bluuebunny/crossref_metadata_2025 huggingface dataset:
Single-Electron Transistor in Silicon-on-Insulator with Schottky-Contact Tunnel Barriers
Authors: Hironobu Fukui Hironobu Fukui , Minoru Fujishima Minoru Fujishima , Koichiro Hoh Koichiro Hoh
Published: October 2002

We have proposed a novel single-electron transistor (SET) with Schottky tunnel barriers. The proposed SET can be fabricated by employing the standard salicide process and can be merged in the current CMOS VLSI (complementary metal-oxide-semiconductor-very-large-scale integration). We analyzed its characteristics using the Poisson equation and the master equation based on the semi-classical theory. Calculation results show that the proposed SET has good cutoff characteristics similar to those of conventional MOSFETs (metal-oxide-semiconductor-field-effect transistors) while its gate-periodic characteristics are similar to those of conventional SETs.
Gain and Threshold of Quantum Dot Lasers: Theory and Comparison to Experiments
Authors: Marius Grundmann Marius Grundmann , Dieter Bimberg Dieter Bimberg
Published: October 2002

A theory for gain and threshold of quantum dot lasers operating with inhomogeneously broadened dot ensembles is developed. Separate vs. simultaneous electron and hole capture and thermal vs. non-thermal carrier distributions and vertically coupled stacks are considered. In realistic lasers thermally distributed carriers allow lower threshold currents than non-thermal ensembles. Stacked quantum dots provide larger maximum gain but have a priori a higher threshold. However, vertical coupling leads to a redistribution of the carrier population and subsequently to similarly low thresholds as for lasers operating with single sheets of dots. Theoretical predictions are compared to experiments on quantum dot lasers operating on self-organized InAs/GaAs quantum dots.
Super-High-Density Optical Disk Using Deep Groove Method
Authors: Morita Seiji , Madoka Nishiyama Madoka Nishiyama , Takehiko Ueda Takehiko Ueda
Published: October 2002

An optical disk with a deeper-than-usual groove has been manufactured. The deeper the groove, the less cross-erase occurs. By adjusting the groove depth, cross-erase is suppressed even if the track pitch is narrowed to 0.5 µm. Also, we found another groove depth which cancels both cross-talk and cross-erase. Finally, we obtained a high-density optical disk with a deep groove, the track pitch and the minimum mark length of which are 0.5 µm and 0.35 µm, respectively.
CW Metal Arc Discharge Under High Vacuum
Authors: Moritake Tamba Moritake Tamba
Published: October 2002

A CW metal arc discharge ion source, which does not use a any trigger electrode operating under high vacuum, has been developed. For stable sustenance of the CW metal arc in the high-vacuum condition, an electrically floated metal cover is applied to the cathode. The experimental result shows that the metal arc is mainly governed by the rule that the product of the pressure and arc length should be constant. Using an electrically floated metal cover, a copper metal plasma has been produced by vacuum DC arc discharge at a pressure of about 8×10-6 Torr in a magnetic field above 3.2 kG. This paper describes the marked decrease in the resolution of a single focusing mass spectrometer caused by high ion temperature. A double focusing ion mass spectrometer is applied to obtain more detailed information on the multicharged ions. The data which show the charged state of iron ions at a pressure of about 4×10-6 Torr will be presented. In order to explain the mechanism of forming highly charged states, the variation of the space potential is considered.
X-Ray Circular Dichroic Bragg Reflections from a GdCo/Ag Multilayer
Authors: Hashizume Hiroo , Ishimatsu Naoki , Sakata Osami , Hosoito Nobuyoshi , Emoto Takeshi , Lee Ki-Bong , Lee Dong-Ryeol , Iwazumi Toshiaki
Published: October 2002

Bragg peaks are observed in difference resonant specular reflectivity signals from a GdCo/Ag multilayer in a flipping magnetic field for circularly polarized X-rays. The element-specific X-ray scattering at the L
3 absorption edge of Gd directly evidences layers of magnetically ordered Gd ions stacked at a regular spacing of the multilayer 51 Å period. The Bragg peaks show a negative polarity, which is accounted for by the property of the resonant magnetic-charge interference scattering.
Improved High-Density Phase-Change Recording
Authors: Bernardus A. J. Jacobs Bernardus A. J. Jacobs , Johan P. W. B. Duchateau Johan P. W. B. Duchateau
Published: October 2002

