bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface Wave Measurements during Gelation Process of Tungstic Acid
Authors: Motonaga Kazuhiro , Okabe Hirotaka , Matsushige Kazuhiro Hara
Published: October 2002

In order to investigate the gelation process of tungstic acid, surface wave measurements at several frequencies (50–200 Hz) were carried out with a deflected-laser-light detection system using surface waves excited with a PZT bimorph vibrator. During the gelation process, marked changes were observed in the surface wave velocity and amplitude. From the relationship between the frequency and wave number of the surface wave in the sol and gel states, it was found that the surface wave in the sol state was mainly the surface tension wave, and that in the gel state, the Rayleigh wave. We also estimated surface tension in the sol state and shear elastic modulus in the gel state from the present experimental results. The results of the present investigations demonstrate the usefulness of the surface wave measurement for studying the gelation process beyond the transition point.
Electronic States of Fullerenes on Silicon Surfaces
Authors: Tsuyoshi Yamaguchi Tsuyoshi Yamaguchi
Published: October 2002

Electronic states of a model cluster C70Si70H46 of the C70 molecule on the Si(111)7×7 surface are calculated by the discrete variational Xα ( DV- Xα) method with the linear combination of atomic orbital (LCAO) basis. Due to the electron transfer from the Si substrate, the molecule has an ionicity, C70
-2.31. The highest occupied molecular orbital (HOMO) is the dangling bond orbital of the Si surface. Six occupied orbitals and five unoccupied orbitals near the HOMO of the C70 molecule have high charge density around single bonds on pentagons. The maximum point of these charge densities over one half of the C70 molecule is about 0.5 Å higher than that over the other half of the C70 molecule. The charge density of three occupied (two unoccupied) nearly degenerate orbitals is high in three (four) regions over the C70 molecule which has nearly C
s
( D2) symmetry. This should be compared with the STM images of the adsorbed C70 molecule.
Real Space Observation of Standing Waves at Metal Surfaces and the Determination of Surface State Dispersion with the Scanning Tunneling Microscope
Authors: Avouris Yukio Hasegawa
Published: October 2002

Standing waves produced by the scattering and interference of surface state electrons by surface steps and adsorbates are observed in real space using scanning tunneling spectroscopy (STS). From the structure of the standing waves, the wave number of the surface electrons can be obtained as a function of the electron energy. Here we compare the thus obtained dispersion with the results of angle-resolved photoemission and the predictions of a simple theoretical model. Based on these comparisons we determine the best way of performing the STS experiment and analyze the results to obtain a reliable measure of the dispersion of surface states.
Photoluminescence Studies of Semiconducting Polycrystalline CdTe Films
Authors: Aguilar-Hernández Jorge , Contreras-Puente Gerardo , Zelaya-Angel Juan Manuel Figueroa-Estrada
Published: October 2002

We report the first systematic measurements of the temperature dependence of the photoluminescence (PL) in the range of 10–300 K in CdTe. The experiments were carried out on semiconducting CdTe films of high quality grown by a modified close-spaced vapour transport (CSVT) technique. Several luminescence bands were observed, one around 1.4 eV showing a temperature-independent behaviour, and another band located around 1.52 eV, at 300 K, showing a strong temperature dependence. The excitonic origin of this band at low temperatures has been confirmed by the dependence of the PL intensity on the excitation intensity. A band-to-band luminescent recombination component at high temperatures is also observed. This study allows us to elucidate the nature and basic physical properties of the bound exciton as well as the temperature dependence of the band gap.
Role of Steps in GaAs Heteroepitaxial Growth on InAs(001) Surfaces
Authors: Shunsuke Ohkouchi Shunsuke Ohkouchi , Nobuyuki Ikoma Nobuyuki Ikoma
Published: October 2002

The role of steps during the initial stages of GaAs growth on InAs surfaces was investigated by scanning tunneling microscopy (STM). The surface structures of a nominally (001) InAs substrate and a misoriented (001) InAs substrate tilted by 1° towards the [111]B direction were observed by STM after a certain amount of GaAs deposition. In the case of a nominally (001) surface, a growth mode transition from two-dimensional (2D) to 3D island growth occurred when more than 0.75 ML GaAs was deposited. On the other hand, in the case of a vicinal surface, a growth mode transition did not occur when the same amount of GaAs was deposited onto the surface. In this case, GaAs-selective growth attached to the step edges and crack formation extending in the [11̄0] direction were observed in the STM images. These results indicate that the initial growth stages of GaAs heteroepitaxy on an InAs vicinal surface are different from those on a nominally (001) InAs surface due to the existence of steps.
Observation of GaAs(110) Surface by an Ultrahigh-Vacuum Atomic Force Microscope
Authors: Sugawara Yasuhiro , Ohta Masahiro , Hontani Kouji , Morita Seizo , Osaka Fukunobu , Ohkouchi Shunsuke , Suzuki Mineharu , Nagaoka Hideki , Mishima Shuzo , Okada Takao
Published: October 2002

Atomic-resolution imaging of a GaAs(110) surface with an ultrahigh-vacuum atomic force microscope (UHV-AFM) was performed for the very first time. We also observed that the rectangular lattice of the surface is atomically destroyed by sequential scanning. This atomic destruction might be due to the vertical loading force of the probing tip. Furthermore, we observed that the rows of atomic protrusions along the [11̄0] direction were slightly in zigzag, and might be interpreted as quasi-one-dimensional zigzag chains consisting of alternating Ga and As atoms on the GaAs(110). These results suggest that the UHV-AFM has the potential for investigating semiconductor surfaces with dangling bonds on an atomic scale.
Local Ordering and Lateral Growth of Initial Thermal Oxide of Si(001)
Authors: Udagawa Masaharu , Sumita Masaaki Niwa
Published: October 2002

