Study On Simulation And Experiment Of Ground Wafer Shape In Rotational Grinding Method

With faster developing of integrated circuits (IC) manufacturing technology, the diameter of silicon wafer trends to be larger and larger in order to increase the yields of chips and decrease the cost per bit. At the same time, The width of line is getting more and more slender and the requirement of flatness is much higher in order to enhance IC integrated density. The traditional machining technics with character of lapping and eroding cannot satisfy the need of machining wafer of large dimension. The rational grinding which has a lot of excellent performance, has widely used in both manufacturing of the silicon wafer media and back thinning of the pattern wafer. And the rational grinding is considered as the most promising technology for processing the large scale silicon wafer at present. But now there are many problems to be solved, for example, the wafer is easily to warp and the machining accuracy of wafer shape is difficult to achieve.In this paper, based on rotational coordinates method, a theoretical model of ground wafer shape in rotational grinding process is developed in which many critical factors including the parameters of a porous ceramic vacuum chuck dressing and silicon wafer grinding etc., are considered. Based on the model, the equation of ground wafer shape and the formula of total thickness viaration (TTV) which is an important character of wafer surface quality are educed. Through the model, computer simulation software about ground wafer shape is developed with VC++ 6.0 and OpenGL. Through simulation, dressed vacuum chuck shape and the ground wafer shape is predicted and the relationship between ground wafer shape and effect factors is given.On the base of above theory, a series of process experiments of wafer grinding are carried out on a VG401MKâ…¡ grinding machine. The effect of the dressed vacuum chuck shape and the process parameters, including the rotational speed of the cup grinding wheel, the down feed rate of the grinding wheel spindle, the rotational speed of the chuck table and the roll angle and pitch angle of grinding wheel spindle, on ground wafer shape is studied. At the same time, the theoretical model of ground wafer shape and the simulation is verified by comparing with simulation results and the experimental measurement.The study results provide theoretical basis and available technical ways to predict the wafer shape. And it is important to improve the flatness of ground wafer and selecte theproper parameters of grinding process. The study is also propitious to realizing high precision shape of large size wafer in ultra-precision grinding method.