SiC Seed Crystal Facet Control for Polytype Stability
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Solution Overview
Problem
The challenge is to suppress the formation of linear c-plane facets during the initial stage of SiC single-crystal growth, especially for larger diameters, while maintaining the quality and thickness of the seed crystal, as existing techniques fail to stabilize screw dislocations and control facet shapes effectively.
Innovation Solution
A seed crystal configuration with a {0001}-plane uppermost portion and multiple planes enclosing the periphery, where the offset angles and angles defined by ridge lines satisfy specific formulas to ensure a stable, dotted or small-circle-shaped c-plane facet formation, preventing linear facet formation and maintaining high-quality crystal growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the diameter of the grown crystal is increased to meet demand for larger SiC single crystals, then the crystal size is improved, but heterogeneous polytypes are readily formed due to unstable c-plane facet shape
Solution Approach 1:
The invention applies preliminary action by pre-forming a specific c-plane facet shape (circular or elliptical with controlled aspect ratio) on the seed crystal surface before growth begins. This preliminary shape control ensures that even as the crystal grows to larger diameters, the c-plane facet maintains a stable geometry that prevents heterogeneous polytype formation throughout the entire growth process.
Solution Approach 2:
The invention changes geometric parameters by controlling the aspect ratio of the c-plane facet within a specific range (0.5 to 2.0) and positioning it at a specific offset distance from the seed crystal center. By optimizing these parameters, the facet shape remains stable during growth of larger diameter crystals, suppressing polytype heterogeneity while allowing increased crystal size.
2Reliability
If a screw dislocation formation region is provided to suppress heterogeneous polytypes, then polytype stability is improved, but screw dislocations are densely formed over the entire formation region causing degradation in crystal quality
Solution Approach 1:
The invention applies local quality by creating a concentrated screw dislocation source at a specific location (the offset c-plane facet) rather than distributing screw dislocations throughout the entire growth surface. This localized approach maintains polytype stability through the offset facet geometry while limiting screw dislocation density to specific regions, thereby preserving overall crystal quality.
3Ease of manufacture
If the c-plane facet is allowed to form naturally during initial crystal growth, then the growth process is simple, but the facet shape becomes unstable and elongated leading to heterogeneous polytypes
Solution Approach 1:
The invention applies preliminary action by pre-forming the c-plane facet with a controlled circular or elliptical shape and specific aspect ratio on the seed crystal before growth begins. This preliminary shaping prevents the facet from developing an unstable elongated form during initial growth, maintaining shape stability throughout the process while keeping the overall manufacturing approach simple.
4Shape
If the offset angle of planes enclosing the facet formation region is increased to control facet shape, then facet shape control is improved, but the seed crystal thickness must be increased which is not acceptable
Solution Approach 1:
The invention changes geometric parameters by optimizing the offset distance of the c-plane facet from the seed crystal center and controlling the aspect ratio within specific ranges. By adjusting these parameters rather than increasing offset angles, the facet shape is effectively controlled without requiring increased seed crystal thickness, maintaining a practical device geometry.
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 effectively suppresses linear c-plane facet formation, stabilizes screw dislocations, and ensures high-quality SiC single-crystal growth without increasing seed crystal thickness, even for larger diameters, by optimizing the angles and areas of the growth planes.
Implementation Method 1
a growth step of growing an SiC single crystal on a growth plane of the seed crystal for SiC single-crystal growth
Implementation Method 2
slight fluctuation of sublimated gas concentration on the growth plane
Data Source
AI summary
A seed crystal for SiC single-crystal growth includes a facet formation region containing a {0001}-plane uppermost portion and n (n>=3) planes provided enclosing the periphery of the facet formation region. The seed crystal for SiC single-crystal growth satisfies the relationships represented by formula (a): Bkk-1<=cos−1(sin(2.3 degrees)/sin Ck), formula (b): Bkk<=cos−1(sin(2.3 degrees)/sin Ck), and formula (c): min(Ck)<=20 degrees. In the formulas, Ck is an offset angle of a k-th plane, Bkk-1 is an angle defined by an offset downstream direction of the k-th plane and a (k−1)-th ridge line, and Bkk is an angle defined by the offset downstream direction of the k-th plane and a k-th ridge line.