Plasma based process control of reactive sputtering
Final Report Abstract
The project ”Plasma-based process control of reactive sputtering processes” dealt with strategies to optimize industrial plasma processes, using reactive sputtering as an example. The project involved the development of experimental and theoretical knowledge on the underlying physical and chemical processes, as well as the application of control engineering methods. To address the complex research questions, three groups of the Department of Electrical Engineering and Information Technology at Ruhr-Universität Bochum (RUB) joined their forces: the Chair of Applied Electrodynamics and Plasma Technology, the Chair of Theoretical Electrical Engineering, and the Chair of Automation Engineering. The traditional control of plasma processes is based on empirical methods, where an optimal combination of externally adjustable process parameters (such as high-frequency power, voltage, gas pressure and flow rate, magnetic field strength) is found to ensure process success. Once this ”recipe” is established, it should not be deviated from. However, this approach can be problematic as the relationship between the adjustable parameters and the process outcome is often very indirect. Additionally, disturbances caused by equipment drift and external influences cannot be effectively addressed. In this project, an alternative plasma-based process control strategy, based on a solid scientific understanding of the process, was developed and tested for the first time. The new strategy aims to improve process efficiency and quality by monitoring and controlling internal state variables such as electron density or boundary sheath voltages. This requires suitable in-situ diagnostics to capture these internal variables without disturbing the process. Mathematical models of the functional relationships between the externally adjustable process parameters and the internal state variables, as well as between the internal state variables and the final process success are also required to determine the optimal control inputs. To realize the concept, a reactive sputtering process for depositing thin dielectric Al2O3 films using a capacitive radio-frequency magnetron discharge was considered as example. The relevant coating system is well known and existing resources at RUB could be utilized. However, the focus was not on optimizing this specific process, but on the development of methods for systematically realizing plasma-based process control. Therefore, a complex sputter process was chosen, which poses high demands on the process control due to a pronounced hysteresis. To master this process, details of plasma-surface interactions had to be understood, methods for controlling the energy distribution functions of the film-determining plasma particles had to be developed, and fundamental questions regarding discharge dynamics had to be clarified, such as electron heating and cross-field particle transport. The methodology developed in this project can be transferred to other plasma processes.
Publications
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Magnetic control of nonlinear electron resonance heating in a capacitively coupled radio frequency discharge. Plasma Sources Science and Technology, 28(11), 115021.
Oberberg, M.; Engel, D.; Berger, B.; Wölfel, C.; Eremin, D.; Lunze, J.; Brinkmann, R. P.; Awakowicz, P. & Schulze, J.
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The Multipole Resonance Probe-based controller: a technology to investigate plasma-based deposition. Journal of Instrumentation, 14(10), P10007-P10007.
Woelfel, C.; Oberberg, M.; Berger, B.; Engel, D.; Brinkmann, R.P.; Awakowicz, P.; Lunze, J. & Schulze, J.
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Electron power absorption dynamics in magnetized capacitively coupled radio frequency oxygen discharges. Plasma Sources Science and Technology, 29(10), 105004.
Wang, Li; Wen, De-Qi; Hartmann, Peter; Donkó, Zoltán; Derzsi, Aranka; Wang, Xi-Feng; Song, Yuan-Hong; Wang, You-Nian & Schulze, Julian
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The magnetic asymmetry effect in geometrically asymmetric capacitively coupled radio frequency discharges operated in Ar/O2. Plasma Sources Science and Technology, 29(7), 075013.
Oberberg, M.; Berger, B.; Buschheuer, M.; Engel, D.; Wölfel, C.; Eremin, D.; Lunze, J.; Brinkmann, R. P.; Awakowicz, P. & Schulze, J.
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Control-oriented plasma modeling and controller design for reactive sputtering. IFAC Journal of Systems and Control, 16, 100142.
Woelfel, Christian; Oberberg, Moritz; Berger, Birk; Engel, Dennis; Brinkmann, Ralf Peter; Schulze, Julian; Awakowicz, Peter & Lunze, Jan
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Resonant sheath heating in weakly magnetized capacitively coupled plasmas due to electron-cyclotron motion. Physical Review E, 104(4).
Zhang, Quan-Zhi; Sun, Jing-Yu; Lu, Wen-Qi; Schulze, Julian; Guo, Yu-Qing & Wang, You-Nian
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Experimental investigations of plasma dynamics in the hysteresis regime of reactive RF sputter processes. Plasma Sources Science and Technology, 31(6), 065007.
Roggendorf, J.; Berger, B.; Eremin, D.; Oberberg, M.; Engel, D.; Wölfel, C.; Zhang, Quan-Zhi; Awakowicz, P.; Lunze, J. & Schulze, J.
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Electron dynamics in planar radio frequency magnetron plasmas: I. The mechanism of Hall heating and the µ-mode. Plasma Sources Science and Technology, 32(4), 045007.
Eremin, Denis; Engel, Dennis; Krüger, Dennis; Wilczek, Sebastian; Berger, Birk; Oberberg, Moritz; Wölfel, Christian; Smolyakov, Andrei; Lunze, Jan; Awakowicz, Peter; Schulze, Julian & Brinkmann, Ralf Peter
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Electron dynamics in planar radio frequency magnetron plasmas: II. Heating and energization mechanisms studied via a 2d3v particle-in-cell/Monte Carlo code. Plasma Sources Science and Technology, 32(4), 045008.
Eremin, D.; Berger, B.; Engel, D.; Kallähn, J.; Köhn, K.; Krüger, D.; Xu, L.; Oberberg, M.; Wölfel, C.; Lunze, J.; Awakowicz, P.; Schulze, J. & Brinkmann, R. P.
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Electron dynamics in planar radio frequency magnetron plasmas: III. Comparison of experimental investigations of power absorption dynamics to simulation results. Plasma Sources Science and Technology, 32(4), 045009.
Berger, B.; Eremin, D.; Oberberg, M.; Engel, D.; Wölfel, C.; Zhang, Q.-Z.; Awakowicz, P.; Lunze, J.; Brinkmann, R. P. & Schulze, J.
