Materials Science Forum Vols. 740-742

Abstract: 4H-SiC epitaxial films grown on 4H-SiC in CVD reactor VP508GFR are investigated using FTIR, X-Ray diffraction, C-V measurements, stylus profiler and DIC optical microscopy.

Abstract: We discuss a correlated reduction in the cross sections of two neighboring micropipes (MPs) along their axes (generally parallel to the growth direction). Such variations in MP cross sections can lead to MP healing. We provide experimental evidence of this effect and discuss its reasons and a possible mechanism. Our main idea is that MPs can remotely interact with each other by the exchange of full-core dislocations. We propose a theoretical model describing the energetics of this process.

Abstract: Basal plane dislocations (BPDs) converting to threading edge dislocations (TEDs) has been observed in 4H-SiC epilayers after thermal annealing at high temperatures. Grazing incidence reflection synchrotron X-ray topography was used to investigate the dislocation behaviors. It is argued that the conversion is achieved by constricted BPD segments cross-slipping to the prismatic plane and TED glide on its slip plane. Higher conversion ratio and better surface morphology were achieved by performing ion implantation and annealing before epitaxial growth.

Abstract: The bulk properties of thermally grown SiO₂ on 4H-SiC(0001) substrates were thoroughly investigated by capacitance-voltage (C-V) measurement, atomic force microscopy (AFM), spectroscopic ellipsometry (SE), x-ray photoelectron spectroscopy (XPS), and secondary ion mass spectrometry (SIMS). The equivalent oxide thickness (EOT) extracted from the capacitance-voltage (C-V) characteristics of TiN/SiO₂ capacitors was proportional to the physical thickness (T_phys), but the slope of the linear fit was found to be 1.11, indicating that the permittivity of SiO₂ on 4H-SiC formed by thermal oxidation is only about 3.5, which is lower than the commonly accepted value of 3.9. Since XPS analysis revealed that the oxide of SiC was stoichiometric and the atomic concentration of residual carbons in the oxide measured by SIMS was sufficiently low (10¹⁷ cm^-3), the low permittivity of thermal oxides of 4H-SiC may originate from the reduced bulk density, which can be predicted by the Clausius-Mossotti relation.

Abstract: 10 kV class 4H-SiC bipolar diodes have been fabricated. Two different edge terminations (Mesa/JTE or MESA/JTE with JTE rings) with two different junction bend radius have been designed and tested. Measurement results show that the inclusion of JTE rings improve the edge termination efficiency. The measurements indicate also a better reverse performance of diodes with larger bend radius.

Abstract: In this study, a 6 inch 3C-SiC wafer has been grown and processed to realize an Al⁺-implanted layer underneath the film surface. The structural damaging has been carefully analyzed by X-Ray Diffraction (XRD) and micro-Raman spectroscopy. Raman analysis on a grazing angle polished film, after the implantation process, has been conducted and a spectral region (between 825 and 925 cm^-1) has been identified as an interesting footprint of the crystal damaging. Thermal treatments on implanted samples at doses as low as 4x10¹⁴ cm^-2 have shown a capability of the 3C-SiC crystal structure to recover from damaging. Reciprocal space mapping on (004) 3C-SiC lattice points suggests a total recovery at an annealing temperature of 1350 °C.

Abstract: 3C-SiC have been epitaxially grown through vapour phase expitaxy under a different grow conditions. Key electrical properties of these SiC layers have been characterised by fabrication and measurement of metal-SiC-metal devices. The electrical properties of SiC grown at different conditions have been analysed based on their structural and crystalline quality.

Abstract: Threshold voltage (V_TH) instability, channel mobility and oxide reliability have been investigated for meta-oxide-semiconductor (MOS) structures on 4H-SiC (11-20) face using various gate oxidation procedures. Channel mobility of n-channel MOSFET with a gate oxide by pyrogenic oxidation is higher than that by dilute-DRY oxidation followed by a nitrous oxide (N₂O) post-oxidation annealing (POA). On the other hand, oxide reliability for the pyrogenic oxides is poor compared with the dilute-DRY/N₂O oxides. A Hydrogen POA is effective in an improvement of channel mobility for both oxides, but causes a harmful effect on V_TH stability. Temperature dependence of V_TH instability indicates that MOS structure grown by dilute-DRY followed by N₂O POA is suitable for a practical use of SiC MOS power devices.

Abstract: A comparative research of the cathodoluminescence and electrical characteristics of the samples 4H-SiC irradiated with high energy Xe ions (167 MeV) in wide range fluencies 4x109 –1x1011 cm-2 at temperatures 250C and 5000C are presented. After irradiation these samples were thermal annealed at 5000C for 30 min. Far-action effect at a depth of more than one order of magnitude of stopping distance was observed under Xe ions irradiation in 4H-SiC. An increase of the ion Xe fluencies increased the concentration of radiation-induced defects that resulted in rise of the compensation effect of conductivity in samples. Irradiation of 4H-SiC by Xe ions at 5000C was accompanied with "dynamic annealing" some low-temperature radiation-induced defects, which led to a partial recovery of the electrical characteristics of devices. The thermal annealing of irradiated samples led to additional partial annealing of radiation defects, which increases the radiation resource of devices based on 4H-SiC.

Abstract: In this paper, we present the formation of extended epitaxial defects, such as carrot defects, from threading screw dislocations (TSDs) with a morphological feature at the surface of the substrates. It was confirmed using highly sensitive surface observation, atomic force microscopy (AFM) and KOH etching that the surface roughness around a TSD was observed as the morphological feature and TSDs with such a morphological feature formed extended epitaxial defects with high frequency of appearance compared to usual TSDs without any features. The density of TSDs with such morphological feature depended on the polishing methods. Furthermore, we observed that the formation and shapes of extended defects from TSDs with such morphological feature were affected by step-bunching at the surface of the epilayers.