bluuebunny/crossref_metadata_2025 huggingface dataset:
Control of an Easy-Axis on Nematic-Polymer Interface by Light Action to Nematic Bulk
Authors: Voloshchenko Dmitry , Khyzhnyak Anatolii , Reznikov Yuriy , Reshetnyak Victor
Published: October 2002

An appearance of an easy orientation axis of a nematic liquid crystal on the isotropic aligning surface under the light absorption by in-bulk azo dye molecules is observed. It is shown that orientation of LC molecules in the irradiated region is close to the direction of the exciting beam polarization. Accompanying to aligning, the surface driven reorientation effect has been studied. A threshold as well as a nonthreshold reorientation of the director toward the light-induced easy axis were observed. The value of the light-induced anchoring energy depends on the exposure time and achieves 2.5×10-3 erg/cm2. The experimental data are explained within the framework of adsorption of phototransformed molecules from the LC bulk onto the aligning surface.
Atomic-Layer Chemical-Vapor-Deposition of SiO 2 by Cyclic Exposures of CH 3OSi(NCO) 3 and H 2O 2
Authors: Shunsuke Morishita Shunsuke Morishita , Yasutaka Uchida Yasutaka Uchida , Masakiyo Matsumura Masakiyo Matsumura
Published: October 2002

Atomic-layer chemical-vapor-deposition (AL-CVD) of SiO2 has been achieved by cyclic exposures of CH3OSi(NCO)3 and H2O2 at room temperature. The deposition rate was saturated at about 2.0 Å/cycle i.e., equal to the ideal quasi-monolayer/cycle. The surface roughness after 100 deposition cycles was found to be less than ±10 Å by atomic force microscopy (AFM). Film properties were also evaluated by auger electron spectroscopy (AES), X-ray photoemission spectroscopy (XPS), and Fourier transform IR (FT-IR) spectroscopy.
Step Structures on Vicinal InAs (001) under ( 2×4) and ( 4×2) Surface Reconstructions
Authors: Ikoma Nobuyuki , Shunsuke Ohkouchi Shunsuke Ohkouchi
Published: October 2002

Step structures on InAs (001) vicinal surfaces under two different surface reconstructions were investigated by scanning tunneling microscopy. On an InAs surface misoriented by 1° toward the [110] direction, relatively straight monolayer steps along the [11̄0] direction were observed under an As-stabilized (2×4) reconstruction. On the other hand, step-bunching of about 10 monolayers was detected under an In-stabilized (4×2) reconstruction. On an InAs surface misoriented by 1° toward the [11̄0] direction, ragged monolayer steps roughly running parallel to the [110] direction were seen under the (2×4) reconstruction. However, relatively straight steps along the [110] direction with step-bunching of 2-3 monolayers were observed under the (4×2) reconstruction. These results indicate that thermodynamically favorable step structures are different between the (2×4) and (4×2) reconstructions.
Electronic Structures of Wurtzite GaN, InN and Their Alloy Ga1-xInxN Calculated by the Tight-Binding Method
Authors: Yang Tao , Nakajima Sadanojo , Shiro Sakai Shiro Sakai
Published: October 2002

The semi-empirical tight-binding method is used to investigate band structures of wurtzite III-V nitride semiconductors. The tight-binding band structures of GaN and InN are first obtained by fitting the data to experiments and more accurate calculations. To obtain better description of the band structures, second-nearest-neighbor s and p state interactions are included and Ga 3d and In 4d electrons are treated as band states. Then, the band structure of the alloy Ga1-
x

In

x

N is predicted based on the obtained tight-binding parameters and a pseudobinary alloy model. The predicted alloy band gaps are in good agreement with experimental ones. The electron effective masses of the alloy are also presented. The effects of the second-nearest-neighbor interactions and nearest-neighbor s-d and p-d state interactions on the band structures are discussed in detail.
Effect of Intense Intersubband Optical Excitation on the Electron Distribution in GaAs/AlAs Quantum Wells
Authors: Soichiro Tsujino Soichiro Tsujino , Hidefumi Akiyama Hidefumi Akiyama , Hiroharu Sugawara Hiroharu Sugawara , Mathilde Rüfenacht Mathilde Rüfenacht , Yutaka Kadoya Yutaka Kadoya , Takeshi Noda Takeshi Noda , Hiroyuki Sakaki Hiroyuki Sakaki
Published: October 2002

Hot electrons were generated in n-doped GaAs/AlAs multiple quantum wells by optical intersubband excitation and their energy distributions were studied at 10 K. By measuring photoluminescence (PL) spectra, the hot-electron temperatureTelwas quantitatively evaluated, taking into account such effects as the degenerate distribution of electrons, impurity-induced level broadening, and the distribution of holes. It was found that, when the intensityPof the excitation was 30 kW cm-2, i.e. a few percent of the onset intensity for absorption saturation,Telincreased from 10 K to 120 K while the lattice temperature remained unchanged. WhenPwas between 10 W cm-2and 30 kW cm-2, the rise ofTelwas well explained by the balance between the photon energy absorption and the energy loss due to the LO phonon emission inside the ground subband.
Effect of Electric Field on Electron Cyclotron Resonance Plasma Etching
Authors: Nishioka Kyusaku , Fujiwara Nobuo
Published: October 2002

Recent studies of etching technology using plasma indicate that serious problems are induced by a charge build-up. The charge build-up causes radiation damage and distortion of etched profiles. These problems are induced by a non-neutrality of charge supply to the surface. By controlling the electric potential of surface material with a dc power supply, dependences of damage and pattern distortions on charge-up are investigated. Keeping the net current to the wafer zero is effective for reducing the radiation damage. The profile distortions occur due to the potential difference between mask and etched material. The profile is improved by setting the applied dc potential equal to floating potential.
Comprehensive X-Ray Diffraction Study of YBa 2Cu 3O 7-δ Thin Films
Authors: Z. Moshfegh A. , H. Fatollahi A. , Q. Wang Y. , Y. Sun Y. , H. Hor P. , A. Ignatiev A. Ignatiev
Published: October 2002

