bluuebunny/crossref_metadata_2025 huggingface dataset:
Optically Interconnected Kohonen Net for Pattern Recognition
Authors: Doi Takeshi , Namba Tohru , Uehara Akihito , Nagata Makoto , Miyazaki Seiichi , Shibahara Kentaro , Yokoyama Shin , Iwata Atsushi , Tadashi Ae Tadashi Ae , Masataka Hirose Masataka Hirose
Published: October 2002

The test chip of optically interconnected Kohonen net which realizes the parallel pattern recognition was designed and fabricated. The optical waveguides, micromirrors and photodiodes were integrated on a Si wafer and complementary metal oxide semiconductor (CMOS) chips were bonded on the same Si wafer. The optical input data are distributed to the CMOS circuits by the branched waveguide and the distances between the input and the reference data are calculated. This test circuit operated at a frequency of 6.7 MHz.
Excitonic Emission in GaN Films on AlN Substrates Using Microwave-Excited N Plasma Method
Authors: Kai Ayako , Okada Kiyohiko , Yamada Yoichi , Taguchi Tsunemasa , Sasaki Fumio , Kobayashi Shunsuke , Tani Toshiro , Taniguchi Hitofumi
Published: October 2002

Hexagonal gallium nitride (GaN) films are grown on aluminum nitride ceramic substrates in gallium and nitrogen plasmas excited by microwaves. The band-edge photoluminescence properties of the GaN films are investigated at 77 K and at room temperature. A strong ultraviolet (UV) emission, consisting of two components with different decay characteristics, is observed. The fast decay component is due to free exciton recombination and the slow one is ascribed to recombination of localized excitons.
Low-Temperature Oxidation of Silicon by O2 Cluster Ion Beams
Authors: Akizuki Makoto , Matsuo Jiro , Ogasawara Satoru , Harada Mitsuaki , Doi Atsumasa , Yamada Isao
Published: October 2002

High-quality SiO2 films up to 11 nm thick were grown on Si substrate surfaces at room temperature by O2 cluster ion irradiation. No damage was observed after N2 annealing at 400°C for 30 min in the I-V characteristics of the thermally grown gate oxides irradiated with 5 keV Ar cluster ions. These results indicate that O2 cluster ions strongly enhanced the oxidation with low irradiation damage.
Clarification of Nitridation Effect on Oxide Formation Methods
Authors: Kuroi Takashi , Shirahata Masayoshi , Okumura Yoshinori , Shimizu Satoshi , Teramoto Akinobu , Anma Masatoshi , Masahide Inuishi Masahide Inuishi , Hirokazu Miyoshi Hirokazu Miyoshi
Published: October 2002

The electrical characteristics of gate dielectrics have been intensively studied. We examined four types of gate dielectrics: thermal oxide films formed in a pyrogenic steam ambient, those in a dry oxygen ambient, chemical vapor deposition (CVD) oxide films, and the thermal/CVD stacked oxide films. The effects of nitridation on oxide properties have been also systematically investigated using the nitrogen implantation technique. It is found that hot-carrier degradation can be improved by nitridation irrespective of the oxidation methods. This improvement is attributed to the suppression of interface state generation and the reduction in the number of electron traps in the oxide films. Our extensive investigation concludes that the nitridation of gate oxide films by nitrogen implantation is very promising for the improvement in reliability in spite of the difference in oxide formation methods.
Formation of SiOF Films by Plasma-Enhanced Chemical Vapor Deposition Using (C2H5O)3SiF
Authors: Kitoh Hideyuki , Muroyama Masakazu , Sasaki Masayoshi , Iwasawa Misako , Kimura Hitoshi
Published: October 2002

A new Plasma-Enhanced Chemical Vapor Deposition (PECVD) method using (C2H5O)3SiF: tri-ethoxy-fluoro-silane as an interlayer dielectric film is proposed based on considerations of gas chemistry. RF power dependence of the film characteristics is investigated, and it is clarified that fluorine stability is improved with increasing RF power. The relative dielectric constant of the films deposited at the power of more than 700 W is about 3.5. Moisture absorption of the film formed from TEFS at 900 W is smaller than that of the SiOF film formed from C2F6 added TEOS.
Trap Generation Induced by Local Distortion in Amorphous Silicon Dioxide Film
Authors: Chioko Kaneta Chioko Kaneta
Published: October 2002

The generation mechanism, the stable atomic configuration, and the properties of intrinsic charge traps in amorphous silicon dioxide (a-SiO2) are investigated employing the ab initio molecular orbital method applied to a cluster model. It is found that an injected hole is trapped in a nonbonding 2p orbital of an oxygen atom even though there are initially no defects and impurities in a-SiO2. Thus, it acts as a trap for an electron. The local distortion in a-SiO2 structure, especially the stretching of a Si–O–Si, induces the hole trapping. It is also found that the effect of the local distortion on electron trapping is small.
Properties of Ferroelectric BaMgF4 on Si(100), (110) and (111) Substrates Obtained by Post-Deposition Rapid Thermal Annealing
Authors: Kim Kwang-Ho , Ishiwara Je-Deok Kim
Published: October 2002

Substrate orientation dependence of metal-ferroelectric BaMgF4-silicon capacitors obtained by post-deposition rapid thermal annealing was investigated. Fluoride films were deposited on Si(100)-, (110)- and (111)-oriented wafers in an ultrahigh-vacuum system at a substrate temperature of 300°C. Post-deposition annealing was conducted for 10 s at 600°C. The resistivity of the ferroelectric BaMgF4 film increased from a typical value of 1–2×1011 Ω\cdotpcm before annealing to about 5×1013 Ω\cdotpcm at 1 MV/cm, and the interface state density of the BaMgF4/Si interface decreased to 5–8×010/cm2·eV. Apparent remanent polarizations of BaMgF4 films on (100)- and (111)-oriented silicon wafers were about 0.5–0.6 µC/cm2 and that of film on the (110) wafer was about 1.2 µC/cm2.
Recovery of Silicon Surface after Reactive Ion Etching of SiO2 using CHF3/C2F6 Plasma
Authors: Kwon Kwang-Ho , Park Hyung-Ho , Kim Kyung-Soo , Kim Chang-II , Sung Yung-Kwon
Published: October 2002

