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 QR3: Magnetically Enhanced Plasmas |
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Chair: Ben Longmier, University of Michigan Room: Nassau Room |
Thursday, October 3, 2013 3:30PM - 4:00PM |
QR3.00001: Plasma regimes in high power pulsed magnetron sputtering Invited Speaker: Teresa de los Arcos High Power Pulsed Magnetron Sputtering (HPPMS) is a relatively recent variation of magnetron sputtering where high power is applied to the magnetron in short pulses. The result is the formation of dense transient plasmas with a high fraction of ionized species, ideally leading to better control of film growth through substrate bias. However, the broad range of experimental conditions accessible in pulsed discharges results in bewildering variations in current and voltage pulse shapes, pulse power densities, etc, which represent different discharge behaviors, making it difficult to identify relevant deposition conditions. The complexity of the plasma dynamics is evident. Within each pulse, plasma characteristics such as plasma composition, density, gas rarefaction, spatial distribution, degree of self-sputtering, etc. vary with time. A recent development has been the discovery that the plasma emission can self-organize into well-defined regions of high and low plasma emissivity above the racetrack (spokes), which rotate in the direction given by the E$\times$B drift and that significantly influence the transport mechanisms in HPPMS. One seemingly universal characteristic of HPPMS plasmas is the existence of well defined plasma regimes for different power ranges. These regimes are clearly differentiated in terms of plasma conductivity, plasma composition and spatial plasma self-organization. We will discuss the global characteristics of these regimes in terms of current-voltage characteristics, energy-resolved QMS and OES analysis, and fast imaging. In particular we will discuss how the reorganization of the plasma emission into spokes is associated only to specific regimes of high plasma conductivity. We will also briefly discuss the role of the target in shaping the characteristics of the HPPMS plasma, since sputtering is a surface-driven process. [Preview Abstract] |
Thursday, October 3, 2013 4:00PM - 4:15PM |
QR3.00002: Sensitivity analysis via kinetic global modeling of rotating spokes in HiPIMS Sara Gallian, Jan Trieschmann, Thomas Mussenbrock, William N.G. Hitchon, Ralf Peter Brinkmann High Power Impulse Magnetron Sputtering discharges are characterized by high density plasma (peak electron density 10$^{18}$ - 10$^{20}$ m$^{-3}$) in a strong magnetic field (100 mT), with highly energetic secondary electrons (500 - 1000 eV). The combination of these factors results in a discharge showing a vast range of instabilities, in particular, a single rotating high emissivity region is often observed. This highly ionized region -or spoke- shows a stationary behavior in the current plateau region and rotates with $\Omega \approx$ kHz.\footnote{A. Hecimovic et al. (2013), submitted} We apply a global model that evolves the electron energy distribution function self-consistently with the rate equations for Ar and Al species. The volume average is performed \emph{only} in the structure region and a net neutral flux term is imposed to model the spoke rotation. Outside the spoke region, the neutral densities are evolved according to a phenomenological fluid model.\footnote{S. Gallian et al. (2013), submitted} The model is solved using a relaxation method. We present a sensitivity analysis of the resulting steady state on the different physical mechanisms and comment on the anomalous electron transport observed. [Preview Abstract] |
Thursday, October 3, 2013 4:15PM - 4:30PM |
QR3.00003: Kinetic simulation of neutral particle transport in sputtering processes Jan Trieschmann, Sara Gallian, Ralf Peter Brinkmann, Thomas Mussenbrock, Stefan Ries, Nikita Bibinov, Peter Awakowicz For many physical vapor deposition applications using sputtering processes, knowledge about the detailed spatial and temporal evolution of the involved gas species is of great importance. Modeling of the involved gas dynamic and plasma processes is however challenging, because the operating pressure is typically below 1~Pa. In consequence, only kinetic descriptions are appropriate. In order to approach this problem, the dynamics of sputtered particle transport through a neutral gas background is simulated. For this study, a modified version of the three-dimensional Direct Simulation Monte Carlo (DSMC) code \textit{dsmcFoam} [1] is utilized. The impact of a transient sputtering wind is investigated in a generic reactor geometry, which may be used for dc Magnetron Sputtering (dcMS), High Power Impulse Magnetron Sputtering (HiPIMS), as well as sputtering in capacitively coupled discharges. In the present work a rarefaction of the background gas is observed. Moreover in pulsed mode the temporal dynamics of the rarefaction and subsequent recovery of the background gas is investigated.\\[1ex] [1] T.J. Scanlon \textit{et al.}, Computers and Fluids \textbf{39}, 2078--2089 (2010). [Preview Abstract] |
Thursday, October 3, 2013 4:30PM - 4:45PM |
QR3.00004: Effect of anomalous electron cross-field transport on electron energy distribution function in a DC-RF magnetized plasma discharge Yevgeny Raitses, Vincent Donnelly, Igor Kaganovich, Valery Godyak The application of the magnetic field in a low pressure plasma can cause a spatial separation of cold and hot electron groups. This so-called magnetic filter effect is not well understood and is the subject of our studies. In this work, we investigate electron energy distribution function in a DC-RF plasma discharge with crossed electric and magnetic field operating at sub-mtorr pressure range of xenon gas [1]. Experimental studies showed that the increase of the magnetic field leads to a more uniform profile of the electron temperature across the magnetic field. This surprising result indicates the importance of anomalous electron transport that causes mixing of hot and cold electrons. High-speed imaging and probe measurements revealed a coherent structure rotating in E cross B direction with frequency of a few kHz. Similar to spoke oscillations reported for Hall thrusters [2], this rotating structure conducts the largest fraction of the cross-field current. [1] Y. Raitses, J. K. Hendryx, and N. J. Fisch, IEPC-2009-024, in the Proceedings of the 31st International Electric Propulsion Conference, September, 2009, Ann Arbor, MI; [2] C. L. Ellison, Y. Raitses and N. J. Fisch, Phys. Plasmas 19, 013503 (2012). [Preview Abstract] |
Thursday, October 3, 2013 4:45PM - 5:00PM |
QR3.00005: Proof of principle experiments for helicon discharges in hydrogen Stefan Briefi, Ursel Fantz In order to reduce the amount of power required for generating CW hydrogen discharges with high electron densities and a high degree of dissociation via RF coupling, the helicon concept is investigated. For this purpose a small laboratory experiment (length of the discharge vessel 40 cm, diameter 10 cm) has been built up. The RF generator has a maximum power of 600 W (frequency 13.56 MHz) and a Nagoya type III antenna is applied. As water cooling was avoided in constructing the experiment for simplicity, the induction coils can only generate a rather low magnetic field up to 14 mT. The performed investigations cover a variation of the RF power and the magnetic field in a pressure range between 0.3 and 10 Pa. Around a magnetic field of 3 mT the low field peak which is typical for helicon discharges could be observed. As the high density mode of helicon discharges has not yet been reached, a different RF generator (2 MHz, 2 KW) and water cooled induction coils will be applied in a next step in order to increase the available power and the magnetic field. [Preview Abstract] |
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