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Six-inch silicon carbide single crystal wafers

Japanese company Nippon Steel have developed a new method of producing 6" SiC wafers which can be used in large-area power devices for applications in automobiles and rapid-transit railways.

 At the Advanced Technology Research Laboratories of its Technical Development Bureau, Nippon Steel Corporation has successfully grown a six-inch diameter SiC single-crystal wafer.

 Six-inch SiC wafer

SiC is a key material for high performance next generation power semiconductor devices. Compared to silicon used in the manufacture of diodes, transistors and other semiconductor devices, SiC is capable of suppressing the power-conversion loss to less than half when used in various electronic devices. Its excellent high-voltage and heat resistance properties make SiC suitable for use in photovoltaic power generation, automotive (EV, HEV, etc.) and other power electronic applications.

Power semiconductors using SiC wafers also raise expectations of significant reductions in power loss and CO2 emission.

High-quality SiC wafers currently on the market predominantly have 3-inch and 4-inch diameters, and semiconductor-manufacturers’ development and commercialisation of semiconductors are being made based upon the availability of such SiC wafers.

But, there is a very strong need for greater efficiency in device production and also for the development and commercialisation of SiC devices in the large-current & high-voltage segment requiring large-aperture SiC wafers.

Volume production of six-inch SiC wafers is expected to increase the efficiency of SiC device production and to decrease the cost of device manufacture.

Six-inch wafers will make it possible to manufacture large-area devices for controlling larger currents and higher voltages, extending applications to automobiles (EV/HEV, etc.), rapid-transit railways, and other areas.

Because of its potential, the 6-inch SiC wafer has also been the subject of research and development in the national project of the Ministry of Economy, Trade and Industry in Japan, as a next-generation material capable of enhancing industrial competitiveness based on energy-saving technology.

SiC single crystal wafers are usually manufactured by sublimation, a recrystallisation method; the reactor is heated to over 25000C and the growth of the SiC single crystal is achieved by having vapour sublimated from the SiC material in powder form to recrystallise on top of seed crystals.

In 2007, using its own sublimation- recrystallisation method established through long years of R&D efforts, the firm developed and established a mass production technique for manufacturing high-quality 4-inch SiC wafers, which Nippon Steel Materials started selling in 2009.

In the sublimation-recrystallisation method, the growth of crystals of compounds at ultra-high temperatures makes process control difficult. The major problem is that with an increase in the size of crystal diameters, there is an increasing tendency for crystals to become susceptible to cracking induced by crystal defects and thermal stress.

By accelerating R&D efforts to resolve these problems, and based on numerical simulation technology, Nippon Steel developed a process using ultra-high-temperature equipment and  operating conditions suitable for 6-inch diameter wafers. The process successfully restrained crystal defects and crystal cracks in the growth of large-diameter crystals, and the firm manufactured what it claims is Japan’s first 6-inch SiC aperture wafer.

Part of this R&D program was subsidised under the “Novel Semiconductor Power Electronics Project Realising Low Carbon Emission Society” of the New Energy and Industrial Technology Development Organization (NEDO).

Nippon Steel says that in order to establish its 6-inch wafer manufacturing technology, it will continue efforts to achieve further product stability and productivity. The firm will also pursue the development of 6-inch SiC epitaxial film manufacturing.
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