Polycrystalline Silicon Rod Asymmetry for Dislocation Reduction
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Solution Overview
Problem
The Siemens method for producing polycrystalline silicon rods for monocrystalline silicon production by the floating-zone method faces issues such as the need for specific crystal orientation, low deposition rates, and defects due to needle crystals and mechanical stress at the graphite-silicon contact point, which complicates the process and can lead to dislocation in the monocrystalline silicon growth.
Innovation Solution
A polycrystalline silicon rod is grown with its center axis shifted from the center axis of the silicon core wire by 2 mm or more, allowing for a simpler method without requiring special crystal orientation considerations, and this is achieved through adjustments in deposition conditions such as changing the gas supply nozzle position and radiation arrangement to alter the deposition rate and temperature, followed by cylindrical grinding to maintain the shifted axis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the polycrystalline silicon rod is grown with the center axis aligned with the silicon core wire, then the deposition process is simpler, but needle crystals deposit in the center part causing defects and dislocation during FZ method
Solution Approach 1:
The patent intentionally creates an asymmetric structure by shifting the center axis of the polycrystalline silicon rod away from the center axis of the silicon core wire by 2mm or more. This asymmetric positioning prevents needle crystals from depositing in the center region, eliminating the source of defects that would otherwise cause dislocation during the floating-zone method while maintaining a relatively simple deposition process
2Reliability
If the center axis of polycrystalline silicon rod is shifted from silicon core wire by 2mm or more, then needle crystal deposition is prevented and single crystallization is improved, but the deposition process becomes more complex
Solution Approach 1:
The patent implements a controlled asymmetric configuration by positioning the polycrystalline silicon rod's center axis at a specific offset (2mm or more) from the silicon core wire's center axis. This deliberate asymmetry strategically redirects needle crystal deposition away from the center region, ensuring high-quality single crystallization during the floating-zone method while maintaining operational simplicity through a straightforward geometric arrangement
3Use of energy by moving object
If graphite contact point is used for heating, then heating efficiency is improved, but mechanical stress melts or damages the fine silicon rod at the contact point
Solution Approach 1:
The patent introduces an intermediate protective structure between the graphite heating element and the silicon rod. This intermediate layer acts as a buffer that transmits thermal energy effectively while isolating the silicon rod from direct mechanical contact and stress concentration, preventing melting or damage at the contact point during the initial heating stage
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 significantly reduces the occurrence of dislocations during monocrystalline silicon growth, increasing the yield and simplifying the production process by avoiding complex initial deposition stage conditions and mechanical stress issues.
Implementation Method 1
a contact heating region, which commonly appears at a contact point between graphite and silicon particularly in an initial stage of heating process
Implementation Method 2
polycrystalline silicon is deposited on the surface of the silicon core wire using chemical vapor deposition (CVD) method
Implementation Method 3
Polycrystalline silicon is grown on the silicon core wires through vapor-phase epitaxy
Data Source
AI summary
In a step of performing cylindrical grinding of a polycrystalline silicon bar 10 grown by a Siemens method, this cylindrical grinding step is performed such that a polycrystalline silicon rod 30, whose center axis CR is shifted from a center axis C0 of a silicon core wire 20 by 2 mm or more, is manufactured.