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Research paper−259−Synthesiology - English edition Vol.3 No.4 pp.259-267 (Mar. 2011) In this paper, we shall explain the vapor deposition growth of diamonds, and then describe the increased high plasma density and nitrogen addition to solve the aforementioned issues in the single-crystal CVD diamond synthesis, particularly for the homoepitaxial growth. Then we shall address the development of the methods for shaping the diamond, an ultra-hard material, into the form of a wafer.2 Development of the diamond synthesis by vapor depositionThe chemical vapor deposition (CVD) is a method where raw material gas (in the case of diamond, hydrocarbon gas such as methane and hydrogen) is broken down by heat or plasma under subatmospheric pressure, and the growth seeds produced undergo a chemical reaction on the substrate surface to grow into a diamond film[2]-[13].The CVD synthesis of diamond based on thermal decomposition published in the 1950s had extremely slow growth rate, and was an unrealistic method due to the graphite inclusions. By the end of the 1960s, it was known that the graphite components could be selectively etched due to the presence of atomic hydrogen. However, the CVD diamond research rapidly lifted off in 1982~1983, after the National Institute for Research in Inorganic Materials (currently National Institute for Materials Science (NIMS)) published the production method of atomic hydrogen, and reported that it was possible to synthesize diamond at the growth rate of m/h level[14][15]. These methods were called the hot filament CVD and microwave plasma CVD methods. In these methods, the methane gas diluted by hydrogen was decomposed by tungsten filament or microwave plasma heated to about 2200 ºC, and the diamond grains were grown 1 IntroductionUntil recently, the single-crystal diamonds were industrially manufactured using the high-temperature high-pressure method. The Ib type or the yellow crystals containing nitrogen are mass-produced for use in machine tools. Single crystals with high purity and low defect can be synthesized, and it is also possible to manufacture near-perfect single crystals to be used as dispersive crystals for radiated light[1]. However, the size limit of the single crystal using the high-temperature high-pressure method is about 1 cm, and further increase in size is difficult because that will require large-scale pressure equipment. In contrast, the chemical vapor deposition (CVD) method used for the synthesis of polycrystalline diamond and homoepitaxial film has less size limit compared to the high-temperature high-pressure method. Therefore, there are several R&Ds for the single crystal synthesis using the CVD method to increase the size and to reduce the cost. Our R&D objective is to use the substrate in the next-generation power devices, and we aim to fabricate a 2-inch wafer needed for the manufacture line of the current prototype device. The single-crystal substrate with maximum 1 cm size that can be fabricated by ultrahigh-pressure synthesis is Ib type, and it is very expensive at 1 to 2 million yen. Cost reduction by one digit or more is expected by using the CVD method.The reason that the CVD method has been used only for the synthesis of diamond film but not for the synthesis of bulk crystal until recently was because the growth speed was slow and the single-crystal growth could not be maintained over a long time due to the occurrence of abnormal grains. The solutions to these issues are the main topics in the research for the single-crystal CVD diamond synthesis. - Enlargement of crystal size by microwave plasma CVD and wafer fabrication technology-Akiyoshi Chayahara*, Yoshiaki Mokuno, Nobuteru Tsubouchi and Hideaki YamadaDiamond Research Laboratory, AIST 1-8-31 Midorigaoka, Ikeda 563-8577, Japan *E-mail : Original manuscript received May 6, 2010, Revisions received June 14, 2010, Accepted June 14, 2010Industrial application of diamond has been limited to the use of its hardness, e.g., in machining tools, because large size crystals of diamond are difficult to synthesize and very expensive. If these problems are solved, it can be used for various purposes. Diamond is called ‘an ultimate semiconductor’ and is located after SiC or GaN in the semiconductor roadmap. If power electronic devices with diamond are realized which utilize its operability under high temperature and the highest thermal conductivity among all materials, the inverters for automobiles can be operated without cooling devices, which lead to energy saving through the reduction of power loss as well as the reduction of weight of the cooling system. The purpose of this paper is to report the process of enlarging the size of single-crystalline diamond using vapor phase epitaxy and the fabrication of diamond wafers.Development of single-crystalline diamond wafersKeywords : Single-crystalline diamond, microwave plasma CVD, crystal growth[Translation from Synthesiology, Vol.3, No.4, p.272-280 (2010)]

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