The initial stages of the thermal (600° C) oxide growth of Si (001) clean surfaces were studied by scanning tunneling microscopy (STM). Oxide growth starts from both step edges and terraces. At 120L, almost the entire surface was covered by oxides. Steps could still be identified, and the apparent roughness had a local minimum at this O2 exposure. These results indicate that the first layer is oxidized quite uniformly. Some local orderings of the initial oxides were observed on the terraces, which may enhance the oxide growth in the lateral (parallel to the surface) direction.
Evaporation Rates of Oxides from Undoped and Sb-Doped Si Melts under Atmospheres of Pure Ne, Ar, and Kr
Authors: Huang Xinming , Terashima Kazutaka , Tokizaki Eiji , Whitby Shigeyuki Kimura
Published: October 2002

The effect of gaseous Ne, Ar, and Kr on the evaporation rates of oxides from undoped and Sb-doped Si melts was investigated. By measuring the weight loss of a melt using a thermogravimetric method, we determined the evaporation rate of different species from the melts. The measurements were done at a melt temperature of 1442° C and a background gas pressure of 1.02 atm. Because Ar is predominantly used as the background gas in the semiconductor industry, we report evaporation rates relative to the rates under an atmosphere of pure Ar. For the evaporation of SiO from an undoped Si melt, Ne enhanced the evaporation rate by 37% and Kr suppressed the evaporation rate by 13%. For the evaporation of antimony from an Sb-doped Si melt, Ne enhanced the evaporation rate by 18% and Kr suppressed the evaporation rate by 24%. For the evaporation of antimony oxide from an Sb-doped melt, Ne enhanced the evaporation rate by 4% and Kr suppressed the evaporation rate by 63%. We therefore conclude that, compared with Ar, Ne enhances and Kr suppresses the evaporation of oxides from undoped and Sb-doped Si melts. We show that the background gas affects evaporation through gas-phase diffusion; the diffusion coefficient of the evaporating species is the highest in Ne and the lowest in Kr. In addition, we show that the transport of the evaporating species in the melt to the surface also influences the overall evaporation rates.
Electromigration Characteristics of Cu–Al Precipitate in AlCu Interconnection
Authors: Shingubara Shoso , Nishida Hiroyuki , Hiroyuki Sakaue Hiroyuki Sakaue , Yasuhiro Horiike Yasuhiro Horiike
Published: October 2002

The behavior of a CuAl precipitate during a direct-current stressing test in an Al–2% Cu interconnection was investigated from observations employing scanning electron microscopy and energy-dispersive X-ray microanalysis. Movement of a CuAl precipitate into the anode direction, accompanied with changes of shape and size, was frequently observed. Measurement of the drift velocity of CuAl precipitates was carried out for the first time, which revealed a value an order of magnitude less than that of solid solute Cu atoms. The obtained activation energy of 0.77 eV corresponds to Cu interface diffusion between a CuAl precipitate and Al lattice. Interaction between two adjacent CuAl precipitates was observed in such a manner that one precipitate became smaller while the other precipitate at the anode site became larger. It is considered that the Cu atoms which constituted the precipitate were transferred to the other precipitate at the anode site by solid-solute electromigration.
Probing Inhomogeneous Lattice Deformation at Interface of Si(111)/SiO2 by Optical Second-Harmonic Reflection and Raman Spectroscopy
Authors: Jung Y. Huang Jung Y. Huang
Published: October 2002

Optical second-harmonic generation (SHG) and Raman spectroscopy have been applied to investigate surface strain/stress appearing at the interface between Si(111) and thermally grown SiO2 layers. From the frequency shift and spectral broadening of the optical phonon mode of Si(111) covered by a 608-Å-thick oxide layer, a tensile stress of 19 kbar was obtained. The azimuthal distribution of the reflected second-harmonic (SH) signal varies with the thickness of surface oxide. To deduce the strain in the lattice-deformed layer, a simple microscopic theory based upon the bond additivity model was proposed, and an agreement between the results of SHG and Raman spectroscopy was achieved. This study suggests that SHG is a sensitive technique for examining surface stress/strain between two lattice-mismatched layers. Therefore it can be useful for the study of the structure of Si1-
x

Ge

x

and many other strained-layer systems.
High Resolution Transmission Electron Microscopic Studies on a Superconductor YPd2B2Cx Compound
Authors: Ikeda Shozo , Fujii Hiroki , Kimura Takashi , Kumakura Hiroaki , Kazuo Kadowaki Kazuo Kadowaki , Kazumasa Togano Kazumasa Togano
Published: October 2002

The structure of superconducting boride-carbide YPd2B2C

x

has been investigated by electron microscopy. The 3D structure of the reciprocal lattice has been constructed from a series of electron diffraction patterns obtained by tilting. The symmetry of intensity distribution together with the reflection condition of h+k+l=2n shows that the crystal has body-centered tetragonal symmetry, I4/mmm. The lattice constants are a=0.38 and c=1.08 nm. The structural images of [100], [110] and [001] zones are observed. Computed images and diffraction patterns based on the same structure as LuNi2B2C can be fit with the observed HRTEM images and with intensity distribution of electron diffraction patterns, respectively. It is concluded that the structure of YPd2B2C

x

is basically the same as that of LuNi2B2C.
Nonstoichiometric Properties of Bi-Substituted Yttrium Iron Garnet Sputtered Films
Authors: Komuro Eiju , Hirano Teruyoshi , Tatsuru Namikawa Tatsuru Namikawa , Yohtaro Yamazaki Yohtaro Yamazaki
Published: October 2002

