Design Of Magnetic Field Generator For Magnetorheological Finishing Of Semiconductor Wafers

The magnetorheological finishing of semiconductor wafers is a new kind of finishing method that uses the magnetorheological effect of magnetorheological finishing fluid(MRFF)to smooth the wafer surface.The formation of gradient magnetic field is the key to the generation of magnetorheological effect.The magnetic field generator is a core device in a semiconductor wafer magnetorheological finishing machine for generating a specifically distributed gradient magnetic field in a polishing area.The performance of the magnetic field generator plays a decisive role in the processing capacity of the magnetorheological finishing machine.In the magnetorheological planar finishing of semiconductor wafers,the permanent magnet cluster magnetic field generator can effectively balance the polishing efficiency and the polishing quality.Therefore,the research and design for this kind of magnetic field generator have been carried out in this paper.First of all,the analytical model is established between the design parameters and the magnetic field distribution in the MRFF.Secondly,the influence of the parameters on the magnetic field in the MRFF was analyzed.On the basis of these,the parameters optimization of magnetic field generator is studied.Then the optimum design parameters and permanent magnet pole arrangement are determined.Finally,the design and manufacture of the magnetic field generator are completed.The research contents and outcomes of this paper are as follows:A theoretical solution model for the spatial magnetic field of magnetic field generator in a single medium is established.On the basis of the theory of spatial magnetic field analysis of the single permanent magnets,the method of solving the magnetic field distribution of the magnetic field generator in the single medium space is established,in order to solve the spatial magnetic field solving problem of the multi permanent magnet in the magnetic field generator.Moreover,the theoretical analysis model of magnetic field distribution in magnetorheological finishing fluid is established.Based on the theoretical analysis model,the mapping relationship between the design parameters of the magnetic field generator and the magnetic field distribution in the MRFF is further studied.Firstly,to solve the problem of magnetic field in MRFF,the idea of using mirror image method to analyze the double media and double interface spatial magnetic field is put forward.Secondly,the mapping model of magnetic field generator related design parameters and magnetic field distribution in MRFF is established.Finally,the mapping model is verified by special case analysis and simulation comparison.On the basis of determining the main factors affecting the magnetic field in the MRFF in the magnetic field generator,the influence of the design parameters of the magnetic field generator on the magnetic field in MRFF is analyzed.According to the correlation model,the corresponding curves between the parameters of the magnetic field generator and the related magnetic field parameters in the MRFF are obtained.According to the analysis results,a preliminary screening of the magnetic pole arrangement is performed,and the reasonable value range of parameters of the magnetic field generator is determined.In order to optimize the design scheme of the magnetic field generator,a method to solve the parameter optimization problem of the magnetic field generator is proposed.Firstly,the mathematical model for parameter optimization of magnetic field generator is established.Secondly,the parameters optimization of magnetic field under two feasible magnetic poles is solved by means of using the artificial bee colony(ABC)algorithm,and both the optimal design parameters and the optimal magnetic pole arrangement of the magnetic field generator are obtained through analysis and comparison.Finally,the magnetic field generator of magnetorheological finishing for semiconductor wafers is designed and manufactured according to the relevant parameters and the arrangement of magnetic poles.