Papers by Keyword: Threading Edge Dislocation

Abstract: In this study, we investigated the origin of line-shape defect in 4H-SiC epitaxial wafers. The inspection results revealed that such defects resulted from the substrate entirely and accompanied with dislocation lines during the epitaxial process. Although the defect surface condition with nanometer level of roughness seemed to do little harm to the initial electrical characteristics of power devices, dislocation lines possibly resulted in high leakage current when reverse voltage was applied. To reduce line-shape defects, it is essential to reduce defects and threading dislocations in substrates and to develop a nondestructive method for wafer screening.

Abstract: Phase contrast microscopy (PCM) technique was demonstrated as the effective non-destructive discrimination method of TSDs and TEDs in 4H-SiC epitaxial layers in comparison with conventional polarized light microscopy, PL topography, KOH etch pit inspection and X-ray topography. The appearance of TSDs and TEDs by the PCM method is subtly modified by not only the consisting burgers vector but also the crystalline quality of the epitaxial layer or the substrate as the background. To extract more detailed information on the dislocations, the PCM inspection requires further investigation.

Abstract: Shifts in the spatial distribution of threading dislocations in 150 mm 4H SiC wafers were examined as a response to intentional changes in both the flow of the nitrogen source gas used to control resistivity during bulk crystal growth, and the growth rate. The density of threading edge and screw dislocations was found to be more evenly distributed in wafers produced under a high-growth rate, low-resistivity process. This result corresponded to a flattening of the resistivity distribution, and a ~34% reduction in on-and off-facet resistivity differential. The effect was attributed to regularized 4H island coalescence due to modulation of step terrace width.

Abstract: We observed fine surface morphology of silicon carbide wafers using a low energy scanning electron microscope (LESEM). Typical kinds of surface defects were observed by LESEM. After low temperature KOH treatment, it is confirmed that positions of etch pits are the same positions of these defects. Correlation between LESEM imaging and cross-sectional scanning transmission electron microscopy (STEM) of the same defects reveals threading dislocations and basal plane dislocations at the core of the defects.

Abstract: A threading dislocation (TD) in 4H-SiC, which was currently interpreted as a perfect threading edge dislocation (TED) by synchrotron monochromatic-beam X-ray topography (SMBXT) and molten KOH etching with Na₂O₂ additive, was performed comparative characterization using weak-beam dark-field (WBDF) and large-angle convergent-beam electron diffraction (LACBED) methods. The TD was suggested to be dissociated into a dislocation pair which can be observed in the WBDF image of g=-12-10. The TD, which was identified as b//[-12-10] by SMBXT observation, was unambiguously determined as b=1/3[-12-10] by LACBED analysis. In the case of perfect TED, it was found that the direction of Burgers vector derived from SMBXT observation corresponds to LACBED analysis.

Abstract: In this paper, we found origin of V_F degradation of SiC bipolar devices other than a basal plane dislocation (BPD) in the SiC substrate. A V_F degradation of the 4H-SiC PiN diodes with low-BPD wafers was evaluated and its origins were discussed. Some diodes suffered V_F degradation, even though they were fabricated on BPD-free area. PL mapping, TEM image, and optical observation after KOH etching showed that there were Shockley stacking faults and combined etch-pits arrays, which were presumed to be caused by the device process.

Abstract: This paper demonstrates the X-ray three-dimensional topography of basal-plane dislocations (BPDs) and threading edge dislocations (TEDs) in 4H-SiC. Cross-sectional imaging shows the propagation of BPDs from a substrate to an epilayer and the conversion of BPDs into TEDs near the epilayer/substrate interface. The strain analysis of TEDs exhibits the image of strains in the order of ±10-5. The observed strain images correlate well to simulation results.

Abstract: This paper demonstrates the X-ray three-dimensional (3D) topography of basal-plane dislocations (BPDs) and threading edge dislocations (TEDs) in 4H-SiC for the first time. Stereographic topographs are obtained for BPDs and TEDs, showing the propagation of BPDs from a substrate to an epilayer and the conversion of BPDs into TEDs near the epilayer/substrate interface. Strain analysis is also demonstrated for a TED, providing the image of strains in the order of ±10-5. It is verified that the 3D topography is successfully applicable to BPDs and TEDs.

Abstract: Burgers vector directions of threading edge dislocations (TEDs) in 4H-SiC epitaxial layer are distinguished by grazing incidence high resolution topography. Based on comparison between appearance of KOH etch pits and direction of TED Burgers vector, the size difference of the TED etch pits is found to be dependent on their Burgers vector directions. Examining TEDs in the epilayer by topography, the Burgers vector direction of basal plane dislocations (BPDs) in the substrate is identified. Correspondence between the topography contrast and the sense of a BPD is also investigated.

Abstract: Observations of dislocation nucleation occurring at substrate surface scratches during 4H-SiC CVD homoepitaxial growth are reported. Sub-surface residual damage associated with the scratches is observed to act as nucleation sites for basal plane dislocations (BPDs), threading edge dislocations (TEDs) and threading screw dislocations (TSDs) in the epilayer. TEDs and BPDs replicate from the surface intersections of basal plane dislocation half-loops injected into the substrate surface. A model for the nucleation mechanism of TSDs, which nucleate in opposite sign pairs, is presented which involves overgrowth of surface indentations associated with the scratch during step flow growth. Atomic steps which approach these local surface indentations can collapse creating pairs of opposite sign screw dislocations which have Burgers vector magnitude equal to the magnitude of the step disregistry created during the collapse.