes such as: (i) radiation trapping of $3p^54p \to 3p^54s$ emissions resulting from the high number densities of atoms in Ar($3p^54s$) levels, (ii) electron-impact excitation from atoms in Ar($3p^54s$) resonance levels, and (iii) the effect of non-Maxwellian EEDFs. The agreement between values of the plasma parameters obtained by fitting the model spectra to measured spectra are compared with direct experimental measurements of the corresponding parameters by Langmuir probes and white light absorption spectroscopy under a variety of plasma conditions (pressure, RF power, Ar/Ne/N$_2$ gas mixtures). [Preview Abstract] |
Thursday, October 7, 2010 2:30PM - 2:45PM |
PR2.00002: Dynamic evolution of transient plasma as measured with laser-collision induced fluorescence Ed Barnat Laser-collision induced fluorescence (LCIF) is utilized to produce two-dimensional maps of electron densities and electron temperatures in helium plasmas. In this presentation, the basics of the technique are discussed and means of implementing the technique are described. Particular emphasis is placed on maximizing the temporal resolution that can be realized with the technique while maintaining reasonable (usable) LCIF signals. The LCIF technique is applied to transient plasmas excited by square wave voltages applied to an electrode immersed in the plasma. When the electrode is biased positive with respect to the grounded chamber walls, additional ionization is observed and both the electron density and electron temperature increase. On the other hand, when the electrode is biased negative with respect the grounded chamber, the formation of an ion sheath is observed to form around the electrode. With the LCIF technique, we capture the two-dimensional evolution of this sheath. [Preview Abstract] |
Thursday, October 7, 2010 2:45PM - 3:00PM |
PR2.00003: Estimations of electron temperature and electron density in argon-based reactive plasmas based on diode laser absorption spectroscopy Koichi Sasaki, Ryota Asaoka A metrological method which is suitable for monitoring plasma processing tools in factories is significantly required from the industrial point of view. In this work, we propose a method for estimating electron temperature and electron density in argon-based reactive plasmas. This method is based on the measurements of the densities of two metastable states of argon ($4s[3/2]^{\rm o}_2$ and $4s'[1/2]^{\rm o}_0$) by diode laser absorption spectroscopy. The densities of the two metastable states obtained experimentally are compared with those evaluated by using a population- kinetics model, where the production and loss rates of the metastable states are given as functions of the electron density and the electron temperature. We demonstrated this method in an inductively-coupled N$_2$/Ar mixture plasma. As a result, rough agreement between the proposed method and a Langmuir probe measurement was obtained. This method would be applicable to in-situ monitoring of plasma processing tools in factories because of the low cost, the small footprint, and the maintenance-free operation of a diode laser. [Preview Abstract] |
Thursday, October 7, 2010 3:00PM - 3:15PM |
PR2.00004: Determination of electron densities by means of laser absorption spectroscopy in ICPs Yusuf Celik, Dirk Luggenhoelscher, Uwe Czarnetzki, Mitsutoshi Aramaki A novel method to determine electron densities in pulsed low pressure ICP discharges via absorption spectroscopy on argon metastables is presented. The laser system used in the experiment is an external cavity diode laser (ECDL) in Littrow configuration tuned at a vacuum wavelength of 696.73 nm. The temporal evolution of the line-integrated absorption from metastable argon atoms in the Ar2s5 state in the afterglow is recorded. An analytical expression for the decay of metastables is presented which allows the determination of electron densities. For the analysis, the spatial density profile inside the chamber and the line-integration of the detected signal is taken into account. The results obtained with this technique are compared to Langmuir probe measurements. Both techniques show good agreement. Furthermore, metastable densities and gas temperatures are determined by scanning the laser wavelength over the Doppler-shaped absorption profile. [Preview Abstract] |
Thursday, October 7, 2010 3:15PM - 3:30PM |
PR2.00005: Geometry considerations for EEDF measurements using Langmuir probes Steven Shannon, Ahmed El Saghir, Elijah Martin Langmuir probes are currently the only practical diagnostic for the measurement of electron energy distribution functions in low temperature plasmas, particularly at low densities. The electron energy distribution function is obtained from a probe's electrical characteristic through the integral relationship originally presented by Druyvestyen in 1930 for a planar probe configuration.\footnote{Druyvesteyn M.J.,``Der Niedervoltbogen'' Z. Phys.,vol. 64,1930, pp. 781-798} In this current work, a formulation of Druyvestyen's integral relationship that considers typical probe geometries such as infinite cylindrical, spherical, and finite cylindrical systems will be presented. These integral solutions will be compared to the planar derivation typically employed to look at the effect of geometry on electron energy distribution function measurement from the electrical characteristics of various probe geometries for typical plasma conditions, including non-maxwellian EEDF's. These integral formulations are then used to look at the impact of probe geometry in EEDF measurements made in a toroidal RF source. [Preview Abstract] |
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