Study On The Material Removal Characteristics Of Magnetorheological-hydrodynamic Compound Polishing Technique

The rapid advancement in semiconductor technology has prompted an increasing demand for the processing of the ultra-smooth surface.In addition,as the size of semiconductor wafers keeps increasing and the processing precision requirements continue to rise,the requirements for the wafer processing efficiency,processed surface flatness,surface roughness,and processing damage have also raised to a higher level,leading to tremendous challenges for developing the super-smooth,damage-free wafer surface polishing technology.This paper focused on studying the planarization processing of semiconductor wafers.Through combining the principle of cluster magnetorheological polishing and the principle of hydrodynamic polishing,the paper proposed the magnetorheological-hydrodynamic compound polishing technique.In present paper,the processing characteristics of the magnetorheological-hydrodynamic compound polishing and its polishing mechanisms were studied by conducting theoretical simulation analysis and polishing experiments.In order to obtain an ideal magnetorheological-hydrodynamic compound polishing disc,three kinds of polishing discs with different wedge-shaped grooves(Type A,B,and C)were designed based on the principle of hydrodynamic pressure.The distribution of the fluid field of different wedge-shaped grooves was studied using the numerical calculation in Matlab and simulation study in Fluent.It was found that the peak value and its distribution of the hydrodynamic pressure were directly determined by the wedge angle a and the width angle ? of the wedge-shaped groove.The wedge angle a of the wedge-shaped groove directly affected the convergence rate of the wedge space,which subsequently affected the flow state and peak value of the flow field.As the wedge angle? got wider,the convergence rate of the wedge space increased,and the fluid was squeezed by a greater degree,resulting in a higher peak value of hydrodynamic pressure.The width angle ? of the wedge-shaped groove directly affected the width of the wedge-shaped area,thereby affecting the position and the peak value of hydrodynamic pressure.The smaller the width angle ?,the sooner the hydrodynamic pressure reached the peak level,resulting in smaller peak value and a closer position.The test of polishing force and actual polishing experiments were conducted using three kinds polishing disks with the above three kinds wedge-shaped structures.The results of the polishing force proved the correctness of the numerical calculation and simulation results.The surface polishing experiment on the silicon wafer demonstrated that polishing discs using Type C groove yielded the largest height H,width Y,and removal area S of the surface traces of the silicon wafer,meaning that Type C groove removed the most surface materials,which indicated that Type C groove was the most suitable type for making the magnetorheological-hydrodynamic compound polishing disc.To study the material removal characteristics of the magnetorheological-hydrodynamic polishing compound technique,the polishing experiments were conducted using the magnetorheological-hydrodynamic compound polishing disc with Type C groove.The magnetorheological-hydrodynamic polishing device was used to conduct the force testing experiment on parameters including the concentration of carbonyl iron powder,the abrasive concentration,the workpiece rotation speed,and the machining gap.The Kistler-9171A rotating dynamometer was used to measure the polishing force characteristics of several main parameters(carbonyl iron powder concentration,abrasive concentration,workpiece speed,and machining gap).Results showed that as the carbonyl iron powder concentration increased,both the positive polishing pressure Fn and the shear force Ft gradually increased.As the abrasive concentration increased,both Fn and Ft first increased and then decreased,and when the abrasive concentration was 5wt%,both Fn and Ft no longer increased.The workpiece speed and the machining gap had similar influences.With the rise of the workpiece speed and the machining gap,both the positive pressure Fn and the shear force Ft increased first and then decreased.The positive pressure Fn and the shear force Ft reached their respective maximum values when the workpiece speed reached 150 r/min or when the machining gap was 0.6 mm.The results of the experiment on studying the main parameters of the magnetorheological-hydrodynamic polishing technique showed that the hardness and concentration of the abrasive particles had similar effects on the material removal characteristics.With the increase in the hardness or concentration of the abrasive particles,the depth H,width Y,and the cross-sectional area S also increased.As the abrasive particle size increased,the polishing depth H and the cross-sectional area S also increased,whereas the polishing width Y became smaller gradually.With the increase in the carbonyl iron powder concentration,the polishing depth H,the width Y,and the removal cross-sectional area S first increased and then decreased.When the concentration of the carbonyl iron powder was 35 wt%,the polishing depth H,width Y,and the removal cross-sectional area S all reached their maximum levels.As the workpiece speed rose,the polishing depth H and the removal cross-sectional area S first increased and then decreased,whereas the polishing width Y continuously increased.When the rotating speed of workpiece was 200 r/min,both the polishing depth H and the removal cross-sectional area S reached their maximum levels.As the machining gap increased,both the polishing depth H and the removal cross-sectional area S decreased,whereas the polishing width Y increased first and then decreased.When the machining gap was 0.4 mm,the polishing depth H and the removal cross-sectional area S reached their maximum levels.Optimizing the primary parameters of magnetorheological-hydrodynamic polishing could achieve an improved polishing technique with greater removal efficiency and better uniformity.