Numerical Analysis Of Melt/Crystal Interface Shape In Large Diameter Single Silicon Crystal Growth

With the rapid development of integrated circuit industry, device manufacturer demand high quality mono-crystalline silicon, such as high purity, high uniformity, high integrity and major diameter. Generally speaking, with the increase of crystal diameter, it is hard to transfer the latent heat caused by the solidification. So, the radial temperature gradients increased resulted in high melt-crystal interface deflection. It will eventually result in poor quality crystal or affect the crystal growth. To avoid this deflection, it is of importance to control the interface during process of crystal growth. To take into account the relationship between the interface shape and defect formation, stress distribution and solute segregation, the thesis has researched on interface controlling and related studies of crystal growth, especially on melt flow.Due to the high-temperature environment and high cost, experimental investigate and in-situ observation are quite different. Therefore, crystal growth modeling, especially on the heat flow, has attracted much attention in the research and technology development. Finding an effective way to control crystal growth through simulation is extremely useful. We have investigated the effects of structure of furnace and process parameters on the interface shape and melt flow.We optimized the heat-shield structure, position, material and designed new type heater. Using the optimized heat-shield we obtain high quality crystal and increase crystallization rate. Based on the analysis of thermal stress and heat fluxes, the pulling rate could be further increased without increased the probability of macro-dislocation generation. The analysis of temperature field suggested that optimum heat-shield can decrease the melt-crystal interface deflection and avoid the overcooling of melt free surface. Using new type heater could decrease the energy consumption to reduce cost.In order to research the effects of various driving forces on the interface shape and melt flow, we change the driving forces such as surface tension, crystal rotation, crucible rotation, argon shear stress and buoyancy respectively. The result show that the melt will form a clockwise vortex during buoyancy and surface tension act on the melt and that the melt form an anti-clockwise vortex during crystal rotation and argon shear stress act on the melt. Applying the faster crystal rotation will increase the interface deflection and advance the speed of melt flow underneath the crystal. Applying the faster crucible rotation could obtain more flatten interface, however, increase the hater power. In addition, we study the effect of magnetic field on the interface and melt flow. Numerical result shows that adopting vertical magnetic field the interface shape will more smooth and the oxygen content in melt will be increased. Using CUSP magnetic field, we take into account the strength of magnetic field, the radius of coils, the distance of coils and the relative position between the melt free surface and the zero gauss face of the coils. With the increase of magnetic strength, the interface becomes more flat. Especially when the strength is0.5T, the interface becomes the straight line.We study the interface deflection and melt flow during different stage of crystal growth. The result show that with the crystal length increasing the interface will become more concave and the thermal stress above the interface will increase. The melt-crystal interface shape and the melt flow regime are strongly sensitive to the rate of rotations of both crystal and crucible. Obtaining low deflection shape we could control precisely the combination of crystal and crucible rotation rate or decrease the pulling rate. In addition, using the same furnace and control parameters, with the increase of crystal diameter, the interface will become more concave and the thermal stress in the crystal will increased.