Mitigation of energetic ion debris from Gd plasma using dual laser pulses and the combined effect with ambient gas

For the next-generation beyond extreme ultraviolet lithography(EUVL) sources, gadolinium(Gd) plasma with emission wavelength at 6.7 nm seems to be the leading candidate. Similar to the Sn target 13.5 nm light source, ion debris mitigation is one of the most important tasks in the laser-produced Gd plasma EUV source development. In this paper,a dual-laser-pulse scheme, which uses a low energy pulse to produce a pre-plasma and a main pulse after a time delay to shoot the pre-plasma, is employed to mitigate the energetic ion generation from the source. Optimal conditions(such as pre-pulse energy and wavelength, and the time delay between the pre-pulse and the main pulse for mitigating the ion energy) are experimentally obtained, and with the optimal conditions, the peak of the ion energy is found to be reduced to1/18 of that of a single laser pulse case. Moreover, the combined effect by applying ambient gas to the dual-pulse scheme for ion debris mitigation is demonstrated, and the result shows that the yield of Gd ions is further reduced to around 1/9 of the value for the case with dual laser pulses.     

多电荷态气脉冲式ECR离子源(摘要)

A new type of pulse sources of multicharged ions,namely,a quasi-gasdynamic ECR source is propose.Its main difference from the classical ECR ion sources is a different,quasi-gasdynamic regime of plasma confinement in a magnetic trap.A zero-dimensional model was constructed that describes gas breakdown, formation of charge state distribution in a plasma,and plasma flux through the plugs of the trap.A wide spectrum of model experimental studies was covered.Plasma was produced and heated by a pulse(1ms) gyrotron at the frequency of 37.5GHz and power of 100kW in a cusp magnetic trap with magnetic field in plugs up to 2.5T.Such a trap has axisymmetric configuration and allows one to realize a quasi-gasdynamic regime of confinement with reliable stabilization of MHD perturbations.It was demonstrated that with such a confinement regime it is possible to generate multicharged ions and create intense(more than 1A/cm~2)ion fluxes through the trap plugs.Comparison of results of calculations and data of experiments shows that they are in a good agreement,which allows us to predict with a high degree of certainty creation of an ECR source of a new generation. The data obtained were used to design a pulse quasi-gasdynamic ECR ion source with pumping at the frequency of 100GHz,effective trap size lm,average ion charge in plasma comparable with that in the best classical MCI ECR sources but with an order of magnitude higher flux density and absolute magnitude of plasma flux through trap plugs.Creation of intense plasma fluxes allows one to extract high-current MCI beams of high brightness.Transverse homogeneity of a plasma flux makes it possible to use multi-aperture extraction system for formation on broad intense MCI beams.     

SECRAL在18GHz频率下产生强流高电荷态离子束的初步结果

A Superconducting ECR ion source with Advanced design in Lanzhou (SECRAL) was successfully built to produce intense beams of highly charged ions for Heavy Ion Research Facility in Lanzhou (HIRFL).The ion source has been optimized to be operated at 28GHz for its maximum performance.The superconducting magnet confinement configuration of the ion source consists of three axial solenoid coils and six sextupole coils with a cold iron structure as field booster and clamping.For 28GHz operation,the magnet assembly can produce peak mirror fields on axis 3.6T at injection,2.2T at extraction and a radial sextupole field of 2.0T at plasma chamber wall.A unique feature of SECRAL is that the three axial solenoid coils are located inside of the sextupole bore in order to reduce the interaction forces between the sextupole coils and the solenoid coils. During the ongoing commissioning phase at 18GHz with a stainless steel chamber,tests with various gases and some metals have been conducted with microwave power less than 3.2kW and it turned out the performance is very promising.Some record ion beam intensities have been produced,for instance,810eμA of O~(7 ),505eμA of Xe~(20 ),306eμA of Xe~(27 ),21eμA of Xe~(34 ),2.4eμA of Xe~(38 ) and so on.To reach better results for highly charged ion beams,further modifications such as an aluminium chamber with better cooling,higher microwave power and a movable extraction system will be done,and also emittance measurements are being prepared.     

