电负性气体的掺入对容性耦合Ar等离子体的影响

本文利用朗缪尔静电探针对掺入了电负性气体O₂, Cl₂, SF₆的由4068 MHz激发的单射频容性耦合Ar等离子体进行了诊断测量. 测量结果表明: 随着电负性气体流量的增加, 电子能量概率分布函数出现了高能峰, 高能峰且有向高能侧漂移的现象; 电负性气体掺入Ar等离子体后显著降低了等离子体的电子密度; 电子温度随着电负性气体流量比的增加而升高. 另外, 本文还测量了掺入三种电负性气体后在不同流量比下的混合气体等离子体的电负度α . 对实验现象进行了初步的解释. 关键词： 电负性等离子体 电子密度 电子温度 电负度     

甚高频激发容性耦合氩等离子体的电子能量分布函数的演变

甚高频激发的容性耦合等离子体由于离子通量和能量的相对独立可控而受到人们的关注. 本文采用朗缪尔探针诊断技术测量了40.68 MHz激发的容性耦合Ar等离子体的特性(如电子能量概率分布、电子温度和密度等)随宏观参量的演变情况. 实验结果表明, 电子能量概率分布随着气压的增加从双麦克斯韦分布逐步转变为单麦克斯韦分布并最终演变为Druyvesteyn分布, 而射频激发功率的增加促进了低能电子布居数的增强; 在从等离子体放电中心移向边界的过程中, 低能电子的布居数显著下降, 而高能电子的布居则有所上升; 放电极板间距的变化直接导致了等离子体中电子加热模式的转变. 另外, 我们也对等离子体中的高低能电子密度和温度的分配情况进行了讨论.     

不同频率驱动下容性耦合Ar等离子体随气压变化的放电特性

讨论了在驱动频率分别为13.56MHz、40.68MHz、94.92MHz和100MHz,功率为40W,气压由3.3～26.6Pa下的容性耦合Ar等离子体的放电特性。利用光谱相对强度法分别诊断了电子激发温度和电子密度。采用粒子模拟和蒙特卡罗碰撞模型(PIC/MCC),模拟了上述实验条件下中心处电子密度和电子能量概率分布(EEPF)。结果表明,在每一个驱动频率下,电子密度均随放电气压的增加而增加,而电子温度则随气压增加而降低。驱动频率为13.56MHz和40.68MHz的电子密度随气压变化趋势几乎一致,而94.92MHz和100MHz的电子温度则随气压变化趋势几乎一致。通过比较EEPF,电子温度随气压的增加有下降的趋势,与光谱诊断结果基本吻合。     

200kV/100kA低抖动环轨式多通道场畸变开关

 研制了一种200kV/100kA环轨式场畸变开关。对该开关以Ar，N₂，SF₆及SF₆/N₂，SF₆/Ar 混合气为工作介质的耐压及触发性能研究结果表明：该开关耐压最大偏差小于自击穿电击的4%；欠压比大于等于自击穿电击80%时，抖动极差小于2ns，标准方差抖动小于等于1ns；实现了多通道导通，通道数大于等于3；开关工作范围极大，在欠压比大于等于自击穿电击20%时抖动极差小于2.85ns。     

射频容性耦合Ar/O_2等离子体的轴向诊断

实验通过朗缪尔探针辅助激光诱导解离技术对27.12 MHz驱动的不同含氧量条件下容性耦合Ar等离子体进行了诊断研究.通过质量流量计改变通入Ar与O_2的流量以得到不同含氧量的等离子体.结果表明,由于氧气的分解吸附反应需要消耗电子,致使朗缪尔探针测得的电子能量概率函数(EEPF)的中能部分随着含氧量的上升而下降.射频输入功率增加时电子密度的上升引起了电子-电子碰撞热化,从而使EEPF由Druyvesteyn分布向麦克斯韦分布转变.在功率电极附近,由于鞘层边界附近的电子氧气分子碰撞时的分解吸附反应使得鞘层区附近的负离子密度较高.另外,负离子密度沿着轴向呈现勺型分布的特征.这主要是由于负离子在双极电场作用下向等离子体放电中心扩散的过程中所存在的负离子产生与损失的反应过程导致.     

