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激光轰击金属液面溅射过程的数值模拟

NUMERICAL SIMULATION OF LASER BOMBARDMENT ON METAL SURFACE SPLASHING PROCESS

  • 摘要: 目前, 极紫外光被认为是制备特征尺寸小于7 nm芯片所必备的光源, 激光轰击液态金属锡靶是其产生的主要方式之一. 采用体积分数(volurne of fluid, VOF)方法建立了激光轰击金属锡液面产生溅射的模型, 并对液料溅射和雾化的演化过程进行了数值模拟, 研究了冠状水花的产生机制以及雾化时的流场变化. 在此基础上, 进一步研究了金属液态锡在不同的能量、光斑直径和脉宽的激光轰击下溅射产生的冠的宽度和高度随时间演化情况. 研究表明: 在激光辐照产生的高压等离子体的高速冲击下, 液膜经历快速运动、冠状射流和雾化3个阶段, 液膜生长主要原因是惯性力作用; 液膜上下两端存在较大的速度梯度是射流形状发生变化的主要原因; 冠边缘处雾化现象的产生是由Rayleigh-Taylor和Plateau-Rayleigh不稳定性共同作用的结果. 在激光轰击下, 冠的高度和宽度随激光能量增加而增大, 但随着时间推移, 冠宽和冠高的增长速率逐渐减小; 激光光斑和脉宽对冠宽及冠高的影响较为复杂, 在前期影响较小, 在后期冠宽及冠高随它们数值增加而减小.

     

    Abstract: Currently, extreme ultraviolet light (EUV) is regarded as an indispensable light source for fabricating chips with feature sizes smaller than 7 nm, which results from liquid metal tin subjected to laser bombardment. In this paper, the method of volume of fluid (VOF) was used to establish a model on fluid sputtering resulting from laser irradiation a liquid metal surface, and to simulate the evolutionary process of splashing and atomization. The formation mechanism of coronal spray and changes in the flow field during atomization were studied further. Moreover, it was also investigated that the evolution of crown width and height produced by splashing liquid tin was subjected to laser with various energy, spot diameters, and pulse widths. The results reveal that the liquid film undergoes three distinct stages, namely rapid motion, coronal jet formation and atomization, when it was subjected to the high-speed impact of high-pressure plasma generated by laser irradiation. In this process, inertial force is identified as the primary factor for contributing to the expansion of the liquid film. The significant velocity gradients between the upper end and lower one of the liquid film lead to the shape variation of the jetting fluid. Furthermore, the atomization phenomenon at the crown edge is the outcome of a instabilities from Rayleigh-Taylor and Plateau-Rayleigh. When the liquid film is exposed to laser bombardment, the height and width of the crown increase with the increase of laser energy. However, the rate of growth for crown width and height gradually diminishes with time going on. The influence of the applied laser spot size and pulse width on crown dimensions is not obvious at the initial stage when the applied values enhance, while the crown width and height decrease during the later stage.

     

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