Interaction between plasma and electromagnetic field in ion source of 10 cm ECR ion thruster

Through diagnosing the plasma density and calculating the intensity of microwave electric field, four 10 cm electron cyclotron resonance (ECR) ion sources with different magnetic field structures are studied to reveal the inside interaction between the plasma, magnetic field and microwave electric field. From the diagnosing result it can be found that the plasma density distribution is controlled by the plasma generation and electron loss volumes associated with the magnetic field and microwave power level. Based on the cold plasma hypothesis and diagnosing result, the microwave electric field intensity distribution in the plasma is calculated. The result shows that the plasma will significantly change the distribution of the microwave electric field intensity to form a bow shape. From the boundary region of the shape to the center, the electric field intensity varies from higher to lower and the diagnosed density inversely changes. If the bow and its inside lower electric field intensity region are close to the screen grid, the performance of ion beam extracting will be better. The study can provide useful information for the creating of 10 cm ECR ion source and understanding its mechanism.     

ECR离子源束流发射度的实验研究

利用最新自行研制的电扫描发射度探测系统, 在ECR离子源上进行了一系列关于ECR离子源引出束流发射度的研究. 这套电扫描发射度探测系统安装在中国科学院近代物理研究所(兰州)的LECR3试验平台的束运线上. 试验中, 通过测量相关参数, 研究了磁场、微波、掺气效应及负偏压效应等对引出束流发射度的影响. 利用实验所得的结果与关于ECR等离子体和离子源束流发射度的半经验理论, 分析推导了离子源各可调参数与ECR等离子体的直接关系, 这为分析探索ECR离子源的工作机制提供了一定的参考依据.     

Influence of noble gases on electron cyclotron heated hydrogen plasma

A quartz-chamber 2.45-GHz electron cyclotron resonance ion source (ECRIS) is designed at Peking University for the diagnostic purpose. Experimental results show that the added noble gases in hydrogen could cause a decrease of electron temperature and an increase of electron density. In this work, a numerical model is upgraded for ECR plasma generated by mixed gases. On this basis, the model is applied for the composed hydrogen plasma with additional noble gases. And dependences of neutral gas density and electron density on electron temperature are presented for individual gas (He, Ar, and H₂) and gas mixture, respectively. The calculated results are basically in accordance with the diagnostic results of ECRIS.     

Plasma parameter diagnosis using hydrogen emission spectra of a quartz-chamber 2.45 GHz ECRIS at Peking University

A quartz-chamber 2.45 GHz electron cyclotron resonance ion source(ECRIS) was designed for diagnostic purposes at Peking University [Patent Number: ZL 201110026605.4]. This ion source can produce a maximum 84 m A hydrogen ion beam at 50 k V with a duty factor of 10%. The root-mean-square(RMS) emittance of this beam is less than 0.12π mm mrad. In our initial work,the electron temperature and electron density inside the plasma chamber had been measured with the line intensity ratio of noble gases. Based on these results, the atomic and molecular emission spectra of hydrogen were applied to determine the dissociation degree of hydrogen and the vibrational temperature of hydrogen molecules in the ground state, respectively. Measurements were performed at gas pressures from 4×10~(-4) to 1×10~(-3) Pa and at input peak RF power ranging from 1000 to 1800 W. The dissociation degree of hydrogen in the range of 0.5%-10% and the vibrational temperature of hydrogen molecules in the ground state in the range of 3500-8500 K were obtained. The plasma processes inside this ECRIS chamber were discussed based on these results.     

用于半导体加工的腔耦合－磁多极型ECR源的研究

本实验室研制出一台谐振腔耦合一多极场位形的电子回旋共振（ＥＣＲ）微波等离子体源（ＭＥＰ）。采用朗谬探针和离子能量分析器，测量了ＭＥＰ中Ａｒ等离子体的放电特性。实验结果表明．ＭＥＰ能在很宽的运行参数范围，高效率地产生具有较高密度、较低离子温度和空间电位的大面积均匀等离子体，特别适合于半导体加工应用研究。     

