Simulation Analysis on the SAPMAC Crystal Growth Process of Large Size Sapphire

The SAPMAC(sapphire growth technique with micro-pulling and shoulder at cooled center) process has investigated by numerical simulation method.The characteristics of several different crystal growth stages have been analyzed and compared with Czochralski method,temperature gradient technique and bridgman technique etc.Base on the results of simulation and techniques of different crystal growth stages,the system and control techniques of crystal growth were improved;the conventional SAPMAC furnace was modified with the heat dissipation parameters increased,the heating temperature decreased,the temperature falling curve improved,the additional axial and radial temperature gradient adjusted,so the necking-down,shoulder-extending,iso-diameter and tailing process of the crystal growth can be controlled.The experiment results testified that the grown crystal has better quality and larger size by the improved system of crystal growth and control techniques.

The goal of the research presented here is to apply a global analysis of an inductively heated Czochralski furnace for a real sapphire crystal growth system and predict the characteristics of the temperature and flow fields in the system. To do it, for the beginning stage of a sapphire growth process, influence of melt and gas convection combined with radiative heat transfer on the temperature field of the system and the crystal-melt interface have been studied numerically using the steady state two-dimensional finite element method. For radiative heat transfer, internal radiation through the grown crystal and surface to surface radiation for the exposed surfaces have been taken into account. The numerical results demonstrate that there are a powerful vortex which arises from the natural convection in the melt and a strong and large vortex that flows upwards along the afterheater side wall and downwards along the seed and crystal sides in the gas part. In addition, a wavy shape has been observed for the crystal-melt interface with a deflection towards the melt.


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