±100 kV气体轨道开关击穿特性

 研制了一种用于快Marx发生器的三电极场畸变结构的气体轨道开关,针对3种不同的绝缘介质N₂、干燥空气和SF₆/Ar混合气体开展了轨道开关的自击穿特性和触发特性研究。结果表明:轨道开关的自击穿电压与气压基本呈现线性关系,并且在相同实验条件下,相对于N₂和干燥空气,当绝缘介质为SF₆/Ar混合气体时,轨道开关具有工作电压范围宽、工作系数低、触发击穿延时短、抖动小的优点。采用数码相机拍摄了开关导通过程中形成的放电通道积分图像,初步研究了绝缘介质、电流大小等因素对开关形成多通道的影响。结果表明:提高触发电压、充电电压和放电电流及采用SF₆/Ar混合气体均能够有效增加放电通道数目。     

60MHz电容耦合等离子体中电子能量分布函数特性研究

甚高频(频率大于30 MHz)耦合放电源由于能产生大面积高密度的等离子体而受到了人们的广泛关注. 采用电流、电压探针以及朗缪尔探针诊断技术对60MHz射频激发产生的容性耦合等离子体的放电特性及电子行为进行了研究. 实验结果表明,等离子体的等效电阻/电容随着射频输入功率的增加而减小/增加;等离子体中电子行为不仅依赖于射频输入功率,还与放电气压密切相关;放电气压的增加导致电子能量概率分布函数(EEPF)从双温Maxwellian分布向Druyvesteyn分布转变,而且转变气压远低于文献所报道的数值,这主要是由于在60MHz容性耦合等离子体中电子反弹共振加热效率大为降低. 关键词： 甚高频容性耦合等离子体 朗缪尔探针诊断 电子加热模式     

SF6-N2混合气激光触发延迟抖动特性研究

 研究了SF₆-N₂混合气在四倍频Nd:YAG激光脉冲作用下的触发特性。实验结果表明：充SF₆-N₂混合气的火花隙的触发延迟和抖动、最低可触发阈值随充气压力及混合气中SF₆含量上升而上升，随激光波长减小而减小，火花隙的触发延迟和抖动随焦距的减小而减小。由于SF₆-N₂混合气的介电强度、触发延迟和抖动与混合气中SF₆含量之间均存在非线性关系，作为开关工作介质，SF₆-N₂混合气的综合性能较好的SF₆含量范围是5%～45%。     

激光触发SF6-N2混合气体开关的数值模拟

 在气体放电物理的基础上，对SF₆和N₂采用双光子电离模型，对碳氢化合物的光电离采用3能级模型，并考虑了混合气体的热电离和激光对气体的欧姆加热作用，建立了激光触发SF₆-N₂混合气体开关的数值模型，模拟了激光触发SF6-N2混合气体多级间隙开关实验。激光触发延迟时间的计算值与实验结果符合较好。理论计算表明：激光触发SF₆-N₂混合气体间隙开关的延迟时间随SF₆含量的增加呈上升趋势，而随激光脉冲能量、充气压力等的上升呈下降趋势。     

“无水”NiCo2O4纳米棒在电化学无酶葡萄糖传感中的应用

本文介绍了棒状NiCo₂O₄的制备,并将其修饰玻碳电极作为无酶葡萄糖传感器. 通过简单的水热反应合成了NiCo₂O₄,然后在商用微波炉中对NiCo₂O₄进行处理,以消除水热合成过程中可能引入的残存水. 扫描电镜、透射电镜、X射线衍射谱和X射线光电子能谱分析表明,微波处理前后结构无变化. 通过EDS对Ni,Co,O原子比例的分析,证明微波处理对残存水的消除作用. 微波处理的NiCo₂O₄(M-NiCo₂O₄)作为葡萄糖传感器的灵敏度高达431.29 μA mM^-1 cm^-2. 最后,将M-NiCo₂O₄在水中浸泡不同时间后,其对葡萄糖的感应性能下降. 结果表明,水热过程中引入的残存水对其电化学性能有很强的影响,微波预处理对其电化学性能也有着重要的影响.     

