Simulation And Control Of Wafer Surface Shape In Back Grinding Of Wafer With Outer Rim

3D stacked packaging technology is an effective means to improve the electrical performance and integration of microelectronic products below 7nm.Wafer ultra-thinning is a necessary prerequisite for realizing 3D packaging.At present,large-scale wafers with a diameter of 12 inches(300 mm)are mainly used in the manufacture of microelectronic products.The Back Grinding of Wafer with Outer Rim(BGWOR)technology came into being to solve the risk of warpage and chipping of ultra-thin large-size wafers.Back Grinding of Wafer with Outer Rim is a newer carrierless thinning technique.This technique can greatly increase the stiffness and strength of thinned wafers.At present,scholars at home and abroad have little research on the backside edge grinding of wafers.This paper studies the control theory and method of wafer surface shape and reveals the changing law of wafer surface shape in Back Grinding of Wafer with Outer Rim.The main research work and research conclusions of the paper are as follows:.(1)Based on the principle of edge-retaining grinding and combined with kinematics theory,a mathematical model of the three-dimensional grinding marks,wafer surface shape and radial thickness of the Back Grinding of Wafer with Outer Rim based on geometrical relationship is established.And by using the established mathematical model,Matlab was used to simulate and analyze the influence law of the change of the grinding marks shape and surface shape and radial thickness of the wafer under different inclination angles of the grinding wheel.The influence of the inclination angle and radius of the grinding wheel of the chuck dressing on the variation trend of the radial thickness after the Back Grinding of Wafer with Outer Rim was simulated and analyzed.The research results show that the inclination angle of the BGWOR grinding wheel,the inclination angle and the radius of the chuck dressing wheel have a great influence on the wafer grinding surface shape and radial thickness distribution.(2)In order to explain the large difference between the theoretically predicted surface shape and the experimentally measured shape in the middle position of the wafer radius,a residual height model and a wafer surface shape model considering the influence of the residual height are established.The simulation analysis of the grinding residue height at the minimum grinding grain density under different process parameters is carried out.When the grinding wheel and speed ratio of #1000 is 25,the maximum surface shape error caused by the residual height can reach 3 μm.Then two methods are proposed to improve the surface shape of wafer in Back Grinding of Wafer with Outer Rim: reducing the grinding residue height and adjusting the inclination angle of the grinding wheel axis.The inclination angle model of the grinding wheel axis required to offset the grinding residual height was deduced,and the required inclination angle of the grinding wheel axis under different parameters was simulated and analyzed.The research results show that the proposed two methods can effectively improve the surface shape accuracy of wafer edge grinding.(3)Taking the wafer ultra-precision grinding and polishing machine(GP300)as the research object,combined with its three-dimensional model,it is divided into units and the coordinate system of each unit is established.Using the theoretical modeling method of multibody system,the error transfer model of the grinding and polishing machine is established.Then,a wafer surface model of Back Grinding of Wafer with Outer Rim considering the error of the grinding and polishing machine is established,and the sensitivity analysis of the positional accuracy of the grinding and polishing machine and the wafer TTV is carried out by using Matlab.The research results show that the 10 angle errors at the joint surface of each unit of the grinding and polishing machine has a great influence on the position accuracy of the equipment and the TTV of the wafer.