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中国物理学会期刊

外扩型电磁场控制筒形阴极内等离子体放电输运特性的仿真研究

CSTR: 32037.14.aps.68.20190583

Simulation study on plasma discharge and transport in cylindrical cathode controlled by expanding electromagnetic field

CSTR: 32037.14.aps.68.20190583
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  • 筒形阴极由于具有向内放电的特性, 可改善高功率脉冲磁控溅射技术放电不稳定、溅射材料离化率差异大等缺陷. 然而其产生的等离子体仅能依靠浓度差扩散的方式向基体运动, 沉积速率并没有明显改善, 尤其是在远离阴极区域. 使用外扩型磁场对离子运动进行引导, 可实现等离子体的聚焦和远距离输运, 从而减少离子损失, 提高沉积效率. 本文从模拟和实验的角度对磁场的布局与设置进行研究, 并获得不同磁场条件下的等离子体空间和时间输运特性及其对薄膜沉积的影响. 结果表明电磁场的引入不仅可以大幅提高筒形阴极内等离子体的引出效率, 实现不同程度的引出或聚焦, 而且对等离子体放电也产生明显的增强或减弱, 可根据不同的需求或材料进行精确调控. 通过控制磁场, 可获得较强的HiPIMS放电和较高的沉积速率, 实验结果与仿真预测相符合. 该工作完善了HiPIMS沉积技术在沉积效率上的不足, 拓宽了筒形阴极的溅射工艺窗口和适用范围, 有助于HiPIMS更进一步的推广与应用.

     

    High-power impulse magnetron sputtering (HiPIMS) is a new magnetron sputtering technique which can produce high-density plasmas with a high ionization rate and prepare coatings with a good performance such as large density and high adhesion. To obtain stable discharge and universal materials’ ionization rates, a cylindrical cathode is proposed based on the hollow cathode effect. However, the unusual plasma transport results in a large loss of ions and a low deposition rate. To solve these problems, an expanding electromagnetic field is proposed to control the plasma transport in this work. The particle in cell/Monte Carlo collision (PIC/MCC) method and the plasma diffusion model are used to simulate the plasma transport in and out of the cylindrical cathode with different currents in the electromagnetic coils, respectively. The simulation results reveal that different electromagnetic fields can achieve different plasma density distributions, resulting in different accumulated positions and different diffusion paths. When the coil current is positive, the resistance to axial motion of electrons is small but the resistance to radial motion is large, so that the hollow cathode effect is weakened and the plasma beam tends to output uniformly. When the coil current is negative, the resistance to axial motion of electrons is large but the resistance to radial motion is small, so that the hollow cathode effect is enhanced and the plasma tends to gather on the central axis and then diffuses outward. To verify the simulation results, Ar/Cr HiPIMS discharge experiments are carried out with the cylindrical cathode in a homemade vacuum system. The experiment results indicate that the threshold voltage, the plasma flow shape, the optical emission spectrum (OES) intensity, and the deposition distribution are determined by the electromagnetic coil current. The variation tendency is in coincidence with the prediction of the simulation. Consequently, by adding an expanding electromagnetic field, the plasma discharge in the cylindrical cathode can be easily controlled and the deposition rate is greatly enhanced. This electromagnetic control strategy not only realizes the enhancement and effective control of plasma, but also improves the homogeneity and the deposition rate of the coatings, thus laying a foundation for the industrial application of HiPIMS.

     

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