The effects of SF6 or NF3 gas plasma and subsequent rapid thermal anneal (RTA) treatment for the recovery of modified silicon surfaces after reactive ion etching (RIE) with CHF3/ C2F6 plasma were investigated using X-ray photoelectron spectroscopy and secondary ion mass spectrometry. NF3 or SF6 plasma treatment effectively removed the residue layer and impurities in the silicon substrate were removed by the subsequent RTA treatment at 700° C. The effects of NF3 or SF6 plasma and the additional RTA treatment in recovering the reactive ion etched silicon surface were also studied by measuring the leakage current densities and the barrier heights of post-treated PtSi/n-type Si Schottky barrier diodes. The minimum leakage current and the maximum barrier height were obtained after NF3 plasma and subsequent RTA treatment, which constitute the most probable recovery process for silicon surfaces contaminated by RIE.
Excimer-Laser Crystallization of Silicon-Carbon Films and Their Thin-Film Transistor Application
Authors: Choi Kwangsoo , Uchida Yasutaka , Masakiyo Matsumura Masakiyo Matsumura
Published: October 2002

We have crystallized silicon-carbon ( SiC

x

) film using the ArF excimer-laser annealing method. From the AES (auger electron spectroscopy) depth profile, the crystallized film was confirmed with uniform concentration of carbon in the film. The resistivity of an undoped film with a carbon content of 0.2 was decreased to about 2.3×102 Ω cm, and it changed only slightly even under intense illumination of AM1 100 mW/cm2. This film was used as the active layer of thin-film transistors (TFTs). The electron field-effect mobility was 0.35–2 cm2/Vs, which is similar to the typical mobility of the a-Si TFT.
Photoinduced Destruction of Polar Structure in Dye-Pendant Polymers Studied by Second-Harmonic Generation
Authors: Aoki Hiroaki , Ishikawa Ken , Hideo Takezoe Hideo Takezoe , Atsuo Fukuda Atsuo Fukuda
Published: October 2002

Second-harmonic generation (SHG) was observed in polymer/azo dye systems during light irradiation. The SHG activity produced by poling was completely lost by partial trans-cis isomerization in dye-pendant systems, while this phenomenon was observed less in a dye-dispersed system. Taking account of the observations in various polymer matrices, we concluded that the destructive process of the poled structure is amplified through a movement of the polymer main chain induced by the partial photoisomerization of chromophores.
Transport Mechanisms in Evaporated C60 Film Evaluated by Means of Field Effect
Authors: Keiichi Kaneto Keiichi Kaneto , Kazuya Yamanaka Kazuya Yamanaka , Kouichi Rikitake Kouichi Rikitake , Takahiro Akiyama Takahiro Akiyama , Wataru Takashima Wataru Takashima
Published: October 2002

Electrical transport in an evaporated C60 film is studied by means of the field effect. Characteristics of the field effect transistor (FET) show an enhancement n-channel type with the threshold voltage of 2.0 V. At room temperature, the field effect mobility and the carrier density are estimated to be 4.8 ×10-5 cm2/( Vs) and 5.6 ×1014 cm-3, respectively. Activation energies of the mobility and conductivity have nearly the same value of 0.54 eV The transport mechanism is discussed in terms of the hopping transport.
Improvement of the Sintering and Dielectric Characteristics of Surface Barrier Layer Capacitors by CuO Addition
Authors: Cheng-Fu Yang Cheng-Fu Yang
Published: October 2002

Calcined (Ba0.8Sr0.2)(Ti0.9Zr0.1)O3 (BSTZ) with added CuO is used as an improved material with which to fabricate surface (or reduction-reoxidation) barrier layer capacitors (BLCs). The CuO-containing BSTZ appears to have less temperature, frequency, and bias dependence of the dielectric characteristics and a lower sintering temperature ( 1325°C versus 1390°C) as compared to BSTZ without CuO. For the same annealing conditions, for example, annealing at 1000°C for 60 min, the effective dielectric constant of CuO-added BSTZ (sintering at 1325°C) is larger than that of BSTZ without CuO (sintering at 1390°C). The addition of MnO accelerates the annealing process, causing the semiconductive ceramics to reoxidize into dielectric materials within 30 min. CuO addition can lead to an important competitive merit for BSTZ dielectrics, especially in the fabrication of surface BLCs with an easily controllable fabrication process to give stable dielectric characteristics.
Characterization of Czochralski Silicon Wafers Grown at a Low Growth Rate by Photoluminescence Spectroscopy
Authors: Mototsugu Hamada Mototsugu Hamada , Takashi Katoda Takashi Katoda
Published: October 2002

Microdefects in silicon wafers were characterized based on photoluminescence measurements obtained with a high sensitivity Fourier-transform (FT)-Raman spectrometer. Some luminescence peaks were obtained from a crystal which was pulled at a low growth rate while they were not observed from a crystal which was pulled at a normal rate. The luminescence peaks were observed in the region of the wafers where ring-oxidation-induced-stacking-faults (ring-OSF) were formed and inside the ring. By comparing the behavior of annealing-induced defects, that is D-line and P-line defects, and the grown-in defects observed in low-growth-rate crystals, it was concluded that the grown-in defects were P-line defects. Based on the PL intensity of the peak at 0.75 eV which was observed from a crystal pulled at a low growth rate, it was found that the effect of the thermal history of a crystal pulled at 0.8 mm/min was equivalent to an annealing at 500°C for 3 h.
Thermal Desorption Study on Silicon Surfaces during Fluorine Removal Process with Atomic Deuterium Exposure
Authors: Yoji Saito Yoji Saito , Tohru Kubota Tohru Kubota
Published: October 2002