微型电子回旋共振离子推力器离子源结构优化实验研究

微型电子回旋共振(ECR)离子推力器可满足微小航天器空间探测的推进需求. 为此, 本文开展直径20 mm的微型ECR离子源结构优化实验研究. 根据放电室内静磁场和ECR谐振区的分布特点, 研究不同微波耦合输入位置对离子源性能的影响, 结果表明环形天线处在高于ECR谐振强度的强磁场区域时, 微波与等离子体实现无损耦合, 电子共振加热效果显著, 引出离子束流较大. 根据放电室电磁截止特性, 结合微波电场计算, 研究放电容积对离子源性能的影响, 实验表明过长或过短的腔体长度会导致引出离子束流下降甚至等离子体熄灭. 经优化后离子源性能测试表明, 在入射微波功率2.1 W、氩气流量14.9 μg/s下, 可引出离子束流5.4 mA, 气体放电损耗和利用率分别为389 W/A和15%.     

圆筒电极对离子磁电加热的影响

高效的磁电加热不仅能够提高电子回旋共振(ECR)等离子体的离子温度,还能改善离子的径向和轴向分布,促进ECR等离子体在化学气相沉积金刚石膜刻蚀中的应用.将磁电加热系统中的圆环电极改进为圆筒电极,研究了圆筒电极对离子磁电加热的影响,对比了圆筒和圆环电极加热离子的区别.结果表明:在同一阳极偏压下,圆筒比圆环电极更有利于提高离子温度,圆筒电极加热时各径向位置的离子温度升高的幅度较大,其中圆筒电极内部的离子温度径向分布差异较大,而圆筒下游的离子温度径向分布比较均匀;磁电加热对离子密度的影响很小;采用圆筒电极加热时,有利于离子向轴向下游的输运,改善了离子的轴向均匀性.     

14.5GHz紧凑型、低成本、全永磁ECR离子源

A compact 14.5GHz electron cyclotron resonance (ECR) ion source for the production of slow, multiply charged ions has been constructed,with the plasma-confining magnetic field produced exclusively by permanent magnets.Microwave power of up to 175W in the frequency range from 12.75 to 14.SGHz is transmitted from ground potential via a PTFE window into the water-cooled plasma chamber which can be equipped with an aluminum liner.The waveguide coupling system serves also as biased electrode,and two remotely-controlled gas inlet valves connected via an insulating break permit plasma operation in the gas- mixing mode.A triode extraction system sustains ion acceleration voltages between 1kV and 10kV.The ECR ion source is fully computer-controlled and can be remotely operated from any desired location via Ethernet.     

高电荷态ECR离子源

介绍了目前ECR离子源的发展状况和国际上几台典型的ECR离子源.Electron cyclotron resonance (ECR) ion source is the most efficient facility for producing highly charged ions. So far more than 1 emA of O 6+ and 0.02 eμA of U 55+ have been delivered by ECR ion source. In this paper the latest development of ECR ion source is presented and several typical ECR ion sources in the world is introduced.     

电子回旋共振放电电离特性的PIC/MCC模拟

A theoretical and computational model is presented to study the ionization of the argon electron cyclotron resonance(ECR)microwave discharge using a quasi-three-dimensional electromagnetic particle-in- cell plus Monte Carlo collision method.The interaction between the charged particles and microwave fields are described by the electromagnetic mode of particle-in-cell method.The collision processes are treated with Monte Carlo method.The simulation code is the original work.The results of the particle simulation for the ECR discharge of argon gas which include the microscopic features of charged particles and the electromagnetic characteristics of the ECR discharge plasma,and also the transient phenomena have been presented.     

电子回旋共振离子推力器放电室等离子体数值模拟

电子回旋共振离子推力器属于静电型推力器,具有寿命长、比冲高、结构简单、可靠性高等优点,适用于深空探测等长时间空间飞行任务.放电室是一个关键部件,其内部通过电子回旋共振产生等离子体.针对放电室内等离子体流场建立飘移-扩散近似模型,采用迎风格式有限差分法对该模型进行数值求解,得到了放电室内不同时刻的等离子体流场分布及其演化规律.数值模拟结果可以为推力器的设计和实验研究提供有用信息.     

