低密度SnO2靶激光等离子体极紫外光及离带热辐射

极紫外光刻技术是我国当前面临35项“卡脖子”关键核心技术之首.高极紫外光转换效率和低离带热辐射的激光等离子体极紫外光源是极紫外光刻系统的重要组成部分.本文通过采用激光作用固体Sn和低密度SnO₂靶对极紫外光源以及其离带热辐射进行研究.实验结果表明,两种形式Sn靶在波长为13.5 nm附近产生了强的极紫外光辐射.由于固体Sn靶等离子体具有较强自吸收效应,在光刻机中心工作波长13.5 nm处的辐射强度处于非光谱峰值位置.而低密度SnO₂靶具有较弱的自吸收效应,其所辐射光谱的峰值恰好位于13.5 nm处.相比于固体Sn靶,低密度SnO₂靶中处于激发态的Sn离子发生跃迁所产生的伴线减弱,使其在13.5 nm处的光谱效率提升了约20%.另一方面,开展了极紫外光源离带热辐射(400—700 nm)的实验研究,光谱测量结果表明离带热辐射主要是由连续谱所主导,低密度SnO₂靶中含有部分低Z元素O(Z=8),导致其所形成的连续谱强度低,同时离带辐射时间短,因而激光作用低密度SnO₂靶所产生的离带...     

基于强激光辐照固体锡靶产生极紫外光源的实验研究

建立了一套利用高功率YAG激光器辐照固体锡靶产生高转换效率极紫外光 (extreme ultraviolet) 源的实验装置.利用建立的实验装置开展了极紫外光源的强度和转换效率与抽运激光强度关系的实验研究,发现极紫外光源的转换效率随抽运激光强度的变化具有饱和效应.实验发现：当抽运激光能量达到250mJ时,极紫外光源的转换效率最高,波长为13.5nm处0.27nm带宽范围内的极紫外光源的能量转换效率为1.6%,此时对应的激光强度为1.8×10¹¹W/cm². 关键词： 极紫外光 转换效率     

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。     

双激光脉冲打靶形成Gd等离子体的极紫外光谱辐射

高端芯片制造所需要的极紫外光刻技术位于我国当前面临35项"卡脖子"关键核心技术之首.高转换效率的极紫外光源是极紫外光刻系统的重要组成部分.本文通过采用双激光脉冲打靶技术实现较强的6.7 nm极紫外光输出.首先,理论计算Gd¹⁸⁺—Gd²⁷⁺离子最外层4d壳层的4p-4d和4d-4f能级之间跃迁、以及Gd¹⁴⁺—Gd¹⁷⁺离子最外层4f壳层的4d-4f能级之间跃迁对波长为6.7 nm附近极紫外光的贡献.其后开展实验研究,结果表明,随着双脉冲之间延时的逐渐增加,波长为6.7 nm附近的极紫外光辐射强度呈现先减弱、后增加、之后再减弱的变化趋势,在双脉冲延时为100 ns处产生的极紫外光辐射最强.并且,在延时为100 ns处产生的光谱效率最高,相比于单脉冲激光产生的光谱效率提升了33%.此外,发现双激光脉冲打靶技术可以有效地减弱等离子体的自吸收效应,获得的6.7 nm附近极紫外光谱宽度均小于单激光脉冲打靶的情形,且在脉冲延时为30 ns时刻所产生的光谱宽度最窄,约为单独主脉冲产生极紫外光谱宽度的1/3.同时...     

LD泵浦全固态608.1nm和频激光器

本文报道了一种全固态腔内和频608.1 nm激光器。在激光谐振腔两个分臂中,两支激光二极管分别泵浦Nd: YVO₄和Nd: YAG晶体,分别选择1 342 nm波长(Nd: YVO₄晶体的⁴F_3/2-⁴I_13/2谱线)与1 112 nm波长(Nd: YAG晶体的⁴F_3/2-⁴I_11/2谱线)振荡并进行腔内和频。通过优化谐振腔设计,腔内两个波长获得了较好的模式匹配。在两个分臂的交叠部分,利用LBO I类相位匹配进行和频,获得和频608.1 nm激光输出。实验表明,当Nd: YVO₄与Nd: YAG晶体泵浦功率分别为600和740 mW时,获得了功率为23.8 mW、波长为608.1 nm激光输出,激光输出稳定、噪声低。利用本文提出的和频结构是获得608.1 nm激光输出较为有效的方法。     

激光诱导放电等离子体极紫外辐射的模拟

极紫外光刻是目前新一代超高集成度半导体芯片制造流程中重要的一环,激光诱导放电等离子体是极紫外光源产生的重要技术手段之一.本文基于全局状态方程、原子结构计算程序、碰撞辐射模型建立了一个辐射磁流体力学模型,对激光诱导放电等离子体的动力学特性及极紫外的辐射特性进行模拟,模拟复现了放电过程中的箍缩现象,得到的极紫外光的转化效率与实验符合.研究发现放电电流的上升速率对极紫外光的产生有极大的影响,该结果对后续极紫外光输出功率、转化效率以及光谱纯度的提升有重要的指导意义.     

