【作者】 蒋相站；

【导师】 王友年； 陆文琪；

【作者基本信息】 大连理工大学 ， 等离子体物理， 2011， 博士

【摘要】 双频容性耦合等离子体源(DF-CCP)是最近几年发展起来的一种新型的等离子体源,它通过采用一个高频源和一个低频源来共同激发等离子体,可以实现等离子体密度和离子能量的单独控制,能够获得很好的刻蚀速率和均匀性。DF-CCP可以产生大面积较均匀的高密度等离子体,其实验装置结构简单,操作容易,符合半导体工业生产的需求,因此这种等离子体源得到了广泛的应用。在介质刻蚀方面,它目前正逐步取代其它效率较低的等离子体源。然而在实际应用中,这种双频容性耦合等离子体的均匀性、双频电源的解耦和用于刻蚀的离子的能量分布受到了各种放电参数的影响,使得其应用受到了一定的局限,因此,有必要对该等离子体的物理特性进行深入系统的研究。由于这种双频放电中存在着很强的高次谐波干扰,直接对其电学参数进行实验诊断是比较困难的。具体来说,实验诊断面临的问题是怎样实现在不影响等离子体放电的情况下对其进行原位诊断,获得等离子体密度、电子温度、电子能量分布函数和离子能量分布等有价值的数据信息。基于此目的,本论文采用自主研制的全悬浮双探针诊断系统,实现了对DF-CCP等离子体密度和电子温度的空间测量；系统研究了双频电源在不同放电参数下的耦合效应。最后,利用具有能量分辨能力的四极杆质谱测量系统对Ar/O2混合气体放电展开了研究,获得了不同放电条件下的离子能量分布和平均能量。论文的前三章分别是绪论、实验诊断方法和实验装置的介绍；后三章是本论文的主要研究结果,第四章研究的是双频容性耦合等离子体的空间均匀性,并且给出了部分实验结果和二维流体模拟的比较,第五章研究了双频电源的耦合效应,第六章研究了Ar/O2混合气体放电的离子能量和平均能量分布。第一章绪论介绍了低温等离子体在微电子工业中的应用,分析比较了几种常见的等离子体源,阐述了本论文所采用的双频容性耦合等离子体源的特性,对DF-CCP的理论和实验研究进展做了详细的综述,指出了研究中存在的问题,给出了本文的研究内容和安排。第二章,较详细地介绍了等离子体实验诊断经常采用的几种诊断方法的原理,包括单探针和双探针法、质谱法以及发射和吸收光谱法。第三章,介绍了我们的实验装置,包括DF-CCP放电装置、全悬浮双探针诊断系统及四极杆质谱诊断系统。第四章,利用自主研制的全悬浮双探针,在不同放电参数下对等离子体密度及电子温度的径向及轴向分布进行了系统的研究。研究结果表明：气压、低频功率、放电间距和低频频率对等离子体密度的径向均匀性影响较大,而高频电源的功率对其影响不大；选择合适的放电参数,可以获得径向均匀性较好的等离子体。电子温度与等离子体密度的变化趋势大体相反。等离子体密度的轴向分布显示,随着气压的升高,从驱动电极到地电极呈现出由对称抛物线分布向非对称抛物线分布的变化,最大值逐渐偏向驱动电极处。气压升高,电离源逐渐偏向驱动电极处,而且放电电极的不对称造成电极附近的鞘层厚度不对称,从而导致等离子体密度轴向分布的不对称。高频功率的增加能够提高等离子体密度,而低频功率增加可以使等离子体密度降低。电子温度受轴向位置的影响较小,变化平稳。对这种放电等离子体进行了二维流体模拟,结果表明实验结果和流体模拟结果变化趋势基本一致,两者符合得较好。第五章,利用全悬浮双探针诊断系统研究了DF-CCP高低频电源的耦合效应。通过对腔室中心点的等离子体密度和电子温度的测量,分析了放电间距、气压和高低频频率组合等对耦合效应的影响。研究结果表明,高低频电源具有较强的耦合效应,实现完全解耦是比较困难的。增加低频功率,在较低的高频功率下,等离子体放电类似于单频放电,低频功率的加入对等离子体放电起促进作用,密度逐渐增加；而当高频功率较大时,鞘层扩展,主等离子体区域减小,等离子体密度逐渐降低,电子温度逐渐升高。在较小的放电间距下,等离子体密度随低频功率的增大而降低,电极间距较大时,二次电子发射起了很重要的作用,增加低频功率,等离子体密度增大。气压较低时,增加低频功率,等离子体密度变化不大,较容易实现解耦；而随着气压的升高,电子碰撞加剧,欧姆加热效率升高,随着低频功率增加,等离子体密度也呈现出增大的趋势,相同高低频功率下的等离子体密度随着气压的升高而降低。低频频率较小时,等离子体密度变化幅度小,较容易实现解耦。第六章,利用四极杆质谱仪研究了Ar/O2混合气体放电的离子能量分布和平均能量的影响因素,质谱仪收集的离子穿过鞘层由下电极直接进入质谱小孔,属于原位诊断。研究了低频功率、放电气压、低频频率和氧气的含量对Ar+离子和O2+离子的影响。研究结果表明,增加低频功率,鞘层电势增加,离子穿过鞘层获得更高的能量,Ar+离子和O2+离子的能量逐渐增大,高能峰向高能区移动,能量宽度加大。Ar+离子由于共振电荷交换反应损失掉较多的能量,不同的低频功率下,其平均能量均低于O2+离子。气压升高时,Ar+离子在穿越鞘层过程中的碰撞次数较多,其双峰结构越来越不明显,高能峰逐渐消失,低能区离子越来越多,而O2+离子的碰撞截面较小,其碰撞效应不明显,能量分布受气压的影响不大。增加低频频率,离子能量逐渐由中频机制向高频机制变化,Ar+离子和O2+离子的能量分布的宽度都减小,双峰结构逐渐变得不明显。增大氧气含量,电离率增大,Ar+离子和O2+离子的高低能峰均向高能区移动,最大能量值逐渐右移。同等条件下的Ar+离子的平均能量均低于O2+离子。更多还原

【Abstract】 Dual-frequency capacitively coupled plasma (DF-CCP) source is becoming a new type plasma source in recent years. The plasma is drived by the higher frequency (HF) and the lower frequency (LF) power supply, so the separate control of plasma density and ion energy can be realized in a DF-CCP. The higher etching rate and uniformity can be obtained. DF-CCP can produce uniform plasma in large area. The device operates easily, has a simple structure and lower cost, thus it meets the requirements of the semiconductor industrial production. This plasma source has been widely used, is gradually replacing other less efficient plasma source in dielectric etching. In practice, its uniformity, frequency decoupling and the ion energy distribution for etching are modulated by various discharge parameters. The limitation of DF-CCP has been made, therefore, it is necessary to do an in-depth investigation.It is difficult to do the direct experimental measurement in DF-CCP because of the strong harmonic interference. Specifically, the