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Papers by Atsuyuki Fukano

Introduction Silicon industry is now paying attention to high-k and SiON dielectric materials as ... more Introduction Silicon industry is now paying attention to high-k and SiON dielectric materials as a candidate gate insulator beyond ultra-thin (<1nm) SiO2 film. The present limitations in ultra-thin SiO2 film are, however, defects in the Si-O interface which is a source of leakage current. In order to improve insulating performance, sub-oxide layer in the interface must be minimized in thickness. Our approach is to densify the SiO2 film to minimize defect density. There are several polymorphous for SiO2 with different packing (density); i.e. stishovite (4.35g/cm), coesite (2.93g/cm), quartz (2.6 ~ 2.65g/cm), tridymite (2.28 ~ 2.33g/cm) and cristobalite (2.32g/cm). High density SiO2 in an amorphous form is also known; i.e. lechatelierite (2.5 ~ 2.65g/cm). Densification of glassy silica is achieved by high pressure. Density of thermally oxidized SiO2 film on the silicon wafer is 2.14 ~ 2.23g/cm.[1] High density forms are expected to have less defects; e.g oxygen imperfection. Recent...

Optical properties of self-assembled Ge islands grown on Si(001) (日本電子顕微鏡学会第46回シンポジウム材料のナノ・生物のナノ) -- (ポスターセッション "7th International Symposium on Advanced physical Fields(APF-7)"との合同セッション)

電子顕微鏡, 2001

Low Temperature Growth of Silicon Dioxide Thin Films by UV Photo-oxidation

MRS Proceedings, 2002

The low-temperature growth of thin SiO2 layers for gate insulators in very large-scale integrated... more The low-temperature growth of thin SiO2 layers for gate insulators in very large-scale integrated (VLSI) circuits is becoming an urgent topic of silicon technology. In contrast, to conventional thermal oxidization processes (T>900°C), ultraviolet (UV) photo-oxidation of silicon technology is a promising approach for low-temperature growth of silicon dioxide thin films. We have grown silicon dioxide thin films at low temperature (T<500 °C) using an excimer lamp with various wavelengths and evaluated the quality of thin SiO2 layers as well as the SiO2–Si interface. We found that the SiO2 layers (t<5 nm) grown by UV photo-oxidation show significant differences in physical properties, such as density profile, from those of thermal oxidization, i.e., the higher average density 2.23 g/cm3 and more constant distribution, making the SiO2–Si interface region, so-called “transition layer” less eminent. Superior characteristics of ultra-thin SiO2 layer grown by UV photo-oxidation are ...

Japanese Journal of Applied Physics, 2005

The effects of argon plasma bombardment and subsequent heat treatments on the structure of YBa 2 ... more The effects of argon plasma bombardment and subsequent heat treatments on the structure of YBa 2 Cu 3 O y thin films were studied. We find that the argon plasma processing modifies the yttrium composition through the formation of Y 2 O 3 islands (serving as an yttrium reservoir) and solid-state diffusion. The scanning electron microscopy (SEM) images show that the argon plasma bombardment accelerates the growth of Y 2 O 3 islands which are thinned and washed away during the subsequent annealing in vacuum. Complimentary techniques (X-ray diffraction and X-ray absorption spectroscopy) show that the structural disorder caused by argon plasma processing is recovered by heat treatment in vacuum while oxygen vacancies are compensated by the final ozone treatment. The results reveal the individual roles of sequential treatments of YBa 2 Cu 3 O y thin films which improve the electrical properties of ramp-edge Josephson junctions.

Journal of Applied Physics, 2003

Highly insulating ultrathin SiO2 films (<5 nm) were grown by means of vacuum ultraviolet photo... more Highly insulating ultrathin SiO2 films (<5 nm) were grown by means of vacuum ultraviolet photooxidation, by use of 126, 172, and 222 nm wavelength photons generated by excimer lamps. The ultrathin silicon dioxide films were grown onto the Si(001) substrate, at low temperature (<500 °C). We found that the densities of photooxidized SiO2 films were 13%–35% higher than that of thermally oxidized SiO2 film. The density profile was obtained by x-ray reflectivity and showed a remarkable decrease in the SiOx (suboxide) layer thickness at the SiO2−Si interface, in comparison with thermally oxidized conventional oxides. The Si 2p photoelectron spectrum confirmed that the SiOx layer was negligibly thin. High insulating performance of the SiO2 film was demonstrated.

