The main methods for growing silicon carbide single crystals include Physical Vapor Transport (PVT), Top-Seeded Solution Growth (TSSG), and High-Temperature Chemical Vapor Deposition (HT-CVD).

Among these, the PVT method has become the primary technique for industrial production due to its relatively simple equipment setup, ease of operation and control, and lower equipment and operational costs.

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Key Technical Points of SiC Crystal Growth Using the PVT Method

To grow silicon carbide crystals using the PVT method, several technical aspects must be carefully controlled:

1. Purity of Graphite Materials in the Thermal Field
   The graphite materials used in the crystal growth thermal field must meet strict purity requirements. The impurity content in graphite components should be below 5×10⁻⁶, and for insulation felts below 10×10⁻⁶. Specifically, the contents of boron (B) and aluminum (Al) must each be below 0.1×10⁻⁶.

2. Correct Polarity of Seed Crystal
   Empirical data shows that the C-face (0001) is suitable for growing 4H-SiC crystals, while the Si-face (0001) is appropriate for 6H-SiC growth.

3. Use of Off-Axis Seed Crystals
   Off-axis seeds can alter the growth symmetry, reduce crystal defects, and promote better crystal quality.

4. Reliable Seed Crystal Bonding Technique
   Proper bonding between the seed crystal and the holder is essential for stability during growth.

5. Maintaining Stability of the Growth Interface
   During the entire crystal growth cycle, the growth interface must remain stable to ensure high-quality crystal development.

 

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Core Technologies in SiC Crystal Growth

1. Doping Technology for SiC Powder

Doping SiC powder with cerium (Ce) can stabilize the growth of a single polytype such as 4H-SiC. Practice has shown that Ce doping can:

• Increase the growth rate of SiC crystals;

• Improve crystal orientation for more uniform and directional growth;

• Reduce impurities and defects;

• Suppress backside corrosion of the crystal;

• Enhance the single crystal yield rate.

2. Control of Axial and Radial Thermal Gradients

Axial temperature gradients impact the crystal polytype and growth rate. A gradient that is too small can lead to polytype inclusions and reduced material transport in the vapor phase. Optimizing both axial and radial gradients is critical for fast and stable crystal growth with consistent quality.

3. Basal Plane Dislocation (BPD) Control Technology

BPDs form mainly due to shear stress exceeding the critical threshold in SiC crystals, activating slip systems. As BPDs are perpendicular to the growth direction, they typically arise during crystal growth and cooling. Minimizing internal stress can significantly reduce BPD density.

4. Vapor Phase Composition Ratio Control

Increasing the carbon-to-silicon ratio in the vapor phase is a proven method for promoting single polytype growth. A high C/Si ratio reduces macrostep bunching and retains surface inheritance from the seed crystal, thus suppressing the formation of undesired polytypes.

5. Low-Stress Growth Techniques

Stress during crystal growth may lead to curved lattice planes, cracks, and higher BPD densities. These defects can carry over into epitaxial layers and negatively impact device performance.

Several strategies to reduce internal crystal stress include:

• Adjusting thermal field distribution and process parameters to promote near-equilibrium growth;

• Optimizing crucible design to allow the crystal to grow freely without mechanical constraint;

• Improving the seed holder configuration to reduce the thermal expansion mismatch between the seed and graphite during heating, often by leaving a 2 mm gap between the seed and holder;

• Refining annealing processes, allowing the crystal to cool down with the furnace, and adjusting temperature and duration to fully relieve internal stress.

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Trends in SiC Crystal Growth Technology

1. Larger Crystal Sizes
SiC single crystal diameters have increased from just a few millimeters to 6-inch, 8-inch, and even 12-inch wafers. Larger wafers boost production efficiency and reduce costs, while meeting the demands of high-power device applications.

2. Higher Crystal Quality
High-quality SiC crystals are essential for high-performance devices. Despite significant improvements, current crystals still exhibit defects such as micropipes, dislocations, and impurities, all of which can degrade device performance and reliability.

3. Cost Reduction
SiC crystal production is still relatively expensive, limiting broader adoption. Reducing costs through optimized growth processes, increased production efficiency, and lower raw material costs is crucial for expanding market applications.

4. Intelligent Manufacturing
With advancements in artificial intelligence and big data technologies, SiC crystal growth is moving toward intelligent, automated processes. Sensors and control systems can monitor and adjust growth conditions in real-time, improving process stability and predictability. Data analytics can further optimize process parameters and crystal quality.

The development of high-quality SiC single crystal growth technology is a major focus in semiconductor materials research. As technology advances, crystal growth methods will continue to evolve and improve, providing a solid foundation for SiC applications in high-temperature, high-frequency, and high-power electronic devices.