Semicera Semiconductor plans to increase the production of core components for semiconductor manufacturing equipment globally. By 2027, we aim to establish a new 20,000 square meter factory with a total investment of 70 million USD. One of our core components, the silicon carbide (SiC) wafer carrier, also known as a susceptor, has seen significant advancements. So, what exactly is this tray that holds the wafers?
In the wafer manufacturing process, epitaxial layers are built on certain wafer substrates to create devices. For example, GaAs epitaxial layers are prepared on silicon substrates for LED devices, SiC epitaxial layers are grown on conductive SiC substrates for power applications like SBDs and MOSFETs, and GaN epitaxial layers are constructed on semi-insulating SiC substrates for RF applications such as HEMTs. This process heavily relies on chemical vapor deposition (CVD) equipment.
In CVD equipment, substrates cannot be placed directly on metal or a simple base for epitaxial deposition due to various factors like gas flow (horizontal, vertical), temperature, pressure, stability, and contamination. Therefore, a susceptor is used to place the substrate on, enabling epitaxial deposition using CVD technology. This susceptor is the SiC-coated graphite susceptor.
SiC-coated graphite susceptors are typically used in Metal-Organic Chemical Vapor Deposition (MOCVD) equipment to support and heat single-crystal substrates. The thermal stability and uniformity of SiC-coated graphite susceptors are crucial for the growth quality of epitaxial materials, making them a core component of MOCVD equipment(leading MOCVD equipment companies such as Veeco and Aixtron). Currently, MOCVD technology is widely used in the epitaxial growth of GaN films for blue LEDs due to its simplicity, controllable growth rate, and high purity. As an essential part of the MOCVD reactor, the susceptor for GaN film epitaxial growth must have high-temperature resistance, uniform thermal conductivity, chemical stability, and strong thermal shock resistance. Graphite meets these requirements perfectly.
As a core component of MOCVD equipment, the graphite susceptor supports and heats single-crystal substrates, directly affecting the uniformity and purity of film materials. Its quality directly impacts the preparation of epitaxial wafers. However, with increased usage and varying working conditions, graphite susceptors are easily worn out and are considered consumables.
MOCVD susceptors need to have certain coating characteristics to meet the following requirements:
- -Good coverage: The coating must completely cover the graphite susceptor with high density to prevent corrosion in a corrosive gas environment.
- -High bonding strength: The coating must bond strongly to the graphite susceptor, withstanding multiple high-temperature and low-temperature cycles without peeling off.
- -Chemical stability: The coating must be chemically stable to avoid failure in high-temperature and corrosive atmospheres.
SiC, with its corrosion resistance, high thermal conductivity, thermal shock resistance, and high chemical stability, performs well in the GaN epitaxial environment. Additionally, the thermal expansion coefficient of SiC is similar to graphite, making SiC the preferred material for graphite susceptor coatings.
Currently, common types of SiC include 3C, 4H, and 6H, each suitable for different applications. For example, 4H-SiC can produce high-power devices, 6H-SiC is stable and used for optoelectronic devices, while 3C-SiC is similar in structure to GaN, making it suitable for GaN epitaxial layer production and SiC-GaN RF devices. 3C-SiC, also known as β-SiC, is mainly used as a film and coating material, making it a primary material for coatings.
There are various methods to prepare SiC coatings, including sol-gel, embedding, brushing, plasma spraying, chemical vapor reaction (CVR), and chemical vapor deposition (CVD).
Among these, the embedding method is a high-temperature solid-phase sintering process. By placing the graphite substrate in an embedding powder containing Si and C powder and sintering in an inert gas environment, an SiC coating forms on the graphite substrate. This method is simple, and the coating bonds well with the substrate. However, the coating lacks thickness uniformity and may have pores, leading to poor oxidation resistance.
Spray Coating Method
The spray coating method involves spraying liquid raw materials onto the graphite substrate surface and curing them at a specific temperature to form a coating. This method is simple and cost-effective but results in weak bonding between the coating and substrate, poor coating uniformity, and thin coatings with low oxidation resistance, requiring auxiliary methods.
Ion Beam Spraying Method
Ion beam spraying uses an ion beam gun to spray molten or partially molten materials onto the graphite substrate surface, forming a coating upon solidification. This method is simple and produces dense SiC coatings. However, the thin coatings have weak oxidation resistance, often used for SiC composite coatings to improve quality.
Sol-Gel Method
The sol-gel method involves preparing a uniform, transparent sol solution, covering the substrate surface, and obtaining the coating after drying and sintering. This method is simple and cost-effective but results in coatings with low thermal shock resistance and susceptibility to cracking, limiting its widespread application.
Chemical Vapor Reaction (CVR)
CVR uses Si and SiO2 powder at high temperatures to generate SiO vapor, which reacts with the carbon material substrate to form an SiC coating. The resulting SiC coating bonds tightly with the substrate, but the process requires high reaction temperatures and costs.
Chemical Vapor Deposition (CVD)
CVD is the primary technique for preparing SiC coatings. It involves gas-phase reactions on the graphite substrate surface, where raw materials undergo physical and chemical reactions, depositing as an SiC coating. CVD produces tightly bonded SiC coatings that enhance the substrate’s oxidation and ablation resistance. However, CVD has long deposition times and may involve toxic gases.
Market Situation
In the SiC-coated graphite susceptor market, foreign manufacturers have a significant lead and high market share. Semicera has overcome core technologies for uniform SiC coating growth on graphite substrates, providing solutions that address thermal conductivity, elastic modulus, stiffness, lattice defects, and other quality issues, fully meeting MOCVD equipment requirements.
Future Outlook
China’s semiconductor industry is developing rapidly, with increasing localization of MOCVD epitaxial equipment and expanding applications. The SiC-coated graphite susceptor market is expected to grow quickly.
Conclusion
As a crucial component in compound semiconductor equipment, mastering the core production technology and localizing SiC-coated graphite susceptors is strategically important for China’s semiconductor industry. The domestic SiC-coated graphite susceptor field is thriving, with product quality reaching international levels. Semicera is striving to become a leading supplier in this field.
Post time: Jul-17-2024