Global modeling of HiPIMS systems: transition from homogeneous to self organized discharges

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RUHR-UNIVERSITÄT BOCHUM Global modeling of HiPIMS systems: transition from homogeneous to self organized discharges S. Gallian 1, J. Trieschmann 1, T. Mussenbrock 1, W. N. G. Hitchon 2 and R.

1 RUHR-UNIVERSITÄT BOCHUM Global modeling of HiPIMS systems: transition from homogeneous to self organized discharges S. Gallian 1, J. Trieschmann 1, T. Mussenbrock 1, W. N. G. Hitchon 2 and R. P. Brinkmann 1 1 Lehrstuhl für Theoretische Elektrotechnik, Ruhr-Universität Bochum 2 Department of Electrical and Computer Engineering, University of Wisconsin-Madison gallian@tet.rub.de

2 High Power Pulse Magnetron Sputtering substrate IEDF Vsh non-magnetized plasma bulk high energy ions surface interaction target magnetized plasma bulk ne 1019 m 3, γion 1 non-equilibrium Ionized Physical Vapor Deposition technique High degree of ionization of sputtered vapor allows film growth control and high film quality High power pulse of low frequency and low duty cycle to cathode V. Kouznetsov et al., Surface and Coatings Technology, 122 (2-3): 290-3, / 14

3 Characteristics of HiPIMS plasmas: Film quality vs. efficiency PRO: Highly energetic metal ions ( 10 ev) CONTRA: Reduced deposition rate (µm/h) HiPIMS plasmas are non-stationary and show self-organization in symmetry breaking structures Plasma composition evolves during discharge A Hecimovic, at al., PSST, 21 (2012) / 14

emission III IV II Cu Discharge Current (A) 40 20 0 100 200 Time (µs) Ar Ar2 Metal M e- M

4 Plasma regimes: different self-organization and chemistry (Exposure time 100 ns) Regime II: emission chaotic Regime III: stable rotating frequency: spokes Regime IV: homogeneous emission III IV II Cu Discharge Current (A) Time (µs) Ar Ar2 Metal M e- M Metal M M2 M e- Metal de los Arcos, J Phys D 46, (2013) Winter, J Phys D 46, (2013) 4 / 14

5 Working Hypothesis on Spokes Formation and Evolution HiPIMS discharges sustained by secondary electrons (metal target at -500 V) Only Ar and M2 produce secondary electrons, M cannot (density M M2) Intermediate/high currents high sputtering high metal density self sputtering sputtering Ar Ar2 Metal M e- self sputtering M M Metal M2 Metal M e- quenching e- ℇion M M Metal High M and M density discharge quenches Discharge re-organizes into "spokes", which rotate toward regions of low M and high Ar density High ionization regions (spokes) not necessary once population of M2 sufficiently high. 5 / 14

6 Homogeneous Volume-Averaged Models Rate equations for heavy species: nar, nar, nar 4s, nar 4s0 nal, nal, nal2 Integrated collision cross sections σj (m2) Maxwellian Equilibrium Global Model (MEGM): Kinetic Global Model (KGM): Electron continuity and energy conservation equations Boltzmann s equation for an isotropic eedf f (ε, t) Low current Low current Intermediate current High current 6 / 14

7 Convergence Procedure Raw experimental data Iteration until calculated matches imposed current Voltage (V) I calculated MEGM: P ηpwr IDVb evir KGM: S(ε, t) = ηpwrγsec IAr (t) G(ε) evir F. Guimaraes, et al., J of Vacuum Science and Technology A, 9(1): , / 14

8 Convergence Procedure: eventual feedback Variable resistance modeled via time varying power coupling efficiency Voltage (V) Raw experimental data Iteration until calculated matches imposed current Vb Rc Vb Vt(t) plasma R(t) On the fly feedback ηpwr for better convergence 8 / 14

9 Low current case (2 102 ma/cm2) ial iar dashed: MEGM solid: KGM Already at low current, the MEGM is inappropriate 9 / 14

10 Intermediate current case (1 103 ma/cm2) doubly charged ions non relevant need feedback on coupling efficiency ne Te ial iar ne I feedback nar nal I no feedback close to self sputtering nal2 10 / 14

11 High current case (4 103 ma/cm2) Al cannot produce secondary electrons Al2 still negligible onset of self sputtering 11 / 14

12 Compare all current cases For all cases: ion species drift to target as soon as created SRT SRT kal,ionnenal = Γ, k n n = Γ Ar,ion e Ar Al Ar VIR VIR Differences come into play in Al rate eqn ( 0 low to intermediate ID dnal ΓAl,diff ΓAl,diff SRT kal,ionnenal Γ Y Γ Y k n n Ar,ion e Ar Al ssp Al sp dt L VIR L > 0 high ID need to enhance Al diffusion and Ar ionization! x 5 Al diff x 10 Ar diff 12 / 14

Conclusions if enough Ar is ionized the discharge can be maintained even in self sputtering moving ionization regions self sputtering region 50 A High M and M density discharge quenches X

13 Conclusions if enough Ar is ionized the discharge can be maintained even in self sputtering moving ionization regions self sputtering region 50 A High M and M density discharge quenches X Discharge re-organizes into "spokes", which rotate toward regions of low M and high Ar density X High ionization regions (spokes) not necessary once population of M2 sufficiently high WIP 13 / 14

14 Thank you for the attention The authors acknowledge funding by the Deutsche Forschungsgemeinschaft within the frame of SFB-TR / 14

KINETIC DESCRIPTION OF MAGNETIZED TECHNOLOGICAL PLASMAS

KINETIC DESCRIPTION OF MAGNETIZED TECHNOLOGICAL PLASMAS Ralf Peter Brinkmann, Dennis Krüger Fakultät für Elektrotechnik und Informationstechnik Lehrstuhl für Theoretische Elektrotechnik Magnetized low