What are the challenges of silicon carbide substrate production?

Silicon carbide (SiC) is a material that possesses high bond energy, similar to other hard materials like diamond and cubic boron nitride. However, the high bond energy of SiC makes it difficult to crystallize directly into ingots via traditional melting methods. Therefore, the process of growing silicon carbide crystals involves the use of vapor phase epitaxy technology. In this method, gaseous substances are gradually deposited on the surface of a substrate and crystallized into solid crystals. The substrate plays a vital role in guiding the deposited atoms to grow in a specific crystal direction, resulting in the formation of an epitaxial wafer with a specific crystal structure.

Cost-effectiveness

Silicon carbide grows very slowly, usually only about 2cm per month. In industrial production, the annual production capacity of a single crystal growth furnace is only 400-500 pieces. In addition, the cost of a crystal growth furnace is as high. Therefore, the production of silicon carbide is an expensive and inefficient process.

In order to improve production efficiency and reduce costs, epitaxial growth of silicon carbide on the substrate has become a more reasonable choice. This method can achieve mass production. Compared with directly cutting silicon carbide ingots, epitaxial technology can more effectively meet the needs of industrial production, thus improving the market competitiveness of silicon carbide materials.

Cutting difficulty

Silicon carbide (SiC) not only grows slowly, resulting in higher costs, but it is also very hard, making its cutting process more difficult. When using diamond wire to cut silicon carbide, the cutting speed will be slower, the cut will be more uneven, and it is easy to leave cracks on the surface of silicon carbide. Additionally, materials with high Mohs hardness tend to be more fragile, with silicon carbide wafers more likely to break during cutting than silicon wafers. These factors result in the relatively high material cost of silicon carbide wafers. Therefore, some automakers, such as Tesla, that initially consider models using silicon carbide materials may ultimately choose other options to reduce the cost of the entire vehicle.

Crystal quality

By growing SiC epitaxial wafers on the substrate, the crystal quality and lattice matching can be effectively controlled. The crystal structure of the substrate will affect the crystal quality and defect density of the epitaxial wafer, thereby improving the performance and stability of SiC materials. This approach allows the production of SiC crystals with higher quality and fewer defects, thereby improving the performance of the final device.

Strain adjustment

The lattice matching between the substrate and the epitaxial wafer has an important influence on the strain state of the SiC material. By adjusting this matching, the electronic structure and optical properties of the SiC epitaxial wafer can be changed, thus having an important impact on the performance and functionality of the device. This strain adjustment technology is one of the key factors in improving the performance of SiC devices.

Control material properties

By epitaxy of SiC on different types of substrates, SiC growth with different crystal orientations can be achieved, thereby obtaining SiC crystals with specific crystal plane directions. This approach allows tailoring the properties of SiC materials to meet the needs of different application areas. For example, SiC epitaxial wafers can be grown on 4H-SiC or 6H-SiC substrates to obtain specific electronic and optical properties to meet different technical and industrial application needs.