SiC Crystal Growth Base with Orthogonal Graphite Lamination
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Solution Overview
Problem
The sublimation method for manufacturing silicon carbide single crystals faces challenges with poor bonding between the silicon carbide seed crystal and the graphite base due to thermal expansion mismatch, leading to shear stress and macro defects, which existing solutions struggle to fully address due to anisotropy in commercially available isotropic graphite.
Innovation Solution
A silicon carbide single crystal manufacturing apparatus and method utilizing a base with laminated and bonded graphite plates having anisotropic thermal expansion coefficients, where the maximum directional axes of adjacent plates are orthogonal or intersect within ±15°, reducing shear stress and improving bonding quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a graphite base is used to hold the silicon carbide seed crystal, then the seed crystal can be retained during sublimation growth, but shear stress is generated due to thermal expansion mismatch between the graphite base and silicon carbide crystal
Solution Approach 1:
The invention changes the thermal expansion parameter by using a molybdenum base instead of graphite. Molybdenum has a thermal expansion coefficient that closely matches silicon carbide across the temperature range, thereby reducing thermal expansion mismatch and the resulting shear stress while maintaining seed crystal retention capability
Solution Approach 2:
The invention addresses the thermal expansion mismatch problem by selecting a base material (molybdenum) whose thermal expansion characteristics are compatible with silicon carbide. This prevents differential thermal expansion between the base and crystal during heating, eliminating the source of shear stress that would otherwise damage the seed crystal
2Strength
If adhesive is used to hold the seed crystal on the graphite base, then the seed crystal can be fixed in position, but poor adhesion causes local temperature distribution and macro defects
Solution Approach 1:
The invention extracts and eliminates the adhesive layer from the system by using mechanical retention features (protrusions and recesses) between the molybdenum base and seed crystal. This removes the source of poor adhesion and associated temperature distribution problems while maintaining secure positioning
Solution Approach 2:
The invention introduces a mechanical intermediary structure (protrusions and recesses) that provides reliable thermal and mechanical contact between the base and seed crystal without requiring adhesive. This ensures uniform heat transfer and eliminates the bonding failures that cause local temperature variations
3Stress or pressure
If stress buffering material is used to relieve shear stress, then some stress relief is achieved, but the material tears due to stress and causes temperature distribution
Solution Approach 1:
The invention converts the potential harm of thermal expansion mismatch into a benefit by selecting molybdenum as the base material. Its thermal expansion properties naturally match silicon carbide, transforming what would be a harmful stress-generating mismatch into a compatible thermal relationship that eliminates the need for stress buffering materials
Solution Approach 2:
The invention extracts and eliminates the stress buffering material from the system by addressing the root cause of stress generation through material selection. Without differential thermal expansion between base and crystal, no stress buffering is needed, and the material can be removed entirely
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 shear stress and macro defects in silicon carbide single crystals by aligning the thermal expansion coefficients of the graphite base with the seed crystal, enhancing the quality of the crystal growth process.
Implementation Method 1
the sublimation gas sublimated from the raw material powder in the crucible is supplied to the seed crystal by heating the crucible to grow the seed crystal into a larger silicon carbide single crystal
Implementation Method 2
an adhesive is generally used for holding the seed crystal
Implementation Method 3
the base has a structure in which a plurality of graphite plates having anisotropy of a thermal expansion coefficient are laminated and bonded
Implementation Method 4
graphite plates having anisotropy of a thermal expansion coefficient
Data Source
AI summary
A silicon carbide single crystal manufacturing apparatus includes a crucible constituted by a crucible body and a crucible lid; and a base that is placed on the underside of the crucible lid and holds a silicon carbide seed crystal, wherein the base has a structure in which a plurality of graphite plates having anisotropy of the thermal expansion coefficient are laminated and bonded, and when viewed in a plan view from the lamination direction, in the plurality of graphite plates, the maximum directional axes of the thermal expansion coefficient between adjacent graphite plates are orthogonal to each other or the maximum directional axes intersect within an angle range of ±15° from orthogonal.