SiC coated graphite bases are commonly used to support and heat single crystal substrates in metal-organic chemical vapor deposition (MOCVD) equipment. The thermal stability, thermal uniformity and other performance parameters of SiC coated graphite base play a decisive role in the quality of epitaxial material growth, so it is the core key component of MOCVD equipment.
In the process of wafer manufacturing, epitaxial layers are further constructed on some wafer substrates to facilitate the manufacturing of devices. Typical LED light-emitting devices need to prepare epitaxial layers of GaAs on silicon substrates; The SiC epitaxial layer is grown on the conductive SiC substrate for the construction of devices such as SBD, MOSFET, etc., for high voltage, high current and other power applications; GaN epitaxial layer is constructed on semi-insulated SiC substrate to further construct HEMT and other devices for RF applications such as communication. This process is inseparable from CVD equipment.
In the CVD equipment, the substrate can not be directly placed on the metal or simply placed on a base for epitaxial deposition, because it involves the gas flow (horizontal, vertical), temperature, pressure, fixation, shedding of pollutants and other aspects of the influence factors. Therefore, a base is needed, and then the substrate is placed on the disc, and then the epitaxial deposition is carried out on the substrate using CVD technology, and this base is the SiC coated graphite base (also known as the tray).
SiC coated graphite bases are commonly used to support and heat single crystal substrates in metal-organic chemical vapor deposition (MOCVD) equipment. The thermal stability, thermal uniformity and other performance parameters of SiC coated graphite base play a decisive role in the quality of epitaxial material growth, so it is the core key component of MOCVD equipment.
Metal-organic chemical vapor deposition (MOCVD) is the mainstream technology for the epitaxial growth of GaN films in blue LED. It has the advantages of simple operation, controllable growth rate and high purity of GaN films. As an important component in the reaction chamber of MOCVD equipment, the bearing base used for GaN film epitaxial growth needs to have the advantages of high temperature resistance, uniform thermal conductivity, good chemical stability, strong thermal shock resistance, etc. Graphite material can meet the above conditions.
As one of the core components of MOCVD equipment, graphite base is the carrier and heating body of the substrate, which directly determines the uniformity and purity of the film material, so its quality directly affects the preparation of the epitaxial sheet, and at the same time, with the increase of the number of uses and the change of working conditions, it is very easy to wear, belonging to the consumables.
Although graphite has excellent thermal conductivity and stability, it has a good advantage as a base component of MOCVD equipment, but in the production process, graphite will corrode the powder due to the residue of corrosive gases and metallic organics, and the service life of the graphite base will be greatly reduced. At the same time, the falling graphite powder will cause pollution to the chip.
The emergence of coating technology can provide surface powder fixation, enhance thermal conductivity, and equalize heat distribution, which has become the main technology to solve this problem. Graphite base in MOCVD equipment use environment, graphite base surface coating should meet the following characteristics:
(1) The graphite base can be fully wrapped, and the density is good, otherwise the graphite base is easy to be corroded in the corrosive gas.
(2) The combination strength with the graphite base is high to ensure that the coating is not easy to fall off after several high temperature and low temperature cycles.
(3) It has good chemical stability to avoid coating failure in high temperature and corrosive atmosphere.
SiC has the advantages of corrosion resistance, high thermal conductivity, thermal shock resistance and high chemical stability, and can work well in GaN epitaxial atmosphere. In addition, the thermal expansion coefficient of SiC differs very little from that of graphite, so SiC is the preferred material for the surface coating of graphite base.
At present, the common SiC is mainly 3C, 4H and 6H type, and the SiC uses of different crystal types are different. For example, 4H-SiC can manufacture high-power devices; 6H-SiC is the most stable and can manufacture photoelectric devices; Because of its similar structure to GaN, 3C-SiC can be used to produce GaN epitaxial layer and manufacture SiC-GaN RF devices. 3C-SiC is also commonly known as β-SiC, and an important use of β-SiC is as a film and coating material, so β-SiC is currently the main material for coating.