By using a simple write strategy we have found that a wide range of linear velocities can be covered for direct overwrite in high-density phase-change recording. This is especially advantageous for data recording where the application of constant angular velocity facilitates fast seek and short random-access times. In the case of repeated overwriting, material flow will limit the number of cycles, particularly if a fixed pseudo-random data pattern is used. We studied how a random bit shift can reduce this problem and found that a relatively large shift of up to 100 bytes was required. Using these techniques in an optimized disc structure we achieved more than 100,000 overwrite cycles on a 2.6 Gbyte 12 cm phase-change disc.
Preparation of Thin Films and Nanosize Powders by Intense, Pulsed Ion Beam Evaporation
Authors: Yatsui Kiyoshi , Grigoriu Constantin , Masugata Katsumi , Weihua Jiang Weihua Jiang , Tomihiro Sonegawa Tomihiro Sonegawa
Published: October 2002

Efficient preparation of thin films has been achieved with a high-density ablation plasma produced by the interaction of an intense, pulsed ion beam with solid targets, a process called ion beam evaporation, having an instantaneous deposition rate of cm/s. In addition to standard front-side deposition, backside deposition, in which the substrate is placed on the reverse side of the holder, has been proposed to produce good quality thin films, though the deposition rate is one order of magnitude less than that in front-side deposition. By cooling of the ablation plasma, ultrafine nanosize ceramic powders, with a typical particle diameter of 10 nm, have been produced. The basic characteristics of the ablation plasma have been clarified by use of 1-D hydrodynamic equations with a simplified model involving primary ion-beam-driven expansion followed by adiabatic expansion into a vacuum. Analytical solutions will be given to define the plasma parameters.
The Low-Pressure Rf Plasma as a Medium for Nitriding Iron and Steel
Authors: Baldwin M. J. , Collinss G. A. , Fewell M. P. , Haydon S. C. , Kumar S. , Short K. T. , Tendys J.
Published: October 2002

This study compares the nitriding efficiency of a low-pressure pure-nitrogen rf plasma for the materials AISI-316 stainless steel, 99.8% iron and the low-alloy steels AISI 4140 and En41B. The process temperature was 400° C; a range of gas pressures and biasing conditions was explored. The treated samples were examined using instrumented microhardness measurements, proton backscattering, X-ray diffraction and other diagnostics. The degree of nitriding is enhanced by increased bombardment by excited neutral molecules. Ion bombardment assists in the nitriding of iron and the low-alloy steels studied, apparently by aiding the production of Fe2-3N. This phase does not form in the nitriding of 316 stainless steel, and therefore treatment of this material is not assisted by ion bombardment. In comparing low-pressure rf plasmas to procedures involving higher pressures and temperatures, the process described here is more appropriate for hardening austenitic stainless steel, but perhaps less appropriate for the other materials.
An Observation of Oxygen Precipitation Retardation Phenomenon Induced by 450°C Anneal in Czochralski Silicon
Authors: Kung Chung-Yuan , Hsu Wei , Horng Chin Ming Liu
Published: October 2002

Two-step (450° C–1000° C) and three-step (1150° C–450° C–1000° C) annealing experiments were carried out to study oxygen precipitation behavior in Czochralski silicon. A distinct retardation of precipitation was observed during the two-step annealing, while the retardation during the three-step annealing was less pronounced. In the three-step annealing, the first high temperature (1150° C) annealing in a N2 ambient caused the retardation of precipitation to occur at short nucleation times. The microstructure characteristics as a function of nucleation (450° C) annealing time were similar in the two-step and three-step annealed samples.
Characterization of Polycrystalline Cu(In,Ga)Se 2 Thin Films Produced by Rapid Thermal Processing
Authors: Alberts V. , Zweigart S. , Schön J. H. , Schock H. W. , Bucher E.
Published: October 2002

