1. Why is there a silicon carbide coating
The epitaxial layer is a specific single crystal thin film grown on the basis of the wafer through the epitaxial process. The substrate wafer and the epitaxial thin film are collectively called epitaxial wafers. Among them, the silicon carbide epitaxial layer is grown on the conductive silicon carbide substrate to obtain a silicon carbide homogeneous epitaxial wafer, which can be further made into power devices such as Schottky diodes, MOSFETs, and IGBTs. Among them, the most widely used is the 4H-SiC substrate.
Since all devices are basically realized on epitaxy, the quality of epitaxy has a great impact on the performance of the device, but the quality of epitaxy is affected by the processing of crystals and substrates. It is in the middle link of an industry and plays a very critical role in the development of the industry.
The main methods for preparing silicon carbide epitaxial layers are: evaporation growth method; liquid phase epitaxy (LPE); molecular beam epitaxy (MBE); chemical vapor deposition (CVD).
Among them, chemical vapor deposition (CVD) is the most popular 4H-SiC homoepitaxial method. 4-H-SiC-CVD epitaxy generally uses CVD equipment, which can ensure the continuation of the epitaxial layer 4H crystal SiC under high growth temperature conditions.
In CVD equipment, the substrate cannot be placed directly on the metal or simply placed on a base for epitaxial deposition, because it involves various factors such as gas flow direction (horizontal, vertical), temperature, pressure, fixation, and falling pollutants. Therefore, a base is needed, and then the substrate is placed on the disk, and then epitaxial deposition is performed on the substrate using CVD technology. This base is the SiC coated graphite base.
As a core component, the graphite base has the characteristics of high specific strength and specific modulus, good thermal shock resistance and corrosion resistance, but during the production process, the graphite will be corroded and powdered due to the residue of corrosive gases and metal organic matter, and the service life of the graphite base will be greatly reduced.
At the same time, the fallen graphite powder will pollute the chip. In the production process of silicon carbide epitaxial wafers, it is difficult to meet people’s increasingly stringent requirements for the use of graphite materials, which seriously restricts its development and practical application. Therefore, coating technology began to rise.
2. Advantages of SiC coating
The physical and chemical properties of the coating have strict requirements for high temperature resistance and corrosion resistance, which directly affect the yield and life of the product. SiC material has high strength, high hardness, low thermal expansion coefficient and good thermal conductivity. It is an important high-temperature structural material and high-temperature semiconductor material. It is applied to graphite base. Its advantages are:
-SiC is corrosion-resistant and can fully wrap the graphite base, and has good density to avoid damage by corrosive gas.
-SiC has high thermal conductivity and high bonding strength with the graphite base, ensuring that the coating is not easy to fall off after multiple high-temperature and low-temperature cycles.
-SiC has good chemical stability to prevent the coating from failing in a high-temperature and corrosive atmosphere.
In addition, epitaxial furnaces of different materials require graphite trays with different performance indicators. The thermal expansion coefficient matching of graphite materials requires adapting to the growth temperature of the epitaxial furnace. For example, the temperature of silicon carbide epitaxial growth is high, and a tray with a high thermal expansion coefficient matching is required. The thermal expansion coefficient of SiC is very close to that of graphite, making it suitable as the preferred material for the surface coating of the graphite base.
SiC materials have a variety of crystal forms, and the most common ones are 3C, 4H and 6H. Different crystal forms of SiC have different uses. For example, 4H-SiC can be used to manufacture high-power devices; 6H-SiC is the most stable and can be used to manufacture optoelectronic devices; 3C-SiC can be used to produce GaN epitaxial layers and manufacture SiC-GaN RF devices because of its similar structure to GaN. 3C-SiC is also commonly referred to as β-SiC. An important use of β-SiC is as a thin film and coating material. Therefore, β-SiC is currently the main material for coating.
SiC coatings are commonly used in semiconductor production. They are mainly used in substrates, epitaxy, oxidation diffusion, etching and ion implantation. The physical and chemical properties of the coating have strict requirements on high temperature resistance and corrosion resistance, which directly affect the yield and life of the product. Therefore, the preparation of SiC coating is critical.
Post time: Jun-24-2024