Plasma characteristics and broadband electromagnetic wave absorption in argon and helium capacitively coupled plasma

A one-dimensional self-consistent calculation model of capacitively coupled plasma(CCP) discharge and electromagnetic wave propagation is developed to solve the plasma characteristics and electromagnetic wave transmission attenuation.Numerical simulation results show that the peak electron number density of argon is about 12 times higher than that of helium, and that the electron number density increases with the augment of pressure, radio frequency(RF) power, and RF frequency. However, the electron number density first increases and then decreases as the discharge gap increases. The transmission attenuation of electromagnetic wave in argon discharge plasma is 8.5-d B higher than that of helium. At the same time, the transmission attenuation increases with the augment of the RF power and RF frequency, but it does not increase or decrease monotonically with the increase of gas pressure and discharge gap. The electromagnetic wave absorption frequency band of the argon discharge plasma under the optimal parameters in this paper can reach the Ku band. It is concluded that the argon CCP discharge under the optimal discharge parameters has great potential applications in plasma stealth.     

双频容性耦合等离子体相分辨发射光谱诊断

采用相分辨发射光谱法, 对双频容性耦合纯Ar和不同含O₂量的Ar-O₂混合气体放电等离子体的鞘层激发模式进行了探究. 在射频耦合电源上极板的鞘层区域处观察到两种电子激发模式: 鞘层扩张引起的电子碰撞激发模式和二次电子引起的电子碰撞激发模式; 并发现这两种激发模式均受到低频射频电源周期的调制. 在纯Ar放电等离子体中, 两种激发模式的激发轮廓相似; 而在Ar-O₂混合气放电等离子体中, 随着含O₂量的增加, 二次电子的激发轮廓变弱. 此外, 利用相分辨发射光谱法对不同含O₂量的Ar-O₂混合气放电下Ar的 750.4 nm谱线的平均低频电源周期轴向分布进行了研究, 得到了距耦合电源上极板约3.8 mm处为双频容性耦合射频等离子体的鞘层边界. 关键词： 双频容性耦合等离子体 等离子体鞘层 发射光谱     

CHF3双频电容耦合放电等离子体特性研究

研究了用于SiCOH 低介电常数薄膜刻蚀的CHF₃气体在1356 MHz/2 MHz,2712 MHz/2 MHz和60 MHz/2 MHz双频电容耦合放电时的等离子体性质.发现2 MHz低频源功率的增大主要导致F基团密度的增大;而高频频率从1356,2712增大到60 MHz,导致CF₂基团的密度增大和电极之间F基团密度的轴向空间不均匀性增加.根据电子温度的分布规律及离子能量随高频源频率的变化关系,提出CF₂基团的产生主要通过电子-中性气体碰撞,而F基团的产生是离子-中性气体碰撞的结果. 关键词： 双频电容耦合放电 3等离子体')" href="#">CHF₃等离子体     

双频容性耦合CF4等离子体放电的二维混合模拟

研究了等离子体反应装置内的等离子体密度、粒子能量与角度分布等参量在装置径向与轴向上的分布特性。在研究过程中应用二维混合模型对CF4气体放电进行模拟。计算结果显示：在电极表面与侧壁附近的鞘层区特性有明显的区别。由于装置侧壁处受电源产生的射频电场的影响较小,侧壁处的鞘层主要由双极扩散机制形成,其产生的径向电场强度较弱,鞘层厚度也较薄。而在电极附近,由于受到射频电场的影响,鞘层的厚度显著增加,指向电极方向的轴向电场强度也远大于指向侧壁方向的径向电场强度。在电极区域内,离子通量分布均匀;在电极边缘与侧壁的间隙内,因电场强度减小,离子通量则发生迅速衰减。在射频电极覆盖的范围内离子能量分布大体上保持不变,电极与侧壁的交界处,由于受到侧壁处径向电场的影响,离子能量分布略有不同。在放电装置的中心区域,入射到电极上的离子角度分布基本保持一致,而在电极边界与装置侧壁的交界处,由于径向电场的影响,离子的垂直入射角增加,以大角度轰击电极的离子数量也显著增加。     

双频容性耦合等离子体密度径向均匀性研究

利用自主研制的全悬浮双探针, 对影响双频容性耦合等离子体径向均匀性的因素进行了研究. 发现低频功率、放电气压和放电间距对径向均匀性有明显影响. 合适的低频功率、放电气压及较大的极板间距可以得到更均匀的等离子体. 采用与实验相同的放电参数, 利用改进的二维流体模型进行理论模拟, 得到了不同极板间距下径向离子密度分布, 并和实验测量结果进行了比较, 两者的变化趋势基本符合. 关键词： 双频容性耦合等离子体 径向均匀性 全悬浮双探针 二维流体模型     

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     

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.     

