Behavior Of Crystal Orientation For Femtosecond Laser Irradiation Of Polycrystalline Silicon

Femtosecond laser processing has short pulse duration,high pulse peak power,thermal effects small and precise targeted focusing.In the case of femtosecond lasers,rapid heating,cooling,and ultra-fast mechanical deformation of materials under extremely strong electronic excitation conditions have triggered researchers'interest in the behavior and properties of materials.Different crystal orientations of materials have different surface atom energy and density,so different crystal orientations have different mechanical,electrical,optical,and chemical properties,and small discrepancy in the physical properties and chemical properties of the crystal orientations can produce different thermal and mechanical responses of the femtosecond laser.In this paper,the polysilicon as the object,using scanning electron microscopy,Raman spectroscopy,Energy Dispersive X-Ray Spectroscopy and electron backscatter diffraction techniques to study the polysilicon structure of femtosecond laser irradiation area,affirm the structure change and crystal orientation relationship.The results show that the(111),(100)and(110)crystal orientation after a single pulsed femtosecond laser irradiation are ablated at the center of the spot,and the edge of the spot is a amorphous ring.When the laser pause energy is above the ablation threshold,the material is ablated and vaporized;when the energy is below the ablation threshold and above the amorphous threshold,the material is amorphized;when the energy is below the amorphous threshold,the material does not change.The ablation threshold of the(111)crystal plane is in the range of 0.455 J/cm~2-0.644 J/cm~2,and the amorphous threshold is 0.240 J/cm~2-0.295 J/cm~2;the ablation thresholds of the(100)and(110)planes are In the range of 0.373 J/cm~2 to 0.522 J/cm~2,the amorphous threshold is 0.259 J/cm~2 to0.303 J/cm~2.The result shows that a femtosecond laser irradiation on polysilicon surface causes the orientation has a slightly change in the amorphous region edge,resulting in 0.1°/?m plastic deformation and depending on crystal plane orientation.(111)orientation deformation region is larger than(100),(110)orientation.Thus different crystal orientation of the amorphous area is different,the deformation region are also different.The(111)crystal orientation amorphous region is larger,so the deformation region is larger,and the(100)and(110)crystal plane amorphous regions are smaller,corresponding deformation region is smaller.The temperature distribution of femtosecond laser irradiation on the surface of the silicon material was simulated using the two temperature model.The results showed that the silicon in the center of the spot experienced ablation,recrystal and gasification,thus maintaining the crystal orientation of silicon substrate material while the spot edge experienced melting and solidification.The(111)crystal orientation spacing is larger than the(100)(110),and the width of the planes is not equal,it is not make for conducive to the transmission of energy from the layer to layer,which leads to the molten silicon need higher energy to solidification;the(111)orientation is a close-packed structure,and the lattice defects are easy to generate,causes easily to form amorphous.Therefore,different crystal orientations have different surface energies and atomic densities,thus cause different growth or removal behaviors in laser irradiation.