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 LW1: Negative Ions |
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Chair: Ane Aanesland, CNRS-Ecole Polytechnique Room: 162 |
Wednesday, October 6, 2010 4:00PM - 4:15PM |
LW1.00001: Formation of High Energy Oxygen Species in RF Magnetron Sputter Plasma Kazuya Goto, Tatsuo Ishijima, Tadashi Morita, Kazunaga Ono, Norikazu Ohshima, Keizo Kinoshita, Hirotaka Toyoda Radio Frequency (RF) magnetron sputtering is an important tool for thin film sputter deposition such as insulated materials. For example, an insulated oxide thin film used in magnetoresistive random access memory (MRAM) is important to control magnetoresistance. During the sputter deposition process, however, energetic particles induce damage to the deposited film, resulting in the device degradation. Recently, we have reported spatially-resolved measurement of the O$^{-}$ energy distribution in an RF magnetron plasma using a quadrupole mass analyzer equipped with a electrostatic energy analyzer, where O$^{-}$ ions up to a few hundred eV were observed with spatial variation of its energy distribution function. Furthermore, O$^{-}$ energy distributions with a strong energy-dependent structure with periodic peaks as a function of the O$^{-}$ kinetic energy have been observed. In this paper, origin of the periodic peaks in O$^{-}$ energy distribution is discussed, based on the energy modulation of O$^{-}$ ions passing through the sheath in front of the grounded wall. Furthermore, energy distribution of high energy O atoms produced from high energy O$^{-}$ ions will be also discussed from a Monte Carlo simulation. [Preview Abstract] |
Wednesday, October 6, 2010 4:15PM - 4:30PM |
LW1.00002: A constricted plasma source for negative ions M.A. Mujawar, S.K. Karkari, M.M. Turner A constricted plasma source is described which is characterized by a dense plasma close to the anode while the plasma expands outwards in a low pressure region (0.6 Pa) because of differential pressure between the cylindrical hollow cathode through which the gas is injected. Detail characterization of plasma parameters namely electron density (n$_{e})$, positive ion density (n$_{+})$ and plasma potential (V$_{p})$ by hairpin, ion flux and floating emissive probes, respectively, reveals the presence of negative ions adjacent to the anode fall region of the expanding plasma when a mixture of Ar/O$_{2}$ was used as compared with the pure electropositive Ar gas. A linear increase of negative ion density (10$^{16}$ m$^{-3})$ with modest operating powers (400 W) as achieved at low working pressure makes this source highly promising for cesium free negative ion sources. [Preview Abstract] |
Wednesday, October 6, 2010 4:30PM - 4:45PM |
LW1.00003: Dynamical transitions and ion acoustic waves in presence of electronegative double layers Nicolas Plihon, Pascal Chabert This paper presents a detailed experimental study of the transition from continuous plasma diffusion to static double-layer and eventually pseudo-periodically propagating double layers when increasing the negative ion fraction in a low pressure, radio frequency driven plasma (in Ar - SF$_6$ mixtures). The transitions between these three states involve the propagation of unstable ion acoustic waves (of the slow branche type). These waves are driven unstable due to the counter-streaming of positive and negative ion. We will show the dynamical richness of the dynamics of these transitions, with turbulence-like features of the ion acoustic activity and long time fluctuations of the ion acoustic wave properties (such as wavelength, amplitude...) We will develop here the link between ion acoustic waves and double layer formation (and propagation) in electronegative gases and compare our experimental work with previous theoretical predictions and recent numerical simulations. [Preview Abstract] |
Wednesday, October 6, 2010 4:45PM - 5:00PM |
LW1.00004: Strong modification of the electron energy distribution function in inductive discharge in SF$_{6}$/Ar Plasmas due to additional capacitive bias with small power input Hyo-Chang Lee, Chin-Wook Chung, Igor D. Kaganovich We have performed experimental study of the electron energy distribution function (EEDF) in inductive discharge in SF$_{6}$/Ar plasmas with additional capacitive bias. The power transferred to the inductive coil was fixed to 100 W and an additional power to the capacitive biased was varied from 0 to 15 W. In case of discharge in 10{\%} SF$_{6}$/90{\%}Ar gas mixture, a small additional power provided by a capacitive bias had little effect on EEDF, whereas in 50{\%} SF$_{6}$/50{\%}Ar gas mixture, the EEDF was strongly modified by capacitive bias. Possible explanation is due to strong reduction of ambipolar potential in the plasma in strongly electronegative gases. In low gas pressure electro-positive plasmas, high energy electrons are heated by large rf field in the sheath, while low energy electrons are confined in the bulk plasma and cannot participate in the sheath heating due to ambipolar potential. In electro-negative plasmas ambipolar potential is small and the sheath heating by capacitive field acts on both low energy electron and high energy electrons. [Preview Abstract] |
Wednesday, October 6, 2010 5:00PM - 5:15PM |
