Bulletin of the American Physical Society
69th Annual Gaseous Electronics Conference
Volume 61, Number 9
Monday–Friday, October 10–14, 2016; Bochum, Germany
Session GT4: Magnetrons I |
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Chair: Tomas Kozak, University of Bohemia Room: 3 |
Tuesday, October 11, 2016 4:00PM - 4:15PM |
GT4.00001: First measurements of the temporal evolution of the plasma density in HiPIMS discharges using THz time domain spectroscopy Steffen M. Meier, Ante Hecimovic, Tsanko V. Tsankov, Dirk Luggen\-h\"olscher, Uwe Czarnetzki High Power Impulse Magnetron Sputtering (HiPIMS), commonly used for coating and deposition applications, are characterized by high power and plasma densities, short pulse lengths and a complex confining magnetic field. This poses great challenges for the diagnostics, both in terms of temporal resolution and in being non-perturbative. Therefore, up to now the plasma density in the confinement region of the magnetron during HiPIMS discharges was known only approximately from numerical simulations or estimations from optical measurements. Our recent development of the dual-frequency multichannel boxcar THz time domain spectroscopy now offers the possibility for a direct measurement of the plasma density in the confinement region of the magnetron. It allows the determination of line-integrated plasma densities above $1 \cdot 10^{12}$ cm$^{-2}$ with a very high temporal resolution in the sub-ns-range. Here, the development of the technique is briefly outlined and its application to a 5 cm diameter HiPIMS discharge with a Ti target under various conditions is presented. Plasma density evolution with a temporal resolution of $\approx 4 \mu$s is shown. The results are correlated to temporally resolved optical emission measurements providing insight into the discharge processes. [Preview Abstract] |
Tuesday, October 11, 2016 4:15PM - 4:30PM |
GT4.00002: An ionization region model of the reactive Ar/O$_2$ high power impulse magnetron sputtering discharge Jon Tomas Gudmundsson, Daniel Lundin, Nils Brenning, Michel A. Raadu, Chunqing Huo, Tiberiu Minea A reactive ionization region model (R-IRM) is developed to describe the reactive Ar/O$_2$ high power impulse magnetron sputtering (HiPIMS) discharge with titanium target. We compare the discharge properties when the discharge is operated in the two well established operating modes, the metal mode and the poisoned mode. Experimentally, it is found that in the metal mode the discharge current waveform displays a typical non-reactive evolution, while in the poisoned mode the discharge current waveform becomes distinctly triangular and the current increases significantly. Using the R-IRM we find that when the discharge is operated in the metal mode Ar$^+$ and Ti$^+$-ions contribute most significantly (roughly equal amounts) to the discharge current while in the poisoned mode the Ar$^+$-ions contribute most significantly to the discharge current while the contribution of O$^+$-ions and secondary electron emission is much smaller. Furthermore, we find that recycling of ionized atoms coming from the target are required for the current generation in both modes of operation. In the metal mode self-sputter recycling dominates and in the poisoned mode working gas recycling dominates, and it is concluded that the dominating type of recycling determines the discharge current waveform. [Preview Abstract] |
Tuesday, October 11, 2016 4:30PM - 4:45PM |
GT4.00003: Standing helicon induced by a rapidly bent magnetic field in plasmas Kazunori Takahashi, Sho Takayama, Atsushi Komuro, Akira Ando An electron energy probability function and an rf magnetic field are measured in an rf hydrogen helicon source, where axial and transverse static magnetic fields are applied to the source by solenoids and to the diffusion chamber by filter magnets, respectively. It is demonstrated that the helicon wave is reflected by the rapidly bent magnetic field and the resultant standing wave heats the electrons between the source and the magnetic filter, while the electron cooling effect by the magnetic filter is maintained. It is interpreted that the standing wave is generated by the presence of spatially localized change of a refractive index. The application to the hydrogen negative ion source used for the neutral beam injection system for fusion plasma heating is discussed. [Preview Abstract] |
