Design of follow-up superconducting Cusp magnetic field and system performance analysis of Czochralski single crystal furnace

Abstract

This paper proposes a magnetic system structure for a single crystal furnace that addresses the issue of unreasonable distribution of magnetic field lines on the free surface caused by DHL (Distance between the lower edge of the heat shield and the liquid surface) fluctuation during early stages of crystal growth. The proposed structure adjusts with the fluctuation of the free surface during the crystal pulling process, enabling the magnetic system to positively impact the thermal system. The thermo-magnetic coupling in a 160-type single crystal furnace before and after magnetic system optimization was simulated using the finite element method. Numerical simulation was employed to compare the temperature gradient, S-L (solid–liquid) boundary temperature distribution, and radial oxygen content in the single crystal furnace before and after magnetic system optimization under the conditions of Cr (crystal rotation) and Gr (graphite crucible rotation). The results reveal that the optimized magnetic system helps adjust the shape of the S-L boundary, decrease the temperature gradient, and lower the oxygen levels at the S-L boundary. However, when the Gr is rotated at high speed, although the S-L interface becomes flatter, the temperature gradient and oxygen concentration at the boundary increase. On the other hand, When Cr is at high speed, the S-L boundary tends to become flatter and the temperature gradient at this boundary decreases, but the oxygen concentration at the S-L boundary increases. Compared to the original single crystal furnace with a fixed magnetic system, the single crystal furnace with a lifting magnetic system experiences a 6.34% reduction in radial temperature gradient and a 3.02% reduction in axial temperature gradient during the actual crystal pulling process parameters. The temperature gradient at the S-L boundary decreases by 36.50%, and the radial average oxygen concentration decreases by 26.58%. Furthermore, the temperature distribution of the crystal and melt becomes more uniform, the oxygen content at the S-L boundary is effectively controlled, and the overall crystal quality improves. These findings can serve as a reference for designing a new magnetic system for a single crystal furnace.