Toshio Tsurushima

Niobium silicide formation induced by Ar-ion bombardment

The effect of Ar‐ion bombardment on evaporated–Nb‐on‐Si systems has been investigated with He backscattering and x‐ray‐diffraction measurements. High‐dose bombardment with energetic Ar ions was found to induce intermixing between Nb and Si in the form of NbSi2. This effect has strong dependence on temperature during bombardment, although it cannot be explained as enhanced diffusion due to radiation damage or ion‐beam heating.

DEEP LEVEL OF IRON-HYDROGEN COMPLEX IN SILICON

Deep levels related to iron in n-type silicon have been investigated using thermally stimulated capacitance (TSCAP) combined with minority carrier injection. The TSCAP measurement reveals two traps of EV+0.31 and EV+0.41 eV. The trap of EV+0.41 eV is a donor due to interstitial iron. The trap of EV+0.31 eV, due to a complex of interstitial iron and hydrogen, is observed in the sample etched chemically with an acid mixture containing HF and HNO3 and annihilates after annealing at 175 °C for 30 min. It is demonstrated that interstitial 3d transition metals such as vanadium, chromium, and iron tend to form complexes with hydrogen in n-type silicon, and the complexes induce donor levels below the donor levels of the isolated interstitial species. This trend is related to the interaction between the metals and hydrogen in the complexes.

Ion-beam modification of TiO2 film to multilayered photocatalyst

We report a dry process to produce a multilayered TiO2 film which has the rutile phase on an anatase substrate, for highly activated photocatalysis. Ar ion beam irradiation changes the anatase surface into rutile at 500°C, which is less than the crystallization temperature of rutile from anatase (600°C). The ion beam modification makes it possible to form rutile thin film on anatase. The multilayered structure should be a promising photocatalyst, theoretically.

Effect of preoxidation on deposition of thin gate-quality silicon oxide film at low temperature by using a sputter-type electron cyclotron resonance plasma

We have studied a method of combining preoxidation and subsequent sputter deposition for fabricating Si oxide films with a thickness of less than 10 nm at low temperature by using a sputter-type electron cyclotron resonance plasma system. As a key process to achieving high quality composite oxide structures, plasma preoxidation was investigated under different gas flow rates at a substrate temperature of 130 °C. The optimum conditions for the preoxidation were clarified. The structural properties of Si oxide formed by this method with the preoxidation were characterized and compared with those of Si oxide which was directly sputtered without a preoxidation step. It was found that the method with the preoxidation provided a useful way of establishing an abrupt Si/SiO2 interface region and achieving films which have a lower network disorder degree. This procedure was then followed by a thermal annealing in Ar ambient at 450 °C. A thin Si oxide film was produced with a fixed charge density of less than 1.0×1...

Deep levels of vanadium and vanadium‐hydrogen complex in silicon

Deep levels in vanadium‐doped n‐ and p‐type silicon have been investigated using deep level transient spectroscopy (DLTS) and concentration profile measurements. The DLTS measurement reveals two electron traps of EC−0.20 eV and EC−0.45 eV, and a hole trap of EV+0.34 eV. These three levels correspond to the transitions between four charge states of interstitial vanadium. Furthermore, an electron trap of EC−0.49 eV is observed near the surface region of n‐type samples etched with an acid mixture containing HF and HNO3. The origin of the trap has precisely been investigated by isochronal anneals and various chemical treatments. From these investigations, it is found that the trap is due to a complex of interstitial vanadium with hydrogen introduced by chemical etching.

Low-temperature deposition of high-quality silicon dioxide films by sputtering-type electron cyclotron resonance plasma

High-quality silicon dioxide films have been deposited at 130 °C by a sputtering technique using an electron cyclotron resonance microwave plasma. Film properties have been studied as a function of O2 flow rate in the range of 2–8 sccm with a constant Ar flow rate of 8 sccm when other plasma conditions were a microwave power of 700 W, and a radio frequency power of 700 W supplied to a target for sputtering. Dielectric breakdown characteristics have been investigated by ramp current–voltage measurements. Films deposited with an O2 flow rate of 5.3 sccm have a dielectric breakdown field of 10 MV/cm, which is close to that of thermally grown silicon dioxide film. The deposition rate was as high as 23 nm/min. Structural properties of films have also been characterized by ellipsometry and infrared absorption spectroscopy, showing that films with O2 flow rates above 4 sccm have near-stoichiometric composition.

Deep levels of chromium‐hydrogen complexes in silicon

Deep levels related to chromium in n‐type silicon have been investigated using deep level transient spectroscopy (DLTS) and concentration profile measurements. The DLTS measurement reveals four electron traps of EC−0.22, EC−0.28, EC−0.45, and EC−0.54 eV in chromium‐doped samples. The trap of EC−0.22 eV is a donor due to interstitial chromium. The other three traps are observed near the surface region of samples etched with an acid mixture containing HF and HNO3 and annihilate after annealing at 175 °C for 30 min. The origin of these traps has been studied by isochronal annealing and various chemical treatments. It is demonstrated that the three electron traps are due to complexes of interstitial chromium and hydrogen.

Growth kinetics of CoSi formed by ion beam irradiation at room temperature

Growth kinetics of cobalt silicide layers formed by ion beam irradiation was investigated at a temperature between room temperature and 100 °C. The CoSi phase was identified by x-ray diffraction of Co/Si samples irradiated with 25 keV argon ions to a dose of 2.0×1015 cm−2. The number of intermixed silicon atoms in the CoSi layers was evaluated as a function of dose, dose rate, and nuclear energy deposition rate at the Co/Si interface for samples irradiated with 40 keV focused silicon ion beams. The growth is shown to be diffusion-limited and attributed to radiation-enhanced diffusion with an activation energy of 0.16 eV. The number of intermixed silicon atoms is approximately proportional to the nuclear energy deposition rate at the initial Co/Si interface, while it is independent of dose rate, which shows that the CoSi phase is formed without contribution of the sample heating caused by irradiation.

Formation Kinetics of Niobium and Molybdenum Silicides Induced by Ion Bombardment

Kinetics of silicide formation induced by ion bombardment was investigated in Nb-deposited-on-Si (Nb/Si) and Mo/Si systems by using a backscattering technique in order to elucidate formation mechanisms. The kinetics was observed to be different in these systems. In Mo/Si, the amount of Si atoms intermixed into the silicide is proportional to (dose)1/2 and independent of the properties of the Si substrate; in Nb/Si, it is proportional to the nuclear energy deposition by the ion at the silicide/Si interface and is affected depending on whether the substrate is amorphous or crystalline. From these results and the temperature dependence observed, it is concluded that defects produced by the ion cause the silicide growth by inducing the reaction at the silicide/Si interface and atomic diffusion in the silicide layer; in Nb/Si the former process is rate limited and in Mo/Si it is the latter.

Behavior of radiation-induced defects and amorphization in silicon crystal

Abstract We have investigated the dose rate dependence of the lateral amorphization of silicon crystals irradiated with 40 keV Si2+ focused ion beams (FIB) as a function of sample temperature. The recovery time of point defects, τ, and the extent of their distribution, d, around the collision cascades produced by impinging ions were evaluated. The amorphous line-width was measured with scanning electron microscopy (SEM) after a selective etching. We have obtained a critical dose rate 1 (τd 2 ) of 1.0 × 1015 cm−2s−1 for radiation at 100°C. The temperature dependence of the critical dose rate suggests that the lateral amorphization is controlled by a simple kinetics of the defects with an activation energy of 0.85 eV. From the value of the activation energy, we speculate that the recovery process of radiation-induced defects is controlled by the migration of interstitial Si atoms.