筒内高功率脉冲磁控放电的电磁控制与优化

高功率脉冲磁控溅射(Hi PIMS)技术被提出以来就受到广泛关注,其较高的溅射材料离化率结合适当的电磁控制,可产生高致密度、高结合力和高综合性能的涂层,但其沉积速率低、放电不稳定、溅射材料离化率差异较大.我们设计了一种筒形溅射源,通过对结构的设计优化,利用类空心阴极放电效应,使问题得到解决.然而其靶面切向磁场不均匀,电子逃逸严重,进而造成等离子体密度偏低,且放电不均匀.本文通过对其放电和等离子体分布进行仿真,提出电场阻挡和磁铁补偿两种方案,研究了不同电场控制条件下的放电行为和等离子体分布.结果表明:增加电子阻挡屏极可以生成势阱,从而有效抑制电子从边缘的逸出;优化后的磁铁补偿可以显著提高靶面横向磁场的均匀性及靶面利用率.两种方案同时作用时,Hi PIMS放电刻蚀环面积更大、且更加均匀.     

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采用另加偏压的单阴极弧氦放电直线等离子体装置对氦等离子体的基本特性进行了研究.对氦轴向输运规律做了描述并与光谱测量数据做了定性地比较.实验结果表明,氦等离子体的电子温度与电子密度均随放电电流、约束磁场的增加而增加.氦原子与氦离子的辐射光谱随放电电流、偏压、磁场的变化规律进行了测量分析,同时氦离子对钨靶积分辐照效应进行了观察.这些结果不但提供了氦等离子体的基本特性,对于研究氦离子与面向等离子材料相互作用导致产生气泡、肿胀、脆化损伤等的评估,特别是对将来伴有(n,α)反应时具有一定的参考价值.     

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

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Hi PIMS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Hi PIMS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Hi PIMS更进一步的推广与应用.     

气压对大面积等离子体片电子密度分布的影响

利用脉冲磁约束线形空心阴极放电装置,在15mT磁场约束下,产生了持续时间为200μs、峰值放电电流为3A、面积为60cm×60cm的大面积等离子体片。采用快帧法和旋转空心阴极法,在90~210Pa内,利用朗缪尔探针首次获得了不同气压的等离子体片的厚度向电子密度分布及其演化构成的二维分布图;研究了在同等峰值放电电流条件下,等离子体片达到最大厚度向峰值电子密度时,气压对所需放电时间、最大厚度向峰值电子密度及电子密度半高宽的影响。结果表明:在相同的峰值放电电流条件下,等离子体片达到最大厚度向峰值电子密度的时间随气压的降低而减小;气压越低,最大厚度向峰值电子密度越大,电子密度半高宽越小。     

圆形复合式磁控溅射阴极设计及其放电特性模拟研究

基于二维有限元算法使用COMSOL软件对圆形复合式磁控溅射阴极的磁场进行了计算,结合Matlab优化工具箱分别采用遗传算法和模拟退火算法对圆形复合式磁控溅射阴极的结构进行优化,得到靶材利用率达到最大的最优结构.对得到的最优化磁控阴极,基于自洽粒子模拟方法,使用VSim软件对不同工况下的放电特性进行了模拟.研究发现随着磁场非平衡度的增加,阴极表面电势降落最大的位置和等离子体聚集的位置,沿着阴极表面外沿不断向阴极中心移动,阴极表面磁场的强度不断减小.随着磁场非平衡度的增加,等离子体密度先增加后减小,鞘层厚度先减小后增加,等离子体的密度和鞘层厚度不仅与磁场非平衡度有关,而且与磁场强度有关.最后根据粒子模拟的结果,对复合式磁控阴极的靶材刻蚀深度进行了研究.研究发现,在优化前后靶材的刻蚀范围从60 mm扩展至整个靶面,极大地提高了靶材利用率.     

