Study On Surface Quality And Material Removal Rate Of Wafer Ultra-precision Grinding

With faster developing of integrated circuits (IC) manufacturing technology, the diameter of silicon wafer trends to be larger in order to increase the yields of chips and decrease the cost per bit And at the same time, the thickness of the prime wafer is also increased to ensure the strength of the wafer. Contrarily, the chip thickness is decreased to meet the requirements of IC package and improve the heat radiation properties of the chip. With the increase of the diameter and thickness of wafer and reduce of chip thickness, the process of wafer is facing many new technology. The high machining accuracy and quality is difficult to achieve because large size wafer is easy to warp. And the high machining efficiency is required because size changes of the wafer and the chip result in the increase of the material removal amount Among the precision process methods, the wafer rotation grinding method is considered as the most promising technology for processing the large scale silicon wafer, which has used in both manufacturing of the silicon wafer media and back thinning of the pattern wafer.In this paper, a kinematics geometry model of the wafer rotation grinding is established. The relationship between grinding marks and the grinding parameters is analyzed. The cutting trajectories of grits on the wafer are predicted by computer simulation. Based on the theoretical model, the length of trajectory, number of grinding marks and grinding stable period are deduced. The relationship between grinding surface quality and the density of grinding marks is theoretically analyzed. The results of computer simulation and theoretical analyses are verified by comparing with the results of experiments, which are conducted on a VG401MKII grinding machine.By the principle of reversal process, the formula of material removal rate (MRR) in wafer rotation grinding process is deduced. The relationship between MRR and the grinding parameters is given.A series of process experiments of wafer grinding are carried out on a VG401MKII grinding machine. The influence of the grit size and the process parameters, including the rotational speed of the cup grinding wheel, the down feed rate of the grinding wheel spindle and the rotational speed of the chuck table, on MRR, spindle motor current and roughness, areanalyzed. The grinding process parameters are proposed to improve grinding efficiency and surface quality on ground wafer.The result provides theory basis and available technique ways to improve the surface quality, increase material removal rate. The study is also propitious to realizing high efficient, ultra-precision and low damage grinding.