Deposition of Tantalum Carbide (TaC) on graphite as a coating barrier during the manufacture of Silicon Carbide (SiC) electronic materials

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The rapidly expanding market for better power semiconductors at present is supplied by silicon and gallium nitride semiconductors. Power semiconductors switch electrical current in a device at high voltages, thereby converting and controlling the electricity. The use of silicon carbide (SiC) semiconductors is gaining interest because they work at much higher power loadings and temperatures, reducing energy loss and increasing the life of devices. Silicon carbide power semiconductors are applied in various industries including automotive, consumer electronics, IT and telecommunication, military and aerospace, and power. They are increasing in popularity in green energy applications such as electric cars and wind turbines.SiC semiconductors are grown in reactors by a process called MOCVD (Metal Organic Chemical Vapour Deposition). As part of this process SiC wafers are mounted onto a coated graphite substrate. A common used method to coat the graphite substrate is chemical vapour deposition (CVD). The coating forms a protective barrier to prevent impurities from the graphite affecting the growth process. Recent developments have demonstrated great promise with tantalum carbide (TaC) as a graphite coating due to its properties as a non-porous material with a very high melting point. These properties produce an extremely reliable and durable protective coating at low cost compared with other compound coatings currently in use. The outcome is a more reliable and efficient growth process with increased output of SiC semiconductors. Aixtron, the world-leading manufacturer of MOCVD reactors for SiC semiconductors, has approached Advanced Furnace Technology (Aftech) to optimise the processes of coating graphite parts with TaC for their MOCVD reactors in the production of SiC semiconductors. The potential for a successful project of this kind would increase the position of Aftech and the UK in the growth markets for SiC semiconductor applications such as solar and wind power, and electric vehicles. Currently Asia-Pacific is dominating the global market and the US Department of Energy is investing millions into various innovative projects (source: Mordor Intelligence). Aftech were approached by Aixtron to carry out this project for two main reasons. Firstly, the failures of current Aixtron suppliers, i.e. in South Korea and the USA. These include delamination (unsticking) of the TaC coating from the graphite substrate, as well as the failure to manufacture parts to scale due to restricted sized furnaces and a lack of capacity to build new, appropriate instruments. Secondly, Aftech possess the relevant experience and expertise to overcome these challenges. The major advantages that Aftech holds over its competitors include the capacity to build its own high temperature furnaces and systems and its experience in developing CVD systems, depositing chemicals such as tungsten carbide, aluminium gallium nitride, gallium arsenide, gallium phosphide, as well as silicon carbide. Aftech is unique in these respects and this provides us with a considerable advantage to optimise the processes of TaC coated graphite as well as manufacturing the end product. We see this as a major opportunity to bring in a new and effective product with a team headed by Dr Zoe Tolkien, who has been successfully working as our research and development officer on projects for optimising coating processes with pyrolytic graphite as well as graphite purity. She has shown great tenacity and promise in this role so far and we are confident in promoting her to develop her talents further through this project.