Bulletin of the American Physical Society
66th Annual Gaseous Electronics Conference
Volume 58, Number 8
Monday–Friday, September 30–October 4 2013; Princeton, New Jersey
Session NR2: Plasma-surface Interactions |
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Chair: Yevgeny Raitses, Princeton Plasma Physics Laboratory Room: Ballroom II |
Thursday, October 3, 2013 10:00AM - 10:15AM |
NR2.00001: Simulating the Spontaneous Formation of Self-Organized Anode Spot Patterns in Arc Discharges Juan Trelles Self-organized pattern formation is a captivating phenomenon common in numerous biological, chemical and physical systems. The experimental observation of self-organized anode patterns in diverse types of electrical discharges, including atmospheric-pressure arc discharges, has been well reported and characterized in the plasma literature. Nevertheless, the capturing of anode pattern formation in arc discharges by fluid flow models has proven exceedingly elusive. For the first time computational simulations, based on a time-dependent three-dimensional thermodynamic nonequilibrium model, reveal the spontaneous formation of self-organized anode attachment spots patterns in a free-burning arc. The characteristics of the patterns depend on the total arc current and on the resolution of the spatial discretization, whereas the main properties of the plasma, such as maximum temperatures, velocity, and voltage, depend only on the former. The obtained patterns qualitatively agree with experimental observations and confirm that the spots originate at the fringes of the arc - anode attachment. The results imply that heavy-species - electron energy equilibration, in addition to thermal instability, has a dominant role in the formation of anode spots in arc discharges. [Preview Abstract] |
Thursday, October 3, 2013 10:15AM - 10:30AM |
NR2.00002: Effects of Asymmetric Secondary Emission on Plasma Properties of ExB Discharges Hongyue Wang, Michael Campanell, Igor Kaganovich, Alexander Khrabrov, Yevgeny Raitses, Dmytro Sydorenko, Guobiao Cai In low-pressure devices, the electron mean free path exceeds the size of the system; therefore, the secondary electrons penetrate the bulk plasma and exit to the opposite wall without undergoing collisions. Thus, secondary electron emission (SEE) fluxes affect the charged particle flux balance on walls far from their origination source. As a result, the sheathes at opposite walls are not independent of each other. In this paper, the emission and recollection of electrons by walls is studied using a 1-D model with the asymmetric secondary emission from the inner and outer walls of the ExB device. Plasma properties in a typical ExB discharge channel were simulated using particle-in-cell EDIPIC code. The potential profile becomes significantly asymmetric with decrease of the left SEE yield as compared to the right one. A large proportion of beam electrons moving towards left are reflected by the left sheath. Simulations results for the sheath potential near the right wall show that it is almost constant and is independent of emission from the left wall. However, change in the SEE at the left wall strongly affects the sheath potential at this wall. The analytic relation between the wall potentials and the SEE yields is derived. SEE asymmetry leads to increase of ion energy loss to the walls due to increase of the sheath potential near the wall with smaller emission. [Preview Abstract] |
Thursday, October 3, 2013 10:30AM - 10:45AM |
NR2.00003: Molecular dynamics simulation of plasma-induced Si substrate damage: Latent defect structures and bias-frequency effects Koji Eriguchi, Asahiko Matsuda, Yoshinori Takao, Kouichi Ono Plasma-induced physical damage (PPD)---the ion bombardment on Si substrate---has been one of the critical issues for fabricating scaled electronic devices [1], because it degrades the device performance and reliability [2]. The typical damaged structure consists of a surface layer and latent defect sites underneath the surface. To minimize PPD, various techniques that control an ion energy distribution function (IEDF) have been developed [3]. In this study, a classical molecular dynamics (MD) simulations [4] were performed in various gas systems (Ar, Xe, Cl, Br etc.) to clarify the latent defect structure and the effects of IEDF on PPD, where incident ion energies were defined to obey a given IEDF---substrate bias frequency. We revealed that both the density of defect site and the damaged-layer thickness were weak functions of IEDF, which are consistent with a binary-collision-based range model and experimental results [5]. \\[4pt] [1] K. Eriguchi and K. Ono, J. Phys. D 41, 024002 (2008).\\[0pt] [2] K. Eriguchi et al., J. Vac. Sci. Technol. A29, 041303 (2011).\\[0pt] [3] A. Kojima et al., Jpn. J. Appl. Phys. 44, 6241 (2005).\\[0pt] [4] H. Ohta and S. Hamaguchi, J. Vac. Sci. Technol. A19, 2373 (2001).\\[0pt] [5] K. Eriguchi et al., Jpn. J. Appl. Phys. 49, 056203 (2010). [Preview Abstract] |
