KeyPoints in the preparation of high-quality silicon carbide single crystals

Preparation Methods of SiC Single Crystals: Focus on PVT Method

The main preparation methods of silicon carbide (SiC) single crystals include Physical Vapor Transport (PVT), Top Seeded Solution Growth (TSSG), and High-Temperature Chemical Vapor Deposition (HT-CVD).
Among them, the PVT method is the most widely adopted in industrial production due to its simple equipment, ease of control, relatively low equipment cost, and operating expenses.

Key Technologies in PVT Growth of SiC Crystals

Schematic diagram of PVT growth structure

Key considerations for growing SiC crystals using the Physical Vapor Transport (PVT) method include:

Purity of Graphite Materials in the Thermal Field

The impurity content in graphite parts must be below 5×10⁻⁶, and the impurity content in insulation felt should be below 10×10⁻⁶.

The concentrations of boron (B) and aluminum (Al) must be less than 0.1×10⁻⁶.

Correct Polarity Selection of Seed Crystal

The C (0001) face is suitable for growing 4H-SiC crystals.

The Si (0001) face is suitable for growing 6H-SiC crystals.

Off-Axis Seed Crystal Usage

Off-axis seeds alter the growth symmetry and help reduce the formation of defects in the crystal.

Good Seed Crystal Bonding Process

Ensures mechanical stability and uniformity during the growth process.

Stable Growth Interface During the Process

Maintaining a stable solid–gas interface is crucial for high-quality crystal formation.

Critical Technologies for SiC Crystal Growth

Doping Technology in SiC Powder

Cerium (Ce) doping in the source powder promotes stable growth of single-phase 4H-SiC crystals.

Benefits include increased growth rate, improved orientation control, reduced impurities and defects, and enhanced single-phase stability and crystal quality.

It also helps suppress backside erosion and improves the single crystallinity.

Control of Axial and Radial Thermal Gradients

Axial thermal gradient affects polytype stability and growth efficiency.

Low gradients can result in unwanted polytypes and reduced material transport.

Proper axial and radial gradients ensure fast growth and stable crystal quality.

Basal Plane Dislocation (BPD) Control

BPDs are caused by shear stress exceeding the critical shear stress of SiC.

These defects form during the growth and cooling stages due to slip system activation.

Reducing internal stress minimizes BPD formation.

Gas Phase Composition Ratio Control

A higher carbon-to-silicon ratio in the gas phase helps suppress polytype conversion.

It reduces large step-bunching, maintains growth surface information, and enhances polytype stability.

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Low-Stress Growth Control

Internal stress leads to lattice bending, crystal cracking, and increased BPDs, negatively impacting epitaxy and device performance.

Key stress reduction strategies include:

• Optimizing thermal field and process parameters to approach equilibrium growth.

• Redesigning crucible structure to allow free crystal expansion.

• Adjusting seed bonding methods, e.g., leaving a 2 mm gap between the seed and graphite holder to accommodate thermal expansion differences.

• Controlling post-growth annealing, including in-situ furnace cooling and optimized annealing parameters to release residual stress.

Development Trends in SiC Crystal Growth Technology
 

In the future, high-quality SiC single crystal growth will advance in the following directions:

Larger Wafer Size

SiC wafer diameter has grown from a few millimeters to 6-inch, 8-inch, and even 12-inch.

Larger wafers improve production efficiency, reduce costs, and meet high-power device requirements.

Higher Quality

While SiC crystal quality has significantly improved, defects such as micropipes, dislocations, and impurities still persist.

Eliminating these defects is critical for ensuring device performance and reliability.

Lower Cost

The current high cost of SiC crystals limits their widespread adoption.

Cost reductions can be achieved through process optimization, improved efficiency, and cheaper raw materials.

Conclusion:

High-quality SiC single crystal growth is a key area of semiconductor material research. With continuous technological progress, SiC crystal growth techniques will evolve further, laying a solid foundation for its application in high-temperature, high-frequency, and high-power electronics.

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