In this study a simple, tolerant and reproducible process has been developed to produce device quality Cu(In,Ga)Se2 thin films. These films were prepared by the rapid thermal processing (RTP) of thermally evaporated Cu–In–Ga–Se metallic precursors. All precursors used in this study were prepared by a new growth process in which all metals (Cu, In and Ga) were evaporated from one single crucible in a Se atmosphere. In this process, developed at Stuttgart University, the stoichiometry of the precursor films was fixed by the amount of material in the crucible and the substrate temperature was kept constant at 200°C. Various rapid thermal processes were considered to optimize the material properties (adhesion, surface morphologies and uniformity) of the compound films. In the case of relatively slow rapid thermal processes (RTP) which involved various ramping steps, films with poor structural properties (inhomogeneous film morphologies and presence of secondary phases) were obtained. A significant improvement in material properties was obtained in the case of rapid heating (in 10 s from 200°C to 550°C) of samples. However, these films were still characterized by the presence of secondary phases. Optimum material properties (homogeneous and dense films) were obtained when the heating profile followed a root function in the critical temperature range around 300°C. Preliminary solar cell devices were fabricated with conversion efficiencies above 6% (total area).
Effects of Floating-Gate Doping Concentration on Flash Cell Performance
Authors: Huang Tiao-Yuan , Jong Fuh-Cheng , Lin Horng-Chih , Chao Tien Sheng , Leu Len-Yi , Young Konrad , Lin Chen-Hsi , Chiu Kuang Y.
Published: October 2002

In this paper we report the effects on flash cell performance of the doping concentration of the horn-shaped floating-gate. It is demonstrated that the floating-gate doping concentration not only determines the work function of the floating-gate, but also affects the resultant interpoly oxide. As a result, the flash cell performance is affected by the floating-gate doping concentration, and should therefore be carefully designed. It is shown that a low doping level ( e.g., <1.7×1018 cm-3) on the floating-gate results in a high threshold voltage of the flash cell, low cell read current, and degraded write/erase cycling endurance. Flash cells with a medium ( e.g., 1.7×1019 cm-3) doping level, on the other hand, depict the lowest threshold voltage, and the highest cell read current; while flash cells with the highest doping level (1.7×1020 cm-3) used in this study depict a medium threshold voltage. This could be ascribed to the fact that both medium and high doping levels result in a degenerate polysilicon floating-gate with a similar work function; however, a higher doping concentration results in a thicker interpoly oxide, and therefore a higher threshold voltage, and lower read current.
Extension of Linear-Velocity Margin in Phase-Change Optical Recording with Variable-Pulse Compensation
Authors: Mizuno Hironobu , Kenichi Takada Kenichi Takada , Michikazu Horie Michikazu Horie
Published: October 2002

Using a variable-pulse compensation method, it was demonstrated that a phase-change optical disk consisting of a stoichiometric Ge2Sb2Te5 active layer and a fixed rapid cooling multilayer structure, which was designed for use at high linear velocity of over 5 m/s, exhibited a satisfactory read/write performance for a wide range of linear velocity, 1.4 m/s–10 m/s. The variable-pulse compensation method includes a variable-pulse division strategy in accordance with the linear velocity in pulse-width modulation recording. For recording an amorphous mark which is n
T length (n: integer, T: the length of one clock cycle), the pulse duration of each divided writing pulse in the n
T period was reduced and laser power was optimized at lower linear velocity to suppress the undesirable heat accumulation in the laser-irradiated area that leads to shrinking the amorphous mark. This assures exact control of molten area formation and its cooling process to obtain clear edges of amorphous marks, and overcomes the recrystallization around the mark in overwriting that is predominant in the low-linear-velocity regime.
Morphological Variation of the Monolayer Surface of Diacetylene during Polymerization at Air-Water Interface
Authors: Shimoyama Susumu Yamada
Published: October 2002

Morphological variation of diacetylene monolayers during solid-state polymerization was investigated by in-situ observation at the air-water interface. For the first time, use of the circular polarized light detection scheme enables observation of the monomer monolayer of diacetylene. We revealed that the spiral structure of the monolayer is already formed even before the polymerization. The surface structure of the monolayer during the polymerization process by UV irradiation was recorded in both air and argon atmospheres. In the argon atmosphere, the surface morphology remains constant during polymerization. On the other hand, a large deformation was found in the unit cell in the presence of oxygen (air). Attempts have been made to establish a molecular model for the monolayer using molecular mechanics calculations.
Characteristics of Photoemission of High Polymers
Authors: Yuji Murata Yuji Murata , Isao Hiyoshi Isao Hiyoshi
Published: October 2002

Measurements of photoemission of various high polymers were carried out in the wavelength region between 160 and 780 nm. The number of photoelectrons is changeable during the measurement depending on the wavelength of incident light because of surface charge-up, photoexcitation of electrons and other effects. The threshold energy of photoemission depends on the light intensity used for illuminating the sample. It is found that high-intensity illumination is necessary to obtain precise threshold energy values for high-polymer samples. For all polymer samples examined, the threshold energies of photoemission were from 3 to 3.5 eV, which are considerably smaller than the values corresponding to the depths of HOMO levels.
In Situ Ellipsometry Studies of ZnS Thin Film Growth
Authors: Soonil Lee Soonil Lee , Byung Hun Park Byung Hun Park , Soo-ghee Oh Soo-ghee Oh
Published: October 2002

