Silicon carbide (SiC) is a wide-bandgap compound semiconductor with excellent properties such as high breakdown field strength (about 10 times that of Si), high drift rate of saturated electrons (about 2 times that of Si), and high thermal conductivity (3 times of Si and 10 times of GaAs). Compared with similar silicon-based devices, SiC devices have the advantages of high temperature resistance, high voltage resistance, good high frequency characteristics, high conversion efficiency, small size and light weight, and have important application potential in electric vehicles, rail transit, high voltage transmission and transformation, photovoltaic, 5G communication and other fields. High-quality, low-cost, large-size SiC single crystal substrate is the basis for the preparation of SiC devices, and mastering The growth and processing technology of SiC crystals with independent intellectual property rights has always been the focus of research in related fields.
Since 1999, the research team of Chen Xiaolong, Key Laboratory of Advanced Materials and Structural Analysis, Institute of Physics, Chinese Academy of Sciences/Beijing National Research Center for Condensed Matter Physics, based on independent innovation, has systematically studied the basic laws of thermodynamics and growth dynamics of SiC crystal growth based on independent innovation, using self-developed growth equipment, understanding the formation mechanism of phase transitions and defects during crystal growth, proposing defects, resistivity control and scaling methods, and forming a series of key technologies from growth equipment to high-quality SiC crystal growth and processing , increasing the diameter of SiC crystals from less than 10 mm (2000) to 2 inches (2005). In 2006, the team took the lead in the industrialization of SiC monocrystalline in China, successfully transformed the research results into Beijing Tianke Heda Semiconductor Co., Ltd., and successfully developed 4-inch (2010) and 6-inch (2014) SiC monocrystalline through the combination of production, education and research. At present, Beijing Tianke Heda has realized the mass production and sales of 4-6 inch SiC substrates, becoming one of the main suppliers of international SiC conductive wafers.
Figure I. 8 inch SiC crystal and wafer photo
The cost of SiC devices is mainly formed by the substrate, epitaxial, tapeout and packaging and testing, and the substrate accounts for up to ~45% of the cost of SiC devices. In order to reduce the cost of a single device, further expand the size of the SiC substrate, increasing the number of devices on a single substrate is the main way to reduce costs. An 8-inch SiC substrate will have a distinct advantage over 6-inch in terms of cost reduction. Internationally, the successful development of 8-inch SiC single crystal substrates has been reported, but so far there has been no product on the market.
The difficulty in the growth of 8-inch SiC crystals is that: first of all, 8-inch seed crystals must be developed; secondly, the problems of uneven temperature field and gas-phase raw material distribution and transportation efficiency caused by large sizes; in addition, it is also necessary to solve the problem of crystal cracking caused by increased stress. On the basis of the existing research, in 2017, Chen Xiaolong researcher, doctoral student Yang Naiji, Associate Researcher Li Hui, Chief Engineer Wang Wenjun, etc. began to study 8-inch SiC crystals, and through continuous research, mastered the distribution of 8-inch growth room temperature field and the characteristics of high-temperature gas-phase transport, took 6-inch SiC as the seed crystal, designed a device conducive to SiC expansion growth, solved the problem of polycrystalline nuclei at the edge of seed crystals during the expansion of diameter growth, designed a new growth device, improved the efficiency of raw material transportation; through multiple iterations, The size of the SiC crystal was gradually expanded; the stress in the crystal was reduced and the crystal cracking was suppressed by improving the annealing process. In October 2021, an 8-inch SiC crystal was initially grown on the self-developed substrate.
Figure II. Raman scattering pattern of an 8-inch SiC chip
Recently, the team has further solved the multi-type phase transition problem by optimizing the growth process, continuously improved the crystal crystal quality, successfully grown a single 4H crystal type of 8-inch SiC crystal, the thickness of the crystal blank is close to 19.6 mm, and processed an 8-inch SiC wafer with a thickness of about 2 mm (Figure 1) and tested it. The Raman scattering pattern and X-ray rocking curve test results show that the grown 8-inch SiC is a 4H crystal form, as shown in Figure 2, and the semi-wide average of the (0004) surface is 46.8 arcsec, as shown in Figure 3. Three Chinese invention patents have been applied for.
The successful development of 8-inch SiC conductive single crystal is another landmark progress made by the Physical Institute in the field of wide bandgap semiconductors, and after the transformation of research and development results, it will help enhance the international competitiveness of the mainland in the SiC single crystal substrate and promote the rapid development of the continental wide bandgap semiconductor industry.
The above work has been strongly supported by the Ministry of Science and Technology, the Xinjiang Production and Construction Corps, the National Natural Science Foundation of China, the Beijing Municipal Science and Technology Commission, the Ministry of Industry and Information Technology, the Chinese Academy of Sciences and other departments.
Figure III. X-ray rocking curve of 8 inches at 4 degrees off-axis SiC wafer (0004) surface
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