SiC Seed Crystal Cushion Ring Mounting for Stress Reduction
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Solution Overview
Problem
Current methods for growing silicon carbide (SiC) crystals face challenges in minimizing stress and defects such as micropipes, screw dislocations, and basal plane dislocations, which limit the quality and performance of SiC crystals and wafers used in semiconductor devices.
Innovation Solution
A method of vapor transport SiC crystal growth where the seed crystal is supported without external stress, using cushion rings to allow thermal expansion and contraction, and is positioned to prevent contact with the reaction cell lid, reducing mechanical constraints and stress during growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the seed crystal is rigidly mounted to the reaction cell lid, then the seed crystal is securely positioned, but thermal stress and mechanical constraints cause defects such as micropipes and dislocations
Solution Approach 1:
The patent employs a flexible mounting mechanism using a resilient member (such as a rubber band or elastic element) to secure the seed crystal to the reaction cell lid. This flexible connection allows the seed crystal to expand and contract thermally without generating stress, while still maintaining secure positioning throughout the crystal growth process.
Solution Approach 2:
The patent changes the mechanical constraint parameter from rigid fixation to flexible mounting. By using a resilient member that can deform elastically, the system accommodates thermal expansion and contraction of the seed crystal, preventing the generation of thermal stress and mechanical constraints that would otherwise cause defects.
2Temperature
If the reaction cell is heated to high temperatures for sublimation, then SiC crystal growth is enabled, but thermal expansion mismatch between the seed crystal and reaction cell causes stress and defects
Solution Approach 1:
The patent explicitly accounts for thermal expansion by using a resilient mounting member that can accommodate the differential thermal expansion between the seed crystal and the reaction cell. The flexible connection allows each component to expand at its own rate without generating stress, solving the thermal expansion mismatch problem inherent in high-temperature crystal growth.
3Productivity
If the seed crystal is positioned close to the source material for efficient growth, then crystal growth rate increases, but contact with the reaction cell lid or mechanical constraints create defects
Solution Approach 1:
The flexible resilient member allows the seed crystal to be positioned in optimal proximity to the source material for high growth rates, while simultaneously providing a compliant mounting that prevents mechanical constraints and contact defects. The resilience of the mounting member absorbs any positional adjustments or thermal movements without creating harmful mechanical constraints.
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 results in SiC crystals with significantly reduced defect densities, including micropipe, screw dislocation, and basal plane dislocation densities, enabling the growth of large, high-quality crystals and wafers with improved performance for semiconductor applications.
Implementation Method 1
Growth of SiC by sublimation... when the container is heated to a temperature sufficient to sublime the source material, the vapors will travel towards the low temperature region and condense on the seed crystal
Implementation Method 2
the vapors will travel towards the low temperature region and condense on the seed crystal
Implementation Method 3
Temperatures in excess of 2,000°C are required to generate vapor stream of Si/ C species by sublimation
Data Source
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AI summary
A method of forming an SiC crystal including placing in an insulated graphite container a seed crystal of SiC, and supporting the seed crystal on a shelf, wherein cushion rings contact the seed crystal on a periphery of top and bottom surfaces of the seed crystal, and where the graphite container does not contact a side surface of the seed crystal; placing a source of Si and C atoms in the insulated graphite container, where the source of Si and C atoms is for transport to the seed crystal to grow the SiC crystal; placing the graphite container in a furnace; heating the furnace; evacuating the furnace; filling the furnace with an inert gas; and maintaining the furnace to support crystal growth to thereby form the SiC crystal.