LW1.00005: Extraction of positive and negative ion beams by discrete and modal focusing effects Eugen Stamate Positive or negative ion beams extracted from plasma are used in a large variety of surface functionalization techniques such as implantation, etching, surface activation, passivation or oxidation. Of particular importance is the surface treatment of materials sensitive to direct plasma exposure due to high heath fluxes, the controllability of the ion incidence angle, and charge accumulation when treating insulating materials. Despite of a large variety of plasma sources available for ion beam extraction, there is a clear need for new extraction mechanisms that can make available ion beams with high current densities that can treat surfaces placed adjacent to the extraction region. This work introduces a new phenomenology for ion beam extraction using the discrete and modal focusing effects associated with three-dimensional plasma-sheath-lenses. Three- dimensional simulations are used to explain the plasma sheath lens design and the extraction mechanism. Experiments are performed in a matrix-ECR plasma source with transversal magnetic filter for electron temperature control. The discharge is operated at pressures below 1 mTorr and low plasma densities for a density ratio of negative ions to electrons larger than 300. The focused ion beams of positive or negative ions are used to induce surface modification on conductive and insulating substrates. [Preview Abstract] |
Wednesday, October 6, 2010 5:15PM - 5:30PM |
LW1.00006: Self-consistent model of an inductive negative ion source Gerjan Hagelaar, Nicolas Kohen, Jean-Pierre Boeuf The experimental fusion reactor ITER will be heated by injection of a fast neutral beam generated by acceleration and neutralization of negative ions. The negative ion source used for this purpose, developed by the IPP Garching, consists of a driver where radio-frequency (RF) power is inductively coupled to the plasma electrons and an expansion chamber containing a magnetic filter. This paper presents the principles of a self-consistent two-dimensional model of this source. The different particle species are described by fluid equations including magnetic fields, inertia, and viscosity, with boundary conditions accounting for surface processes. The charged particle equations are coupled with the Maxwell equations for a fully self-consistent description of the (pre)sheath and RF coupling. We present results for simple configurations to illustrate the main mechanisms controlling the plasma properties: neutral gas depletion in the plasma center due mainly to ionization, compression of the plasma in the source driver by the ponderomotive force, plasma transport in the magnetic filter region. We also discuss several fundamental limitations of the model in describing realistic source conditions. [Preview Abstract] |
Wednesday, October 6, 2010 5:30PM - 5:45PM |
LW1.00007: Production of negative ions at graphite (HOPG) surface in H$_{2 }$ and D$_{2}$ plasmas Ahmad Ahmad, Marcel Carrere, Jean-Marc Layet, Pravin Kumar, Gilles Cartry Negative ion formation by dissociative attachment on molecules in low pressure plasmas has been largely studied, whereas, negative ion formation on surfaces has been few investigated. In this work we show that under positive ion bombardment, a huge number of negative ions are produced on a graphite surface placed in low pressure H$_{2}$/D$_{2}$ plasma. Our goal is to identify the negative ion production mechanisms. In this aim, the graphite sample (HOPG) is put in a helicon reactor, in front of a Hidden EQP mass spectrometer. The sample was exposed to single positive ion dominated H$_{2}$/D$_{2}$ plasma (H$_{3}^{+}$/H$_{2}^{+}$, D$_{3}^{+}$/D$_{2}^{+})$ at low pressures (0.2-1 Pa). The sample is biased negatively with respect to plasma and negative ion energy distribution functions are recorded and analysed. Two surface production mechanisms have been identified: sputtering of adsorbed hydrogen atom as negative ion and backscattering of a positive ion as a negative ion. [Preview Abstract] |
Wednesday, October 6, 2010 5:45PM - 6:00PM |
LW1.00008: Self-consistent 3D PIC-MC model for negative ion extraction from a hydrogen plasma source Serhiy Mochalskyy, Agustin Lifschitz, Tiberiu Minea The development of a high performance negative ion (NI) source constitutes a crucial step in the construction of Neutral Beam Injector of the future fusion reactor ITER. The present knowledge of the ion extraction mechanism from the negative ion source is limited and concerns complex of magnetized plasma sheaths. 3D Particles-in-Cell electrostatic collisional code was developed, specifically designed for this system. This code, called ONIX, was used to investigate the plasma properties and the transport of the charged particles close to a extraction aperture. Results of the production, destruction, and transport of H$^{-}$ in the extraction region are presented. Production of H$^{-}$ is investigated via tree atomic processes: (I) electron dissociative attachment to the vibrationally exited molecules H$_{2}$(v), (II) interaction of the positive ions H$^{+}$ and H$_{2}^{+}$ with the aperture wall and (III) collisions of the neutral gas H, H$_{2}$ with aperture wall. Influence of each process on the total extracted NI current is discussed. The formation of the plasma meniscus and the screening of the extraction field by the plasma are presented here, as well as NI trajectories. [Preview Abstract] |
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