7 December 2011

Nippon Steel develops Japan’s first 6” SiC single-crystal wafer

At the Advanced Technology Research Laboratories of its Technical Development Bureau, Japan’s Nippon Steel Corp has developed 6-inch diameter silicon carbide (SiC) single-crystal wafer, which the firm describes as a key material for the mass production and adoption of high-performance power semiconductor devices in the future.

Compared with silicon wafers used in the manufacture of diodes, transistors and other semiconductor devices, SiC can halve power-conversion loss when used in various electronic devices. It also has excellent high-voltage and heat resistance properties, making it suitable for high-voltage, high-temperature photovoltaic power generation, automotive (EV, HEV etc) and other power electronics applications.

With such features, the broad spread of power semiconductors using SiC wafers raises expectations of significant reductions in power loss and hence a great impact on energy conservation and CO2 emission reduction.

High-quality SiC wafers currently on the market are predominantly 3-inch and 4-inch in diameter, and semiconductor manufacturers’ development and commercialization of devices is based on the availability of such SiC wafers. However, there is great need for higher efficiency in device production and also for the development and commercialization of SiC devices in the large-current and high-voltage segment, calling for large-aperture SiC wafers.

Nippon Steel says that 6-inch SiC wafers should increase the efficiency and lower the cost of SiC device manufacturing. They should also make it possible to manufacture large-area devices for controlling larger current and higher voltage, extending possible applications to automobiles (EV/HEV etc), rapid-transit railways, and other areas.

Because of this potential, 6-inch SiC wafers have also been the focus of R&D in a national project of Japan’s Ministry of Economy, Trade and Industry, as a next-generation material capable of enhancing industrial competitiveness through energy-saving technology.

Single-crystal SiC is usually manufactured using the sublimation-recrystallization method. In equipment heated to temperatures of more than 2500°C, vapor sublimated from SiC material in powder form is recrystallized on top of seed crystals. Using its own sublimation-recrystallization method established over many years of R&D efforts, in 2007 Nippon Steel developed a technique for the mass production of high-quality 4-inch SiC wafers, which Nippon Steel Materials Co Ltd began selling in 2009.

In the sublimation-recrystallization method, the growth of crystals of compounds at ultra-high temperatures introduces difficulties in process control. The major problem is that, with an increase in crystal diameter, 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, Nippon Steel has developed a mechanism for using ultra-high-temperature equipment and process operating conditions, suitable for 6-inch wafers. By restricting crystal defects and crystal cracks in the growth of large-diameter crystals, Nippon Steel has manufactured Japan’s first 6-inch SiC wafer.

Part of the R&D program was subsidized under the ‘Novel Semiconductor Power Electronics Project Realizing Low Carbon Emission Society’ of Japan’s New Energy and Industrial Technology Development Organization (NEDO).

Nippon Steel says that, to establish 6-inch wafer manufacturing technology, it will continue its efforts to achieve further product stability (in order to develop technology for productivity improvement). It also aims to develop 6-inch SiC epitaxial film manufacturing technology.

Tags: Nippon Steel SiC single-crystal wafer

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