Study On Laser Holographic Parallel Cutting Technology And Application Based On Spatial Light Modulation

Silicon wafers,quartz glass and other hard & brittle transparent materials are widely used in integrated circuits,microelectromechanical systems,aerospace and other fields due to their excellent physical and chemical properties.The cutting quality of silicon wafers plays a determining role in the final product quality and economic efficiency.Quartz glass also requires high quality cutting to prevent stress from propagating along the edge defective parts and causing cracking.Traditional tool cutting is a contact processing,and the cut workpiece often has chipping,micro-cracks,contaminants and other cutting defects.Ultrafast laser is used in the cutting field with the advantages of non-contact processing,short pulse width,high peak power,etc.Compared with traditional tool cutting,it has the advantages of small cut width,less debris,and less mechanical damage.However,there are also some problems that need to be solved,such as energy waste and low efficiency of single-focus laser cutting.To address the above problems,this paper proposes an ultrafast laser holographic parallel cutting method based on spatial light modulation.Combined with the computational holography algorithm,the single focus can be modulated into a 2D or 3D spatial focal point array with controllable spatial position and adjustable energy by changing the fractional Fourier transform order.This enables high quality,high efficiency and high flexibility of laser precision cutting.The paper firstly introduced the research status of laser precision cutting technology and laser parallel processing technology.The important fundamental theories,such as the principle of spatial light modulation technology,the numerical operation of fractional Fourier transform,and the common phase-type hologram generation algorithm,were introduced.An ultrafast laser holographic parallel cutting system was built.The weighting function of the GSW(weighted Gerchberg-Saxton)algorithm was optimized.To solve the problem of choosing between quality and efficiency in silicon wafer scribing,the single focus was modulated into a 2D multi-focus arranged along the laser cutting path direction.The computational generation method of the hologram was introduced,and the imaging detection was performed.The effects of different number of focus and various cutting speeds on the cutting quality and efficiency were investigated.The results show that the cutting depth of multi-focus can be increased from 6.6 μm to10.18 μm with specific processing parameters,which is increased 54.24%.The recast layer height of multi-focus can be reduced from 1.32 μm to 0.05 μm,which is basically no recast layer.Aiming at a cutting depth of 12.24 μm,a single focus requires a speed of0.4 mm/s,while a three-focus with the same machining parameters can increase the speed to 1.2 mm/s.To solve the problems of low efficiency and insufficient flexibility in stealth cutting of quartz glass,the single focus was modulated into a 3D multi-focus arranged along the optical axis direction.The refractive index of quartz glass was tested,and the process of generating axial multi-focus by the 3D-GSW algorithm was simulated and analyzed.The results show that the multi-focus uniformity of the algorithm can reach 99.99% and the diffraction efficiency can reach 97%.The actual diffraction efficiency of the written algorithm was tested to be 94.22%.The quartz glass with a thickness of 200 μm was successfully cut by using the axial three-focus laser,and the glass edge was intact without cutting defects such as microcracks and debris.The effect of axial multi-focus with equal energy distribution at different focus intervals on the cross-sectional roughness was investigated,and the results show that the cross-sectional roughness increases with the increase of the focus interval.The smallest surface roughness in the experiment is 2.21μm.The relationship between the multi-focus energy ratio and the thickness of the modified layer was investigated,and a comparison experiment between stealth cutting and laser ablation cutting was performed.