A Brief History of Silicon Carbide

In 1893, Etchison, the discoverer of SiC, designed a resistance furnace with carbon as the core - Etchison furnace, which opened the era of industrial production of silicon carbide by electrically heating the mixture of quartz and carbon, and the method applied for related invention patents.

From the beginning to the middle of the 20th century, silicon carbide is mainly used as an abrasive for grinding and cutting tools because of its excellent hardness and wear resistance.

From the 1950s to the 1960s, with the emergence of chemical vapor deposition (CVD) technology, Rustum Roy, a scientist at Bell Labs in the United States, took the lead in the research of CVD SiC technology, developed the SiC vapor deposition process and made a preliminary exploration of its properties and applications. The deposition of SiC coating on graphite surface was achieved for the first time. The work of Rustum Roy et al. at Bell Laboratories has laid an important foundation for the CVD preparation of SiC coating materials.

In 1963, Bell Laboratories researchers Howard Wachtel and Joseph Wells founded CVD Incorporated to focus on the development of chemical vapor deposition technology for SiC and other ceramic coating materials. In 1974, the industrial production of silicon carbide coated graphite products was realized for the first time. The industrial production of this technology marks the progress of silicon carbide coating technology on the surface of graphite, and has laid the foundation for its wide application in semiconductor, optics, aerospace and other fields.

In the 1970s, researchers at Union Carbide, now a wholly owned subsidiary of Dow Chemical, first applied silicon carbide coated graphite bases to the epitaxial growth of semiconductor materials such as gallium nitride (GaN). This technology is of great significance for the preparation of high-performance gallium nitride based LED(light emitting diode) and laser devices, laying the foundation for the later silicon carbide epitaxy technology, and becoming one of the important milestones in the application of silicon carbide materials in the semiconductor field.

From the 1980s to the early 21st century, with the advancement of manufacturing technology, industrial and commercial applications of silicon carbide coatings expanded from aerospace to automotive, power electronics, semiconductor equipment, and various industrial components as corrosion resistant coatings.

Since the beginning of the 21st century, the development of thermal spraying, PVD and nanoscience technologies has brought new coating preparation methods, and researchers have begun to study and develop nanoscale silicon carbide coatings to further improve the performance of materials.

In general, the preparation technology of CVD silicon carbide coating has undergone continuous progress and breakthroughs in the past decades from laboratory research to industrial application expansion.

There are more than 200 kinds of silicon carbide crystal types, which can be divided into the following three categories according to the different ways of combining C atoms and Si atoms: Cubic structure (3C), hexagonal structure (H) and rhombohedral structure (R), such as 2H-SiC, 3C-sic, 4H-SiC, 6H-SiC and 15R-SiC, etc., the more common can be summarized into the following two categories:

碳化硅的晶体结构 图片来源：维基百科

（1） SiC coating: is a thin film formed from β-SiC, which is formed on the surface of the base material by different coating or deposition processes. This coating is usually used to improve the hardness, wear resistance, corrosion resistance, oxidation resistance and high temperature resistance of the material. Silicon carbide coating has a wide range of applications on a variety of substrate materials such as ceramics, metals, glass and plastics, covering aerospace, automotive manufacturing, electronic equipment and other fields.

石墨表面SiC涂层截面显微结构

（2）

Preparation methods: The preparation methods of SiC coating mainly include chemical vapor deposition (CVD), physical vapor deposition (PVD), spraying technology, electrochemical deposition and slurry coating sintering.

CVD: One of the most common methods for preparing silicon carbide coatings. In the CVD process, the raw material gas containing silicon and carbon is input into the reaction chamber to decompose it at high temperature to generate carbon atoms and silicon atoms, carbon atoms and silicon atoms are adsorbed on the surface of the substrate and bond to generate silicon carbide coating. By controlling the core process parameters, such as gas flow, deposition temperature, deposition pressure and time, the coating thickness, element stoichiometric ratio, grain size, crystal structure and crystal face orientation are controllable and adjusted to prepare the silicon carbide coating to meet the application requirements. Another advantage of this method is that it is suitable for the preparation of large size and complex shape substrate surface silicon carbide coating, and the coating has better adhesion and filling ability. The disadvantage is that the precursors used in the CVD process and the byproducts produced are flammable, corrosive, etc., and the production process is dangerous, while the utilization rate of raw materials is low, and the preparation cost is high.

