Papers by Author: Hirofumi Matsuhata

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Authors: Takashi Tsuji, T. Tawara, Ryohei Tanuma, Yoshiyuki Yonezawa, Noriyuki Iwamuro, K. Kosaka, H. Yurimoto, S. Kobayashi, Hirofumi Matsuhata, Kenji Fukuda, Hajime Okumura, Kazuo Arai
Abstract: The authors fabricated pn diodes with Al+ implantation in p-type epitaxial layers, and investigated the influence of the implantation dose on reverse leakage currents. Only in the highest dose with the Al concentration of 2x1020cm-3, more than 90% of the devices showed high leakage currents above 10-4A at the maximum electric field of 3MV/cm. In such devices, almost all of the emissive spots corresponded to threading screw dislocations (TSDs) by the analysis of emission microscopy and X-ray topography. These TSDs were defined as killer defects with the estimated density of 500cm-2 in the case of the highest dose. The emissions were supposed to be due to microplasmas, since the spectra of the emissions were different from those of heat radiation. Condensation of Al atoms, nitrogen atoms and DI defects were excluded as the origin of the emissions by secondary ion mass spectrometry and low temperature photoluminescence analyses.
Authors: Ryohei Tanuma, Tae Tamori, Yoshiyuki Yonezawa, Hirotaka Yamaguchi, Hirofumi Matsuhata, Kenji Fukuda, Kazuo Arai
Abstract: This paper describes the study of non-hollow-core elementary screw dislocations (SDs) in silicon carbide (SiC) diodes using X-ray microbeam three-dimensional topography. Strain analysis shows that typical screw dislocations having a symmetric strain field tend to cause microplasma breakdown, whereas deformed SDs do not. The symmetry break in SDs will relax the focussing of strain and lessen the formation of defects, thereby leading to the desirable non-leak property.
Authors: Tamotsu Yamashita, Kenji Momose, Daisuke Muto, Yoshiki Shimodaira, Kuniaki Yamatake, Yoshihiko Miyasaka, Takayuki Sato, Hirofumi Matsuhata, Makoto Kitabatake
Abstract: We report our investigation results on triangular-defects formed on 4deg. off 4H-SiC epi- taxial wafers. Triangular-defects that had neither down-falls nor basal-plane dislocations previously reported as origins of triangular-defects at the tips of triangle were investigated by TEM. Our TEM results revealed that foreign materials contamination that were different from well-known down- -falls in size and in composition caused one of the defect formations and abnormal domain forma- tions were implied to occur and thought to relate to defect formations. We also report that several types of microstructure existed in the isosceles of defect during dislocation analyses around triangular-defects by X-ray topography.
Authors: Hirofumi Matsuhata, Hirotaka Yamaguchi, Ichiro Nagai, Toshiyuki Ohno, Ryouji Kosugi, Akimasa Kinoshita
Abstract: Dislocations in a substrate wafer of 4H-SiC with an epi-layer were observed using technique of monochromatic synchrotron X-ray topography in a grazing incidence geometry. Six different Burgers vectors of basal plane dislocations and threading edge dislocations were identified by changing the Bragg reflections, and by analysis of images of dislocation. We identify some relations of the Burgers vector and the dislocation contrast observed for g=11 2 8. Some of these relationships are discussed in this report.
Authors: Tetsuo Hatakeyama, Kyoichi Ichinoseki, Hiroshi Yamaguchi, N. Sugiyama, Hirofumi Matsuhata
Abstract: The origins of certain types of micrometer-scale surface morphological defects on SiC epitaxial layers are clarified using X-ray topography. Two types of surface morphological defects are commonly observed on Si- and C-face epitaxial layers. Relatively large pits (around 4μm×2μm) originate from threading screw dislocations (TSDs). Relatively small pits (around 1.5μm×1μm) originate from threading edge dislocations (TEDs). The shapes and depths of these surface morphological pits depend on the fabrication history of the epitaxial wafers.
