Hatsuo Nakamura

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.

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.

Nondestructive depth profiling using soft X-ray emission spectroscopy by incident angle variation method

We constructed a sample reclining stage for soft X-ray emission spectroscopy (SXES), where we intended to carry out nondestructive depth profiling using an incident angle variation (IAV) method. The penetration depth of an incident electron decreases with a reclining sample stage. One of the characteristics of the IAV method is that the incident electron beam energy is constant; thus, it is easy to obtain information related to a quantitative analysis of the integrated intensity of soft X-ray emission spectra. This method has been applied for a specimen with NiSi2/Si(111) structure. We have analyzed the change in shape of the Si L2,3 emission band spectrum in a region of the Si substrate to the NiSi2 layer, and have shown that we can determine the distribution of the Si element from the integrated intensity of Si L2,3 emission spectra.

Soft X-ray emission spectroscopy study of CaF2(film)/Si(111) : non-destructive buried interface analysis

Abstract A soft X-ray emission spectroscopy (SXES) study under an energetic electron irradiation is first applied to a non-destructive buried interface analysis of a CaF 2 (film ∼ 40 nm)/Si(111) contact system, where the energy of primary electrons, E p , is ≤ 5 keV. The present work has explored the usefulness of the application of the SXES method to the interface study to give rise to the following findings: the CaF 2 /Si(111) interface shows rather sharp transition from the top CaF 2 to the substrate Si, there certainly is a Ca-silicide layer at the CaF 2 /Si(111) interface, the thickness of the silicide layer is estimated to be less than several nm, and the e-beam excited SXES non-destructive study is very powerful to analyze a specimen with rather thick top film (> 40 nm) and thin interface layer (

Ni-silicide formation : dependence on crystallographic orientation of Si substrates

We have analyzed the influence of the crystalline orientation of Si substrates on Ni-silicide formation. Ni-silicide/Si(111) and (100) samples formed through solid-phase reaction (SPR) were examined using soft X-ray emission spectroscopy (SXES), transmission electron microscopy (TEM) and grazing incidence X-ray diffraction. The formation of δ-Ni2Si and NiSi on Si(100) substrate occurs at a lower temperature than that on Si(111). However, the NiSi2 region is found to be formed only on the Si(111) substrate at a lower temperature (Ta=500°C) than previously reported. The NiSi2 regions are located at the interface region of NiSi/Si(111) and have a small island structure. On Si(100) substrates, only the NiSi layer is stably formed in the heat-treatment temperature range of 250-700°C.

Compositional analysis of semiconductor heterojunctions: Structure of SiC (thin buffer layer)/Si(100) system

Abstract Semiconductor heterojunctions of SiC (thin buffer layer)/Si (substrate) were studied by ~100 keV ion scattering. The thickness of the buffer layer was estimated to be ~ 7 nm. The structure of the surface and the interface layer was clarified by measurements under random and channeling-blocking conditions. From the experimental results it is concluded that the thin SiC layer grows epitaxially on an Si(100) surface with a little distortion layer near the interface region between the SiC film (buffer layer) and the Si substrate.

Valence band electronic state of transition-metal silicide TiSi2 studied by soft X-ray emission spectroscopy (SXES)

A soft X-ray emission spectrum (SXES) due to a transition from the valence band to an electron excited Si-L2, 3 level for TiSi2, a transition metal silicide, has shown a clear sharp peak at hν, photon energy, ~98 eV. From the SXES study, it is concluded that a fair amount of the Si s-like electronic state is included in the upper half, especially at the Fermi edge, of the valence band density of state (VB-DOS) of TiSi2. This fact is in clear contrast to dominant proposals given so far, where it is claimed that the upper part of the VB-DOS of TMSis is constructed only by electronic states due to transition metal(d)-Si(p) hybridization.

Valence Band Density of States of the Iron Silicides Studied by Soft X-Ray Emission Spectroscopy.

Electronic states of manganese silicides with the composition of MnSi or MnSi 1.7 were investigated by soft X-ray emission spectroscopy. The formation of MnSi and MnSi 1.7 with single phase was identified by X-ray diffraction. Si-K β and Si-L 2,3 emission-band spectra were measured, where the Si-K β reflects the valence-band density of states with p-symmetry and the latter reflects the one with s- and/or d-symmetry. The spectrum of Si-L 2,3 for MnSi 1.7 was different from that of MnSi. The origin of this difference is discussed in comparison with those of other silicides.

Study of Cr Silicide Formation on Si(100) Due to Solid-Phase Reaction Using Soft X-Ray Emission Spectroscopy

Cr silicide formation on Si(100) substrate is studied by means of an alternative analysis technique: soft X-ray emission spectroscopy (SXES). Intermixing between chromium and silicon is observed at annealing temperatures ≥400° C. A nondestructive depth profile analysis shows that CrSi2 grows homogeneously on Si(100) for specimens heat-treated at 450°C.

Soft X-Ray Spectroscopic Analysis of Ni-Silicides

The valence-band electronic structure of Ni-silicide system, NiSi 2 , NiSi and Ni 2 Si, has been studied by measuring soft X-ray Si L 2,3 emission spectra. It is found that the Si L 2,3 spectra show very different spectral features among these three silicides. The spectra of silicides are compared with the theoretical density of states and discussion is given on the electronic structure of these silicides. It is suggested that Si s electronic state contributes significantly to the upper part of valence-band of the three silicide systems.