A Newly Designed 14.5 GHz All Permanent ECR Ion Source in IMP

A new all permanent ECR (Electron Cyclotron Resonance) ion source LAPECR2 (Lanzhou All Permanent ECRIS No. 2) is now under developing in IMP. This source will be used to set up on thc IMP 400 HV (High Voltage) platform. This HV platform aims to deliver high ion beams from low charge state to very high charge state, so the rigorous requirement to this ECRIS is obvious. To satisfy this requirement, the ion source is designed to be a very large one, which has very large volumc plasma chamber, larger ECR length and mirror length, and very strong 3 -dimension magnetic field. The detail parameters, are shown in Table 1 listed below.     

Experimental results of helicon source

Helicon plasma sources are known as efficient generators of uniform and high density plasma. A helicon plasma source was developed for the investigation of plasma stripping and plasma lenses at the Institute of Modern Physics, CAS. In this paper, the characteristics of helicon plasma have been studied by using a Langmuir four-probe and a high plasma density up to 3.9× 10^13/cm^3 has been achieved with the Nagoya type III antenna. In the experiment, several important phenomena were found： （1） for a given magnetic induction intensity, the plasma density became greater with the increase of RF power; （2） helicon mode appeared at RF power between 300 W and 400 W; （3） the plasma density gradually tended to saturation as the RF power increased to the higher power; （4） a higher plasma density can be obtained by a good match between the RF power and the magnetic field distribution. The key issue is how to optimize the matching between the RF power and the magnetic field. Moreover, some tests on the extraction of ion beams were performed, and preliminary results are given. The problems which existed in the helicon ion source will be discussed and the increase in beam density will be expected by extraction system optimum.     

DECRIS-4离子源的初步测试结果

The ECR ion source DECRIS-4 has been designed and constructed at the FLNR JINR to be used as a second injector of heavy multiply charged ions for the U-400 cyclotron.The design of the magnetic structure of the source was based on the idea of the so-called"magnetic plateau".The axial magnetic field is formed by three independent solenoids enclosed in separated iron yokes.As a result the superposition of the coils and hexapole magnetic fields creates the enlarged resonance volume.The first experiments showed that the source was able to produce more than 300eμA of Ar~(8 ) when only 100W of microwave power was used. During the last experiment almost 500eμA of Ar~(8 ) was extracted with the same power.In this paper we will present the preliminary results with other gaseous ions,such as oxygen,krypton and xenon.     

LAPECR2离子源在320kV高压平台上的试运行

The high charge state all permanent Electron Cyclotron Resonance Ion Source(ECRIS)LAPECR2 (Lanzhou All Permanent magnet ECR ion source No.2)has been successfully put on the 320kV HV platform at IMP and also has been connected with the successive LEBT system.This source is the largest and heaviest all permanent magnet ECRIS in the world.The maximum mirror field is 1.28T(without iron plug)and the effective plasma chamber volume is as large as (?)67mm×255mm.It was designed to be operated at 14.5GHz and aimed to produce medium charge state and high charge state gaseous and also metallic ion beams.The source has already successfully delivered some intense gaseous ion beams to successive experimental terminals.This paper will give a brief overview of the basic features of this permanent magnet ECRIS.Then commissioning results of this source on the platform,the design of the extraction system together with the successive LEBT system will be presented.     