Structural, magnetic and magnetooptical properties of nonstoichiometric Bi-substituted yttrium iron garnet (Bi-YIG) films have been studied in terms of Fe concentration. The garnet films were prepared by rf sputtering using targets which had various Fe contents. In the wide range of Fe content from about 3.9 to 5.4, garnet phases were obtained at an annealing temperature of 650° C. For the Fe contents ranging from 1.9 to 5.1, saturation magnetization increased linearly, and beyond the Fe content of 5.1, it dropped sharply. By considering the magnitude of Faraday rotation of the garnet phase formed in the films (θ F/M
s) and Curie temperature, it is expected that the Bi concentration in the garnet-phase crystallites in the prepared films increases as Fe content increases. It was observed, in energy dispersive X-ray spectrometry (EDX) and secondary ion mass spectrometry (SIMS) analyses, that the excess Bi ions in low-Fe-content films concentrated at the surface, near the film-substrate interface, at the edge of the films and at grain boundaries.
Effects of Uniaxial Compaction Pressure on the Dielectric Properties of BaTiO3/Polyvinylidene Fluoride Composites
Authors: Hsing-I Hsiang Hsing-I Hsiang , Fu-Su Yen Fu-Su Yen
Published: October 2002

In this study, the formation of internal stress, domain switching, phase transition, and dielectric property variations of BaTiO3 particles in the BaTiO3-PVDF composites are investigated. It is found that the characteristics of the composite are highly affected by the magnitude of the compaction pressure employed. The internal stress may change from a state of compressive to tensile as the pressure increases. This is characterized by domain switching, in which the c axis rotates 90°, leaning from perpendicular to the sample surface to parallel. Meanwhile, a larger compaction pressure favors the formation of orthorhombic (o-) BaTiO3, which can result from the effects of internal stress and crystallite size. Composites made of BaTiO3 crystallites with higher internal stress and o-BaTiO3 contents may have higher values of the dielectric constant.
Selective Homoepitaxy of Diamond Thin Films and Investigation of Their Cathodoluminescence
Authors: Tetsuro Maki Tetsuro Maki , Takeshi Kobayashi Takeshi Kobayashi
Published: October 2002

The selective homoepitaxy of diamond thin films has been demonstrated using (CO, B2H6)/H2as the gaseous source and an yttria-stabilized zirconia thin-film mask. By making full use of the selective epitaxy technique, selectively grown p-i-p trilayered epitaxial diamond film, where the area of each layer was reduced successively, has been accomplished. From the cathodoluminescence observation, visible luminescence from each of the layers grown on one chip has been investigated. The spectrum of the inner layer of undoped diamond film was different from that of the same layer without the overlying boron-doped layer. The spatial distribution of the luminescence of the selectively grown epilayers was also observed.
Low Dielectric Constant Interlayer Using Fluorine-Doped Silicon Oxide
Authors: Usami Takashi , Kimiaki Shimokawa Kimiaki Shimokawa , Masaki Yoshimaru Masaki Yoshimaru
Published: October 2002

A new interlayer dielectric film using fluorine-doped silicon oxide (SiOF) for multilevel interconnection of very large scale integration (VLSI) has been fabricated. The film is deposited by a simple technique, which is hexafluoroethane ( C2F6) addition to conventional tetraethoxysilane (TEOS)-based plasma-enhanced chemical vapor deposition (PE-CVD). Si–F bond formation in the film is detected by chemical bonding structural studies using Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). Low dielectric constants caused by Si–F bond formation and good gap-filling ability due to in situ etching by C2F6 plasma are obtained. Therefore, SiOF film has very high applicability as an interlayer dielectric film for advanced VLSI devices.
Etching of Thermally Grown SiO2 by NH4OH in Mixture of NH4OH and H2O2 Cleaning Solution
Authors: Kaigawa Hiroyuki , Koji Yamamoto Koji Yamamoto , Yasuhiro Shigematsu Yasuhiro Shigematsu
Published: October 2002

We have investigated the etching behavior of thermally grown SiO2 by ammonium hydroxide ( NH4OH) in NH4OH–H2O2–H2O cleaning solution (SC-1). The SiO2 etching rate increases with increasing impurity (boron or phosphorus) concentration in the SiO2 as well as concentration of NH4OH and temperature of SC-1 solution. Moreover, postoxidation SC-1 treatment with a low concentration of NH4OH (less than 3.15 wt% of NH4OH) does not degrade or improve oxide reliability. These indicate that if SC-1 treatment, which is performed after post-thin-oxide ( ∼20 nm) or high-impurity-doped Si oxide formation, is carried out in ULSI device fabrication processes, SC-1 with low temperature and low NH4OH concentration must be applied after those processes to minimize SiO2 thickness reduction and preserve oxide reliability.
Mechanism of Contact Charging of Photoconductive Layer for Electrophotography with DC-Biased Conductive Roller
Authors: Hiroyuki Hirakawa Hiroyuki Hirakawa , Yuji Murata Yuji Murata
Published: October 2002

In order to clarify the charging mechanism of a photoconductive layer for electrophotography with a dc-biased conductive roller, we conducted contact charging tests both in air and in vacuum. From the difference between the charging characteristics in air and those in vacuum, we recognized both gaseous discharges at the interface and charge injection as the charging mechanisms.
Stability of a Lithium-Drifted Silicon Detector
Authors: Miyachi Takashi , Ohkawa Shoichi , Matsuzawa Hidemi , Otogawa Takao , Kobayashi Norihiro , Onabe Hideaki
Published: October 2002

The instability of a radiation detector has been studied by means of 1150 nm infrared light. The change in the detector sensitivity is exhibited in photocurrent measurements. Several resonancelike bumps were observed in the conductance of the detector when the aging was incomplete. Using the observed data, we discuss the possible mechanisms which affect detector stability.
Development of Lithium-Drifted Silicon Detectors Using an Automatic Lithium-Ion Drift Apparatus
Authors: Miyachi Takashi , Ohkawa Shoichi , Matsuzawa Hidemi , Otogawa Takao , Kobayashi Norihiro , Ikeda Yasuhiro , Onabe Hideaki
Published: October 2002

