Papers by Author: Y.B. Tian

Abstract: During wafer rotation grinding, the wafer is centered on a porous ceramic vacuum chuck and so; the dressing shape of vacuum chuck becomes a critical factor affecting the flatness of ground wafers. In this paper, a theoretical model of the dressing shape of vacuum chuck in wafer rotation grinding is developed. From the model, the relationship between the dressing shape and the affecting factors is given. The dressing shape is predicted by computer simulations based on theoretic model and the vacuum chuck dressing experiments are conducted to verify the theoretical model. It is shown that the theoretical analysis matches the experimental measuring results very well. The study results provide a theoretical basis for analysis of the relationship between the dressing shape and the flatness of ground wafer, for improving the flatness of ground wafer and for selecting the proper parameters of grinding process.

Abstract: In this paper, the formula of material removal rate (MRR) in wafer rotation grinding process is deduced based on kinematics. The main effect on MRR 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, is both theoretically and experimentally investigated. The influence on MRR of the cup wheel grinding status, the geometric dimension of the cup-grinding wheel, the rigidity of the grinding machine and the coolant is also analyzed. The investigating results show that, the increase of the grit size and the down feed rate of the cup grinding wheel results in great increase of the MRR; the MRR increases as the rotational speed of the cup wheel increases whereas the MRR reduces and the ground surface becomes bad due to size effect if the rotational speed of the cup wheel is overlarge; in normal grinding, the MRR decreases as the rotational speed of the chuck table increases. The results provide a theoretical basis to improve grinding efficiency, reduce grinding cost and select the proper parameters of grinding process.

Abstract: Chemical mechanical polishing (CMP) has already become a mainstream technology in global planarization of wafer, but the mechanism of nonuniform material removal has not been revealed. In this paper, the calculation of particle movement tracks on wafer surface was conducted by the motion relationship between the wafer and the polishing pad on a large-sized single head CMP machine. Based on the distribution of particle tracks on wafer surface, the model for the within-wafer-nonuniformity (WIWNU) of material removal was put forward. By the calculation and analysis, the relationship between the motion variables of the CMP machine and the WIWNU of material removal on wafer surface had been derived. This model can be used not only for predicting the WIWNU, but also for providing theoretical guide to the design of CMP equipment, selecting the motion variables of CMP and further understanding the material removal mechanism in wafer CMP.