Investigation of debris dynamics from laser-produced tin plasma for EUV lithography light source

The dynamics of debris from the laser-produced tin (Sn) plasma was investigated for an extreme ultraviolet light source in order to establish the guideline for the optimum design of a mitigation system, such as a mass-limited target. The dissemination of the Sn atoms from the different shapes of a wire and a mass-limited droplet target were investigated using the laser-induced fluorescence (LIF) imaging method. The Sn droplet targets with a diameter in the range of 5 to 17 μm were prepared by a new droplet generating technique using a pulsed laser. There was a large difference in the angular distribution of Sn atoms in the plane parallel and perpendicular to the wire axis, indicating the curvature of the target surface governed the angular distribution of the ablated species. The spatial distributions of Sn atoms from the droplet targets were similar to those from the curved surface of the wire targets. The ablation dynamics of the droplet observed by a high-speed imaging camera is also discussed.     

极紫外光源锡液滴靶的检测研究

采用正交放置的两路CCD,基于图像采集及处理的方法,建立了极紫外光源锡液滴靶发生装置的锡液滴检测系统,可以实时监测锡液滴的运动状态及稳定性。对本实验室频率为34 kHz的锡靶发生器产生的液滴进行了锡液滴监测实验。监测结果显示,锡液滴直径约为137 m,平均间距为375 m,稳定性较好,并对水平面上横向稳定性进行了分析。     

EUV and fast ion emission from cryogenic liquid jet target laser-generated plasma

A liquid jet of either nitrogen or argon of 20 μm diameter was exposed to intense laser fields with pulse durations between 70 fs and 250 ps, leading to intensities of 10¹⁶ W cm^-2 and 10¹³ W cm^-2, respectively. The emission of extreme UV light and soft X-rays shows the characteristic lines of hydrogen-like nitrogen and carbon-like argon. For nitrogen the emitted photon flux at 250 ps was about two orders of magnitude higher than for 70 fs pulses. A weak dependence on the laser polarization with respect to the liquid jet axis was found. The kinetic energy of the emitted ions easily exceeded 100 keV for nitrogen and 200 keV for argon for a pulse duration close to 2 ps. Received: 21 August 2000 / Revised version: 20 December 2000 / Published online: 22 March 2001     

Highly resolved EUV beam-foil spectra of silicon

Spectra of foil-excited ions at tandem energies in the EUV region show many unclassified lines. In order to provide a basis for term analysis, high resolution spectra of Si are taken using a ruled 600 l/mm grating in 3^rd diffraction order and two holographic gratings of 1,200 l/mm resp. 3,600 l/mm in first diffraction order. With the latter grating the resolution power of a 2.2 m grazing-incidence monochromator is sufficient to measure fine-structure splittings of inter-shell transitions of O VI–O VIII and Si X–Si XII in the wavelength rangeλ < 20 nm. The performance of the gratings is demonstrated.     

激光诱导时间分辨固体表面荧光光谱系统

采用斜射式激发样品光路结构,设计了应用于测试时间分辨固体表面荧光光谱系统。利用该系统研究了氧化锌薄膜在355 nm激光脉冲激发下的时间分辨固体表面荧光光谱。结果表明,该系统能够实现测量时间分辨固体表面荧光光谱,并由此测量了样品的固体表面荧光寿命。该系统结构简单可靠,灵敏度高,响应速度快。     

激光诱导时间分辨固体表面荧光光谱系统

采用斜射式激发样品光路结构,设计了应用于测试时间分辨固体表面荧光光谱系统。利用该系统研究了氧化锌薄膜在355 nm激光脉冲激发下的时间分辨固体表面荧光光谱。结果表明,该系统能够实现测量时间分辨固体表面荧光光谱,并由此测量了样品的固体表面荧光寿命。该系统结构简单可靠,灵敏度高,响应速度快。     

Double electric layer influence on dynamic of EUV radiation from plasma of high-current pulse diode in tin vapor

Generation of high-power pulses of extreme ultraviolet radiation from multi-charged tin plasma is of great interest to many applications. We studied the electric potential distribution in the discharge gap in kind of the electric double layer and its effect on the extreme ultraviolet generation. The local plasma heating by electron beam, formed in the double layer, leads to generation of peak radiation pulses and as a result to an increase in the radiation power.     

高电离态Ti原子EUV光谱的实验研究

在中国原子能研究院HI-13串列加速器上用束-箔技术完成了80 MeV Ti离子和C箔相互作用产生的高电离态离子谱观测,与用激光等离子体技术的实验结果做了比较，大多数谱线与激光等离子体技术的实验结果有较好的符合，有3条谱线是未观测到的.这几条谱线为ⅩⅧ 13.406，ⅩⅧ 14.987，17.439nm, 属于2s2p^{2 4}P_3/2—2p^{3 2}D_3/2, 2s2p^{2 1}S₀—2sp^{3 1}P₁, 4p ¹P₀—5d ¹P₁跃迁. 关键词： 串列加速器 高电荷态原子 激发光谱     

Laser-induced modification of composite Cu-C nanosized particles synthesized using a pulsed electrical discharge in a liquid

Composite copper-containing carbon nanosized structures were synthesized in the plasma of a pulsed electrical discharge, initiated between two graphite electrodes in an aqueous copper chloride solution. We studied the effect of laser radiation on the morphology of the nanoparticles formed, whose properties we studied by optical absorption spectroscopy and transmission electron microscopy. We discuss the mechanisms for nanoparticle formation in a discharge submerged in a liquid, and the possibilities for laser-induced modification of the nanoparticles. We estimated the temperature of the nanoparticles when exposed to laser radiation pulses. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 3, pp. 372–378, May–June, 2008.     

