Key Considerations for Producing High-Quality Silicon Carbide (SiC) Single Crystals

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

Among these, PVT is the most widely adopted method in industrial production due to its relatively simple equipment setup, ease of control, and lower equipment and operational costs.

Technical Highlights of PVT Method for SiC Crystal Growth

When growing SiC single crystals using the PVT method, the following technical aspects are critical:

• Purity of Graphite Materials

The graphite used in the thermal field must meet strict purity requirements. The impurity content in graphite parts should be less than 5×10⁻⁶, while insulation felts should be below 10×10⁻⁶. In particular, boron (B) and aluminum (Al) content must be below 0.1×10⁻⁶.​

• Correct Seed Crystal Polarity Selection

Experiments have shown that the C (0001) face is suitable for growing 4H-SiC, while the Si (0001) face is used for 6H-SiC growth.

• Use of Off-Axis Seed Crystals

Off-axis seeds help break growth symmetry and reduce defects in the resulting crystal.

• High-Quality Seed Bonding Process

Reliable bonding between the seed crystal and substrate is essential for stable growth.

• Maintaining a Stable Growth Interface

Throughout the growth cycle, it is crucial to maintain the stability of the crystal growth interface to ensure uniform quality.

Core Technologies in SiC Crystal Growth

• Doping Technology in SiC Powder

  Doping silicon carbide powder with cerium (Ce) promotes the stable growth of single-polytype 4H-SiC. This doping technique can:

   

  • Increase growth rate;

  • Enhance crystallographic orientation;

  • Suppress impurity incorporation and defect formation;

  • Improve yield of high-quality crystals;

  • Prevent backside corrosion and increase monocrystallinity.

• Axial and Radial Temperature Gradient Control

  The axial gradient significantly affects crystal morphology and growth efficiency. A gradient that's too small may lead to polytype mixing and reduced vapor transport. Optimal axial and radial gradients support fast, stable crystal growth.

• Basal Plane Dislocation (BPD) Control

  BPDs arise when internal shear stress exceeds the critical threshold, typically during growth and cooling. Managing these stresses is key to minimizing BPD defects.

• Gas Phase Composition Ratio Control

  Increasing the carbon-to-silicon ratio in the vapor phase helps stabilize single-polytype growth and prevents macro-step bunching, thereby suppressing polytype formation.

• Low-Stress Crystal Growth Techniques

  Internal stress can lead to lattice distortion, crystal cracking, and increased dislocation density, all of which degrade crystal quality and downstream device performance. Stress can be mitigated through:

   

  • Temperature field and process optimization for near-equilibrium growth;

  • Redesigning crucible structure to allow free crystal expansion;

  • Improving seed mounting methods by leaving a 2 mm gap between the seed and graphite holder to reduce thermal expansion mismatch;

  • Annealing the crystal in-furnace to release residual stress, with careful adjustment of temperature and duration.

Future Trends in SiC Single Crystal Growth Technology

• Larger Crystal Size

  The diameter of SiC single crystals has grown from a few millimeters to 6-inch, 8-inch, and even 12-inch wafers. Scaling up improves production efficiency, reduces cost per unit, and meets the needs of high-power devices.

• Higher Crystal Quality

  While current crystals are vastly improved, challenges remain such as micropipes, dislocations, and impurities. Eliminating these defects is critical for achieving higher-performance devices.

• Cost Reduction

  The high cost of SiC crystal growth is a barrier to widespread adoption. Reducing costs through process optimization, better resource utilization, and cheaper raw materials is a key area of research.

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• Intelligent Manufacturing

  With advancements in AI and big data, intelligent crystal growth is on the horizon. Sensors and automated control systems can monitor and adjust conditions in real time, improving stability and reproducibility. Data analytics can further refine the process to enhance yield and quality.