Parametric study of low frequency rotating structure in high power impulse magnetron sputtering discharges

Sara Gallian, Ralf Peter Brinkmann, William Hitchon

40th IEEE In­ter­na­tio­nal Con­fe­rence on Plas­ma Sci­ence (ICOPS) & Pul­sed Power and Plas­ma Sci­ence (PPPS) 2013, San Fran­cis­co (Ca­li­for­nia), USA, 17-21 June (oral cont­ri­bu­ti­on)


Abstract

HiPIMS discharges are able to produce a high density plasma (peak electron density $10^{18}$ - $10^{20}$ m$^{-3}$) by applying large voltages to a target. Electrons are effectively magnetized by a strong magnetic field ($100$ mT), and exhibit an textbf{E} $times$ textbf{B} drift in the azimuthal direction in the plane of the target. \ Magnetically confined highly ionized plasmas are known to show a vast range of instabilities ranging from MHz (i.e. modified two stream instabilityfootnote{D. Lundin, U. Helmersson, S. Kirkpatrick, S. Rohde, and N. Brenning, emph{Plasma Sources Science and Technology} 17, 025007 (2008).}) to $10$ - $100$ kHz range.footnote{A. Kozyrev, N. Sochugov, K. Oskomov, A. Zakharov, and A. Odivanova, emph{Plasma Physics Reports} 37, 621 (2011).}$^,$ footnote{A. Anders, P. Ni, and A. Rauch. emph{J. of Applied Physics}, 111, 5 (2012).}$^,$ footnote{A. P. Ehiasarian, A. Hecimovic, T. de los Arcos, R. New, V. S. von der Gathen, M. B"oke, and J. Winter. emph{Applied Physics Letters}, 100, 11 (2012).} \ We focus here on the low frequency structure rotating in the same direction, at about $10 % $ of the speed of the textbf{E} $times$ textbf{B} electron drift. Understanding of the formation and behavior of these spoke like structures is fundamental in determining the overall plasma density, discharge current and cross field transport. In an Argon/Aluminum discharge it has been observed that only a single structure rotating with constant angular speed remains when the power density reaches 4 kW/cm$^2$. footnote{A. Hecimovic et al., emph{3rd HiPIMS Conference}, Sheffield UK (2012)} We theorize that this configuration is one of "periodic equilibrium", and we apply a kinetic global model approach to the structure region and evolve the system through a pseudo-transit.footnote{S. Gallian et al., emph{65 th Gaseous Electronics Conference,} Austin TX (2012)}. The species densities $n_text{e}(t), n_text{Ar}(t)$ and $n_text{Al}(t)$ reach a steady state after only a few periods $T = 1/Omega$. We present here an improved chemistry model, and an extensive sensitivity analysis of the resulting steady state on the initial conditions of the simulation.

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