同轴磁场对非平衡磁控溅射系统放电特性的影响

采用激励电流可以调整的电磁线圈来激发非平衡磁场,调整约束磁场和放电空间等离子体状态。实验结果表明调整非平衡磁场显著影响系统的放电特性,使放电特性偏离常规的磁控溅射系统放电特性,增强了等离子体的引出效果。在Ar放电的条件下,详细研究了溅射系统的工作伏安特性随不同的工作气体、气压和溅射功率的变化规律。根据蔡尔得公式,讨论了非平衡磁场对于磁控溅射系统中放电特性的影响规律。     

筒形高功率脉冲磁控溅射源的开发与放电特性

高功率脉冲磁控溅射以较高的溅射材料离化率及其所带来的高致密度、高结合力和高综合性能成为物理气相沉积领域的新宠,然而其沉积速率低、放电不稳定、溅射材料离化率不一等缺点阻碍了其在工业界的推广和应用.针对高功率脉冲磁控溅射技术固有的缺陷,我们从靶源出发,设计了一种筒形溅射源,将放电限制在筒形溅射源内部,放电不稳定喷溅出的"金属液滴"和溅射出来但并未离化的溅射材料无法被负电位的引出栅引出而影响薄膜沉积,只有离化的溅射材料可以引出并沉积形成薄膜,而电子将在筒形溅射源内部反复振荡,和未离化的溅射原子剧烈碰撞,带动进一步离化.本文通过磁场和放电的模拟发现筒形溅射源内部电子、离子呈花瓣状分布,8条磁铁均匀分布的结构具有最优的靶材利用率.据此开发的筒形溅射源可在高功率脉冲磁控溅射条件下正常放电,其放电靶电流随靶电压变化呈现出高功率脉冲磁控溅射典型的伏安特性特征,复合电流施加后,有明显的预离化作用.溅射"跑道"面积占靶材表面的60%以上,筒形溅射源中心的离子电流波形与靶电流波形类似,但相对靶电流延迟约40μs,数值约为靶电流的1/10.结果证明,筒形溅射源可有效地应用到高功率脉冲磁控溅射放电中,并成为促进其推广和应用的一种新路径.     

槽型空心阴极放电中槽底阴极面的电子发射对放电的影响

运用粒子和流体组合模型理论研究了槽型空心阴极放电中槽底阴极面上二次电子发射对放电等离子体特性、电离特性及阴极溅射的影响.研究表明,从槽底阴极面发射的电子在进入负辉区后,可以形成振荡电子,因而具有增强电离的作用.根据各阴极面上的离子的空间分布可以推知槽底附近的阴极面上的溅射较强,这可以解释槽型空心阴极放电实验中观察到的因溅射导致槽底截面形状圆形化的现象.     

槽型空心阴极放电中槽底阴极面的电子发射对放电的影响

运用粒子和流体组合模型理论研究了槽型空心阴极放电中槽底阴极面上二次电子发射对放电等离子体特性、电离特性及阴极溅射的影响.研究表明,从槽底阴极面发射的电子在进入负辉区后,可以形成振荡电子,因而具有增强电离的作用.根据各阴极面上的离子的空间分布可以推知槽底附近的阴极面上的溅射较强,这可以解释槽型空心阴极放电实验中观察到的因溅射导致槽底截面形状圆形化的现象     

级联弧放电氦等离子体特性研究

采用另加偏压的单阴极弧氦放电直线等离子体装置对氦等离子体的基本特性进行了研究。对氦轴向输运规律做了描述并与光谱测量数据做了定性地比较。实验结果表明,氦等离子体的电子温度与电子密度均随放电电流、约束磁场的增加而增加。氦原子与氦离子的辐射光谱随放电电流、偏压、磁场的变化规律进行了测量分析,同时氦离子对钨靶积分辐照效应进行了观察。这些结果不但提供了氦等离子体的基本特性,对于研究氦离子与面向等离子材料相互作用导致产生气泡、肿胀、脆化损伤等的评估,特别是对将来伴有(n, α)反应时具有一定的参考价值。     

