Materials Science Forum Vol. 1062

Abstract: Photoluminescence (PL) imaging provide defect and dislocation characteristics not only in a 4H silicon carbide (SiC) epilayer but also in a substrate. In this work, to detect a large-pit or a bar-shaped stacking fault (BSF) before epilayer growth, we employed PL under various detection conditions. A large-pit was detected as a dark spot on a 4H-SiC substrate due to dislocations orthogonal to a micropipe. The BSF was clearly observed as a bright rectangle by tuning the observation conditions. The finding indicates that device killing defects or dislocations should be detected as soon as possible and thus improve the yield.

Abstract: We propose the new practical and effective method, called Selective E-V-C (Expansion-Visualization-Contraction) technique, to screen out the basal plane dislocations (BPDs) which might cause the forward voltage degradation of SiC devices. Since the method can be adopted at the epi wafer receiving inspection process in early stage of production line, it may replace the very time-consuming so-called "burn-in" operation currently utilized in some device manufacturers.

Abstract: In the present work a deep characterization of 4H-SiC epi-layer was done. A thick layer was epitaxially grown through chemical vapor deposition (CVD) process in a horizontal hot-wall reactor in order to obtain a 250 microns thick epi-layer. This sample will be used as particle detector in hostile environments such as neutron detection in a nuclear fusion reactor. Raman and Photoluminescence (PL) spectroscopy have been used in order to evaluate the general status of epitaxy and, with the support of the Time Resolved Photoluminescence, also important properties such as carrier lifetime and diffusion length have been evaluated. Carrier lifetime evaluation before and after a thermal oxidation process at 1400° C for 48h was estimated, by considering a lifetime increment after oxidation process, due to the decrease of carbon vacancies. Finally, the influence of stacking fault (SF) defects on carrier lifetime was evaluated observing a decrease of the lifetime for the defects at 430 nm (2.88 eV) for both oxidated and non-oxidated samples.

Abstract: 3C silicon carbide is a semiconductor with remarkable properties, making it ideal for the development of long lasting devices, working in harsh environments and under high particle flows. The most significant obstacle to its wider diffusion is the presence of extended, bidimensional and linear defects in its crystal lattice. The purpose of this research is to automatically recognize defects from a TEM image by algorithm that calculates distances and angles.

Abstract: The inversion channel electron mobility in 4H-SiC MOSFETs with NO annealed gate oxides is still well below its theoretical limit. The physical reason behind the reduced mobility is not yet fully established but has for example been attributed to a high density of very fast interface traps close to the conduction band edge. These traps are not detected by high-low CV analysis at room temperature but are observed by conductance spectroscopy at low temperatures. In this study we demonstrate how conventional high-low CV analysis of MOS capacitors at cryogenic temperatures can be applied to detect and quantify these very fast traps.

Abstract: In order to selectively analyze active thin layers close to surface in power devices structures, Raman scattering is necessary with UV excitation. However, the Raman spectra of GaN are usually affected by the direct bandgap photoluminescence of the material, which interferes with the Raman measurements and decreases the quality and resolution of the Raman spectra. In this work, we demonstrate experimentally that nanostructured aluminum films deposed on GaN epitaxial layers decrease the influence of the photoluminescence on the resonant Raman spectra and increase its overall spatial resolution under UV illumination.

Abstract: Improvement of channel mobility is required to improve the performance of the inversion channel MOSFETs using diamond. The previous studies have suggested that high interface defect density (D_it) at the Al₂O₃/diamond (111) interface has a significant impact on the carrier transport property on a channel region. To investigate the physical origins of the high D_it, especially from microscopic point of view, here we investigate Al₂O₃/p-type diamond (111) interfaces using scanning nonlinear dielectric microscopy (SNDM). We find the high spatial fluctuations of Al₂O₃/hydroxyl (OH)-terminated diamond (111) interface properties and their difference by the flatness of the diamond surface.

Abstract: X-ray topography (XRT) presents itself as an attractive non-destructive method to replace industry-standard destructive KOH etching used to measure dislocation density. However, a production-line-compatible XRT has to employ a low scan speed in order to work well with automated image analysis, which makes it impractical for a high-volume manufacturing to scan an entire wafer. We introduce the “radial band” approach to sampling the entire wafer’s area with a single-pass 16 mm tall scan band. Such a band spans the entire range of radii and thus captures the typically strong radial dependence of dislocation density over the entire range, while mostly ignoring the typically weak angular dependence of dislocation density and averaging the inevitable noise over the 16 mm band height. The XRT scan time savings for this approach are roughly 15-fold and 20-fold for 150mm and 200mm wafers respectively.

Abstract: We theoretically study point defects in 3C-SiC for applications in Quantum Technologies, focusing on the neutral silicon vacancy, with an electron spin of 1, magnetically interacting with the SiC nuclear spin bath containing Si-29 and C-13 nuclei. Initially, the system's energetics are explored with ab-initio methods based on the Density Functional Theory. Thereon, we apply a Hahn-echo sequence on the electron spin and study the effects of the bath dynamics on the electron spin's coherence. The Electron Spin Echo Envelope Modulation (ESEEM) phenomenon, due to single nuclear spin flipping processes, and the overall decay, or decoherence, due to the electron spin's entanglement with the bath, are examined. We exploit the Cluster Correlation Expansion (CCE) theory for calculating an approximate version of the coherence function, at various orders of approximation, in order to associate the different coherence function behaviors to given n-body correlations within the bath.

Abstract: In this work, the interface between 4H-SiC and thermally grown SiO₂ is studied using low energy muon spin rotation (LE-μSR) spectroscopy. Samples oxidized at 1300 °C were annealed in NO or Ar ambience and the effect of the ambience and the annealing temperature on the near interface region is studied in a depth resolved manner. NO-annealing is expected to passivate the defects, resulting in reduction of interface traps, which is confirmed by electrical characterization. Introduction of N during annealing, to the SiC matrix, results in a thin, carrier rich region close to the interface leading to an increase in the diamagnetic asymmetry. Annealing in an inert environment (Ar) seems to have much lesser impact on the electrical signal, however the μSR shows a reduced paramagnetic asymmetry, indicating a narrow region of low mobility at the interface.