Single Crystal Pulling Apparatus Magnetic Field Control
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Solution Overview
Problem
Existing single crystal pulling apparatuses using the Czochralski method with horizontal magnetic fields face inefficiencies in central magnetic flux density, leading to reduced growth rates of defect-free crystals, especially at normal oxygen concentrations, and struggle to produce low oxygen concentration crystals efficiently.
Innovation Solution
A single crystal pulling apparatus with a magnetic field generating system featuring main and sub-coils, where the main coils are arranged with a center angle of 100 to 120 degrees and sub-coils aligned with the X-axis, allowing independent current settings to enhance central magnetic flux density and convection suppression, enabling the production of both low oxygen concentration and defect-free region single crystals at high speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the coils are arranged to bend the magnetic force lines to achieve a specific magnetic flux density distribution, then the oxygen concentration in the crystal is reduced, but the central magnetic flux density becomes smaller and the crystal growth speed decreases
Solution Approach 1:
The magnetic field generating apparatus is divided into multiple independent coil units (first pair, second pair, third pair of coils) that can be controlled separately. This segmentation allows each coil unit to contribute differently to the magnetic flux density distribution, enabling simultaneous achievement of low oxygen concentration and high growth speed by optimizing the individual contributions of each coil unit.
Solution Approach 2:
The invention changes the arrangement parameters of the coil units, specifically setting the center angle between adjacent coil units to 60-90 degrees and positioning them at different radial distances from the central axis. By adjusting these geometric parameters and the current applied to each coil, the magnetic flux density distribution is optimized to provide both adequate central flux density for high growth speed and appropriate wall region flux density for oxygen suppression.
2Productivity
If the central magnetic flux density is increased to improve crystal growth speed, then the productivity increases, but the convection suppression at the crucible wall becomes insufficient and oxygen concentration increases
Solution Approach 1:
The magnetic field generating apparatus creates different magnetic flux density characteristics in different regions of the crucible. The coil units are positioned and configured to provide stronger magnetic field influence at the crucible wall regions where oxygen suppression is needed, while maintaining adequate central flux density for growth speed. This local optimization of magnetic field quality resolves the contradiction between global growth speed and local oxygen control.
Solution Approach 2:
The invention adds a radial dimension to the coil arrangement by positioning different coil units at different radial distances from the central axis. This three-dimensional coil configuration allows independent control of magnetic field strength at different radial positions, enabling the system to simultaneously satisfy the requirements for central flux density (affecting growth speed) and wall region flux density (affecting oxygen suppression).
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 high-speed growth of defect-free region single crystals with normal oxygen concentrations and low oxygen concentration crystals, improving productivity and efficiency by finely controlling magnetic field distribution and convection suppression.
Implementation Method 1
an electric field is generated in the horizontal direction perpendicular to both the magnetic field and the convection according to Fleming's right-hand rule. When an induced current flows due to this electric field, a Lorentz force is generated according to Fleming's left-hand rule.
Implementation Method 2
When an induced current flows due to this electric field, a Lorentz force is generated according to Fleming's left-hand rule. The direction of this force is the opposite direction of the flow that is first generated, and convection is suppressed.
Implementation Method 3
a heating heater and a crucible containing a molten semiconductor raw material are arranged
Data Source
AI summary
A single crystal pulling apparatus includes: a pulling furnace having a central axis; and magnetic field generating apparatus around the pulling furnace and having coils, for applying a horizontal magnetic field to molten semiconductor raw material to suppress convection in crucible, in which, main coils and sub-coils are provided, as the main coils, two pairs of coils arranged facing each other are provided, two coil axes thereof are included in the same horizontal plane, a center angle α between the two coil axes sandwiching the X-axis, which is a magnetic force line direction on the central axis in the horizontal plane, is 100 degrees or more and 120 degrees or less, as the sub-coils, a pair of superconducting coils arranged to face each other is provided and its one coil axis is aligned with the X-axis, and current values of the main coils and the sub-coils can be set independently.