In situ annealed high temperature superconducting YBa2Cu3O7-δ thin films have been deposited on an MgO (100) substrate from a single stoichiometric target using DC magnetron sputtering. The films were characterized by X-Ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The effect of varying substrate temperature, T
s, and O2/Ar ratio on lattice parameters and on the degree of orientation of the films were examined. Both c- and a-lattice parameters decreased with increasing T
s. The reduction of c and a-lattice parameters as well as the oxygen deficiency in the films, δ, obey general (T
s - T
0)-4 behavior. We develope a new method to measure a more accurate way to find the degree of preferrential orientation along c and a-axis of the deposited films, (ΔV
006/ΔV
200), at different T
s by using X-ray diffraction theory and JCPDS files to obtain ∣F
(006)/F
(200)∣2. At T
s=735°C, the volume fraction along the c-axis was found to be ΔV

c
≈5.5 ×ΔV

a
corresponding to 85 grains having preferred orientation along c-axis. In addition, we have also measured FWHM of the (006) and (200) peaks by varying T
s. The thickness of the grains were estimated at different substrate temperature using the Scherrer formula.
Electron Paramagnetic Resonance and Mössbauer Spectra of Iron Ions in Bizen Pottery
Authors: Matsuoka Yuki , Ikeya Motoji
Published: October 2002

Electron paramagnetic resonance (EPR) and Mössbauer spectra of Japanese traditional Bizen pottery and its constituent clays have been measured to study the relationship between the color of pottery surface and the relevant states of iron ions ( Fe3+ and Fe2+). Hyperfine signals of Mn2+, presumably in carbonates, and a broad signal at g=2.0 similar to that of hematite ( Fe2O3) were observed for good-quality clay, while a signal at g>9 similar to that of magnetite ( Fe3O4) was observed for poor-quality clay. In pottery, the apparent g-factor of g=4.3 due to a large orthorhombic distortion E(S

x

2-S

y

2) and g=6 due to a large axial field D
S

z

2 were observed in addition to the broad signal around g=2 due to oxidation of iron into Fe2O3. Subtle change of colors resulted in the change of EPR spectra. Mössbauer spectra indicatcd that almost all of the iron ions at the surface of pottery are strongly oxidized into Fe3+ when the pottery is fired in oxidizing atmosphere, while those inside the pottery and at the surface fired at reducing atmosphere are not strongly oxidized into Fe3+.
Electrical Properties of Lead Lanthanum Titanate Thin-Film Capacitors Prepared by Sol-Gel Method
Authors: Lee Su Jae , Jang Min Su , Cho Chae Ryong , Kang Kwang Yong , Han Seok Kil
Published: October 2002

High-quality (Pb1-
x

La

x

)Ti1-
x
/4O3 (x=0.05) [PLT] thin films were fabricated successfully by sol-gel processing onto Pt/Ti/SiO2/Si and p-Si substrates. The optimum route and the conditions for preparing homogeneous and crack-free thin films were systematically investigated. Ferroelectric perovskite phase was observed in the PLT thin films annealed at 600° C for 30 min. We studied the electrical properties of the PLT film capacitors with the metal-ferroelectric-metal (MFM) and the metal-ferroelectric-semiconductor (MFS) structure for use in ferroelectric memories. The dielectric constant and dissipation factor measured for MFM capacitor were 225 and 0.018 at 100 kHz, respectively. The remanent polarization (P
r) and coercive field (E
c) of the PLT film were 8.5 µC/cm2 and 110 kV/cm, respectively. Also the film with 600 nm thickness showed current density as low as 10-6 A/cm2 at the electric field of 200 kV/cm, which corresponds to the electric resistivity of ∼1012 (Ω·cm) and represents excellent insulating properties. The MFS capacitor showed ferroelectric switching properties in C-V characteristics and the memory window of the hysteresis loop was about 1 V in the operation of ±10 V.
Effect of Thermal Curing on Thermomechanical Properties of Polyimide Films Having Rodlike Molecular Skeleton Formed on a Silicon Substrate
Authors: Nomura Hideshi , Masaya Asano Masaya Asano
Published: October 2002

Stresses in polyimide films coated on silicon wafers were measured in situ during the curing and cooling cycles. The films had a single rodlike molecular skeleton. Stress measurements were performed on films of uniform thickness under several different heating rates during the curing cycle. After the stress measurements, the cured polyimide films were examined by thermal mechanical analysis. The stress after the curing cycle increased with increasing heating rate during the curing cycle. Similarly, the thermal coefficient of expansion of the cured polyimide film increased with increasing heating rate. This phenomenom was thought to be caused by the decrease in the degree of in-plane orientation of the polyimide molecular chain with increased heating rate. The in-plane orientation was presumed to be influenced by the evaporation rate of the residual solvent.
Cubic to Tetragonal Phase Transformation of Ultrafine BaTiO3 Crystallites at Room Temperature
Authors: Yen Fu-Su , Hsiang Hsing-I , Chang Yen-Hwei
Published: October 2002

The critical crystallite size for the cubic (c-) to tetragonal (t-) phase transformation of ultrafine BaTiO3 crystallites was examined. Crystallites were prepared by calcination of barium titanyl oxalate tetrahydrate (BTOT) at various temperatures as to obtain crystallites with different sizes. The c- BaTiO3 crystallite which is thermodynamically considered as a high-temperature form can exist at room temperature if the crystallite is smaller than certain size. The critical size for the c→t phase transformation is ∼30 nm. The size may become larger if the crystallite suffers higher lattice strain which can be induced by different powder preparation methods.
High-Sensitivity Channeling Analysis of Lattice Disorder Near Surfaces Using Secondary Electrons Induced by Fast Ions
Authors: Kudo Hiroshi , Fukusho Taro , Tanabe Atsushi , Ishihara Toyoyuki , Inoue Tomoyasu , Satoh Masataka , Yamamoto Yasuhiro , Seki Seiji
Published: October 2002

