4H-SiC Single Crystal Growth via Off-Angle Substrate and Meltback
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Solution Overview
Problem
The production of high-quality 4H—SiC single crystals by the TSSG method often results in substrates with high resistance values and the generation of heterogeneous polymorphs, leading to deteriorated electrical characteristics, especially when doping is involved.
Innovation Solution
A method involving a meltback step with an unsaturated carbon concentration to smooth the seed crystal surface, followed by crystal growth at an off-angle of 60 to 68° from the (0001) surface, preventing the formation of heterogeneous polymorphs and improving morphology regardless of doping presence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a 4H—SiC on-substrate is used for crystal growth, then good morphology can be obtained, but heterogeneous polymorphs other than 4H—SiC are easily generated
Solution Approach 1:
The patent changes the growth parameter by using an off-axis substrate with a specific off-angle range (60° to 68°) instead of a standard on-axis substrate. This parameter change in substrate orientation prevents heterogeneous polymorph generation while maintaining good crystal morphology during liquid phase growth of 4H—SiC single crystals.
2Reliability
If doping is performed to reduce resistance values, then electrical characteristics improve, but heterogeneous polymorphs are generated leading to deteriorated characteristics
Solution Approach 1:
The patent performs preliminary action by optimizing the substrate off-angle before crystal growth begins. By pre-setting the correct substrate orientation (60° to 68° off-angle), the system prevents heterogeneous polymorph formation during subsequent doping processes, allowing electrical characteristics to be improved through doping without the detrimental side effect of polymorph contamination.
3Length of moving object
If the TSSG method is used to grow SiC crystals, then crystal length and diameter can be increased, but trenches and surface roughness may occur
Solution Approach 1:
The patent changes the critical parameter of substrate orientation from on-axis to off-axis with a specific angle range (60° to 68°). This parameter change eliminates trench formation and surface roughness issues that commonly occur in TSSG method, enabling the growth of long crystals with smooth surfaces while maintaining the benefits of the TSSG approach.
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 allows for the production of 4H—SiC single crystals with good morphology and reduced resistance values, ensuring the absence of mixed polymorphs, making them suitable for electronic devices, particularly as substrate materials for power devices.
Implementation Method 1
a meltback step of allowing a raw material solution containing silicon and carbon and having an unsaturated carbon concentration to come into contact with a 4H type silicon carbide seed crystal and to dissolve part of the seed crystal
Implementation Method 2
a crystal growth step of allowing the seed crystal to grow a 4H type silicon carbide single crystal
Data Source
AI summary
A 4H-SiC single crystal having good morphology while preventing heterogeneous polymorphs from being mixed in regardless of the presence or absence of doping in growing a 4H-SiC single crystal by the TSSG method is obtained. When the off-angle on the grown crystal in a method for producing a SiC single crystal by a TSSG method is set to 60 to 68°, heterogeneous polymorphs are less likely to be mixed in during the growth of 4H-SiC single crystal, and if, during that period, a meltback method is used to smooth the surface of the seed crystal and then grow the crystal, it is possible to obtain a grown crystal having good morphology.