LI Zhi-ming, WANG Xi, NIE Jin-song. Hole Morphology in Femtosecond Laser Drilling of Silicon[J]. Acta Photonica Sinica, 2017, 46(10): 1014004
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In the femtosecond laser drilling of silicon material, in order to the influence of the surface plasma effect and hole geometries on the redistribution of the follow-up laser energy, the theoretical model and muti-pulse ablation experiment were established. Theoretical calculation of the damage threshold 0.21 J/cm2is in line with the experimental model measured threshold 0.20~0.25 J/cm2. When the carrier density reaches the critical value Ncr, the excitation of the plasma causes the surface reflectance to rise rapidly. With a larger of laser fluence from 0.5 J/cm2 to 3.0 J/cm2, ablation depth increases to about 1.1um, and while the pulse width from 150fs reduced to 50fs, ablation structure become more similar to the oval ablation profile. What’s more, the effect of different hole structure on the laser beam propagation inside the micro-hole of silicon wafer is obtained by numerically using FDTD method. It’s found that the position of the maximum laser intensity point would be closer to the hole enter by decreasing taper angle from 79℃ to 49℃, which finally cause the excitation of plasma more likely. Besides, under different polarization beam irradiation, the energy distribution at the bottom of the hole induced different special ablation structures. The results show that by increasing laser fluence and decreasing pulse width, the ideal initial pore structure can be obtained so that the subsequent pulse energy is concentrated at the bottom center making the drilling efficiency higher.