Under the channeling condition of 56 MeV O8+, the sensitivity of keV secondary-electron yield to lattice disorder in crystals has been investigated for Si and Ge damaged with 5 keV Ar+, and for epitaxially grown CeO2 on Si and Si on sapphire. The analysis indicates that the ratio of channeling to random yield is a sensitive measure of displaced atoms whose areal density is equivalent to a nanometer-thick amorphous layer on a crystal surface. This technique enables low-density defect analyses where commonly used ion backscattering spectrometry is unapplicable.
Shape of Film Grown on Microsize Trenches and Holes by Chemical Vapor Deposition: 3-Dimensional Monte Carlo Simulation
Authors: Akiyama Yasunobu , Matsumura Satoshi , Nobuyuki Imaishi Nobuyuki Imaishi
Published: October 2002

A semi-microscale 3-dimensional film growth simulation code using a simple Monte Carlo method was developed. This code predicts the step coverage on a trench and a hole of arbitrary shapes and requires much smaller computer memory size and less calculation time than the Direct Simulation Monte Carlo (DSMC) method. The simulation code was evaluated by comparing the results with experimental results of a zirconia ( ZrO2) film grown on a hole. The experiments and/or 3-dimensional simulations indicated that the film grown on the side and bottom walls of a hole is thinner than that of a 2-dimensional trench, and complete occlusion of a hole is more difficult compared with a trench with opening width equal to the hole diameter. The surface reaction rate constant is the most important factor in the occlusion process. When the reaction rate constant is small, the hole is occluded with a thin film. However, when the reaction rate constant is large, there remain a void inside and a small unfilled pinhole through the thick film grown on the top.
Formation of Oxygen-Related Defects Enhanced by Fluorine in BF2
+-Implanted Si Studied by a Monoenergetic Positron Beam
Authors: Uedono Akira , Moriya Tsuyoshi , Kawano Takao , Tanigawa Shoichiro , Nagai Ryo , Umeda Kazunori
Published: October 2002

Defects in 25-keV BF2
+- or As+-implanted Si specimens were probed by a monoenergetic positron beam. For the As+-implanted specimen, the depth profile of defects was obtained from measurements of Doppler broadening profiles as a function of incident positron energy. The major species of the defects was identified as divacancies. For ion-implanted specimens after annealing treatment, oxygen-related defects were found to be formed. For the BF2
+-implanted specimen before annealing treatment, such defects were formed in the subsurface region, where oxygen atoms were implanted by recoil from oxide films. This was attributed to enhanced formation of oxygen-related defects by the presence of F atoms.
Steady State Solutions of Diffusion Equations of Self-Interstitials and Vacancies in Silicon
Authors: Okino Takahisa , Shimozaki Toshitada , Takaue Ryoichi , Onishi Masami
Published: October 2002

Self-interstitial and vacancy diffusion equations taking account of the sink and source of these point defects are analytically studied in the steady state, assuming local equilibrium between these point defects. To determine the physically reasonable solutions, behavior of the point defects at the bulk surface is required as the boundary condition; however this has not been well understood. Therefore, self-interstitial and vacancy concentrations at the bulk surface are tentatively adopted as parameters. It was found that the exact steady state solutions depend on the specimen thickness. Substituting the solutions in the case of dislocation-free silicon into approximate relations, the time t
I or t
V at which self-interstitials or vacancies reach the steady state is determined.
Quantitative Analysis of Trace Water in Monosilane Gas Using Atmospheric-Pressure Ionization Mass Spectrometer with Bicompartment Ion Source
Authors: Mitsui Yasuhiro , Irie Takashi , Iijima Shimpei , Mizokami Kazuaki , Hasumi Keiji , Kuriyama Katsumi
Published: October 2002

Quantitative analysis of trace amount of water at the ppb level or less in monosilane gas was conducted using an atmospheric-pressure ionization mass spectrometer with a bicompartment ion source which prevents Si compound deposition in the ion source. Water ion which is not detected in the usual form of H2O+ due to the lower ionization potential of SiH3
+ than that of H2O+, was detected as cluster ions (SiH3OH2)+, (SiH3OH2H2O)+, (Si2H5OH2)+ and (Si2H5OH2H2O)+. These ions were identified by the collision-induced dissociation method. The intensity of each of these ions changed with monosilane concentration. An independent calibration curve of monosilane concentration was obtained from the total intensity of these ions. In this raw monosilane gas, about 20 ppb of water was detected. This was decreased to 2.5 ppb upon using an adsorption-type purifier. The detection limit (S/N) was estimated to be 5 ppt.
Analysis of Gate Lag in GaAs Metal-Semiconductor Field-Effect Transistor Using Light Illumination
Authors: Sasaki Hajime , Matsubayashi Hiroto , Ishihara Osamu , Konishi Ryosuke , Ando Koshi
Published: October 2002

We have developed a novel method for analyzing the gate lag effect in gallium arsenide (GaAs) metal-semiconductor field-effect transistor (MESFET) using light illumination. It is estimated that the density of trapped electrons at the surface of an active channel layer is above 6×1011 cm-2 from the dependence on photon flux density. Photon energy dependence shows that the electrons are mainly trapped at the GaAs surface. Angle-resolved analysis indicates that the trapped electrons at the active channel layer between the gate and the drain mostly account for the gate lag effect. Temperature dependence of the transconductance (g
m) dispersion shows that the activation energy of this trap is 0.33 eV.
Two-dimensional device simulation demonstrates the similar transient characteristics of the drain current, which originates from the electrons trapped at the GaAs surface.
Evaporation Rate and Saturated Vapor Pressure of Functional Organic Materials
Authors: Yase Kiyoshi , Takahashi Yoshikazu , Ara-kato Norihiko , Kawazu Akira
Published: October 2002

