Polycrystalline Silicon Rod Post-Deposition Energization
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Solution Overview
Problem
Existing methods for manufacturing polycrystalline silicon rods using the Siemens process face challenges in preventing cracks and breakages, particularly due to thermal stress and inadequate control over crystal properties.
Innovation Solution
The method involves a post-deposition energization step where high-frequency current is passed through the polycrystalline silicon rod to create a skin depth shallower than at the end of the deposition step, and a post-deposition heat treatment step where the rod is heated to a temperature higher than the crystal temperature but lower than the melting point, while being energized under conditions that reduce skin depth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-frequency current is passed through the polycrystalline silicon rod during post-deposition energization, then thermal stress is reduced and cracks are prevented, but temperature distribution control becomes more complex
Solution Approach 1:
The patent applies periodic action by implementing post-deposition energization at specific time points after deposition. High-frequency current is passed through the silicon rod in a controlled periodic manner during the cooling phase, allowing thermal stress reduction without continuous heating, thus preventing cracks while managing temperature control complexity.
Solution Approach 2:
The patent utilizes parameter changes by adjusting the frequency and duration of high-frequency current application during post-deposition energization. By changing electrical parameters (frequency, amplitude, timing) rather than continuously adjusting temperature, the system achieves effective thermal stress management and crack prevention with simplified control mechanisms.
2Stability of the object's composition
If the polycrystalline silicon rod is heated to reduce thermal stress, then uniformity of temperature distribution is improved, but energy consumption increases
Solution Approach 1:
The patent applies preliminary action by performing post-deposition energization during the cooling phase rather than during active deposition. By pre-heating the rod slightly before the critical cooling period, the system maintains temperature uniformity and prevents thermal stress without requiring excessive energy input during the energy-intensive deposition process.
Solution Approach 2:
The patent implements continuity of useful action by maintaining controlled energization throughout the cooling period. Rather than applying intense heating only when needed, a continuous low-level energization maintains temperature uniformity throughout the entire cooling process, reducing peak energy requirements while ensuring stability.
3Temperature
If high-frequency current is used to create shallow skin depth, then surface heating is enhanced for stress relief, but penetration depth is reduced
Solution Approach 1:
The patent applies local quality by using high-frequency current to create shallow skin depth that concentrates heating at the surface of the silicon rod. This localized surface heating is precisely what is needed for stress relief during cooling, while the reduced penetration depth prevents excessive internal heating. The different regions of the rod receive appropriate thermal treatment.
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
This approach effectively reduces the likelihood of cracks and breakages by minimizing temperature differences within the rod, thereby enhancing the quality and length of the polycrystalline silicon rods suitable for monocrystalline silicon production by the FZ process.
Implementation Method 1
performing energization under a condition that provides a skin depth D shallower than a skin depth D0 provided at a time when the deposition step ends
Implementation Method 2
performing energization under a condition that provides a skin depth D shallower than a skin depth D0 provided at a time when the deposition step ends
Data Source
AI summary
There is provided a method of manufacturing a polycrystalline silicon rod suitable as a raw material for manufacturing monocrystalline silicon by a FZ process. The method of manufacturing a polycrystalline silicon rod according to the present invention is a method of manufacturing a polycrystalline silicon rod by Siemens process, and includes a post-deposition energization step of, after an end of a deposition step of polycrystalline silicon, performing energization under a condition that provides a skin depth D shallower than a skin depth D0 provided at a time when the deposition step ends. For example, the post-deposition energization step is performed by passage of current at a frequency f higher than a frequency f0 of current that is passed at a time when the deposition step ends.