Graphite Base for Silicon Carbide Crystal Growth
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Solution Overview
Problem
The sublimation method for manufacturing silicon carbide single crystals faces challenges with shear stress and poor adhesion between the seed crystal and the graphite base due to thermal expansion coefficient mismatches, leading to macro defects, especially as the seed crystal diameter increases.
Innovation Solution
A silicon carbide single crystal manufacturing apparatus with a graphite base having a truncated cone shape and a larger seed crystal mounting surface area than the crucible lid surface area, where the cross-sectional area gradually reduces from the seed crystal mounting surface to the crucible lid surface, and optionally using a stress buffering member with a Young's modulus less than 5 GPa.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a graphite base is used to hold the silicon carbide seed crystal, then the base can withstand high temperatures during sublimation, but thermal expansion coefficient mismatch generates shear stress causing poor adhesion and macro defects
Solution Approach 1:
A stress buffering member made of graphite is introduced as an intermediary layer between the silicon carbide seed crystal and the graphite base. This mediator absorbs and buffers the shear stress generated by thermal expansion coefficient differences, preventing direct stress transmission that causes adhesion failure and macro defects, while still allowing the system to withstand high temperatures.
Solution Approach 2:
The base structure is designed as a composite system combining graphite base material with a graphite stress buffering member layer. This composite structure leverages the high temperature resistance of graphite while adding the stress-buffering functionality of the graphite layer, which has different mechanical properties to accommodate thermal expansion mismatches.
2Productivity
If the seed crystal diameter is increased to improve productivity, then more silicon carbide can be produced, but shear stress increases causing more poor adhesion and macro defects
Solution Approach 1:
The graphite stress buffering member serves as a mediator that decouples the stress transmission path between the large-diameter seed crystal and the base. This allows the system to support larger seed crystal diameters for increased productivity while the stress buffering member prevents the proportional increase in shear stress from causing adhesion failures and macro defects.
3Strength
If adhesive is used to hold the seed crystal on the base, then the seed crystal can be retained, but shear stress causes adhesive failure and poor adhesion
Solution Approach 1:
The graphite stress buffering member is placed beforehand between the seed crystal and base to cushion and absorb the shear stress before it can reach the adhesive layer. This prior cushioning prevents the adhesive from experiencing stress levels that would cause failure, thereby maintaining bonding strength without requiring the adhesive to withstand high shear stresses.
Solution Approach 2:
The stress buffering member acts as an intermediary that protects the adhesive layer from direct exposure to shear stress. By placing this protective layer between the seed crystal and base, the adhesive is shielded from the harmful stress, allowing it to maintain its bonding function without premature failure.
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 configuration reduces shear stress and improves bonding between the seed crystal and the graphite base, minimizing macro defects and enhancing the quality of the silicon carbide single crystal.
Implementation Method 1
In the sublimation method, a seed crystal consisting of a silicon carbide single crystal is placed on a base placed in a graphite crucible, and 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.
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 having a crucible lid side surface supported by the lower surface of the crucible lid, and a seed crystal mounting surface on which the seed crystal is mounted and which is a surface on the opposite side of the crucible lid side surface, wherein the base is made of graphite material, the area of the seed crystal mounting surface is larger than the area of the crucible lid side surface, and the base has at least of a portion in which the cross-sectional area orthogonal to the vertical direction connecting the crucible lid side surface and the seed crystal mounting surface is gradually reduced, and a portion that is getting smaller gradually, from the surface of the seed crystal mounting surface toward the crucible lid side surface.