PVD: refers to the use of physical methods under high vacuum conditions, such as thermal evaporation or magnetron sputtering, to vaporize high-purity silicon carbide raw materials and then condense to the substrate surface to form a film. This method can precisely control the thickness and composition of the coating, resulting in a dense silicon carbide coating, suitable for high-precision applications such as cutting tool coating, ceramic coating, optical coating and thermal barrier coating. The disadvantage is that for parts with complex shapes, it is difficult to achieve uniform coverage in grooves or shielded areas, and in addition, the adhesion of the coating to the substrate is insufficient. PVD equipment is expensive because of the need for expensive high vacuum systems and precision control equipment, and at the same time, the deposition rate is slow, the production efficiency is low, and it is not suitable for large-scale industrial production.

Spraying method: It is a method of spraying liquid raw materials on the surface of the substrate, and then curing the raw materials to form a coating at a specific temperature. This method is simple and low-cost, but the prepared coating is weakly bound to the substrate, the coating uniformity is poor, and the coating is thin and the oxidation resistance is low, so other auxiliary methods are needed to improve its performance.

Electrochemical deposition: It is a technology that uses electrochemical reaction to deposit silicon carbide in solution onto the substrate surface to prepare silicon carbide coating. By controlling the electrode potential and the composition of the precursor solution, the uniform growth of the coating can be achieved, and the silicon carbide coating prepared by this method has applications in some specific fields, such as chemical/biological sensors, photovoltaic electronic devices, electrode materials in lithium-ion batteries, and as an anti-corrosion coating.

Slurry coating: The coating material and binder are mixed into a mixture, evenly coated on the surface of the matrix, after drying in an inert atmosphere, the painted workpiece is sintered at high temperature to obtain the required coating. The advantages are that the process is simple and easy to operate, and the coating thickness is easy to control; The disadvantage is that the bonding strength between the coating and the substrate is poor, the thermal shock resistance of the coating is poor, the uniformity of the coating is low, the process consistency is poor, and it is not suitable for the production of mass products.

In general, it is necessary to select the appropriate silicon carbide coating preparation method according to the requirements of application scenarios, considering multiple factors such as the performance requirements of the coating, the characteristics of the substrate and the cost.

SiC coated graphite base has the following functions in MOCVD equipment:

Support carrier: In MOCVD, the semiconductor material can be grown layer by layer on the wafer substrate surface to form a thin film with specific properties and structure. In this process, the SiC coated graphite base acts as a support carrier, providing a robust and stable platform for the epitaxy of semiconductor films. The excellent thermal stability and chemical inertness of the SiC coating maintain the stability of the base at high temperatures, reduce the reaction with corrosive gases, and ensure the high purity and consistent performance and structure of the semiconductor film grown. For example, SiC coated graphite base for GaN epitaxy growth in MOCVD equipment; SiC coated graphite base for epitaxial growth of monocrystalline silicon (plate base, circular base, three-dimensional base, etc.); SiC coated graphite base for SiC epitaxial growth.

Thermal stability and oxidation resistance: High temperature reactions and oxidizing gases may be involved in the MOCVD process, and the SiC coating can provide additional thermal stability and antioxidant protection to the graphite base, preventing its failure or oxidation in high temperature environments. This is essential for the control and consistency of film growth.

Material interface and surface properties control: SiC coatings can affect the interaction between the film and the substrate, thus affecting the growth pattern of the film, lattice matching, and interface quality. By adjusting the characteristics of SiC coatings, more precise material growth and interface control can be achieved, thereby improving the performance of epitaxial films.

Reduced impurity contamination: The ultra-high purity of the SiC coating can reduce impurity contamination from the graphite base, ensuring that the epitaxial film grown has the required high purity. This is critical to the performance and reliability of semiconductor devices.

In summary, in the MOCVD process, the SiC coated graphite base can provide better substrate support, thermal stability and interface control, thereby promoting the growth and preparation of high-quality epitaxial films.

Before 2017, China's SiC coated graphite base products mainly relied on imports. The best quality products come from Xycarb in the Netherlands, whose SiC coated graphite base has a service life of 200 to 300 rounds, while other companies have a slightly shorter service life of 100 to 200 rounds. Foreign manufacturers rely on patent advantages to block China's technology, so that the development of China's semiconductor industry is facing the risk of breaking the chain and blocking the neck.

At present, domestic research institutions are committed to improving the production process of silicon carbide coated graphite base, improving coating quality and uniformity, and reducing production costs. At the same time, they are also studying how to realize the intelligent manufacturing process of silicon carbide coated graphite base to improve production efficiency and product quality. The industry began to increase investment in the industrialization of silicon carbide coated graphite base to improve production scale and product quality to meet the domestic market demand. Recently, research institutions and industry are also actively exploring a new generation of coating technologies, such as the application of TaC coating in graphite bases to improve thermal conductivity and corrosion resistance.

At present, the global silicon carbide coated graphite base market concentration is high, Germany's Sgl Carbon, the Netherlands Xycarb, Japan's Toyo Tanso, is the leader in this field.