Materials Science Forum Vol. 1062

Abstract: In this work, we investigate, by μ-Raman spectroscopy the distribution of stress field on a micro-machined structures. They were realized on a 3C-SiC substrate, grown on a Silicon On Insulator (SOI) wafer, after lithography and etching processes. Various structures, such as strain gauge, single and double clamped beams, were analyzed, showing different stress distributions. All the structures show an intense variation of stress close to the undercut region.

Abstract: A systematic capacitance-voltage (C-V) and time-dependent dielectric breakdown (TDDB) study on silicon carbide (SiC) metal-oxide-semiconductor capacitors (MOSCAPs) that use silicon dioxide (SiO₂) is shown in this paper. Oxides were formed using atomic layer deposition (ALD), low-pressure chemical vapour deposition (LPCVD) or direct thermal growth in nitrous oxide (N₂O) ambient, where both deposited oxides were post-deposition annealed in N₂O ambient, too. The electrical characterisation results reveal that the ALD-deposited and N₂O-annealed oxides show the best capacitance-voltage (C-V) characteristics, with flatband and hysteresis voltages (V_FB) averaging 1.44 V and 0.41 V, respectively. When measuring the leakage current levels at 175°C, the ALD-deposited MOSCAPs’ breakdown electric fields are averaging similar to their counterparts at 9.71 MV/cm. MOSCAPs which utilized ALD-deposited SiO₂ also showed 29% and 345% increased average injected charge-to 63% failure (Q_BD,63%) at 9 MV/cm and 9.6 MV/cm, respectively, when comparing these devices to their direct thermally grown SiO2 counterparts.

Abstract: A non-destructive technique for the characterization of the doped regions inside wide bandgap (WBG) semiconductor structures of power devices is presented. It consists in local measurements of the surface potential by Kelvin Probe Force Microscopy (KPFM) coupled to micro-Raman spectroscopy. The combined experiments allow to visualize the space charge extent of the doped region using the near-field mapping and to estimate its dopant concentration using the Raman spectroscopy. The technique has been successfully applied for the characterization of a WBG SiC (silicon carbide) device.

Abstract: We investigate surface potential fluctuations on SiO₂/SiC interfaces by local capacitance-voltage profiling based on time-resolved scanning nonlinear dielectric microscopy. As experimental indicators of surface potential fluctuations, we measured the spatial fluctuations of local capacitance-voltage and its first derivative profiles through the detection of the voltages at the infection points of the profiles. We show that, even for a sample with a nitrided interface with low interface defect density, the fluctuations of the measured voltages are much higher than the thermal energy at room temperature. This indicates the existence of high potential fluctuations, which can give the significant impacts on the carrier transport at the SiO₂/SiC interface of SiC metal-oxide-semiconductor field effect transistors.

Abstract: This paper presents micro-OBIC measurements performed at different voltages on two devices protected by narrow field rings. At the surface of the device #1, a polyimide layer was deposited during the fabrication process. On the contrary, passivation layer was removed on device #2. Thanks to the micro-OBIC micrometer spatial resolution and the spot size carefully focused, small gaps in the range of 1 μm can be visible on OBIC profiles. Thus, the variation of the μ-obic accurately reflects the topology of each ring.

Abstract: In this work, we compare different quasi-static capacitance-voltage measurement systems by analyzing 4H-SiC n-type MOS capacitors and studying the influence of systematic errors when extracting the interface trap density (D_it). We show that the extracted D_it strongly depends on the calculation of the surface potential due to variations of the integration constant. In addition, the ramp-rate during the quasi-static measurement is identified as a sensitive measurement parameter whose noise level is amplified in the D_it extraction.

Abstract: Synchrotron X-ray topography techniques are used to characterize the microstructures in gallium nitride materials being developed for selective area doping for power electronic applications. Bulk substrates grown by different methods, epitaxial layers that are subject to ion implantation, annealing, etching and regrowth are characterized by X-ray topography in grazing incidence geometry and X-ray rocking curve topography. Strain and tilt maps of ion implanted epitaxial layers and etched and regrown wafers are generated. From the X-ray topographs, it is concluded that ammonothermal grown substrates show the highest quality among other types and most suitable for high-end electronic applications. It is also revealed that epitaxial growth, ion implantation and the annealing process do not change the dislocation distribution, but ion implantation introduces damage, strain and lattice bending effect, which are removed after annealing. Inductively coupled plasma (ICP) etching gives rise to strain variations in the wafer, while using tertiary butyl chloride (TBCl) to etch the wafer does not affect the strain distribution and can remove some damage from a preceding ICP etching process.

Abstract: Synchrotron monochromatic beam X-ray topography has been widely applied to characterize structural defects in SiC crystals. Using ray tracing simulations, the dislocation contrast in X-ray topography under strong diffraction conditions (diffraction takes place at or near Bragg angle) has been intensively investigated. However, the contrast and the configurations of the dislocation images recorded under weak diffraction conditions have not been fully investigated. Recently, we demonstrated that the contrast of dislocations in synchrotron grazing incidence topography under weak diffraction conditions can also be analyzed and interpreted by applying ray tracing principles. In this study, we have extended the application of the ray tracing method to analyze the dislocation contrast in weak beam synchrotron back reflection and rocking curve topography. The ray tracing method is shown to successfully simulate and correlate the contrast of threading screw dislocations at various positions on the rocking curve and thus allow to determine the signs of Burgers vectors.

Abstract: 4H-SiC wafers with 12 um epilayer were implanted at the Tandem Van de Graaff facility at Brookhaven National Laboratory with tunable energy from 13 MeV up to 66 MeV. Lattice strains introduced by the implantation process were characterized in detail by synchrotron rocking curve X-ray topography (SXRCT) and reciprocal space maps (RSMs). It is observed that the strain levels correlate with the atomic mass and energy of acceleration of the dopant atoms.

Abstract: Understanding the depth from which contrast from dislocations is still discernible (the effective penetration depth of the X-rays) in grazing-incidence synchrotron monochromatic beam X-ray topography is of great interest as it enables three-dimensional dislocation configuration analysis and accurate density calculations. To this end, systematic analysis has been performed of topographic and ray-tracing simulated contrast of basal plane dislocations with different Burgers vector and line direction combinations, and a universal method to determine the effective penetration depth based on ray tracing has been developed. This study reveals that the observable dislocation contrast depends on the effective misorientation associated with the dislocation modulated by the photoelectric absorption effect. The dislocations with larger effective misorientation tend to have longer projected length and correspondingly deeper effective penetration depths.