What is SiC coated graphite susceptor
Before introducing the SiC coated graphite susceptor, we need to know where it is used. We know that further epitaxial layers need to be constructed on some wafer substrates to facilitate the manufacture of devices. Typical LED light-emitting devices need to prepare GaAs epitaxial layers on silicon substrates. SiC epitaxial layers are grown on conductive SiC substrates for constructing devices such as SBD, MOSFET, etc. for power applications such as high voltage and high current. GaN epitaxial layers are constructed on semi-insulating SiC substrates, devices such as HEMTs are further constructed for RF applications such as communications. Here you need to use a CVD equipment (of course, there are other technical methods).

Metal Organic Chemical Vapor Deposition (MOCVD) is to use Group III and II elements and Group V and VI elements as growth source materials to deposit on the substrate surface through thermal decomposition reaction to grow various Group III-V (GaN, GaAs, etc.), Group II-VI (Si, SiC, etc.) and thin-layer single crystal materials of multiple solid solutions, is the main means of producing optoelectronic devices, microwave devices, power device materials.

In CVD equipment, the substrate can not be directly placed on the metal or simply placed on a base for epitaxial deposition, because of the gas flow (horizontal, vertical), temperature, pressure, fixed, off pollutants and other factors. Therefore, a susceptor is used, the substrate is then placed on the disk, and then the CVD technique is used to perform epitaxial deposition on the substrate. This base is a SiC-coated graphite base (also called a tray).

Graphite susceptor is one of the core components in MOCVD equipment. It is the carrier and heating element of the substrate substrate. Its performance parameters such as thermal stability and thermal uniformity play a decisive role in the growth quality of epitaxial materials and directly determine the uniformity and purity of thin film materials. Therefore, its quality directly affects the preparation of epitaxial wafers. At the same time, it is extremely easy to lose with the increase of usage times and the change of working conditions, and belongs to consumables.

The excellent thermal conductivity and stability of graphite make it very advantageous as a base member of MOCVD equipment. But if it is only pure graphite, it will also face some problems. In the production process, there will be residues of corrosive gases and metal organics, and the graphite base will corrode the powder, which greatly reduces the service life of the graphite base. At the same time, the falling graphite powder will also pollute the chip. These problems need to be solved in the preparation process of the base.

Coating technology can provide surface powder fixation, enhance thermal conductivity, and balance heat distribution, which has become the main technology to solve this problem. According to the application environment and use requirements of the graphite base, the surface coating should have the following characteristics:

High density and full package: the graphite base as a whole in a high temperature, corrosive working environment, the surface must be fully wrapped, and the coating must have good compactness to play a good protective role.

Good surface flatness: Since the graphite base used for single crystal growth requires very high surface flatness, the original flatness of the base must be maintained after the coating is prepared, that is, the coating surface must be uniform.

Good bonding strength: reducing the difference in thermal expansion coefficient between the graphite base and the coating material can effectively improve the bonding strength between the two, and the coating is not easy to crack after high and low temperature thermal cycles.

High thermal conductivity: High-quality chip growth requires fast and uniform heat from the graphite base, so the coating material should have a high thermal conductivity.

High melting point, high temperature oxidation resistance, corrosion resistance: the coating should be able to work stably in high temperature and corrosive working environment.

Selection of Graphite Coating Materials
Commonly used protective coating materials are mainly the following:

Glass coating: B2O3, P2O5, ZnO, etc;

Ceramic coating: SiC, ZrB2, BN, etc;

Metal coating: Pt, Ir, Hf, Mo, etc;

SiC has many excellent properties, such as high thermodynamic stability, good thermal conductivity, high electron mobility, oxidation resistance, corrosion resistance, thermal expansion coefficient similar to graphite material, and so on. It is an important material for the surface coating of graphite base.

SiC can be divided into cubic structure (C), hexagonal structure (H) and rhombohedral structure (R) according to the combination of C atoms and Si atoms, such as 2H-SiC,3C-SiC,4H-SiC,6H-SiC and 15R-SiC, etc. The more common ones can be summarized into the following two categories:

Α-SiC:4H-SiC,6H-SiC

β-SiC：3C-SiC；

β-SiC has the following advantages:

The synthesis temperature is low, generally 1000~1600 ℃, and the crystal structure is similar to diamond, while α-SiC can be prepared above 2000 ℃, with hexagonal wurtzite structure.

It has higher thermal conductivity, wear resistance, corrosion resistance, etc., which are better than α-SiC.

Therefore, it has more excellent performance in the working environment of β-SiC high temperature and corrosive gas, and has become an important material for the surface coating of graphite base.

Article Source: Zhihu