The evaporation rate and saturated vapor pressure (p) for functional organic materials have been evaluated by thermogravimetry in vacuum. A series of metal phthalocyanines (M-Pc) such as Cu-Pc, Ni-Pc, Pb-Pc and TiO-Pc, Tris(8-hydroxy-quinoline) aluminum complex ( Alq3), fullerene (C60) and tetrathiafulvalene (TTF), tetracyanoquinodimethane (TCNQ) and TTF-TCNQ are examined, together with the relationship between p and the enthalpy of evaporation.
Schottky Barrier on n-Type Al0.14Ga0.86N Grown by Organometalic Vapor Phase Epitaxy
Authors: Khan Mohammad Rezaul Huque , Nakayama Hisashi , Detchprohm Theeradetch , Hiramatsu Kazumasa , Nobuhiko Sawaki Nobuhiko Sawaki
Published: October 2002

Schottky barrier diodes of Au-n-Al0.14Ga0.86N grown by Organometallic Vapor Phase Epitaxy were obtained and characterized between 77 K and 373 K. Under forward bias the value of the ideality parameter n=1.41 and the threshold voltage is 0.75 V. The reverse bias leak current is below 10-10A on a reverse bias of 10 V. The barrier height (ΦB) was determined to be (1.17±0.03) eV and (1.3±0.05) eV by the current-voltage and the capacitance-voltage measurement repectively.
Voltage-Controlled Optical Fiber Coupler Using a Layer of Low-Refractive-Index Liquid Crystal with Positive Dielectric Anisotropy
Authors: Pan Ru-Pin , Liou Shyang-Rong , Chao-Ken Lin Chao-Ken Lin
Published: October 2002

A variable fiber directional coupler is made using liquid crystal as the intermediate cladding layer between two side-polished optical fibers. A nematic liquid crystal with low refractive index and positive dielectric anisotropy is used. An ac electric field is applied to the liquid crystal by applying a voltage across two parallel electrode stripes on the two sides of the fibers. The electric field rotates the molecular orientations and changes the refractive index of the liquid crystal. The coupling ratio between the two fibers is then controlled by the applied voltage. The dependence of the coupling ratio on the applied voltage is studied for various light wavelengths, including a continuous variable range between 1.272 µ m and 1.310 µ m.
Theoretical Characteristics of Surface Electric Potential Sensor with Vibrating Shutter and Its Use for Measuring
Authors: Tada Yasufusa , Yoshiyuki Tomizawa Yoshiyuki Tomizawa
Published: October 2002

A device termed the surface electric potential sensor is described. It is used for detecting the surface electric potential of a charged dielectric film and consists of a vibrating shutter, a sensing electrode, and a preamplifier. The theoretical analysis shows that the sensor has a constant current characteristic, that its sensitivity becomes greater as its vibrating frequency becomes higher, and that the preamplifier has an input resistance which makes the sensitivity maximum. Although the calibrating method for measuring the electric potential using the sensor is not the standard one, it is now in use due to its low cost and the absence of electrical danger. Hence, the method has been compared with the compensation method known as the standard and most accurate one. It is found that more accurate measurement by the calibrating method can be performed using the concept of “correcting distance”.
Optical Haar Wavelet Transforms with Liquid Crystal Elements
Authors: He Zhan , Honma Michinori , Masuda Shin , Nose Toshiaki , Susumu Sato Susumu Sato
Published: October 2002

Optical Haar wavelet transforms are achieved with liquid crystal (LC) elements: patterned-electrode liquid crystal cells serve as generators of optical Haar wavelets, and LC microlens arrays are used in the fabrication of shadow-casting systems. The phase modulation characteristics of the patterned electrode LC cells are investigated by applying a voltage, and the 1-dimension, 2-dimension rectangular and circular Haar wavelets are obtained by adjusting the voltage applied to the LC cells. A shadow-casting system composed of a LC microlens array is proposed. Due to the variability of the focal length of the LC microlens, good optical wavelet transforms can be achieved readily.
Improvement of the Laser Phase Contrast Method for Measuring the Spatial Distribution of Electron Density Fluctuations in Heliotron E
Authors: Kado Shinichiro , Irie Tsutomu , Muraoka Katsunori , Matsuo Keiji , Tanaka Kenji , Kondo Katsumi , Sano Fumimichi , Obiki Tokuhiro
Published: October 2002

The laser phase contrast method is suitable for measuring long wavelength fluctuations propagating perpendicular to the laser beam axis. The obtainable data, which have so far been integrated along line-of-sights, are improved to be spatially resolved along the beam axis by selecting a particular direction of the sheared magnetic field of a toroidal confinement system utilizing a slit attached to a phase plate. First, the spatial resolution was formulated, and its validity was examined using an ultrasonic wave which simulated density fluctuations in plasmas. Then, the method was applied to plasma discharges in the Heliotron E device, and wavenumber (K)-frequency (f=Ω/2π) spectra,S(K,f), shows that the spatial regions were surely resolved.
Ion Bombardment Effect on Hydrogen Content in Boron Thin Films Prepared by Electron Cyclotron Resonance Discharge of Diluted Decaborane Gases
Authors: Yoshifumi Ito Yoshifumi Ito , Masahiro Nishikawa Masahiro Nishikawa
Published: October 2002

Boron thin films are prepared by electron cyclotron resonance discharge of decaborane gas diluted with helium gas. The dependence of the hydrogen content in the films on the bias voltage V
B applied to substrates is investigated at the substrate temperature of 200°C. The hydrogen content are 2–3 at. 6–11 at. and 9.3 at. The bombardment of the ions with energies more than 300 V during the deposition increases the hydrogen content in the boron thin films.
Growth Control and Biophoton Radiation by Plant Hormones in Red Bean
Authors: Kai Shoichi , Moriya Tomoyuki Ohya Kouhei , Fujimoto Tokio
Published: October 2002