Thursday, October 3, 2013 10:45AM - 11:00AM |
NR2.00004: Secondary electron emission yield dependence on the Fermi level in Silicon David Urrabazo, Matthew Goeckner, Lawrence Overzet Secondary Electron Emission (SEE) by ion bombardment plays a key role in determining the properties of many plasmas. As a result, significant efforts have been expended to control the SEE coefficient (increasing or decreasing it) by tailoring the electron work function of surfaces. A few recent publications point to the possibility of controlling the SEE coefficient of semiconductor surfaces in real time through controlling the numbers of electrons in the conduction band near the surface. Large control over the plasma was achieved by injecting electrons into the semiconductor just under the cathode surface via a subsurface PN junction. The hypothesis was that SEE is dependent on the numbers of electrons in the conduction band near the surface (which is related to the position of the Fermi level near the surface). We are testing the validity of this hypothesis. We have begun fundamental ion beam studies to explore this possible dependence of SEE on the Fermi energy level using Si. Various doping levels and dopants are being evaluated and the results of these tests will be presented. [Preview Abstract] |
Thursday, October 3, 2013 11:00AM - 11:15AM |
NR2.00005: Experimental Evidence of Change in Sheath Properties due to Secondary Electron Emission in a Crossed Field Plasma Setup Kapil Sawlani, John Foster The nature of plasma transport across the magnetic field in crossed-field (CF) devices remains largely an unsolved problem. This can be further complicated by the presence of secondary electrons derived from electron impact on walls. The coupling of these electrons to the bulk plasma and their role in CF plasma transport is also not well understood. The emission of secondary electrons from wall surfaces also affects the sheath potential, thus impacting energy transport to the wall. In this work, a benchtop apparatus is used to elucidate the role that secondary electrons play in regards to CF transport and energy flow to the walls. An electron beam is used to generate a secondary electron plume at the surface of an insulating target. The CF device plasma response to these secondary electrons is assessed by measuring changes to the potential distribution in the sheath of the irradiated target and the measured electron energy distribution function. The variation in the discharge voltage at fixed emission current is also determined which yields insight into CF impedance. The effect of the variation of the electron beam's angle of incidence on the CF current is also characterized. An attempt is made to relate phenomena and trends observed in this work with those in Hall thrusters. [Preview Abstract] |
Thursday, October 3, 2013 11:15AM - 11:30AM |
NR2.00006: Combined plasma and molecular dynamics simulations for a better prediction of plasma surface interactions: Cryogenic etching of silicon with fluorine-containing gases Stefan Tinck, Erik Neyts, Annemie Bogaerts A hybrid Monte Carlo-fluid plasma model as well as molecular dynamics (MD) simulations are applied together to obtain detailed information on surface reaction mechanisms during plasma processing. With this modeling setup, results on the surface behavior of fluorine plasma species etching Si wafers at room and cryogenic temperatures will be discussed. When numerically investigating low pressure plasmas used for microelectronics applications, one should always consider wall effects if possible. Especially in low pressure plasmas, where collisions with the reactor walls and wafer are quite probable compared to gas phase collisions, knowing at which rate the plasma species are lost or produced at these surfaces is of utmost importance. Unfortunately, the probabilities of wall reactions such as sticking, reflection, incorporation, etching or sputtering are often not well known. With MD, these surface reaction probabilities can be calculated and applied as input in the plasma simulation. In this modeling setup, surface probabilities as a function of surface temperature, chemical composition and reactor operating conditions are obtained and considered for the overall plasma simulation for a better description of the investigated plasma process. [Preview Abstract] |