Discharge characteristic of very high frequency capacitively coupled argon plasma

The discharge characteristics of capacitively coupled argon plasmas driven by very high frequency discharge are studied. The mean electron temperature and electron density are calculated by using the Ar spectral lines at different values of power(20 W–70 W) and four different frequencies(13.56 MHz, 40.68 MHz, 94.92 MHz, and 100 MHz). The mean electron temperature decreases with the increase of power at a fixed frequency. The mean electron temperature varies nonlinearly with frequency increasing at constant power. At 40.68 MHz, the mean electron temperature is the largest. The electron density increases with the increase of power at a fixed frequency. In the cases of driving frequencies of 94.92 MHz and 100 MHz, the obtained electron temperatures are almost the same, so are the electron densities. Particle-in-cell/MonteCarlo collision(PIC/MCC) method developed within the Vsim 8.0 simulation package is used to simulate the electron density, the potential distribution, and the electron energy probability function(EEPF) under the experimental condition.The sheath width increases with the power increasing. The EEPF of 13.56 MHz and 40.68 MHz are both bi-Maxwellian with a large population of low-energy electrons. The EEPF of 94.92 MHz and 100 MHz are almost the same and both are nearly Maxwellian.     

Experimental study on parameters of dust plasma in SiH4/C2H4/Ar discharges

Measurements of dust plasma parameters were carried out in the discharges of （SiH4/C2H4/Ar） mixtures. Dust particles were formed in the capacitively coupled radio-frequency discharge of these reactive mixtures in a cylindrical chamber. Langmuir probe was employed for diagnosing and measuring the important plasma parameters such as electron density and electron temperature. The results showed that the electron density dropped, and in contrast the electron temperature rose when the dust particles formed. The curves of the electron density and temperature versus the RF power and pressure were presented and analysed. Further, it was found that the wriations of electron temperature and the size of dust void with the RF power followed the similar trends. These trends might be useful for understanding more about the characteristics of dusty voids.     

Review of relaxation oscillations in plasma processing discharges

Relaxation oscillations due to plasma instabilities at frequencies ranging from a few Hz to tens of kHz have been observed in various types of plasma processing discharges. Relaxation oscillations have been observed in electropositive capacitive discharges between a powered anode and a metallic chamber whose periphery is grounded through a slot with dielectric spacers. The oscillations of time-varying optical emission from the main discharge chamber show, for example, a high-frequency (\sim 40~kHz) relaxation oscillation at 13.33Pa, with an absorbed power being nearly the peripheral breakdown power, and a low-frequency ( \sim 3 Hz) oscillation, with an even higher absorbed power. The high-frequency oscillation is found to ignite plasma in the slot, but usually not in the peripheral chamber. The kilohertz oscillations are modelled using an electromagnetic model of the slot impedance, coupled to a circuit analysis of the system including the matching network. The model results are in general agreement with the experimental observations, and indicate a variety of behaviours dependent on the matching conditions. In low-pressure inductive discharges, oscillations appear in the transition between low-density capacitively driven and high-density inductively driven discharges when attaching gases such as SF₆ and Ar/SF₆ mixtures are used. Oscillations of charged particles, plasma potential, and light, at frequencies ranging from a few Hz to tens of kHz, are seen for gas pressures between 0.133 Pa and 13.33 Pa and discharge powers in a range of 75--1200 W. The region of instability increases as the plasma becomes more electronegative, and the frequency of plasma oscillation increases as the power, pressure, and gas flow rate increase. A volume-averaged (global) model of the kilohertz instability has been developed; the results obtained from the model agree well with the experimental observations.     