Hydrogen passivation of multi—crystalline silicon solar cells

The effects of hydrogen passivation on multi-crystalline silicon (mc-Si) solar cells are reported in this paper. Hydrogen plasma was generated by means of ac glow discharge in a hydrogen atmosphere. Hydrogen passivation was carried out with three different groups of mc-Si solar cells after finishing contacts. The experimental results demonstrated that the photovoltaic performances of the solar cell samples have been improved after hydrogen plasma treatment, with a relative increase in conversion efficiency up to 10.6\%. A calculation modelling has been performed to interpret the experimental results using the model for analysis of microelectronic and photonic structures developed at Pennsylvania State University.     

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     

Evolution of vacuum ultraviolet emission in dual-frequency capacitively coupled plasmas

In plasma material processing, vacuum ultraviolet (VUV) emission is released from gas discharges, leading to undesirable results. Energetic VUV photons enable the creation of an electron-hole pair current when their energy is larger than the bandgap energy of the plasma-facing top layer during plasma material processing. For example, the high energy of VUV photons from helium (21.2 eV), argon (11.6 eV), and oxygen (13.6 eV) is sufficient to generate induced currents in SiO₂ thin films. These feedstock gases are widely used in many procedures utilizing low-temperature industrial plasmas. Thus, the VUV emission evolution with both the power ratio between high (60 MHz) and low (2 MHz) frequencies and pulse duty ratio of the low-frequency radio frequency (rf) power in a dual-frequency capacitively coupled plasma, which is indispensable in modern plasma etching processes, was investigated. Both the power ratio between high and low frequencies and the pulse duty ratio changed the electron temperature, leading to evolution of the VUV emission intensity.     

He-O2高气压下电容耦合辉光放电数值分析

采用一维的等离子体流体力学模型研究了氦气-氧气高气压下电容耦合放电过程。分别给出了间隙为1.6,2.4和3.2 mm时外加电压的有效值与放电电流有效值特征曲线,并与已有的实验数据作对比,结果表明计算得到的电压-电流特征曲线与实验数据符合得很好。研究发现：氦气-氧气高气压下电容耦合放电过程中荷质比较大的离子在鞘层中的分布随着外电场的变化而变化,而荷质比较小的粒子在整个放电区域基本不随外电场变化而变化;同时杂质形成正负离子在主等离子体区域两端出现了峰值。     

Diagnosis of a low pressure capacitively coupled argon plasma by using a simple collisional-radiative model

This paper proposes a simple collisional-radiative model to characterise capacitively coupled argon plasmas driven by conventional radio frequency in combination with optical emission spectroscopy and Langmuir probe measurements. Two major processes are considered in this model, electron-impact excitation and the spontaneous radiative decay. The diffusion loss term, which is found to be important for the two metastable states (4s[3/2]₂, 4s'[1/2]₀), is also taken into account. Behaviours of representative metastable and radiative states are discussed. Two emission lines (located at 696.5 nm and 750.4 nm) are selected and intensities are measured to obtain populated densities of the corresponding radiative states in the argon plasma. The calculated results agree well with that measured by Langmuir probe, indicating that the current model combined with optical emission spectroscopy is a candidate tool for electron density and temperature measurement in radio frequency capacitively coupled discharges.     

One-dimensional hybrid simulation of the electrical asymmetry effect caused by the fourth-order harmonic in dual-frequency capacitively coupled plasma

A one-dimensional hybrid model was developed to study the electrical asymmetry effect(EAE) caused by the fourthorder harmonic in a dual-frequency capacitively coupled Ar plasma.The self-bias voltage caused by the fourth-order frequency changes periodically with the phase angle,and the cycle of self-bias with the phase angle is π/2,which is half of that in the second-order case.The influence of the phase angle between the fundamental and its fourth-order frequency on the ion density profiles and the ion energy distributions(IEDs) were studied.Both the ion density profile and the IEDs can be controlled by the phase angle,which provides a convenient way to adjust the sheath characters without changing the main discharge parameters.     

The effects of process conditions on the plasma characteristic in radio-frequency capacitively coupled SiH4/NH3/N2 plasmas: Two-dimensional simulations

A two-dimensional (2D) fluid model is presented to study the behavior of silicon plasma mixed with SiH4 , N2 , and NH3 in a radio-frequency capacitively coupled plasma (CCP) reactor. The plasma-wall interaction (including the deposition) is modeled by using surface reaction coefficients. In the present paper we try to identify, by numerical simulations, the effect of variations of the process parameters on the plasma properties. It is found from our simulations that by increasing the gas pressure and the discharge gap, the electron density profile shape changes continuously from an edge-high to a center-high, thus the thin films become more uniform. Moreover, as the N2 /NH3 ratio increases from 6/13 to 10/9, the hydrogen content can be significantly decreased, without decreasing the electron density significantly.     

