Study On The Polishing Characteristics Of The Solid-liquid Interface Of The Workpiece Chuck In Magnetorheological Wafer Polishing

Magnetorheological polishing of semiconductor wafers is a method of ultra-smooth flattening of wafer surfaces by using the rheological behavior of magnetorheological polishing solution in a magnetic field.The current requirements for the surface shape accuracy,surface roughness and sub-surface damage level of semiconductor wafers required for integrated circuits are increasing,and accordingly the requirements for magnetorheological polishing equipment are becoming higher and higher.Similar to chemical mechanical polishing,the most common problem in magnetorheological planar polishing is the wafer edge effect,which seriously affects the flatness of the polished wafer surface;in addition,there are also problems such as low polishing efficiency and polishing solution utilization due to the polishing solution not being smoothly introduced into the polishing area.Most of the current research on these problems is focused on the magnetic field generation device and polishing process parameters,and very little research has been conducted on the structure of the workpiece clamping disc.In this paper,based on the research conducted by domestic and foreign scholars,the effect of workpiece clamping disc structure on wafer edge effect and polishing solution utilization is studied through theoretical analysis and simulation.The main research contents are as follows.(1)The mathematical model of polishing characteristics at the solid-liquid interface of the workpiece clamping disc was established.Based on the continuity equation,momentum equation and Bernoulli equation of polishing fluid flow,the effect of polishing fluid flow through the abruptly shrinking gap and the gradually shrinking gap on the flow rate,flow rate and local loss coefficient is analyzed theoretically,which is used as the basis for optimizing the edge shape of the workpiece clamping disc;the effect of the abruptly shrinking gap and the gradually shrinking gap on the flow rate,flow rate and pressure distribution of the polishing fluid between the workpiece clamping disc and the liquid-carrying disc is analyzed through modeling and simulation,which verifies the correctness of the theoretical analysis.The effects on the flow rate,flow rate and pressure distribution on the wafer surface when the workpiece clamping disc and the liquid carrier disc are formed as the abruptly shrunken gap and the gradually shrunken gap respectively are analyzed by modeling and simulation to verify the correctness of the theoretical analysis.(2)The influence of four typical workpiece clamping disc edge shapes on the polishing process is studied.The simulation model is established and simulated for four typical curved workpiece clamping disc edge shapes,and the influence of different workpiece clamping disc edge shapes on the polishing fluid flow rate,flow rate and pressure distribution on the wafer surface is comprehensively compared and analyzed,and the influence of the radius of curvature of the arc on the polishing fluid flow rate,flow rate and pressure distribution on the wafer surface is further investigated on the basis of the better edge shape of the convex arc type.The optimal edge shape of the workpiece clamping disc was finally determined to be the convex arc type and the radius of curvature of the arc was 21 mm.(3)The influence of the structure parameters of the holding ring of the workpiece chuck on the edge effect of the wafer is studied.Firstly,the influencing factors of the wafer surface material removal rate during the polishing process are analyzed theoretically.Secondly,the simulation analysis is based on the optimal workpiece chuck edge shape after adding the different retaining ring structure parameters(holding ringwafer gap).,Holding ring width,holding ring thickness)on the wafer edge effect,while comprehensively considering the impact of the holding ring structure parameters on the polishing liquid flow,the holding ring-wafer gap is 0.75 mm,the holding ring width is9.25 mm,when the thickness of the retaining ring is the same as the thickness of the wafer,it is the best conclusion to improve the edge effect of the wafer.