Thursday, October 3, 2013 11:30AM - 11:45AM |
NR2.00007: Reversible plasma-based functionalization of advanced carbon materials Eva Kovacevic, Johannes Berndt, Thomas Strunskus, Nicolas Camara, Christophe Cachoncinlle, Mireille Gaillard, Chantal Boulmer-Leborgne Advanced carbon materials, such as graphene, carbon nanotubes or nanoparticles possess unique chemical and physical properties that make them interesting for wide area of applications, ranging from their use in electronics, as fillers for novel composite materials or as base for the development of new chemical sensors and catalysts. The key challenge to be overcome for actual applications is the simple and stable tuning of the surface properties of these materials. This contribution deals with the capacitively coupled discharges that are a versatile tool for the synthesis of such materials and at the same time also suitable for their surface modifications. We focus here on our results concerning the production and controlled and reversible covalent functionalization of advanced carbon materials. The quality of the deposits and the effect of the plasma treatments are analyzed by means of transmission electron microscopy, near edge X-ray absorption fine structure spectroscopy (NEXAFS), high resolution X-ray Photoelectron Spectroscopy (XPS), and contact angle measurements. Special attention is paid to the reversibility of the plasma induced functionalization by use of plasma based EUV photon irradiation. [Preview Abstract] |
Thursday, October 3, 2013 11:45AM - 12:00PM |
NR2.00008: Optimization of plasma ionization sources for ambient mass spectrometry surface analysis Kirsty McKay, Jun-Seok Oh, Andrew Bowfield, Tara Salter, James Walsh, Ian Gilmore, James Bradley The use of low-temperature atmospheric pressure plasma sources in ambient surface analysis mass spectrometry has received growing interest in recent years. Due to their unique chemical and electrical properties plasmas provide a gentle and efficient means of ionizing surface compounds in their natural environment, with little to no sample preparation required. In this study we investigate how these plasma ionization sources might be optimized for ambient surface analysis techniques. An ambient molecular beam mass spectrometer from Hiden Analytical Ltd. (HPR-60) is used to monitor the charged ion species emanating from two different plasma sources, a pulse modulated RF (13.56MHz) plasma needle and a continuous wave kHz plasma jet, under different operating parameters. Both time-averaged and time-resolved ion intensity measurements reveal the species present in the discharges and the underlying production and loss mechanisms for different operating conditions. To assess the effectiveness of each of these plasmas sources as tools for surface ionization/desorption, a number of different pharmaceutical and polymer surfaces were analyzed in both positive and negative ion mode using a hybrid linear trap quadrupole (LTQ) orbitrap mass spectrometer, due to its increased mass sensitivity. [Preview Abstract] |
Thursday, October 3, 2013 12:00PM - 12:15PM |
NR2.00009: Plasma-Surface Interactions and Feature Profile Simulations Paul Moroz, Daniel Moroz Plasma-surface interactions are rather complex in most cases. One has to take into account not only sticking of gaseous species from plasma to the surface of solid materials or a set of chemical reactions on the surface producing solid and gaseous products, but also interactions of atoms within deeper layers of the material. Etching, deposition, and implantation processes usually go on at the same time. Energetic particles, such as ions or fast neutrals, could penetrate and etch materials even in conditions when significant polymer layers are present. Here, we present a 2D and 3D feature profile simulator FPS3D which is based on the cellular model and takes into account finite penetration depths of energetic particles. It can also do simulations for very delicate conditions, such as ALD, when materials are deposited only by a single atomic layer at a time. Using cells each containing a single molecule could introduce significant errors into calculations as sizes of molecules could differ significantly, and thus we are using a different approach trying to mimic MD simulations with various approximations and on a larger scale. The code is applicable to nanometer through micrometer range of features, at least, and it is fast both for 2D and 3D simulations. [Preview Abstract] |
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