磁流变变间隙动压平坦化加工的工艺及机理

为提高光电晶片的磁流变抛光效率并实现其超光滑平坦化加工，提出其磁流变变间隙动压平坦化加工方法，研究不同变间隙条件下蓝宝石晶片的材料去除率和表面粗糙度随加工时间的变化，并分析磁流变变间隙动压平坦化加工机理。结果表明:通过蓝宝石晶片对磁流变抛光液施加轴向低频挤压振动，其抛光压力动态变化且磁流变液产生挤压强化效应，使抛光效率与抛光效果显著提升。在工件下压速度为1.0 mm/s，拉升速度为3.5 mm/s，挤压振动幅值为1 mm条件下磁流变变间隙动压平坦化抛光120 min后，蓝宝石晶片的表面粗糙度R_a由 6.22 nm下降为0.31 nm，材料去除率为5.52 nm/min，相较于恒定间隙磁流变抛光，其表面粗糙度降低66%，材料去除率提高55%。改变变间隙运动速度可以调控磁流变液的流场特性，且合适的工件下压速度和工件拉升速度有利于提高工件的抛光效率和表面质量。 

Process and mechanism of magnetorheological variable gap dynamic pressure planarization finishing

In order to improve the magnetorheological polishing efficiency of photoelectric wafer and realize its ultra smooth planarization, the magnetorheological variable gap dynamic pressure planarization method is proposed. The changes of material removal rate and surface roughness of sapphire wafer with processing time under different variable gap conditions are studied, and the magnetorheological variable gap dynamic pressure planarization finishing mechanism is analyzed. The results show that the axial low-frequency extrusion vibration is applied to the magnetorheological polishing fluid through the sapphire wafer, the polishing pressure changes dynamically, and the magnetorheological fluid produces extrusion strengthening effect, which significantly improves the polishing efficiency and polishing effect. Under the conditions of workpiece pressing speed of 1.0 mm/s, lifting speed of 3.5 mm/s and extrusion vibration amplitude of 1 mm, the surface roughness R_a of sapphire wafer decreased from 6.22 nm to 0.31 nm and the material removal rate was 5.52 nm/min. Compared with constant gap magnetorheological polishing, the surface roughness decreased by 66% and the material removal rate increased by 55%. Changing the moving speed of variable gap can regulate the flow field characteristics of magnetorheological fluid, and the appropriate workpiece pressing speed and workpiece lifting speed are conducive to improve the polishing efficiency and surface quality of workpiece.