An accelerated desorption of fluorine adsorbates from silicon surfaces is induced by atomic deuterium (or hydrogen) exposure at low substrate temperature. The reaction processes have been investigated with in situ Auger analysis and thermally stimulated desorption spectroscopy (TDS) measurements. The experimental results of both fluorine decay and TDS spectra indicate that two kinds of the reaction products including SiDF molecules desorb from the surface in the initial stage of the reaction between the atomic deuterium and the fluorinated silicon. With the decrease in fluorine coverage, SiDF molecules desorb as the main reaction products. A deuterium-passivated silicon surface is obtained by atomic deuterium treatment at 200° C for 30 min from the fluorinated surface.
Pit and Mound Formation on Arc-Evaporated Carbon Thin Film Using Scanning Tunneling Microscopy
Authors: Tsukasa Abe Tsukasa Abe , Kazuhiro Hane Kazuhiro Hane , Sigeru Okuma Sigeru Okuma
Published: October 2002

The etching of arc-evaporated carbon film with scanning tunneling microscopy (STM) was studied in comparison with that of highly oriented pyrolytic graphite (HOPG). The arc-evaporated carbon film was etched with STM only in air or in water vapor and at a sample bias voltage positive to the tip. These etching characteristics were similar to those for HOPG. After the carbon film was etched by a high bias voltage, the isolated carbon film was frequently exfoliated by STM scanning. On the other hand, a mound was also formed on the arc-evaporated carbon film below the tip when a high bias voltage (∼4 V) was applied to the film. The surface mound was formed at both polarities of the tip voltage and was not affected by atmospheric conditions. The mound area was characterized by Auger electron spectroscopy (AES). The Auger spectrum showed that the substrate material migrated to the carbon film.
Improvement of Rinsing Efficiency after Sulfuric Acid Hydrogen Peroxide Mixture (H2SO4/H2O2) by HF Addition
Authors: Messoussi Rochdi , Verhaverbeke Steven , Yabune Tatsuhiro , Nose Masashi , Ohmi Tadahiro
Published: October 2002

We report on the improvement in efficiency of deionized water rinsing after using a H2SO4/H2O2/HF mixture which produces hydrophobic Si surfaces by means of fluorine passivation, providing better sulfur removal and shorter rinsing time than the conventional H2SO4/H2O2 mixture. After removing this passivation agent by rinsing in deionized water, the surfaces are still covered with chemical oxide, which protects them from organic contamination. Furthermore this treatment does not induce surface roughening.
Characterization of Praseodymium-doped InP Epilayers Grown by Liquid-Phase Epitaxy
Authors: Gwo-Cherng Jiang Gwo-Cherng Jiang
Published: October 2002

The various degrees of incorporation of praseodymium (Pr) into InP during liquid-phase epitaxial growth from an In-rich solution were investigated by double-crystal X-ray diffraction, Hall effect, and low-temperature photoluminescence (PL) measurements to investigate the effect of Pr concentration on structural, electrical, and optical properties. The lattice mismatch varies slightly with increasing Pr concentration in the growth melts. This variation in lattice mismatch with increasing Pr concentration is observed together with the shift of the PL emission energy. Examinations of the electrical property reveal that all the Pr-doped samples exhibit n-type conduction. Depending on the extent of Pr doping in the growth melts, InP epilayers have carrier concentrations ranging from 1017 cm-3 to 1016 cm-3 and mobilities varying from 1330 to 3800 cm2/V·s. It is also revealed that the impurities are gettered by Pr ions during liquid-phase epitaxial growth but the Pr-related defects formed in high Pr-doped melts may act as scattering centers and cause carries mobilities to decrease. It is found that epitaxial growth from the melt with 0.25–0.29 wt% Pr produces of the epitaxial layers highest quality. No intra-4f-shell transition line is observed from InP layers even at very high Pr concentrations.
Sol–Gel Processing of Pb1-xLaxTi1-x/4O3 Thin Films
Authors: Soe Ko Ko Kyaw , Masaki Maeda Masaki Maeda , Ikuo Suzuki Ikuo Suzuki
Published: October 2002

Thin films of lanthanum-modified lead titanate were fabricated by sol–gel processing. The complex alkoxides were prepared by reacting Pb acetate and La acetate with an equimolar solution of titanium tetraisopropoxide and acetylacetone. Acetylacetone was added to titanium tetraisopropoxide as a chelating agent. Thin films were deposited on Si(100), Pt/Si(100) and Pt/MgO(100) substrates by dip-coating. X-ray diffraction analyses were carried out to investigate the crystalline phase assignment and crystallographic orientation in the thin films. Thin films deposited on Si(100), Pt/Si(100) and Pt/MgO(100) substrates exhibited the perovskite single phase and showed no preferred orientation.
Relationship between Raman Spectra and Crystallinity of CdS Films Grown by Cathodic Electrodeposition
Authors: Shirai Katsunori , Moriguchi Yukihisa , Ichimura Masaya , Akira Usami Akira Usami , Manabu Saji Manabu Saji
Published: October 2002

CdS films were cathodically electrodeposited from acidic solutions (pH=2.5) containing CdSO4 and Na2S2O3. Raman scattering of these films was measured using the 514.5 nm line of an Ar ion laser as the light source. The longitudinal-optical (LO) phonon peak of CdS was observed between 300–310 cm-1. The full width at half-maximum (FWHM) of the peak was a large value of 18.2 cm-1 for as-deposited films, but decreased to 12.7 cm-1 after the films were annealed at 500° C. These results are consistent with those of other structural and optical characterizations, and thus the Raman spectroscopy was found to be useful for the characterization of the electrodeposited CdS films.
Temperature Dependence of Raman Spectra in Si-doped GaAs/AlAs Multiple Quantum Wells
Authors: Matsumoto Toshiyuki , Haraguchi Masanobu , Fukui Masuo , Kubo Hitoshi , Hamaguchi Chihiro
Published: October 2002

