带有射频偏压源的感性耦合Ar/O_(2)/Cl_(2)等离子体放电的混合模拟研究

在刻蚀工艺中,通常会在感性耦合等离子体源的下极板上施加偏压源,以实现对离子能量和离子通量的独立调控.本文采用整体模型双向耦合一维流体鞘层模型,在Ar/O_(2)/Cl_(2)放电中,研究了偏压幅值和频率对等离子体特性及离子能量角度分布的影响.研究结果表明:当偏压频率为2.26 MHz时,随着偏压的增加,除了Cl^(–)离子和ClO^(+)离子的密度先增加后降低最后再增加外,其余带电粒子、O原子和Cl原子的密度都是先增加后基本保持不变最后再增加.当偏压频率为13.56和27.12 MHz时,除了Cl^(–)离子和Cl^(+)_(2)离子外,其余粒子密度随偏压的演化趋势与低频结果相似.随着偏压频率的提高,在低偏压范围内(<200 V),由于偏压源对等离子体加热显著增加,导致了带电粒子、O原子和Cl原子的密度增加;而在高偏压范围内(>300 V),由于偏压源对等离子体加热先减弱后增强,导致除了Cl^(+)_(2)离子和Cl^(–)离子外,其余带电粒子、O原子和Cl原子的密度都是先下降后增加的.此外,随着偏压频率的增加,离子能量分布中的高能峰和低能峰彼此靠近,离子能峰间距变窄,并最终变成单峰结构.本文的结论对于优化等离子体刻蚀工艺具有重要意义.

大面积矩形感性耦合等离子体源的三维流体力学模拟

利用自主开发的三维流体力学模型程序,对面向平板显示工艺和光伏工艺的大面积矩形感性耦合氩等离子体源进行了数值模拟.该模型自洽地求解了带电粒子以及中性粒子的流体方程和感应电场的波动方程.利用此模型,研究了气压、功率以及线圈形状对各种等离子体参数的三维空间分布和均匀性的影响.研究结果表明,当放电气压较低时(4 mTorr),电子密度的空间分布比较均匀,且电子密度的最大值出现在腔室的中心区域.感性沉积功率密度、激发态氩原子密度以及电子温度的最大值出现在线圈的下方.随着放电功率的增加,即从1000 W增加到4000 W,电子密度显著提高,但电子密度的空间分布变化不大.随着放电气压的升高,电子密度的均匀性明显下降,即电子密度的最大值主要局域在线圈下方.这是因为在较高的气压下,带电粒子与背景气体的碰撞增加,因此使得带电粒子的密度分布变得局域.此外,文章还研究了不同的线圈结构对于等离子体均匀性的影响.结果表明当气压较高(20 mTorr)时,使用3×3阵列线圈产生的等离子体的均匀性优于盘香型线圈,即通过改变线圈结构可以实现对等离子体均匀性的调控.文章的研究成果有助于加深对大面积矩形感性耦合等离子体放电特性的认知,这对于优化平板显示工艺以及光伏工艺至关重要.

3D fluid model analysis on the generation of negative hydrogen ions for negative ion source of NBI

A radio-frequency(RF) inductively coupled negative hydrogen ion source(NHIS) has been adopted in the China Fusion Engineering Test Reactor(CFETR) to generate negative hydrogen ions.By incorporating the level-lumping method into a three-dimensional fluid model,the volume production and transportation of H^(-) in the NHIS,which consists of a cylindrical driver region and a rectangular expansion chamber,are investigated self-consistently at a large input power(40 k W) and different pressures(0.3–2.0 Pa).The results indicate that with the increase of pressure,the H^(-) density at the bottom of the expansion region first increases and then decreases.In addition,the effect of the magnetic filter is examined.It is noteworthy that a significant increase in the H^(-) density is observed when the magnetic filter is introduced.As the permanent magnets move towards the driver region,the H^(-) density decreases monotonically and the asymmetry is enhanced.This study contributes to the understanding of H-distribution under various conditions and facilitates the optimization of volume production of negative hydrogen ions in the NHIS.

