Analytical research and experiment on prediction model of directional solidification process and phase transition interface:solar-grade polysilicon
It is difficult to control and predict the solidification process and the morphology of phase transition interface in sealed directional solidification.The directional solidification(D-S)process model of solar-grade polysilicon is solved by analytic method,and a high precision mathematical model of solidification process is obtained.The solidification height,instantaneous solidification rate and melt temperature distribution can be calculated from the easily measured heat dissipation temperature and solidification time.By solving the Poisson equation,a 3D model of phase transition interface was established.It is revealed that the heat flow rate q value on the side wall of the melt is the key factor to influence the interface morphology,which provided quantitative analysis basis for solidification process control.The large size(0.90 m×0.90 m×0.35 m)ingot casting experiments were carried out using 3303 industrial silicon as raw material in YITIPV vacuum ingot furnace.For the geometrically symmetric phase transition interface,the maximum deviation between the mathematical model and the experimental curve is 4.43%;for the irregular phase transition interface,the maximum deviation is 8.68%,and the solidification process model is modified according to the experimental results.The prediction accuracy and reliability of the 3D phase transition interface model were verified by detecting the parameters such as impurity content,resistivity and minority carrier lifetime,and comparing the typical phase transition interface morphologies of the four ingots.
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