Papers by Keyword: Off-Orientation

Abstract: The C-face (0001) 4H-SiC surface morphology produced by etching using chlorine trifluoride gas was studied, focusing on the influence of the off-orientation. The etching pit at the 4^o off-oriented surface was formed at a temperature higher than 973 K, which was higher than 623 K for the on-axis surface. At 1073 K, the hexagonal-shaped etching pits were observed after the etching at the chlorine trifluoride gas concentration of less than 3 %. In the temperature range lower than 900 K, the mirror surface could be maintained after the etching. Thus, the mirror surface and the pitted surface are expected to be formed on the 4^o off-oriented surface by means of appropriately adjusting the parameters, such as the temperature and the chlorine trifluoride gas concentration.

Abstract: SiC crystal ingots were grown on 6H-SiC dual-seed crystal with different surface properties by a PVT (Physical Vapor Transport) technique. And then SiC crystal wafers sliced from the SiC ingots were systematically investigated in order to find out the dependence of surface properties for seed on the polytype formation. While n-type SiC crystals exhibiting the 4H polytype were grown on seed crystal having high root-mean-square (rms) value, 6H-SiC crystals were grown on seed having lower rms value. However, 6H polytype was maintained on on-axis and off-axis seeds during the entire growth period. The crystal quality of 6H-SiC single crystals grown on on-axis seed were revealed to be slightly better than that of 6H-SiC crystal grown on off-axis seed.

Abstract: C-plane substrates with off-orientation to <1120 > may stabilize the grown polytype, but the stacking fault density (SFD) increases from zero in the on-axis sample to 4500 cm-1 (7.7° off). The SF form preferentially at the seed-crystal-interface by a kinetically induced rearrangement of surface ad-atoms on m-facets. Most SF start in bundles with an average distance of 100 .m, which are subdivided in smaller bundles with 8 .m distance. They start preferentially from the upper corner of the vertical non-polar plane of bunched steps, which may be composed of small pyramids with m-facet surfaces. The dislocation density could decrease with increasing SFD by a pinning mechanism.

Abstract: This work presents results on the growth of thick epitaxial layers on 4° off-oriented 4HSiC in a commercially available hot-wall CVD system. Results on background doping level, homogeneity of thickness and doping, and run-to-run reproducibility will be shown. Defect structures we observed on 4° off-oriented substrates only are discussed. AFM measurements are presented to show the degree of step-bunching. 6.5 kV PiN-diodes with an active device area of 5.7 mm2 were fabricated and electrically characterized. In spite of the surface defects and stepbunching, up to 50% of the devices per wafer fulfilled our strict yield criteria even at 6.5 kV. Up to the onset of avalanche, the devices exhibited extremely low leakage currents. These results turn the cheaper 4° off-oriented substrates into a promising choice for producing higher volumes of highvoltage SiC power devices at reasonable costs.