Laser-induced plasma by two-color excitation

With a superposition of a nanosecond infrared-laser pulse and its second harmonic, the threshold of plasma formation in gasses as well as the energy transfer efficiency from the laser field to the plasma can be significantly improved in comparison to purely monochromatic radiation. We present experimental results in air at pressures between 0.4 and 3 bar; in this pressure range, the threshold energy for the superposition is reduced by ≈30% as compared to that of pure infrared radiation, while the energy transfer slope efficiency is equal to the IR efficiency at high pressures and somewhat less at lower pressures. Possible mechanisms responsible for this effect are discussed.     

Optical emission spectra from microwave oxygen plasma produced by surfatron discharge

This paper is devoted to a systematic study of the production of molecular and atomic ions and excited atoms in a microwave oxygen plasma generated by surfatron in a quartz tube (i.d. 6 mm). The content of O ₂ ⁺ , O⁺ and O is measured, using the optical emission spectroscopy, in a wide range of oxygen pressures (from 3.5 Pa to 10² Pa) and microwaves powers (from about 30 W to 300 W) delivered into the plasma. It is shown that the content of individual species O2⁺, O⁺ and O strongly depends on the conditions, particularly operating pressurep and the microwave powerP, under which plasma is created. It means that the chemical reactivity of microwave plasma also strongly depends onp andP. It is of great importance for many practical applications, e.g. for a reproducible production of thin films with prescribed properties.The authors wish to express their thanks to the Grant Agency of Academy of Sciences of the Czech Republic for the support of this research. This work was done under Academy of Sciences Grant No. 11020.     

Laser-induced pattern formation in liquid sulfur

Liquid sulfur is a well-known liquid which exhibits a polymerization transition at T_p=159 °C. Recently, it was found from our experiments that such a transition can be induced below T_p through laser illumination and that an iridescent pattern appears under strong illumination with a pulsed laser of more than 60 mJ/cm² pulse. It is proposed that the visible change in iridescence is due to a macroscopic reconstruction of laser-generated polymers and that a laser-induced phase transition takes place from a freely expanded polymer phase to an ordered polymer phase when increasing the laser illumination. To further examine this possibility, the time variation of the iridescent pattern has been fully investigated using a macro lens, a polarized microscope and an optical microscope. In an analysis of the iridescent pattern, a rapid decrease in the area was observed after an initial slow decrease, suggesting a type of phase transition. Results from the observation of a quenched sulfur sample with a polarized microscope gave evidence that the iridescent region consists of polymers. Through observation of the liquid with a microscope, a striped pattern with micrometer sized spacing was noted in the iridescent pattern. A drastic color change was observed in the pattern from its generation to its disappearance. Sample thickness dependence of the pattern was also observed. These results were well explained by assuming the self-arrangement of laser-generated colloidal polymers.     

Influence of plasma discharge operating regime and laser beam intensity on optogalvanic spectra

The optogalvanic (OG) spectrum — over the tuning range of R 6G dye (568 nm to 605 nm) — of a Pr/Ne discharge tube is studied. The positive OG signals are approximately two orders of magnitude larger than the negative OG signals. The magnitude of the signals depend mainly on the operating regime of the discharge. Specifically, operation of the discharge in the abnormal glow regime leads to an enhancement in the negative OG signals. The operating point on theV-I characteristic of the discharge should be stipulated. To study the variation of the OG signal with the intensity of the laser beam two OG signals, of different polarities, were examined. We observed that with respect to positive OG signals, there is a trend towards pumping saturation. A minimum threshold of 0.3 kW laser power is required to generate negative OG signals. For the same attenuation in the laser beam there is a ten times more efficient reduction in the negative OG signals than in the case of positive OG signals. This confirms the important role of metastable atoms in the conduction in gas discharges.The hypothesis that negative OG signals can be obtained only abnormal glow regime needs more experimental data. The required study of the temporal variation in the OG signal with increase in the discharge current is being carried out and the results are to be published.     

