Control of the electron temperature by varying the resonance zone width in ECR plasma

The electron temperature (T_e) in an electron cyclotron resonance plasma is clarified to depend on the spatial profiles of the microwave-power absorption by both the electromagnetic-waves measurement and the simulation of microwave power absorption. It is found that T_e is controlled by varying the magnetic field configuration and/or the microwave frequency since the power absorption profile is influenced by the effective resonance width. In fact, T_e is observed to decrease with decreasing the magnetic field gradient at the resonance point for N₂, Ar and O₂/Ar plasma.     

Langmuir probe diagnostics of microwave electron cyclotron resonance (ECR) plasma

A Langmuir probe diagnostics is done on the microwave ECR generated plasma in a 2.45 GHz, 1.5 kW facility set up in our laboratory (for thin film deposition) by inserting a probe in the plasma close to substrate location (640 mm away from main ECR zone). A program using Graphical User Interface (GUI) was used for data analysis of I-V probe characteristics to obtain the radial electron energy distribution function (EEDF) in plasma. Plasma parameters such as charged particle density (n_e and n_i), electron temperature (T_e), plasma potential (V_pl) and floating potential (V_float) were estimated at substrate location for two incident microwave power levels at a fixed operating pressure. These parameters were estimated by different methods like orbital motion limited (OML) theory, electron energy distribution function (EEDF) and conventional method. The results obtained by the different methods are compared and observed differences are explained. The results indicate that even though the diffusion of plasma at the substrate location is mainly forced by particle collisions that lead to radial plasma uniformity, it still shows a non-Maxwellian behavior for the electrons with two groups having different energies.     

The effects of the operational parameters of the reactor on ECR plasma characteristics

A two-dimensional axis-symmetric model is adopted to investigate the characteristics of an electron cyclotron resonance plasma. The mass conservation equations of electrons, positive ions, and metastable atoms, the electron energy equation, and the Poisson equation are used in this multi-component system. The magnetic field generated by coils was computed numerically. The distributions of temperature and density of electrons are calculated by the finite difference method. The results of the numerical simulation for argon plasma shows that, in the phase of a long-time discharge, the electron temperature in the resonance chamber is higher than that in the reactor chamber, and electron density in the resonance chamber is lower than that in the reactor chamber. In addition, the effects of pressure on the two distributions are illustrated and discussed.     

Diagnostics of microwave ECR generated plasma: Effect of contaminated reference electrode

Langmuir probe diagnostics is performed on microwave ECR generated plasma that is routinely being used in our laboratory for plasma assisted chemical vapour deposition (CVD) and metal organic chemical vapour deposition (MOCVD) applications. Diagnostics is performed on Argon plasma when the plasma generation chamber was new and also after the prolonged use of this chamber for plasma assisted CVD applications. Clear differences in the values of plasma parameters from the two cases were observed and these differences are explained. The investigations reported here clearly indicate the important role of reference electrode in plasma diagnostics experiments and also suggest that it is very important to have the proper (uncontaminated) reference electrode during plasma diagnostics particularly when measurements are performed in the contaminated chamber.     

Beam plasma discharge at low magnetic field as plasma source for plasma processing reactor

The aims of the research are to study the nature of an effect detected earlier for the formation of ion flows from a beam plasma discharge and to determine possible applications of this effect. These flows propagate in a beam plasma discharge on a normal to the discharge axis. It has been found that the acceleration of ions is a consequence of the potential gradient between an area with a high level of microwave oscillations and a peripheral area of plasma. The results of physical experiments qualitatively correlate with computer simulation data. The analysis of the physical mechanism of the effect has enabled a way of effective control of the flow energy and density to be found. The capability to change the mean energy of the ion flow in the range from 20 up to 70 eV with increase in its density by an order has been demonstrated. A possible application of the effect is a novel plasma processing reactor for treatment of materials used in electronics engineering. In particular, soft etching technology of AlGaAs barrier layers in semiconducting AlGaAs/InGaAs/GaAs heterostructures has been demonstrated.     

Adjustment of electron temperature in ECR microwave plasma

In glow discharge plasma used for processing of materials, the electron temperature affects directly reactive species determining results of plasma processing of materials. In this paper, the experiment results of adjustment of electron temperature (T_e) in an Electron Cyclotron Resonance (ECR) device in H₂ and H₂+CH₄ plasmas are given by two methods. One method to adjust T_e is the grid method, by installing a floated or biased grid in the plasma; the T_e can be increased or decreased. Another method is noble gases doped into the discharge gases; increasing noble gas concentration can decrease T_e in a certain scale. The changes of species in plasma are inspected by the optical emission spectroscope and mass spectroscope when T_e is dropped.     

