The semiconductor industry requires that the purity of the graphite materials used be as high as possible. Especially for graphite devices that are directly in contact with semiconductor materials, such as crucibles and sintering molds, a large amount of impurities will contaminate the semiconductor materials. Therefore, not only must the purity of the graphite raw materials used be strictly controlled, but they must also be graphitized at high temperatures to minimize ash content.
The semiconductor industry requires that the graphite materials used have a fine particle size. Graphite with a fine particle size is not only easy to process to high accuracy but also has high high-temperature strength and low loss. In particular, molds used for sintering require high processing accuracy. Since graphite devices used in the semiconductor industry (including heaters and sintering dies) need to withstand repeated heating and cooling processes, the graphite materials used are required to have good dimensional stability and thermal shock resistance at high temperatures to improve the service life of the devices.
Graphite made from uncalcined petroleum coke is a fine-grained structural material with high mechanical strength. It can be used to make electronic technical products, such as crucibles, thin plates, discs, heat shields for vacuum furnaces and high-frequency electric furnaces, graphite dishes for melting pure metals, grippers (chucks) for high-temperature experimental devices, hot press molds, and filters. This material can be used in an inert or protective atmosphere at temperatures below 2500°C.
Ultra-pure high-strength graphite with a protective layer is made by purifying and degassing ordinary fine-structured graphite in a vacuum, followed by surface density-enhancing treatment with pyrolytic carbon. Their products (heaters, discs, graphite dishes, etc.) can be used to prepare silicon thin films by the gas epitaxial growth method. The thickness of the density-enhancing protective layer formed by pyrolytic carbon does not exceed 2 mm. A thin layer of pyrolytic graphite with a thickness of no more than 0.1 mm can also be deposited on the surface of the density-enhanced article.