We investigated the temperature dependence of Raman spectra due to two coupled longitudinal-optical phonon-collective intersubband excitations in Si-doped GaAs/AlAs multiple quantum wells. The frequency of the respective coupled modes shifts with a change in the electron density in intersubbands related to the modes. The Raman intensity due to the higher-frequency coupled mode becomes weaker with increasing temperature. Under a certain condition, electron density in the ground subband changes with the temperature because of the temperature dependence of the Fermi energy. Furthermore we observed a reproducible drastic position shift of the Raman peak originating from the higher-frequency coupled mode with temperature.
Effects of Sol–Gel Processing Variables on the Texture Growth of LiNbO3 Thin Film
Authors: Won Dong Hoon , Hur Nam Hwi , Kwangsoo No Kwangsoo No
Published: October 2002

Highly oriented lithium niobate ( LiNbO3) thin films were fabricated using the sol–gel spin coating method. The effects of the sol–gel processing variables, such as reflux time, crystallization temperature and substrate, on the development of texture on the thin film were investigated. The film made from the solution refluxed for 5 h and deposited on a sapphire (012) substrate showed highly oriented growth at the crystallization temperature of 500° C. The film had homogeneous and pore-free microstructure. The film made from the solution refluxed for 1 h showed only preferred orientation and porous microstructure under the same processing conditions. The thin films deposited on MgO(100) substrates were polycrystalline. The crystallization temperature and the film thickness significantly affected the crystallinity and the orientation of the films.
Pulsed Field Magnetization of Melt-Processed Y–Ba–Cu–O Superconducting Bulk Magnet
Authors: Mizutani Yoshitaka Itoh
Published: October 2002

Magnetic fluxes can be trapped in a melt-processed Y–Ba–Cu–O (YBCO) bulk superconductor at 77 K by applying a pulsed magnetic field with a rise time of 0.8 or 2.4 ms. We found that trapped fluxes increase with increasing intensity of applied field up to 1.9 T, but decrease beyond this value, resulting in a peak in the applied field dependence of trapped fluxes. It is also found that creep of trapped fluxes can be largely suppressed when pulsed fields exceeding 1.9 T are applied. Other new phenomena characteristic of pulsed field magnetization were also found and discussed. All these results can be explained by taking into account the significant contribution of the viscous force and the resulting heat generation due to the viscous motion of fluxes.
Thermal Degradation Study of Polyethylene Using 1H NMR
Authors: Lee Chang Hoon , Lee Cheol Eui , Han Jae Hong , Suh Kwang S.
Published: October 2002

We have studied the thermal degradation of polymer samples of low density polyethylene (LDPE) and crosslinked polyethylene (XLPE) by 1H nuclear magnetic resonance. The spin-lattice relaxation in these systems was explained using the two-phase model for semicrystalline polymers. It was found that the microscopic environments of the 1H nuclei due to thermal degradation were reflected in the spin-lattice relaxation times (T
1) and the line shapes. The degree of crystallinity was also determined.
Selective Dry Etching to Reveal Compositional Inhomogeneity in Co–Cr Magnetic Films
Authors: Asahi Masayoshi , Maeda Koji Takei
Published: October 2002

We studied a selective dry-etching method designed to reveal compositional inhomogeneity in Co–Cr alloy magnetic films. The dry etching was carried out using reactive sputtering with CO2 as the working gas. Preferential etching of Co was confirmed by depth profiling using Auger electron spectroscopy. The compositional microstructure revealed by the dry etching was observed using scanning electron microscopy.
Effects of Photoinitiator on the Properties of Polymer Ball Type Polymer Dispersed Liquid Crystal Films
Authors: Chang Shoou-Jinn , Fuh Chin-Maw Lin
Published: October 2002

The effects of photoinitiator on the properties of “polymer ball” type polymer dispersed liquid crystal (PDLC) films have been studied. It was found that the size of the polymer balls is larger for samples prepared with a smaller photoinitiator concentration. The threshold voltage will become higher for samples with a larger polymer balls. Also, the off-state transmission will become higher and the contrast ratio will become smaller for samples prepared with a smaller photoinitiator concentration.
Piezoelectric and Ferroelectric Properties of Polyurea Thin Films Copolymerized by Vapor Deposition Polymerization of Aliphatic and Aromatic Monomers
Authors: Hattori Takeshi , Takahashi Yoshikazu , Masayuki Iijima Masayuki Iijima , Eiichi Fukada Eiichi Fukada
Published: October 2002

Thin films of polyurea were prepared by vapor deposition polymerization of 1,9-diaminononane and 4,4′-diphenyl-methane-diisocyanate. The films were mechanically tenacious and easily separated from the substrate surface, similar to aliphatic polyurea films. Piezoelectric stress constant e
31 ( =4 mC/m2) and pyroelectric constant p
3 (=8 µ C/m2 K) were obtained for poled films. Ferroelectric hysteresis was also observed. Annealing the deposited film under an electric field decreased the ionic conductivity as well as the residual polarization of the D–E hysteresis curve. The oriented urea dipoles gave rise to piezoelectricity but the ionic polarization did not. Three relaxation processes in the temperature dependence of elastic constant c
1 and dielectric constant ε
3 were observed at -150° C (γ), -50° C (β), and 130° C (α), similar to those for aliphatic polyureas. The piezoelectric constant e
31 remained unchanged until about 100° C, where depolarization took place due to α relaxation.
A Comparison of the Selective Etching Characteristics of Conventional and Low-Temperature-Grown GaAs over AlAs by Various Etching Solutions
Authors: Zhao Rong , Lau Wai Shing , Tow Chong Chong Tow Chong Chong , Ming Fu Li Ming Fu Li
Published: October 2002