The design and application of electron cyclotron resonancedischarges

During the past ten years electron cyclotron resonance (ECR) plasma-processing technology has matured into a diverse assortment of ECR plasma reactor and plasma source design concepts and has been extensively applied to numerous low-pressure plasma processing applications. This paper reviews the substantial progress made in the design and application of ECR plasma technology in recent years. Five representative ECR reactor/source designs from large-area 450-cm² discharges to compact plasma sources inserted into molecular-beam epitaxy (MBE) machines are described in detail. The performance of these ECR devices is evaluated by computing performance figures of merit from the available experimental data. These calculations are then compared with the behavior as predicted from a global model of the discharge. This comparison suggests that global plasma models can be employed as an approximate method for ECR reactor design. More extensive diagnostics and numerical models that investigate the spatial variation of ion density and ion energy distributions are also presented. Several illustrative ECR plasma-processing applications are discussed. These include submicron etching of silicon, etching of III-V and II-VI electronic and photonic devices, and the epitaxial growth of GaN. The variety and the sophistication of these applications demonstrate that low-pressure high-density ECR plasma processing technology has evolved into a very useful, versatile group of plasma-processing machines     

不同磁路电子回旋共振离子源引出实验

空间推进所用的电子回旋共振离子源(ECRIS)应具有体积小、效率高的特点. 本文研究的ECRIS使用永磁体环产生磁场, 有效减小了体积, 该离子源利用微波在磁场中加热电子, 电子与中性气体发生电离碰撞产生等离子体. 磁场在微波加热电子的过程中起关键作用, 同时影响离子源内等离子体的约束和输运. 通过比较四种磁路结构离子源的离子电流引出特性来研究磁场对10 cm ECRIS性能的影响. 实验发现: 在使用氩气的条件下, 特定结构的离子源可引出160 mA的离子电流, 最高推进剂利用率达60%, 最小放电损耗为120 W·A^-1; 所有离子源均存在多个工作状态, 工作状态在微波功率、气体流量、引出电压变化时会发生突变. 离子源发生状态突变时的微波功率、气体流量的大小与离子源内磁体的位置有关. 通过比较不同离子源的引出离子束流、放电损耗、气体利用率、工作稳定性的差异, 归纳了磁场结构对此种ECRIS引出特性的影响规律, 分析了其中的机理. 实验结果表明: 保持输入微波功率、气体流量、引出电压不变时, 增大共振区的范围、减小共振区到栅极的距离, 离子源能引出更大的离子电流; 减小共振区到微波功率入口、气体入口的距离能降低维持离子源高状态所需的最小微波功率和最小气体流量, 提高气体利用率, 但会导致放电损耗增大. 研究结果有助于深化对此类离子源工作过程的认识, 为其设计和性能优化提供参考.     

Synthesis of carbon nanotubes by ECR plasma-assisted chemical vapor deposition

Carbon nanotubes have been grown using an electron cyclotron resonance (ECR) plasma source at a substrate temperature of 500 °C. Methane has been used as the source gas. A network of carbon nanotubes has been observed in scanning electron microscopy. Transmission electron microscopy revealed that the structure consists of straight, Y-junction and ring-like nanotubes. Further, electron diffraction of the nanotubes confirms a graphite crystal structure. PACS 81.16.He; 68.37.Lp; 68.37.Hk; 85.35.Kt; 75.75.+a     

A computer model of particle balance in ECR ion sources

The investigation of the widespread model of particle balance and energy transport [1–5] for calculating the ion charge state distribution (CSD) in an electron cyclotron resonance (ECR) ion source [6] is given. The modification of this model that makes it possible to describe the confinement and accumulation processes of highly charged ions in ECR plasma for the case of gas mixing is more precisely discussed. The discussion of the new technique for calculating the time confinement of ions and electrons, which is based on the Pastukhov theory [7, 8], is given: calculation of confinement times during two step minimization of special type functionals. The preliminary results obtained with this approach have been compared with available experimental data. The text was submitted by the authors in English.     