周期极化KTiOPO4晶体和频单块非平面环形腔激光产生连续单频589nm黄光

单次通过周期极化KTiOPO₄晶体和频单块非平面环形腔1064 nm与1319 nm激光产生连续单频589 nm黄光. 通过琼斯矩阵模拟计算对单块非平面Nd:YAG晶体参数进行了优化设计, 实验获得1080 mW和580 mW的连续单频1064 nm和1319 nm激光输出. 两束激光单次通过周期极化KTiOPO₄晶体和频产生14.8 mW, M²=1.14的589 nm黄光, 相应的和频效率为0.9%. 研究了周期极化KTiOPO₄温度对和频效率的影响, 得到其温度接收带宽为1.5℃. 通过改变1064 nm Nd:YAG晶体的温度可实现589 nm黄光波长精确对应钠原子D_2a吸收谱线, 调谐精度达到0.164 pm.     

脉冲CO_2激光烧蚀锡靶等离子体的数值模拟

使用一维辐射流体力学程序MULTI模拟了脉冲CO_2激光烧蚀平面锡靶的过程,研究了脉冲宽度、峰值功率密度、靶材初始密度对锡等离子体电子密度、电子温度的时空分布的影响,并结合统计分析得到最有利于产生13.5nm极紫外光的激光脉冲宽度。模拟结果表明,脉冲宽度为100~200ns的长脉冲激光产生的等离子体有利于实现极紫外输出的最佳条件,通过分析等离子体的电子密度、电子温度的分布对这一结论进行了解释。临界电子密度区域有效吸收了脉冲能量,而低密度的羽辉对激光与极紫外辐射的吸收很少。采用长脉冲激光,使得辐射极紫外等离子体持续时间更长,是提高极紫外辐射效率的有效手段。同时模拟还发现,靶材初始密度对等离子体参数的影响不大。     

Gd靶激光等离子体6.7nm光源的实验研究

本文对Gd靶激光等离子体极紫外光源进行了实验研究, 在 6.7 nm附近获得了较强的辐射, 并研究了6.7 nm 附近光辐射随打靶激光功率密度变化的规律以及收集角度对极紫外辐射的影响. 同时, 对平面Gd靶激光等离子光源的离子碎屑角分布进行了测量, 发现从靶面的法线到沿着靶面平行方向上Gd离子数量依次减少. 进一步研究结果表明采用0.9 T外加磁场的条件下可取得较好的Gd 离子碎屑阻挡效果.     

激光等离子体13.5 nm极紫外光刻光源进展

半导体产业是高科技、信息化时代的支柱。光刻技术,作为半导体产业的核心技术之一,已成为世界各国科研人员的重点研究对象。本文综述了激光等离子体13.5 nm极紫外光刻的原理和国内外研究发展概况,重点介绍了其激光源、辐射靶材和多层膜反射镜等关键系统组成部分。同时,指出了在提高激光等离子体13.5 nm极紫外光源输出功率的研究进程中所存在的主要问题,包括提高转换效率和减少光源碎屑。特别分析了目前已实现百瓦级输出的日本Gigaphoton公司和荷兰的ASML公司的极紫外光源装置。最后对该项技术的发展前景进行了总结与展望。     

Emission characteristics of debris from CO<Subscript>2</Subscript> and Nd:YAG laser-produced tin plasmas for extreme ultraviolet lithography light source

We describe a comparative study of the emission characteristics of debris from CO₂ and Nd:YAG laser-produced tin plasmas for developing an extreme-ultraviolet (EUV) lithography light source. Tin (Sn) ions and droplets emitted from a Sn plasma produced by a CO₂ laser or an Nd:YAG laser were detected using Faraday cups and quartz crystal microbalance (QCM) detectors, respectively. The droplets were also monitored by using silicon substrates as witness plates. The results showed higher ion kinetic energy and lower particle emission for the CO₂ laser than the Nd:YAG laser for the same laser energy (50 mJ). The average ion energy was 2.2 keV for the CO₂ laser-produced plasma (LPP), and 0.6 keV for the Nd:YAG LPP. The debris accumulation of the CO₂ LPP detected by the QCM detectors, however, was less than one fourth of that of the Nd:YAG LPP for the same laser energy. Using ion energy data, the mirror lifetime is estimated for the CO₂ and Nd:YAG lasers. In both cases, the upper limit of the number of shots was of the order of 10⁶. PACS  52.38.DX; 52.38.Ph; 52.38.Mf     

Micro-pinch formation and extreme ultraviolet emission of laser-induced discharge plasma

Extreme ultraviolet(EUV) source produced by laser-induced discharge plasma(LDP) is a potential technical means in inspection and metrology. A pulsed Nd:YAG laser is focused on a tin plate to produce an initial plasma thereby triggering a discharge between high-voltage electrodes in a vacuum system. The process of micro-pinch formation during the current rising is recorded by a time-resolved intensified charge couple device camera. The evolution of electron temperature and density of LDP are obtained by optical emission spectrometry. An extreme ultraviolet spectrometer is built up to investigate the EUV spectrum of Sn LDP at 13.5 nm. The laser and discharge parameters such as laser energy, voltage, gap distance,and anode shape can influence the EUV emission.     

