•We report synchrotron X-ray topographic observation of triangular defects in a 4H-SiC epi-wafer.•We characterize selected triangular defects by Raman spectroscopy, high-resolution TEM and Nomarski microscopy.•A formation mechanism of these triangular defects is postulated.Triangular defects are frequently observed in 4H-SiC homoepitaxial layers and their existence is reported to greatly degrade the performance of corresponding p-n junction diodes. Regarding the formation mechanisms of these defects, there have been a few models postulated before, which will be briefly reviewed here. In this study, we have observed a significant number of triangular defects in a 150mm n-/n+ commercial 4H-SiC homoepitaxial wafer using Nomarski Microscopy and Synchrotron X-ray topography (SXRT). The observed defects show varying morphology and complexity. In order to investigate their complex microstructures and gain insight on the formation mechanism, selected triangular defects were characterized by high resolution transmission electron microscopy (HRTEM) and micro-Raman spectroscopy. Results confirm that all the triangular defects have a 3C-SiC nature. In addition, {111} twins and double positioning boundaries (DPBs) were frequently observed inside the triangular defects. Based on these observations, a model has been developed to interpret the formation mechanism of these defects. In this model, the introduction of downfall particle during epitaxy creates a large triangular on-axis terrace, on which 3C-SiC crystals nucleate 2-dimensionally and grow under no constraint, eventually overgrown by 4H-SiC growth steps.

•We demonstrate the dislocation line direction determination using SWBXT.•We develop a new technique to determine threading dislocations Burgers vectors.•Ray tracing simulation is used to provide dislocation contrast.•The spatial distribution for different types of dislocations is investigated.Synchrotron X-ray Topography is a powerful technique to study defects structures particularly dislocation configurations in single crystals. Complementing this technique with geometrical and contrast analysis can enhance the efficiency of quantitatively characterizing defects. In this study, the use of Synchrotron White Beam X-ray Topography (SWBXT) to determine the line directions of threading dislocations in 4H–SiC axial slices (sample cut parallel to the growth axis from the boule) is demonstrated. This technique is based on the fact that the projected line directions of dislocations on different reflections are different. Another technique also discussed is the determination of the absolute Burgers vectors of threading mixed dislocations (TMDs) using Synchrotron Monochromatic Beam X-ray Topography (SMBXT). This technique utilizes the fact that the contrast from TMDs varies on SMBXT images as their Burgers vectors change. By comparing observed contrast with the contrast from threading dislocations provided by Ray Tracing Simulations, the Burgers vectors can be determined. Thereafter the distribution of TMDs with different Burgers vectors across the wafer is mapped and investigated.

•DSSFs bounding partials have been verified to be Si-core for the leading and C-core for the trailing.•g.b analysis and ray tracing simulation verify the preferential motion of the Si-core partials.•HTEM image shows a (62) stacking sequence confirming the presence of double Shockley faults.We recently reported on the formation of overlapping rhombus-shaped stacking faults from scratches left over by the chemical mechanical polishing during high temperature annealing of PVT-grown 4H–SiC wafer. These stacking faults are restricted to regions with high N-doped areas of the wafer. The type of these stacking faults were determined to be Shockley stacking faults by analyzing the behavior of their area contrast using synchrotron white beam X-ray topography studies. A model has been proposed to explain the formation mechanism of the rhombus shaped stacking faults based on double Shockley fault nucleation and propagation. In this paper, we have experimentally verified this model by characterizing the configuration of the bounding partials of the stacking faults on both surfaces using synchrotron topography in back reflection geometry. As predicted by the model, on both the Si and C faces, the leading partials bounding the rhombus-shaped stacking faults are 30° Si-core and the trailing partials are 30° C-core. Using high resolution transmission electron microscopy, we have verified that the enclosed stacking fault is a double Shockley type.

•SWBXT has been used to image and analyze a unique star stacking fault pattern in 4H-SiC wafers.•The six-pointed star fault comprises multi-layered rhombus-shaped Shockley stacking faults.•Formation of the star fault is associated with micropipe and basal and prismatic dislocations.•Formation involves the operation of a double-ended Frank–Read partial dislocation source.•Mechanism leads to 4H to 3C polytype transformation in the vicinity of the micropipe.Synchrotron White Beam X-ray Topography (SWBXT) has been used to image and analyze a distinctive stacking fault pattern observed in 4H-SiC wafers. The pattern often consists of a six-pointed star comprised of multiple layers of rhombus-shaped stacking faults with three different fault vectors of the Shockley type bounded by 30° Shockley partial dislocations. Formation of this stacking fault pattern is associated with a micropipe at its center which can act as nucleation sites for dislocation half-loops belonging to the primary basal (1/3〈11−20〉(0001)) slip system and occasionally the secondary prismatic (1/3〈11−20〉{1−100}) slip systems. In this case, the rhombus-shaped Shockley type stacking faults are nucleated on the basal plane by dissociation of 1/3〈11−20〉 pure screw dislocations cross-slipped from the prismatic plane and subsequent expansion caused by glide of the leading partial and locking of the trailing partial by interaction with 60° 1/3〈−2110〉 dislocations on the basal plane. Based on these observations, a formation mechanism involving the operation of a double-ended Frank–Read partial dislocation source has been proposed. In the limit, this glide and cross-slip mechanism leads to 4H to 3C polytype transformation in the vicinity of the micropipe by a mechanism similar to that proposed by Pirouz and Yang (1993) [21].