Control of High Power Pulsed Magnetron Discharge by Monitoring the Current Voltage Characteristics

Discharge current voltage (IV) curves are directly measured at the target of a high impulse power magnetron sputtering (HiPIMS) plasma for the target materials aluminium, chromium, titanium and copper. These discharge IV curves have been correlated with ICCD camera images of the plasma torus. A clear connection between the change in the discharge IV curve slopes at specific currents and the appearance of localized ionization zones, so‐called spokes, in a HiPIMS plasma is identified. These spokes appear above typical target current densities of 2 A/cm². The slope of the discharge IV curves, at current densities when spokes are formed, depends on the mass of the target atoms with a higher plasma conductivity for higher mass target materials. This is explained by the momentum transfer from the sputter wind to the argon background gas, which leads to higher plasma densities for heavier target materials. The change in the VI curve slope can be used to identify the spokes regime for HiPIMS plasmas, as being mandatory for deposition of good quality materials by HiPIMS. Consequently, the discharge IV curve slope monitoring can be regarded an essential control approach of any industrial HiPIMS process, where discharge IV curves are much easier accessible compared to more complex diagnostics such as time and space resolved ICCD camera measurements. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Improvement of the efficiency of a glow discharge-based ion emitter with oscillating electrons

Ion emission from the plasma of a low-pressure (≈5×10⁻² Pa) glow discharge with electrons oscillating in a weak (≈1 mT) magnetic field is studied in relation to the cold hollow cathode geometry. A hollow conic cathode used in the electrode system of a cylindrical inverted magnetron not only improves the extraction of plasma ions to ≈20% of the discharge current but also provides the near-uniform spatial distribution of the ion emission current density. The reason is the specific oscillations of electrons accelerated in the cathode sheath. They drift in the azimuth direction along a closed orbit and simultaneously move along the magnetic field toward the emitting surface of the plasma. A plasma emitter with a current density of ≈1 mA/cm² over an area of ≈100 cm² designed for an ion source with an operating voltage of several tens of kilovolts is described.     

Experimental Investigations of Discharge Characteristics and Plasma Parameters of a Cylindrical Cathode Discharge in a Magnetic Field. II. Plasma Parameters

The experimental determination of the main plasma parameters (i.e. plasma potential, plasma density, electron temperature, intensity of plasma radiation) in the negative glow of a cylindrical cathode discharge in magnetic field is presented. The influence of electrode configuration, gas pressure, discharge current and magnetic field on plasma parameters and their radial distribution is analysed.     

Nonself-sustained arc discharge in anode material vapors

The basic characteristics of the nonself-sustained arc discharge in a vapor of the anode material are studied. The influence of thermoemission parameters of the cathode on volt-ampere characteristics of the discharge is described. It is established that in a free mode of the discharge cathode operation, when the discharge current I_D is lower than the current of the thermoelectron emission from the discharge cathode I_C, the deposition rate of the films q is directly proportional to the discharge current I_D. In the compelled mode of the cathode operation, when I_D>I _C, q~W_D², where W_D=I_D U_D with U_D being the discharge voltage. It is shown that the magnetic field increases the plasma density and changes the density profile from n(x)-1/x² to n(x)-1/x with x being a distance along the flow. The motion of created plasma flow is shown to have a noncollisional character with constant electron temperature of 5-7 eV along the flow. The values of plasma potential and electric field in the flow are determined; the values of cathodic and anodic potential drops in the discharge are evaluated. The angular distributions of ion and neutral fluxes in the created plasma flow are described. It is shown that the plasma flows parameters depend substantially on the working material. With use of crossed electric and magnetic fields, the flow ionization coefficient was enhanced up to 85% for the discharge in Ti vapors, and 35% for the discharge in Cu vapors     

The Influences of the Magnetic Field Strength on the Magnetic Confinement of Primary Electrons in an Ion Source

This paper deals with the simulation of trajectories of energetic electrons under the influence of a multi-cusp magnetic field produced by a permanent magnet assembly in a ring cusp geometry which is designed for supporting a plasma based ion source. The primary electrons are assumed as being emitted from a cathode located coaxially with the cylindrical discharge chamber. The volume of the region occupied by the electron trajectories and the magnetic trapping time were evaluated and plots are presented showing the effects of the surface magnetic field strength of the magnets on the volume and the mean confinement time of primary electrons in the ion source.     