In situ ellipsometry was used to study the initial growth of ZnS thin films deposited by RF magnetron sputtering, via the variations of the ellipsometric constants Δ and ψ. We found that the growth curves, Δ versus ψ curves measured in real time, followed the closed trajectories with a well-defined thickness period, and also that they were reproducible even at the very beginning of film growth under the given deposition conditions. From the inversion analysis of the ellipsometric constants, we were able to determine not only the thickness and the refractive index of the growing film, but also the threshold thickness at which bulklike film growth started and the corresponding bulklike refractive index. Moreover, it was confirmed that ZnS thin film growth was governed by an islandlike growth mechanism, not by the layer-by-layer growth mechanism. Finally, an empirical function, to which the thickness-dependent variation of the refractive index was fitted, was introduced.
Simulation of Monolithic Silicon LLL Scanning X-Ray Interferometer
Authors: Bianc Giuseppe Bertolotto , Giovanni Mana Giovanni Mana , Gianfranco Zosi Gianfranco Zosi
Published: October 2002

A model of a monolithic silicon LLL scanning X-ray interferometer capable of displacements up to 100 µm is described. It can be used for the measurement of the (220) lattice plane spacing of silicon in studies concerning the Avogadro constant and for the calibration of linear displacement transducers having sub-nanometer sensitivity.
Positive-Negative Inversion of Silicon Based Resist Materials: Poly(di-n-hexylsilane) for Ion Beam Irradiation
Authors: Seki Shu , Kanzaki Kenichi , Yoshida Yoichi , Tagawa Seiichi , Shibata Hiromi , Asai Keisuke , Ishigure Kenkichi
Published: October 2002

The present paper describes radiation induced solubility changes and emission spectra of poly(di-n-hexylsilane) and their temperature dependence on. Poly(di-n-hexylsilane) has a clear phase transition temperature at around 312 K with change of the silicon skeleton structure. Radiation induced reactions differed greatly above and below this temperature, showing large emission spectral changes. High LET (linear energy transfer; energy deposition rate of incident particles per 100 Å ion beams induced main chain crosslinking in the polymer. PDHS behaved as a negative-type resist material below 312 K, although it had been previously confirmed that PDHS had shown positive-type resist properties for UV light, electron beams, X-rays, low LET proton beams at any temperature range and for higher LET He ion beams at a temperature above 312 K.
Defect-Controlled Selective Epitaxial Growth of GaP on Si by Migration-Enhanced Epitaxy under Atomic Hydrogen Irradiation
Authors: Takuto Tsuji Takuto Tsuji , Hiroo Yonezu Hiroo Yonezu , Mikihiro Yokozeki Mikihiro Yokozeki , Yasufumi Takagi Yasufumi Takagi , Yasuhiro Fujimoto Yasuhiro Fujimoto , Naoki Ohshima Naoki Ohshima
Published: October 2002

We investigated the properties of deposition of GaP on dry-SiO2 and SiNx masks using molecular beam epitaxy (MBE) or migration-enhanced epitaxy (MEE) under atomic hydrogen irradiation and attempted the selective epitaxial growth of GaP-on-Si. The critical substrate temperature, below which poly-GaP was deposited on a mask layer, was lower for dry-SiO2 than that for SiNx, and was lowered by MEE rather than MBE. As a result, the selective epitaxial growth of GaP was achieved by MEE using the dry-SiO2 mask. It was found that the formation of large anti-phase domains expanding into the surface was suppressed by forming a P-prelayer at low temperature. It was also confirmed that the density of misfit dislocations at the GaP–Si hetero-interface was remarkably reduced with a decrease in the growth area.
The Crystal Structure of Solid C70
Authors: Nagaosa Ryuji Komori , Takashi Hatae Takashi Hatae , Yasuhiko Miyamoto Yasuhiko Miyamoto
Published: October 2002