Deposition and Etching of Thin Films by Means of Beam Plasma Discharge with Tube-Like Electron Beam

The efficiency of energy dissipation caused by the mechanism of turbulent plasma heating from a tube-like electron beam in a electronegative gas is measured calorimetrically. Amorphous Si-layers are deposited from a SiH₄/Ar discharge both on conducting and nonconducting substrates and are analyzed by means of Auger-spectrometry. The velocity and specific energy of etching of SiO₂-layers in a CF₄-plasma are determined. Measured etching velocities of tungsten surfaces biased differently against the space potential provide information on the mechanism of plasma etching in a SF₆-plasma. Simultaneously performed Langmuir-probe measurements permit predictions to be made on the properties of the etching plasma.     

脉冲射频容性耦合氩等离子体的发射探针诊断

利用工作在浮点模式下的发射探针,对500 Hz脉冲调制的27.12 MHz容性耦合氩气等离子体的空间电位和电子温度的时变特性进行了诊断.等离子体空间电位是通过测量强热状态下的发射探针电位获得的,而电子温度则是由发射探针在冷、热状态下的电位差来估算得到.测量结果表明:脉冲开启时,空间电位会快速上升并在300μs内趋于饱和;当脉冲关断后,空间电位经历了快速下降后趋于稳定的过程.电子温度在脉冲开启时存在过冲并趋于稳定的特征;而在脉冲关断期间,电子温度在300μs内则快速下降到0.45 e V后略有上升.无论在脉冲开启或关断期间,空间电位基本上都随功率和气压的变化存在有线性的依赖关系;而放电功率对脉冲开启期间过冲电子温度与稳态电子温度差异的影响较大.针对空间电位和电子温度在各阶段及不同放电条件下的时变特性,给出了相应的解释.     

Characterization of electronegative plasmas

The characterization of the plasma state is of great interest in industrial applications based on plasma enhanced chemical vapour deposition (CVD) processes. We have performed experiments on a capacitively coupled radio frequency discharges in air and SF₆. The use of gases containing electronegative components, such as oxygen or fluorine, leads to quite peculiar discharges, due to the presence of negative ions which affects the transport properties of such a plasma. Plasma parameters have been measured by means of movable electrostatic Langmuir probes. The implementation of a suitable numerical model of gas-phase chemistry and transport phenomena allow us to predict the amount of negative ions. In particular we show that the ion to electron density ratio strongly depends on the diffusion process and on ion recombination rates. Thus measuring it leads to a better understanding of ion diffusion and in particular of the ambipolar electric field.     

Measurements of plasma parameters in capacitively coupled radio frequency plasma from discharge characteristics: Correlation with optical emission spectroscopy

Plasma parameters from the discharge characteristics of a 13.56 MHz capacitively coupled radio frequency Ar plasma are evaluated on the basis of homogeneous discharge model for wide range of operating pressure. The homogeneous discharge model of capacitively coupled radio frequency discharge is modified to take into account the nonlinear plasma series resonance effect. The effect of drift velocity of the electron due to change in radio frequency electric field and operating pressure is also considered. Considerable dependent of plasma parameters on the drift velocity of the electron as well as on the plasma series resonance effect are observed in low pressure. An irregular variation of calculated plasma density with operating pressure is observed, which is reconfirmed with optical emission spectroscopy.     

13.56 MHz 低频功率对60 MHz射频容性耦合等离子体的电特性的影响

使用补偿朗缪尔探针诊断技术,研究了60MHz/13.56MHz双频激发容性耦合等离子体的空间电子行为,得到了电子能量概率函数(EEPF)随径向位置和低频输入功率的演变行为. 实验结果表明,13.56MHz射频输入功率的变化主要影响低能电子的布居,其影响随气压升高而加大. 在等离子体放电中心以外,EEPF呈现出双峰分布的特性,同时发现从放电中心到极板边缘,次能峰有逐渐向高能区漂移的现象,次能峰的出现显示了中能电子的增强的加热效应. 通过EEPF方法,计算了等离子体的电子温度、电子密度. 讨论了等离子体中的电 关键词： 双频激发容性耦合等离子体 朗缪尔探针诊断 电子加热模式