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 focal spot size on in-band 13.5 nm extreme ultraviolet emission from laser-produced Sn plasma

The effect of focal spot size on in-band 13.5 nm extreme ultraviolet (EUV) emission from laser-produced Sn plasmas was investigated for an EUV lithography light source. Almost constant in-band conversion efficiency from laser to 13.5 nm EUV light was noted with focal spot sizes from 60 to 500 microm. This effect may be explained by the opacity of Sn plasmas. Optical interferometry showed that the EUV emission must pass through a longer plasma with higher density when the focal spot is large, and strong reabsorption of EUV light was confirmed by a dip located at 13.5 nm in the spectrum.     

Spectral and ion emission features of laser-produced Sn and SnO_2 plasmas

We have made a detailed comparison of the atomic and ionic debris, as well as the emission features of Sn and SnO_2 plasmas under identical experimental conditions. Planar slabs of pure metal Sn and ceramic SnO_2 are irradiated with1.06 μm, 8 ns Nd:YAG laser pulses. Fast photography employing an intensified charge coupled device(ICCD), optical emission spectroscopy(OES), and optical time of flight emission spectroscopy are used as diagnostic tools. Our results show that the Sn plasma provides a higher extreme ultraviolet(EUV) conversion efficiency(CE) than the Sn O2 plasma.However, the kinetic energies of Sn ions are relatively low compared with those of SnO_2. OES studies show that the Sn plasma parameters(electron temperature and density) are lower compared to those of the SnO_2 plasma. Furthermore, we also give the effects of the vacuum degree and the laser pulse energy on the plasma parameters.     

极端远紫外光刻的等离子体光源及其光学性质研究进展

现代技术的飞速发展需要集成电路不断小型化，因而开发下一代光刻光源以满足小型化的要求成为当前的一项紧迫任务。目前工业界确定的下一代光刻光源是波长为13．5nm的极端远紫外（EUV）光源，它能够把光刻技术扩展到32nm以下的特征尺寸，氙和锑材料的等离子体光源被认为是这种光源的最佳候选者。文章在介绍EUV光刻原理和EUV光源基本概念的基础上，讨论了目前研究得最多、技术最成熟的激光产生的和气体放电产生的等离子体EUV光源，对EUV光源的初步应用进行了简单介绍，并着重对氙和锑材料产生的等离子体发射性质和吸收性质的实验与理论研究进展进行了详细介绍与讨论。目前的理论研究进展表明，统计物理模型还不能很好地预测氙和锑等离子体的发射与吸收光谱，因此迫切需要发展细致能级物理模型，以得到更为精确的等离子体光学性质参数，并用于指导实验设计。提高EUV转换效率。     

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。     

Pump–probe studies of EUV and X-ray emission dynamics of laser-irradiated noble gas droplets

The interaction of high intensity 100-ps laser pulses with micron-sized noble gas (argon and krypton) droplets is experimentally investigated via a series of pump–probe experiments monitoring the delay-dependent X-ray and extreme ultraviolet (EUV) emission, and by imaging frequency-doubled probe light scattered from the interaction region. An understanding of the time scales for this interaction is important for optimization of EUV sources for next-generation lithography that utilizes laser-produced plasmas (LPP). Depending on the spectral region of interest, the type of emission, and the droplet characteristics, the effective emission lifetime was found to extend from a few hundred picoseconds to as long as several nanoseconds, in agreement with the expected plasma expansion, EUV excitation, and recombination emission time scales. Received: 22 August 2002 / Accepted: 8 February 2003 / Published online: 28 May 2003 RID="*" ID="*"Corresponding author. Fax: +1-301/3149-363, E-mail: riq@wam.umd.edu     

Laser-plasma extreme ultraviolet source at 6.7?nm using a rotating cryogenic Xe target

A laser-plasma source comprising a rotating cryogenic solid-state Xe target has been studied for use in extreme ultraviolet lithography (EUVL) systems equipped with La/B₄C mirrors. The laser-to-EUV power conversion efficiency (CE) of the cryogenic Xe target was improved to achieve a maximum CE of 0.15?% at 6.7?nm with 0.6?% bandwidth. We successfully demonstrated the continuous generation of EUV light with an average power of 80?mW at 6.7?nm with 0.6?% bandwidth using a Nd:YAG slab laser at a repetition rate of 320?Hz and an average power of 100?W. Scaling-up of the laser-plasma source for use as a future EUVL source is also discussed.