A fast hybrid simulation approach of ion energy and angular distributions in biased inductively coupled Ar plasmas

In this work,a two-dimensional hybrid model,which consists of a bulk fluid module,a sheath module and an ion Monte-Carlo module,is developed to investigate the modulation of ion energy and angular distributions at different radial positions in a biased argon inductively coupled plasma.The results indicate that when the bias voltage amplitude increases or the bias frequency decreases,the ion energy peak separation width becomes wider.Besides,the widths of the ion energy peaks at the edge of the substrate are smaller than those at the center due to the lower plasma density there,indicating the nonuniformity of the ion energy distribution function(IEDF)along the radial direction.As the pressure increases from 1 to 10 Pa,the discrepancy of the IEDFs at different radial positions becomes more obvious,i.e.the IEDF at the radial edge is characterized by multiple low energy peaks.When a dual frequency bias source is applied,the IEDF exhibits three or four peaks,and it could be modulated efficiently by the relative phase between the two bias frequencies.The results obtained in this work could help to improve the radial uniformity of the IEDF and thus the etching process.

低气压感性耦合等离子体源模拟研究进展

感性耦合等离子体源具有放电气压低、等离子体密度高、装置结构简单等优点,因此常被用于材料刻蚀及表面处理工艺中.为了深入了解感性耦合等离子体的特性及其与表面的相互作用,数值模拟成为了目前人们普遍采用的研究手段之一.针对具体问题,可以选择不同的模拟方法,如整体模型、流体力学模型、流体力学/蒙特卡罗碰撞混合模型、偏压鞘层模型、粒子模拟/蒙特卡罗碰撞混合模型等.其中,整体模型计算效率最高,常被用于模拟复杂的反应性气体放电.但整体模型无法给出各物理量的空间分布,因此二维及三维的流体力学模型,也得到了人们的广泛关注.在低气压等极端的放电条件下,由于电子能量分布函数显著偏离麦氏分布,则需要耦合蒙特卡罗碰撞模型,来精确地描述等离子体内部的动理学行为.此外,通过耦合偏压鞘层模型,还可以自洽地模拟鞘层的瞬时振荡行为对等离子体特性的影响.对于等离子体中的非局域及非热平衡现象,则需要采用基于第一性原理的粒子模拟方法来描述.最后对目前感性耦合放电中的前沿问题进行了展望.

常压等离子体对柔性多孔材料表面处理均匀性的研究进展

柔性多孔材料在当今众多前沿科学与技术领域发挥着重要作用,其表面改性将进一步赋予其多样和优异的表面性能,拓展其在功能和智能可穿戴等领域的应用.常压等离子体技术由于低温、低能耗、高效、环保、低成本、不改变材料本体特性、易于实现卷对卷制备等优势,在应用环境、样品材料选择上展现出良好的适应性,在低熔点柔性材料大面积低成本表面处理方面具有很好的应用前景和研究价值.本文综述了近年来常压等离子体柔性多孔材料表面改性的几个实例及在新材料、新能源、环保、生物医学中的应用.探讨了柔性多孔材料常压等离子体均匀处理所遇到的稳定性及渗透性的问题与挑战.综述了本课题组在常压等离子体稳定放电、卷对卷常压等离子体多孔介质处理及内部渗透性和均匀性方面的研究工作,介绍了本课题组在常压等离子体纳米颗粒膜沉积动力学及膜结构调控方面的突破和思路.常压等离子体柔性多孔介质表面处理技术走向应用仍然存在诸多挑战,需要结合常压等离子体的放电方式及特性、处理材料的结构及加工特性、等离子体和材料的相互作用等来进行综合考虑,才能提供合理可行的解决方案.

