激光锡等离子体极紫外光源发射光谱诊断研究

doi:10.3964/j.issn.1000-0593(2025)07-1834-08

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摘要：由于具有发光体积小、能量转换效率高、稳定性高和非相干等特点，激光等离子体极紫外（LPP-EUV）光源在先进半导体制造与量测、材料表面分析和EUV计量学等领域应用广泛。本文开展了1 μm固体激光Sn等离子体EUV光源发射光谱诊断研究。首先，在真空中测量了不同激光峰值功率密度下1 μm激光激发固体Sn靶等离子体的13.5 nm带内辐射能量、7~24 nm EUV波段和350~750 nm 可见光（VIS）波段的发射光谱，计算了能量转换效率（CE）和光谱纯度（SP），分析了激光峰值功率密度对Sn等离子体EUV光谱、VIS光谱、CE和SP的影响规律。在本实验的参数范围内，CE随着激光峰值功率密度的提升先快速增大后缓慢减小，在激光峰值功率密度为5.2×10¹¹ W·cm^-2时达到最大值2.47%。SP随激光峰值功率密度的提升而增大，在1.5×10¹² W·cm^-2时达到最大值7.52%。然后，基于Sn等离子体VIS波段的时间分辨光谱，采用萨哈-玻尔兹曼图法和斯塔克展宽法计算了等离子体起爆后60～160 ns的电子温度（T_e）和电子密度（n_e），研究了真空中Sn等离子体T_e和n_e随时间的演化规律，并进一步分析了T_e和n_e对EUV波段辐射和13.5 nm带内辐射的影响规律。结果表明，激光峰值功率密度的上升会导致等离子体T_e和n_e的上升，T_e和n_e的变化影响着不同电荷态离子的分布，进而导致EUV辐射谱分布的变化。在本实验的参数范围内，随着T_e和n_e增大，CE先增大后减小，而SP一直增大。过低的T_e会导致Sn等离子体UTA峰位未达到13.5 nm，过高的T_e会导致更多的驱动激光能量转化为13.5 nm以下的EUV辐射，造成CE未达到最优。以上研究结果为固体激光驱动LPP-EUV光源的工程化研发，以及我国自主开展EUV光刻、EUV计量与检测提供了研究基础与技术支持。

关键词：极紫外光源；激光等离子体；发射光谱诊断；等离子体温度；电子密度

Abstract：Due to their characteristics of a small luminous volume, high energy conversion efficiency, high stability, and coherence, laser-produced plasma extreme ultraviolet (LPP-EUV) light sources are widely used in the fields of advanced semiconductor manufacturing and inspection, material surface analysis, and EUV metrology. In this work, the emission spectrum diagnosis of a one μm solid-state laser Sn plasma EUV light source was carried out. First, the 13.5 nm in-band radiation energy, the emission spectrum of the 7~24 nm EUV band, and the 350~750 nm visible light (VIS) band of 1 μm laser-excited solid Sn target plasma in vacuum under different laser peak power densities were measured. The energy conversion efficiency (CE) and spectral purity (SP) were calculated, and the influence of laser peak power density on EUV and VIS spectrum, CE, and SP of Sn plasma was analyzed. Within the parameter range of this experiment, CE increases rapidly at first and then decreases slowly with the increase in laser peak power density, reaching a maximum value of 2.47% at a laser peak power density of 5.2×10¹¹ W·cm^-2. SP increases with the increase of laser peak power density and reaches a maximum value of 7.52% at 1.5×10¹² W·cm^-2. Then, based on the time-resolved VIS spectrum of Sn plasma, the electron temperature (T_e) and electron density (n_e) from 60 to 160 ns after plasma initiation were calculated using the Saha-Boltzmann plot and Stark broadening method, and the temporal evolution of T_e and n_e of Sn plasma in vacuum was studied. The influence of T_e and n_e on EUV band radiation and 13.5 nm in-band radiation was further analyzed. The results show that an increase in laser peak power density leads to an increase in plasma T_e and n_e, and the changes in T_e and n_e affect the distribution of ions with different charge states, causing a change in the EUV radiation spectral distribution. Within the parameter range of this experiment, CE initially increases and then decreases with the increase of T_e and n_e, whereas SP continues to increase. A Te value that is too low will prevent the UTA peak of Sn plasma from reaching 13.5 nm, and a T_e value that is too high will cause more driving laser energy to be converted into EUV radiation below 13.5 nm, resulting in CE not reaching its optimal value. The above research results provide a research foundation and technical support for the engineering development of solid-state laser-driven LPP-EUV light source, as well as the independent development of EUV lithography, EUV metrology, and inspection in China.

Key words：Extreme ultraviolet light source; Laser-produced plasma; Emission spectrum diagnosis; Plasma temperature; Electron density

收稿日期: 2024-11-04 修订日期: 2024-12-26

中图分类号:

O433.1

基金资助: 国家自然科学基金项目(62405336)，中国博士后科学基金第74批面上项目（2023M743643），国家资助博士后研究人员计划项目（GZB20230791）资助

通讯作者: 林楠 E-mail: nanlin@siom.ac.cn

作者简介: 胡桢麟，1995年生，中国科学院上海光学精密机械研究所博士后 e-mail: huzhenlin@siom.ac.cn
王天泽，1993年生，中国科学院上海光学精密机械研究所博士研究生 e-mail: tzwang@siom.ac.cn
胡桢麟，王天泽：并列第一作者

引用本文:

胡桢麟，王天泽，何梁，林楠，冷雨欣，陈卫标. 激光锡等离子体极紫外光源发射光谱诊断研究[J]. 光谱学与光谱分析, 2025, 45(07): 1834-1841.
HU Zhen-lin, WANG Tian-ze, HE Liang, LIN Nan, LENG Yu-xin, CHEN Wei-biao. Research on Emission Spectrum Diagnosis of Laser-Produced Tin Plasma Extreme Ultraviolet Source. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2025, 45(07): 1834-1841.

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