In this work we report the selective etching characteristics of GaAs grown by molecular beam epitaxy over AlAs etch-stop layer in four etching solutions. We show that these solutions, which are commonly used for selective etching of GaAs grown at the conventional temperature of 600° C (HT GaAs) are also effective for low-temperature GaAs grown at 230° C with annealing at 600° C (a-LT GaAs) and low-temperature-grown GaAs without annealing (LT GaAs). In these solutions, the etching rates of LT GaAs and a-LT GaAs are lower than that of HT GaAs and hence the selectivities of LT GaAs and a-LT GaAs over AlAs are lower than that of HT GaAs over AlAs. The succinic acid/ H2O2 solution with pH=4.2 was found to be the best selective etchant. Furthermore, we observed, for the first time, that the AlAs etch-stop layer tended to fail at the periphery of the etched windows, resulting in void formation if the etching was excessive. It took a longer time for this to happen in the succinic acid/ H2O2 solution than in other solutions investigated.
Nitrogen Incorporation Kinetics during the Sublimation Growth of 6H and 4H SiC
Authors: Onoue Kozo , Nishikawa Takeshi , Katsuno Masakazu , Ohtani Noboru , Hirokatsu Yashiro Hirokatsu Yashiro , Masatoshi Kanaya Masatoshi Kanaya
Published: October 2002

Nitrogen incorporation kinetics during the sublimation boule growth of SiC have been studied in terms of several growth parameters. 6H and 4H SiC crystals were heavily doped with nitrogen as a donor. It was found that the growth rate has little influence on the doping concentration, indicating that nitrogen incorporation is not kinetically limited at normal growth rates in the sublimation growth. On the other hand, surface polarity and polytype were found to influence the nitrogen incorporation kinetics at the growth front. By optimizing the growth conditions, bulk resistivities as low as 7.6×10-3 Ω cm and 5.3×10-3 Ω cm were obtained for 6H and 4H SiC, respectively.
Microscopic Kinetic Mechanism in Current-Induced Conversion on Si(001) Vicinal Surface
Authors: Hirokazu Ohmi Hirokazu Ohmi , Tetuya Uchida Tetuya Uchida , Koh Wada Koh Wada
Published: October 2002

The microscopic mechanism of current-induced domain conversion phenomena on the Si(001) vicinal surface during annealing is studied using the kinetic equation derived by the path probability method (PPM) in irreversible statistical mechanics along with the Monte Carlo simulation. In addition to evaporation, our model takes account of the three effects related to migration of surface atoms: anisotropic migration on the Si(001) 2×1 reconstructed surface, the electromigration effect and asymmetry in step kinetics (Schwoebel effect) which takes the difference in the kinetics between two types of steps into account. The numerical calculation of the kinetic equation reproduces the domain conversion when the Schwoebel effect exists. The differences in the movements of two types of steps and the spreading velocities of major domains observed during domain conversion are also shown. The results suggest that the combination of the three migration effects causes the difference in the kinetics of atoms between two types of steps, which leads to the domain conversion. The results of the Monte Carlo simulation are in good agreement with those of the PPM.
Surface Orientation of Cyanobiphenyl Liquid Crystal Monolayer and Pretilt Angle under Various Rubbing Strengths
Authors: Shirota Koichiro , Yaginuma Michio , Sakai Takahiro , Ishikawa Ken , Hideo Takezoe Hideo Takezoe , Atsuo Fukuda Atsuo Fukuda
Published: October 2002

We have determined the orientational distribution function (ODF) of a liquid crystal (LC) monolayer on rubbed polyimide films by optical second-harmonic generation (SHG) using the maximum entropy method without assuming the independence of the polar and azimuthal angular distributions. The LC samples used were a homologous series of 4'-n-alkyl-4-cyanobiphenyl (n CB; n=5–8). The rubbing strength dependence of the pretilt angle was also measured and was found to be classified into two types according to even or odd number of carbon atoms in the alkyl chain. However, we could not observe a distinct difference in ODFs of 7CB and 8CB monolayers to explain the two kinds of rubbing strength dependence of the pretilt angle.
Contribution of Kinetic and Potential Emission to keV Singly Charged Ion-Induced Electron Emission from a Metal Surface
Authors: Nishimura Kenji , Ohya Kaoru , Kawata Jun
Published: October 2002

A Monte Carlo simulation model of kinetic emission (KE) of electrons from a gold surface due to impact of He+ and Ar+ ions is combined with a model of potential emission (PE) due to the Auger neutralization of the projectile ions. The emphasis is placed on the energy distribution and emission statistics of electrons, as well as the total electron yield, in the keV impact energy range where KE and PE contribute with comparable importance to the electron yield. At low impact energies, PE dominates the electron yield, which decreases (increases) with increasing energy of He+ ( Ar+) ions. With the onset of KE, the electron yield due to He+ impact begins to increase, and with further increase in energy, KE dominates the electron yield. This causes large changes in the peak energy and the shape of the energy distribution of emitted electrons. For He+ impact, the calculated emission statistics deviate from the observed statistics, whereas for Ar+ impact, a reasonable agreement between them is obtained.
Computational Studies on Plasma Generation and Erosion in a Rectangular Magnetron Sputtering System
Authors: Shunji Ido Shunji Ido , Kosuke Nakamura Kosuke Nakamura
Published: October 2002

A 3-dimensional simulation of electron orbits is applied to a planer magnetron sputtering system with rectangular magnets. Collisions between electrons and neutral gas atoms of Ar are considered and the ionization points are assumed to approximate the distribution of sputtering plasmas. The effect of external magnetic fields on the control of the shape of magnetic fields in this calculation model is examined. By applying the external magnetic fields, the distribution of plasma density as well as the position of erosion on the target can be controlled.
The Influence of Magnetic Plugging on RF Plasma Density
Authors: Nishimura Kimihiro , Yoshino Yasushi , Sawara Atsuo , Ohta Tadayuki , Sunagawa Michio , Takashi Ohzone Takashi Ohzone
Published: October 2002

