Papers by Author: Isaho Kamata

Abstract: To reduce manufacturing costs, high-quality 150 mm 4H-SiC wafers were grown at over 1.5 mm/h by high-temperature chemical vapor deposition. The dislocations in the initial growth stage did not increase compared with those in the seed crystal. The dislocation densities decreased during crystal growth, and the densities of threading dislocations and basal plane dislocations at the growth thickness of 7.1 mm were 1186 and 211 /cm², respectively. The resolved shear stress, which is the cause of the increase in dislocations during growth, was calculated based on thermal fluid simulations; the shear stress of the grown crystal with a flat surface was small compared with that of the convex-shaped crystal. The dislocations did not increase likely because the crystals grown at high speeds were relatively flat. In addition, the decrease in dislocations was attributed to the frequent annihilation of dislocations due to the growth at a high temperature (2490 °C).

Abstract: 4H-SiC surfaces before and after epitaxial growth (substrate and epitaxial layer surfaces) were investigated by mirror projection electron microscopy (MPJ) and atomic force microscopy (AFM). On the epitaxial layer surface, two types of short-step-bunchings (SSBs) were observed, one of which featured double grooves and protrusion perpendicular to the step-flow direction and the other, a single groove and protrusion. We also investigated the substrate surface and detected features of sub-surface damage and dislocations. These surfaces were compared and the relationship between the SSBs on the epitaxial layer surface and sub-surface damages and dislocations on the substrate surface were discussed.

Abstract: The effects of high-speed wafer rotation for 4H-SiC epitaxy in newly developed 150 mm vertical reactor is investigated by simulation analysis. The simulation model shows a good agreement with experimental results. It is revealed that a combination of high-speed wafer rotation as high as 1000 rpm and relatively high system pressure of 267 mbar is effective to reducing boundary layer thickness above the 4H-SiC wafer, and greatly enhances the epitaxial growth rates. The growth rate increase ~2 times using the combination of high-speed wafer rotation and relatively high system pressure.

Abstract: Possibilities of very fast 4H-SiC crystal growth using a high-temperature gas source method are surveyed by computational simulation and experimental studies. The temperature range suitable to obtain high growth rates are investigated by simulating temperature dependences of growth rates for H₂+SiH₄+C₃H₈ and H₂ +SiH₄+C₃H₈+HCl gas systems. Simulation and experimental results demonstrate that an increase in source gas flow rates as well as gas-flow velocities enhance growth rates. High growth rates exceeding 1 mm/h are experimentally obtained using both gas systems. Single crystal growth on a 3-inch diameter seed crystal is also demonstrated.

Abstract: This paper demonstrates high-resolution photoluminescence (PL) imaging and discrimination of threading dislocations in 4H-SiC epilayers. Threading screw dislocations (TSDs) and TEDs are distinguished by differences in PL spot size and spectrum. We found that TEDs are further discriminated into six types according to their Burgers vector directions by the appearance of PL imaging. Cross-sectional PL imaging reveals inclination angles of threading dislocations across a thick epilayer.

Abstract: This paper reports on evidence of high-quality and very fast 4H-SiC crystal growth achieved using a high-temperature gas source method. The formation of threading screw dislocations (TSDs) during crystal growth was examined by comparing synchrotron X-ray topography images taken for a seed and grown crystals, while the generation of a high density of new TSDs is observed under improper growth condition. High-quality crystal growth retaining the TSD density of the seed crystal was accomplished under an improved condition, even for a very high growth rate of 2.1 mm/h.

Abstract: This paper introduces our recent challenges in fast 4H-SiC CVD growth and defect reduction. Enhanced growth rates in 4H-SiC epitaxial growth by high-speed wafer rotation and in a high-temperature gas source method promoting SiC bulk growth by increasing the gas flow velocity are demonstrated. Trials and results of deflecting threading dislocations by patterned C-face 4H-SiC epitaxial growth are also shown.

Abstract: A single wafer type 150 mm vertical 4H-SiC epitaxial reactor with high-speed wafer rotation was developed. The rotation of the wafer at high speed significantly enhances the growth rate, and high growth rates of 40–50 μm/h are possible on 4°off-cut 4H-SiC substrates. In addition, a low defect density and smooth surface without macro step bunching can be achieved. Excellent uniformity of thickness and doping concentration was obtained for a 150 mm wafer at a high growth rate of 50 μm/h.

Abstract: Photoluminescence images and spectra of threading screw dislocations (TSDs) and threading edge dislocations (TEDs) were obtained and compared with synchrotron X-ray topography images. Discrimination between TSDs and TEDs by analysis of PL spot size in the imaging technique as well as PL spectra of the dislocations in a near infrared region is demonstrated. We also have succeeded in cross-sectional PL imaging of threading dislocations in a thick epilayer.

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.