Research On The Heat Transfer Characteristics Of Polycrystalline Silicon During Vacuum Directional Solidification And Its Influence On The Quality Of Ingots

A multi-field coupling model of heat-flow-thermal stress was established to investigate the influence of the Marangoni convention which caused by the surface tension of the melt on quality for the multicrystalline silicon(mc-Si)growth during the vacuum directional solidification(VDS)process.The simulation result showed that the Marangoni effect had a significant effect on the distribution of temperature and thermal stress during the VDS process,due to it enhanced the flow and the convective heat transfer coefficient of the silicon melt.The enhanced flow made the temperature of silicon melt more homogeneous and the radial temperature gradient reduced,which led to the flatter solid/liquid(s/1)interface.But the temperature gradient of the crystal increased,which resulted in the increscent thermal stress of the silicon ingot.The crystal growth quality was better with a pulling-down rate of 10gm/s,in which case the(111)surface was advantageous throughout the entire multicrystalline growth process by XRD detection.The reliability of the numerical simulation result was verified by the experiment.A multi-field coupling model of heat-flow-thermal stress was established to investigate different pulling-down rates(5 ?m/s,10 ?m/s,15 ?m/s)on quality for the mc-Si growth at the presence of the Marangoni effect during the VDS process.The simulation results show that the melt flow rate was increased due to the existence of Marangoni effect,which made the heat transfer of silicon material greatly change.With the increase of the pulling-down rate,the axial temperature gradient of the silicon and the thermal stress of the crystal were also increased,and the most stable and flat solid/liquid interface appeared at 10?m/s.The experimental results also confirmed that the silicon ingot crystals of 10 ?m/s,which had larger columnar grains were the best.The accuracy of the simulation results was verified.On the basis of the above model,the influence of the fast and slow process on the heat transfer characteristics of the mc-Si growth process was studied.The results show that while the energy consumption of vacuum directional solidification was effectively reduced under this process,but the thermal stress of the mc-Si ingot was much large.Moreover,the solid/liquid interface shape of the solidified front was not stable to maintain the plane type.Therefore,it was not beneficial to improve the quality of mc-Si ingot.