刺络、拔罐治疗咳喘30例

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如何对大班幼儿进行区域活动指导

改革开放以来,教育行业不断深化和发展,在幼儿园教育改革中,幼儿的自主学习能力提高与培养成为人们关注的重点,在幼儿园教学中,区域活动的教学模式渐渐替代教学中的集体模式。本文以幼儿园区域活动中的指导教学为中心,理论联系实际,探讨教师们在此模式下,如何对幼儿进行有效指导。

基于球形网格划分的二值化点云特征描述子

针对现有大部分三维特征描述子应用于低成本传感器获取的低质量点云数据时,在抗噪性、时间效率和内存占用等方面存在的问题,提出了一种局部参考坐标系构建方法。本文利用该局部参考坐标系设计了一种基于球形网格划分的二值化特征描述子。所提的局部参考坐标系基于消除二义性的法线确定Z轴,将特征点球邻域重心与特征点构建的向量在法平面上的投影作为X轴。Z轴的可重复性和球邻域重心的唯一性,使得所提局部参考坐标系对高斯噪声和点密度变化具有极强的鲁棒性,所提局部参考坐标系具有极佳的泛化性和时间效率。二值化特征描述子无论是对高质量模拟数据,还是对低质量实测点云都具有较好的描述性,对各数据集均能获得次优的性能。二值化特征描述子具有极高的时间效率,且仅占用616 bit的存储空间,极小的时间和内存开销使其更适用于需要实时响应的应用场景。

从社会历史批评视角再论茨威格《象棋的故事》

奥地利作家斯蒂芬·茨威格创作的中篇小说《象棋的故事》,是其生前发表的最后一部小说,悲痛地讲述了一个遭到纳粹精神折磨的人的经历。本文从20世纪30、40年代的欧洲社会历史入手,以社会历史批评的视角再论《象棋的故事》,由小说具有的真实性、倾向性、社会效果等进行深入解读,挖掘文本背后蕴含的社会价值与历史价值。

相位角对容性耦合电非对称放电特性的影响

电非对称效应作为一种新兴技术,被广泛用于对离子能量和离子通量的独立调控.此外,在改善等离子体的径向均匀性方面,电非对称效应也发挥了重要作用.本文采用二维流体力学模型,并耦合麦克斯韦方程组,系统地研究了容性耦合氢等离子体中当放电由多谐波叠加驱动时,不同谐波阶数k下的电非对称效应,重点观察了相位角θ_n对自偏压以及等离子体径向均匀性的影响.模拟结果表明:在同一谐波阶数下,自偏压随相位角θ_n的变化趋势不尽相同,且当k增大(k> 3)时,自偏压随最高频相位角θ_k的变化范围逐渐减小.此外,通过调节相位角θ_n,可以改变轴向功率密度和径向功率密度的相对关系,进而实现对等离子体径向均匀性的调节.研究结果对于利用电非对称效应优化等离子体工艺过程具有一定的指导意义.

Changes of the electron dynamics in hydrogen inductively coupled plasma

Changes of the electron dynamics in hydrogen （H2） radio-frequency （RF） inductively coupled plasmas are investigated using a hairpin probe and an intensified charged coupled device （ICCD）. The electron density, plasma emission intensity, and input current （voltage） are measured during the E to H mode transitions at different pressures. It is found that the electron density, plasma emission intensity, and input current jump up discontinuously, and the input voltage jumps down at the E to H mode transition points. And the threshold power of the E to H mode transition decreases with the increase of the pressure. Moreover, space and phase resolved optical emission spectroscopic measurements reveal that, in the E mode, the RF dynamics is characterized by one dominant excitation per RF cycle, while in the H mode, there are two excitation maxima within one cycle.

Fluid simulation of inductively coupled Ar/O_2 plasmas:Comparisons with experiment

In this work, a two-dimensional fluid model has been employed to study the characteristics of Ar/O2 radio frequency（RF） inductively coupled plasma discharges. The emphasis of this work has been put on the influence of the external parameters（i.e., the RF power, the pressure, and the Ar/O2 gas ratio） on the plasma properties. The numerical results show that the RF power has a significant influence on the amplitude of the plasma density rather than on the spatial distribution.However, the pressure and the Ar/O2 gas ratio affect not only the amplitude of the plasma density, but also the spatial uniformity. Finally, the comparison between the simulation results and the experimental data has been made at different gas pressures and oxygen contents, and a good agreement has been achieved.

