Bulletin of the American Physical Society
65th Annual Gaseous Electronics Conference
Volume 57, Number 8
Monday–Friday, October 22–26, 2012; Austin, Texas
Session DT2: Low Pressure Plasma Sources |
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Chair: Prashanth Kothnur, Applied Materials, Inc. Room: Classroom 203 |
Tuesday, October 23, 2012 10:00AM - 10:15AM |
DT2.00001: Two-Dimensional Electron and Metastable Density Profiles Produced in Helium Fast Ionization Wave Discharges Brandon Weatherford, Edward Barnat, Zhongmin Xiong, Mark Kushner Fast ionization wave (FIW) discharges are those in which nanosecond-duration pulses at high overvoltage are used to initiate large volume breakdown at elevated pressures. This presentation summarizes recent studies of spatial distributions of electron and metastable production in a helium FIW discharge. Two-dimensional laser collision-induced fluorescence (2D-LCIF) is used to generate spatially and temporally resolved maps of electron and metastable densities produced by a FIW with positive polarity pulses of $>$10 kV, with 20 ns duration and $\sim $3 ns rise time. The results show that radial profiles depend strongly on operating pressure (1-20 Torr) and pulse repetition rate (0.2-2 kHz); these trends are discussed and correlated with measured FIW propagation velocities and estimates of the effective reduced electric field (E/N) in the FIW wavefront. Differences between the electron and metastable profiles are related to the uniformity of energy deposition in FIWs. Results from a two-dimensional computational model are presented, which capture similar trends as those seen in experiment. A comparison between experimental and modeling results is discussed to provide additional insights into the physical processes behind FIW propagation. [Preview Abstract] |
Tuesday, October 23, 2012 10:15AM - 10:30AM |
DT2.00002: A Plasma Based OES-CRDS Dual-mode Portable Spectrometer for Trace Element Detection: Emission and Ringdown Measurements of Mercury Peeyush Sahay, Susan Scherrer, Chuji Wang Design and development of a plasma based optical emission spectroscopy-cavity ringdown spectroscopy (OES-CRDS) dual-mode portable spectrometer for \textit{in situ} monitoring of trace elements is described. A microwave plasma torch (MPT) has been utilized, which serves both as an atomization and excitation source for the two modes, viz. OES and CRDS, of the spectrometer. Operation of both modes of the instrument is demonstrated with initial measurements of elemental mercury (Hg). A detection limit of 44 ng mL$^{-1}$ for Hg at 253.65 nm was determined with the emission mode of the instrument. Severe radiation trapping of 253.65 nm line hampers the measurement of Hg in higher concentration region ($>$ 50 $\mu $g ml$^{-1})$. Therefore, a different wavelength, 365.01 nm, is suggested to measure Hg in that region. Ringdown measurements of the metastable 6s6p $^{3}$P$_{0}$ state of Hg in the plasma using a 404.65 nm palm size diode laser was conducted to demonstrate the CRDS mode of the instrument. Along with being portable, dual-mode, and self-calibrated, the instrument is capable of measuring a wide range of concentration ranging from sub ng mL$^{-1}$ to several $\mu $g ml$^{-1}$ for a number of elements. [Preview Abstract] |
Tuesday, October 23, 2012 10:30AM - 10:45AM |
DT2.00003: Relaxation of High Power Microwave Surface Plasma Sterling Beeson, Andreas Neuber The electron loss mechanisms related to the relaxation of pulsed rf-generated plasma are investigated. A 3 MW, 3 $\mu$s width, 50 ns risetime high power microwave pulse is transmitted through a dielectric window that terminates a WR-284 (S-band) waveguide filled with insulating gas where the investigated plasma is formed across this window on the atmospheric side. This produces electron densities on the order of $10^{14}$ cm$^{-3}$ for pressures of 10 to 400 torr in air, N$_{2}$ and argon environments. This plasma attenuates the pulse on the order of -40 to -10 dB during peak electric field amplitudes. Using a multi-standard waveguide coupler to inject a low power probing signal, the post-pulse attenuation values are measured and used to quantify the temporal evolution of the electron density. This technique is confirmed by means of verifying the attachment rates in an air environment and 2-body recombination rate in a N$_{2}$ environment. The major recombination processes for high pressure argon plasma are identified, e.g. 3-body recombination becomes dominant within the first few microseconds after pulse termination. The measured rates for recombination are compared with sparsely available data and models from literature in the regime of interest. [Preview Abstract] |
Tuesday, October 23, 2012 10:45AM - 11:00AM |
DT2.00004: Fundamental TE$_{11}$ Mode and Plasma Interaction in a Cylindrical Waveguide Sanjay K. Tomar, Hitendra K. Malik Microwave and plasma interaction has got applications in charged particle acceleration, travelling wave tube amplifiers, gyrotrons, etc. During the propagation of the microwave in a waveguide, it is seen that its wavelength gets larger if the plasma is filled in the waveguide, and also the field of the microwave gets altered. In addition, the plasma density distribution is modified. In the present work, we simulate the problem of this type of interaction by considering the fundamental TE$_{11}$ mode and the plasma filled cylindrical waveguide. We assume that the fundamental mode encounters the plasma in another cylindrical waveguide of the same size. We derive a wave equation using Maxwell's equations for the microwave field along with the contribution of plasma and solve this by using fourth-order Runge-Kutta method. Then the perturbed density is studied in greater detail for the different profiles of the plasma density. The effect of electron temperature, waveguide radius, microwave field and its frequency are studied on the perturbed density that takes the form of bunches. [Preview Abstract] |
