In semiconductor epitaxy, the susceptor is one of the most critical process components. Beyond simply supporting the wafers mechanically, it directly influences the temperature field, gas flow distribution, and contamination level inside the reaction chamber. As a result, it has a decisive impact on epitaxial layer thickness uniformity, defect density, and batch-to-batch consistency.
In recent years, SiC-coated graphite susceptors have been widely adopted in silicon epitaxy, GaN epitaxy, SiC epitaxy, and LED epitaxy. This trend is driven by clear process and materials science considerations.
1. Basic Structure and Advantages of SiC-Coated Graphite Susceptors
A SiC-coated graphite susceptor typically consists of two parts:
- Graphite substrate – Low density, easy to machine, and high thermal conductivity, making it suitable for large-size and complex-profile carrier structures;
- Surface SiC coating – A dense polycrystalline SiC layer, usually deposited by CVD, directly exposed to high temperature, corrosive atmospheres, and process gases.
This “graphite + SiC coating” combination integrates the structural and thermal advantages of graphite with the high-temperature stability, chemical inertness, and low contamination of silicon carbide. It is now one of the most mature susceptor solutions in epitaxy applications.
2. Requirements in Silicon Epitaxy
Silicon epitaxy is typically carried out above 1100 °C in atmospheres containing H₂ and HCl, both of which are corrosive. Power and high-voltage silicon devices are extremely sensitive to metallic impurities and defects, and impose very strict requirements on epitaxial thickness uniformity and doping uniformity.
In this scenario, the susceptor must provide:
- High dimensional and thermal expansion stability at elevated temperature to ensure flat wafer support;
- Favorable radiative and conductive properties to establish a stable and uniform temperature field;
- Extremely low levels of metallic contamination and particle generation.
Bare graphite in HCl/H₂ atmospheres tends to be etched and oxidized, with risks of powdering and impurity release. By applying a high-purity SiC coating, the exposed surface becomes silicon carbide, significantly reducing metallic impurity release and particle generation, while maintaining excellent corrosion and thermal stability. This better meets the reliability and lifetime requirements of mid- to high-end silicon epitaxy lines.
3. Key Considerations in GaN and LED Epitaxy (MOCVD)
GaN and LED epitaxy are typically performed in MOCVD reactors at about 1000 °C, in atmospheres containing high flows of NH₃ and H₂, along with various metal-organic precursors such as TMGa, TMAl, and TMIn. These conditions are corrosive and generate complex residues.
MOCVD susceptors are usually multi-pocket and multi-zone designs, and must ensure consistent temperature and gas flow distribution across multiple wafers under high-speed rotation. In this context, SiC-coated graphite offers several advantages:
- Excellent resistance to NH₃/H₂ environments, maintaining a dense and stable coating during long-term high-temperature operation;
- Well-controlled infrared emissivity, which facilitates temperature field calibration and batch-to-batch repeatability;
- Low particle levels, achieved by optimizing the microstructure and surface roughness of the SiC coating to reduce adhesion and flaking of decomposition residues, thereby mitigating bright/dark defect points on LED wafers.
For production lines moving toward Mini/Micro LED, these advantages in temperature uniformity and cleanliness become particularly critical.
4. Extreme Conditions in SiC Epitaxy
SiC epitaxy is generally performed using CVD processes at temperatures of 1500–1650 °C, with Cl-based gases, high carbon precursor concentrations, and relatively high gas velocities. Such extreme conditions impose stringent demands on the susceptor:
- The material must exhibit excellent high-temperature strength and thermal shock resistance;
- It must maintain dimensional and shape stability over multiple rapid thermal cycles;
- Its thermal expansion behavior should match that of SiC wafers as closely as possible to minimize warpage and stress-induced defects.
In this application, SiC-coated graphite shows clear advantages. The graphite substrate contributes high thermal conductivity and low thermal inertia, enabling fast and controllable temperature response. The surface SiC coating, being of the same material class as SiC wafers, has similar thermal expansion behavior, which helps improve epitaxial thickness uniformity and reduce wafer warpage. By adjusting coating thickness, phase composition, and residual stress, the susceptor can be tailored to different reactor designs and process schemes.
5. Common Technical Requirements Across Different Epitaxy Processes
Although silicon, GaN/LED, and SiC epitaxy differ in process conditions, they share common core requirements for susceptors:
1.Thermal performance
High thermal conductivity and controlled radiative properties are required to form uniform and reproducible temperature fields.
2.Chemical stability and corrosion resistance
The susceptor must remain dense and stable during long-term exposure to H₂, NH₃, HCl, and Cl-based gases at high temperature, without significant erosion.
3.Low contamination and low particle generation
The coating must have controlled metallic impurity levels and resist powdering or particle formation under harsh conditions, thereby reducing epitaxial defects and reactor cleaning frequency.
4.Mechanical and thermo-mechanical reliability
The susceptor must retain its dimensions and shape over many thermal cycles, avoiding adverse impacts on wafer flatness and stress state.
The SiC-coated graphite concept is essentially a comprehensive materials and structural optimization around these shared requirements.
6. Why Select SiC-Coated Graphite as the Epitaxy Susceptor?
Taking all factors into account, the choice of SiC-coated graphite as an epitaxy susceptor can be summarized as follows:
1.Balanced performance and cost
Compared with monolithic SiC parts, SiC-coated graphite maintains key surface performance while significantly reducing machining difficulty and overall cost, making it better suited for large, multi-pocket, and complex structures in mass production.
2.Favorable thermal and radiative matching
The graphite substrate provides excellent thermal conductivity and design flexibility, while the SiC coating offers thermal properties closer to Si, SiC, and GaN wafers, improving temperature control accuracy during epitaxy.
3.High-temperature chemical stability and low contamination
High-purity SiC coatings exhibit outstanding stability in harsh process atmospheres, effectively suppressing metallic impurity release and particle generation, and thereby lowering device failure risk.
4.Customizable coating systems
By tuning coating thickness, composition, and process parameters, the susceptor can be customized for different epitaxial material systems and reactor types.
For production lines targeting high-voltage, high-reliability, and high-uniformity power devices, RF devices, and advanced LED products, SiC-coated graphite susceptors have become the mainstream choice that balances process window, line stability, and overall cost.
7. Semicera: SiC Coating Solutions for Multiple Epitaxy Processes
In the field of SiC-coated graphite components in China, Semicera currently has large-scale coating capacity and a well-established process system, and is among the leading coating suppliers in terms of scale. For different epitaxy processes, Semicera has developed differentiated and customized coating solutions:
- For silicon epitaxy, Semicera offers SiC coatings with low metallic impurities, low roughness, and high flatness, meeting strict requirements on thickness uniformity and metal contamination control;
- For GaN and LED epitaxy, the coating structure is optimized for MOCVD conditions, combining resistance to NH₃/H₂ corrosion with uniform radiative properties and low particle levels;
- For SiC epitaxy, high-temperature, corrosion-resistant, and thermal-shock-resistant thick coatings are developed to match various reactor types and process windows, ensuring long-term stable operation.
Post time: Nov-21-2025