Cusp Magnetic Field Control for Uniform Oxygen in Silicon Crystals
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Solution Overview
Problem
Existing methods for producing silicon single crystals using a cusp magnetic field in the CZ method face issues such as increased oxygen concentration and deteriorated in-plane distribution, leading to device failures and reduced yield, particularly when producing large-diameter crystals.
Innovation Solution
A method involving a cusp magnetic field formed by an upper and lower coil in a pulling furnace, with specific rotational rates and magnetic field settings, including a magnetic field minimum plane position and intensity, to control oxygen concentration and distribution, achieving a silicon single crystal with low oxygen concentration and uniform in-plane distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the crystal rotational rate is set to a low rate (5 rpm or less), then the crystal can be pulled up stably, but the resistivity and in-plane distribution of oxygen deteriorate
Solution Approach 1:
The patent applies parameter changes by optimizing the crystal rotational rate to a specific range (7-12 rpm) rather than using low rates, and simultaneously adjusts the magnetic field intensity (800-1200 G) and position (10-50 mm from melt surface) to achieve both stable crystal pulling and uniform oxygen distribution. This multi-parameter optimization resolves the contradiction between stability and uniformity.
Solution Approach 2:
The cusp magnetic field acts as an intermediary that mediates between the crystal rotation and oxygen distribution. By positioning the magnetic field minimum plane at specific distances from the melt surface and controlling the field intensity, the magnetic field modifies the convection patterns and oxygen transport, enabling uniform distribution even at higher rotation rates.
2Temperature
If the magnetic field central position is elevated with increased solidification ratio, then the melt temperature is stabilized, but the oxygen concentration in the product portion increases and yield is reduced
Solution Approach 1:
The patent applies local quality by positioning the magnetic field minimum plane at specific locations (10-50 mm from melt surface) rather than uniformly distributing it. This localized magnetic field positioning creates specific convection patterns in particular regions of the melt, stabilizing temperature while controlling oxygen distribution in the product portion through localized field effects.
Solution Approach 2:
The patent employs dynamics by adjusting the magnetic field position and intensity dynamically during the crystal pulling process. The magnetic field parameters are optimized based on the solidification ratio and crystal growth stage, allowing adaptive control of both temperature stability and oxygen concentration throughout the production process.
3Productivity
If the crystal rotational rate is increased to 13 rpm or more for large-diameter crystals, then production efficiency improves, but diameter fluctuation increases and operation continuation becomes impossible
Solution Approach 1:
The patent resolves this contradiction by changing the parameter range for crystal rotational rate to an optimized interval (7-12 rpm) that balances productivity and diameter stability. Simultaneously, the magnetic field intensity (800-1200 G) and position (10-50 mm from melt surface) are adjusted to maintain diameter uniformity at these rotation rates, enabling sustained operation for large-diameter crystal production.
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 method enables efficient production of silicon single crystals with oxygen concentration of 2×10^17 atoms/cm^3 or less and Radial Oxygen Gradient (ROG) of less than 8%, meeting the quality requirements for power and RF devices without degrading production performance.
Implementation Method 1
a cusp magnetic field formed by an upper coil and a lower coil provided in a pulling furnace
Implementation Method 2
a rotational rate of the silicon single crystal to 7 rpm or more and 12 rpm or less, a rotational rate of a quartz crucible to 1.0 rpm or less
Data Source
AI summary
A method for producing silicon single crystal by CZ method using a cusp magnetic field formed by upper and lower coils coil provided in pulling furnace, the silicon single crystal is pulled up in a straight-body step by setting a rotational rate of the silicon single crystal to 7 rpm or more and 12 rpm or less, rotational rate of a quartz crucible to 1.0 rpm or less, position of a magnetic field minimum plane of the cusp magnetic field in a range of 10 mm downward to 5 mm upward from a raw-material melt surface, and intensity of magnetic field of cusp magnetic field at intersection of plane having same height as magnetic field minimum plane and inner wall of quartz crucible from 800 to 1200 G. Method for efficiently producing silicon single crystal having lower oxygen concentration and better in-plane distribution of oxygen concentration compared to conventional techniques.