Bulletin of the American Physical Society
60th Gaseous Electronics Conference
Volume 52, Number 9
Tuesday–Friday, October 2–5, 2007; Arlington, Virginia
Session WF2: Plasma Diagnostics II |
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Chair: Timo Gans, Queen's University - Belfast Room: Doubletree Crystal City Crystal Ballroom B |
Friday, October 5, 2007 10:30AM - 11:00AM |
WF2.00001: Laser-aided diagnostics of reactive plasmas for better understanding of material processing Invited Speaker: The roles of plasma diagnostics in the development of plasma- aided material processing are classified into two categories. One is to provide deep understanding of reactive plasmas, which is indispensable for the efficient development of new processing technologies via laboratory experiments. The other role is to monitor the operation conditions of plasma processing tools in factories in order to realize efficient mass production. Laser-aided diagnostics have mainly played the former role in the last two decades, but they have potential applications in plasma monitoring tools which are required strongly from the industrial point of view. In this talk, we will show two examples of laser-aided precise diagnostics for laboratory experiments and an example of laser-aided monitoring of reactive plasmas. The first diagnostics is the measurement of sheath electric field in an electronegative Ar/SF$_6$ plasma by laser-induced fluorescence-dip spectroscopy. We observed a stepwise electric field distribution which was induced by the localized reflection of negative ions. The second diagnostics is laser-induced fluorescence imaging spectroscopy. We visualized two-dimensional distributions of radical densities and the velocity distribution function of Fe atoms in magnetron sputtering plasmas. The final one is a method for estimating electron density and electron temperature of a processing plasma based on diode laser absorption spectroscopy. This method would be utilized as a plasma monitoring tool because of the low cost and the maintenance-free operation of the diode laser. [Preview Abstract] |
Friday, October 5, 2007 11:00AM - 11:15AM |
WF2.00002: Measurement of Absolute Carbon Atom Density in Reactive Plasmas using Vacuum Ultraviolet Absorption Spectroscopy with Microdischarge Hollow Cathode Lamp Hajime Sasaki, Seigo Takashima, Masaru Hori Carbon atoms play an important role in the reactive plasma processes such as carbon nanostructure formation, etching and so on. In order to realize the smart plasma processing, it is very important to measure the absolute C atom density in the process plasma using carbon based gasses, because the C atoms have a high sticking coefficient. We have developed a measurement technique for absolute C atom densities using a vacuum ultraviolet absorption spectroscopy (VUVAS) employing a microdischarge hollow cathode lamp (MHCL). Helium gas containing a small amount of CO$_{2}$ gas was used as the gas of the MHCL. The transition lines 2p3s$^{3}$p$_{2}$-2p$^{23}$P$_{2}$ at 165.7 nm were used for C atom measurements. By using VUVAS system, we measured the absolute C atom density in the CO-ICP at the pressure of 8.0 Pa. The densities increased from 1.7x10$^{11}$ to 9.5x10$^{13}$ cm$^{-3}$ when the RF power increased from 10 to 1000 W. his measurement method will be useful for the plasma processing for synthesize a diamond like carbon, carbon nanotube and so on. [Preview Abstract] |
Friday, October 5, 2007 11:15AM - 11:30AM |
WF2.00003: Optical probe for space resolved measurement of atom densities in reactive plasmas Shunji Takahashi, Seigo Takashima, Koji Yamakawa, Shoji Den, Hiroyuki Kano, Masaru Hori Atomic radicals such as H, N, O, and C play important roles in process plasmas. We have developed a compact measurement system of these atom densities in the reactive plasmas using a vacuum ultraviolet absorption spectroscopy (VUVAS) with a microdischarge hollow cathode lamp (MHCL). However, the two opposite ports are basically necessary to measure the densities using the system. Moreover, it is difficult to measure the spatial distribution of the densities. In this study, the monitoring probe for the atomic radicals has been developed. The probe installed to the plasma was 2.7 mm in diameter. The port for the measurements was one. It enables us to measure the spatial distribution of the atom densities by moving the probe along the chamber radius. Using the probe, the spatial distribution of the H atom densities in the remote H$_{2}$ plasmas was successfully measured at the pressure of 1.33 Pa, the RF power of 300 W. The densities decreased drastically from 1.2 x 10$^{12}$ cm$^{-3}$ to 4.4 x 10$^{11}$ cm$^{-3}$ near the chamber wall. [Preview Abstract] |
Friday, October 5, 2007 11:30AM - 11:45AM |
WF2.00004: Direct measurements of neutral density depletion by two-photon absorption laser-induced fluorescence spectroscopy (TALIF) Laurent Liard, Ane Aanesland, Gary Leray, Jacques Jolly, Pascal Chabert The neutral ground state density of xenon is measured by spatially resolved laser-induced fluorescence spectroscopy with two-photon excitation (TALIF) giving direct access to the neutral density depletion in high density plasmas. Significant neutral depletion is measured in the diffusion chamber of a magnetized, high density helicon reactor operated in xenon. The depletion at the centre of the core increases with increasing magnetic field, increasing rf power and decreasing fill pressure. The neutral depletion is due to the high electron pressure in the centre of the discharge which has been measured by Langmuir probe techniques. Temporal behaviour has also been studied both at ignition and extinction of the plasma. [Preview Abstract] |
Friday, October 5, 2007 11:45AM - 12:00PM |
WF2.00005: Plasma induced by Resonance Enhanced Multi-Photon Ionization (REMPI) in Inert Gas Mikhail Shneider, Zhili Zhang, Richard Miles We present a model for REMPI plasma evolution in the neutral inert gas (argon) during and after the ionizing laser pulse. The theory of REMPI breakdown is considered in 1D cylindrical geometry and includes time dependent continuity equations in the diffusion-drift approximation for plasma components: Rydberg atom states excited in 3 photon process, electrons, Ar+ and Ar2+ ions. The Poisson equation for potential and the electron heat transfer equation together with 1D gasdynamic Navier-Stokes equations are also included. Both ionization by REMPI and by collisions of bulk electrons with atoms are taken into account. Our study demonstrates the complete process of REMPI plasma generation and decay in the inert gas together with the gas dynamic equations. Plasma expansion represents a classical ambipolar diffusion. It is shown that gas becomes involved in the motion not only by the pressure gradient due to the heating, but also because of momentum transfer from the charged particles to gas atoms. Gas heating and momentum transfer from charged particles result in a weak shock or acoustic wave. The time dependence of the total number of electrons computed in the theory is in agreement with the results of the coherent microwave scattering experiment. [Preview Abstract] |
Friday, October 5, 2007 12:00PM - 12:15PM |
WF2.00006: Coherent Microwave Rayleigh Scattering from Resonance Enhanced Multiphoton ionization in argon Zhili Zhang, Mikhail Shneider, Richard Miles Microwave scattering from a resonance enhanced multi-photon ionization (REMPI) produced plasma provides a new means for the direct, time accurate observation of the free electrons and thus a new method for high sensitivity REMPI spectroscopy of a gas and a new method for the measurement of electron formation and loss processes. The REMPI plasma acts as a coherent microwave scatterer, with the scattering electric field amplitude proportional to the number of electrons. Since the size of the REMPI plasma is small compared to the microwave wavelength, the scattering falls into the Rayleigh regime. Multiphoton ionization and electron recombination processes are studied in argon using this method. A time dependent one dimensional plasma dynamic model is developed to predict the time evolution of the microwave scattering from the plasma. Experimental results of the argon ionization spectrum and electron recombination rates are in good agreement with the model predictions. [Preview Abstract] |
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