用于电离层环境模拟器的ECR等离子体源

为了经济地考验空间电离层等离子体对处于其中的飞行器表面的作用,需要在地面建立等离子体环境模拟器。本文就是为空间电离层环境模拟器研制的扩散型极低气压、低电子温度和极低密度的紧凑型电子回旋共振等离子体源的研制。结果显示在等离子体源下游50cm处,在10-2～10-3Pa范围内获得了电子温度低于5eV,密度在104～106cm-3范围内的较为均匀的等离子体束流,基本满足了空间环境模拟实验的需要。     

Thin films deposition with ECR planar plasma source

The results of film deposition of pure tungsten as well as intermetallic compound of NdFeB type on various substrates using planar ECR plasma source (with multipole magnetic field) developed in our laboratory are presented. The frequency of 2.45 GHz was generated within the magnetic system by two-slot antenna. The ions of ECR argon plasma are used for target sputtering. The main plasma parameters are density 10¹⁰ cm⁻³, T_e15 eV, ions energy 20 eV, ion current density 3.5 mA/cm² at the ultimate magnetron power. Under sputtering of Nd₈Fe₈₆B₆ target the amorphous films with high adherence and thickness of 5 μm were formed on the substrate. The deposition rate of tungsten films (target biasing 900 V) was 0.59 nm/s. The fine-grained films with high adhesion were obtained. They were tested against heat loads up to 100 J/cm² produced under irradiation of coatings with plasma streams.     

Development of large diameter ECR plasma source

To develop ECR plasma source for industrial applications, we produced a large diameter ECR plasma and examined radial profiles of the ion saturation current as a function of pressure and power. It was found that ECR plasma uniform over 300 mm is produced for pressures higher than 1 mTorr and the electron temperature decreases with increasing pressures.     

Surface modification of steel surfaces by electron beam excited plasma processing

The nitriding performance of low power electron beam excited plasma is investigated by characterizing the surface of nitrided low alloy Cr-Mo steels. In this research, a particular attention was given to the effect of the acceleration voltage and processing time on the composition and hardness of the processed samples. In an attempt to maximize the dissociation of N₂, the acceleration voltages applied in our experiments were set within a range that corresponds to the maximum dissociation cross-section of N₂. The results show that the peak intensity of the alpha Fe observed for the unprocessed sample decreases as the acceleration voltage increases. Moreover, the peak intensities depicting the formation of the nitride compound layers, Fe₄N and Fe₃N phases, increases with the acceleration voltage of the electron beam. Consequently, the surface hardness of the treated low alloy steel was increased by more than two times that of the unprocessed specimen.     

ECR微波等离子体氮化铁基材料的参数研究

以纯铁和 38CrMoAl为例给出了用电子回旋共振微波等离子体氮化的实验结果 ,并给出了气体成分及配比、时间、温度、偏压等工艺参数对氮化结果的影响。指出在 0 1Pa的工作气压下 ,采用N2 H2混合气体 ,样品温度接近 50 0℃ ,微波功率 2 0 0～ 2 50W ,可在样品表面形成氮化层 ,使样品表面硬度显著提高。改变N2 和H2 比例将改变样品氮化层中ε相和γ′相的比例。样品施加合适的负偏压有利于氮化     

A comparison of nitrous oxide and hydrogen ECR plasma discharges for silicon solar cell passivation

The passivation of crystalline Si solar cells using nitrous oxide (N₂O) electron cyclotron resonance (ECR) plasma discharges has been studied and compared with ECR hydrogen passivation. The cells consisted of ECRCVD grown microcrystalline Si emitter layers on single crystal Si (sc-Si) and multicrystalline Si (mc-Si) substrates, without anti-reflective coatings or surface texturing. For cells on sc-Si substrates, hydrogen passivation is more effective at a substrate temperature of 300 °C and low microwave power (300 W). With increased power (500 W) H₂ is less effective than N₂O due to hydrogen plasma damage leading to a significant fall in the cell fill factor. In comparison with H₂, N₂O discharges lead to a significantly better (by > a factor of 2) improvement in the performance of cells on mc-Si substrates for treatment times of ≤15 min at a passivation temperature of 300 °C and 300 W microwave power. XPS measurements suggest that a surface oxide layer containing N and C atoms is formed by the N₂O plasma which, most likely, reduces the surface state density and, hence, carrier recombination.     