The influences of magnetic plugging on Ar plasma density of a radio frequency (RF) plasma were studied. Various combinations of SmCo magnets placed outside a vacuum chamber formed various magnetic field patterns. Plasma density is measured using a double probe method. We obtained a high-density plasma (N
e∼5×1010 cm-3) with a narrow central area using magnetic plugging.
Theory of Transient Reflecting Grating in Fluid/Metallic Thin Film/Substrate Systems for Thin Film Characterization and Electrochemical Investigation
Authors: Shen Qing , Akira Harata Akira Harata , Tsuguo Sawada Tsuguo Sawada
Published: October 2002

A general theory was developed to calculate the diffraction signals from a transient reflecting grating (TRG) at metallic thin film/substrate interfaces and liquid/solid interfaces. The TRG signals for an Au film/soda lime glass system were experimentally measured and theoretically calculated to examine their agreement. It was found theoretically and experimentally that longitudinal acoustic pulses and echoes with ultrahigh-frequency components (>10 GHz) propagating normal to the sample surfaces are generated and can be detected at the surfaces of thin films, using the TRG technique, along with surface acoustic waves. By using the time intervals of two neighboring longitudinal acoustic echoes, thicknesses or longitudinal acoustic wave velocities for opaque thin films were determinable. Furthermore, it was shown that this method is applicable to the analysis of electrochemical interfaces in situ, through changes in the thermal and longitudinal acoustic properties of electric double layers with electrochemical potentials.
Observation of Molecular Layers in (2-(4,5-bis(thiomethyl)-1,3-dithiol-2-ylidene)-5- (4,5-ethylenedithio-1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene) (TMET-TTP) Single Crystals by Means of Scanning Tunneling Microscopy
Authors: Takahashi Teruo , Mori Takehiko , Ishikawa Ken , Takezoe Hideo , Fukuda Atsuo , Misaki Yohji , Yamabe Tokio
Published: October 2002

Scanning tunneling microscope (STM) observation has been made on single crystals of (TMET-TTP)

x

A (TMET-TTP: 2-(4,5-bis(thiomethyl)-1,3-dithiol-2-ylidene)-5-(4,5-ethylenedithio-1,3-dithiol-2-ylidene)-1,3,4,6- tetrathiapentalene), where A is PF6, ReO4, AuI2 or ClO4. The STM images with molecular resolution were observed in the conducting b
c-plane, and were in accord with the results of X-ray observation. The S atoms in the thiomethyl groups are concluded to be responsible for the bright spots. The structural distortion in the ClO4 salt as indicated by X-ray analysis was observed as domain structures of about 100 nm×100 nm area, though direct observation of different molecular alignments due to different space groups could not be made.
Stripe Direction Dependence of Mesa Angle Formed on (100) InP by Selective Etching using HCl Solution
Authors: Munehisa Tamura Munehisa Tamura , Ki-Chul Shin Ki-Chul Shin , Naoki Serizawa Naoki Serizawa , Shigehisa Arai Shigehisa Arai
Published: October 2002

Stripe direction dependence of mesa angle formed on (100) InP substrate was investigated by selective wet chemical etching using HCl solution with a GaInAs epitaxial mask layer. As a result, it was found that undercut-free etching can be nearly obtained with the stripe formed along the <011 > direction whereas large undercut due to anomalous etching occurred along the <010 > direction.
Sub-0.1 µm Patterning with High Aspect Ratio of 5 Achieved by Preventing Pattern Collapse
Authors: Yoshio Yamashita Yoshio Yamashita
Published: October 2002

High resolution patterns of deep sub-quarter micron delineated by X-ray, E-beam and optical lithographies have been widely reported. Pattern collapse during the development steps has become the main obstacle to obtaining higher resolution. To overcome this difficulty a very low surface tension rinser has been evaluated in development processes. Perfluorohexane has a low surface tension of about 10 dyne/cm. For 0.08 µ m lines and spaces a high aspect ratio of more than 5 can be delineated in 0.45-µ m-thick ZEP resist using perfluorohexane as a rinser, whereas an aspect ratio of more than 4 cannot be achieved using water or conventional organic solvent rinsers.
Surface Analysis during Plasma Etching by Laser-Induced Thermal Desorption
Authors: Herman Irving P. , Donnelly Vincent M. , Cheng C.-C. , Guinn Keith V.
Published: October 2002

The use of laser desorption (LD) to desorb species from the surface and laser-induced fluorescence (LIF) to detect them in the gas phase during etching of Si(100) in a high-charge-density plasma of Cl2 and Cl2/HBr mixtures is reviewed. The LD-LIF intensities of SiCl and SiBr are used to track the surface coverages of SiCl

x
(a
d
s) and SiBr

x
(a
d
s), respectively, as a function of RF power, DC bias, and partial pressure, and as a function of time when the plasma is turned on and off. In-line X-ray photoelectron spectroscopy (XPS), the use of which is validated by these in situ LD-LIF studies, is employed after etching to calibrate the surface coverages obtained from the LD-LIF measurements.
In Situ Fourier Transform Infrared Measurements of Si Surface and Bulk Plasmas in Cl2/O2 and HBr/O2 Electron Cyclotron Resonance Plasma Etching: Influence of Oxygen on Reaction Products
Authors: Kazuyasu Nishikawa Kazuyasu Nishikawa , Tatsuo Oomori Tatsuo Oomori , Kouichi Ono Kouichi Ono , Mutumi Tuda Mutumi Tuda
Published: October 2002