Using a computer-controlled drift apparatus, we have developed lithium-ion drift techniques to produce large-size silicon detectors with a high success rate. Based on the improved techniques, we have made detectors with a 115×25×2 mm3 sensitive volume. The variation of the detector sensitivity has been shown to be homogeneous over the measurement area using 1150 nm infrared light.
In Situ Ellipsometric Monitoring of the Growth of Polycrystalline Silicon Thin Films by RF Plasma Chemical Vapor Deposition
Authors: Tachibana Kunihide , Shirafuji Tatsuru , Hayashi Yasuaki , Maekawa Shinji , Morita Tatsuo
Published: October 2002

Polycrystalline silicon thin films have been deposited by RF plasma-enhanced chemical vapor deposition (CVD) using SiF4, SiH4 and H2 gases at a substrate temperature of 300° C. Growth of the films has been monitored by spectroscopic ellipsometry, and time resolved film compositions have been investigated. The film deposited with SiH4 diluted by H2 at a power level of 500 mW/cm2 showed crystal fraction of 50%, and it increased up to 80% with addition of SiF4, although the deposition rate decreased and the surface roughness was enhanced. These results suggest that preferential etching of amorphous tissue brings about the increase of crystalline fraction. Crystallization of the film was verified by transmission electron microscopy along with the decrease in hydrogen content shown by the infrared absorption spectrum.
Characterization of Direct-Contact Via Plug Formed by Using Selective Aluminum Chemical Vapor Deposition
Authors: Takeyasu Nobuyuki , Kawano Yumiko , Kondoh Eiichi , Katagiri Tomoharu , Yamamoto Hiroshi , Hiroshi Shinriki Hiroshi Shinriki , Tomohiro Ohta Tomohiro Ohta
Published: October 2002

A novel via plug structure, direct-contact via plug with a submicron diameter, has been realized by selective aluminum (Al)-chemical vapor deposition (CVD). In this structure, the Al plug is in direct contact with the lower and upper level Al interconnects. It was found to be essential to carry out all three processes continuously in a high vacuum: surface cleaning by reactive ion etching (RIE), plug formation by selective Al-CVD and sputter deposition of upper level Al film. The via structure has no heteromaterial interfaces along the current path. Electrical characteristics were evaluated and were compared with those of the conventional tungsten (W) plug. The via chain resistance in 0.5 µm diameter was 0.25 Ω/via, which was found to be 1/3 of that of a W-filled plug, and the interface resistance was estimated to be extremely low. Electromigration (EM) tolerance was also found to be better than that of a W plug. Our data demonstrated that the direct-contact Al-CVD plug was very suitable for realizing high-performance LSI with lower process cost.
A Novel LOCal Oxidation of Silicon (LOCOS)-Type Isolation Technology Free of the Field Oxide Thinning Effect
Authors: Park Tai-su , Seong Joon Ahn Seong Joon Ahn , Sung Tae Ahn Sung Tae Ahn
Published: October 2002

A novel LOCal Oxidation of Silicon (LOCOS)-type isolation technology free of the field oxide thinning effect, named POlysilicon (poly-Si) Spacer LOCOS (POS-LOCOS), has been developed. After the first field oxidation, poly-Si is deposited and etched anisotropically. Then, at the narrow field region, substantial amount of poly-Si remains after etching, while only spacers are formed at the ends of the field region for the wide region, and then the second oxidation is performed by oxidizing poly-Si. POS-LOCOS eliminates the field oxide thinning effect. Devices with POS-LOCOS show less variation in the isolation size, lower peripheral junction leakage current, and higher field transistor threshold voltages at narrow isolation region compared to the conventional LOCOS isolation. Almost the same N+/N+ punchthrough characteristics are obtained with POS-LOCOS and conventional LOCOS, and transistors with POS-LOCOS show low leakage current and normal drain current (I
d)-gate voltage (V
g) characteristic. It is expected that POS-LOCOS will help extend the lifetime of the LOCOS-type isolation to the next generation of the integrated circuit (IC) technology.
Fabrication of Diamond Films at Low Pressure and Low-Temperature by Magneto-Active Microwave Plasma Chemical Vapor Deposition
Authors: Yara Takuya , Yuasa Motokazu , Shimizu Manabu , Makita Hiroshi , Hatta Akimitsu , Suzuki Jun-ichi , Toshimichi Ito Toshimichi Ito , Akio Hiraki Akio Hiraki
Published: October 2002

We succeeded in fabrication of diamond films at substrate temperature of 80° C by using the magneto-active microwave plasma chemical vapor deposition (CVD) method at low pressure (0.1 Torr) with forced substrate cooling. The magneto-active microwave discharge enables us to use high-density microwave plasma under low pressure. High-density plasma-enhanced CVD under low-pressure is advantageous for low-temperature synthesis of diamond films because of decrease in thermal flux to the substrates from neutral gases heated in the plasma. Deposited films were investigated by scanning electron microscopy (SEM), Raman scattering spectroscopy, thin-film X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The fabricated films are randomly oriented polycrystalline diamond of fine crystallite size (below 100 Å). The deposition rate of the diamond films decreased with decreasing substrate temperature in the range below 400° C.
Synthesis of Diamond Using Low Pressure Plasma Jet
Authors: Sakiyama Satoshi , Osamu Fukumasa Osamu Fukumasa , Keiichirou Aoki Keiichirou Aoki
Published: October 2002