The growth kinetics of seeds of red beans ( Phaseolus angularis ) was investigated by externally adding various hormones (gibberellin (GA3)), abscisic acid (ABA) and indole acetic acid (IAA)) during germination. For root growth of red beans, GA3 always acted as an activator while ABA as an inhibitor. IAA was both an activator and an inhibitor depending on its concentration. Root growth could be described by a stochastic logistic equation. The hormone concentration dependences of coefficients of the equation were determined. The hormone influences on biophoton radiation were also investgated. With GA3, the intensity of spontaneous bioluminescence increased with time and showed two strong radiation periods, in which strong localization of bioluminescence was induced. However with ABA and IAA, weaker bioluminescences were observed. The location of the strong radiation induced by GA3 was determined as the growing point near a root cap, by use of a two-dimensional photon counting system.
Heuristic Method for Phase-Conflict Minimization in Automatic Phase-Shift Mask Design
Authors: Moniwa Akemi , Terasawa Tsuneo , Nakajo Kyoji , Sakemi Jun'ya , Okazaki Shinji
Published: October 2002

A shifter placement program has been developed for alternate-type phase-shift masks that require a 180°-phase difference between adjacent aperture pairs. Using a heuristic approach, this program minimizes the number of phase conflicts that arise when adjacent apertures are forced to have the same phase. Adjacent aperture relationships are expressed by an undirected graph; the phase conflicts are found in the closed loops containing an odd number of apertures. Minimization is achieved by listing these loops and identifying the adjacent aperture pairs that occur in more than one loop. The validity of this algorithm was demonstrated using test patterns.
Experimental Verification of an Aerial Image Evaluation Method and Its Application to Studies of Attenuated Phase-Shifting Masks
Authors: Shimizu Hideo , Uesawa Fumikatsu , Oda Tatsuji , Sugawara Minoru
Published: October 2002

Attenuated phase-shifting masks can improve the resolution of optical lithography, and an accurate aerial image evaluaton method is necessary for optimizing parameters. In a positive-tone chemically amplified resist, WKR-PT2, the actual resist pattern size can be easily estimated from the aerial image. This was experimentally verified by evaluating both binary and attenuated phase-shifting masks, and it was established that the secondary peak resolution limits can also be estimated from an aerial image. Further study indicated that this resolution limit in dense patterns is determined by numerical aperture, wavelength, and target hole size. Optimization of numerical aperture and pattern layout is necessary before attenuated phase-shifting masks can be put to practical use.
Projection Exposure with Variable Axis Immersion Lenses: A High-Throughput Electron Beam Approach to “Suboptical” Lithography
Authors: Hans C. Pfeiffer Hans C. Pfeiffer
Published: October 2002

IBM's high-throughput e-beam stepper approach PRojection Exposure with Variable Axis Immersion Lenses (PREVAIL) is reviewed. The PREVAIL concept combines technology building blocks of our probe-forming EL-3 and EL-4 systems with the exposure efficiency of pattern projection. The technology represents an extension of the shaped-beam approach toward massively parallel pixel projection. As demonstrated, the use of variable-axis lenses can provide large field coverage through reduction of off-axis aberrations which limit the performance of conventional projection systems. Subfield pattern sections containing 107 or more pixels can be electronically selected (mask plane), projected and positioned (wafer plane) at high speed. To generate the entire chip pattern subfields must be stitched together sequentially in a combination of electronic and mechanical positioning of mask and wafer. The PREVAIL technology promises throughput levels competitive with those of optical steppers at superior resolution. The PREVAIL project is being pursued to demonstrate the viability of the technology and to develop an e-beam alternative to “suboptical” lithography.
Reduction of X-Ray Irradiation-Induced Pattern Displacement of SiN Membranes Using H+ Ion Implantation Technique
Authors: Ashikaga Kinya , Tsuboi Shinji , Yamashita Yoshio , Ohta Tsuneaki , Noda Syuichi , Kasai Masanori , Hoga Hiroshi
Published: October 2002

We have developed a technique for improving X-ray irradiation stability of silicon nitride (SiN) X-ray mask membrane using H+ implantation. This technique can realize the reduction of X-ray irradiation-induced pattern displacement to less than 20 nm after X-ray absorption with a dose of 30 MJ/cm3 by optimizing the implantation dose to 4×1015/ cm2 at 150 keV.
It is found that the mechanism of the reduction of the displacement is that the stress change after X-ray absorption in the implanted layer (top to 1.1 µ m in depth) of SiN film compensates the stress change in the unimplanted layer (1.1 to 2.0 µ m (bottom) in depth).
X-Ray Lithography with a Wet-Silylated and Dry-Developed Resist
Authors: Oizumi Hiroaki , Yamashita Yoshio , Ogawa Taro , Soga Takashi , Yamanaka Ryoko
Published: October 2002

X-ray lithography with a wet-silylated and dry-developed resist has been investigated in order to overcome pattern collapse during wet development and to delineate fine-pitch and high-aspect-ratio patterns. In addition, the applicability to sub-0.1 µ m patterning is discussed. Silylation solution consists of B[DMA]DS (bis(dimethylamino)dimethylsilane) or HMCTS (hexamethylcyclotrisilazane) as the silylating agent, MCA (methyl cellosolve acetate) as the diffusion promoter and a solvent xylene. Silylation characterization and determination of optimum composition of the silylation solution have been performed using Fourier transform infrared spectroscopy (FTIR) measurement. Using the optimal wet-silylation and dry-developed resist system, 0.15 µ m line-and-space patterns of 1 µ m-thick resist (aspect ratio=6.5) and 0.08 µ m line-and-space patterns of 0.5 µ m-thick resist (aspect ratio=6) can be successfully delineated.
Investigation of Resist Pattern Deformation in Chemical Amplification Resists on SiNx Substrates
Authors: Yamanaka Ryoko , Hattori Takashi , Mine Toshiyuki , Toshihiko Tanaka Toshihiko Tanaka
Published: October 2002

