Research On Femtosecond Laser Ablation Of Silicon Based On Molecular Dynamics Simulations

With the rapid development of our microelectronics technology, nanotechnology,defense engineering, aerospace engineering and other fields, ablation micro-scale andnano-scale, phase change and heat transfer issues become more and more important. Asthe object under ablation micro-scale and nano-scale and heat transfer process involvesspatial and temporal scales are very small, it is very difficult and expensive to get physicalparameters from experimental measurement. And with the rapid development ofcomputer technology, it is more clearly for numerical simulation method to analyze thefactors affecting the processing of laser processing quality. Molecular Dynamicssimulations based on Stillinger-Weber potential and z-layer energy model was employedto study266nm uniform femtosecond laser ablation of silicon surfaces in this paper. Wefocused on the macroscopic quantities in the plane, such as configuration, temperatureand density.Propagation of the thermal wave in the process of laser irradiation leads to phasechanges associated with melting and resolidification of silicon which cause it is difficultto keep its original crystal structure. Furthermore, some defects in the material areappeared, such as irregular deformation and defects of material. For reducing suchinfluence, water-jet guided laser was also investigated by observing the variation ofthermal wave versus time compared with the conventional case.According to the numerical simulation results, the propagation speed of the laserinduced thermal wave was about6417m/s in this paper which is close to the weightedaverage of the transverse and acoustic phonon velocities of6533m/s in Si(100). Thepropagation speed of thermal wave is close to the sound speed of film phonons, heatpropagation direction of phonon energy transport dominated the other direction.Propagation speed of thermal wave is close to the sound speed of phonon. Moreover, thepropagation speed of density wave was about6479m/s in this paper which is similar tothe propagation speed of thermal wave. Simulation results show that thermal affectedzone become smaller and density wave almost remain the same position and disappearedmore quickly which can improve the processing quality obviously because of effect ofwater-jet cooling.