With the use of the forced constricted type plasma jet, the synthesis of diamond is attemped under low pressure, in order to realize large area deposition at a high rate. The effect of the ambient gas pressure on the deposition rate and deposition area of the film is studied. It is clarified that the deposition area is extended markedly with decreasing gas pressure. Furthermore, diamond films are successfully synthesized without the large decrease of the deposition rate, even at 5 Torr.
Photoinduced Surface Deposition of Metallic Silver: Basic Research for Its Application to Optical Recording Devices
Authors: Takeshi Kawaguchi Takeshi Kawaguchi , Shigeo Maruno Shigeo Maruno
Published: October 2002

The photoinduced surface deposition (PSD) phenomenon has been studied for its application to a new optical recording device. The pattern formed by photodeposited Ag particles could be erased by annealing or illumination. The pattern could be effectively fixed by coating the sample surface with semitransparent metallic film such as Au. These are assumed useful properties for the application, in addition to the high contrast and high resolving power of the pattern. The PSD phenomenon was also found to be markedly influenced by atmosphere. From the temperature dependence of the PSD phenomenon (-20 to +50° C), it was found that the maximum of the PSD photosensitivity was at around room temperature, and that the resolving power dramatically decreased with an increase in temperature, irrespective of atmosphere.
Fourier Analysis-Based Method for High-Frequency Performance Calculation of Heterojunction Bipolar Transistor
Authors: Gregory Khrenov Gregory Khrenov , Victor Ryzhii Victor Ryzhii , Sergey Kartashov Sergey Kartashov
Published: October 2002

A method to evaluate high-frequency performance of heterojunction bipolar transistors based on Fourier analysis of the non-stationary collector current response is proposed. The nonequilibrium electron transport and velocity overshoot effects are taken into account by ensemble Monte Carlo particle simulation. The influence of the emitter and collector capacitances on the high-frequency performance are also included in our consideration. It is found that the conventional method for cut off frequency calculation underestimates its value. Experimental results reported in the literature are compared with the results of numerical simulation. The comparison shows high accuracy and validity of the developed method.
Influence of Electron Scattering on Current Gain of Heterojunction Bipolar Transistor Operating in Coherent Regime
Authors: Gregory Khrenov Gregory Khrenov , Victor Ryzhii Victor Ryzhii , Elena Kulkova Elena Kulkova
Published: October 2002

We have analyzed the transport of electrons in the base of a heterojunction bipolar transistor operating in the coherent regime. The analysis is based on the Boltzmann transport equation for the one-electron distribution function. The influence of electron scattering on the transistor current gain in the frequency range beyond the usual cut-off frequency is included in the proposed model. It is demonstrated that the scattering of the electrons in the base region strongly affects the current gain of the heterojunction bipolar transistor in the extended frequency range. Conditions on the relationship between the electron transit times in the base and collector regions and electron scattering rate in the base, which are necessary for the implementation of the current gain beyond the usual cut-off frequency, are found.
Effects of Hydrogen and Bias on Single-Crystal Al Growth on Vicinal Si by DC Magnetron Sputtering
Authors: Yokoyama Shin , Ichikawa Hiroshi , Yoshiyuki Ichikawa Yoshiyuki Ichikawa , Mitsumasa Koyanagi Mitsumasa Koyanagi
Published: October 2002

The crystallinity of single-crystal Al(110) film grown on a vicinal Si(100) substrate has been improved by adding a small amount of hydrogen (0.5%) into the sputtering gas (Ar) and applying a positive substrate bias voltage. By utilizing these effects and grazing incidence growth, the growth temperature can be lowered to ≤200° C, resulting in a better surface morphology. The excess amount of hydrogen (5%) and negative substrate bias cause degradation of the film quality. The growth model involving the roles of hydrogen and substrate bias has also been proposed.
Solderability of Electroless Nickel Alloys Using Wetting Balance Technique
Authors: Chwan-Ying Lee Chwan-Ying Lee , Kwang-Lung Lin Kwang-Lung Lin
Published: October 2002

Solderability of electroless nickel-alloy deposits was investigated by the wetting balance technique. The wetting time, wetting force and dewetting can be obtained from the wetting curve. Four parameters, wetting time, percentage of theoretical force, stability of wetting and solderability index, were applied to determine the effects of the soldering variables including two kinds of flux, substrates of electroless nickel-alloy deposits and their solderability. In general, wetting time decreases with an increase in soldering temperature. The rosin-activated flux has a stronger fluxing effect than organic acid. Among the investigated items, solderability index and contact angle are quite sensitive to the base metal material. The electroless Ni–Cu–P deposit and the electroless Ni–P with Au-coated deposit exhibit good wetting behavior with contact angles of 25°<θ<45° when using RA flux. On the other hand, poor wettability, with contact angles of 65°<θ<90°, was observed for the deposits investigated in this work using OA flux.
Application of High-Resolution Film for Lithography to Synchrotron X-Ray Topography
Authors: Mizuno Kaoru , Iwami Masayuki , Hashimoto Eiji , Kino Kazuyoshi Ito
Published: October 2002

A high-resolution film for lithography is applied to a detector for synchrotron radiation topography, instead of a nuclear plate. The film shows much better resolution than that of the plate although exposure time an about 500 times longer is required. The size distribution of interstitial loops grown as vacancy sources in a nearly perfect aluminum crystal after a temperature rise is examined from the white beam topograph.
Growth Behavior of GaAs in Metalorganic Vapor Phase Epitaxy onto ZnSe
Authors: Mitsuru Funato Mitsuru Funato , Shizuo Fujita Shizuo Fujita , Shigeo Fujita Shigeo Fujita
Published: October 2002

