‌Optimization of Defects and Purity in SiC Crystals by TaC Coating

1.The defect density has decreased significantly

The TaC coating almost completely eliminates the carbon encapsulation phenomenon by isolating the direct contact between the graphite crucible and the SiC melt, significantly reducing the defect density of microtubes. Experimental data show that the density of microtube defects caused by carbon coating in the crystals grown in TaC coated crucibles is reduced by more than 90% compared with traditional graphite crucibles. The crystal surface is uniformly convex, and there is no polycrystalline structure at the edge, while ordinary graphite crucibles often have edge polycrystallization and crystal depression and other defects.

2. Impurity inhibition and purity improvement

TaC material has excellent chemical inertness to Si, C and N vapors and can effectively prevent impurities such as nitrogen in graphite from diffusing into the crystal. GDMS and Hall tests show that the nitrogen concentration in the crystal has decreased by more than 50%, and the resistivity has increased to 2-3 times that of the traditional method. Although a trace amount of Ta element was incorporated (atomic proportion < 0.1%), the overall total impurity content was reduced by more than 70%, significantly improving the electrical properties of the crystal.

3. Crystal morphology and growth uniformity

The TaC coating regulates the temperature gradient at the crystal growth interface, enabling the crystal ingot to grow on a convex curved surface and homogenizing the edge growth rate, thus avoiding the polycrystallization phenomenon caused by edge overcooling in traditional graphite crucibles. The actual measurement shows that the diameter deviation of the crystal ingot grown in the TaC coated crucible is ≤2%, and the crystal surface flatness (RMS) is improved by 40%.

The regulation mechanism of TaC coating on thermal field and heat transfer characteristics

Performance comparison of TaC coating with other crucible materials

‌Material Type‌	‌Temperature Resistance‌	‌Chemical Inertness‌	‌Mechanical Strength‌	‌Crystal Defect Density	‌Typical Application Scenarios
‌TaC Coated Graphite	≥2600°C	No reaction with Si/C vapor	Mohs Hardness 9-10, strong thermal shock resistance	<1 cm⁻² (micropipes)	High-purity 4H/6H-SiC single crystal growth
‌Bare Graphite	≤2200°C	Corroded by Si vapor releasing C	Low strength, prone to cracking	10-50 cm⁻²	Cost-effective SiC substrates for power devices
‌SiC Coated Graphite	≤1600°C	Reacts with Si forming SiC₂ at high temperatures	High hardness but brittle	5-10 cm⁻²	Packaging materials for mid-temperature semiconductors
‌BN Crucible	<2000K	Releases N/B impurities	Poor corrosion resistance	8-15 cm⁻²	Epitaxial substrates for compound semiconductors

The TaC coating has achieved a comprehensive improvement in the quality of SiC crystals through a triple mechanism of chemical barrier, thermal field optimization and interface regulat

• The defect control microtube density is less than 1 cm⁻², and the carbon coating is completely eliminated
• Purity improvement: Nitrogen concentration <1×10¹⁷ cm⁻³, resistivity > 10⁴ Ω · cm;
• The improvement of thermal field uniformity in growth efficiency reduces power consumption by 4% and extends the crucible life by 2 to 3 times.