Method for preparing silicon carbide coating
At present, the preparation methods of SiC coating mainly include gel-sol method, embedding method, brush coating method, plasma spraying method, chemical gas reaction method (CVR) and chemical vapor deposition method (CVD).
Embedding method:
The method is a kind of high temperature solid phase sintering, which mainly uses the mixture of Si powder and C powder as the embedding powder, the graphite matrix is placed in the embedding powder, and the high temperature sintering is carried out in the inert gas, and finally the SiC coating is obtained on the surface of the graphite matrix. The process is simple and the combination between the coating and the substrate is good, but the uniformity of the coating along the thickness direction is poor, which is easy to produce more holes and lead to poor oxidation resistance.
Brush coating method:
The brush coating method is mainly to brush the liquid raw material on the surface of the graphite matrix, and then cure the raw material at a certain temperature to prepare the coating. The process is simple and the cost is low, but the coating prepared by brush coating method is weak in combination with the substrate, the coating uniformity is poor, the coating is thin and the oxidation resistance is low, and other methods are needed to assist it.
Plasma spraying method:
The plasma spraying method is mainly to spray melted or semi-melted raw materials on the surface of the graphite matrix with a plasma gun, and then solidify and bond to form a coating. The method is simple to operate and can prepare a relatively dense silicon carbide coating, but the silicon carbide coating prepared by the method is often too weak and leads to weak oxidation resistance, so it is generally used for the preparation of SiC composite coating to improve the quality of the coating.
Gel-sol method:
The gel-sol method is mainly to prepare a uniform and transparent sol solution covering the surface of the matrix, drying into a gel and then sintering to obtain a coating. This method is simple to operate and low in cost, but the coating produced has some shortcomings such as low thermal shock resistance and easy cracking, so it cannot be widely used.
Chemical Gas Reaction (CVR) :
CVR mainly generates SiC coating by using Si and SiO2 powder to generate SiO steam at high temperature, and a series of chemical reactions occur on the surface of C material substrate. The SiC coating prepared by this method is closely bonded to the substrate, but the reaction temperature is higher and the cost is higher.
Chemical Vapor Deposition (CVD) :
At present, CVD is the main technology for preparing SiC coating on the substrate surface. The main process is a series of physical and chemical reactions of gas phase reactant material on the substrate surface, and finally the SiC coating is prepared by deposition on the substrate surface. The SiC coating prepared by CVD technology is closely bonded to the surface of the substrate, which can effectively improve the oxidation resistance and ablative resistance of the substrate material, but the deposition time of this method is longer, and the reaction gas has a certain toxic gas.
The market situation of SiC coated graphite base
When foreign manufacturers started early, they had a clear lead and a high market share. Internationally, the mainstream suppliers of SiC coated graphite base are Dutch Xycard, Germany SGL Carbon (SGL), Japan Toyo Carbon, the United States MEMC and other companies, which basically occupy the international market. Although China has broken through the key core technology of uniform growth of SiC coating on the surface of graphite matrix, high-quality graphite matrix still relies on German SGL, Japan Toyo Carbon and other enterprises, the graphite matrix provided by domestic enterprises affects the service life due to thermal conductivity, elastic modulus, rigid modulus, lattice defects and other quality problems. The MOCVD equipment can not meet the requirements of the use of SiC coated graphite base.
China’s semiconductor industry is developing rapidly, with the gradual increase of MOCVD epitaxial equipment localization rate, and other process applications expansion, the future SiC coated graphite base product market is expected to grow rapidly. According to preliminary industry estimates, the domestic graphite base market will exceed 500 million yuan in the next few years.
SiC coated graphite base is the core component of compound semiconductor industrialization equipment, mastering the key core technology of its production and manufacturing, and realizing the localization of the whole raw material-process-equipment industry chain is of great strategic significance for ensuring the development of China’s semiconductor industry. The field of domestic SiC coated graphite base is booming, and the product quality can reach the international advanced level soon.
Post time: Jul-24-2023