Taizoh Sadoh

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 175u2009°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.

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.

Diffusion of vanadium in silicon

The diffusion profiles of vanadium in silicon have been investigated. In the temperature range 950–1200u2009°C an in‐depth profile measurement by deep level transient spectroscopy was used, and in the temperature range 600–800u2009°C an annealing experiment which employed a technique for profiling the concentration of deep levels within a depletion region was used. From the two kinds of concentration‐profile measurements, the diffusion coefficient of interstitial vanadium in silicon was determined, and it is represented by the expression DV= 9.0×10−3 exp(−1.55/kT) cm2u2009s−1.

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 175u2009°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 100u2009°C. The CoSi phase was identified by x-ray diffraction of Co/Si samples irradiated with 25 keV argon ions to a dose of 2.0×1015u2009cm−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.

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.

Deep states in silicon on sapphire by transient-current spectroscopy

It is demonstrated that deep states in silicon on sapphire (SOS) films can be evaluated by transient-current spectroscopy (TCS). In the TCS spectra, a broad peak extending over 100–200 K was observed for the 6000-A-thick n-type SOS film. Assuming the value of capture cross section to be 10−15 cm2 and independent of temperature, the density distribution of deep states was estimated. The density distribution shows a peak of 1.2×1012 cm−2u2009eV−1 at EC−0.25 eV. Raman backscattering spectroscopy was also performed to evaluate the stress in the silicon film. It was concluded that the defects detected by TCS should be caused by the compressive stress of 6.2×108 Pa in the silicon film.

Behavior of Defects Induced by Low-Energy Ions in Silicon Films

Behavior of defects induced by low-energy (5 keV at maximum) argon ions or protons in 600 nm thin silicon crystals has been investigated. A significant amount of defects diffuse from the damaged surface layers to the deeper regions even at room temperature, and act as the carrier traps and the scattering center that affect the electrical properties of the films. Most of the defects disappaer after annealing at 300°C. Electrical and thermal properties of the defects depend on the creation rate of Frenkel pairs.

Electrical passivation of B-doped Si through thin films used in VLSI fabrication

Atomic hydrogen diffusion through the thin films used in VLSI fabrication is investigated by measuring the electrically passivated boron (B) profile in silicon (Si) substrate under the films. After hydrogen plasma treatment, carrier concentration profiles in Si are measured using a spreading resistance profiler, and translated to the electrically passivated B profiles. The CVD oxide gave rather small hydrogen diffusivity in comparison with thermal oxide. Effective hydrogen diffusivities in Si under thermal oxides were evaluated at 150, 200, and 250°C. The effective hydrogen diffusivity in 0.01 μ cm B-doped Si was determined as 1.2 x 10−12 cm2 s−1 at 200°C. The difference in the hydrogen behaviour between the thermal oxide and the CVD oxide is analyzed numerically by a trap-included diffusion model, by fitting it to the passivated B profile in Si. Hydrogen trap densities in the thermal oxide and the CVD oxide were estimated to be NT ≤ 1.0 × 1017 and NT ⋍ 1.0 × 1019 cm−3, respectively. The diffusion through CVD oxide was slow because of the high density traps in the film. CVD oxide is more effective than thermal oxide as a retardation film against atomic hydrogen penetration into the VLSI devices in the dry cleaning process using hydrogen plasma. The passivations of B in Si under Si3N4, aluminum, and poly Si films were not observed. These films might be much more effective than CVD oxide films in the protection of devices in the short term, typically 3 h, during hydrogen surface cleaning in VLSI processes.