Papers by Keyword: Etch Pit

Abstract: 4H-SiC homo-epitaxial film was grown by adding HCl gas with a high Cl/Si ratio in CVD process, and defect formation and origin of the defect were investigated by confocal differential interference contrast (CDIC) microscope, PL imaging and normal differential interference contrast (DIC) microscope. It was found that a large number of large bumps are formed on the film grown at a high Cl/Si ratio of 30, and a large number of PL defects on bare substrate before the film growth are also observed. Coordinates where the bumps on the film are observed were good agreement with those where the PL defects on the bare substrate are observed. An etch pit sample on reproduced substrate from which epitaxial film was removed was fabricated by etching process using molten KOH+Na₂O₂, and some types of etch pits which might be originated from threading edge dislocations (TEDs), threading screw dislocations (TSDs) and basal plane dislocations (BPDs) in the substrate were observed. The coordinates where the etch pits on the reproduced substrate are observed were also good agreement with those where the bumps on the epitaxial film are observed. Therefore, it was clarified that a large number of the bumps abnormally grown on the epitaxial film are originated from the dislocations in the substrate.

Abstract: To reduce the on-resistance in vertical power transistors, backside thinning is required after device processing. However, it is difficult to thin silicon carbide (SiC) wafers with a high removal rate by conventional mechanical processing because their hardness and brittleness cause cracks and chips during thinning. Therefore, the authors have attempted to thin SiC wafers using plasma chemical vaporization machining (PCVM), which is plasma etching using high-pressure plasma. PCVM has a high removal rate because of the high radical density in the high-pressure plasma, and it does not form a damaged layer on the processed surface because of the low ion energy. The authors have already achieved a very high removal rate of 15.6 μm/min by PCVM. However, many etch pits were generated on the wafer during PCVM in these high-speed machining conditions. Therefore, this study, using molten potassium hydroxide (KOH) etching, investigated the cause of such etch pits and found that they may stem from threading screw dislocation in the wafers. In addition, this research considered a process for reducing an etch pit size and succeeded in doing so by controlling wafer temperature.

Abstract: In order to understand the crystal defects of beta-gallium oxide (β-Ga₂O₃) in more detail, we classified the crystal defects of a 2-inch substrate of β-Ga₂O₃ (001) single crystal. As a result of observing the etch pits formed by molten alkali etching using scanning electron microscope (SEM) and atomic force microscope (AFM), we succeeded in observing six different etch pit shapes. These etch pit shapes are categorized into “Cicada I type”, “Cicada II type”, “Cannonball type”, “Trapezoid type”, “Bar type”, and “Shell type”. We consider that “Cicada I type” and “Cicada II type” are etch pit shapes caused by planar defects, and “Cannon ball type” is etch pit shapes due to dislocations. In addition, “Trapezoid type”, “Bar type”, and “Shell type” are deduced the result of surface morphology.

Abstract: We have studied threading dislocations (TDs) in 4H-SiC by means of X-ray topography (XRT) taken under 6 equivalent g-vector of 11-28 and two different chemical etching methods. Threading screw and mixed-type dislocations (TSDs and TMDs) can be distinguished and the direction of the a-components of TMDs can be determined by XRT. Efforts have been made to examine if there are features of etch pits that can be used to distinguish TMDs from TSDs.

Abstract: Threading dislocations (TDs) in an HVPE-grown free-standing GaN substrate have been studied by means of etch pit method using molten KOH+Na₂O₂ solution, cathodoluminescence (CL) mapping and transmission electron microscopy (TEM). We have focused on the correlation between (1) Burgers vectors of TDs, (2) their appearances as dark spots in CL image, and (3) geometries of corresponding etch pits. Based on the above results, dislocation categorization for GaN by using etch pits or CL is discussed.

Abstract: Threading dislocations (TDs) in 4H-SiC have been studied by comparing etch pits formed by NaOH vapor etching with results of synchrotron monochromatic-beam X-ray topography (XRT) taken under different g-vectors. Burgers vectors determined based on XRT results were utilized to investigate the etch pit characteristics of edge (TED), screw (TSD) and mixed (Burgers vector b=c+a, TMD) threading dislocations. It has been found that pit formation by NaOH vapor etching was very different to that by conventional molten KOH etching. We discuss the possibility of using NaOH vapor etching to distinguish TMDs from TSDs, and report a variety of characteristic etch pits formed by this method and their correlations to dislocation behavior.

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: An etch pit shape of off-angled 4H-SiC Si-face formed by different halogen gases such as chlorine trifluoride (ClF3) and a mixed gas (O2+Cl2) of oxygen and chlorine in nitrogen (N2) ambience has been studied. One kind of etch pit with the crooked hexagon was formed at etching temperature under 500oC. The angle of etch pit measured by the cross-sectional atomic force microscope image was about 10o from the [11-20] view. A dislocation type of the etch pit was discussed in comparison with the etch pit shape and an X-ray topography image.

Abstract: The etch pits on the C-face 4H-SiC substrate was produced by chlorine trifluoride gas at various temperatures. The etch pit density showed the comparable value to the current dislocation density level of the Si-face 4H-SiC, when the etching was performed around 713 K. Thus, the etch pit density obtained by this technique is expected to reveal the crystal quality.

Abstract: The wide size distribution of the hexagonal etch pit of screw dislocations (SD) in 4H-SiC wafer was found in spite of the narrow size distribution of the SD pit in epitaxial film. Calculation on the basis of the strain energy equation indicated that etch pit size depends on the Burgers vector and dislocation tilt. Size variation of SD etch pits in 4H-SiC wafer fabricated by sublimation method is explained to be caused by the dislocation tilt by observing the sizes and the positions of etch pits from the surface of the epitaxial film to the inside of 4H-SiC wafer. The SDs in 4H-SiC wafer fabricated by sublimation method propagate to c-axis direction in macroscopic but changing tilt in microscopic.