Tuesday, October 23, 2012 11:00AM - 11:15AM |
DT2.00005: A first step toward the modeling of instabilities in high power pulse magnetron sputtering plasmas Sara Gallian, Denis Eremin, Torben Hemke, Thomas Mussenbrock, Ralf Peter Brinkmann, William N.G. Hitchon High Power Pulsed Magnetron Sputtering (HPPMS) is a novel Ionized Physical Vapor Deposition (IPVD) technique, able to achieve an ultra dense plasma with a high ionization degree among the sputtered atoms. This is accomplished by applying a large bias voltage to the target in short pulses with low duty cycle. Several authors have recently reported the presence of rotating structures during a HPPMS discharge. According to the experimental observations, these emissions peaks rotate with constant angular velocity $\Omega$, when the discharge parameters are held constant. Here, we attempt to describe these structures with a collection of simplified models with increasing levels of detail. We start by solving analytically a system of 1D Advection-Diffusion-Reaction equations for the electron $n_{\rm{e}}(\theta,t)$ and neutral $n_{\rm{n}}(\theta,t)$ densities. Then, we focus on the secondary electron behavior and follow the evolution of their energy. In the light of previous results, we develop a time dependent global model for the ionization region. We solve self-consistently the rate equations for background gas and metal species. The secondary electrons are responsible for the main inelastic collision processes and are therefore treated in detail, kinetically. [Preview Abstract] |
Tuesday, October 23, 2012 11:15AM - 11:30AM |
DT2.00006: MAGPIE: A new linear plasma device for studying fusion relevant plasma-surface interactions Cormac Corr, Cameron Samuell, Boyd Blackwell, John Howard, Juan Caneses, Romana Lester Plasma-surface interactions are crucial to determining the success of ITER and the ultimate viability of generating fusion power under steady state conditions. The first walls of magnetic fusion reactors must sustain large particle and heat fluxes and present a major challenge to achieving fusion power. To answer fundamental questions about the science of plasma-surface interactions at the complex fusion boundary a new purpose-built linear plasma device, the prototype MAGnetized Plasma Interaction Experiment (MAGPIE), has been constructed at The Australian National University (ANU) to develop novel diagnostics and test materials under aggressive plasma conditions. In this work we employ optical emission spectroscopy, electrostatic probes and fast imaging to characterize the plasma environment and its interaction with various materials. It will be shown that a well-collimated plasma is created in the downstream region with a diameter of about 2 cm. High-energy electrons are observed along the axis of the discharge and the power deposition region is transferred to where the magnetic field maximum occurs in the downstream region. These findings indicate that efficient non-collisional heating occurs downstream of the plasma source. [Preview Abstract] |
Tuesday, October 23, 2012 11:30AM - 11:45AM |
DT2.00007: Two-Dimensional Particle-in-Cell Simulation of Cylindrical Magnetron Sputters for the Improvement of Target Utilization Min Young Hur, Hyowon Bae, In Cheol Song, Ho-Jun Lee, Hae June Lee Magnetron sputtering has been commonly used for the deposition of a wide range of industrial thin film coating. This method has almost no restrictions in the target materials and the magnetic field enables lower pressures operation. Conventional flat type sputters generate ion-bombardment sputtering in only a localized region of target where electric fields and magnetic fields are perpendicular to each other. Therefore, the utilization efficiency of the target material is about 20$\sim$30\%. To overcome this drawback, a rotating cylindrical target is devised to make uniform sputtering on the target. In this paper, the difference of the physical effects of ions on the targets between the flat-type and the cylindrical-type sputters is investigated using a two-dimensional particle-in-cell (PIC) simulation with Monte Carlo collisions. Especially for the calculation of cylindrical field solver with a finite difference method, an image charge method is introduced instead of solving the Poisson equation directly. Simulation Diagnostics include the plasma density, the distributions of energy and angle of incident ions on the target, and the deposition profiles on the substrate calculated by a ray-trace particle deposition model. The analysis for the rotating speed and the magnet structure is [Preview Abstract] |
Tuesday, October 23, 2012 11:45AM - 12:00PM |
DT2.00008: Simulations of magnetically enhanced capacitively coupled plasma discharges using CFD-ACE+ Ananth Bhoj, Mustafa Megahed, Vladimir Kudriavtsev Many plasma processing reactors employ strong magnetic fields to confine or otherwise manipulate the discharge to optimize wafer surface processing [1]. The multi-physics modeling platform CFD-ACE+ was extended to account for the presence of strong magnetic fields on plasma transport in the chamber. The transport coefficients for electrons assume tensor forms whose components are dependent on those of the applied magnetic field. The capacitively coupled plasma (CCP) model either accepts an externally computed magnetic field supplied via user subroutines or uses the solution computed within the magnetic module that addresses the magnetic vector potential equation. In this work, latter approach has been applied to model an Ar discharge in axisymmetric magnetically enhanced CCP reactor configuration. Parametric results over a range of pressures demonstrated the effect of the magnetic field on changing discharge uniformity and plasma density.\\[4pt] [1] http://meetings.aps.org/Meeting/GEC09/Event/107279 [Preview Abstract] |
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