problem of experimental diagnosis is how to achieve original diagnosis and can not disturb the plasma discharge, obtain the plasma density, electron temperature, electron energy distribution function and ion energy distribution and other valuable data. For this purpose, a newly developed complete floating double probe diagnostic system is used to measure the space plasma density and electron temperature. The coupling effect of dual frequency sources at different discharge parameters is researched. Finally, we research the Ar/O2 mixed gas discharge through the quadrupole mass spectrometry system. The ion energy distribution and average energy are obtained under different discharge conditions. The first three chapters are the introduction, experimental diagnostic methods and experimental setup description. The last three chapters are the main findings. Chapter 4 is the investigation of the spatial uniformity of dual-frequency capacitively coupled plasma, and some of the experimental results are compared with two-dimensional fluid simulation results. Chapter 5 is the investigation of coupling effect in the dual frequency sources, In Chapter 6, we investigate the ion energy distribution and average energy of the Ar/O2 mixed gas discharge.In the first chapter of the introduction, we introduce the low temperature plasma application in microelectronics industry, analyze and compare several common plasma sources, describe the DF-CCP source in detail, review the theoretical and experimental research progess in detail, point out the problems in investigation. Finally, we introduce the investigation contents and arrangement in this thesis. In Chapter 2, we introduce the principle of the common experimental diagnostic methods in detail, including the single probe and double probe method, mass spectrometry, optical emission spectrometry (OES) and absorption spectrometry (AS). Chapter 3 describes our experimental setup, including the DF-CCP discharge device, the newly developed complete floating double probe diagnostic system and quadrupole mass spectrometry diagnostic system.In Chapter 4, the plasma density and electron temperature of the radial and axial distributions at different discharge parameters are investigated using the newly developed complete floating double probe diagnostic system. The results show that pressure, low-frequency power and electrode spacing can influence the radial uniformity obviously, high-frequency power has little effect. If select the appropriate discharge parameters, we can get a good radial uniformity. Electron temperature and plasma density generally have the opposite trend. The axial distribution from the drive electrode to ground electrode displays that the plasma density shows from symmetric to asymmetric parabolic distribution when pressure increases, the maximum biases to the drived electrode. As the pressure increases, ionization source tends to the drived electrode gradually and asymmetric discharge electrodes cause sheath thickness near the electrode becoming asymmetry, resulting in asymmetric axial distribution of plasma density. Increasing high-frequency power can improve the axial plasma density, and low frequency power increase can cause the axial plasma density decreases. Electron temperature has less affected in the axial position, changes