| In this paper,the typical semiconductor wafer is used as the processing object,and the preparation and performance of Magnetorheological polishing fluid(MRPF)is optimized to solve the problems of traditional MRPF.Based on the magnetic Coulomb’s law,the shear stress model is established to study the rheological properties of MRPF.The rheological properties of MRPF under different polishing parameters are studied by using the method of fluid dynamics simulation,and the key factors affecting the polishing quality are determined.The main contents and achievements are as follows:(1)In order to meet the performance requirements of MRPF for semiconductor wafer,the effects of magnetic particles,abrasive particles,surfactants,thixotropic agents and other components are analyzed,and a new proportion method is proposed to improve the composition of each component.In the process of preparation,the combination of surface modification and viscosity base solution is used to meet the application requirements of rheological property,sedimentation stability and oxidation resistance.The preparation process of MRPF is improved by reasonable use of stirring and ultrasonic dispersion.The rheological property after re dispersion is consistent with the initial rheological property,which met the specific use requirements.(2)According to the magnetic dipole theory,the reasonable hypothesis of the chain forming mechanism of MRPF is made,and the micro position model of magnetic particles and abrasive particles is established.Based on the magnetic Coulomb’s law,the external shear stress required for the slip of magnetic particles is calculated,and then the exponential distribution is introduced to establish the shear stress model.Through the analysis of the influence of magnetic particles,abrasive particles,magnetic field strength and other variables on the shear stress in the model,the predicted values are basically consistent with the experimental data,which verifies the practicability of the model in guiding the preparation of polishing liquid and predicting the shear stress of MRPF.(3)The simulation model of MRPF process is established by ANSYS / Fluent,and the rheological property in the polishing process is simulated.Through the simulation of the influence of polishing head speed and polishing pad speed on the torque and viscosity of MRPF,it is found that the polishing pad speed has a great influence on the rheological property,which leads to the irregularity of the viscosity curve.The experimental results show that the surface quality of wafer will be decreased when the polishing speed is too high.Increasing the polishing head speed can maintain the rheological properties of MRPF and obtain high quality wafer surface. |