In situ Fourier transform infrared (FTIR) absorption spectroscopy, electrostatic probe measurements and optical emission spectroscopy have been used to investigate reaction products during Si etching in HBr/O2 electron cyclotron resonance plasmas, in comparison with the results obtained in Cl2/O2 plasmas. In HBr/O2 plasmas, the plasma parameters were found to be almost constant within the range of the percentage of O2 gas flow rate to total gas flow rate of 0–10% by electrostatic probe measurements. The ratio of emission intensity of O atom to that of Br atom during Si etching was almost the same as that during SiO2 etching, while the ratio of emission intensity of O atom to that of Cl atom during Si etching was much lower than that during SiO2 etching. In FTIR absorption spectra, silicon bromides SiBrx (x=1–4) were not detected in the gas phase during Si etching in HBr/O2 plasmas at the present level of detection. A chemical shift of the position of a peak related to silicon oxides was observed, indicating the existence of silicon oxybromides on the Si surface. On the Si surface, FTIR absorption spectra revealed asymmetric Si–O stretching vibrational mode after Si etching even in pure HBr plasmas. Thus, Si etching mechanisms in HBr/O2 plasmas were considered to be different from those in Cl2/O2 plasmas.
Effects of Conductivity of Polysilicon on Profile Distortion
Authors: Chi Kyeong Koo , Shin Hwa Sook , Yoo Won Jong , Jung Chan Ouk , Young Bum Koh Young Bum Koh , Moon Yong Lee Moon Yong Lee
Published: October 2002

The profile distortion, notch, in the etching of gate lines with high-density plasmas is becoming more deleterious as ULSI devices are being further scaled down. Dependence of the etch profiles on the polysilicon conductivity was studied for various spacings of line-and-space patterns. The notch depth was deeper for polysilicon with higher conductivity. The image potential was employed to account for the dependence of notch on conductivity. To measure the net positive charges which are known to contribute to the notch phenomenon, we observed the ion and electron current waveforms from patterned and unpatterned wafers as a function of bias power. The results showed that the surface of the patterned wafer is more positively charged than that of the unpatterned wafer, and the net charge can be reduced by raising the bias power. However, an increase in the bias power lowers the selectivities over both thin gate oxide and photoresist.
Mechanism for CF Polymer Film Deposition through Deep SiO2 Holes in Electron Cyclotron Resonance Plasma
Authors: Ono Tetsuo , Hamasaki Ryoji , Mizutani Tatsumi
Published: October 2002

The deposition rate of CF polymer film at the bottom of SiO2 microholes is measured and the mechanism is studied using a multichannel capillary array (MCA). Deposition rate increases as the angle of tilt in the hole decreases when rf bias is applied to the substrate. The smaller the diameter of the hole, the larger the increase in deposition rate. Pb from the MCA material was detected in film deposited through the MCA, and CF polymers deposited through the MCA are more carbon-rich than those deposited without the MCA. These results suggest that polymers reach the bottom of the hole by being etched off and redeposited on the sidewall. The increase in deposition rate at the bottom causes RIE (reactive ion etching) lag, thus it is important to maintain a perpendicular hole angle for holes with small diameters.
Planar Shadowing of Fast Ion Beams in Si and Ge Crystals Bombarded with 5 keV Ar+
Authors: Fukusho Taro , Tanabe Atsushi , Kudo Hiroshi , Ishihara Toyoyuki , Seki Seiji
Published: October 2002

We have measured shadowing patterns for Si and Ge crystals bombarded with 5 keV Ar+, using keV secondary electrons induced by 56 MeV O8+. In the planar shadowing patterns, the increase in the electron yield due to Ar+ bombardment can be directly related to the thickness of the damaged layer on the crystal surface, as previously found for axial shadowing. The results indicate that not only axial but also planar shadowing in the damaged crystals can be accounted for in terms of the effective target thickness responsible for the keV electron yield.
Improvement on Fluorine Effect under High Field Stress in Tungsten-Polycide Gated Metal-Oxide-Semiconductor Field-Effect Transistor with Oxynitride and/or Reoxidized-Oxynitride Gate Dielectric
Authors: Chen Chii-Wen , Fang Yean-Kuen , Lee Kan-Yuan , Hsieh Jang-Cheng , Liang Mong-Song
Published: October 2002

Fluorine (F) ions which deduced from tungsten-polycide (W-polycide) formation and affected on metal-oxide-semiconductor (MOS) devices with pure oxide, oxynitride (NO) and re-oxidized oxynitride (ONO) gate dielectric under high field stress were investigated in detail. Although a significant amount of interface states were detected by charge pumping technique in NO and ONO device with W-polycide gate in comparison with that devices with polysilicon gate, however, it is found that NO, and especially ONO gate dielectric, can effectively improve the hot-carrier degradation in W-polycide gated MOS field-effect transistor (FET). This mechanism is well interpreted with a model about F ions increasing the nitrogen concentration at the interface between gate dielectric and Si substrate according to the result of secondary ion mass spectrometry (SIMS) analysis.
A Comparison of Defect States in Tantalum Pentoxide (Ta2O5) Films after Rapid Thermal Annealing in O2 or N2O by Zero-Bias Thermally Stimulated Current Spectroscopy
Authors: Lau Wai Shing , Khaw Kee Keong , Qian Peng Wei , Sandler Nathan P. , Chu Paul K.
Published: October 2002

The concentration of shallow defect states in Ta2O5 films was found to be greatly reduced, resulting in much less leakage current in Al/Ta2O5/Si capacitors, if N2O was used instead of O2 for post-deposition annealing. The superiority of N2O is explained by the formation of a slightly thicker SiO

x

diffusion barrier, which can reduce Si contamination coming from the Si substrate into the Ta2O5 film.
Calculation of Stress Concentration at the Edge of Island Layer: Demonstration for GaAs/Si
Authors: Nakajima Kazuo , Ochiai Kuninori Kitahara
Published: October 2002

