射频空心阴极放电中电子加热机制的实验研究

在氩气环境下对射频驱动下空心阴极的放电特性进行了实验研究,得到了不同工作条件下射频空心阴极放电中的电子密度、电子能量几率分布函数等结果。研究结果表明,相比于平板电极容性耦合射频放电,空心结构电极的射频放电能获得更高的电子密度。在形成空心阴极效应后,等离子体密度随电压、气压的升高而增大。通过EEPF进一步分析了射频空心阴极放电电子加热机制随p D值、工作电压的变化。发现当p D增加时,射频空心阴极放电中电子加热机制从以振荡鞘层对高能电子的随机加热为主逐渐转变为对等离子体中电子的欧姆加热为主;当逐渐提升电压时,电子本身获得能量机制则由开始的欧姆加热转到了向后来的随机加热。     

射频等离子体中和器的设计与实验研究

随着电推进技术的发展,对具有高抗中毒性中和器的需求日益紧迫。为此,基于射频放电基本原理,设计了一款可采用多种工质且具有高抗中毒能力的射频等离子体中和器,搭建了真空实验平台进行试验研究,获得了发射电流随射频功率和氙气流量的变化曲线。工质气体电离后,离子被置于放电室内的石墨柱负电极收集,电子被置于放电室出口外的金属板正电极引出。研究结果表明,该射频等离子体中和器能有效地发射电子形成电流,且增大射频功率和氙气流量可以提高电流。当射频功率达到220 W,流量达到或超过4 mL/min(标准状态)时,中和器发射电流达到1 A以上。因此,射频等离子体中和器作为电推力器羽流离子中和装置具有一定的研究价值和应用前景。     

基于均匀离子密度的容性耦合射频放电等离子体的实验诊断研究北大核心CSCD

容性耦合射频(CCRF)放电可用于制备大体积、均匀、低温非热平衡等离子体,已得到了国内外的广泛关注。针对CCRF放电过程中等离子体参量的诊断问题,本文提供了一种基于均匀离子密度的描述CCRF放电的等效回路模型(ECM),并根据等效阻抗原理引入能量平衡方程,对等离子体特征参量电子密度n_e和电子温度T_e进行了诊断,诊断结果与等离子体发射光谱诊断结果相一致。实验结果表明:在一般的CCRF放电过程中,放电电流与放电电压波形呈正弦曲线,高次谐波成分较少且总的谐波强度小于基波信号的11%,可以采用ECM描述等离子体放电状态。随着射频输入功率的增加,等离子体电子密度线性增加,但电子温度变化不明显,鞘层厚度逐渐减小,主等离子体区厚度增加;随着工作气体压强的升高,电子密度和电子温度均减小。对于较高的气压,放电在不同的输入功率下分为低功率下的α模式和高功率下的γ模式,这主要是极板表面的俄歇发射过程引起的。     

基于均匀离子密度的容性耦合射频放电等离子体的实验诊断研究

容性耦合射频(CCRF)放电可用于制备大体积、均匀、低温非热平衡等离子体,已得到了国内外的广泛关注。针对CCRF放电过程中等离子体参量的诊断问题,本文提供了一种基于均匀离子密度的描述CCRF放电的等效回路模型(ECM),并根据等效阻抗原理引入能量平衡方程,对等离子体特征参量电子密度n_e和电子温度T_e进行了诊断,诊断结果与等离子体发射光谱诊断结果相一致。实验结果表明:在一般的CCRF放电过程中,放电电流与放电电压波形呈正弦曲线,高次谐波成分较少且总的谐波强度小于基波信号的11%,可以采用ECM描述等离子体放电状态。随着射频输入功率的增加,等离子体电子密度线性增加,但电子温度变化不明显,鞘层厚度逐渐减小,主等离子体区厚度增加;随着工作气体压强的升高,电子密度和电子温度均减小。对于较高的气压,放电在不同的输入功率下分为低功率下的α模式和高功率下的γ模式,这主要是极板表面的俄歇发射过程引起的。     

射频激励铜离子激光器的功率消耗

通过对射频激励激光器放电电压、电流以及相位的精确测量,基于射频放电等离子体等效电路,得出等离子体总电阻(包括等离子体总电阻和鞘层电阻分量),经非线性最小平方拟合分别得到等离子体电阻和鞘层电阻,进而定量地得到等离子体和鞘层功率消耗,鞘层电压以及鞘层厚度随放电电流变化的关系,借此可以诊断出射频放电处于α或γ放电。研究表明在中等气压氦气中随着气体压强的增加和电流的增加,气体的放电模式将从α放电为主转向γ放电为主。     

