Reduction in Background Carrier Concentration for 4 H -SiC C-face Epitaxial Growth
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Reduction in Background Carrier Concentration for 4H-SiC C-face Epitaxial Growth Johji Nishio1,2, Hirokuni Asamizu2,3, Mitsuhiro Kushibe1,2, Hidenori Kitai2 and Kazutoshi Kojima2 1 Corporate R&D Center, Toshiba Corporation, 1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki 212-8582, Japan 2 Advanced Power Electronics Research Center, Advanced Industrial Science and Technology (AIST), Central 2-13, 1-1-1 Umezono, Tsukuba 305-8568, Japan 3 Research and Development Division, ROHM Co., Ltd., 21 Saiin Mizosaki-cho, Ukyo-ku, Kyoto 615-8585, Japan ABSTRACT Reduction in background carrier concentration has been investigated for 4H-SiC C-face epitaxial growth in order to be applied for ultra-high voltage power devices. Optimizing epitaxial growth parameters made it possible to achieve 7.6x1013 cm-3 as the background carrier concentration within a whole area of specular 3-inch wafers. In addition to the background carrier concentration reduction, epitaxial film thickness variation, surface defect density and the carrier lifetime have been confirmed to fulfill the requirements for the devices. INTRODUCTION In the last few decades, the development of SiC semiconductors has made significant progress not only in material quality but also in device performances. For ultra-high voltage power devices with blocking voltage capability over 20 kV, which are thought promising as the next-generation SiC devices, the carrier concentration for the epitaxially grown drift layer is required around 2 ×1014 cm-3. In order to meet this requirement, the background carrier concentration for the epitaxial layer should be controlled lower than 1 ×1014 cm-3. The dominant element determining the background carrier concentration is considered to be residual nitrogen donor. In case of Si-face epitaxial growth, it has been reported that the carrier concentration control is possible by nitrogen doping, however there are risks of the conductivity type converting to p-type depending on the growth condition, such as undoped and higher C/Si ratio, and of the surface roughness increasing when the film thickness becomes thicker [1]. The C-face epitaxial growth is superior to these risks naturally, however, the lowest background carrier concentration reported so far was relatively highly n-type of 4.2 ×1014 cm-3 [2]. In other words, it has been considered that controlling the background carrier concentration lower on the C-face epitaxial growth is extremely difficult [3,4]. Therefore, there is few research conducted for ultra-high voltage power devices using C-face, so far. In order to realize the ultra-high voltage power devices on the C-face, the epitaxial growth parameters have been investigated how effective in reducing the background carrier concentration and finally optimized them, in the current study. Also, the uniformity of the film thickness and the surface defects together with the carrier lifetime were checked if they meet the device requirements.
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