| Indium phosphide(InP)is an important ?-? compound semiconductor material,and can effectively reduces transmission loss and improves transmission efficiency in optical communication.InP has high electron transfer rate and good optical performance,and it is also an ideal substrate material for microwave devices,high-speed and frequency devices and optoelectronic integrated circuit components.As a substrate material,it is required that the surface has an extremely low surface roughness,and no surface/subsurface damage to meet the requirement of epitaxial layer growth.Therefore,it is necessary to polish the wafer.In order to overcome the dependence on chemical action,reduce the pollution and cost in the material removal process,this paper uses the cluster magnetorheological finishing(MRF)to polish InP wafer.The performance of InP,finishing parameters and finishing mechanism were studied to achieve super smooth processing of InP wafer.Firstly,nano-indentation experiments were implemented to detect the nano-mechanical properties of InP.The experiments show that the nano-hardness of InP is 7.26 GPa and the elastic modulus is 79.15 GPa.As the load increases,the plastic energy increases,and the ratio of elastic recovery gradually decreases.Through the nano-scratch test,it is found that the critical load from brittle to ductile of <l10> crystal orientation is lower than the <100> crystal orientation.The fracture and surface defects is more likely to occur during the scratch process Moreover,as the rate of loading increases,the critical load from brittle to ductile decreases,the fracture and surface defects is more severe.This indicates that,the stability of pressure that the single abrasive acts on the workpiece can influence the finishing quality.Secondly,the cluster MRF process of InP was studied.Through the single factor experiments and orthogonal experiments,the effects of different abrasive parameters,machining gap and the speed of each component on the polishing were studied.And the optimization finishing process of InP was obtained by the experiments: the abrasive type is silicon carbide,the abrasive particle size is W3,the mass fraction of abrasive is 4%,the machining gap is 1.2mm,the rotation speed of finishing plate,workpiece and magnetic pole are 40r/min,500r/min and 30r/min,the oscillation rate is 200mm/min.The surface roughness of InP wafer can reduce to 0.35 nm and the material removal rate can reach to 2.5 ?m/h using the optimized technology.Thirdly,the kinetic analysis of the particles in the MRF slurry was carried out based on the discrete element method,and the evolution process of the particle motion was simulated.The influence of different abrasive parameters on the chain structure was studied.As the concentration of abrasive increases,the degree of cluster aggregation decreases,and the magnetic potential energy of the polishing slurry increases,so the stability of the finishing slurry decreases.And the abrasive is more likely to accumulate,which has a tendency to reduce the quality of the finishing surface.When the abrasive has a large size,the polishing slurry system has a small magnetic potential energy,and the stability of the polishing slurry increases,and the abrasive dispersion is more uniform,which lead to a tendency to improve the quality of the finishing surface.However,when the size of abrasive is too large,the pressure from abrasive to workpiece is too large.And then the mechanical damage of surface increases which has a tendency to reduce the quality of the finishing surface.When the abrasive particle size is similar to the particle size of the iron powder,the polishing quality is better.Finally,the material removal rate model of the cluster MRF of InP was established based on the mechanical properties of InP wafer,the microstructure of the finishing slurry and the motion trajectory of the workpiece.The model was modified based on the experimental results.And the average goodness of fit between the model results and the experimental results is 0.91.The fitting effect is good. |
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