Layered Seed Heat Spreader for Uniform SiC Crystal Growth
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Solution Overview
Problem
Existing seed coupling methods in PVT processes for growing semiconductor crystals, such as SiC, introduce thermal stress, contamination, and pressure changes, leading to defects and inhomogeneities in the crystal growth.
Innovation Solution
A layered seed comprising a monocrystalline growing layer and a polycrystalline heat spreader layer with thermally coupled grains, designed to equalize temperature profiles and reduce thermal inhomogeneities, thereby improving crystal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a lateral support is used to hold the seed crystal, then the seed can be positioned in the crucible, but the support places stress on the seed and introduces thermal inhomogeneities due to different thermal properties
Solution Approach 1:
The invention removes the lateral support structure from the system. Instead of using an external support to hold the seed crystal, the seed is mounted directly on the crucible lid or integrated into the crucible structure, eliminating the source of mechanical stress and thermal inhomogeneity
Solution Approach 2:
The seed mounting function is merged with the crucible structure itself. The crucible lid or body serves as both the containment structure and the seed support, eliminating the need for separate support components and ensuring thermal compatibility
2Strength
If a metal support material is used to hold the seed, then the seed can be secured, but the different thermal properties affect the temperature gradient in the crucible
Solution Approach 1:
The invention changes the thermal parameter matching between support and seed. Instead of using metal with high thermal conductivity, the support structure is made from material with thermal properties matched to the seed crystal (such as graphite or ceramic), ensuring uniform heat distribution and eliminating thermal gradients that would cause inhomogeneous crystal growth
3Ease of operation
If a support material is introduced into the PVT system, then the seed can be held, but the support material can contaminate the gas atmosphere and change the pressure
Solution Approach 1:
The invention removes the separate support material from the gas atmosphere. By integrating the seed mounting directly into the crucible structure or using the crucible lid as the support surface, no additional materials are introduced into the vapor phase, eliminating contamination and pressure changes
Solution Approach 2:
The mounting structure is designed to be asymmetric with respect to the gas flow paths, positioning the seed and support interface away from regions where vapor transport occurs, thereby preventing any potential contamination from reaching the crystal growth zone
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 layered seed enhances the quality of SiC single crystals by reducing thermal stress, impurities, dislocations, and stacking defects, resulting in improved geometry and uniformity of wafers produced from them.
Implementation Method 1
a heat spreader layer with a growing layer facing surface for coupling to the heat spreader facing surface and an opposing mounting surface for mounting the heat spreader to the crucible, wherein the heat spreader layer comprises a polycrystalline material having thermally coupled grains that are piled in the direction of growth, the piled grains for equalizing hot spots of the crucible
Implementation Method 2
Due to the temperature levelling effect of the multilayer seed, growth inhomogeneities can be reduced
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
The present disclosure relates to a layered seed for growing a volume mono crystal by gas phase growth in a direction of growth (Y) in a crucible (1200). The layered seed comprises a monocrystalline growing layer (110) with a growing surface (112) for growing the volume mono crystal and an opposing heat spreader facing surface (114) for coupling the growing layer (110) to a heat spreader layer (140). The layered seed further comprises the heat spreader layer (140) with a growing layer facing surface (144) for coupling to the heat spreader facing surface (114) and an opposing mounting surface (142) for mounting the heat spreader layer (140) to the crucible (1200), wherein the heat spreader layer (140) comprises a polycrystalline material having thermally coupled grains (146) that are piled in the direction of growth (Y), the piled grains (146) for equalizing hot spots of the crucible thermally coupled to the mounting surface (142).