大气压下甲烷等离子枪的光谱诊断研究

以甲烷为反应气体,氩气为辅助气体,通过大气压介质阻挡放电等离子枪,制备纳米类金刚石.在此过程中,利用发射光谱对甲烷等离子体中产生的活性粒子进行光学发射特征的原位诊断.通过对检测到的发射光谱谱图的研究,证实了CH、C2、Hα等自由基粒子的存在,研究了不同的实验参数,如放电电压和气体流量对CH活性粒子发射强度的影响,并由此分析了甲烷可能的离解过程,同时计算了不同条件下的电子温度.结果表明,随着输入电压及CH4流量的增加,CH自由基的发射强度随之增加.根据掺入甲烷的Ar原子谱线计算出电子温度,其范围在0.4eV～0.6eV之间,而且随着输入电压及气体流量的增加而降低.     

射频激励铜离子激光器的功率消耗

通过对射频激励激光器放电电压、电流以及相位的精确测量，基于射频放电等离子体等效电路，得出等离子体总电阻(包括等离子体总电阻和鞘层电阻分量)，经非线性最小平方拟合分别得到等离子体电阻和鞘层电阻，进而定量地得到等离子体和鞘层功率消耗，鞘层电压以及鞘层厚度随放电电流变化的关系，借此可以诊断出射频放电处于α或γ放电。研究表明在中等气压氦气中随着气体压强的增加和电流的增加，气体的放电模式将从α放电为主转向γ放电为主。     

放电参量对射频容性耦合等离子体电子密度的影响

为了提高射频容性耦合等离子体电子密度,研究放电参量对其的影响。通过采用朗缪双探针法诊断分析了放电气压、气体组分、射频功率以及掺Hg等放电参量对圆柱形射频容性耦合等离子体放电装置的电子密度的影响。结果表明:随放电气压的增加,电子密度呈现出先增大后减小的变化,在30Pa-550Pa下,电子密度随气压的增大而增加,在550Pa-650Pa下,电子密度随气压的增大而减小;往Ar中通入一定体积分数的He,有增加等离子体电子密度的影响,且当He的体积分数为15%时,电子密度最大;等离子体电子密度随射频功率的增大而增加;向Ar中掺少量的Hg,有明显增加等离子体电子密度的效果。     

交叉型天线感应耦合等离子体源放电特性及均匀性

本文介绍了一种交叉型天线射频感应耦合等离子体源,射频天线穿过交叉排列的石英管内置于真空腔体中.本文运用朗谬尔探针方法诊断了放电等离子体的参量及其均匀性,运用发射光谱技术进行了Af谱线[4s'(1/2)0-4p'(1/2)]的发光强度的表征,并使用自制的Rogowski线圈测量了天线中的射频电流变化.结果表明,等离子体放电随着射频输入功率的增加存在着E模式向H模式的转变,H模式放电时发光强度及射频电流明显增大.电子温度随气压的增大而降低,几乎不受功率的影响.该等离子体源所产生的等离子体密度较高,等离子体均匀性在中心±60mm区域内优于90%.     

直线等离子体装置中氩等离子体热负荷特性研究

利用自建的单阴极直流弧光放电直线等离子体装置研究了氩等离子体的稳态热负荷特性,拟为研究等离子体性质、及其与壁材料相互作用提供一定的参考。研究表明,实验中产生的氩等离子体热负荷可达0.5 MW/m2,能持续稳定放电5h以上;氩等离子体热负荷与输入功率成正比,热效率随输入功率的增加而增大;等离子体热负荷强烈依赖于磁场和气体流量,磁场越强、流量越高热负荷越大;同时,增加气体流量或增强磁场,均可显著提高等离子体热效率。通过测量相同条件下距离阳极等离子体喷口215和430mm处的热负荷发现,两处热负荷相差2倍,表明在轴向上热负荷与距离成反比。     

Low refraction properties of F-doped SiOC:H thin films prepared by PECVD

Low refractive index materials which F-doped SiOC:H films were deposited on Si wafer and glass substrate by low temperature plasma enhanced chemical vapor deposition (PECVD) method as a function of rf powers, substrate temperatures, gas flow ratios (SiH₄, CF₄ and N₂O). The refractive index of the F-doped SiOC:H film continuously decreased with increasing deposition temperature and rf power. As the N₂O gas flow rate decreases, the refractive index of the deposited films decreased down to 1.378, reaching a minimum value at an rf power of 180 W and 100 °C without flowing N₂O gas. The fluorine content of F-doped SiOC:H film increased from 1.9 at.% to 2.4 at.% as the rf power was increased from 60 W to 180 W, which is consistent with the decreasing trend of refractive index. The rms (root-mean-square) surface roughness significantly decreased to 0.6 nm with the optimized process condition without flowing N₂O gas.     