Growth modes in metalorganic vapor phase epitaxy (MOVPE) of GaAs on ZnSe under various growth conditions are investigated and compared. It is found from transmission electron microscopy (TEM) observation that GaAs growth at 550°C and low V/III ratios (≤5) is highly 3-dimensional, whereas the growth at low temperatures ( ≤500°C) or high V/III ratios (≥10) is 2-dimensional. Migration of Ga-related clusters seems to be responsible for the 3-dimensional growth. Using this variation of the growth modes, a quantum well structure is fabricated and the possibility to fabricate a quantum dot is also indicated.
Chemical Vapor Deposition of Anti-Reflective Layer Film for Excimer Laser Lithography
Authors: Gocho Tetsuo , Ogawa Tohru , Masakazu Muroyama Masakazu Muroyama , Jun-ichi Sato Jun-ichi Sato
Published: October 2002

We report a new anti-reflective layer (ARL) film for KrF excimer lasers, which makes excimer laser lithography applicable to mass production of devices with a design rule tighter than 0.35 µm. The ARL film, which is composed of SiO

x

N

y

:H, was deposited with a higher SiH4/N2O ratio than in conventional PECVD (Plasma Enhanced Chemical Vapor Deposition) conditions. The SiO

x

N

y

:H films, with optimal refractive indices, were easily deposited by varying the SiH4/N2O ratio as a PECVD parameter. Using the SiO

x

N

y

:H film to fabricate a 16MSRAM gate structure, variations in photoresist absorption were significantly reduced.
Solution Growth of CuGaS2 Using In as a Solvent under Controlled S Vapor Pressure
Authors: Kato Takamasa , Kazunori Hagimoto Kazunori Hagimoto , Takashi Matsumoto Takashi Matsumoto
Published: October 2002

Growth of CuGaS2 bulk crystals by the temperature difference method under controlled S vapor pressure has been investigated. The synthesized crystals were CuGa

x

In1-
x

S2 solid solutions, and the In alloy composition, 1-x, depended on both the growth temperature and the S vapor pressure.
Silicon Wafer Orientation Dependence of Metal Oxide Semiconductor Device Reliability
Authors: Nakamura Kou , Ohmi Kazuyuki , Yamamoto Kazuma , Makihara Koji , Ohmi Tadahiro
Published: October 2002

The reliability of very thin gate oxides is studied using Si(100) and Si(111) wafers. When Si(111) wafer is oxidized to form thick oxide such as field oxide, the Si–SiO2 interface microroughness increases. The increased microroughness degrades the dielectric breakdown characteristics. Moreover, the oxide films on Si(111) are inferior to those on Si(100) in reliability even when the Si–SiO2 interface microroughness is of the same level. Oxide quality is determined by silicon wafer orientation.
Elastic Property Dependence on Layer Periodicity in Cu/Ni Superlattices
Authors: Jankowski Alan F. , Edward M. Sedillo Edward M. Sedillo , Jeffrey P. Hayes Jeffrey P. Hayes
Published: October 2002

Cu/Ni superlattices are prepared by magnetron sputter deposition and structurally characterized with X-ray diffraction measurement. A 1.2–4.5 nm range of layer pair spacings is produced in a series of 1–2-µm-thick films which have a [111] textured growth. Uniaxial tensile testing is used to produce load-displacement curves from free-standing Cu/Ni films and calibration standards of Cu and Ni films. Direct measurement of the yield and ultimate stresses as well as Young's modulus is performed for the Cu/Ni films. The measured Young's modulus shows a bimodal variation with layer pair spacing. A maximum increase of 50% in Young's modulus, above the rule-of-mixtures value, is measured for a 2-nm-thick layer pair sample. The yield stress behavior follows the modulus trend with layer pair spacing, whereas the ultimate stress inversely follows the trend, that is, the stiffest samples are the most brittle. Isothermal annealing of the 2-nm-thick Cu/Ni sample progressively homogenizes the layered structure and diminishes the modulus enhancement to the rule-of-mixtures value.
Emittance Measurement of High-Brightness Microbeams
Authors: Ishizuka Hiroshi , Nakahara Yuriko , Kawasaki Sunao , Musyoki Stephen , Shimizu Hiroshi , Watanabe Akihiko , Shiho Makoto
Published: October 2002

Arrays of microtriodes have recently become available due to the development of microfabricated field-emission electron sources. Computer simulation has shown that the brightness of beams emitted by them is significantly higher than that of the common microbeams, and possible application of the accelerated beam to free electron lasers has been discussed. Experimentation on beam generation has started, but methods for diagnosing the beam have not yet been established. Difficulty is predicted, because of the high brightness, in applying the conventional methods of emittance measurement. In this paper we propose a new method that determines the emittance without using apertures. The cross section of a converging beam is elongated by a quadrupole lens, and parameters of the emittance ellipse are obtained from the beam size on a screen when changing either the strength or the axial position of the quadrupole lens.
Surface Morphology of Lead-Based Thin Films and Their Properties
Authors: Atsuki Tsutomu , Soyama Nobuyuki , Sasaki Go , Yonezawa Tadashi , Ogi Katsumi , Sameshima Katsumi , Hoshiba Kazuhiro , Nakao Yuichi , Kamisawa Akira
Published: October 2002

Surface morphology of lead-zirconate-titanate [PZT(52/48)] thin films prepared by sol-gel processing on Pt/Ti/ SiO2/Si substrates was studied. When the atomic ratio [Pb/(Zr+Ti)] of PZT gel films was 1, rosette structure was observed in the films after annealing at 600° C for one hour. The crystal structure of the rosette was identified as perovskite and that of the other area was nonperovskite, by electron diffraction analysis. Lead deficiency in the non-perovskite phase caused by lead diffusion into the bottom electrode was detected by energy dispersive X-ray spectroscopy and Auger electron spectroscopy. In order to prepare PZT films with a smooth surface, the following four means were efficient: addition of lead excess, rapid thermal annealing (RTA), adoption of buffer layer, and preparation of crystal nucleus on the substrate.
Fatigue Characteristics of Sol-Gel Derived Pb(Zr, Ti)O3 Thin Films
Authors: Amanuma Kazushi , Takashi Hase Takashi Hase , Yoichi Miyasaka Yoichi Miyasaka
Published: October 2002

