Design Of Variable Permanent Magnetic System For Single Crystal Growth

Growth of Czochralski(CZ) silicon crystals is the most common and perfect one in industry. During the growth of CZ silicon, the thermal convection of silicon melt plays more and more important roles in controlling silicon crystal quality. It is found that the mass transport in silicon melt was controlled by its diffusion while the growth is under magnetic field. Supported by the National 863 program "Developing and industrialization of the permanent magnet for single crystal growth",a variable permanent magnetic system for single crystal growth is studied.In this paper,the mostly work is to design the magnet structure,the mechanical and auto-control system.To design the magnet structure,finite element method is used to analyze the permanent magnetic field.Two kinds of permanent magnet structure are designed,and,and both of them can produce steady and homogeneous magnetic field.The field produced by the single-ring permanent magnet is invariable. The field produced by the double-ring permanent magnet can be changed by adjusting the angle between the inner and the outer annular magnet.To design the mechanical and auto-control system,the worm wheel is used to drive the outer annular magnet.The magnetic field changing and the speed regulation are achieved by controlling a stepping motor and an AC asynchronous motor with a frequency transformer.