脉冲容性耦合放电中电子密度和温度的演化机制研究

发布时间：2018-03-10 15:33

本文选题：脉冲放电　切入点：朗缪尔探针　出处：《清华大学》2015年博士论文　论文类型：学位论文

【摘要】：目前低温等离子体脉冲放电在工业界得到了广泛的应用,尤其是在材料表面处理领域。相比于传统的稳态放电,脉冲放电形式有着众多优势,比如通过调节脉冲频率和占空比可以更灵活地控制不同活性粒子的通量,减少表面电荷沉积以及缓解离子轰击带来的表面损伤等等。由于脉冲放电中不同物理过程发生的时间尺度差异很大,导致关键的放电参数(例如电子密度和温度)有着明显地非线性动态弛豫的演化特征。因此只有采用时间分辨的实验测量和模型分析才能够深入地了解进而操控脉冲放电的物理特性。然而放电暂态过程普遍和放电气压、功率、气体种类、脉冲频率和占空比等等外部控制参数紧密相关,放电物理非常复杂,目前与之相关的报道结果尚有很多不足之处。本论文在不同脉冲容性耦合放电条件下结合测量与模型,探究了电子密度和温度的演化特征并揭示了其中的物理机制。本论文主要内容为:(一)从实验上确认了在余辉早期由容性耦合引起的位移电流对朗缪尔探针测量电子密度的干扰,并建立了从等离子体到探针的等效电路模型对其进行了定量讨论。进一步地,在强容性耦合情形下提出了修正探针数据的方法,修正后的结果能够与其他独立的实验测量结果吻合。(二)建立了能满足较宽实验条件并且同时包含鞘层塌缩和电子-电子散射作用机制的模型,用于描述低气压惰性气体余辉中电子密度和温度的演化,结果与实验测量相吻合。作为比较,前人报道的模型只适用于高密度等离子体情形,并且没有讨论电子密度空间分布位形的影响。(三)在电负性氧气脉冲放电中发现了不同余辉时长下由记忆效应引起的电子密度演化特征,通过建模分析提出了短脉冲情形下由氧分子亚稳态碰撞解吸附和电子碰撞分解吸附主导的电子循环过程,揭示了在余辉晚期氧分子亚稳态和振动激发态对电子超弹性散射导致的电子加热效应。(四)在惰性气体脉冲放电中结合模型和实验讨论了分步电离、射频功率传输、电子温度演化、分子气体掺杂以及离子在放电边界逃逸对功率加载期间电子密度弛豫的影响;在四氟化碳脉冲放电中讨论了带电粒子密度和中性自由基团密度在整个脉冲周期内的演化机制,并总结了氟原子主要的产生和损失过程。
[Abstract]:At present, low temperature plasma pulse discharge has been widely used in industry, especially in the field of material surface treatment. Compared with conventional steady state discharge, pulse discharge has many advantages. For example, the flux of different active particles can be controlled more flexibly by adjusting the pulse frequency and duty cycle. Reduction of surface charge deposition and mitigation of surface damage caused by ion bombardment, etc., because the time scales of different physical processes in pulse discharge vary greatly. The key discharge parameters (such as electron density and temperature) have the characteristic of nonlinear dynamic relaxation. Therefore, only time-resolved experimental measurement and model analysis can deeply understand and manipulate them. The physical properties of pulse discharge. However, the transient process of discharge is widespread and the discharge pressure, The external control parameters such as power, gas type, pulse frequency and duty cycle are closely related, and the discharge physics is very complicated. At present, there are still many shortcomings in the related reports. In this paper, the measurements and models are combined under different pulse capacitive coupling discharge conditions. The evolution characteristics of electron density and temperature are investigated and the physical mechanism of electron density and temperature is revealed. The main content of this thesis is to confirm experimentally the measurement of displacement current induced by capacitive coupling to Langmuir probe in the early afterglow. Interference of electron density, An equivalent circuit model from plasma to probe is established to quantitatively discuss it. Furthermore, a method for correcting probe data is proposed in the case of strong capacitive coupling. The modified results are in agreement with other independent experimental results. (2) A model which can satisfy the wider experimental conditions and include the mechanism of sheath collapse and electron-electron scattering is established. It is used to describe the evolution of electron density and temperature in the afterglow of low pressure inert gas. The results agree well with the experimental measurements. The effect of spatial distribution of electron density on electron density is not discussed. (3) the characteristics of electron density evolution caused by memory effect have been found in electronegative oxygen pulse discharge with different afterglow duration. By modeling and analyzing, an electron cycle process dominated by metastable collision desorption of oxygen molecules and electron collision decomposition adsorption is proposed in the case of short pulses. The electron heating effect caused by electron superelastic scattering caused by metastable and vibrational excited states of oxygen molecules in the late afterglow period is revealed. (4) in the inert gas pulse discharge, the stepwise ionization and radio frequency power transmission are discussed in combination with the model and experiments. The effects of electron temperature evolution, molecular gas doping and ion escape at the discharge boundary on the electron density relaxation during power loading; The evolution mechanism of charged particle density and neutral radical group density over the whole pulse period was discussed in the pulse discharge of carbon tetrafluoride, and the main generation and loss processes of fluorine atoms were summarized.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：O53;O461

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