射频感性耦合氢等离子体放电模式转换及回滞的模拟研究

发布时间：2018-06-07 13:05

本文选题：射频感性耦合等离子体 + 模式转换　；参考：《大连理工大学》2016年博士论文

【摘要】：射频感性耦合等离子体(Inductively Coupled Plasma, ICP)源具有放电气压低,等离子体密度高,均匀性易于控制,装置简单,无需外加直流磁场等优点,因此它在半导体工艺和材料处理等领域得到了广泛应用。众所周知,ICP源中存在两种放电模式：容性放电模式(E模式)和感性放电模式(H模式)。当调节外界放电参数(如线圈电流、输入功率、匹配网络中串联电容、放电频率及气压等)时,等离子体放电模式会发生转换,等离子体参数(如等离子体密度、电子温度等)以及放电回路电学参数(如线圈电流、电压以及等效回路阻抗等)会发生突变,往返调节放电参数时,等离子体参数及放电回路电学参数还会出现回滞现象。这种放电模式转换及回滞行为会引起放电的不稳定,对工业过程产生很大影响,因此研究ICP源的模式转换及回滞行为,对控制和优化等离子体工艺具有重要意义。因此,本论文的研究目的是：针对平面线圈型ICP源装置,将二维流体力学模型、等效回路模型、电磁场模型及电子的Monte-Carlo (MC)模型进行耦合,研究射频感性耦合氢等离子体源的模式转换及回滞过程中各等离子体参数以及等效回路电学参数的演化规律,分析放电模式转换及回滞现象的特点及内在机制。在论文第一章中,首先概述了等离子体微细加工工艺,综述了几种典型的低温等离子体源及其放电特点,详细描述了ICP源的装置结构特点、激发原理以及存在的两种放电模式。同时,系统地阐述了ICP源模式转换及回滞的理论和实验研究进展以及依然存在的一些问题。最后给出了本文的研究内容和规划。在第二章中,详细介绍了含有外电路回路的流体模型。该模型是由等离子体的等效回路模块、电磁场模块及流体力学模块耦合而成。等效回路模块包括四部分：射频电流源、匹配网络、容性支路和感性支路,用来计算等效回路的电学参数,如线圈电流、电压和各电路元件阻抗等。电磁场模块是通过求解麦克斯韦方程组来计算ICP源放电腔室内射频电磁场的空间分布。流体力学模块是通过求解流体力学方程组来得到等离子体各宏观状态参数,如粒子密度、电子温度等。此外,本章最后还介绍了模拟中所使用的数值方法。在第三章中,用上述含有外电路回路的流体模型,采用数值模拟的方法系统地研究了射频感性耦合氢等离子体放电模式转换以及回滞行为。首先通过调节匹配网络中的串联电容C1,分析了氢等离子体模式转换过程中电子密度、温度等状态参数以及电磁场空间分布的演化规律。结果表明,随着C1的增加,放电由容性模式主导转换为感性模式主导,等离子体密度突然升高,电子密度最大值由腔室中心处移动到r=6 cm处。同时,电子温度突然降低,并且电子温度分布变化很大；电磁场空间分布随模式转换变化不大,但是幅值发生很大变化,容性电场显著降低,感性电场显著升高。此外,通过往返调节C1,研究了不同气压下外界回路对回滞过程的影响。研究结果表明,气压为100 mTorr时,当增大C1时,放电模式由E模式转换为H模式,当减小C1时,放电模式由H模式转换为E模式,并且E模式转换到H模式时的C1值与H模式转换到E模式时的C1值不同,有明显的回滞环产生。等离子体电学参数,如线圈电流和电压、等离子体电阻和电感等,随着C1的改变也出现明显跳变及回滞现象。当气压为20 mTorr时,往返调节C1,等离子体状态参数和电学参数出现明显的跳变,但是没有回滞产生。最后,固定C1,通过调节输入电流的大小,研究了不同气压下输入电流对模式转换及回滞过程的影响。当输入电流达到一定值时,放电由E模式转换到H模式。减小输入电流时,放电由H模式转换到E模式。与调节C1时相似,当气压比较高时,有明显的回滞现象产生。气压低时,往返调节输入电流没有回滞产生。在第四章中,为了考察ICP源中电子的非局域动力学行为对模式转换及回滞现象的影响,将含有外电路回路的流体模型扩展为流体／电子MC混合模型。在该混合模型中,等离子体的宏观行为由流体力学模型确定,电子与中性粒子的碰撞则由MC方法给出。首先应用该混合模型,研究了不同气压下,电子能量分布函数(Electron Energy Distribution Function, EEDF)随着模式转换的变化。较高气压下,当放电处于E模式时,低能电子较少。H模式下,低能电子增加,高能电子损耗严重。然而在较低气压时,E模式下并没有出现较强的低能电子峰,这是由于氢气是非Ramsauer效应气体,低能电子可以通过碰撞来得到有效加热。并且高气压下,模式转换前后EEDF变化比较明显,而低气压下,EEDF变化较小：其次通过将混合模型与纯流体模型计算结果进行对比,分析了电子的动力学效应对模式转换和回滞的影响。最后通过改变放电气压,研究了气压对模式转换及回滞的影响。结果表明：放电由E模式转换到H模式的临界串联电容值随着气压的升高先减小后增大,在气压为50 mTorr时达到最小值。气压比较低时,没有回滞产生,随着气压的逐渐升高,回滞开始出现,并且回滞环逐渐增大。在第五章中,给出了本文的主要结论、创新点以及对未来工作的展望。
[Abstract]:The Inductively Coupled Plasma (ICP) source has the advantages of low discharge pressure, high plasma density, easy to control uniformity, simple device and no external DC magnetic field. Therefore, it has been widely used in the fields of semiconductor technology and material processing. It is known that there are two kinds of discharge modes in the ICP source. Capacitive discharge mode (E mode) and inductive discharge mode (H mode). When regulating the external discharge parameters (such as coil current, input power, matching network series capacitance, discharge frequency and air pressure, etc.), plasma discharge mode will change, plasma parameters (such as plasma density, electron temperature, etc.), and electrical parameters of discharge circuit. The number (such as the coil current, voltage and equivalent circuit impedance) will change. When the discharge parameters are adjusted, the plasma parameters and electrical parameters of the discharge circuit will still be hysteresis. This type of discharge mode conversion and hysteresis will cause the instability of the discharge and have a great influence on the industrial process. Therefore, the mode conversion of the ICP source will be studied. It is of great significance to control and optimize the plasma process. Therefore, the purpose of this paper is to study the coupling of two-dimensional hydrodynamics model, equivalent loop model, electromagnetic field model and electronic Monte-Carlo (MC) model for a planar coil type ICP source. In the first chapter of the paper, the plasma micro processing technology is summarized, and several typical low-temperature plasma sources and their discharge characteristics are reviewed in detail. This paper describes the structure characteristics of the ICP source, the principle of excitation and the existing two kinds of discharge modes. At the same time, the theoretical and experimental research progress of ICP source mode conversion and hysteresis and some problems still exist. Finally, the contents and plans of this paper are given. In the second chapter, the external circuit circuit is introduced in detail. The model is composed of the equivalent circuit module of plasma, the electromagnetic module and the fluid mechanics module. The equivalent circuit module consists of four parts: the RF current source, the matching network, the capacitive branch and the inductive branch, which are used to calculate the electrical parameters of the equivalent circuit, such as the coil