Saddle-Shaped Superconducting Coils for Single Crystal Pulling
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Solution Overview
Problem
Current single crystal pulling apparatuses face challenges in achieving high magnetic field efficiency, uniform oxygen concentration, and defect-free crystal growth due to inadequate magnetic field distribution and coil arrangement, leading to issues with thermal convection suppression and oxygen incorporation in the crystal.
Innovation Solution
A single crystal pulling apparatus with saddle-shaped superconducting coils arranged in a specific configuration to enhance magnetic field generation efficiency, allowing for a higher magnetic flux density near the growth interface, which suppresses convection and oxygen incorporation, and enables the growth of defect-free crystals with reduced oxygen concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional circular superconducting coils are used, then the magnetic field distribution is relatively simple, but the magnetic field efficiency is insufficient and oxygen concentration cannot be uniformly controlled
Solution Approach 1:
The patent divides the coil system into multiple independent saddle-shaped coils arranged at specific angles (0°, 45°, 90°, 135°) around the crucible. Each coil can be independently controlled to generate specific magnetic field components, enabling precise control of the overall magnetic field distribution and oxygen concentration uniformity in the crystal.
Solution Approach 2:
The patent employs asymmetric saddle-shaped coils with specific geometric configurations rather than symmetric circular coils. The coils are positioned at non-uniform angular intervals and have asymmetric winding patterns that generate optimized magnetic field distributions for suppressing convection and controlling oxygen incorporation during crystal growth.
2Reliability
If the magnetic field strength is increased to suppress convection, then thermal convection is better suppressed, but the crystal pulling speed must be reduced
Solution Approach 1:
The patent creates locally optimized magnetic field zones using saddle-shaped coils positioned at specific locations around the crucible. The magnetic field strength and direction are tailored for different regions of the melt, providing effective convection suppression at the crystal-melt interface while maintaining favorable conditions for continuous crystal growth and higher pulling speeds.
Solution Approach 2:
The patent employs dynamic control of the magnetic field parameters, allowing adjustment of field strength and coil currents during the crystal growth process. This enables optimization of the balance between convection suppression and pulling speed by adapting the magnetic field conditions to different growth stages and requirements.
3Manufacturing precision
If saddle-shaped superconducting coils are used with specific arrangement, then magnetic field efficiency is improved and oxygen concentration is reduced, but the device structure becomes more complex
Solution Approach 1:
The patent uses saddle-shaped coils with curved geometries that follow the cylindrical symmetry of the crucible. The saddle shape provides optimized magnetic field distribution patterns that are more effective than linear or circular coils, generating field lines that better conform to the melt geometry and improve crystal growth quality while maintaining reasonable structural complexity.
4Manufacturing precision
If the magnetic field center is positioned higher near the melt surface, then oxygen concentration in crystal is reduced, but the magnetic field efficiency decreases
Solution Approach 1:
The patent transitions from conventional two-dimensional coil arrangements to a three-dimensional configuration using saddle-shaped coils positioned at multiple vertical levels and angular positions. This spatial arrangement enables the magnetic field center to be effectively positioned higher near the melt surface while maintaining field efficiency through the distributed coil geometry that provides both vertical and horizontal field components.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The apparatus achieves a significant reduction in oxygen concentration and suppresses growth striations, enabling the growth of defect-free crystals at higher speeds with improved magnetic field efficiency and uniform temperature gradients.
Implementation Method 1
a magnetic field generating apparatus provided around the pulling furnace and having superconducting coils, for applying a horizontal magnetic field to the molten semiconductor raw material by energizing the superconducting coils to suppress convection of the molten semiconductor raw material in the crucible
Implementation Method 2
the molten liquid is subjected to an movement suppression force by the magnetic force lines generated by the energization of the superconducting coils
Implementation Method 3
a heater for heating and melting the semiconductor raw material in the crucible is provided around the crucible
Implementation Method 4
the crystal grows in the solid/liquid interface layer to produce a single crystal
Data Source
AI summary
The present invention is a single crystal pulling apparatus which includes a pulling furnace having a central axis and a magnetic field generating apparatus having coils, and applies a horizontal magnetic field to a molten semiconductor raw material, wherein the coils are saddle-shaped, two pairs of the coils are provided with the coils of each pair arranged facing each other, two coil axes in the two pairs of coils are included in the same horizontal plane, when a magnetic force line direction on the central axis of the pulling furnace in the horizontal plane is defined as a X-axis, and a direction perpendicular to the X-axis in the horizontal plane is defined as a Y-axis, a center angle α between the two coil axes sandwiching the X-axis is 90 degrees or less and an inter-coil angle β between adjacent superconducting coils sandwiching the Y-axis is 20 degrees or less. As a result, the coil height can be reduced by increasing the magnetic field generation efficiency, the magnetic field center can be raised to near the melt surface of the semiconductor raw material, and it is possible to provide a single crystal pulling apparatus and a single crystal pulling method capable of pulling a single crystal with an even lower oxygen concentration than before and a defect-free crystal at a higher speed can be obtained.