Mechanical Analysis and Measurements of a Multicomponent NbTi/Cu Superconducting Magnets Structure for the Fully Superconducting Electron Cyclotron Resonance Ion Source

A fully superconducting electron cyclotron resonance(ECR) ion source(SECRAL Ⅱ) is currently being built in the Institute of Modern Physics,Chinese Academy of Sciences.Its key components are three superconducting solenoids(Nb-Ti/Cu) and six superconducting sextupoles(Nb-Ti/Cu).Different from the conventional superconducting ECR magnetic structure,the SECRAL Ⅱ includes three superconducting solenoid coils that are located inside the superconducting sextupoles.The SECRAL Ⅱ can significantly reduce the interaction forces between the sextupole and the solenoids,and the magnets can also be more compact in size.For this multi-component SECRAL Ⅱ generating its self Held of ~8T and being often exposed to the high self Geld,the mechanical analysis has become the main issue to keep their stress at 200 MPa on coils.The analytical and experimental results in mechanics are presented in the SECRAL Ⅱ structure.To improve the accuracy and efficiency of analysis,according to the composite rule of micromechanics,the equivalent uniform windings are used to simuiate the epoxy-impregnated Nb-Ti/Cu coils.In addition,using low temperature strain gauges and a wireless fast strain acquisition system,a fundamentai experiment on the strains developments of a sextupole is reported.Finally,based on our analysis,the stresses and deformations for its assembly of each SECRAL Ⅱ coil will be further optimized.     

A Microwave Air Plasma Source under Atmospheric Pressure

We develop a new cavity with a mode similar to TE13 to produce microwave plasma, named APMPS Ⅱ, which is able to produce a mass of air plasma with diameter of around 6 cm, equipped with about 3 kW input power under one atmosphere. The plasma seems to be homogeneous without significant filamentous discharge as observed by common camera device. We present the theory of this cavity, show the distribution of electric field of several planes inside the cavity and give some experimental results.     

14.5GHz紧凑型、低成本、全永磁ECR离子源

A compact 14.5GHz electron cyclotron resonance (ECR) ion source for the production of slow, multiply charged ions has been constructed,with the plasma-confining magnetic field produced exclusively by permanent magnets.Microwave power of up to 175W in the frequency range from 12.75 to 14.SGHz is transmitted from ground potential via a PTFE window into the water-cooled plasma chamber which can be equipped with an aluminum liner.The waveguide coupling system serves also as biased electrode,and two remotely-controlled gas inlet valves connected via an insulating break permit plasma operation in the gas- mixing mode.A triode extraction system sustains ion acceleration voltages between 1kV and 10kV.The ECR ion source is fully computer-controlled and can be remotely operated from any desired location via Ethernet.     

脉冲激光辐照液滴锡靶等离子体极紫外辐射的实验研究

采用波长13.5 nm的极紫外光作为曝光光源的极紫外光刻技术是最有潜力的下一代光刻技术之一, 它是半导体制造实现10 nm及以下节点的关键技术. 获得极紫外辐射的方法中, 激光等离子体光源凭借转换效率高、收集角度大、碎屑产量低等优点而被认为是最有前途的极紫外光源. 本文开展了脉冲TEA-CO₂激光和Nd:YAG激光辐照液滴锡靶产生极紫外辐射的实验, 对极紫外辐射的谱线结构以及辐射的时空分布特性进行了研究.实验发现: 与TEA-CO₂激光相比, 较高功率密度的Nd:YAG激光激发的极紫外辐射谱存在明显的蓝移; 并且激光等离子体光源可以认为是点状光源, 其极紫外辐射强度随空间角度变化近似满足Lambertian分布.     

