Study On The Mechanism Of Laser-assisted Cluster Magnetorheological Polishing Of Optoelectronic Wafer

Sapphire and single crystal SiC are representative optoelectronic chip materials,which are often used to manufacture optoelectronic components and micro-electronic components due to their unique material characteristics.Sapphire,for example,because of the high melting point,high hardness,good pervious to light quality good,excellent electrical insulation,cooling characteristics and material chemical composition is not easy to be changed,such as outstanding characteristics,is widely applied in the production of aviation spacecraft optical sensors,infrared window and mobile phone and mobile phone camera window screen and so on,due to the high thermal conductivity,Therefore,it is often used in CMOS integrated circuit components.Since the crystal structure of sapphire belongs to tripartite crystal system,more strict requirements are put forward for its super-smooth and flatness processing.In this paper,through the experimental study of cluster magnetorheological polishing after femtosecond laser induced modification of photoelectric wafer materials,the composite polishing of photoelectric wafers with high efficiency and precision is realized.The cluster magnetorheological polishing process and flat surface formation mechanism of single crystal SiC,sapphire and other photoelectric wafer materials pretreated by femtosecond laser are studied.Firstly,the surface of sapphire substrate was modified by femtosecond laser(?=515nm),and then the sapphire surface was polished by cluster magnetorheological method.It was found that the surface roughness of sapphire substrate was lower after femtosecond laser modification.The influences of femtosecond laser processing parameters,such as scanning speed,scanning spacing,laser pulse repetition frequency and single pulse energy,on the removal rate and surface roughness of polishing materials were analyzed by single factor experiment system,and the optimization process of sapphire surface modification by femtosecond laser was obtained:The laser scanning speed is 100 mm/s,the scanning interval is 10?m,the repetition frequency is 200 k Hz,and the single pulse energy is 6.45?J.Secondly,the optimized components of the magnetorheological polishing solution for laser-assisted photoelectric wafer were obtained by single factor experiment.The abrasive type was diamond,the abrasive particle size was W1,the abrasive mass fraction was 5wt%,the p H value was 11,and the magnetic carbonyl iron powder mass fraction was 25wt%.The surface roughness Ra of sapphire decreased from 0.174?m to 4.1 nm after 4 h processing,and the material removal rate reached 1.48 nm/min.Finally,based on X-ray photoelectron spectroscopy and X-ray diffraction detection technology,the chemical and physical properties of the femtosecond laser modified surface of sapphire and silicon carbide and other substrate materials were analyzed.It was found that the femtosecond laser pretreatment can produce Si O₂-dominated oxide layer and amorphous layer on the surface of single crystal SiC.However,the surface of sapphire substrate after femtosecond laser pretreatment has no oxidation reaction,only the phenomenon of amorphous and microcrystalline,and the removal rate of single crystal SiC material by femtosecond laser pretreatment is more than double that of the material without femtosecond laser treatment.The results show that the oxide layer plays an important role in improving the material removal rate,while the amorphous and microcrystalline of the optoelectronic wafer materials play a secondary role in improving the material removal rate.