Bulletin of the American Physical Society
61st Annual Gaseous Electronics Conference
Volume 53, Number 10
Monday–Friday, October 13–17, 2008; Dallas, Texas
Session VF1: Glows |
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Chair: R. Dussart, GREMI, CNRS/Université d'Orléans Room: Salon E |
Friday, October 17, 2008 8:00AM - 8:30AM |
VF1.00001: Study of Planar Surface Wave Excited Plasma Invited Speaker: The need for plasma processing has increased as miniaturization in semiconductor manufacturing goes ahead. In these processes, a large-diameter plasma source is required with respect to 300mm wafer size. A Radial Line Slot Antenna (RLSA) driven surface-wave-sustained plasma is a potential best candidate to various applications with respect to damage free process. Many researches focus on the control of plasma density and electron temperature in RLSA technique. However, the plasma stability and uniformity control are less implemented in the practice. In recent years, we study sheath formation and plasma behavior at the interface, where the surface wave propagate, by using electromagnetic particle-in-cell simulation techniques. The simulations include the effects of ionization, and allow us to study the buildup of plasma density associated with ionization in the presence of the large fields of the RF-enhanced sheath. Our results show both the mechanism of plasma generation and heating at the plasma dielectric interface and the strong effect on geometric design of dielectric. Various scenarios are of interest, and help us to design an optimal RLSA driven plasma source, where the plasma stability and uniformity are firmly sustained under the various process conditions. Plasma diagnosis is carried out to reveal the more essential difference in plasma behavior between our RLSA and a custom inductively coupled plasma (ICP) source. [Preview Abstract] |
Friday, October 17, 2008 8:30AM - 8:45AM |
VF1.00002: Hybrid modelling of an ac-driven low-pressure He-Xe lamp discharge Detlef Loffhagen, Florian Sigeneger The spatiotemporal evolution of the column plasma of an ac-driven glow discharge in He-Xe mixtures is analyzed by means of hybrid modelling. The theoretical description of the cylindrical, axially homogeneous discharge plasma is based on the coupled solution of hydrodynamic equations for the charge carriers and neutral species in the plasma, equations of the external electric discharge circuit for the determination of the axial electric field, the Poisson equation describing the behaviour of the radial space charge field and the time-dependent, radially inhomogeneous Boltzmann equation providing the transport and rate coefficients of the electrons. Results of the periodic behaviour of the plasma in a discharge tube with a diameter of 18 mm at a gas pressure of 2.5 Torr using a mixture of 98\% helium and 2\% xenon are discussed. Pronounced structural changes of the particle and flux densities of the different plasma components, the electric field components and the energy distribution of the electrons are found. In particular, the electron energy flux changes between a purely outward directed flux and a partly inward and outward directed one during the period. The comparison with experimental data of discharge voltage and current as well as excited state densities of xenon shows good agreement between calculated and measured data. [Preview Abstract] |
Friday, October 17, 2008 8:45AM - 9:00AM |
VF1.00003: Role of metastable molecules and negative ions in dc and rf oxygen discharges Gordon K. Grubert, Detlef Loffhagen, Florian Sigeneger For various technological oxygen plasma applications it is supposed that the metastable molecules play a decisive role for the charge carrier production and consequently, the negative ions deform the electric potential intensely. To analyze the influence of these species, a self-consistent theoretical description for an oxygen discharge between plane electrodes has been performed. A hydrodynamic approach including the continuity equations for the particle densities in addition with the drift-diffusion approximation for the fluxes of all relevant species coupled with Poisson's equation for the determination of the space-charge field has been adapted. The electronic transport and rate coefficients are determined by solving the stationary, spatially homogeneous electron Boltzmann equation in multiterm approximation. The pressure range from 10 to 100~Pa has been investigated for typical dc and rf discharge conditions. It was found that the metastable molecule densities are orders of magnitude smaller than expected and their spatial profiles are similar to diffusion profiles. Furthermore, the influence of the negative ions on the electric potential is found to be negligible. This work is supported by the Deutsche Forschungsgemeinschaft within SFB TR 24. [Preview Abstract] |
Friday, October 17, 2008 9:00AM - 9:15AM |
VF1.00004: Scaling Relationship for Energetic Electron Beams Propagating in Air R.F. Fernsler, S.P. Slinker, S.G. Lambrakos Electron beams are the most efficient means for producing plasmas in air and other gases, and unlike discharges, beams ionize gas at rates almost directly proportional to the concentrations of the constituents. In addition, because the beam is responsible for ionization, the temperature of the plasma electrons (which far outnumber the beam electrons) is unusually low. The plasma potential and ion energies at adjoining surfaces are therefore low as well, properties that are important for certain applications. Electron beams are thus unique as a plasma source. Unfortunately, predicting the ionization generated by a beam over its entire range is difficult, and particle codes are usually used to do so. In this work scaling relationships for energy loss and scattering are combined with a particle code to construct a purely algebraic formulation capable of predicting the beam energy deposited in field-free, homogeneous air. This formulation is then combined with a simple fluid model to predict the plasma density and temperature. By this means, plasmas generated in air can be predicted easily and algebraically at every point in space for beams having an initial energy of several keV or more. Similar models are possible in media other than air. [Preview Abstract] |
Friday, October 17, 2008 9:15AM - 9:30AM |
VF1.00005: Effect of Electron Energy Distribution Function on Global Model for High Power Microwave Breakdown at High Pressure Sang Ki Nam, John Verboncoeur The effect of a wide spectrum of reaction kinetics is very important in high power microwave (HPM) breakdown in molecular gases. However, it is not practical to investigate breakdown including detailed reaction kinetics using particle simulation due to the computational expense. Therefore, a fast volume-averaged global model was developed for the purpose of investigating the effect of reaction kinetics and plasma parameters for multiple species needed to model molecular gases. Since the global model is a fluid-based model, it requires specification of the electron energy distribution function (EEDF). Most global models assume a Maxwellian distribution for the EEDF. The electrons, however, are not in equilibrium unless the electron-electron collision is dominant. The assumption of a Maxwellian EEDF produces inaccurate reaction rate coefficients for the plasma discharge and results in incorrect plasma parameters especially at high pressure. We examine the effect of the EEDF on the global model and develop a method to find the proper approximation of the EEDF to improve fidelity of the prediction of the HPM breakdown at high pressure. [Preview Abstract] |
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