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, it is necessary to use a base, and then place the substrate on the disc, and then use CVD technology to epitaxial deposition on the substrate, which 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.
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