Materials Science Forum Vols. 778-780

Abstract: We evaluate the velocity of stacking faults (SFs) expansion under various current and temperature levels on the pn diodes by electroluminescence (EL) observation in situ. The driving force of the SFs expansion is analyzed on the basis of the experimental results. The velocity of the SFs expansion increases in proportional to the current density at the every junction temperature levels. The activation energy for the velocity of the SFs expansion is estimated.

Abstract: In this paper, we report a newly developed dislocation-revealing etch pit method for 4H-SiC single crystal, which can distinguish edge (TED, Burgers vector b=a), elementary screw (TSD, b=1c) and mixed (TMD, b=c+a) threading dislocations. In this method, vaporized NaOH gas was used to etch the Si-face of a SiC wafer at substrate temperature around 950 °C. By a side-by-side comparison between the optical images of the etch pits and the X-ray topographic (XRT) images, it has been found that threading dislocations (TDs) in SiC could be revealed as hexagonal etch pits with distinct geometrical features (shape, size and facet orientation) depending on their Burgers vectors. Based on these results, we consider this etch pit method as an easily-operated and inexpensive technique to categorize TDs, and it may help to promote our understanding on the different roles that these types of TDs have played in the performance degradation of SiC power devices.

Abstract: The aim of this review is to present the observation of low-energy ion implanted SiC and annealing them by using TEM. By detail analyses of the TEM images and results of SRIM, ion implanted SiC was classification four structure depending on the ion concentration in a few ten nm shallow region. This results suggest that crystal structure in a few nm shallow region can be controled by concentration of the ion implant. And SiC was re-crystallized single poly-type after annealed at 1500°C. But, defects in end of amorphous region affect to recover the damaged structure .

Abstract: A kind of broken carrot defects which are not parallel to the step flow direction are observed on 4H-SiC epilayer surfaces. We use the molten KOH and polishing methods to reveal the structure and source of the broken carrots. It is shown that the broken carrot defects still contain the prismatic stacking fault (SF) and basal plane SF and originate from threading screw dislocation on the substrate. The presence of other substrate threading dislocation can disturb the expansion of prismatic SF. This leads to the appearance of the broken carrot.

Abstract: The conventional KOH etching method at elevated temperatures is an easy way to study SiC dislocations, but presents problems due to an increased etch rate. Here, we examine the application of low temperature KOH treatment for the analysis of dislocation cores and etch pits in SiC. A low energy scanning electron microscope (SEM) is effective to classify dislocation kinds. The scanning transmission electron microscope (STEM) observation of thick samples prepared by the in situ micro-sampling technique enables evaluation of detailed dislocation properties.

Abstract: The damage induced at the cut surface of SiC crystal by slicing were investigated by Raman scattering method and transmission electron microscopy. Electric discharge machining (EDM) predominately forms cracks, silicon, carbon and 3C-SiC by 6H-SiC pyrolysis and wiresawing with loose abrasive (WSLA) induces triangular crystal disordered area, stacking faults and dislocation loop bundles by stressing at the cut surfaces of SiC crystal.

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: 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: Micro-Raman characterization has been used as alternative technique to the photoluminescence in order to detect and study 4H-SiC stacking faults. The alteration of the crystalline stacking sequence perturbs the phonon-plasmon coupling which acts between the crystalline phonon modes and the electronic plasma, due to the doping element (N). The shape and the symmetry of the Longitudinal optical Raman mode is strongly correlated to the doping level of the material thus, through the monitoring of the Raman mode, the spatial morphology of the defect can be completely recovered and compared to the results provided by photoluminescence technique. The results show that such a technique allows a very fast inspection on large wafer, because it is totally independent of the stacking fault photoluminescence signals, which cover a large energy range, up to 0.7 eV.