Device Development And Experimental Research Of Magnetorheological Hydrodynamic Compound Flatness Polishing

The electronic information manufacturing industry is a national basic and strategic industry.Its foundation is the ultra-precision planarization processing technology of semiconductor substrates based on the design,manufacture and related support of semiconductor chips.As the size of semiconductor wafers continues to increase,the integration of electronic devices integrated on the wafers increases,requiring wafer surface to be flat,surface roughness to sub-nanometer levels,and ultra-smooth and no damage,which is super-surface on the semiconductor wafer.Smooth flattening technology presents new challenges.In order to realize the high-efficiency ultra-smooth and damage-free flattening polishing of photoelectric materials,especially semiconductor materials,the paper proposes a magnetorheological hydrodynamic compound flatness polishing technology.Based on the cluster magnetorheological polishing technology,the wedge-shaped groove is designed on the polishing disk surface,and the magnetorheological effect is generated.The high viscosity,high shear properties,etc.produce hydrodynamic polishing pressure,which in turn improves removal efficiency and processing quality.Firstly,the magnetorheological hydrodynamic composite flattening polishing method is analyzed,including magnetorheological polishing,hydrodynamic pressure polishing and its composite principle.The theoretical calculation and analysis of the polishing disc wedge structure are carried out by Matlab software,and the influence law of structural parameters is studied.It is found that the gap between the wedge disk and the workpiece is better in the interval of 0.2mm-0.8mm,the wedge angle is better in the range of 3°-5°,and the influence of the wedge groove width is studied,which lays a foundation for the design of the polishing disk.Secondly,based on the principle of magnetorheological hydrodynamic composite flattening polishing,a magnetorheological hydrodynamic composite flattening polishing device is designed.The device mainly comprises four modules: optical vibration isolation self-leveling platform,three-dimensional motion system,composite polishingdevice,and control system.The four modules are designed and selected,and the magnetorheological hydrodynamic composite flattening polishing experimental platform is built.The feasibility of the polishing method is verified by the single crystal silicon polishing experiment.The machining efficiency can be increased by 50% to 80% by composite polishing,and the surface roughness Ra can reach 2.50 nm after 4 hours of machining.Then,the Kistler-9171 A rotary dynamometer is used to study the polishing force in the magnetorheological hydrodynamic composite flattening polishing.The influence of different machining gaps,workpiece rotation speed and polishing liquid ratio on the polishing force is analyzed.The results show that the larger the machining gap,the lower the polishing positive pressure Fz and the shear force Ft.The higher speed of the workpiece disk,the larger the polishing positive pressure Fz and the tangential force Ft firstly increases and then decreases.The polishing positive pressure Fz decreases as the rotation speed of the polishing disk firstly increases,and the tangential force Ft firstly increases and then decreases.The concentration of carbonyl iron powder is proportional to the polishing positive pressure Fz.The larger the concentration of carbonyl iron powder,the larger the polishing force Fz and the shear force Ft.When the iron powder concentration is 35wt%,the tangential force Ft does not continue to increase.As the abrasive concentration increases,the polishing force Fz increases and tends to stabilize,but the tangential force Ft firstly increases and then decreases.Finally,a two inch monocrystalline silicon wafer is subjected to a system of magnetorheological hydrodynamic composite flattening polishing process,and a single factor experiment is performed on the machining gap,processing time,iron powder concentration,and abrasive concentration.The rotation speed of polishing disk,workpiece disk and the cam are selected.The orthogonal test of the rotational speed is carried out to analyze the influence of various process parameters on the material removal rate and processing quality of the workpiece.The optimum process parameters are as follows: the gap between the polishing disc and the workpiece is 0.4 mm,the processing time is 4 h,the iron powder concentration is 35 wt%,and the abrasive concentration is 5wt%,the workpiece speed is 600r/min,the polishing disc speed is60r/min,and the cam speed is 150r/min.The single crystal silicon wafer is subjected to a polishing experiment by the optimum process,and the processing is performed for 4hours to obtain a material removal rate of 5.10 mg/h and a surface roughness Ra of 2.31 nm.