NUMERICAL SIMULATION OF LASER BOMBARDMENT ON METAL SURFACE SPLASHING PROCESS

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.