微波气体放电等离子体与余辉中的动理学研究

研究了微秒脉冲聚焦微波束气体放电等离子体的动理学过程。数值模型基于自洽求解的微波电场亥姆霍兹方程、粒子连续性方程以及电子能量、气体分子振动能量和平动能量的平衡方程,并与等离子体动理学反应互相耦合。对比了国外报道的近期两项相关实验：次MW级X波段9.4 GHz微波氮气击穿和MW级W波段110 GHz微波大气击穿。在次MW级实验中,计算所得电子激发态N₂(C³Π_u)的数密度与实验所测发射光谱第二正带隙的强度一致;在MW级实验中,模拟结果重复了发射光谱测量所得振动温度和平动温度对放电气压的依赖关系。结果揭示了上述模拟和实验符合的内在物理机制。     

纳秒脉冲空气辉光放电等离子体及应用

采用基于半导体断路开关的纳秒脉冲高压电源,在两个金属电极之间产生放电区间为1 600 mm×100 mm×25 mm的常压辉光空气等离子体。等离子体发生器采用负高压针电极阵列与平板阳极结构,针电极的直径为1 mm,长度为20 mm,针电极之间的间隔为20 mm,针电极与平板零电位之间的距离为25 mm,在每个负高压针电极末端周围同时形成圆锥形辉光放电,在平板地电极则形成大面积辉光放电。采用电压探针测量了该新型等离子体的放电特性,结果表明：放电脉冲的上升时间为26 ns,最高脉冲输出峰值电压为27 kV;利用该辉光等离子体对幅宽为1 000 mm聚四氟乙烯薄膜进行了表面改性处理,处理后其表面接触角由原来的124°降到69°,亲水性能大为提高。     

Spectroscopic diagnostics for an electrical discharge plasma in a liquid

We conducted spectroscopic studies of an electrical discharge plasma in a liquid, used for synthesis of nanosized particles of metals and their compounds. From the intensity ratio of the copper lines, we estimated the electron temperature, and from the Stark broadening of the hydrogen lines H _α we determined the electron density in the electrical discharge plasma. Information about the concentration of copper atoms in the discharge was obtained from analysis of the spectra in the region of resonance lines of copper. We carried out a comparative analysis of the plasma parameters for spark and arc discharges in water, ethanol, and air. Based on the equation of state for an ideal plasma, taking into account the Debye correction, we estimated the pressure in the plasma channel.     

燃烧产物组成激光诱导荧光光谱的测量

对激光诱导荧光（LIF）光谱技术在燃烧过程中的应用进行研究，介绍测量燃烧过程中常见自由基OH和NO的LIF光谱的实验方案，以及采用激光诱导荧光光谱技术测量小分子荧光光谱的方法，利用YAG激光器、染料激光器、CO2激光器、光谱仪、ICCD等设备对燃烧产物中常见小分子自由基OH和NO进行了测量，从实验中得到了自由基OH和NO的荧光光谱。实验结果表明，荧光光谱与激发波长无关，但是激发波长改变后，荧光强度因离开最佳波长而有所下降，这符合分子荧光光谱的特征。与其他光谱技术相比，激光诱导荧光光谱技术具有极高的选择性和灵敏度。     

激光等离子体闪光高速摄影法实验研究

 通过对激光等离子体进行诊断,可以获取激光等离子体重要的参数和演变规律。使用高速CCD对激光等离子体闪光进行拍摄,研究了不同激光能量下激光诱导空气击穿产生的等离子体的形状、大小、颜色以及激光等离子的发展变化特性。实验表明：等离子体在空间上呈发光液滴状,且逆着激光束的方向膨胀。随着激光能量的增大,等离子体在水平方向和竖直方向的尺寸逐渐增大,增大趋势逐步变小。     

Laser-induced fluorescence measurements of velocity within a Hall discharge

The results of a study of laser-induced fluorescence velocimetry of neutral and singly ionized xenon in the plume and interior portions of the acceleration channel of a Hall thruster plasma discharge operating at powers ranging from 250 to 725 W are described. Axial ion and neutral velocity profiles for four discharge voltage conditions (100 V, 160 V, 200 V, 250 V) are measured as are radial ion velocity profiles in the near-field plume. Ion velocity measurements of axial velocity both inside and outside the thruster as well as radial velocity measurements outside the thruster are performed using laser-induced fluorescence with nonresonant signal detection on the xenon ion 5d[4]_7/2–6p[3]_5/2 excitation transition while monitoring the signal from the 6s[2]_3/2–6p[3]_5/2transition. Neutral axial velocity measurements are similarly performed in the interior of the Hall thruster using the 6s[3/2]⁰ ₂–6p[3/2]₂transition with resonance fluorescence collection. Optical access to the interior of the Hall thruster is provided by a 1-mm-wide axial slot in the insulator outer wall. While the majority of the ion velocity measurements used partially saturated fluorescence to improve the signal-to-noise ratio, one radial trace of the ion transition was taken in the linear fluorescence region and yields a xenon ion translational temperature between 400 and 800 K at a location 13 mm into the plume. Received: 27 September 2000 / Revised version: 2 March 2001 / Published online: 9 May 2001     

Laser-induced coherent modulation of solid and liquid surfaces

The interaction of a single spatially coherent, polarized laser beam with an interface possessing microscopic roughness leads to inhomogeneous energy deposition due to the interference between the incident beam and scattered interface fields. At high intensities this can lead to spatially periodic melting or vaporization of solid or liquid layers, and temporary or permanent modification of the interface. We review our experimental and theoretical work and discuss the detailed electrodynamics, spatial spectra, surface structure and temporal growth characteristics of this phenomenon.