Tsukasa Kuroda

Study of Oxidation of TiSi2 Thin Film by XPS

Titanium was deposited on a single-silicon wafer and made to form TiS2 by thermal annealing in vacuum. Samples were then oxidized at temperatures from 100 to 1000°C for 60 min in air. When the oxidized TiS2 was studied by X-ray photoelectron spectroscopy (XPS) in conjunction with argon-ion sputtering, SiO2 was found to be dominant in the oxide products at various oxidation temperatures. Full-width at half maximum (FWHM) and Si/Ti atomic ratio analyses led to the conclusion that various Ti oxides exist in oxidized TiSi2, but that the intermediate Ti-silicides (TiSi and Ti5Si3) do not. The growth of a Ti-free layer of SiO2 at 1000°C was also observed. SEM micrographs showed that no surface morphologies varied before or after oxidation in air at temperatures from 100 to 800°C. Above 1000°C, however, the TiSi2 film was thermally grooved at its grain boundaries, and the grain sizes were increased. Analytic electron-microscope photographs showed that the crystalline grains consisted of TiSi2, but that the grain boundaries lay within the Ti-free zone.

Field-ion microscopy of GaAs and GaP

Abstract Clean surfaces of GaAs and GaP were studied by field-ion microscope (FIM). Field-ion images with ordered surfaces were first obtained in pure hydrogen, neon-50% hydrogen and pure neon gases at 78 K, by using channeltron electron multiplier arrays (CEMA). The field-ion images of GaAs were quite similar to those of GaP with respect to the surface structure and the image contrast. They showed the anisotropies of the ion emission and the surface structure between the [111] and [ 1 1 1 ] orientations. Ring steps expected from a spherical surface were observed on the (111) and {100} planes, but not on the [ 1 1 1 ] and {110} planes. The regional brightness of the FIM patterns was discussed in terms of the Knor and Muller model and the atomic and electronic structures of the surface. The image field of these crystals was much lower than that of metals usually used in FIM. For example, the image field strength for the hydrogen and GaAs system was about 1.1 V/A. The reduction of the field necessary to image was also discussed in terms of the field penetration effect.

On field-evaporation end forms of a bcc metal surface observed by a field ion microscope

Abstract Distinct differences in the field-evaporation end forms of W, Ta, and Mo are investigated by comparing the temperature dependence of the contribution of polarization energy and binding energy to the field-evaporation energy. The field-evaporation end form at low temperature is influenced mainly by the polarization energy of atoms under the influence of a strong field; its magnitude decreases in the following sequence: Ta, W and Mo. As the field-evaporation temperature is raised the influence is gradually transferred from polarization energy to binding energy. Binding energies except for the {001} planes, which are estimated from the Morse potential energy, are in fair agreement with the experimental results. The field-evaporation end forms at high temperature are mainly influenced by the magnitude of the activation energy due to the self-migration of the atoms on the surface of each crystal planes. The influence of residual gases and the change of field-evaporation mechanism are discussed.

Atom-probe fim studies of β-SiC whiskers

Abstract The 〈111〉-oriented whiskers of β-SiC, which is a semiconductor of the zinc blende structure, were studied by an atom-probe field ion microscope. Spectra of the number of field-evaporated ions versus their mass to charge ratio for A [111]-and B [111]-oriented tips were different from each other. Both the atomic ions and the molecular ions of SiC were observed for the two oriented tips. The mechanism of the field-evaporation of β-SiC has been discussed from the spectra in connection with the fact that the distinct difference between the two orientations was found in the field emission patterns of the field evaporated tips.

