Akimasa Kinoshita

Photoemission study of 6H-SiC(0001)Si face

Abstract We have studied heat-treated 6H-SiC(0001)Si face with photoemission spectroscopy using synchrotron radiation (SR-PES) and low energy electron diffraction (LEED). LEED patterns of SiC 1 × 1, and graphite 1 × 1 were observed at annealing temperatures of 900, 1000, 1100 and 1250°C, respectively. By annealing at ≥ 1100°C the selvedge of ∼ 1 nm from the surface of 6H-SiC(0001)Si face becomes C-rich. surface structure might be caused by change of the Si state mainly in the depth of ≤ 0.5 nm of 6H-SiC(0001)Si face. At ∼ 1100 and ∼ 1250°C, graphite-layers are formed on the selvedge of 1 nm of the 6H-SiC(0001) surface although the number of graphite- and/or carbon layer at ∼ 1100°C could be less than that at ∼ 1250°C.

Application of Monte Carlo Simulation to a Structural Analysis for Two-Layered/Substrate System

Monte-Carlo simulation (MCS) using X-ray emission due to electron beam excitation is applied to determine the film thickness of a one-layer/substrate system. So far, the characteristic X-ray intensity has been used in this kind of simulation. However, it is difficult to utilize this method for a complicated system such as a multilayered structure. We succeeded in determining the layer thicknesses for a two-layered system, by a new method using characteristic Si-L2,3 soft X-ray emission band spectra. This method is shown to be promising for the quantitative analysis of multilayer and complicated systems. In this study, a quantitative analysis using both MCS and Si-L2,3 emission band spectra is demonstrated for the NiSi/NiSi2/Si system.

Electronic and Structural Analysis of 6H-SiC(0001̄)3×3 Reconstructed Surface

The 6H-SiC(000) C 3×3 reconstructed surface was studied by PES using synchrotron radiation, LEED and AES. This surface with contamination free was obtained by ex-situ surface treatment and annealing at 900°C without Si flux in the UHV. The p-p height ratio of AES signals, Si (LVV) / C (KLL), was measured as a function of annealing temperature for (000) surfaces to show a clear decrease with increasing temperature above 900°C. Discussion was given for the relation of this ratio with reconstructed surfaces. It was found that the photoemission spectra in the valence band region had the structure located at 0.9 eV below Fermi level. The signal should be originated from a surface state.

Evaluation of Schottky barrier height on 4H-SiC m-face for Schottky barrier diode wall integrated trench MOSFET

We proposed an Schottky barrier diode wall integrated trench MOSFET (SWITCH-MOS) for the purposes of shrinking the cell pitch and suppressing the forward degradation of the body diode. A trench Schottky barrier diode (SBD) was integrated into a trench gate MOSFET with a wide shielding p+ region that protected the trench bottoms of both the SBD and the MOS gate from high electrical fields in the off state. The SBD was placed on the trench sidewall of the plane (m-face). Static and transient simulations revealed that SWITCH-MOS sufficiently suppressed the bipolar current that induced forward degradation, and we determined that the optimum Schottky barrier height (SBH) was from 0.8 to 2.0 eV. The SBH depends on the crystal planes in 4H-SiC, but the SBH of the m-face was unclear. We fabricated a planar m-face SBD for the first time, and we obtained SBHs from 1.4 to 1.8 eV experimentally with titanium or nickel as a Schottky metal.

Characterization of the buried interface in a Ni (film)/3C-SiC (substrate) system using SXES

We investigated the interface reaction between Ni (film) and 3C-SiC (substrate) after heat treatment by soft X-ray emission spectroscopy (SXES). Si atoms were found to react with Ni atoms at the interface by heat treatment at 600–800°C. The reacted product was identified as Ni2Si. Carbon atoms are concluded to be in a graphite-like state in the reacted film from the spectral shape of the CKα. Those carbon atoms were found to be distributed around the interface region.

Application of Monte Carlo Simulation to Structural Analysis by Soft X-Ray Emission Spectroscopy for a Silicide/Si-Bulk System

A Monte-Carlo (MC) simulation is applied to the quantitative microanalysis of a film/substrate system. The characteristic X-ray intensity is used in this simulation. However, it is difficult to determine the film thickness for a multilayer/substrate system which consists of two elements in this method using characteristic X-ray intensity only. In order to overcome this difficulty, we utilized the characteristic Si–L2,3 soft X-ray emission band spectra which have their own spectral shapes for silicides and Si, and are expected to be superior to the conventional method using band X-rays only. In the measurement of the Si–L2,3 spectrum for a silicide/Si system at a certain incident energy, the obtained Si–L2,3 spectrum exhibits the increasing characteristic of the film material spectrum with the increase in film thickness. By using this characteristic, quantitative analysis using both MC simulation and Si–L2,3 emission band spectra is demonstrated for the CoSi2/Si system in this study.

Positron Trapping Sites Originating from Oxide Interfaces on 4H-SiC C(0001)- and Si(0001)-Faces

Gate oxide layers grown by dry and wet oxidation on 4H-SiC C(0001)- and Si(0001)-faces have been measured by positron annihilation spectroscopy. The incident positron energy, which corresponds to the peak of Doppler-broadening W-parameter curves, was chosen to characterize the SiC/oxide interfaces. Positron trapping sites with lifetimes in the range of 0.16–0.32 ns were detected, and the lifetimes for the C(0001) face were longer than those for the Si(0001) face. Age–momentum correlation measurements revealed that the origin of these trapping sites is neither the SiC bulk nor the SiC vacancies, suggesting that defective oxide layers exist at the interface.

A pn-SiC diode as a radiation detector

We evaluated pn-SiC (silicon carbide) particle detectors exposed to 5.486 MeV alpha particles from a sealed radioactive source of /sup 241/Am and 3.26 eV (380 nm) pulsed Ultra-Violet (UV) light at 100 Hz from a Light Emitting Diode (LED). The pn junction SiC diode was made by the implantation of phosphorus (P) ions (140, 60, 90 keV) into p-type 6H-SiC epitaxial layers (5 /spl mu/m) grown onto p/sup +/-type substrates. The mean pulse height from detector increased with the supplied reverse bias voltage for each irradiation, alpha particles and UV light. We discuss relation of the pulse height distribution obtained by the UV light and the alpha particles to the depletion width with diffusion length of carriers.