This paper describes the pattern deformation in chemical amplification resists on SiN

x

substrates. Pattern deformation was observed not on the Si substrates, but on the SiN

x

substrates, even for a thin film of 1.2 to 1.5 nm depth. To clarify the resist-substrate interaction, the substrates were analyzed by attenuated total reflection Fourier transform infrared spectroscopy (FTIR-ATR) and X-ray photoelectron spectroscopy (XPS). From those analyses, the surface Si-OH group was found to be an important factor contributing to pattern deformation. The Si-OH group on Si is not affected by the acid generated in the resist during exposure. However, the protected Si-OH group on SiN

x

is de-protected by the acid, and the unprotected Si-OH group on SiN
x
acts as an acid trap. Moreover, Si-OH groups are sites for the resist residue formation. Therefore, the Si-OH group on a SiN
x
substrate is found to cause the pattern deformation.
Maskless Deposition of Au on GaAs by Low-Energy Focused Ion Beam
Authors: Kito Kuniyoshi , Yanagisawa Junichi , Monden Kentaro , Nakayama Hiromasa , Yuba Yoshihiko , Gamo Kenji
Published: October 2002

Direct deposition of Au films on GaAs substrate was performed using low-energy focused ion beam (FIB) irradiation. Pure Au film was obtained and current-voltage (I–V) characteristics of the Au/GaAs contacts were measured. The degradation of I–V characteristics compared to those of Au/GaAs contacts formed by evaporated Au was observed even for deposition at an energy of 50 eV due to ion-irradiation-induced damage. The I–V characteristics were somewhat improved by annealing at 200°C for 1 min. As an example of application, a Au gate was formed on a GaAs/AlGaAs heterostructure using low-energy FIB direct deposition, and current control capability was demonstrated.
Synchrotron-Radiation-Assisted Surface Processes of Diethylzinc on GaAs(100)
Authors: Gheyas Syed Irfan , Ogata Toshihiro , Nishio Mitsuhiro , Urisu Tsuneo , Hiroshi Ogawa Hiroshi Ogawa
Published: October 2002

The effect of sapphire-window-transmitted synchrotron radiation (longer than 150 nm photon illumination) and white-light synchrotron radiation (SR) on diethylzinc (DEZn), adsorbed on GaAs(100) at various temperatures, was investigated in situ using X-ray photoelectron spectroscopy (XPS). Illumination with light longer than 150 nm seems to have little impact on the adsorbed state whereas white light SR decomposes DEZn effectively, with the efficiency of dissociation for an adlayer of thickness around 3 nm to be roughly about 2.1×10-3 per shorter than 150 nm photons. The dissociation of DEZn seems to trigger the formation of clusters or islands of metallic zinc. At 115 K, we found that carbons and/or hydrocarbons desorb during white-light SR-assisted dissociation, and the desorption stops once dissociation is completed. In the process carbon decreases by approximately 40% at most regardless of the amount of excess photons available for the scission of all the Zn-C bonds. The surface becomes carbon-free once it is heated up to about 560 K.
White-light SR irradiation of DEZn at 300 K, on the other hand, helps to desorb all carbon species, leaving a clean Zn coverage over the GaAs(100) surface.
Well Structure by High-Energy Boron Implantation for Soft-Error Reduction in Dynamic Randam Access Memories (DRAMs)
Authors: Takehisa Kishimoto Takehisa Kishimoto , Yang-Keun Park Yang-Keun Park , Mikio Takai Mikio Takai , Yoshikazu Ohno Yoshikazu Ohno , Kenichirou Sonoda Kenichirou Sonoda , Hirokazu Sayama Hirokazu Sayama , Tadashi Nishimura Tadashi Nishimura , Atsushi Kinomura Atsushi Kinomura , Yuji Horino Yuji Horino , Kanenaga Fujii Kanenaga Fujii
Published: October 2002

The susceptibility against soft-errors in dynamic random access memories (DRAMs) has been evaluated using nuclear microprobes by monitoring various addresses of a memory cell array to determine the influence of upper wiring layers such as word lines, bit lines and other patterns. The correlations between irradiated positions of microprobes and monitored cell positions were discussed. The effect of buried implanted layers against carrier collection has also been investigated using ion-beam-induced-current (IBIC) measurement. IBIC measurement revealed that the retrograde well structure was more effective in suppressing soft errors than conventional well structures in bulk or epitaxial substrates.
Emission Characteristics of Ion-Implanted Silicon Emitter Tips
Authors: Hirano Takayuki , Kanemaru Seigo , Tanoue Hisao , Junji Itoh Junji Itoh
Published: October 2002

An ion implantation technique has been applied to control the energy band structure of Si field-emitter tip surface. B+or P+ions were implanted after fabrication of a gated emitter structure. No changes in emitter structure were observed after ion implantation and successive annealing at 800° C. Current-voltage (I-V) characteristics of n, p, p/n and n/p emitter tips were measured: p/n indicates an n-type tip with B+ions implanted into the tip surface. It was found from the experimental results that n and p/n tips hadI-Vcharacteristics in agreement with the Fowler-Nordheim theory. The p and n/p tips, on the other hand, exhibited a current saturation property in high electric field. The present saturation mechanism is explained by considering the energy band structure of the tip surface.
Fabrication of Petal-Shaped Vertical Field Emitter Arrays
Authors: Gamo Hidenori , Kanemaru Seigo , Junji Itoh Junji Itoh
Published: October 2002

