Bulletin of the American Physical Society
74th Annual Gaseous Electronics Conference
Volume 66, Number 7
Monday–Friday, October 4–8, 2021;
Virtual: GEC Platform
Time Zone: Central Daylight Time, USA
Session KW72: Magnetically Enhanced Plasmas |
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Chair: Thomas Mussenbrock, Bochum University Room: Virtual GEC platform |
Wednesday, October 6, 2021 3:45PM - 4:00PM |
KW72.00001: Operating modes of a magnetized direct-current discharge in helium Dmitry Levko, Rochan Upadhyay, Laxminarayan L Raja A high-pressure direct current magnetron discharge is analyzed using a self-consistent two-dimensional fluid model. This discharge has potential interest in plasma switching applications due to its ability to generate rather dense (plasma density ~1019 m-3) stable nonequilibrium plasmas at the pressures ~13.3 Pa (100 mTorr). This discharge has several advantages over nanosecond pulsed high pressure discharges used in conventional plasma switchers since it operates at much lower voltages and lower gas pressures, with the advantage of much longer cathode lifetime. In the present paper, we analyze the operating modes of this magnetron discharge for the conditions close to that of Sommerer et al., J. Phys. D: Appl. Phys. 52, 435202 (2019). We observe the subnormal and normal modes of the magnetron operation whose physics differs from that typical for unmagnetized plasmas. |
Wednesday, October 6, 2021 4:00PM - 4:15PM |
KW72.00002: Electron heating transition in direct current magnetron sputtering discharges Bocong Zheng, Yangyang Fu, Huihui Wang, Keliang Wang, Thomas Schuelke, Qi Hua Fan Electron heating in direct current magnetron sputtering (DCMS) discharges is investigated via fully kinetic particle-in-cell/Monte Carlo collision simulations. The similarities in DCMS of different dimension scales are observed. Under conditions of high pressure p or weak magnetic field B, the electron heating in DCMS is found mainly within the sheath. As the pressure decreases or the magnetic field increases, the electron heating shifts to the bulk plasma region, accompanied by the appearance of breathing oscillations; meanwhile, the electron mobility approaches the ion mobility, and an appreciable time-averaged potential drops outside the sheath. It is further confirmed that with the reduction of similarity invariant B/p or pd, the breathing oscillations are suppressed due to the increase in wavelength or the decrease in characteristic scale of discharge. In other words, with the onset and development of breathing oscillations, the electron heating mechanism transitions from sheath energization to Ohmic heating in the bulk plasma region. The characteristics of breathing oscillations and the transition of electron heating mechanism are scale-invariant under similar discharge conditions due to the electron kinetic invariance. The results of this study contribute to a more comprehensive understanding of the fundamentals of magnetron discharge. |
Wednesday, October 6, 2021 4:15PM - 4:30PM |
KW72.00003: Fundamental investigations of the hysteresis effect in magnetically enhanced reactive sputter processes Birk Berger, Julian Roggendorf, Dennis Engel, Christian Woelfel, Denis Eremin, Jan Lunze, Ralf Peter Brinkmann, Peter Awakowicz, Julian Schulze Capacitively coupled radio-frequency plasmas are frequently used in the industry to facilitate the processing of surfaces by e.g. etching and/or deposition. A typical process conducted in such a discharge is the deposition of aluminum oxide layers which can be facilitated by using an aluminum target and introducing oxygen to the inert gas background such as argon. In these discharges, a hysteresis effect on basic plasma parameters, e.g. electron density, DC self-bias, symmetry parameter, is observed when the oxygen flux is increased or decreased, respectively. In this work, we examine this hysteresis experimentally. A magnetron-like magnetic field configuration is added to the powered electrode to increase the heavy particle flux to the target. Using a variety of diagnostic tools, namely VI probe, Lambda probe (partial pressure of oxygen), Multipole Resonance Probe (electron density), retarding field energy analyzer (ion energy distribution function), and phase resolved optical emission spectroscopy (electron dynamics), a new aspect of the hysteresis effect is investigated: It is found that the electron dynamics are altered by the surface conditions of the target which leads to a change of the discharge symmetry and, hence, of the ion flux. Finally, the resulting layers at different operation points are analyzed with a profilometer (grow rate) and energy-dispersive X-ray spectroscopy (composition of the films). |
Wednesday, October 6, 2021 4:30PM - 4:45PM |
KW72.00004: Plasma series resonance in capacitive discharges with transverse magnetic field Dennis Engel, Birk Berger, Christian Woelfel, Jan Lunze, Peter Awakowicz, Julian Schulze, Denis Eremin, Ralf Peter Brinkmann Capacitive plasma discharges are a key technology in modern industries. Adding magnetic fields to such discharges leads to enhanced characteristics such as higher densities and increased ion flux. Similar to unmagnetized discharges, a lumped element description can be used to understand the basic behavior. In capacitively coupled discharges without magnetic field the plasma series resonance can be understood by the interaction of the sheaths, modeled by nonlinear capacitors and the bulk electrons’ inertia, modeled by an inductance [1]. Deriving the lumped elements from the cold-plasma model for a magnetized discharge, where the magnetic field is transverse to the electric field, leads to a more complex scheme. By analyzing a typical case with low pressure of 0.5 Pa, a typical applied frequency of 13.56 MHz and a magnetic flux density of 5 mT, it can be seen that the behavior of the discharge totally changes compared to the unmagnetized case. The plasma series resonance vanishes, which can be explained by a change of the bulk response from an inductive to a capacitive one. This can also be seen in 1d3v PIC/MCC-simulations. |
Wednesday, October 6, 2021 4:45PM - 5:00PM |
KW72.00005: Identification of gradient drift instability evolving into a rotating spoke in a crossed field plasma Liang Xu, Denis Eremin, Ralf Peter Brinkmann The rotating low frequency and large scale structures referred to as spokes are frequently observed in low temperature E × B plasma devices. Spoke can result in the electron anomalous transport across the magnetic field, prohibiting the establishment of a predictive model for the optimization and operation of E × B plasma devices. So far, fundamental aspects of the spoke are not well understood and one of the core questions under open debate is the driving mechanism behind the formation of the rotating spoke. This work provides direct evidence of gradient drift instability being the origin of a rotating spoke in a crossed field plasma using 2D radial-azimuthal fully kinetic PIC/MCC simulations. The kinetic model exhibits a pronounced rotating spoke and a clear linear-nonlinear transition and reveals the whole perturbation spectrum of the gradient drift instability in the linear stage: Simon-Hoh, lower-hybrid and ion sound modes. The two-fluid dispersion relation of the gradient drift instability was utilized to interpret the linear development of instabilities in the simulations. It was shown the simulated spectrum and growth rate agree very well with the theoretical dispersion relation over the investigated cases. The most linearly unstable mode was found to be the lower hybrid instability and the mode transition into the m=1 macroscopic rotating structure after saturation of the linear phase is accompanied by an inverse energy cascade. |
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