Papers by Keyword: X-Ray Topography

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Authors: Yu Yang, Jian Qiu Guo, Balaji Raghothamachar, Michael Dudley, Swetlana Weit, Andreas N. Danilewsky, Patrick J. McNally, Brian R. Tanner
Abstract: We present in-situ observations of the dynamical operation of multiple double-ended Frank-Read dislocation sources in a PVT-grown 4H-SiC wafer under thermal gradient stresses. The nucleation of these sources is facilitated by a specific configuration consisting of one basal plane dislocation (BPD) segment pinned by two threading edge dislocations (TEDs). This configuration is formed during PVT crystal growth by deflection of TEDs on to the basal planes by macrosteps and re-deflection of resulting BPDs back into TEDs. Under the influence of thermal gradient stresses induced by heating inside a double ellipsoidal mirror furnace, the pinned BPD segment glides and activates dislocation multiplication by the double Frank-Read source mechanism. A more intricate mechanism of swapping of TED pinning points between Frank-Read sources lying on same basal plane is identified, enabling one dislocation loop to effectively “pass through” the other dislocations on same basal plane.
Authors: Jawad ul Hassan, Peder Bergman, Anne Henry, Henrik Pedersen, Patrick J. McNally, Erik Janzén
Abstract: We report on the growth of 4H-SiC epitaxial layer on Si-face polished nominally on-axis 2” full wafer, using Hot-Wall CVD epitaxy. The polytype stability has been maintained over the larger part of the wafer, but 3C inclusions have not been possible to avoid. Special attention has given to the mechanism of generation and propagation of 3C polytype in 4H-SiC epilayer. Different optical and structural techniques were used to characterize the material and to understand the growth mechanisms. It was found that all 3C inclusions were generated at the interface between the substrate and the epitaxial layer, and no 3C inclusions were initiated at later stages of the growth.
Authors: J.H. Edgar, L.H. Robins, S.E. Coatney, L. Liu, J. Chaudhuri, K. Ignatiev, Z. Rek
Authors: D.J. Ewing, Qamar-ul Wahab, Sergey P. Tumakha, Leonard J. Brillson, X.Y. Ma, Tangali S. Sudarshan, L.M. Porter
Abstract: In this study, we performed a statistical analysis of 500 Ni Schottky diodes distributed across a 2-inch, n-type 4H-SiC wafer with an epilayer grown by chemical vapor deposition. A majority of the diodes displayed ideal thermionic emission when under forward bias, whereas some diodes showed ‘double-barrier’ characteristics with a ‘knee’ in the low-voltage log I vs. V plot. X-ray topography (XRT) and polarized light microscopy (PLM) revealed no correlations between screw dislocations and micropipes and the presence of double-barrier diodes. Depth resolved cathodoluminescence (DRCLS) indicated that certain deep-level states are associated with the observed electrical variations.
Authors: I. Brazil, Patrick J. McNally, N. Ren, L. O'Reilly, A. Danilewsky, T.O. Tuomi, A. Lankinen, A. Säynätjaki, R. Simon, Stanislav I. Soloviev, L.B. Rowland, Peter M. Sandvik
Abstract: We present herein a first comparative analysis of the quality of 50 mm and 75 mm diameter SiC wafers, purchased directly from vendors across the world, types including the most widely available configurations. Large Area White Beam Synchrotron Back Reflection X-Ray Topography was used to analyse selected ~1cm2 regions at various locations on up to 10 different bulk SiC wafers. The study concentrated particularly on the density and distribution of threading screw dislocations (TSDs). We also examined all wafers for basal plane dislocation (BPDs) densities and distributions. Alarmingly large variation in wafer quality was observed. TSD densities vary from a minimum of 0 cm-2 (in a-plane material) to values as large as over 2,000 cm-2 on some n-type 4H-SiC wafers. TSD densities on individual wafers can also vary by similar magnitudes, e.g. 500cm-2 to 2,500 cm-2 on two regions only 2 cm apart on a 50 mm diameter wafer. Computer-based image process analysis was used to present a statistical analysis of the distributions of defects. For example algorithms created in MATLAB®, Image Processing Toolbox, isolated possible TSD locations allowing rapid counting to be performed. These counts were confirmed by manual counting of selected unmodified images.
Authors: Takayoshi Shimura, Takuya Matsumiya, Naoki Morimoto, Takuji Hosoi, Kentaro Kajiwara, Jun Chen, Takashi Sekiguchi, Heiji Watanabe
Abstract: A synchrotron white x-ray microbeam diffraction method was employed to investigate lattice distortion in multicrystalline silicon for photovoltaic cells. The measurements were carried out by scanning the sample, and transmission Laue patterns were observed at each position on the sample. Intensity and position maps of the Laue spots showed the distribution of the crystalline quality of the grains and the bending of the lattice planes. Strain and bending distributions were extracted from an analysis of Laue spots at diagonal positions, and these were compared with those obtained by other techniques.
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.
Authors: Václav Paidar, Pavel Lejček, M. Polcarová, J. Brádler, Alain Jacques
Abstract: Grain boundary motion was studied in situ at elevated temperatures by x-ray topography using synchrotron radiation. In addition to the position of grain boundary, other crystal defects that may interact with the moving boundary were observed simultaneously. Two types of bicrystals with the [001] rotation axis were selected for the experiments, the first one with a high coincidence S5 misorientation of about 37° and the other one with no coincidence of two crystals for the misorientation of 45°. The geometrical differences between chosen bicrystals are examined and attention is also paid to faceting – local orientations of the boundary plane.
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