Solid State Phenomena Vol. 342

Abstract: The feasibility of thin 4H-SiC layers bonded on an alternative carrier substrate for the application as substrate in SiC epitaxy is investigated. Epitaxial layers grown on such substrates are compared to those on state-of-the-art conventional substrates from different sources. The performance of the substrates is judged by the occurrence of killer defects in the epitaxial layer as analyzed using a PL scanning tool. Additional investigations on the material properties were carried out using X-ray topography and Atomic Force Microscopy, yielding information on the crystallinity, the lattice curvature, and the surface properties of the epitaxial layers.

Abstract: The recently introduced corona charge non-contact capacitance-voltage technique, CnCV, is analyzed considering the production needs of epitaxial SiC wafers. The interfering mechanism of charge dissipation on fresh epitaxial 4H-SiC is identified as surface diffusion and is effectively eliminated by optimized ultraviolet pretreatment (UVPT). It is shown that optimized UVPT increases the CnCV dopant measurement voltage range and the depth of profiling. Concurrent UVPT and measurement provides a practical solution for improving throughput for multiple wafers. Electrical defect mapping shows that UVPT reduces the effective defect size. This will be helpful to avoid defects in patterns used for CnCV dopant measurements.

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: The carbon vacancy (V_C) is a lifetime-killer defect that hinders the correct functionality of 4H-SiC bipolar devices. Until now, different methods based on carbon interstitial injection, have been proposed, in order to reduce its concentration. However, if on one hand these methods effectively reduce the V_C concentration in the epilayer, on the other they cannot prevent the re-generation of V_C occurring during the manufacture of a p-i-n diode, e.g., p+ implantation and activation. In the following contribution, we employ PIII of B for the formation of the anode for a p-i-n diode. We show that by PIII, it is possible to simultaneously form a p⁺n junction with a low concentration of V_C in the drift layer.

Abstract: We carried out chemical mechanical polishing (CMP) on commercially available 6 inch SiC wafers (epi-ready products) with slurries containing different abrasive types and evaluated the latent scratch density from the mapping measurement of the wafers using mirror projection electron microscope (MPJ). Comparing to the wafer before polishing, the latent scratch density decreased on the wafer polished with MnO₂+KMnO₄, while that increased by polishing with Al₂O₃+KMnO₄. The two-step polishing using first Al₂O₃+KMnO₄ and then SiO₂+H₂O₂ can reduce the latent scratch density to the same level as that with MnO₂+KMnO₄, but long polishing time is required because of the low polishing rate in the process with SiO₂+H₂O₂. We investigated the reason why MnO₂ slurry can suppress the occurrence of latent scratches by a polishing test on a wafer with an SiO₂ film on its (0001)Si surface. The results suggest the oxidation of the SiC surface is rate-determining step for polishing with MnO₂+KMnO₄. It was also found that wafers without an SiO₂ film could not be polished with only MnO₂ abrasives. Thus the mechanical contribution to polishing by MnO₂ abrasives in KMnO₄-based slurry is smaller than the chemical contribution, which can suppress the occurrence of latent scratches. KMnO₄-based slurry containing MnO₂ abrasives performs the CMP process with low latent scratch density in a time shorter than that containing Al₂O₃ or SiO₂ abrasives.

Abstract: The polyurethane coatings containing different concentration of graphene oxide were prepared. Their physicochemical properties were characterized by XRD and SEM. The tribological behaviors were also investigated by ring-on-block tests. Results revealed that the TDI adsorb on the surface of GO through reaction with O-H. The COF were extremely sensitive to the GO concentration of PU coatings filled. The COF of pure PU coating was 0.185, whereas it is sharply decreased when 1.0 wt% GO was added. Smaller COF was obtained as the GO concentration increase and to minimize when GO concentration is 2.0 wt%. Friction reduced mechanism of GO was further investigated. Two reasons were responsible for this phenomenon. The one was that the GO itself possessed the capacity of anti-wear and friction reduction. Another one was the GO dispersed in the PU coatings could increase the strength of the coatings by the mean, which was similar to dispersion strengthening.

Abstract: Ag-Bi coatings were synthesized on copper substrate using brush plating with a cyanide-free electroplating solution for electrical contact applications. Phase constituents, surface morphology, and microhardness of the deposited coatings were characterized. It is found that grain refinement into the nanosized range can be observed for the Ag-Bi coatings with dense and compact microstructure. The electroplated Ag-Bi alloy displayed an apparent hardness increase compared with the pure silver coating. Ag-Bi alloy coatings show promise in the field of electrical contact components used in the electrical power industry.

Abstract: Due to the huge impact of temperature on mechanical and tribological properties of polymer composites, polyimide composites reinforced with glass fiber and aramid fiber were fabricated. The composites were treated by the alternate temperature from-50 °C to 150 °C with 200 cycles. The comparation of the test results were analyzed and discussed before and after alternate temperature treatment.