Expanded Graphite Crucible Protection Sheet for Silicon Crystal Growth
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Solution Overview
Problem
Current crucible apparatuses face issues with the flexibility and thermal conductivity of expanded graphite sheets, leading to poor workability, thermal uniformity, and increased production costs due to high-quality, high-purity requirements, which result in quality degradation and cost inefficiencies in silicon single crystal manufacturing.
Innovation Solution
A crucible protection sheet made of expanded graphite with specific characteristics, including a compression ratio of 20% or higher, planar thermal conductivity of 120 W/(m·K) or higher, and controlled impurity levels, is used between the inner and outer crucibles to enhance shock absorption, thermal uniformity, and gas shielding, while maintaining cost-effectiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If an expanded graphite sheet is used as a crucible protection sheet, then flexibility and compressibility are improved, but planar thermal conductivity becomes insufficient leading to poor temperature uniformity
Solution Approach 1:
The patent applies parameter changes by controlling the bulk density of the expanded graphite sheet within a specific range (0.3 to 1.5 Mg/m³) to simultaneously achieve adequate flexibility for ease of operation and sufficient planar thermal conductivity for temperature uniformity. This optimized parameter range resolves the contradiction between these two opposing requirements.
2Ease of operation
If the bulk density of the expanded graphite sheet is reduced to improve flexibility, then compressibility is improved, but planar thermal conductivity decreases
Solution Approach 1:
The patent resolves this contradiction by defining an optimal bulk density range (0.3 to 1.5 Mg/m³) that balances compressibility and planar thermal conductivity. Within this range, the expanded graphite sheet achieves sufficient compression ratio for cushioning while maintaining adequate thermal conduction for temperature uniformity, eliminating the need to sacrifice one property for the other.
3Manufacturing precision
If high-purity materials are used to ensure product quality, then purity is improved, but production cost increases
Solution Approach 1:
The patent applies local quality by implementing a protective barrier (expanded graphite sheet and/or pyrocarbon coating) between the crucible and molten silicon. This localized protection prevents impurity contamination at the critical interface without requiring the entire crucible system to be made of extremely high-purity materials, thereby reducing overall production cost while maintaining product quality.
Solution Approach 2:
The expanded graphite sheet and pyrocarbon coating serve as intermediary protective layers that prevent direct contact between the crucible and molten silicon. These intermediaries block the transmission of impurities from the crucible to the silicon, allowing the use of lower-purity, more cost-effective crucible materials while still ensuring high product quality.
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
The solution improves workability, prevents crucible damage, ensures uniform heating, and reduces production costs by maintaining high product quality without the need for extremely high-purity materials, effectively addressing the limitations of existing technologies.
Implementation Method 1
the compression ratio represented by the following equation (2) is 20% or higher: Compression ratio (%)＝[(t1−t2)/t1]×100 where t1 is the thickness (mm) after applying a pre-load (0.686 MPa±1％) for 15 seconds, and t2 is the thickness (mm) after applying a total pressure (34.3 MPa±1％) for 60 seconds
Implementation Method 2
the planar thermal conductivity is 120 W/(m·K) or higher
Implementation Method 3
the reaction of the SiO gas or the like generated from the inner crucible with the outer crucible can be prevented since the pyrocarbon coated on the surface reacts with the SiO gas or the like
Data Source
AI summary
A crucible protection sheet is provided that can prevent damages to an inner crucible, hinder an outer crucible from silicon-carbidization, and transmit heat from the outer crucible to the inner crucible uniformly.In a crucible having an inner crucible 2 and an outer crucible 3, the crucible protection sheet is arranged between the two crucibles and is made of expanded graphite. The planar thermal conductivity is 120 W/(m·K) or higher, the gas permeability is less than 1.0×10−4 cm2/s, and the compression ratio is 20% or higher when the sheet is compressed in a thickness direction at a pressure of 34.3 MPa. Since the compression ratio is high, the effect of preventing breakage is great when inserting the inner crucible, improving workability and preventing the inner crucible from tilting inside the outer crucible. In addition, even though the compression ratio is high, the thermal conductivity is kept to such a degree that the inner crucible can be heated uniformly, and the gas shielding capability is also ensured. As a result, the outer crucible is prevented from silicon-carbidization and thickness decrease.