Influence of magnetic filter field on the radio-frequency negative hydrogen ion source of neutral beam injector for China Fusion Engineering Test Reactor

In the design of negative hydrogen ion sources,a magnetic filter field of tens of Gauss at the expansion region is essential to reduce the electron temperature,which usually results in a magnetic field of around 10 Gauss in the driver region,destabilizing the discharge.The magnetic shield technique is proposed in this work to reduce the magnetic field in the driver region and improve the discharge characteristics.In this paper,a three-dimensional fluid model is developed within COMSOL to study the influence of the magnetic shield on the generation and transport of plasmas in the negative hydrogen ion source.It is found that when the magnetic shield material is applied at the interface of the expansion region and the driver region,the electron density can be effectively increased.For instance,the maximum of the electron density is 6.7×10^(17)m^(-3)in the case without the magnetic shield,and the value increases to 9.4×10^(17)m^(-3)when the magnetic shield is introduced.

Simulations of standing wave effect,stop band effect,and skin effect in large-area very high frequency symmetric capacitive discharges

In this paper,Maxwell equations are coupled with a radially localized global model and an analytical sheath model to investigate the electromagnetic effects under various frequencies and electron powers in large-area very high frequency symmetric capacitive argon discharges.Simulation results indicate that both the vacuum wavelength and the sheath width decrease with frequency,leading to the reduced surface wavelength.As a result,the standing wave effect becomes pronounced,causing the fact that the radial profiles of the electron density,radio frequency voltage,and sheath width shift from uniform over center-high to multiple-node.When the frequency is close to or higher than the series resonance frequency,the surface waves cannot propagate to the radial center because of the significant radial damping.Due to the lack of power deposition near the radial center,the electron density is nearly zero there,i.e.the stop band effect.As power increases,the higher electron density leads to the decrease of the skin depth.Therefore,the importance of the skin effect gradually exceeds that of the standing wave effect,giving rise to the transition from the center-high to edge-high electron density profiles.The method proposed in this work could help to predict the plasma distribution under different discharge conditions in a few minutes,which is of significant importance in optimizing the plasma processing.

Fundamental study towards a better understanding of low pressure radio-frequency plasmas for industrial applications

Two classic radio-frequency(RF) plasmas, i.e., the capacitively and the inductively coupled plasmas(CCP and ICP),are widely employed in material processing, e.g., etching and thin film deposition, etc. Since RF plasmas are usually operated in particular circumstances, e.g., low pressures(m Torr-Torr), high-frequency electric field(13.56 MHz-200 MHz),reactive feedstock gases, diverse reactor configurations, etc., a variety of physical phenomena, e.g., electron resonance heating, discharge mode transitions, striated structures, standing wave effects, etc., arise. These physical effects could significantly influence plasma-based material processing. Therefore, understanding the fundamental processes of RF plasma is not only of fundamental interest, but also of practical significance for the improvement of the performance of the plasma sources. In this article, we review the major progresses that have been achieved in the fundamental study on the RF plasmas,and the topics include 1) electron heating mechanism, 2) plasma operation mode, 3) pulse modulated plasma, and 4) electromagnetic effects. These topics cover the typical issues in RF plasma field, ranging from fundamental to application.

Modulation of the plasma uniformity by coil and dielectric window structures in an inductively coupled plasma