A Study of CCl2F2 Magnetron Ion Etching Damage and Contamination Effects in Silicon

X-ray photoelectron spectroscopy has been used to evaluate Si surfaces exposed to magnetron plasma in CCl2F2 gas. Plasma exposure of Si surfaces results in a contamination film 12–33 A thick and a damaged layer in the Si substrate. The contamination film consists of C–C, C–F, and C–Cl–F and/or F–F bondings. In addition, the C and F atoms penetrate into the Si substrate. On the other hand, the damaged layer consists of lattice defects and the contamination by the C and F atoms. Furthermore, from electrical measurements on Al/n-Si Schottky diodes, the damage depths are determined as a function of rf power. It is found that the damage depths correlate with the energy of ions impinging on the Si surface during plasma exposure.

X‐ray photoelectron spectroscopy of Si/Pt and Pt/Si layers on GaAs

The difference in the chemical reactions between Si/Pt/GaAs and Pt/Si/GaAs systems have been investigated using x‐ray photoelectron spectroscopy. For the Si/Pt/GaAs system, annealing at 450 °C leads to out‐diffusion of Ga and As atoms to the surface of the deposited film. On the other hand, for the Pt/Si/GaAs system, no Ga and As atoms out‐diffuse to the surface. This indicates that the interface at GaAs is more stable for the Pt/Si/GaAs system than for the Si/Pt/GaAs system. The difference in these interfacial reactions is due to the difference in chemical states of Pt atoms when Pt atoms come in contact with GaAs.

Enhanced dry etching of silicon with deuterium plasma

The etching of Si and SiO2 for H2 and D2 plasma exposure has been investigated. The Si is etched rapidly by a factor of 34 for D2 plasma exposure compared with H2 plasma exposure. On the other hand, the etching rate of SiO2 does not change. This suggests a possibility of dry etching of Si with D2 gas.

Interfacial Reactions of Ni, Si/Ni and Ni/Si Films on (100)GaAs

The interfacial reactions of Ni, Si/Ni and Ni/Si films on GaAs have been investigated by X-ray photoelectron spectroscopy. In the 450°C-annealed Ni/GaAs system, the interfacial reaction occurred extensively, resulting in formation of the Ni-Ga, Ni-As and Ni-Ga-As compounds. In the annealed Si/Ni/GaAs system, the reaction began at both the Si/Ni and Ni/GaAs interfaces. The Ni silicide formed by intermixing at the Si/Ni interface play a role as a barrier film in preventing out-diffusion of the Ga and As atoms from the Ni/GaAs interface. On the other hand, in the Ni/Si/GaAs system, annealing produced intermixing at the Ni/Si interface but hardly any interfacial reaction at the GaAs substrate.

High-Barrier Schottky Diodes on N-Type Si(100) Due to Hydrogen Plasma

Electrical characteristics of Al/Si diodes exposed to hydrogen-containing plasmas have been measured. The Schottky barrier heights increase compared with that of a control diode. The Schottky barrier height increases consistently with an increase in an applied rf power or hydrogen concentration in the plasma. Furthermore, the Si surface exposed to argon or hydrogen plasma has been observed by X-ray photoelectron spectroscopy. It is concluded that exposure of the Si surface to hydrogen plasma produced a hydrogenated amorphous layer in the Si substrate. Therefore, the increase in the Schottky barrier height is attributed to the formation of the Schottky barrier at the interface between the Al metal and the hydrogenated amorphous layer.

X-Ray Photoelectron Spectroscopy of Pt/GaAs Interfacial Reactions

Pt/GaAs interfacial reactions were studied by X-ray photoelectron spectroscopy combined with argon ion sputtering. Even at room temperature, the reaction occurred to form a Pt-rich Pt-Ga compound and unreacted As. It was found that Pt interacts with Ga in GaAs at the beginning of the reaction. The top surface of the deposited Pt film was covered with As. Annealing at 200°C formed PtAs2 and the same Pt-Ga compound that was found in the as-deposited state. The top surface was covered with Ga because As and its oxides sublimated during annealing. Annealing at 450°C produced islands of Ga-rich Pt-Ga compound on the sample surface. A ternary compound was formed in the surface region outside the islands.