We have invented a novel field emitter array (FEA) with a petal-shaped design. The emitter has a metal-disk fitted into a silicon (111) pyramidal hole; viewed from an angle it resembles the petal of a flower. We have elucidated the relationships between the detailed structure and the emission characteristics and have achieved the threshold voltage of 60 V, the emission current of 20 µA at the gate voltage of 150 V and the anode current fraction of 90% in this new structure. We could fabricate the present FEA as easily as the disk-shaped lateral FEA, and it gives a much higher anode current fraction than does the latter. We have also investigated the improvement of the surface condition of the emitter, and obtained the lowest threshold voltage of 17 V with metal-coated FEAs.
Electrochemical Scanning Tunneling Microscopy and Atomic Force Microscopy Observations on Si(111) in Several Solutions
Authors: Ando Atsushi , Miki Kazushi , Shimizu Tetsuo , Matsumoto Kazuhiko , Morita Yukinori , Tokumoto Hiroshi
Published: October 2002

Electrochemical scanning tunneling microscopy (ESTM) and atomic force microscopy (AFM) images of hydrogen-terminated Si(111) in several solutions have been studied to evaluate the performance of the AFM method. In dilute H2SO4 solution, the overall features of AFM images were similar to those of ESTM images, suggesting that both images reflect the topography of the bare H-Si(111) surface. However, AFM images in ultrapure water and in dilute NaOH solution were successfully obtained, while ESTM images were not. These results indicate that AFM is a powerful method for studying topographic change of Si in solutions during the wet cleaning process.
Different Hydrogen Passivation Mechanisms between Low-Temperature and High-Temperature Poly-Si TFT's
Authors: Kim Yong-Sang , Choi Kwon-Young , Han Min-Koo
Published: October 2002

We have investigated the different hydrogen passivation effects on low-temperature (LT) processed and high-temperature (HT) processed poly-Si thin-film transistors (TFT's). The hydrogen passivation on LT poly-Si TFT's results in the increase of the field-effect mobility and the decrease of the threshold voltage, while the hydrogenation increases the field-effect mobility and decreases the leakage current in HT poly-Si TFT's. The effective trap-state densities of LT poly-Si TFT before and after 5 h of hydrogenation are estimated at about 4×1012/cm2 and 1.5×1012/cm2, while those of HT poly-Si TFT are about 1.5×1012/cm2 and 1.2×1012/cm2, respectively. The activation energy of HT poly-Si TFT has been increased significantly in the off state with hydrogen passivation, whereas that of LT device has been decreased remarkably in the on state.
Effects of Dissolved Oxygen in HF Solution on Silicon Surface Morphology
Authors: Ogawa Hiroki , Ishikawa Kenji , Suzuki Miki T. , Hayami Yuka , Shuzo Fujimura Shuzo Fujimura
Published: October 2002

Surface morphology changes on atomically flat hydrogen-terminated Si(111) in various dissolved oxygen concentration (DOC) hydrofluoric acid (HF) solutions were studied using Fourier-transformed IR attenuated total reflection spectroscopy (FT-IR-ATR). The sharp absorption peak attributed to silicon monohydrides at the surface terraces decreases and the absorption peaks attributed to silicon monohydrides at the surface steps, dihydrides and trihydrides increase with immersion time in HF solutions at any DOC.
These results indicate that the atomically flat hydrogen-terminated surfaces were roughened in HF solutions and the rate of such spectral change, i.e., surface morphology change, decreased as the DOC of HF solution decreased. Such surface morphology change implies that the HF solution etches silicon surface, therefore, the dissolved oxygen in an HF solution plays an important role in the silicon etching.
Improvements of Electrical Characteristics of Hf/p-Si(100) Interfaces by H-Termination
Authors: Zaima Shigeaki , Kojima Jun , Hayashi Masakazu , Ikeda Hiroya , Iwano Hirotaka , Yukio Yasuda Yukio Yasuda
Published: October 2002

Effects of H-termination of Si(100) surfaces on electrical characteristics of Hf/p-Si interfaces have been examined. It is confirmed by high-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS) that the H-terminated surface, prepared by wet treatments in HF and then in water, is very stable for native oxidation and adsorption of oxygen. Effective dielectric layer thicknesses of H-terminated Hf/p-Si interfaces are 1/4-1/3 smaller than those of nonterminated ones, and the ideality factors in current-voltage characteristics are very close to unity. Deep levels at E
v+0.14, E
v+0.43 and E
v+0.52 eV are observed for 460° C-annealed diodes by deep-level transient spectroscopy (DLTS), the densities of which are reduced below the detection limit by annealing at 580° C. It can be concluded that the H-termination is markedly effective in improving electrical characteristics of Hf/p-Si interfaces.
High-Temperature Etching of PZT/Pt/TiN Structure by High-Density ECR Plasma
Authors: Yokoyama Seiichi , Ito Yasuyuki , Ishihara Kazuya , Hamada Kazuyuki , Ohnishi Shigeo , Kudo Jun , Keizo Sakiyama Keizo Sakiyama
Published: October 2002

Submicron patterning technologies for the PZT/Pt/Ti/TiN/Ti structure with a spin on glass (SOG) mask were demonstrated using a high-density ECR plasma and a high substrate temperature above 300° C. A 30%-Cl2/Ar gas was used to etch a lead zirconate titanate (PZT) film. No deposits remained, which resulted in an etched profile of more than 80°. A 40%-O2/Cl2 gas was used to etch a Pt film. The etching was completely stopped at the Ti layer. 30-nm-thick deposits remained on the sidewall. They were removed after dipping in hydrochloric acid. The etched profile of a Pt film was more than 80°. The Ti/TiN/Ti layer was etched with pure Cl2 gas. The size shift from the SOG mask was less than 0.1 µ m. Interdiffusion between SOG and PZT was not detected by transmission electron microscopy and energy dispersive X-ray spectroscopy (TEM-EDX) analysis.
Novel Oxygen Free Titanium Silicidation (OFS) Processing for Low Resistance and Thermally Stable SALICIDE (Self-Aligned Silicide) in Deep Submicron Dual Gate CMOS (Complementary Metal-Oxide Semiconductors)
Authors: Kotaki Hiroshi , Nakano Masayuki , Hayashida Shigeki , Kakimoto Seizou , Mitsuhashi Katsunori , Junkou Takagi Junkou Takagi
Published: October 2002