Research on advanced evaluation method for dynamic process with use of synchrotron light sources

Kokuritsu Kikan Genshiryoku Shiken Kenkyu Seika Hokoku-Sho, 2004

Ground State at Low Landau Level Filling Factors in Two-Dimensional Systems of GaAs/AlGaAs Heterostructures in Strong Magnetic Fields(Research in High Magnetic Fields)

Science reports of the Research Institutes, Tohoku University. Ser. A, Physics, chemistry and metallurgy, 1996

UV Photo-Oxidation of Silicon: A Novel Growth Method of Ultra-Thin SiO2 Films

AIP Conference Proceedings, 2004

Superior insulating performance is found for dense silicon dioxide ultra‐thin films (∼3 nm) grown... more Superior insulating performance is found for dense silicon dioxide ultra‐thin films (∼3 nm) grown by UV photo‐oxidation of silicon. Density profile obtained by glazing incidence x‐ray reflectivity shows that the high density (2.32 g/cm3) SiO2 is formed on Si(100) surface at much lower temperature (<450 °C) than thermal oxidation, using 126 nm photons. The sharp and flat interface within 1–2 monolayers is revealed by high resolution transmission electron microscopy. The film density is strongly dependent on wavelength around 172–126 nm, suggesting that the specific excited species of oxygen is involved in the growth mechanism. Unique properties of photo‐oxidized silicon dioxide are related to the modified Si‐O network structure and ring statistics.

Magnetic alignment system for bumps on an integrated circuit device

Magnetic random access memory

System and method for generating a flat mask design for projecting a circuit pattern to a spherical semiconductor device

Manufacturing metal dip solder bumps for semiconductor devices

Spherical semiconductor device and method for fabricating the same

The Journal of Physical Chemistry C, 2009

The initial nucleation and growth processes of CdSe nanocrystals in a microfluidic reactor are st... more The initial nucleation and growth processes of CdSe nanocrystals in a microfluidic reactor are studied by in situ extended X-ray absorption fine structure (EXAFS) in conjunction with UV-visible absorbance and photoluminescence spectra. On the basis of a surface reaction kinetics equation, the analytical expressions of the particle size and concentration are proposed. The surface reaction rate constant calibrated by UV-visible absorbance spectra at longer reaction time (>2.4 s) was used to estimate the particle size and concentration within the first 2.4 s of reaction. A burst of nucleation at 1-2 s with the smallest nucleus size of ∼1.3 nm was observed after rapidly heating the reaction solution in the microfluidic reactor. This initial nucleation burst was associated with a rapid particle size increase within ∼3 s, and after that the growth rate was slowed. It is demonstrated that the combination of in situ EXAFS with a microfluidic reactor provides a valuable way for studying the kinetics of nanocrystals synthesis in solution.

Ligand Effects of Amine on the Initial Nucleation and Growth Processes of CdSe Nanocrystals

The Journal of Physical Chemistry C, 2010

... nanocrystals. Foos et al.(11) and Jose et al.(17) reported that the addition of amine to the ... more ... nanocrystals. Foos et al.(11) and Jose et al.(17) reported that the addition of amine to the TOPO coordinating solvent delayed the initial nucleation of the CdSe particles as compared with the TOPO-alone synthesis, while Pradhan et al. ...

Experiments on localization in Landau subbands with the Landau quantum number 0 and 1 of Si inversion layers

Surface Science, 1990

ABSTRACT

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2003

For high throughput/energy-resolution fluorescence X-ray detection in X-ray absorption spectrosco... more For high throughput/energy-resolution fluorescence X-ray detection in X-ray absorption spectroscopy (XAS), a novel Ge pixel array detector (PAD) with 100 segments has been developed. Using a monolithic approach, a high packing density (88%) with nearly perfect commission rate (99%) were achieved, resulting in a dramatic improvement in packing density compared to the close-packed multi-element detector (57%). Two types of PAD was built with the pixel thickness of 7.5 and 10 mm. Each segment has an active area of 22 mm 2. The average energy resolution at 5.9 keV was ca. 220 eV (6 ms shaping time) and 240 eV (0.5 ms shaping time). High efficiency in X-ray detection in a wide energy range (5-60 keV) was confirmed. The present data acquisition system, CAMAC-based hybrid electronics, is capable of independent energy-analysis and recording all channels with a maximum 100 kcps per channel or 10 MHz in total. Elimination of elastic and inelastic scattering improved the systematic error in XAS, as demonstrated by an XAS application to a photo-induced phase transition.

Journal of the Physical Society of Japan, 1988

Journal of Synchrotron Radiation, 2006

A Ge pixel array detector with 100 segments was applied to fluorescence X-ray absorption spectros... more A Ge pixel array detector with 100 segments was applied to fluorescence X-ray absorption spectroscopy, probing the local structure of high-temperature superconducting thin-film single crystals (100 nm in thickness). Independent monitoring of pixel signals allows real-time inspection of artifacts owing to substrate diffractions. By optimizing the grazing-incidence angle and adjusting the azimuthal angle ', smooth extended X-ray absorption fine structure (EXAFS) oscillations were obtained for strained (La,Sr) 2 CuO 4 thin-film single crystals grown by molecular beam epitaxy. The results of EXAFS data analysis show that the local structure (CuO 6 octahedron) in (La,Sr) 2 CuO 4 thin films grown on LaSrAlO 4 and SrTiO 3 substrates is uniaxially distorted changing the tetragonality by $ 5 Â 10 À3 in accordance with the crystallographic lattice mismatch. It is demonstrated that the local structure of thin-film single crystals can be probed with high accuracy at low temperature without interference from substrates.