Research On The Damage Mechanisms Of Silicon Materials Irradiated By Combined Millisecond And Nanosecond Laser

In this dissertation,millisecond(ms)laser,nanosecond(ns)laser and the combined pulse laser(CPL)that consists of ms laser and ns laser are applied to interact with semiconductor materials.The temperature rise,the melting damage threshold,the through-hole threshold and the damage morphology are studied during a single ms pulse laser and the CPL irradiation.The underlying damage mechanisms are analyzed by experiment and numerical simulation.During the ms laser and CPL irradiation,the temperature rise of silicon surface is measured in real time using an infrared thermometer.The variation histories of the center temperature of silicon surface are obtained with different energy density of incident laser.Based on the theory of heat conduction and thermal elastoplasticity,a two-dimensional axisymmetric model is established for the interaction bewteen laser and silicon.Then,the temperature and stress field are calculated,and the numerical results are compared between the single ms laser irradiation and CPL irradiation.The surface damage thresholds of silicon induced by ms laser,ns laser and CPL are investigated experimentally,using the infrared thermometer and visible light reflection method.Based on the statistics of a large number of experimental datas,the concept of threshold boundary is proposed which can be used to estimate the damage threshold quickly.The corresponding melting damage thresholds are obained via numerical calculation,63.7 J/cm2,2.52 J/cm2 and 32.9 J/cm2,especially.From the experiment and calculation,it is found that the melting damage threshold of silicon induced by CPL is significantly lower than that of the single ms laser,which can be declinded by 39%.The drilling process of silicon is studied which is irradiated by a ms laser with high energy density.The through-hole threshold of the silicon wafer with certain parameters is obtained by experiment and calculation.A variety factors for the through-hole threshold are considered,and it is found that the increase of the doping concentration can reduce the through-hole threshold.Comparing with the single ms laser irradiation,CPL irradiation can reduce the through-hole threshold of silicon wafer,and the effect is more obvious with lower doping concentration.Moreover,the through-hole threshold can be reduced with the decrease of delay time and the increase of ns laser's energy density,and it will finally reach a certain value.The surface damage morphologies of silicon irradiated by a single ms laser and CPL are studied experimentally.Comparing with the single ms laser irradiation,the surface damage caused by CPL is more serious.Besides the cleavage crack,surface ablation and fold are also observed.It is found that the melting depth decreases with the increase of delay time.Based on the experimental and numerical results,it is put forward that the damage mechanism and damage effect of CPL-silicon interaction are closely related to the preheating effect of ms laser,the thermal-mechanical damage of ns laser,and the combined effect of the two laser pulses.The outcome of this dissertation can provide reference for ms laser,ns laser and CPL processing of semiconductor materials in the future.