The effects of coil and dielectric window structures on the plasma distribution are examined in a cylindrically symmetric planar inductively coupled plasma(ICP).A two-dimensional(2 D)fluid model is employed to investigate the design issues of ICP source for etching.When the gradient coil structure is applied at 400 W and 20 mTorr,the ionization rate caused by the power deposition decreases at the reactor center as compared to that in a reactor with a planar coil above the planar dielectric window,and a rather uniform plasma is obtained.However,for the vertical coil geometry,all the coils move to the position of the outermost coil,and the peaks of the power deposition and ionization rate appear at the radial edge of the substrate.In this case,the plasma density is characterized by an edge-high profile.Further,it is observed that the plasma uniformity is improved by increasing the source power under a gas pressure of 20 mTorr and becomes better when the gas pressure increases to 30 mTorr with the source power being fixed at400 W in the gradient coil configuration,but the uniformity of plasma worsens with the rising source power or pressure due to the strong localization in the vertical coil geometry.Moreover,when the discharge is sustained in a reactor with a stepped dielectric window at r=0.135 m,the best plasma uniformity is obtained at 400 W and 20 m Torr because the ionization rate is enhanced at the outermost coil,and the dielectric window at r=0.135 m blocks the diffusion of plasma towards the axis.In addition,higher source power and lower gas pressure produce more uniform plasma for the designs with a stepped window near the symmetry axis.When the dielectric window is stepped at r=0.135 m,the non-uniformity of plasma initially decreases and then increases with the increase in source power or gas pressure.When the dielectric window is stepped at the radial edge of the chamber,the plasma uniformity is improved by increasing the source power and gas pressure due to the enhanced ionization at the larger radius caused by the severe localization.

Influence of dielectric materials on uniformity of large-area capacitively coupled plasmas for N_2/Ar discharges

The effect of the dielectric ring on the plasma radial uniformity is numerically investigated in the practical 450-mm capacitively coupled plasma reactor by a two-dimensional self-consistent fluid model. The simulations were performed for N2/Ar discharges at the pressure of 300 Pa, and the frequency of 13.56 MHz. In the practical plasma treatment process,the wafer is always surrounded by a dielectric ring, which is less studied. In this paper, the plasma characteristics are systematically investigated by changing the properties of the dielectric ring, i.e., the relative permittivity, the thickness and the length. The results indicate that the plasma parameters strongly depend on the properties of the dielectric ring. As the ratio of the thickness to the relative permittivity of the dielectric ring increases, the electric field at the wafer edge becomes weaker due to the stronger surface charging effect. This gives rise to the lower N~+ ion density, flux and N atom density at the wafer edge. Thus the homogeneous plasma density is obtained by selecting optimal dielectric ring relative permittivity and thickness. In addition, we also find that the length of the dielectric ring should be as short as possible to avoid the discontinuity of the dielectric materials, and thus obtain the large area uniform plasma.

Discontinuity of mode transition and hysteresis in hydrogen inductively coupled plasma via a fluid model

A new type of two-dimensional self-consistent fluid model that couples an equivalent circuit module is used to in- vestigate the mode transition characteristics and hysteresis in hydrogen inductively coupled plasmas at different pressures, by varying the series capacitance of the matching box. The variations of the electron density, temperature, and the circuit electrical properties are presented. As cycling the matching capacitance, at high pressure both the discontinuity and hysteresis appear for the plasma parameters and the transferred impedances of both the inductive and capacitive discharge components, while at low pressure only the discontinuity is seen. The simulations predict that the sheath plays a determi- native role on the presence of discontinuity and hysteresis at high pressure, by influencing the inductive coupling efficiency of applied power. Moreover, the values of the plasma transferred impedances at different pressures are compared, and the larger plasma inductance at low pressure due to less collision frequency, as analyzed, is the reason why the hysteresis is not seen at low pressure, even with a wider sheath. Besides, the behaviors of the coil voltage and current parameters during the mode transitions are investigated. They both increase （decrease） at the E to H （H to E） mode transition, indicating an improved （worsened） inductive power coupling efficiency.

Electronic dynamic behavior in inductively coupled plasmas with radio-frequency bias

The inflexion point of electron density and effective electron temperature curves versus radio-frequency （RF） bias voltage is observed in the H mode of inductively coupled plasmas （ICPs）. The electron energy probability function （EEPF） evolves first from a Maxwellian to a Druyvesteyn-like distribution, and then to a Maxwellian distribution again as the RF bias voltage increases. This can be explained by the interaction of two distinct bias-induced mechanisms, that is： bias- induced electron heating and bias-induced ion acceleration loss and the decrease of the effective discharge volume due to the sheath expansion. Furthermore, the trend of electron density is verified by a fluid model combined with a sheath module.