Authors: Hirotaka Yamaguchi, Hirofumi Matsuhata, Ichiro Nagai
Abstract: We have investigated dislocation image of 4H-SiC wafers projected on synchrotron X-ray topographs taken under different positions in the rocking curve of a diffraction peak. The diffraction geometry was grazing-incidence extremely asymmetric and the diffraction vectors were g = 1 1 2 8 and 112 8. The weak-beam images were demonstrated for basal-plane dislocations and threading-screw dislocations. The basal-plane dislocation images became narrower in width at the off-Bragg conditions, and they were decomposed to separate lines under the weak-beam condition. The threading-screw dislocations showed changes in their shape and contrast as the crystal set was tilted from the rocking-curve peak, and finally the characteristic images near the dislocation core were observed under the weak-beam condition. The origin of these weak-beam images is unclear, but it will offer detailed analysis of the dislocations.
Authors: Takasumi Ohyanagi, Chen Bin, Takashi Sekiguchi, Hirotaka Yamaguchi, Hirofumi Matsuhata
Abstract: The breakdown failure points in the 4H-SiC PiN diodes were analyzed by the electron beam induced current (EBIC). We focused on the failure, which showed the avalanche breakdown, and we determined the failure points by an emission microscopy. We observed the basal plane dislocation around the failure point and at measured temperatures below 200K we found the dark spots in the EBIC. However, in the X-ray topography image, no spots were found around the dislocations. We therefore think that these spots originated from the metal contamination. The electric field was multiplied due to a permittivity change, and this multiplication caused the avalanche breakdown.
Authors: Naoyuki Kawabata, Atsushi Tanaka, Masatoshi Tsujimura, Yoshinori Ueji, Kazuhiko Omote, Hirotaka Yamaguchi, Hirofumi Matsuhata, Kenji Fukuda
Abstract: We investigated the effect of the basal plane dislocation (BPD) density in 4H-silicon carbide (SiC) substrates on the forward voltage (Vsd) degradation of body-diodes. Using reflection X-ray topography, the BPD density was automatically estimated from the substrates prior to fabrication of metal–oxide–semiconductor field-effect transistors (MOSFETs). A strong positive correlation was found between the Vsd shift, which was calculated from the difference before and after forward bias stress at 160 A/cm2 for ~500 hours, and the BPD density of the substrate. We show that it is possible to predict Vsd shifts from the BPD densities of SiC substrates prior to the fabrication of MOSFETs. In addition, we examined the origin of stacking faults (SFs) as a result of the application of forward bias stress. We presume that SFs are formed by BPDs converted to threading edge dislocations at the epi/sub interface, as well as by BPDs penetrating into the epitaxial layer.
Authors: Takuma Suzuki, Hirotaka Yamaguchi, Tetsuo Hatakeyama, Hirofumi Matsuhata, Junji Senzaki, Kenji Fukuda, Takashi Shinohe, Hajime Okumura
Abstract: The causes of extrinsic failures in time-dependent dielectric breakdown characteristics of gate oxide on C-face of 4H-SiC are examined by comparing breakdown points of tested gate oxides with the images of X-ray topography and those of differential interference contrast microscopy. We have concluded as follows: (1) surface morphological defects that originate from threading screw dislocations degrade reliability of gate oxides. (2) These surface defects are not necessarily found on every wafer. (3) Crystallographic defects are not killer defects of MOSFET per se.
Authors: Noboru Ohtani, Masakazu Katsuno, T. Fujimoto, S. Sato, Hiroshi Tsuge, Wataru Ohashi, Hirofumi Matsuhata, Makoto Kitabatake
Abstract: Defect formation during the early stages of physical vapor transport (PVT) growth of 4H-SiC was investigated using high resolution x-ray diffraction (HRXRD). Characteristic lattice bending behaviors were revealed in the nearby seed crystal regions of grown crystals. The lattice bending was localized in close proximity to the seed/grown crystal interface, and the (0001) basal planes bended convexly toward the growth direction, indicative of the insertion of extra-half planes pointing toward the growth direction during the initial stages of crystal growth. This paper discusses the possible mechanisms of the observed lattice bending and sheds light on the defect formation processes during PVT-growth of 4H-SiC single crystals.
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