Controlled synthesis of alumina nanoparticles using inductively coupled thermal plasma with enhanced quenching

Synthesis of alumina nanoparticles in an Ar-O₂ inductively coupled radio frequency (rf) plasma controlled by axial quench gas injection was investigated. The flow and temperature fields for various quench gas flow rates in the plasma reactor, as well as the corresponding quench rates, were predicted using a renormalization group (RNG) k-ε turbulence model. Nanosize alumina particles were synthesized from the vapor phase by oxidation of aluminum in the plasma. The collected products were characterized by means of field emission scanning electron microscopy (FE-SEM), dynamic light scattering (DLS), and BET surface area analysis. The dependences of particle size and shape on the injection position and the flow rate of the quench gas were discussed.     

Planar plasma etching of chromium

We have investigated the plasma etching characteristics of chromium thin films in an rf planar (parallel plate) reactor. The experimental work was performed using a commercial reactor operating at 13.56 MHz with power variable up to 500 W. The etch rate of the Cr films deposited on glass substrates by e-beam evaporation was measured as a function of the concentration of O₂ in a CCl₄/O₂ gas mixture, the total flow rate of input gases and the rf power density. Using a total gas flow of 15 sccm and an input power density of 0.4 W cm^?2, the maximum etch rate was obtained in CCl₄ plasma containing 40% O₂. It was found that doubling the number of the substrates in the reactor decreased the etch rate by 20%. Also, the etch rate at the back of the reactor was twice that at the front. Methods to alliviate non-uniformity and loading effects are discussed and the mechanism of plasma etching of Cr is examined through the effect of various processing parameters on the etching characteristics.     

碳氟感应耦合等离子体的SiO2介质刻蚀的研究

使用感应耦合等离子体技术,通过改变源气体流量比R(R=[C4F8]/{[C4F8] [Ar]})、射频源功率、自偏压等条件进行了SiO2介质刻蚀实验研究。碳氟等离子体的特征由朗谬探针和发射光谱技术来表征。结果表明,SiO2的刻蚀速率随放电源功率和射频自偏压的增大而单调上升,与R的关系则存在R=8%处的刻蚀速率峰值。C2基团的发射谱线强度随R的变化类似于SiO2刻蚀速率对R的依赖关系,对此给出了解释。在此基础上,对SiO2介质光栅进行了刻蚀。结果显示,在较大的R及自偏压等条件下,刻蚀后的槽形呈轻微的锥形图案,同时光刻胶掩膜图形出现分叉。结合扫描电镜技术对此进行了分析,认为光刻胶表面与侧面的能量传递和聚合物再沉积是导致出现上述现象的原因。     

Inductively coupled plasma reactive ion etching of titanium thin films using a Cl2/Ar gas

Inductively coupled plasma reactive ion etching of titanium thin films patterned with a photoresist using Cl₂/Ar gas was examined. The etch rates of the titanium thin films increased with increasing the Cl₂ concentration but the etch profiles varied. In addition, the effects of the coil rf power, dc-bias voltage and gas pressure on the etch rate and etch profile were investigated. The etch rate increased with increasing coil rf power, dc-bias voltage and gas pressure. The degree of anisotropy in the etched titanium films improved with increasing coil rf power and dc-bias voltage and decreasing gas pressure. X-ray photoelectron spectroscopy revealed the formation of titanium compounds during etching, indicating that Ti films etching proceeds by a reactive ion etching mechanism.     

Effects of rf power on the structural properties of carbon nitride thin films prepared by plasma enhanced chemical vapour deposition

Carbon nitride (CN_x) thin films were deposited by radio frequency plasma enhanced chemical vapour deposition (rf PECVD) technique from a gas mixture of methane (CH₄), hydrogen (H₂) and nitrogen (N₂). The effects of rf power on the structural properties of CN_x thin films were discussed in this paper. It was found that rf power had significant effects on the growth rate, structural and morphological properties of the deposited films. The point of transition of the growth rate trend marked the equilibrium condition for primary and secondary reactions in growth kinetics of the film with respect to rf power. The films grown at this optimum rf power were most ordered in structure with high surface roughness and had the lowest N incorporation. This work showed that H etching effects and ion bombardment effects increase with increase in rf power and strongly influenced the structure of the CN_x films.     

