Closed magnetic field constructed by unbalanced magnetron sputtering (MS) cathodes has been a general means of developing the MS coating system. However, owing to the difficulties in characterizing the complex plasma behaviors, there are still no quantitative criteria or design bases for some critical points, such as the effective object, the working mechanism, the closure condition, the layout logic and the effectivity of the closed magnetic field. Here in this work, out of the movements of charged particles in magnetic field, the motion behaviors of electrons and ions in the vacuum chamber are studied and it is also revealed that the closed magnetic field can affect mainly the electrons and further control the distributions of ions. A Monte-Carlo collision (MCC) model of the closed magnetic field MS coating system is established by test-electron to characterize the plasma transport characteristics, and the electron constraint and coating deposition efficiency are studied by different layouts of the magnetron cathodes and the ion sources. The simulation results show that the cathode numbers and vacuum chamber size determine the constraint effect on electrons in closed magnetic field. By 8 MS cathodes and the chamber radius of 0.5 m, the proportion of the overflow electrons can decrease to 1.77%. To increase the proportion of the electrons in the coating region, four coupled magnetic fields are introduced in the center of vacuum chamber. The studies of cathode type, rotation angle and magnetic field direction reveal that the proportion of the overflow electrons is less than 3%. A local dense plasma distribution and a continuous uniform plasma distribution can be observed in the vacuum chamber, corresponding to the same and opposite layout in magnetic poles of the MS cathodes and the ion sources, and the proportion of the electrons in the coating region significantly increases to 53.41% and 42.25%, respectively.
Plasma simulation is important to study the plasma discharge systematically, especially for the anode layer ion source which has the complex geometrical characteristics of the discharge structures. However, owing to the complex solution domain formed by the geometric profile of the anode and cathode, the traditional simulation models show extremely small computational efficiency and poor convergence. This paper presents a separated simulation for the ion source structure and the plasma discharge, respectively, where the cathode geometric parameters (including the size, the shape and the relative position of the inner and outer cathodes) are simplified to two magnetic mirror parameters (the magnetic mirror ratio <i>R</i><sub>m</sub> and the magnetic induction intensity at the center of the magnetic mirror <b><i>B</i></b> <sub>0</sub>) firstly and a high-efficient particle-in-cell/Monte Carlo collision (PIC/MCC) model is established to improve the computational efficiency and stability of the plasma simulation later. As a result, the convergence time of the plasma simulation is shortened significantly from 1 μs to 0.45 μs, and by which the influences of the geometrical characteristics of the discharge structure on the plasma properties are systematically studied. The simulation results reveal that magnetic mirror with <i>R</i><sub>m</sub>=2.50 and <b><i>B</i></b> <sub>0</sub>=36 mT can constraint the plasma at the centre zone between the inner and outer cathode. When the discharge center of the plasma is consistent with the magnetic mirror center, the anode layer ion source presents both high density output of ion beam current and significantly reduced cathode etching, suggesting the best balance obtained between the output and cathode etching.
Etching of the cathodes in magnetron sputtering determines the plasma discharge properties and deposition efficiency. In high-power and high-ionization discharges, etching becomes more complicated, resulting in inaccurate results if the conventional models are still used. This work aims at establishing an accurate dynamic model for high-power and high-ionization discharges by combining the cellular automata (CA) method and particle-in-cell/Monte Carlo collision (PIC/MCC) method, in which all the interactions pertaining to the etching morphology, plasma density, electric field, and magnetic field are considered. In high-power discharges such as continuous high-power magnetron sputtering (C-HPMS), strong self-sputtering and intense gas rarefaction stemming from the high temperature in the vicinity of the target influence the etching behavior. Compared to the experimental results, the morphology simulated by the dynamic etching model shows an error of only 0.8% in C-HPMS, which is much less than that obtained by the traditional test-electron Monte Carlo (MC) method (10.1%) and static PIC/MCC method (4.0%). The dynamic etching model provides more accurate results to aid the development and industrial application of high-power magnetron sputtering.
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