Fatigue mechanisms of sol-gel derived Pb(Zr–Ti)O3 (PZT) thin films and the effects of La addition on the fatigue characteristics were investigated. For PZT(40/60) and PZT(53/47), the remanent polarization (P
r) and the coercive field (E
c) decreased with switching cycles. These properties were restored by heating the fatigued films above their Curie temperature. This result indicates that domain pinning is the dominant fatigue mechanism for PZT(40/60) and PZT(53/47). On the other hand, for PZT(70/30), P

r
was almost constant and E
c increased with switching cycles; this implies that the fatigue mechanism for PZT(70/30) is different from that for PZT(40/60) and PZT(53/47). Addition of La to the PZT(53/47) film reduced space charge in the film, though did not improve fatigue characteristics.
High-Deposition-Rate Growth of Lead Titanate Zirconate Films by Reactive Electron Beam Coevaporation
Authors: Mochizuki Shoichi , Toshiyuki Mihara Toshiyuki Mihara , Tadashi Ishida Tadashi Ishida
Published: October 2002

Lead titanate zirconate (PZT) thin films were prepared by reactive coevaporation of lead, zirconium and titanium with an electron beam gun. To promote oxygenation of deposited films, mixed gas of oxygen and ozone was used. A PZT film with a single perovskite phase was obtained at a substrate temperature of 550° C without post-thermal annealing on a lead titanate film. The deposition rate was 50 nm/min, which was much higher than that in the case of the sputtering method. The axial ratio (c/a) of the tetragonal perovskite phase decreased with the increase of zirconium content.
Improvement of Temperature Dependence of Piezoelectric Elements
Authors: Harashima Kunihiro Nagata
Published: October 2002

The relationships between the equivalent circuit constants of a piezoelectric element and the piezoelectric d
33- and g
33-constants were first clarified. The temperature dependence of the composed equivalent circuit constants was then decreased by connecting the piezoelectric element to a temperature-compensating capacitor, either in series or in parallel. Furthermore, new sandwich-like piezoelectric elements consisting of stacked piezoelectric ceramic and dielectric ceramic layers were constructed to decrease the dependence on temperature. The piezoelectric d
33-constant of Pb(Zr, Ti)O3 changed by about 15% over the temperature range of 0 to 160° C. The new sandwich-like element, however, exhibited a change of less than 3% over the same temperature range.
Electrooptic Properties of Two-Stage Sintered (Pb1-xLax)(Zr, Ti)O3: X/65/35 Ceramics (X=6–9)
Authors: Oshima Kazuhiro , Tsuzuki Kaoru
Published: October 2002

Several conditions for the 2-stage sintering method have been refined to improve the optical quality of (Pb, La)(Zr, Ti)O3 (PLZT) ceramics, and electrooptical properties of fabricated PLZT ceramics with the composition of (6–9)/65/35 were examined. Ceramics which were obtained from mixed oxide (MO) powders exhibited better electrooptic characteristics (better transmittance, smaller residual birefringence, larger electrooptic coefficients) than those from coprecipitated (CP) powders under common processing conditions. For several compositions of MO-PLZT, smaller E
c was attained, as compared with reported ones. A marked improvement in electrooptic coefficients (R=6.3×10-16 m2/V2, V
π=130 V, with 0.30 mm thickness) was also observed for MO-PLZT 9/65/35 ceramics.
Modeling of the Hole Current Caused by Fowler-Nordheim Tunneling through Thin Oxides
Authors: Hemink Gertjan , Tetsuo Endoh Tetsuo Endoh , Riichiro Shirota Riichiro Shirota
Published: October 2002

A new model for the substrate hole current that occurs during Fowler-Nordheim (FN) stress of thin oxides is proposed. The model is based on the assumption that hot hole injection occurs at the anode. The probability that a hole is emitted in the oxide and contributes to the hole current is described by an empirical relation that is a function of the effective barrier height and the average energy of the electrons arriving at the anode. To compute the average electron energy in the oxide, an energy dependent energy relaxation distance is used. The results obtained with the model are in very good agreement with the measurements for oxides within a thickness range of 5.5 to 12.5 nm.
Optical Associative Memory Using LiNbO3:Fe Hologram and BaTiO3 Phase Conjugate Mirror
Authors: Chen Zhiming , Yago Makoto , Adachi Masatoshi , Shiosaki Tadashi , Akira Kawabata Akira Kawabata
Published: October 2002

Experimental investigation is presented of an all-optical associative memory using a LiNbO3:Fe hologram and BaTiO3 phase conjugate mirror which is an improved self-pumped phase conjugate mirror with high response speed for a µ W-order of the magnitude signal beam. In our experiment, a 40 µ W readout light beam is used and an associated output is obtained within 2 s. Nonlinear reflectivity of the phase conjugate wave is expected to reflect the strongest signal and to improve the signal-to-noise ratio.
Phase Sequence in Smectic Liquid Crystals Having Fluorophenyl Group in the Core
Authors: Hatano Jun , Hanakai Yoshihiro , Furue Hirokazu , Uehara Hiroyuki , Saito Shin'ichi , Murashiro Katsuyuki
Published: October 2002

