Carbon Core Wire Holder for Silicon Rod Stress Reduction
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Solution Overview
Problem
The Siemens process for producing polysilicon rods faces challenges with stress-induced cracks due to thermal expansion and cooling, particularly in larger diameter rods, where existing methods either compromise strength or are complex and costly.
Innovation Solution
A core wire holder with a circular truncated cone-shaped silicon core wire holding portion and a chamfered curved surface is used, dispersing stress and reducing heat transfer, made from carbon with a thermal expansion coefficient matching silicon, to prevent cracks without weakening the holder.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cooling means is provided for water-cooling the inside of the device to protect the electrode from high temperature atmosphere, then the electrode is protected from high temperature, but the core wire holder and silicon core wire are cooled at the contact portion, causing high stress and cracks in the leg portion of the silicon rod
Solution Approach 1:
A carbon core wire holder is introduced as an intermediary component between the metal electrode and the silicon core wire. This carbon holder acts as a thermal barrier that prevents direct heat transfer from the cooled electrode to the silicon core wire, thereby reducing thermal stress and preventing cracks in the silicon rod leg portion while still allowing effective cooling of the electrode.
Solution Approach 2:
The material parameter of the core wire holder is changed from metal (SUS, copper) to carbon. Carbon has different thermal conductivity and thermal expansion properties compared to metal, which allows it to serve as a thermal barrier while maintaining electrical conductivity and mechanical strength, thus resolving the contradiction between electrode protection and silicon rod stress reduction.
2Productivity
If the diameter of the silicon rod is increased to produce a long silicon rod with large diameter to obtain a large amount of silicon, then the silicon production amount is increased, but distortion and local load increase causing the leg portion to break
Solution Approach 1:
The carbon core wire holder serves as a protective intermediary that shields the silicon core wire from excessive cooling at the contact portion. This reduces thermal stress in the leg portion, enabling the production of larger diameter silicon rods without compromising structural strength or causing breaks.
Solution Approach 2:
The carbon core wire holder utilizes its thermal expansion properties to accommodate the thermal stress generated during cooling. Carbon's thermal expansion coefficient is closer to silicon than metal is, which helps reduce the thermal mismatch and minimizes stress concentration in the leg portion of large diameter silicon rods.
3Stability of the object's composition
If a method for temporarily raising and then reducing the temperature of the silicon rod is used to reduce distortion, then the distortion in the silicon rod is reduced, but the process becomes more complex and costly
Solution Approach 1:
Instead of implementing complex temperature control processes, a simple carbon core wire holder is used as a passive thermal barrier. This intermediary component naturally reduces heat transfer from the electrode to the silicon core wire, eliminating the need for active temperature regulation systems and simplifying the overall process.
Solution Approach 2:
The carbon core wire holder is a simple, inexpensive component that provides effective thermal barrier functionality. It is easier and cheaper to implement this simple structural solution than to develop complex temperature control systems, making the invention more cost-effective.
4Loss of energy
If a core wire holder provided with annular pleats is used to reduce heat transfer, then heat conduction from electrodes is reduced, but the core wire holder itself becomes partially thin with decreased strength
Solution Approach 1:
The material parameter of the core wire holder is changed from metal to carbon, which provides better thermal barrier properties without requiring structural modifications like annular pleats. This maintains the structural strength of the core wire holder while effectively reducing heat transfer to the silicon core wire.
Solution Approach 2:
The invention uses carbon as a composite material that combines thermal barrier properties with structural strength. Carbon's unique material properties allow it to provide effective thermal isolation without compromising the mechanical strength required to support the silicon rod, avoiding the need for thin-walled pleated structures.
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
Effectively reduces stress and crack formation in the leg portion of silicon rods during cooling, maintaining strength and simplifying production, while being cost-effective and industrially practical.
Implementation Method 1
made from carbon with a thermal expansion coefficient matching silicon, to prevent cracks without weakening the holder
Implementation Method 2
distortion and local load caused by expansion or shrinkage of such a large silicon rod increases at a silicon deposition stage or a cooling stage after the deposition
Data Source
AI summary
A core wire holder 3 attached on an electrode 2 placed on a bottom panel of a device 20 for producing silicon by Siemens process includes a silicon core wire holding portion 9 being generally circular truncated cone-shaped, and holding and energizing a silicon core wire 4. The silicon core wire holding portion 9 includes a generally circular truncated cone having an upper surface formed with a silicon core wire insertion hole 7 for holding the silicon core wire 4, and the silicon core wire holding portion 9 includes an upper surface and a side surface, which form a ridge having a curved surface and serving as a chamfered portion 8.