An improved shear lag analysis was proposed to precisely calculate longitudinal stress distribution in hetero- structures with island layers. It is assumed that each layer consists of many imaginary thin layers in order to calculate internal stress distributions over the entire heterostructure. This method is applied to the calculation of stress in a GaAs/Si heterostructure whose GaAs layer is separated or selectively grown similarly to the island layer, in order to determine the effect of island layer on the concentration of stress at the island edge and on the reduction of stress in the GaAs layer. In the stress distribution in the Si layer close to the heterointerface, a sharp and high peak of tensile stress appears at the edge of the GaAs island layer with misfit dislocations. This stress distribution agrees with the experimental one measured by Raman scattering. The tensile stress in the GaAs layer with misfit dislocations can be clearly reduced by decreasing the length of the GaAs island layer.
Effect of the Critical Current Density and the Junction Size on the Leakage Current of Nb/Al–AlOx/Nb Superconducting Tunnel Junctions for Radiation Detection
Authors: Joosse Koen , Nakagawa Hiroshi , Akoh Hiroshi , Takada Susumu , Maehata Keisuke , Ishibashi Kenji
Published: October 2002

Nb/Al–AlO

x

/Nb superconducting tunnel junctions (STJ's) designed for X-ray detection have been fabricated. The behavior of the low-temperature subgap leakage current, which severely limits the energy resolution obtained in such devices, is investigated. From trends in the dependence of the leakage currents on the critical current density and the size of the STJ, as well as from the low-temperature current-voltage characteristics, and an analysis of the base electrode surface morphology, it is concluded that physical defects in the barrier region are the most probable cause of the leakage currents. Suggestions are given for optimization of the device processing.
Transmission Electron Microscopy Observation and Third-Order Optical Nonlinearity of CdSe-Doped Glass Thin Films Prepared by Ion-Beam Sputtering Method
Authors: Tabata Akimori , Matsuno Noriaki , Suzuoki Yasuo , Teruyoshi Mizutani Teruyoshi Mizutani
Published: October 2002

The structure of CdSe-doped silica glass thin films prepared by ion-beam sputtering (IBS) method was investigated by transmission electron microscopy (TEM) and electron diffraction. The mean diameter of the CdSe particles in this study was about 3 nm. The structure of the particles was hexagonal. The third-order optical nonlinearity of the films was also investigated by a degenerate four-wave mixing (DFWM) method. |χ(3)| was found to be about 1×10-8 esu and |χ(3)|/α was 1×10-12 esu·cm.
Resonant Multiphoton Ionization of H2by an ArF Laser and Application to Atmospheric Molecules
Authors: Maeda Mitsuo , Okada Tatsuo , Hirakawa Yasuyuki , Uchiumi Michihiro , Muraoka Katsunori
Published: October 2002

When a tunable ArF laser beam was focused into a pulsed H2gas jet, three-photon ionization and gas breakdown were resonantly enhanced at 193.28 nm. The ionization efficiency was calculated using a rate equation model. Based on the results, resonant multiphoton ionization of atmospheric species was discussed, considering the application of this scheme to laser-controlled lightning. N2molecules can be efficiently ionized at a wavelength of 283.1 nm by a tunable laser. Applying a similar analytical model to N2allowed the estimation of the laser energy required to form a long (100 m) weakly ionized (1013cm-3) channel in the atmosphere.
Annealing Effects on Second Harmonic Generation of Segmented KTiOPO4 Waveguides
Authors: Noriko Yamada Noriko Yamada , Yukihiro Yamamoto Yukihiro Yamamoto
Published: October 2002

Annealing effects on second harmonic generation of a segmented KTiOPO4 waveguide fabricated by ion-exchange of Rb/Ba for K have been studied. Conversion efficiency was not affected by annealing at 250° C for 20 min but was greatly reduced by annealing at 400° C for 20 min. The results of selective etching by KOH/KNO3 showed that domain inversion of an ion-exchanged region remained even after annealing at 400° C. The lower conversion efficiency of the sample annealed at 400° C can be partly explained in terms of the lower power density of the fundamental beam and a relatively shallower depth of domain inversion than that of the waveguide due to the deepening of the waveguide caused by the diffusion of Rb and Ba inside the KTiOPO4 crystal.
Self-Mode Locking of a Hybrid CO 2 Laser with Two Transversely Excited Atmosphere Sections
Authors: Koichi Sasaki Koichi Sasaki
Published: October 2002

Self-mode-locked outputs were obtained from the second transversely excited atmosphere (TEA) section of a hybrid CO2 laser with two TEA sections, by controlling the gain of the cw section and discharge timing of the two TEA sections. The present self (passive)-mode locking was induced by the combination tone polarizations due to the beat note between two longitudinal modes from the first TEA section.
Blue Photoluminescence from Si-Doped Amorphous Silica Films by RF Sputtering
Authors: Yoshida Satoshi , Hanada Teiichi , Tanabe Setsuhisa , Naohiro Soga Naohiro Soga
Published: October 2002

Si-doped amorphous silica films were prepared by rf magnetron sputtering. Blue photoluminescence (PL), with a peak wavelength of about 450 nm, was observed from films with relatively low Si content after thermal annealing. PL intensity showed the dependence on annealing temperature. The peak wavelength of this PL was very similar to that of oxygen-deficient silica glass. However, PL excitation spectra and the temperature dependence of blue PL intensity showed that the origin of this blue PL was different from that of blue PL for oxygen-deficient silica glass.
Origin of Fatigue in Ferroelectric Perovskite Oxides
Authors: Kaoru Miura Kaoru Miura , Masahiro Tanaka Masahiro Tanaka
Published: October 2002

We calculated the electronic states of ferroelectric perovskite oxides, ATiO3, using the discrete variational Xα cluster method. The bond order of the π bonds between Ti 3d and O 2p as a function of titanium ion displacement in PbTiO3 shows a maximum. This result suggests that the magnitude of ferroelectricity is related to the magnitude of the π bonds. We also found that the occupancy of s electrons in A ions increases the strength of π bonds between a titanium ion and oxygen ions. This result also suggests that the magnitude of ferroelectricity is related to the magnitude of the π bonds. Therefore, we propose that the appearance of oxygen vacancies is one of the origins of fatigue in PZT because the π bonds between a titanium ion and oxygen ions are weakened by remaining electrons of oxygen vacancies.