Polysilicon Reactor Inner Wall Anti-Corrosion Layer
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Solution Overview
Problem
The production of high-purity polycrystalline silicon for semiconductors is hindered by the contamination of dopant impurities from the inner wall of reaction vessels, particularly when the temperature exceeds 370°C, leading to reduced quality and increased impurity levels beyond the desired 100 ppt atomic ratio.
Innovation Solution
A reactor with an anticorrosive layer composed of a chromium-nickel-silicon alloy (R = [Cr] + [Ni] - 1.5 [Si] ≥ 40%) and a heat conductive layer is used, along with pressurized cooling water circulation to maintain the inner wall temperature below 370°C, reducing contamination and efficiently recovering heat for reuse.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the inner wall temperature of the reaction vessel is increased to improve deposition efficiency, then the productivity of polycrystalline silicon is improved, but the purity of polycrystalline silicon deteriorates due to increased dopant impurity release from the inner wall
Solution Approach 1:
The inner wall structure is segmented into multiple functional layers: a base layer providing structural support, an intermediate layer with moderate thermal conductivity, and a surface layer with low thermal conductivity and high heat resistance. This segmentation allows the inner wall to maintain structural integrity while controlling heat transfer to minimize dopant release.
Solution Approach 2:
The inner wall is constructed using composite materials with specifically selected thermal and mechanical properties. The combination of materials creates a structure that can withstand high deposition temperatures while maintaining a cooler interface with the polycrystalline silicon, thereby reducing dopant impurity release without compromising deposition efficiency.
2Manufacturing precision
If conventional cooling methods are used to reduce inner wall temperature, then the purity of polycrystalline silicon is improved, but the heat recovery efficiency deteriorates
Solution Approach 1:
A specially designed inner wall structure acts as an intermediary between the high-temperature deposition environment and the cooling system. This intermediate structure controls heat transfer rates, allowing sufficient cooling to maintain purity while enabling heat recovery from the process.
Solution Approach 2:
The thermal conductivity parameter of the inner wall materials is carefully selected and varied across different layers. By changing the thermal conductivity parameter from the base layer to the surface layer, the system achieves optimal balance between cooling efficiency for purity maintenance and heat recovery capability.
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 limits dopant impurity incorporation in polycrystalline silicon to below 100 ppt atomic, achieving high-purity silicon production while recovering heat for further use, thereby enhancing the semiconductor material quality and energy efficiency.
Implementation Method 1
a heat conductive layer provided between the anticorrosive layer and the cooling water flow passage
Implementation Method 2
the heat conductive layer comprising a second alloy material having heat conductivity higher than that of the first alloy material
Implementation Method 3
polycrystalline silicon is grown on the surface of the silicon core by a CVD (Chemical Vapor Deposition) method
Data Source
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AI summary
An inner wall 11 of a reactor 10 has a two-layer structure: an anticorrosive layer 11a comprising an alloy material having high anticorrosiveness is provided on the inner side of the reactor contacting a corrosive process gas, and a heat conductive layer 11b for efficiently conducting the heat within the reactor 10 from an inner wall surface to a coolant flow passage 13 is provided on the outer side of the reactor (outer-wall side). The anticorrosive layer 11a comprises an alloy material having a composition for which a value R, defined by R = [Cr] + [Ni] - 1.5 [Si], is not less than 40% wherein[Cr]is a mass content (% by mass) of chromium (Cr), [Ni] is a mass content (% by mass) of nickel (Ni), and [Si] is a mass content (% by mass) of silicon (Si).