Structural Design And Optimization Of Superconducting Magnetic Field

Large-size silicon single crystals are the basic materials for various types of semiconductor devices and integrated circuits in China,and their quality has a direct impact on the performance of electronic devices.How to reduce the content of impurities such as oxygen,carbon,etc.in the silicon single crystal and improve the uniformity of the axial and longitudinal directions of the crystal become the primary goals.It has been found that the introduction of a magnetic field during crystal growth can well suppress the convection in the melt and improve the crystal quality.According to the convection of the melt in the crucible,the analytical convection is analyzed and a magnetic field optimization target is proposed.At present,in the CZ crystal growth system,the magnetic field that can improve the crystal quality is mainly the Cusp magnetic field and the quadrupole magnetic field.The Cusp magnetic field is modeled using the three-dimensional finite element modeling method,and the excitation current is calculated using the established model.Under certain circumstances,the required number of layers of the coil;after determining the number of layers of the magnetic field coil,the effect of the distance between the upper and lower coils of the magnetic field and the thickness of the shield on the strength of the magnetic field was analyzed,and the structural parameters were optimized.The three-dimensional finite element modeling method was used to model the quadrupole magnetic field,and the effect of the number of coil layers and the number of vertical layers on the magnetic field configuration was analyzed using the established model;the number of coil layers was also analyzed under a certain excitation current,and the thickness of the shield on the magnetic field strength.The structure of the quadrupole magnetic field is optimized,and the original orthogonal structure is optimized as a non-orthogonal structure.Under the premise of the same excitation current,shield thickness,and number of coil layers,the simulation results show that the magnetic field obtained by the non-orthogonal structure Both strength and magnetic flux leakage are better than those of orthogonal structures.A combination of numerical simulation and intelligent algorithm was proposed to optimize the Cusp magnetic field structure parameters.The magnetic field strength and magnet volume of three parameter variables,including the total number of coil radial layers,the upper and lower coil spacing,and the shield thickness,are used as objective functions.By establishing a model of a multi-objective function,parameters satisfying the Pareto optimal solution are obtained using the NSGA-? algorithm.Finally,using ANSYS to verify that the optimization of the process parameters to meet the crystal growth requirements.