current, voltage and the impedance of each circuit element. The electromagnetic field module calculates the spatial distribution of the radiofrequency electromagnetic field in the ICP source discharge chamber by solving the Maxwell equation group. The fluid mechanics module obtains the macroscopic state parameters of the plasma, such as the particle density and the electron temperature by solving the fluid mechanics equations. In addition, this chapter also introduces the numerical values used in the simulation. In the third chapter, in the third chapter, using the fluid model containing the external circuit circuit, the numerical simulation method is used to systematically study the mode conversion and hysteresis behavior of the RF inductive coupling hydrogen plasma discharge mode. First, the electron density and temperature in the hydrogen plasma mode conversion process are analyzed by adjusting the series capacitance C1 in the matching network. The results show that with the increase of the C1, the discharge is dominated by the capacitive mode, the plasma density rises suddenly and the maximum electron density moves from the center of the chamber to the r=6 cm. At the same time, the electric temperature decreases suddenly, and the electron temperature distribution changes very well. The spatial distribution of the electromagnetic field varies little with the mode transformation, but the amplitude changes greatly, the capacitive electric field is significantly reduced and the inductive electric field is significantly increased. In addition, the effect of the external loop on the hysteresis of the C1 is studied through a round-trip adjustment. The results show that when the pressure is 100 mTorr, the discharge mode is from E when the C1 is increased. The mode is converted to H mode. When the C1 is reduced, the discharge mode is converted from the H mode to the E mode, and the C1 value of the E mode is converted to the H mode when the C1 value is different from the H mode to the E mode, and there is a clear hysteresis loop. The plasma electrical parameters, such as the coil current and voltage, the plasma resistance and inductance, and so on, are also evident with the C1. When the pressure is 20 mTorr, the C1 is adjusted, the plasma state parameters and the electrical parameters are obviously hopping, but there is no hysteresis. Finally, the effect of input current on the mode conversion and hysteresis is studied by adjusting the input current, and the input current is reached when the input current is reached. At a certain value, the discharge is converted from the E mode to the H mode. When the input current is reduced, the discharge is converted from the H mode to the E mode. When the C1 is adjusted, there is a obvious hysteresis when the pressure is higher. When the pressure is low, the return regulation input current is not stagnant. In the fourth chapter, the non local dynamic line of the electron in the ICP source is investigated. In order to influence the mode conversion and hysteresis, the fluid model with external circuit circuit is extended into a fluid / electronic MC mixture model. In the mixed model, the macroscopic behavior of the plasma is determined by the fluid mechanics model and the collision between electrons and neutral particles is given by the MC method. First, the mixed model is applied to study the different pressure. Under the high pressure, the Electron Energy Distribution Function (EEDF) changes with the mode conversion. When the discharge is in the E mode, the low energy electrons are less.H mode, the low energy electrons increase and the high energy electron loss is serious. However, at lower pressure, there is no strong low energy electron peak in E mode. Because hydrogen is a non Ramsauer effect gas, low energy electrons can be effectively heated by collision. And at high pressure, the change of EEDF is obvious before and after the mode conversion, and the change of EEDF is small under low pressure. Secondly, by comparing the mixed model with the results of the pure fluid model, the dynamic effect of the electron is analyzed. In the end, the effect of pressure on the mode conversion and hysteresis is studied by changing the discharge pressure. The results show that the critical series capacitance value of the discharge from E mode to H mode decreases and then increases with the increase of air pressure, and reaches the minimum at the pressure of 50 mTorr. In the fifth chapter, the main conclusions, innovations and prospects for future work are given in the fifth chapter.
【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O53

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