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Research paper : R&D of SiC semiconductor power devices and strategy towards their practical utilization (K. Arai)−249−Synthesiology - English edition Vol.3 No.4 (2011) research method, the project formed a group consisting of ETL and two companies (Showa Denko K.K. and Denso Corporation; later joined by Nippon Steel Corporation) that have started the growth of SiC monocrystals. The approaches selected for this R&D were the on-site observation of x-ray topography of the crystal growth process and the in-furnace visualization by simulation (Fig. 5)Note 3. In fabricating the device, a micron-order hole accompanied by screw dislocation in the wafer (micropipe) would be fatal. Therefore, the objectives of the project were the fabrication of a two-inch substrate without micropipes and the growth of crystals with external diameter of four inches. An important technological contribution was the scientific presentation of the crystal growth technology that was a corporate know-how that had not been disclosed until then at academic societies. After the completion of the project, the developed technology was transferred to several Japanese companies that wished to manufacture the crystals.In high blocking voltage and high-power vertical power device, the low resistance is achieved by introducing impurities at high concentration (the n-type semiconductor is normally achieved by nitrogen doping) to the substrate crystal. Therefore, to realize the desired device characteristics, the homo-epitaxial monocrystal film growth technology is important where the film is formed on the SiC monocrystal by carefully controlling the film thickness and the impurities concentration. The group led by Professor Matsunami of Kyoto University developed a step-controlled epitaxy where high quality growth could be achieved at relatively low temperature (~1600 ºC) by introducing the off-angle surface. The project introduced an overseas epitaxial growth system with established performance, and the necessary epitaxial film was supplied to the device fabrication group after fine-tuning the growth conditions. On the other hand, a new high-speed epitaxial device was developed (few years later, this achieved a growth rate of over 100 m/h on a three-inch substrate). Near the completion of the project, in addition to the silicon face that was the crystal-forming surface of the device thus far, the epitaxial film growth technology that allowed control of the impurities in the carbon face, which is the other side of the silicon face, was developed. It was demonstrated that the channel mobility of the MOSFET was almost one digit greater compared to the silicon face, and the basic device patent was obtained for the carbon face device (Fig. 6). At present, there are still issues that must be resolved in the carbon face device process, but it is developing into a main technology toward practical utilization.Although the advantage of SiC is that a SiO2 insulating layer can be formed by thermal oxidation, the channel mobility of the MOSFET obtained by oxidation is extremely low compared to the bulk (in normal thermal oxidation, it is two digits less than the mobility of bulk). The thermal diffusion of impurities that worked extremely well in the silicon process could not be used in the SiC process, and the high-temperature ion injection followed by the high-temperature activation process was necessary. The development of low resistance contact formation technology had to be done quickly. Also, the device parameters necessary for the device design were uncertain or unavailable. These issues were handled systematically in the concentrated research method. For the necessary physical property and process evaluations, we asked the cooperation of universities and external organizations. These results helped build the foundation of this field in Japan that was behind in the device technology development, as well as demonstrated the performance of the prototype SiC power device that surpassed the performance of silicon created by the dispersed research method.Another important characteristic of this project was that it was conducted under the Engineering Advancement Association of Japan (ENAA), an organization that emphasized the R&D of system application of the practical utilization research (NEDO project “Development of Fig. 5 Approach for the development of SiC monocrystal growth technologyThe structure inside the furnace was almost never disclosed at the academic societies or any other places.Fig. 6 Development of the carbon-face device technologyThe development of the epitaxial growth technology on the carbon face (C-face) and the channel mobility of MOS fabricated on the face (Morphology of the epitaxial surface (the water-like smudges are image artifact)). Quality, size (diameter, length), etc.Growing crystal・ Numerical analysis・ X-ray and on-site observationLook inside the black box (graphite crucible) by scientific methodsHigh-frequency heating power, upper/lower temperature measurement, structure of crucible, amount of material, voltage, etc.Operation conditionHeating coil~2200 ℃Growing crystalsInsulatingmaterial~2500 ℃Graphite crucibleDevelopment of new furnace structuretpDsDbHtsEmpirical rule 0 . 5 n m TargetRon=1~3 mΩcm2Vbd=600 VField-effect mobility (cm2/ Vs)POAPyro.+H2℃Tox=1100℃Tox=900Vg (V)86420150100500Vs127 cm2/2 inch, thickness 10 µm 100 µm2-inch1 µm10(0001)C face0Oxidation temperature dependency of the MOS interface mobility at the C-face

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