Motohiro Iwami

Raman study on the Ni/SiC interface reaction

Ni/SiC interface reaction was investigated by Raman scattering. The specimen consisted of a 200 nm Ni layer deposited on a both-side polished 6H–SiC wafer with postannealing at 500–1100 °C. Raman spectra were observed from both faces of the specimen, i.e., from the Ni layer side and from the opposite (SiC wafer) side. The spectra showed that nickel silicides were formed by annealing at above 500 °C, and diffusion of Si atoms into the Ni layer played a key role in forming an ohmic contact at above ∼900 °C. It was also found that carbon atoms that did not react with Ni formed nanometer-size clusters. This work clearly demonstrates that Raman scattering is useful for studying interface reactions between metallic electrodes and SiC.

Structural analysis of the heat-treated 4H(6H)-SiC(0001)Si surface

Abstract We have investigated heat-treated 4H- and 6H-SiC(001)Si surfaces using AES, LEED, EELS and STM in ultra high vacuum (UHV). √3 × √3 and 6 × 6 reconstructions were observed in the STM study at ∼1000 and ∼1200°C, respectively. On the other hand, 6√3 × 6√3 superstructure was observed by LEED at ∼1200°C. The AES p-p height ratio of Si ( LVV ) C ( KLL ) decreased at higher temperatures. EELS proved the existence of a graphite layer on top of the specimen surface. Considering these experimental results, the 6 × 6 reconstruction observed by STM can be explained as a moire pattern produced by a graphite layer sitting on top of the SiC surface.

Alloyed interface formation in the AuSi(111)2 × 1 system studied by photoemission spectroscopy

Abstract Room temperature deposition of gold (Au) on the Si(111)2×1 cleaved surface has been studied by photoelectron spectroscopy using synchrotron radiation. Binding energies of Si(2p) and Au(4f) and the splitting of the Au(5d) signal are changed with increasing coverage in a different manner below and above one monolayer coverage and reach to saturation values at 20–100 monolayers. The Au(4f) binding energy and the Au(5d) splitting at saturation are clearly different from those of pure Au metal. The origin of alloying in the AuSi(111)2×1 system is discussed from these results. A new model, “chemical bonding model” is proposed to explain the initial stage of the metallic overlayer formation in the AuSi(111) system.

Preparation of manganese silicide thin films by solid phase reaction

Abstract A thin film formation of MnSi and MnSi 1.7 on a silicon substrate through solid phase reaction has been studied, where MnSi 1.7 is one of the few semiconducting silicides, while MnSi is a metallic one. The growth process and electronic states of manganese silicides with composition of MnSi and MnSi 1.7 are investigated by several methods, including soft X-ray emission spectroscopy.

Construction of a Soft X-Ray Emission Spectroscopy (SXES) Apparatus and Its Application for Study of Electronic and Atomic Structures of a Multilayer System

A soft X-ray emission spectroscopy (SXES) apparatus was constructed using a grating monochromator. The resolution was sufficient to show differences in valence electronic structures of Si compounds including pure Si crystal. A nondestructive analysis of a Ni/Si(111) specimen with heat treatment was carried out using either a clear difference in Si L2,3 SXES spectra of Ni silicide and Si single crystals or the fact that the soft X-ray production depth increases in a solid with increasing energy of a primary electron, Ep. The electronic and atomic structures of the surface and interface of specimens adopted were clarified with Ep varying between 1.5 and 10 keV.

Silicon carbide: fundamentals

Abstract Fundamental issues of silicon carbide, i.e., characteristics, crystal growth, doping of impurity atoms, metal-SiC contacts, electronic devices, etc., are given. Applications for the detection of energetic particles are also shown.

Electronic Structure of Thin Gold Film Deposited on Silicon Substrate Studied by Auger Electron and X-ray Photoelectron Spectroscopies

Auger Electron Spectroscopy (AES) measurements of very thin ( \lesssim150 ?) gold (Au) films deposited on clean surfaces of silicon (Si) substrates are made in order to study Si/Au interface. The AES spectra taken from the surfaces of these Au films are composed of both Si and Au spectra suggesting that the interfaces are diffuse instead of sharp. The Si spectra show splitting and are different from those of pure Si. Since the same splitting can be observed in the specimen obtained by quenching from Si?Au eutectic liquid, X-ray Photoelectron Spectroscopy (XPS) is applied to the same kind of quenched specimen to investigate the origin of the splitting, through the changes in the XPS spectrum of Au d-band compared with that of pure Au. Itis proposed that Si in the diffuse interface region is metallic with 4 valence electrons (3s and 3p) to interact with 6s and 5d-electrons of Au.

A new application of soft X-ray spectroscopy to a non-destructive analysis of a film/substrate contact system: Carbonized-layer (ultra-thin-film)/Si(100)

Abstract Valence band, Si L2.3 and C K, soft X-ray spectroscopy (SXS) by the electron excitation method has been applied for the first time to a non-destructive analysis of hetero-interfaces, i.e. Si(100) surfaces with an ultra-thin-film on top, and the valence band spectra show a clear change from that of pure SiC to that of pure Si with the primary electron energy, Ep, from 0.85 to 4 keV. The present work explores the usefulness of this new application of the SXS method by studying experimentally the carbonized-layer (ultra-thin-film)/Si(100) system and the following results were obtained: the carbonized-layer is found to be a thin SiC layer which grows uniformly on the Si(100) surface, the SiC/Si(100) interface shows a rather sharp transition to the Si substrate and the thickness of the SiC layer is estimated to be ≲ 20 nm with possible undulation.

Observation of iron pileup and reduction of SiO2 at the Si‐SiO2 interface

It was found by secondary‐ion mass spectrometry in‐depth profiling technique that approximately 1×1020 iron atoms/cm3 accumulated at the Si‐SiO2 interface of oxidized silicon crystals where iron was introduced by the indiffusion prior to the oxidation at 1000 °C and above. The origin of iron accumulation is ascribed to the iron precipitation from the bulk silicon. It was also found that iron atoms that diffuse in through the bulk from the lapped backside of a preoxidized sample were trapped and aggregated at the front Si‐SiO2 interface. An interesting observation is shown that the above indiffusing iron also entered into the oxide region near the interface possibly to reduce SiO2.

Annealing effect on surfaces of 4H(6H)SiC(0001)Si face

Abstract We have investigated 4H- and 6HSiC(0001)Si faces prepared by heat treatment using Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) in ultra high vacuum (UHV). The following were elucidated: 3 × 3 reconstruction was observed on the surface prepared at ∼ 1000°C, while 6 × 6 superstructure was observed for a specimen prepared at ∼ 1200°C. The 6 × 6 reconstruction can be explained as a moire pattern produced by a graphite layer sitting on top of SiC surface. Also AES p-p height ration of Si(LVV) C(KLL) decreased at a higher temperature for 4HSiC than for 6HSiC, which could be due to the fact that the bond strength of 4HSiC is more than that of 6HSiC.