smoothly. Two-dimensional fluid simulation is done to this plasma discharge. The results show that experiment and fluid simulation results are consistent.In Chapter 5, we investigate the coupling effect of dual frequency sources using the newly developed complete floating double probe diagnostic system. We analyze the mechanism of the coupling effect by measuring the plasma density and electron temperature in the center of the discharge space. The electrode spacing, pressure and high and low frequency combination have contribution to the coupling effect. The results show that, high and low frequency sources have a strong coupling effect; it is difficult to achieve complete decoupling. Increase the low frequency power, when high frequency power is lower, the plasma diacharge is similar to single-frequency discharge, plasma density will gradually increase; as high frequency power become higher, sheath expansion, the main plasma region decreases, plasma density gradually reduces, but the electron temperature gradually increases. In the small space discharge, the plasma density decreases with the low-frequency power increases. When electrode spacing is large, low-frequency power increase, the secondary electron emission plays an important role, which leads to plasma density increase. When pressure is lower, the plasma density changes little with the low-frequency power increase, it is easier to achieve decoupling, as pressure is high, electron impact becomes intense, ohmic heating efficiency increases, the plasma density also increases, but decreases with increasing pressure under the same high-frequency power. When high and low frequency combination is large, plasma density has a little change, it is easier to achieve decoupling.In Chapter 6, the ion energy distribution and average energy of Ar/O2 mixed gas discharge are investigated using quadrupole mass spectrometer. The diagnostics is in situ because ions enter the mass spectrometer hole directly through the sheath under the low electrode. The low-frequency power, pressure, low-frequency frequency and oxygen content can influence Ar+ and O2+ ions. The results show that when low-frequency power increases, potential increases in the sheath, the ions obtain higher energy through the sheath, the energy of Ar+ and O2+ ions increases, high energy peak moves to high energy area, the energy width increases. More energy of Ar+ ions is lost because of resonant charge exchange reaction, the average energy of Ar+ ions is lower than O2+ ions in different low-frequency power. When pressure rises, collisions of Ar+ ions are more in the process of crossing the sheath, the bimodal structure becomes vaguely, and disappears gradually, but low energy ions are more and more. The influence of pressure to O2+ ions is not obvious because of the smaller ion collision cross section. When low-frequency frequency increases, the ion energy changes from middle-frequency to high-frequency mechanism, the energy width of Ar+ and O2+ ions decrease, bimodal structure becomes vaguely. The oxygen content increases, ionization rate increases, high energy peaks of Ar+ and O2+ ions move to high energy area, the maximum energy value gradually shifts to high energy area. The average energy of Ar+ ions is lower than the O2+ ions under the same condition.更多还原