The phase sequence of a new family of chiral smectic liquid crystals, represented by 4-(1-methylhepthyloxycarbonyl) 3-fluorophenyl 4′-dodecylbiphenyl-4-carboxylate (MHFPDBC), were investigated by measurements of dielectric dispersion under various bias field strengths. Three phases, ferrielectric smectic Cγ
* phase (SmCγ
*), antiferroelectric phase (AF) and ferrielectric phase (FI), were confirmed between ferroelectric SmC* phase and antiferroelectric SmC
A

* phase. In the dielectric measurements around the ferrielectric phases, an opposite bias treatment prior to the application of the target bias field strength is important. Observed dielectric relaxation modes were discussed together with the results of electrooptical and conoscopic observations.
Current-Voltage Characteristics of Silicon on Insulator Metal Oxide Semiconductor Field Effect Transistors in Ballistic Mode
Authors: Kenji Natori Kenji Natori
Published: October 2002

Current-voltage characteristics of ultrathin silicon on insulator n-type MOSFETs (metal oxide semiconductor field effect transistors) operating in ballistic transport mode are given. They are derived with the similar guiding principle as that used in quantum point contact. The obtained result is independent of channel length, and is expressed with elementary parameters without depending on ambiguous carrier mobility. They show triode and pentode operational modes similarly to the normal MOSFET. When inversion carriers are degenerate, saturation current is independent of temperature and is proportional to the carrier density to the power of 1.5.
Influence of Grown-in Hydrogen on Thermal Donor Formation and Oxygen Precipitation in Czochralski Silicon Crystals
Authors: Hara Akito , Koizuka Masaaki , Aoki Masaki , Fukuda Tetsuo , Hiroshi Yamada-Kaneta Hiroshi Yamada-Kaneta , Haruhisa Mori Haruhisa Mori
Published: October 2002

Using hydrogen-enhanced thermal donor formation and hydrogen-enhanced oxygen precipitate nuclei formation, we confirmed the presence of hydrogen in as-grown Czochralski (CZ) silicon (Si) ingots. Hydrogen concentrations in as-grown ingots were very low at 2.5×1011cm-3. We found that even such a small amount of hydrogen influences the quality of as-grown CZ Si crystals due to hydrogen-enhanced oxygen precipitate nuclei formation caused byin situannealing during crystal growth. Reducing hydrogen contamination during crystal growth is important in obtaining high-quality CZ Si crystals.
Effects of Anodization Current Density on Photoluminescence Properties of Porous Silicon
Authors: Ban Takuya , Koizumi Tomohiro , Haba Shingo , Nobuyoshi Koshida Nobuyoshi Koshida , Yoshiyuki Suda Yoshiyuki Suda
Published: October 2002

Photoluminescence (PL) mechanisms of porous Si (PS) have been investigated by
comparing Fourier transform infrared (FTIR) absorption structures with PL properties
obtained using a He–Cd laser as a photoexcitation source. PS samples investigated
were prepared by anodization at different anodization current densities (i
a)
or by different total electric charge densities (q
T). The densities of Si–H
and Si–H2 species and the amount of oxygen are constant independent of
both i
a and q
T, and the oxygen is inferred to exist on the topmost
surface of the PS layer. On the other hand, the PL intensity depends only on i
a
and increases drastically with increasing i
a. Therefore, there is no relationship
between the PL intensity and the hydride densities or the amount of oxygen, indicating
that newly formed surface complexes, related to hydrogen or oxygen, including hydrogenated
amorphous Si, are not essential to the PL origin, and that the Si atomic configuration,
at least within the ∼ 100 Å detection depth in the PL experiment, varies
with the change of i
a. Macroscopic structures such as porosity and specific
surface area were evaluated to be unchanged among the samples. The FTIR and PL results
together with this evaluation suggest that photoluminescent elements, which do not
affect the macroscopic structures fundamentally, exist in the region of the internal
surface of PS pores and the number of elements increases with increasing i
a.
A quantum-sized crystallite is a most promising photoluminescent element for which
these results are well explained. The PL peak energies were almost constant among
the samples, which suggests that the minimum size of the quantum-sized crystallites, during anodization, is limited.
Time-Resolved X-Ray Diffraction Measurement of Silicon Surface during Laser Irradiation under Grazing-Incidence Conditions
Authors: Kojima Shigeru , Liu Kuang-Yu , Kudo Yoshihiro , Kawado Seiji , Ishikawa Tetsuya , Matsushita Tadashi
Published: October 2002

The time-resolved X-ray diffraction measurement under frequency-doubled Nd:YAG
laser (λ=0.53 µ m) irradiation was carried out using the “out of plane”
reflections at the BL-16 (MPW-beamline) in the Photon Factory (KEK). The “out of plane”
333 reflection showed that the lattice expansion in the lateral direction due to the
present pulsed-laser irradiation was negligible. From the skew 422 reflection at a glancing
angle of 2.3 mrad, which was near the critical angle for the total reflection, the
temperature rise in silicon thin surface layers (less than 75 nm) was estimated to be
210° C from the shift of peak position at 50 ns after laser irradiation
at a laser power density of 160 mJ/cm2.
Latch-up Suppressed Insulated Gate Bipolar Transistor by the Deep p+ Ion Implantation under the n+ Source
Authors: Lee Byeong-Hoon , Yun Chong-Man , Kim Han-Soo , Choi Min-Koo Han
Published: October 2002

A novel insulated gate bipolar transistor (IGBT) structure, which employs the self aligned deep p+ buried region enveloping all the area under the n+ source, is proposed and verified by SUPREM IV and PISCES-IIB simulation. The simulation results show that the latch-up current is found to increase up to about 10 times compared with the conventional structure when the implantation dose of the p+ buried region and the p-body are 1×1015 cm-2 and 1×1014 cm-2, respectively. The variation of the threshold voltage is within 0.1 V although the implantation dose of the p+ buried region increases from 1×1014 cm-2 to 1×1015 cm-2.