SiC Single Crystal Growth via A-Axis Orientation
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Solution Overview
Problem
Current methods for producing large-sized silicon carbide (SiC) single crystals with high quality are hindered by the limitations of the Lely method, which results in low defect density and limited diameter, and alternative methods introduce crystal faults or lattice mismatch issues when using joined seed crystals or Si substrates.
Innovation Solution
A method involving sequential growth and cutting of SiC single crystals in specific directions and angles to create larger seed crystals, allowing for efficient enlargement without introducing crystal defects, using high-temperature sublimation and crystal-growing techniques, and employing seed crystals with optimized orientations and treatments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the Lely method is used to produce SiC single crystals, then the crystal quality is high with low defect density, but the crystal diameter is limited to approximately 1 cm²
Solution Approach 1:
The invention divides the crystal growth process into multiple stages: first growing a crystal in the c-axis direction to establish high quality, then cutting and re-orienting to grow in the a-axis direction to increase diameter. This segmentation allows each stage to optimize for its specific goal without compromising the other.
Solution Approach 2:
The invention transitions from one-dimensional growth (c-axis direction only) to two-dimensional enlargement by incorporating a-axis direction growth. This dimensional change enables diameter expansion while preserving crystal quality through controlled cutting and re-orientation operations.
2Reliability
If the modified Lely method is used to enlarge crystal diameter by repeating growth in the c-axis direction, then crystal quality is maintained, but production time exceeds one year for 2 inches enlargement
Solution Approach 1:
The invention introduces a-axis direction growth as a second dimension to the traditional c-axis growth. This enables rapid diameter enlargement without the time-consuming repeated c-axis growth cycles, reducing production time from over one year to a fraction of that time while maintaining crystal quality.
Solution Approach 2:
The invention performs preliminary cutting and re-orientation of the crystal to optimize its configuration for rapid a-axis growth. This preliminary preparation enables subsequent fast enlargement without compromising quality, avoiding the need for repeated slow growth cycles.
3Area of stationary object
If small seed crystals are joined side by side to achieve large diameter, then crystal size is enlarged, but crystal faults such as dislocations emanate from boundary surfaces
Solution Approach 1:
Instead of joining multiple small crystals horizontally to increase diameter, the invention inverts the approach by growing vertically in the a-axis direction from a single seed crystal. This eliminates boundary surfaces between joined crystals, preventing dislocation formation while achieving large diameter.
Solution Approach 2:
The invention segments the growth process into controlled stages of cutting and re-orientation rather than segmenting the crystal into multiple joined pieces. This process segmentation avoids creating boundary surfaces that would act as defect sources.
4Area of stationary object
If Si substrate is used to grow cubic SiC and then heat treated to convert to hexagonal SiC, then large diameter wafer is produced, but lattice mismatch defects survive after heat treatment
Solution Approach 1:
The invention changes the growth parameters by using a-axis direction growth instead of c-axis growth, and employs direct SiC seed crystals instead of Si substrates. This parameter change eliminates lattice mismatch issues while achieving large diameter through controlled crystal orientation and growth direction.
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 method enables the production of large, high-quality SiC single crystals with reduced defects, allowing for the efficient enlargement of crystal size while maintaining crystallinity, suitable for applications in semiconductor devices and power control elements.
Implementation Method 1
The Lely method incurs difficulty in enabling addition to diameter and barely allows the production of a crystal approximating to 1 cm2 at most. The large SiC single crystal available to date has been produced by using the Lely crystal as a seed crystal, repeating growth of crystal in the same direction (mainly in the direction of the c-axis) by using the sublimation and recrystallization method called the modified Lely method
Implementation Method 2
repeating growth of crystal in the same direction (mainly in the direction of the c-axis) by using the sublimation and recrystallization method called the modified Lely method, and enlarging the crystal in the direction of the a-axis little by little
Data Source
AI summary
A method for the production of an SiC single crystal includes the steps of growing a first SiC single crystal in a first direction of growth on a first seed crystal formed of an SiC single crystal, disposing the first SiC single crystal grown on the first seed crystal in a direction parallel or oblique to the first direction of growth and cutting the disposed first SiC single crystal in a direction of a major axis in a cross section perpendicular to the first direction of growth to obtain a second seed crystal, using the second seed crystal to grow thereon in a second direction of growth a second SiC single crystal to a thickness greater than a length of the major axis in the cross section, disposing the second SiC single crystal grown on the second seed crystal in a direction parallel or oblique to the second direction of growth and cutting the disposed second SiC single crystal in a direction of a major axis in a cross section perpendicular to the second direction of growth to obtain a third seed crystal, using the third seed crystal to grow thereon a third SiC single crystal, and cutting the third SiC single crystal grown on the third seed crystal in such a manner as to expose a {0001} crystal face, thereby obtaining an SiC single crystal. The method enables the crystal to be enlarged efficiently without impairing crystallinity.