Polycrystalline Silicon Rod Residual Stress Control
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Solution Overview
Problem
Polycrystalline silicon rods manufactured using the Siemens method often experience high residual stress due to temperature differences across their cross-section, leading to cracks and breakages during processing, which compromises product integrity and safety, and existing methods to reduce stress either lower production efficiency or require additional processing steps.
Innovation Solution
The process involves maintaining a temperature difference of 200°C or less across the cross-section of the polycrystalline silicon rod for at least an hour before completion, using a high-frequency power supply to uniform the surface temperature, and employing a dopant to adjust electrical resistivity, while growing dummy rods to radiate heat and reduce temperature gradients, thereby minimizing residual stress without significantly impacting production efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the diameter and length of polycrystalline silicon rods are increased to meet growing demand, then production capacity is improved, but the temperature difference across the cross-section increases leading to greater residual stress and more cracks
Solution Approach 1:
The patent applies parameter changes by controlling the temperature difference across the rod cross-section to be 200°C or less during the deposition process. This parameter control prevents excessive thermal stress while allowing large diameter and length rods to be produced, thus maintaining both productivity and reliability
2Stress or pressure
If conventional methods are used to reduce residual stress by cooling the rod, then stress is reduced, but production efficiency is significantly lowered
Solution Approach 1:
The patent applies preliminary action by controlling the temperature distribution during the deposition process itself, rather than applying corrective cooling after deposition. By maintaining appropriate temperature difference (≤200°C) during growth, residual stress is prevented from forming in the first place, avoiding the need for post-processing cooling steps that would reduce productivity
3Stress or pressure
If the temperature of the surface is gradually decreased to reduce stress, then residual stress is reduced, but the reaction speed and production rate are lowered
Solution Approach 1:
The patent maintains the deposition temperature within the optimal range of 900-1200°C while controlling the temperature gradient across the cross-section to ≤200°C. This parameter optimization ensures both low residual stress and high reaction speed, avoiding the need to reduce surface temperature which would slow the deposition rate
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 residual stress to 22 MPa or less, minimizing the risk of cracks and breakages during processing, while maintaining production efficiency and ensuring safer handling of the rods.
Implementation Method 1
using a high-frequency power supply to uniform the surface temperature
Implementation Method 2
employing a dopant to adjust electrical resistivity
Implementation Method 3
growing dummy rods to radiate heat and reduce temperature gradients
Implementation Method 4
The surface of the inverted U-shaped silicon core wire is heated by feeding an electric current thereto until it becomes at 900 to 1200° C.
Implementation Method 5
a silane-based raw material gas is typically brought into contact with a silicon core wire being heated. Then, polycrystalline silicon is deposited on a surface of this silicon core wire with a chemical vapor deposition (CVD) method
Data Source
AI summary
The present invention is related to a polycrystalline silicon rod manufactured with a Siemens method. The polycrystalline silicon rod having a length of 1 m or more in a longitudinal direction. An absolute value of a difference between compressive stress and tensile stress in residual stress in the longitudinal direction on a circumferential surface of the polycrystalline silicon rod is 22 MPa or less.