Tuesday, October 11, 2016 4:45PM - 5:00PM |
GT4.00004: Anomalous cross-B field transport and spokes in HiPIMS plasma Ante Hecimovic, Christian Maszl, Volker Schulz-von der Gathen, Achim von Keudell The rotation of localised ionisation zones, i.e. spokes, in magnetron discharge is investigated as a function of discharge current, ranging from 10 mA (current density 0.5 mA cm$^{\mathrm{-2}})$ to 140 A (7 A cm$^{\mathrm{-2}})$. The presence of spokes throughout the complete discharge current range indicates that the spokes are an intrinsic property of a magnetron sputtering plasma discharge. Up to discharge currents of several amperes, the spokes rotate in a retrograde ExB direction and beyond the spokes rotate in a ExB direction. In this contribution we present experimental evidence that anomalous diffusion is triggered by the appearance of spokes rotating in the ExB direction. The Hall parameter $\omega_{\mathrm{ce}}\tau_{\mathrm{c}}$, product of the electron cyclotron frequency and the classical collision time, reduces from Bohm diffusion values (16 and higher) down to the value of 3 as spokes appear, indicating anomalous cross-B field transport. The ion diffusion coefficients calculated from a sideways image of the spoke is six times higher than Bohm diffusion coefficients, which is consistent with the reduction of the Hall parameter. [Preview Abstract] |
Tuesday, October 11, 2016 5:00PM - 5:15PM |
GT4.00005: The self scattering regime of reactive high power impulse magnetron sputtering of chromium and nitrogen Wolfgang Breilmann, Christian Maszl, Ante Hecimovic, Jan Benedikt, Achim von Keudell High power impulse magnetron sputtering (HiPIMS) is a technique for deposition of thin films. It is essential to understand the plasma dynamics in reactive HiPIMS to improve the process of thin film deposition. In this work we investigate the influence of nitrogen admixture to an argon-chromium HiPIMS discharge. Time resolved ion energy distribution functions (IEDF) were measured by means of time and energy resolved mass spectrometry with a temporal resolution of 2\,$\mu s$. The measurements were performed for 150\,$\mu s$ long HiPIMS pulses with a repetition frequency of 20\,Hz. A 2'' target was used. The working gas mixture was varied from pure argon to pure nitrogen with a constant pressure of 0.5\,Pa. Peak current densities of 1.5\,$A/cm^2$ and 4\,$A/cm^2$ were chosen. When operating at high current and pure nitrogen atmosphere the IEDFs of chromium show that only a small amount of ions reaches the mass spectrometer, while for the low current case this is not observed. It is postulated that self-scattering of chromion ions by chromium ions reduces the flux to the mass spectrometer. This is very pronounced in the case of pure nitrogen due to increased confinement of the discharge, and thus a higher density of charged particles in front of the target. [Preview Abstract] |
Tuesday, October 11, 2016 5:15PM - 5:30PM |
GT4.00006: Scattering of magnetized electrons at the boundary of low temperature plasmas Dennis Krueger, Jan Trieschmann, Ralf Peter Brinkmann Magnetized low temperature plasmas with magnetic fields of some 10 to 100 mT are characterized by an electron Larmor radius small compared to all other length scales of the system. In this regime, the classical drift approximation applies. Inside the plasma boundary sheath, this approach breaks down, as the sheath scale is given by the Debye length, which is even smaller than the Larmor radius. When applying different models for these domains, an appropriate boundary condition for the interface has to be utilized. This work investigates the dynamics at this interface with the help of a 3D kinetic single electron model. A comprehensive comparison of two selected sheath models, a classical bohm sheath and the assumption of a hard wall is implemented. Thereby the influence of these models with respect to specific gyro coordinates is investigated and used to characterize the respective system dynamics. Moreover effects like the drift of the guiding center due to the large $\vec{E}\times\vec{B}$ drift inside the sheath, which leads to a cross field diffusion similar to collisions outside the sheath, is analyzed and compared. [Preview Abstract] |
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