Hiroaki Iwakuro

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.

A New High Current Gain 4H-SiC Bipolar Junction Transistor with Suppressed Surface Recombination Structure: SSR-BJT

A new 4H-SiC Bipolar Junction Transistor with Suppressed Surface Recombination structure: SSR-BJT has been proposed to improve the common emitter current gain which is one of the main issues for 4H-SiC BJTs. A Lightly Doped N-type layer (LDN-layer) between the emitter and base layers, and a High Resistive P-type region (HRP-region) formed between the emitter mesa edge and the base contact region were employed in the SSR-BJT. A fabricated SSR-BJT showed a maximum current gain of 134 at room temperature with a specific on-resistance of 3.2 mΩcm2 and a blocking voltage VCEO of 950 V. The SSR-BJT kept a current gain of 60 at 250°C with a specific on-resistance of 8 mΩcm2. To our knowledge, these current gains are the highest among 4H-SiC BJTs with a blocking voltage VCEO more than about 1000 V which have been ever reported.

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.

Abrupt reduction in poly-Si etch rate in HBr/O2 plasma

The effect of oxygen on polycrystalline-Si (poly-Si) and SiO2 etching in hydrogen bromide (HBr) reactive ion etching plasmas has been studied by measuring etch rates and using x-ray photoelectron spectroscopy (XPS) to study compositional changes in the surface layer. The etch rate of the poly-Si increases dramatically from 30 to 235 nm/min as the O2 concentration increases from 0% to 25%, whereas the SiO2 etch rate gradually decreases from 3 to 1 nm/min. Above 30% O2 in HBr, the poly-Si etch rate abruptly decreases by a factor of 16 compared with that at 25%. From XPS analysis, it is found that the abrupt decrease of the poly-Si etch rate at O2 concentrations of more than 30% is closely related with the composition and thickness of an SiBrxOy layer formed during the HBr/O2 plasma exposure. The SiBrxOy layer has a composition of nearly SiO2. Br ions cannot permeate the SiBrxOy layer formed in plasmas containing 30% O2 in HBr (or greater), and therefore, the poly-Si etch terminates.

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.

Interfacial layers of high-barrier Schottky diode of Al/n-type (100)Si exposed to H2 plasma

Al/Si Schottky diodes were fabricated from n-type silicon wafers which were exposed to several kinds of plasma in a magnetron using gases of hydrogen, deuterium, helium, nitrogen, oxygen and argon. The influence of plasma exposure on the Schottky barrier height is examined. The Schottky barrier height increases for only H2-containing plasma exposure. Hydrogen plays an important role in the increase of the Schottky barrier height. The plasma-exposed silicon surfaces are characterized by transmission electron microscopy, X-ray photoelectron spectroscopy and secondary ion mass spectrometry. H2 plasma exposure produces both a surface hydrogen-absorbing zone about 10 nm thick and a zone including planar defects under the hydrogen-absorbing zone. In Ar plasma exposure, the only zone including planar defects is formed from the surface to 30 nm in Si. The increase in the Schottky barrier height can be attributed to the formation of the hydrogen-absorbing zone in Si.