Experimental study of the dependence of beam current on injection magnetic field in 6.4 GHz ECR ion source

The ion current from an electron cyclotron resonance (ECR) heavy ion source depends on the confining axial and radial magnetic fields. Some efforts were made by earlier workers to investigate magnetic field scaling on the performance of the ECR source. In order to study the dependence of the ion current on the injection magnetic field in the 6.4 GHz ECR source, we have measured the current by varying the peak injection field and have inferred that the variation of the current is exponential up to our maximum design injection field of 7.5 kG. An attempt has been made to understand this exponential nature on the basis of ion confinement time.     

微波ECR全方位离子注入制备类金刚石碳膜的结构及摩擦学性能研究

利用微波ECR全方位离子注入技术，在单晶硅（100）衬底上制备类金刚石薄膜.分析结果表明，所制备的类金刚石碳膜具有典型的类金刚石结构特征，薄膜均匀、致密，表面粗糙度小，摩擦系数小.其中，薄膜的结构和性能与氢流量比关系密切，随氢流量比的增加，薄膜的沉积速率减小，表面粗糙度降低，且生成sp³键更加趋向于金刚石结构，表面能 更低，从而使摩擦系数大幅降低. 关键词： 全方位离子注入 类金刚石碳膜 拉曼光谱 摩擦磨损     

Energy dispersive X-ray spectroscopy for ECR plasma diagnostics

Electron-ion bremsstrahlung spectra down to 4 keV emitted from plasmas of the 7.25 GHz electron cyclotron resonance (ECR) ion source of the Forschungszentrum Rossendorf and of the 14.5 GHz ECR ion source of the Technische Universität (TU) Dresden were de-convoluted using a newly developed integration method. In the approximation of isotropy in velocity space this method yields the exact electron energy distribution function. The high energetic electrons are clearly separated into two Boltzmann distributed populations. Their densities and temperatures could be estimated. Higher frequencies of the microwave can increase the hot and warm electron densities by orders of magnitude. First results are obtained for the behaviour of this populations belonging to the mixture (argon — oxygen). Gas mixing increases the densities of these populations. The influence of the electron energy distribution function on X-ray line intensities is discussed.     

Organic contaminants removal by oxygen ECR plasma

Recently electron cyclotron resonance (ECR) plasma have been explored for wafer cleaning applications, since it is known to do less damage to silicon surface than conventional plasma. Organic contaminants removal efficiency and plasma radiation damage of the ECR plasma cleaning have been investigated. In oxygen ECR plasma cleaning, the plasma exposure time needed to remove the organic contaminants on the silicon surface down to the detection limit is 40 s, but the one to reach the lowest surface roughness is 10 s. The leakage current level of the MOS capacitor made using the Si substrate exposed to oxygen ECR plasma for 40 s is 8 × 10⁻⁹ A. The optimum exposure time determined by considering the contaminants removal efficiency and the plasma radiation damage (or the leakage current level) is 40 s. Organic contaminants seem to be removed through both sputter-off mechanism by oxygen ion bombardment and evaporation mechanism by chemical reactions with excited oxygen atoms.     

Electron boltzmann kinetic equation averaged over fast electron bouncing and pitch-angle scattering for fast modeling of electron cyclotron resonance discharge

The electron distribution function (EDF) in an electron cyclotron resonance (ECR) discharge is far from Maxwellian. The self-consistent simulation of ECR discharges requires a calculation of the EDF on every magnetic line for various ion density profiles. The straightforward self-consistent simulation of ECR discharges using the Monte Carlo technique for the EDF calculation is very computer time expensive, since the electron and ion time scales are very different. An electron Boltzmann kinetic equation averaged over the fast electron bouncing and pitch-angle scattering was derived in order to develop an effective and operative tool for the fast modeling (FM) of low-pressure ECR discharges. An analytical solution for the EDF in a loss cone was derived. To check the validity of the FM, one-dimensional (in coordinate) and two-dimensional (in velocity) Monte Carlo simulation codes were developed. The validity of the fast modeling method is proved by comparison with the Monte Carlo simulations. The complete system of equations for FM is presented and ready for use in a comprehensive study of ECR discharges. The variations of plasma density and of wall and sheath potentials are analyzed by solving a self-consistent set of equations for the EDF.