Silicon Carbide and Related Materials 2006

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Authors: Matthias Stockmeier, Rainer Hock, Octavian Filip, Boris M. Epelbaum, Albrecht Winnacker, Andreas Magerl
Authors: Kevin M. Speer, David J. Spry, Andrew J. Trunek, Philip G. Neudeck, M.A. Crimp, J.T. Hile, C. Burda, P. Pirouz
Abstract: pn diodes have recently been fabricated from 3C-SiC material heteroepitaxially grown atop on-axis 4H-SiC mesa substrate arrays [1,2]. Using an optical emission microscope (OEM), we have investigated these diodes under forward bias, particularly including defective 3C-SiC films with in-grown stacking faults (SFs) nucleated on 4H-SiC mesas with steps from screw dislocations. Bright linear features are observed along <110> directions in electroluminescence (EL) images. These features have been further investigated using electron channeling contrast imaging (ECCI) [3]. The general characteristics of the ECCI images—together with the bright to dark contrast reversal with variations of the excitation error—strongly suggest that the bright linear features are partial dislocations bounding triangular SFs in the 3C-SiC films. However, unlike partial dislocations in 4H-SiC diodes whose recombination-enhanced dislocation motion serves to expand SF regions, all the partial dislocations we observed during the electrical stressing were immobile across a wide range of current injection levels (1 to 1000 A/cm2).
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: Yi Chen, Govindhan Dhanaraj, William M. Vetter, Rong Hui Ma, Michael Dudley
Abstract: The interactions between basal plane dislocations (BPDs) and threading screw and edge dislocations (TSDs and TEDs) in hexagonal SiC have been studied using synchrotron white beam x-ray topography (SWBXT). TSDs are shown to strongly interact with advancing basal plane dislocations (BPDs) while TEDs do not. A BPD can cut through an individual TED without the formation of jogs or kinks. The BPDs were observed to be pinned by TSDs creating trailing dislocation dipoles. If these dipoles are in screw orientation segments can cross-slip and annihilate also potentially leaving isolated trailing loops. The three-dimensional (3D) distribution of BPDs can lead to aggregation of opposite sign edge segments leading to the creation of low angle grain boundaries (LAGBs) characterized by pure basal plane tilt of magnitude determined by the net difference in densities of the opposite sign dislocations. Similar aggregation can also occur against pre-existing prismatic tilt boundaries made up of TED walls with the net difference in densities of the opposite sign dislocations contributing some basal plane tilt character to the LAGB.
Authors: D. Kurt Gaskill, Michael A. Mastro, Kok Keong Lew, Brenda L. VanMil, Rachael L. Myers-Ward, Ronald T. Holm, Charles R. Eddy
Abstract: A set of three 4H-SiC wafers with manufacturer specified micropipe density of 0-5 cm-2 were characterized by x-ray diffraction (XRD) maps before and after final chemical-mechanical polish. After final polish, the wafers were also investigated with atomic force microscopy, radius of curvature measurements and cross-polarization (x-pol) mapping. It was found that there was largely a lack of correlation between the XRD and x-pol maps, which strongly suggests that x-pol is insensitive to crystalline imperfections to which XRD is sensitive.
Authors: Tomohisa Kato, Tomonori Miura, Keisuke Wada, Eiji Hozomi, Hiroyoshi Taniguchi, Shin Ichi Nishizawa, Kazuo Arai
Abstract: In this study, we report defect analysis in 4H-SiC crystals of high nitrogen doping grown by sublimation method, and we discuss key points for defect restraint. The growth was performed in two kinds of growth directions; c-axis and a-axis. In the c-axis grown crystal with carrier density greater than 1×10-19cm-3, defect propagation was confirmed in the vertical direction for a growth direction affected by the doping by x-ray topography. This phenomenon was not observed in the a-axis grown crystals. In sublimation growth, the quantity of impurities tends to increase as growth rate decreases. Therefore, in the c-axis growth of doped 4H-SiC bulk crystals, we have to be careful so that dopant does not increase too much without intention in grown layers with lower growth rate, for example at the beginning and end of the growth.
Authors: Sakwe Aloysius Sakwe, Yeon Suk Jang, Peter J. Wellmann
Abstract: Wet chemical etching using molten KOH is the most frequently applied method to reveal structural defects in SiC. Until now etching kinetics of SiC in planes different from the polar cplane has not been reported. In this paper we report on defect etching of SiC in non-polar faces. Using a calibrated KOH defect-etching furnace with possibilities to set accurate etching temperatures we have etched SiC samples of various orientations to (i) study defect occurrence and their morphologies (ii) set KOH defect etching parameters for SiC for these orientations and (iii) investigate etching kinetics in relation to anisotropy/surface polarity. For non-polar planes of the same orientations a comparison in etching kinetics and defect morphologies in crystals grown in different directions is presented.
Authors: Ping Wu, Ejiro Emorhokpor, Murugesu Yoganathan, Thomas Kerr, Jie Zhang, Esteban Romano, Ilya Zwieback
Abstract: Several morphological defects in 4H SiC epitaxial wafers, including Comets and Triangles, may significantly impact on the yield and reliability of SiC devices. The formation of these epilayer defects is closely related to the substrate quality. This paper focuses on the study of the substrate quality and its relationship with defects in the epilayers. The crystalline quality of 4H n+ substrates has been characterized by x-ray diffraction, and the distribution of dislocations has been determined using etching in molten KOH. The relationship between Comet and Triangle epilayer defects and the dislocations has been established. A 10-fold reduction in the overall dislocation density in the 4H SiC substrates was achieved through technological improvements. The improvement was validated by the reduction in the number of the epilayer defects.
Authors: R. Ishii, Toshiyuki Miyanagi, Isaho Kamata, Hidekazu Tsuchida, Koji Nakayama, Yoshitaka Sugawara
Abstract: We investigated the location of the nuclei of Shockley-type stacking faults (SSFs) in the 4H-SiC pin diodes, using electroluminescence (EL) imaging. The nuclei of SSFs were identified as three types, located (i) on the mesa edge, (ii) in the surface region, and (iii) inside the epilayer. We compared the frequency of the nuclei according to these three locations for the (0001) and (000-1) pin diodes. The number of SSFs originated from the nuclei inside the epilayer in the (000-1) pin diodes was much less (<4 cm-2) than that in the (0001) pin diodes. However, the numbers of SSF nuclei (0.3 ~ 0.8 per device) located on the mesa wall and the surface region in the (000-1) pin diodes were comparable to the (0001) pin diodes. We also investigated the process responsible for generating the SSF nuclei.
Authors: Igor Matko, Bernard Chenevier, Jean Marie Bluet, Roland Madar, Fabrice Letertre, Wahib Saikaly
Abstract: QuaSiC TM substrates can be obtained by transferring a single crystal SiC layer onto a poly SiC substrate using the Smart Cut TM technology. In order to overcome the difficulty of limited thickness, an important improvement has been demonstrated, which consists in obtaining thick SiC structure by growing epitaxial SiC layers on top of transferred layers. The aim of this work is a structural analysis of such layers by Transmission Electron Microscopy and Photoluminescence.

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