双脉冲CO2激光液滴Sn靶等离子体与EUV辐射特性的研究

Extreme ultraviolet lithography(EUVL) with a wavelength of 13.5 nm is being considered as the most promising candidate for the next generation of semiconductor manufacturing. The EUV sources technology is the most challenge of EUVL. Due to its both high conversion efficiency(CE) and low-debris emission, pulsed CO2 laser produced tin-based droplet target plasmas is being considered the most suitable sources for the EUVL setup.In order to get high CE and low-debris laser produced plasma EUV source, a double pulse laser irradiation scheme is firstly proposed in China, which consits a prepulse of Nd:YAG laser and a main pumping pulse of CO2 laser.Both double laser pulse parameters and size of droplet target will be optimized to achieve the best results.The physical mechanism of EUV emissions and debris generation of CO2 laser produced tin droplet target plasmas will be further investigated theoretically and numerically. The technique of debris mitigation will be studied by applying buffer gas, static electric field or magnetostatic field. By optimizing the parameters, a low debris and narrow band EUV sources will be obtained and the 2% in-band at 13.5 nm EUV-CE is expected to reach 4%.

国际上广泛认为波长13.5 nm的极紫外光刻(EUVL)是下一代半导体光刻最主要的候选技术，而EUV光源是制约EUVL技术的主要瓶颈。基于脉冲CO2激光液滴Sn靶的EUV光源具有高转换效率(CE)和低碎屑的特性，是未来EUVL设备最合适的光源。本项目在国内率先提出利用Nd:YAG激光作为预脉冲，CO2激光作为主脉冲，实验研究预脉冲后CO2激光作用液滴锡靶等离子体与极紫外辐射的特性，通过优化脉冲激光和液滴锡靶尺寸等参数，获得高CE和低碎屑特性的等离子体光源EUV输出。通过数值模拟与理论分析，深入理解脉冲CO2激光驱动液滴Sn靶EUV辐射及产生等离子体碎屑的物理机制。通过施加缓冲气体、静电场或静磁场等方法研究碎屑的减缓屏蔽方法。在优化实验参数的基础上，实现低碎屑、窄带宽、中心波长13.5 nm处2%带宽转换效率达到4%的双脉冲激光液滴Sn靶EUV辐射光源。

基于激光等离子体的 13.5 nm 极紫外光源的极紫外光刻技术可进一步降低光刻工艺节点至 10 nm 以下，从而成为最有希望的下一代光刻技术。液滴锡靶以及预脉冲激光技术的引入，极大地推进了激光等离子体极紫外光源的转换效率及碎屑产额。本项目以激光等离子体极紫外光源的产生为研究背景，搭建了脉冲激光与液滴锡靶相互作用同步系统，开展了双脉冲激光作用下液滴锡靶等离子体动力学特性的实验研究。脉冲激光所产生的锡等离子体中的高能锡离子碎屑，可直接侵害光源系统中的各光学元件，特别是EUV收集镜，从而影响光源的运行寿命，实验中通过优化激光与液滴靶参数，并施加缓冲气体，电磁场等措施获得了最佳的转换效率与最低碎屑产额的激光等离子体光源EUV输出。通过脉冲激光液滴Sn靶等离子体的理论分析与数值模拟有助于我们对激光等离子体EUV辐射与等离子体碎屑特性的理解。