| Because laser has the advantages of high directivity,high monochromaticity and high brightness,it is playing a more and more important role in laser precision processing,medicine,military and other fields.however,the wavefront amplitude and hyperbolic propagation mode of laser Gaussian distribution also limit the development of laser applications.Especially in the semiconductor industry,the demand for wafers is increasing day by day.The unbonding of wafers by laser is a potential application at present.The non-uniform distribution of energy of traditional Gaussian beam will cause problems such as bonding surface damage or warping,so in this paper,according to the demand of laser unbonding in semiconductor field,a set of aspheric surface is studied and simulated to shape the Gaussian beam into a square flat-topped beam.then a beam shaping system based on spatial light modulator is designed and verified by some experiments.The specific research contents are as follows:1.First of all,this paper introduces Kirchhoff diffraction theory,matrix optics and ABCD law in beam propagation theory,analyzes the common theoretical model of flat-topped beam,and discusses the law of function factor and intensity distribution of flattened beam.Because the flat Lorentz beam model is simple in structure and easy to calculate,the analytical solution can be easily obtained,so the flat-topped Lorentz beam is selected as the exit beam theoretical model of the aspherical beam shaping system in this paper.2.The aspheric beam shaping system is simulated by using ZEMAX optical design software.200 rays are traced by ZPL macro language,and the shape parameters of two aspheric surfaces are obtained.the radius of the circular spot after shaping is 7.5mm,and its energy uniformity is 85.6%.After that,two orthogonal cylindrical lenses are used to optimize the shape of the output spot of the system,and the optimized output spot becomes a rectangular spot.The beam uniformity of different working distance is calculated,and the variation range of flat-top beam uniformity is less than 5% when the focal depth offset of the system is less than ±10m,which can basically meet the application requirements.After the completion of the basic design,the tolerance of the system is analyzed,and 50 samples are analyzed by Monte Carlo,and the beam uniformity of the worst sample can meet the requirements,indicating that the system can basically meet the needs of practical use.3.The basic theory of beam shaping by spatial light modulator is analyzed.The traditional GS algorithm and the improved GS weighting algorithm are compared and analyzed.The shaping effects of the two algorithms on the fundamental mode Gaussian beam are simulated by MATLAB.The beam uniformity of the improved GS weighting algorithm is 89.4% and the energy efficiency is betterThe utilization rate is 92%.Compared with the traditional GS algorithm,the beam uniformity is improved by 10.8% and the energy utilization is reduced by 6%.The method of adding blazed grating and marking the phase gray image of light field is used to filter the zero order spot in the shaping light field.The optical path of the beam shaping system of the spatial light modulator is built,and the ablation experiment is carried out on the gold sheet and bonding adhesive material by using the system.The experimental results show that the laser distribution presents a flat top distribution after the beam shaping system.The uniformity of the final output flat top beam is 82.37% and the energy utilization rate of the system is 88%.The boundary of the laser impact area on the surface of the processed material is clear and the overall removal effect is good. |
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