Effect of pressure and space between electrodes on the deposition of SiN_xH_y films in a capacitively coupled plasma reactor

The fluid model, also called the macroscopic model, is commonly used to simulate low temperature and low pressure radiofrequency plasma discharges. By varying the parameters of the model, numerical simulation allows us to study several cases, providing us the physico-chemical information that is often difficult to obtain experimentally. In this work, using the fluid model, we employ numerical simulation to show the effect of pressure and space between the reactor electrodes on the fundamental properties of silicon plasma diluted with ammonia and hydrogen. The results show the evolution of the fundamental characteristics of the plasma discharge as a function of the variation of the pressure and the distance between the electrodes. By examining the pressure-distance product in a range between 0.3 Torr 2.7 cm and 0.7 Torr 4 cm, we have determined the optimal pressure-distance product that allows better deposition of hydrogenated silicon nitride(Si N_x H_y)films which is 0.7 Torr 2.7 cm.     

Effect of driving frequency on electron heating in capacitively coupled RF argon glow discharges at low pressure

A one-dimensional(1D) fluid model on capacitively coupled radio frequency(RF) argon glow discharge between parallel-plates electrodes at low pressure is established to test the effect of the driving frequency on electron heating. The model is solved numerically by a finite difference method. The numerical results show that the discharge process may be divided into three stages: the growing rapidly stage, the growing slowly stage, and the steady stage. In the steady stage,the maximal electron density increases as the driving frequency increases. The results show that the discharge region has three parts: the powered electrode sheath region, the bulk plasma region and the grounded electrode sheath region. In the growing rapidly stage(at 18 μs), the results of the cycle-averaged electric field, electron temperature, electron density, and electric potentials for the driving frequencies of 3.39, 6.78, 13.56, and 27.12 MHz are compared, respectively. Furthermore,the results of cycle-averaged electron pressure cooling, electron ohmic heating, electron heating, and electron energy loss for the driving frequencies of 3.39, 6.78, 13.56, and 27.12 MHz are discussed, respectively. It is also found that the effect of the cycle-averaged electron pressure cooling on the electrons is to "cool" the electrons; the effect of the electron ohmic heating on the electrons is always to "heat" the electrons; the effect of the cycle-averaged electron ohmic heating on the electrons is stronger than the effect of the cycle-averaged electron pressure cooling on the electrons in the discharge region except in the regions near the electrodes. Therefore, the effect of the cycle-averaged electron heating on the electrons is to "heat" the electrons in the discharge region except in the regions near the electrodes. However, in the regions near the electrodes, the effect of the cycle-averaged electron heating on the electron is to "cool" the electrons. Finally, the space distributions of the electron pressure cooling the electron ohmic heating and the electron heating at 1/4 T, 2/4 T, 3/4 T, and 4/4 T in one RF-cycle are presented and compared.     

Characteristics of a dual‐radio‐frequency cylindrical inductively coupled plasma

The plasma parameters such as electron density, effective electron temperature, plasma potential, and uniformity are investigated in a new dual‐frequency cylindrical inductively coupled plasma (ICP) source operating at two frequencies (2 and 13.56 MHz) and two antennas (a two‐turn high‐frequency antenna and a six‐turn low‐frequency (LF) antenna). It is found that the electron density increases with 2 MHz power, whereas the electron temperature and plasma potential decrease with 2 MHz power at a fixed 13.56 MHz power. Moreover, the plasma uniformity can be improved by adjusting the LF power. These results indicate that a dual‐frequency synergistic discharge in a cylindrical ICP can produce a high‐density, low‐potential, low‐effective‐electron‐temperature, and uniform plasma.     

Diagnostic of capacitively coupled radio frequency plasma by homogeneous discharge model

In this Letter, a plasma diagnostic technique is reported to evaluate the plasma parameters of capacitively coupled radio frequency argon plasma on the basis of homogeneous discharge model. The technique is implemented for wide range of operating pressure ranging from few mTorrs to atmospheric pressure. Considerable dependence of plasma parameters on the plasma series resonance effect and the drift velocity of the electron for low pressure plasma and on the ion density for atmospheric pressure plasma jet were observed.     

电子回旋共振-射频双等离子体沉积氧化硅薄膜过程中的射频偏压效应

本文利用六甲基乙硅氧烷(HMDSO)和氧气(O2)为反应气体,利用微波电子回旋共振-射频双等离子体化学气相沉积法沉积氧化硅薄膜,并利用发射光谱对等离子体特性进行原位诊断.研究表明,RF偏压对氧化硅薄膜沉积速率和薄膜中的化学键结构产生有意义的影响.小的直流自偏压会略微提高沉积速率;但随着直流自偏压的增加,离子轰击效应及刻蚀作用加强,薄膜的沉积速率下降.在13.56MHz和400kHz两个不同射频频率条件下所沉积的薄膜中,O和Si的比例基本相同,均超过2∶1;但400kHz射频偏压下薄膜中的碳成分比例比13.56MHz条件下的要高得多.这可以归因为高的射频偏压的应用不仅可增强离子轰击效应,而且与体等离子体相互作用,使高活性的氧原子增多;而低频偏压的作用主要是增强离子轰击效应.