A low resistance and thermally stable TiSi2 self aligned silicide (SALICIDE) for deep submicron p+ and n+ dual gate complementary metal-oxide semiconductors (CMOS) has been developed. This was achieved through the use of a novel oxygen free silicidation (OFS) process using a reaction between a titanium included nitrogen ( Ti

x

N

y

) and an oxygen free poly-Si-gate. The oxygen free poly-Si was realized using low pressure chemical vapor deposition (LPCVD) system with nitrogen flow Load-Lock chamber. The OFS TiSi2 film did not agglomerate after the treatment of the RTA at 1050° C for 20 s in a N2 atmosphere and the additional furnace annealing at 900° C for 30 min. in a N2 atmosphere. For both n+ and p+ gates, low sheet resistances (about 2.8 Ω /square.) were achieved under the 0.2 µ m size.
An Investigation on the Short Channel Effect for 0.1 µm Fully Depleted SOIMOSFET Using Equivalent One Dimensional Model
Authors: Koh Risho , Haruo Kato Haruo Kato
Published: October 2002

An analytical model for the short channel effect for the silicon on insulator metal oxide semiconductor field effect transistor (SOIMOSFET) is proposed. The two dimensional potential problem is reduced to a one dimensional problem, using a virtual electrode which is equivalent to the drain and the source electrodes. The behavior for the short channel effect is also discussed using this model.
Fabrication of Novel Si Double-Barrier Structures and Their Characteristics
Authors: Yuki Koichiro , Hirai Yoshihiko , Morimoto Kiyoshi , Inoue Kaoru , Niwa Masaaki , Juro Yasui Juro Yasui
Published: October 2002

A novel Si (silicon)-based double-barrier structure (DBS) is newly proposed to study Si resonant tunneling devices. To form a thin Si single-crystal plate as a quantum well, anisotropic wet chemical etching and thermal oxidation are adopted. The DBS has a 43 nm-wide Si quantum well and 2.3 nm-thick SiO2 barriers. The electrical characteristic exhibits negative differential conductance (NDC).
Turn-off Transient Analysis of a Double Diffused Metal-Oxide-Semiconductor Device Considering Quasi Saturation
Authors: Chung-Min Liu Chung-Min Liu , James B. Kuo James B. Kuo
Published: October 2002

This paper reports the turn-off transient of a double diffused metal-oxide-semiconductor (DMOS) device considering the quasi-saturation behavior. Based on the two-dimensional (2D) simulation result, during the input ramp-down period of 100 ps, the accumulated electrons below the gate oxide are pushed toward the p region below the lateral channel toward the source, causing a surge in source current. After the input ramp-down period, these electrons are withdrawn from the drain by the quasi-saturation current.
Thermal Runaway Tolerance in Double-Heterojunction Bipolar Transistors
Authors: Hidaka Osamu , Morizuka Kouhei , Hiroshi Mochizuki Hiroshi Mochizuki
Published: October 2002

On the double-heterojunction bipolar transistor (DHBT) with a narrow band-gap base, collector current is strongly impeded at a high current level where the base-pushout effect occurs. This phenomenon was studied in conjunction with the thermal stability of transistors. The experimental comparison of Si/SiGe/Si-DHBT with a Si bipolar junction transistor (Si-BJT) confirmed that SiGe-DHBTs are more stable with regard to thermal runaway than Si-BJTs.
Low-Temperature Scanning Tunneling Spectroscopy of a-Axis-Oriented PrBa2Cu3Oy Films on YBa2Cu3Ox
Authors: Koyanagi Masao , Kashiwaya Satoshi , Matsuda Mizushi , Takashima Hiroshi , Koji Kajimura Koji Kajimura
Published: October 2002

In order to elucidate the mechanism of the long-range proximity effect, a-axis-oriented PrBa2Cu3O

y

(PBCO) thin films with thickness up to 50 nm deposited on a-axis-oriented YBa2Cu3O

x

(YBCO) films were studied by low-temperature scanning tunneling spectroscopy at 4.2 K. Stable- and unstable-STM-image areas were observed at the PBCO surface. The stable-STM-image areas decreased when the thickness of PBCO increased. Gap structures were also observed in conductance spectra in these stable-STM-image areas. These results and the long-range proximity effect in YBCO/PBCO/YBCO junctions are discussed in terms of the model in which PBCO consists of small-scale conductive and nonconductive regions.
A Model for Threshold Voltage Shift under Positive and Negative High-Field Electron Injection in Complementary Metal-Oxide-Semiconductor (CMOS) Transistors
Authors: Tomasz Broż Tomasz Broż , Y. David Chan Y. David Chan , Chand R. Viswanathan Chand R. Viswanathan
Published: October 2002

High-field electron injection is an attractive tool for investigation of properties of thin dielectric layers. The paper discusses the threshold voltage degradation of complementary metal-oxide-semiconductor (CMOS) devices due to high field oxide stressing. Both the filling of existing oxide hole and electron traps and the generation of new defects, namely bulk electron traps and interface states, are carefully considered. It is shown that monitoring of stress voltage transients during constant-current electron injection into the device gate oxide may be very helpful in understanding degradation phenomena. A qualitative model is proposed to explain different behavior and susceptibility of the threshold voltage of CMOS devices to F-N stress-induced degradation. The model is based on differences in charge trapping and detrapping in different regions of very thin gate oxides under different stress conditions in p-type MOS (PMOS) and n-type MOS (NMOS) transistors.