激光等离子体极紫外光刻光源

研究并讨论了下一代光刻的核心技术之一—激光等离子体极紫外光刻光源。简要介绍了欧美和日本等国极紫外光刻技术的发展概况,分析了新兴的下一代13.5 nm极紫外光刻光源的现状,特别讨论了国内外激光等离子体极紫外光刻光源的现状,指出目前其存在的主要问题是如何提高光源的转化效率和减少光源的碎屑。文中同时概述了6.x nm（6.5～6.7 nm）极紫外光刻光源的最新研究工作。最后,介绍了作者所在研究小组近年来在极紫外光源和极紫外光刻掩模缺陷检测方面开展的研究工作。     

Characterization of a laser-plasma extreme-ultraviolet source using a rotating cryogenic Xe target

A laser-plasma source for extreme-ultraviolet (EUV) light that uses a rotating cryogenic solid-state Xe target has been characterized. We focused on parameters at the wavelength of 13.5 nm with 2% bandwidth required for an EUV lithography source and investigated improvements of the conversion efficiency (CE). With the drum rotating, there was an increase in CE and less fast ions compared with the case for the drum at rest. It is considered that the Xe gas on the target surface can produce optimal-scale plasma, and satellite emission lines in Xe plasma effectively increase the EUV intensity, and the ion number is decreased by the gas curtain effect. The dependence of CE on the laser wavelength, laser energy and intensity also studied. As a result, the maximum CE was 0.9% at 13.5 nm with 2% bandwidth under the optimal condition. By continuous irradiation of a Nd:YAG slab laser at a repetition rate of 320 Hz and an average power of 110 W, the target continuously generated EUV light with an average power of 1 W at 13.5 nm with 2% bandwidth. The achieved performances provide valuable information for the design of a future EUV lithography source.     

Effect of Nd:YAG Laser Energy on Multilayer Hollow Nanofiber Target's Extreme Ultraviolet Conversion Efficiency

Extreme ultraviolet (EUV), 13.5 nm, lithography techniques have attracted a great deal of attention because of the mass production of 50 nm critical dimensions as the future generation lithography. One of key issues to be clarified for the development of a 13.5 nm EUV light source is to improve the conversion efficiency (CE). In this paper, hollow multilayer nanofibers were fabricated through the combination of a layer-by-layer (LBL) technique with the electrospinning technique. The obtained hollow fibers were employed as EUV targets. In order to improve the CE, the irradiated laser energy was increased from 10¹⁰ to 10¹¹ W/cm² and the CE was correspondingly increased from 0.43 to 0.83%.     

Bi靶激光等离子体极紫外光源以及碎屑辐射特性研究

激光等离子体极紫外光源具有体积小、稳定性高和输出波长可调节等优势,在极紫外光刻领域发挥着重要的作用。Bi靶激光等离子体极紫外光源在波长9～17 nm范围内具有较宽的光谱,可应用于制造极紫外光刻机过程中所需的极紫外计量学领域。利用平像场光谱仪和法拉第杯对Bi靶激光等离子体极紫外光源以及离子碎屑辐射特性进行了实验研究。在单脉冲激光打靶条件下,实验中观察到Bi靶激光等离子极紫外光谱在波长12.3 nm处出现了一个明显的凹陷,其对应着Si L-edge的吸收,是Bi元素光谱的固有属性。相应地在波长为11.8和12.5 nm位置处产生了两个宽带的辐射峰。研究了两波长光谱特性以及辐射强度随激光功率密度的变化。结果表明,在改变聚焦光斑大小实现不同激光功率密度（0.7×1010～3.1×1010 W·cm-2）过程中,当功率密度为2.0×1010 W·cm-2时两波长处的光辐射最强,其原因归结为Bi靶极紫外光辐射强度受激光能量用于支撑等离子膨胀的损失和极紫外光被等离子体再吸收之间的平衡制约所致。在改变激光能量实现不同激光功率密度过程中,由于烧蚀材料和产生两波长所需高阶离子随着功率密度的增加而增加,增强了两波长处的光辐射。进一步,研究了双脉冲激光对Bi靶极紫外光谱辐射特性影响,实验发现双脉冲打靶下原来在单脉冲打靶时出现在波长13～14 nm范围内的凹陷消失。最后,对单脉冲激光作用Bi靶产生极紫外光源碎屑角分布进行了测量。结果表明,当探测方向从靶面法线方向移动到沿着靶面方向上的过程中,探测到Bi离子动能依次减小,并且离子动能随激光脉冲能量降低而呈线性减小。此项研究有望为我国在研制极紫外光刻机过程所需的计量学领域提供技术支持和打下夯实的基础。     

