Numerical Simulation Of Sapphire Crystal Growth And Inclusions Defect Research

Sapphire crystal material has been widely used in defense technology and civilian areas for its excellent mechanical properties, chemical stability and optical performance. With the continual development in recent years, sapphire becomes dominating in LED substrate application. Thus, the growth of sapphire crystal with large size and high quality has become an important research topic. The Czochralski method is currently one of the most popular techniques for sapphire growth, in which the solid/liquid(S/L) interface shape is the key factor to control crystal quality.This thesis focuses on the influence of growth parameters, such as the vertical distance between the moved coil center and crucible center, crystal rotation and crucible rotation on the S/L interface shape during sapphire crystal growth, as well as on the study of inclusions trajectory in melt with Lagrangian scheme. With coupled multi-physics numerical simulation software(COMSOL Multiphysics) and computational fluid dynamics software(Fluent), two-dimensional and three-dimensional numerical simulations of Czochralski sapphire growth process have been conducted to obtain the S/L interface shape under different growth parameters and to investigate impurity behavior by examing the inclusions trajectory in melt. For the influence of growth parameters, orthogonal design method is adopted to assess their relative influence and to achieve the optimized combination of parameters. For inclusions trajectory, the simplified geometry is adopted for qualitative analysis. Inclusions trajectory in melt with different crystal rotation is obtained. The results show that the S/L interface convexity increases with the Radio-Frequency(RF) coil moving down, decreases as crystal rotation rate increases, and slightly increases as crucible rotates faster during the growth. Furthermore, orthogonal analysis reveals that the crystal rotation is the major factor, followed by the crucible rotation, and that the last is the vertical distance from the coil center to the crucible center. The results also reveal that inclusion trajectories are mainly driven by the melt flow, the relative effects of natural convection and forced convection contribute to different inclusions distributions, and a higher crystal rotation results in less inclusions concentration near the central axis of the crystal. Integrated study of the S/L interface shape and inclusions in this paper can provide valuable information for high quality crystal growth in industrial growth.