Papers by Author: Kazutoshi Kojima

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Authors: Kazutoshi Kojima, Hajime Okumura, Satoshi Kuroda, Kazuo Arai, Akihiko Ohi, Hiroyuki Akinaga
Abstract: Homoepitaxial growth was carried out on 4H-SiC on-axis substrate by horizontal hot wall chemical vapor deposition. By using carbon face substrate, specular surface morphology of a wide area of up to 80% of a 2-inch epitaxial wafer was obtained at a low C/Si ratio growth condition of 0.6. The Micropipe in on-axis substrate was indicated to be filled with spiral growth and to be dissociated into screw dislocations during epitaxial growth. It was found that the appearance of basal plane dislocations on the epitaxial layer surface can be prevented by using an on-axis substrate.
Authors: Kazutoshi Kojima, Tetsuo Takahashi, Yuuki Ishida, Satoshi Kuroda, Hajime Okumura, Kazuo Arai
Authors: Kazutoshi Kojima, Sachiko Ito, Junji Senzaki, Hajime Okumura
Abstract: We have carried out detailed investigations of 4H-SiC homoepitaxial growth on vicinal off-angled Si-face substrates. We found that the surface morphology of the substrate just after in-situ H2 etching was also affected by the value of the vicinal-off angle. Growth conditions consisting of a low C/Si ratio and a low growth temperature were effective in suppressing macro step bunching at the grown epilayer surface. We also demonstrated epitaxial growth without step bunching on a 2-inch 4H-SiC Si-face substrate with a vicinal off angle of 0.79o. Ni Schottky barrier diodes fabricated on an as-grown epilayer had a blocking voltage above 1000V and a leakage current of less than 5x10-7A/cm2. We also investigated the propagation of basal plane dislocation from the vicinal off angled substrate into the epitaxial layer.
Authors: Kenji Fukuda, Makoto Kato, Junji Senzaki, Kazutoshi Kojima, Takaya Suzuki
Authors: Kenji Fukuda, Junji Senzaki, Mitsuhiro Kushibe, Kazutoshi Kojima, Ryouji Kosugi, Seiji Suzuki, Shinsuke Harada, Takaya Suzuki, Tomoyuki Tanaka, Kazuo Arai
Authors: Junji Senzaki, M. Goto, Kazutoshi Kojima, Kikuo Yamabe, Kenji Fukuda
Authors: Keiichi Yamada, Junji Senzaki, Kazutoshi Kojima, Hajime Okumura
Abstract: The new indicators, effective gate oxide thickness tc and effective gate electrode area D, and their combination are applied for a new analysis method of Fowler-Nordheim (F-N) tunneling characteristics in MOS capacitor having oxide thickness fluctuation. This method considering the conduction properties of F-N tunneling characteristics correlates its characteristics to the oxide reliability. These indicators quantified with the influence of the oxide thickness fluctuation can provide the net values of the electric field and the current density on the gate oxide. This new analysis method will lead to reducing the evaluation time for the reliability assessment.
Authors: Masatoshi Tsujimura, Hidenori Kitai, Hiromu Shiomi, Kazutoshi Kojima, Kenji Fukuda, Kunihiro Sakamoto, Kimiyoshi Yamasaki, Shin-Ichi Takagi, Hajime Okumura
Abstract: In this study, 4H–SiC inversion layers were experimentally evaluated by Hall and split C–V measurements, and scattering mechanisms related to gate oxide nitridation were analyzed. Three typical samples with different crystal plane directions and gate oxidation conditions were prepared, and their total trap density and Hall mobility were compared. Based on the temperature dependence of the Hall mobility, we found that scattering mechanisms differed for each sample. The sample C-face oxynitride which had a high nitrogen density at the metal–oxide–semiconductor (MOS) interface, showed a similar temperature dependency to that of ionized impurity scattering. This result suggests that high-density nitrogen acts as donors that supply free carriers and cause ionized impurity scattering, just like in a bulk crystal. In addition, the sample C-face wet has lowest influence of the Coulomb scattering because of the lowest temperature dependence of Hall mobility and the lowest total trap density.
Authors: Kazuhiro Mochizuki, Shi Yang Ji, Ryoji Kosugi, Kazutoshi Kojima, Yoshiyuki Yonezawa, Hajime Okumura
Abstract: Trench-filling epitaxial growth of 4H-SiC was analyzed based on a simulation model for continuous fluid approximation including the Gibbs-Thomson effect. With the use of the radii of curvature at the top and bottom of the trenches, the proposed model well reproduced the measured dependence of the growth rate on the trench pitch (L) in the case of narrow (L ≤ 6.0 μm) trenches.
Authors: Masayuki Sasaki, Kentaro Tamura, Hideki Sako, Makoto Kitabatake, Kazutoshi Kojima, Hirohumi Matsuhata
Abstract: Surface roughening regions running like scratches are often observed locally after epitaxy film grown on a very flat 4H-SiC wafer surfaces. We investigated generation mechanism of such roughening surface by using X-ray topography and confocal optical microscopy. We found that lattice defects were often introduced during CMP at local regions, and those local regions cannot be recognized by optical microscopy, since very flat surface can be observed. By H2 etching which is preprocess of epitaxy film growth, those lattice defects are almost etched off, but local rough surface consists of pits and step bunching regions appear like scratches, and those local pits and surface roughening regions grew up to step bunching during epitaxy film growth.
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