Papers by Author: Kikuo Yamabe

Abstract: The failure mechanism of a SiC metal-oxide-semiconductor capacitor with a poly-Si gate electrode was investigated by time-dependent dielectric breakdown testing under a 200-nA constant current stress. The capacitor exhibited both hard and soft breakdowns. After dielectric breakdown in both cases, adjacent concaves were observed on the capacitor with a field-emission scanning electron microscope. Additional optical beam-induced resistance changes and photo-emission analysis of a capacitor after hard-breakdown located a failure point on the periphery of a group of adjacent concaves. Cross-sectional scanning transmission electron microscope observation revealed that a narrow, vertical defect had formed at this point on the SiC substrate.

Abstract: The electrical properties of SiO₂/4H-SiC(0001) was characterized, and it was confirmed that the NF₃ added oxidation in O₂ can achieve interface with low interface state density. Optimization of NF₃ added oxidation process was attempted to obtain films with both good interface properties and low leakage current. It was concluded that optimization of oxidation process should take account of obtaining proper balance among the rate of oxidation, which generates impurity carbon, the ability of carbon removal, and the rate of SiO₂ etching which also affects the leakage characteristics.

Abstract: The surface and interface roughness of SiO₂/4H-SiC(0001) was investigated in terms of Si emission from the interface and oxidation induced compressive stress. It was demonstrated that the SiO₂ surface roughness growth was strongly related with oxidation mechanism, as well as SiO₂ on Si substrate. A model for surface roughening was proposed with areal Si density and Young’s modulus to inclusively explain the surface roughness of SiO₂ on various substrates.

Abstract: Atomic force microscopy measurements are carried out on the surface and interface of SiO2 thermally grown on an atomically flat Si surface, and the uniformity of thickness on an atomic scale is investigated. Protuberances on the surface of SiO2 grown at 800 °C in 3.8 % O2 diluted by argon at the atmospheric pressure are generated in the initial stage of oxidation and subsequently increases in height at the same positions. The surface RMS value of SiO2 linearly increases up to the thickness of approximately 5 nm, which almost corresponds to what was called the initial oxidation thickness. This fact indicates that the roughness increase is related to the re-oxidation of SiO emitted from the Si/SiO2 interface during the initial oxidation. Additionally, the surface RMS value is saturated at a value of approximately 0.13 nm. A correspondence between the position of the dimples on the surface and the positions of the protuberances at the interface is also clear. The fact is the direct evidence of the local thinning of the thermally grown SiO2 films. Based on these results, an atomic scale thermal oxidation mechanism is discussed.

Abstract: We report a dynamic and microscopic investigation of electrical stress induced defects in metal-oxide-semiconductor (MOS) devices with high-k gate dielectric by using electron-beam induced current (EBIC) technique. The correlation between time-dependent dielectric breakdown (TDDB) characteristics and EBIC imaging of breakdown sites are found. A systematic study was performed on pre-existing and electrical stress induced defects. Stress-induced defects are related to the formation of electron trapping defects. The origin of pre-existing defects is also discussed in terms of oxygen vacancy model with comparing different gate electrodes.

Abstract: We have succeeded in imaging the leakage sites of hafnium silicate gate dielectrics of metal-oxide-semiconductor field-effect transistors (MOSFETs) by using electron-beam-induced current (EBIC) method. Leakage sites of p-channel MOSFETs were identified as bright spots under appropriate reverse bias condition when the electron beam energy is high enough to generate carriers in the silicon substrate. Most of the leakage sites were observed in the peripheries of shallow trench isolation. These results suggest that some process induced defects are the cause of leakage in these MOSFETs. Our observation demonstrates the advantage of EBIC characterization for failure analysis of high-k MOSFETs.