Papers by Author: Hirofumi Matsuhata

Abstract: Defect formation during the initial stage of physical vapor transport (PVT) growth of 4H-SiC crystals in the [000-1] and [11-20] directions was investigated by x-ray diffraction, defect-selective etching, and micro Raman scattering imaging. X-ray diffraction studies showed that the growths in the [000-1] and [11-20] directions exhibited markedly different behaviors with respect to the defect formation during the initial stage of growth. While a characteristic lattice plane bending was observed for the PVT growth along [000-1], a tilted domain structure was revealed near the grown crystal/seed interface for the growth in the [11-20] direction. Micro Raman scattering imaging revealed that nitrogen enrichment occurred near the grown crystal/seed interface and was associated with compressive stress parallel to the interface. Based on the results, the defect formation mechanisms during the initial stage of PVT growth of 4H-SiC are discussed.

Abstract: In this study, we investigated the annealing temperature dependence of dislocation extension in an ion-implanted region of a 4H-silicon carbide (SiC) C-face epitaxial layer, revealing that a high temperature annealing led to dislocation formation. We also investigated the current-voltage (I-V) characteristics of a 4H-SiC PIN diode with and without these extended dislocations. We demonstrated that the forward biased I-V characteristics of samples with extended interfacial dislocations have a kink at lower current regions.

Abstract: The crystallographic structure of comet-shaped defects observed on C-face 4H-SiC epitaxial film was investigated. The comet-shaped defects consist of head and tail part. The tail part shows symmetrical shape with respect to the (1-100) plane in cross section and narrowing along the step-flow direction. The tail part consists of four 3C domains with characteristic twin boundaries of Σ3 and Σ27. The head part consists of 3C poly-crystalline grains formed during epitaxial film growth and its formation is triggered by 3C-SiC particle contamination.

Abstract: Damaged layers, which are introduced during chemo-mechanical polishing (CMP) underneath the 4°off-cut 4H-SiC wafer surface and cause surface defects formations after epitaxial films growth, are investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM observations show presence of small scratches on wafer surfaces after CMP process. The widths of such scratches are submicron meters, thus it is hard to detect them by optical microscopy. TEM observations show that high-density regions of dislocation loops exist below scratches and the widths of such dislocation loops are much wider than the morphological width. Details of the dislocation structure are also analyzed. It is shown that the high-density dislocation loops cause local surface roughening on the surface of the epitaxial film.

Abstract: The trapezoid-shape defects are one of the most common surface defects on current 4H-SiC epitaxial film surface since they give rise negative impact for MOS-devices. We have investigated structures and origins of the defects. It is discovered that the possible origins of the trapezoid-shape defects are basal plane dislocations (BPDs), threading edge dislocations (TEDs), threading screw dislocations (TSDs),and the short dislocation loops introduced under scratches.

Abstract: Defect formation during the initial stage of physical vapor transport (PVT) growth in the [000-1] and [11-20] directions has been investigated by x-ray reciprocal space mapping (RSM) and defect-selective etching. RSM studies showed that, while the crystal grown in the [000-1] direction did not show a significant degradation of the crystalline quality during the initial stage of growth, the growth in the [11-20] direction resulted in misoriented subgrain structure near the grown crystal/seed interface. The cause of the domain formation is assumed to be the difference in nitrogen concentration between the seed and the grown crystal, and the results indicate that the growth in the [11-20] direction is greatly affected by the nitrogen doping difference.

Abstract: Threading dislocations in 4H-SiC wafer were observed by using a double crystal X-ray topography technique. The incident beam was collimated by the first crystal so that the angular divergence was reduced to sufficiently smaller than the rocking curve of a diffraction of the specimen (the second crystal). At off-Bragg angles, cross-sectional projection of threading dislocations appeared on the topographic images. From these results, we found that outcrops of the screw dislocation at the wafer surfaces suffered from significant strain, giving strong contrast on the topograph even under the condition, $\vec{g}\cdot\vec{b}=0$. In addition, the edge and screw components in the mixed dislocations were clearly distinguished.