微波电子回旋共振等离子体技术及其应用

微波电子回旋共振等离子体是淀积薄膜、微细加工和材料表面改性的一种重要手段。由于这种等离子体电离水平高,化学活性好,可以用来实现基片上薄膜的室温化学气相淀积和反应离子刻蚀,因此对于微电子学、光电子学和薄膜传感器件的发展,这种等离子体会具有重要的意义。此外,采用微波电子回旋共振等离子体原理,没有灯丝的离子源可以提高离子源的使用寿命,可以增加离子束的束流密度。可以确信,微波电子回旋共振等离子体的发展,将把离子源技术提高到一个新的水平。显然,这必将对材料表面改性工艺,包括离子注入掺杂等工艺的发展发挥作用。自从1985年以来,为了得到大容积等离子体而发展了微波电子回旋共振多磁极等离子体,这些技术在薄膜技术、微细加工以及材料表面改性中的应用前景是乐观的。我们将在本文中,介绍微波电子回旋共振等离子体的原理及其应用。     

Universal plasma electron source

The construction of universal plasma electron sources that allows to generate both focused electron beams and large cross-section beams within stationary and pulse mode of operation is proposed, without any essential change in the construction of the source. The special feature of the source is the stability of electron beam parameters over a wide range of pressure (up to 10⁻² mbar), which makes it possible to use it in difficult vacuum conditions caused by intensive gas emission from the treated surface. High stability of the focused electron beam parameters is achieved due to a special configuration of electric and magnetic fields in the region of electron extraction. Generating large cross-section beams, a weak dependence of beam parameters of gas pressure, is achieved by using the method of double-grid stabilization of the emitting plasma surface. Physical processes causing an increase in parameter stability are discussed.     

Formation and expansion of the plasma column under electron beam-metal interaction

The process of expansion of low-energy electrons and ions produced from electron beam evaporation of a metal target in the technological vacuum chamber of an electron beam welding machine is studied. Analyzing the spatial distribution of the particle density that is measured, the radial collisionless plasma motion from the beam region is shown to be prevailing. A model of the free plasma expansion out of the cylindrical source is developed. The relative distribution of the electron density and the electrostatic potential obtained are compared with the experimental results. The knowledge of the plasma parameter distributions in the technological vacuum chamber can be used for remote diagnostics and control of the technology process.     

Effects of RF bias power on electron energy distribution function and plasma uniformity in inductively coupled argon plasma

Changes in the plasma non-uniformity and the electron energy distribution function (EEDF) by increasing RF bias power were observed in inductively coupled plasma using spatially resolved radial EEDF measurements. As the bias power was increased at a fixed ICP power at a low gas pressure, The EEDF was evolved from a bi-Maxwellian to a Maxwellian distribution. The plasma density was decreased in all radial positions and thus plasma non-uniformity was slightly changed. However, strongly improved plasma spatial non-uniformity was observed at a high gas pressure with a decrease in the center-plasma density and an increase in the radial edge-plasma density. This result could be understood by combined effects of the ion acceleration loss and the non-uniform power deposition due to the RF bias power.     

Electrical properties of diamond-like carbon films grown using ECR plasma decomposition of methane

Diamond-like carbon films were deposited on p-type silicon substrates by ECR-plasma decomposition of methane. The films have been characterized by scanning electron microscopy and Fourier transformed infrared spectroscopy. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics were measured allowing interface trapped charges to be estimated. The density of states near to the Fermi level was calculated from the measurements to be of the order of 10¹⁹ cm⁻³ eV⁻¹.     

Plasma diagnostics in plasma processing for nanotechnology and nanolevel chemistry

The author reviews the role of various plasma diagnostics in plasma processing for nanotechnology, and points out some essential methods of spectroscopic methods to diagnose plasmas for nanoprocessing. Two experimental examples are discussed between the characteristics of nanomaterials and plasma parameters. One is measurement of rotation temperature in processing of carbon nanotube. The other is that of vibrational temperature in surface nitriding of titanium by nitrogen plasma processing. We summarize what to measure and how to measure them from the technical viewpoint of plasma diagnostics.     

Plasma diagnostics in plasma processing for nanotechnology and nanolevel chemistry

The author reviews the role of various plasma diagnostics in plasma processing for nanotechnology, and points out some essential methods of spectroscopic methods to diagnose plasmas for nanoprocessing. Two experimental examples are discussed between the characteristics of nanomaterials and plasma parameters. One is measurement of rotation temperature in processing of carbon nanotube. The other is that of vibrational temperature in surface nitriding of titanium by nitrogen plasma processing. We summarize what to measure and how to measure them from the technical viewpoint of plasma diagnostics.     

Langmuir探针诊断微波ECR非平衡磁控溅射等离子体

利用朗谬尔探针诊断了ECR非平衡磁控溅射等离子体,给出了微观等离子体参量随宏观工艺参量变化关系.实验测得基片架附近等离子体密度达到1010～1011数量级,电子温度在(5～10) eV之间.随溅射靶功率变化,等离子体密度在130W时取得最大值;同样随微波源功率变化,等离子体密度在功率为850W时也达到最大值.电子温度、等离子体空间电位变化与等离子体密度呈相同趋势.