环形磁场金属等离子体源冷却流场的数值模拟与优化

环形磁场金属等离子体源作为一种全新的等离子体源结构,可用于产生高度离化、无大颗粒、高密度的离子束流,但传统流道结构不能保证其高效、均匀散热,大功率工作时可能引起密封胶圈的烧蚀失效,需对其冷却流场进行优化设计.利用Solidworks Flow Simulation软件对等离子体源冷却流道进行模拟,分析出入水孔分布角度、孔数、孔径以及入水孔高度对冷却效果的影响规律,并对流道结构参数进行优化.结果表明,增大水孔的周向分布范围,有利于提高散热的均匀性;入水孔设置在结构上层有利于减少冷却水的温度分层现象,使铜套和密封胶圈都处于较好的冷却状态;适当减小孔径有利于增大冷却水射流速度,增大湍流程度强化传热,提高换热效率.优化后的流场结构可以提高冷却水的利用率,在相同流量条件下获得更好的冷却效果,改善等离子体源的放电稳定性,为环形磁场金属等离子体源的冷却结构设计提供理论依据.     

HL-2M装置5 MW中性束加热束线离子源放电室研制

为了给HL-2M装置建设一条5 MW中性束加热束线,开展了中性束加热用热阴极弧放电离子源放电室的研制。这条中性束束线包含4套80 kV/45 A/5 s离子源,放电室的设计指标为850 A/5 s。首先采用CST软件中的电磁工作室对特定几何结构的放电室会切磁场进行了模拟计算,得到了会切磁场分布,验证了会切磁场布局的合理性。针对放电室加工工艺和实验过程中局部拉弧等问题,对放电室结构进行了不断改进。放电室侧壁由40列会切磁体改为7圈环形磁体,阴极灯丝结构从灯丝板结构最终改为陶瓷可伐结构,并且在放电室和加速器之间增加了陶瓷屏蔽。在阴极板结构放电室和阴极陶瓷可伐结构放电室内都获得了正常的弧放电。最终定型的放电室采用周边7圈环形会切磁体和陶瓷可伐结构。在定型的放电室内达到了5 MW中性束束线离子源弧放电的指标。弧放电时间接近5 s,最大弧放电电流达到1 000 A。     

Ion current distribution within a toroidal duct of a filteredvacuum arc deposition system

Vacuum arcs were established on a 90-mm-diameter Ti cathode in a deposition apparatus consisting of a spacer, 122 mm-diameter annular anode, quarter-torus magnetic macroparticle filter, and a deposition chamber. A toroidal magnetic field generally parallel to the torus walls of up to 20 mT was applied. The ion current in various cross-sections of the toroidal duct was measured using: 1) a disc probe of 130-mm diameter, oriented normal to the torus axis used to measure the transmitted ion current, and 2) a hollow cylindrical probe of 135-mm diameter and 25-mm height, whose axis coincided with the torus axis, used to measure ion current losses to the duct wall. The distribution of ion current loss was studied using an 8-segment hollow cylindrical multiprobe, where the individual probes were equally distributed on the circumference of a 130-mm-diameter circle. It was shown that: 1) the ratio of ion currents collected on the cylindrical and disc probes at first decreases with increasing the toroidal field, and then becomes approximately constant; 2) the presence of the large-diameter disc probe does not influence the value of the ion current on the cylindrical probe; and 3) the maximum ion current density near the torus walls is located in the +g direction and displaces in the -(B×g) direction with increasing the toroidal field, where g and B are the vectors of the centrifugal acceleration and the magnetic field, respectively