高频ECR离子源的最新进展

As they are first optimized for their ion losses,ECRISs are always under a fundamental compromise: having high losses and strong confinement at the same time.To help ECR ion source developers in the design or improvement of existing machines,general comments are presented in a review article being soon published. In this 160 pages contribution,fundamental aspects of ECRISs are presented,with a discussion of electron temperature and confinement and ion confinement.Then,as microwaves play a key role in these machines, a chapter presents major guidelines for microwave launching and coupling to ECR plasma.Moreover,once ECR plasma is created,understanding this plasma is important in ion sourcery;and a section is dedicated to plasma diagnostics with an emphasis on the determination of electron and ion density and temperature by vacuum ultraviolet(VUV)spectroscopy.Another chapter deals with the role of magnetic confinement and presents updated scaling laws.Next chapter presents different types of ECRISs designed according to the main parameters previously described.Finally,some industrial applications of ECRISs and ECR plasmas in general are presented like ion implantation and photon lithography.Some hints taken from this review article are presented in the following article.     

“LPP-EUV”光源中的高功率CO_2激光监测与控制系统

为了满足激光诱导等离子体（LPP）体制下极紫外（EUV）光源对CO2激光器提出的稳定性需求,建立了简化的CO2激光传输系统模型,根据光束稳定性需求对光束功率、指向和位置的监测与控制方法进行了理论和实验研究。根据高功率CO2激光传输系统特点,在实验室内建立了上述光束监测和控制实验系统,包括光束功率控制模块、光束指向控制模块和光束参数监测模块,其中光束参数监测模块可实时测量光束功率、指向、尺寸及发散角等重要参数。仿真与实验结果表明：光束功率控制模块对线偏振激光功率的控制接近1%～100%,光束指向控制模块实现的光束指向稳定度在10μrad以内,可满足CO2激光驱动源的高稳定性要求。     

Investigation of contact lithography in the 5–20 nm region with a laser plasma source

In this paper, we present experiments of extreme ultraviolet (EUV) contact lithography based on a compact laser-produced plasma (LPP) and investigated the radiation of the plasma from Cu, Fe, W targets. We measured the depth of development of a polychlorinated methylstyrene (PCMS) resist exposed through a 100 I mm⁻¹ Cu net for times ranging from 10 to 40 minutes using different targets.     

等离子体密度对放电等离子体极紫外光源影响研究

等离子体状态是决定极紫外光源功率和转换效率的最重要因素之一,理论和实验研究上Xe气流量对放电等离子体极紫外光源辐射谱和等离子体状态的影响,对于优化光源工作条件具有重要的意义。理论上,采用碰撞-辐射模型,模拟了非局部热力学平衡条件下,不同电离度的离子丰度分布随电子温度和离子密度的变化。推导了Xe8+~Xe11+离子4d-5p跃迁谱线强度随电子温度的变化趋势。实验上,采用毛细管放电机制,利用罗兰圆谱仪测量和分析了不同等离子体密度条件下,放电等离子体极紫外光谱的变化,分析了Xe气流量对等离子体状态的影响。理论和实验结果表明： 相同的电流条件下,等离子体箍缩时的平均电子温度随着Xe气流量的增加而降低。对于4d-5p跃迁,低电离度离子与高电离度离子谱线强度的比值随着温度的增加而减少。电流28 kA、Xe气流量0.4 sccm(cm3·min-1)时,等离子体Z 箍缩平均电子温度位于29 eV附近。Xe气流量增加时,受离子密度和最佳电子温度的影响,实现Xe10+离子4d-5p跃迁13.5 nm(2%带宽)辐射谱线强度最优化的Xe气流量位于0.3~0.4 sccm之间。