The optical emission spectroscopy study of an rf-plasma-enhanced magnetron sputtering system

Optical emission spectroscopy has been performed for unbalanced DC magnetron sputtering of Cu in Ar atmosphere with the enhanced ionization of inductively coupled plasma. The intensities of Cu, Cu⁺, Ar and Ar⁺ lines were measured at various discharge parameters such as pressure and rf power. Both Cu and Cu⁺ lines intensities initially increase and then decrease with increasing pressure. At the same time, Ar line intensity increases and the Ar⁺ line intensity decreases with increasing pressure. With increasing rf power, all the lines intensities increase at different rates and become saturated when the rf power is greater than 700 W. The rf discharge exhibits mode jumping (E-mode to H-mode) and hysteresis phenomena. When the rf power increases to 400 W, the rf discharge mode jumps from E-mode to H-mode. When the rf power input decreases from 800 to 300 W, the rf discharge mode jumps back from H-mode to E-mode. However, during the mode change, the intensities of all lines are higher when switching from H-mode to E-mode than those when switching from E-mode to H-mode at the same rf power. In the rf power region, the ionization of Cu is significantly enhanced. The reasons of these phenomena are discussed.     

Evolution of etch profile in etching of CoFeB thin films using high density plasma reactive ion etching

Inductively coupled plasma reactive ion etching of CoFeB magnetic thin films patterned with Ti hard mask was studied in a CH₃OH/Ar gas mix. As the CH₃OH concentration increased, the etch rates of CoFeB thin films and Ti hard mask decreased but the etch profiles improved with high degree of anisotropy. The effects of coil rf power, dc-bias voltage and gas pressure on the etch characteristics were investigated. The etch rate increased with increasing coil rf power, dc-bias voltage and decreasing gas pressure. The degree of anisotropy in the etch profile of CoFeB films improved with increasing coil rf power and dc-bias voltage. X-ray photoelectron spectroscopy revealed that the chemical compounds containing Co and Fe components were formed during the etching. However, it was expected that the formation of these compounds could not increase the etch rates of the films due to low volatile compounds despite the improvement in etch profile.     

Investigation of the properties of diamond-like carbon thin films deposited by single and dual-mode plasma enhanced chemical vapor deposition

In this study diamond-like carbon (DLC) films were deposited by a dual-mode (radio frequency/microwave) reactor. A mixture of hydrogen and methane was used for deposition of DLC films. The film structure, thickness, roughness, refractive index of the films and plasma elements were investigated as a function of the radio frequency (RF) and microwave (MW) power, gas ratio and substrate substance. It was shown that by increasing the H₂ content, the refractive index grows to 2.63, the growth rate decreases to 10 (nm/min) and the surface roughness drops to 0.824 nm. Taking into consideration the RF power it was found that, as the power increases, the growth rate increases to 11.6 (nm/min), the variations of the refractive index and the roughness were continuously increasing, up to a certain limit of RF power. The Raman G-band peak position was less dependent on RF power for the glass substrate than that of the Si substrate and a converse tendency exists with increasing the hydrogen content. Adding MW plasma to the RF discharge (dual-mode) leads to an increase of the thickness and roughness of the films, which is attributed to the density enhancement of ions and radicals. Also, optical emission spectroscopy is used to study the plasma elements.     

Characteristics of hydrogenated silicon thin film deposited by RF-PECVD using He-SiH4 mixture

Nanocrystalline silicon thin films (nc-Si:H) were deposited using He as the dilution gas instead of H₂ and the effect of the operating pressure and rf power on their characteristics was investigated. Especially, operating pressures higher than 4 Torr and a low SiH₄ containing gas mixture, that is, SiH₄(3 sccm)/He(500 sccm) were used to induce high pressure depletion (HPD) conditions. Increasing the operating pressure decreased the deposition rate, however at pressures higher than 6 Torr, crystallized silicon thin films could be obtained at an rf power of 100 W. The deposition of highly crystallized nc-Si:H thin film was related to the HPD conditions, where the damage is decreased through the decrease in the bombardment energy at the high pressure and the crystallization of the deposited silicon thin film is increased through the increased hydrogen content in the plasma caused by the depletion of SiH₄. When the rf power was set at a fixed operating pressure of 6 Torr, HPD conditions were obtained in the rf power range from 80 to 100 W, which was high enough to dissociate SiH₄ fully, but meantime low enough not to damage the surface by ion bombardment. At 6 Torr of operating pressure and 100 W of rf power, the nc-Si:H having the crystallization volume fraction of 67% could be obtained with the deposition rate of 0.28 nm/s.