C70 single crystals were synthesized under various conditions. Their morphologies were observed under a scanning electron microscope (SEM), and their structures were examined using an X-ray diffraction technique. The conflicting results of X-ray diffraction experiments on single crystals and powdered ones led us to conclude that abab… stacking was stable at high temperatures while abcabc… stacking was stable at low temperatures. Based on this conclusion, we have selectively synthesized hcp and fcc morphology crystals. This paper will discuss the stable phases of solid C70.
Field-Induced Antiferroelectric-to-Ferroelectric Phase Transition of Lead Niobium Zirconate Titanate Stannate Ceramics
Authors: Yoshikazu Akiyama Yoshikazu Akiyama , Etsuko Fujisawa Etsuko Fujisawa
Published: October 2002

The elastic strain behavior associated with the field-induced antiferroelectric-to-ferroelectric
phase transition has been investigated for
Pb0.99Nb0.02[(Zr1-
x

Sn

x

)1-
y

Ti

y

]0.98O3 ceramics
(PNZST) by means of dielectric, polarization and strain hysteresis measurements. As the applied
electric field intensity increased, a sudden increase in the strain was observed along with a
corresponding change in polarization that is attributable to the phase transition. PNZST ceramics
with optimized composition exhibit a huge strain value of 0.44%, which may make the development
of a new functional transducer device possible.
Investigation of Precursors Formed by Mixing SiH2Cl2 with NH3 for Chemical Vapor Deposition of Silicon nitride Films
Authors: Kusakabe Yoshihiko , Hanaoka Ken-ichi , Komori Hideki , Hiroshi Ohnishi Hiroshi Ohnishi , Ken-ichiro Yamanishi Ken-ichiro Yamanishi
Published: October 2002

Precursors for Silicon nitride films prepared by mixing SiH2Cl2 with NH3 were investigated by in situ Fourier-transform infrared spectroscopy (FT-IR) and mass spectrometry. The FT-IR spectral analysis results indicated that the Cl was removed from SiH2Cl2 by mixing SiH2Cl2 with NH3 at room temperature (R.T.). The analysis results also indicated the existence of radicals which had the chemical bond Si–N. The mass spectral analysis results indicated the existence of the radicals with the mass number of 45–47. From these results, it was concluded that the precursors of SiNH

x

for SiN films were formed by mixing SiH2Cl2 with NH3.
Temperature Characteristics of (Ba1-xSrx)2NaNb5O15 Ceramics
Authors: Kimura Masahiko , Minamikawa Tadahiro , Akira Ando Akira Ando , Yukio Sakabe Yukio Sakabe
Published: October 2002

The (Ba1-
x

Sr

x

)2NaNb5O15 [BSNN] system is a lead-free ferroelectric material that has large
spontaneous polarization and is expected to be applicable for piezoelectric ceramic filter or
oscillator devices. Filter and oscillator materials require high temperature stability, and in
particular, a small temperature coefficient of resonance frequency in a temperature range from
-20 to 80° C (f
r-T
C). The piezoelectric properties of BSNN ceramics were investigated and it was
found that the composition with x=0.6 showed an excellent f
r-T
C of 15.0 ppm/° C. The
composition had anomalies of resonance frequency constant (f
r·t) which were considered to arise
from ferroelastic phase transitions at -100 and 220° C, and f
r·t varied showing a parabolic curve
between -100 and 220° C. The temperature at the top of the curve was around 40° C. The
temperature dependence of f
r·t was fairly small around 40° C because of the inflection of f
r·t
variation, therefore excellent f
r-T
C was obtained for the composition.
Observation of the Crystallization Process from Amorphous PbTiO3 and Pb5Ge3O11 by Atomic Force Microscopy
Authors: Su Jang Masaaki Takashige , Koichiro Takahashi Koichiro Takahashi
Published: October 2002

We used an atomic force microscope (AFM) to study the surface morphology of amorphous samples of PbTiO3 and Pb5Ge3O11 prepared by rapid quenching. Change in surface roughness and grain growth were detected when samples were heated at elevated temperatures.
Analysis of H2-Dilution Effects on Photochemical Vapor Deposition of Si Thin Films
Authors: Oshima Takayuki , Akira Yamada Akira Yamada , Makoto Konagai Makoto Konagai
Published: October 2002

Hg-sensitized photochemical vapor deposition (photo-CVD) of Si thin films at low temperatures using a gas mixture of SiH4 and H2 was analyzed and the concentrations of SiH3 and H in the gas phase were theoretically estimated. The results of the calculation were compared with the properties of the Si thin films, and the roles of atomic H were discussed. With the correlations between the radical concentrations near the growing surface and film properties such as film structure, film quality, and the concentration of bonded hydrogen in a-Si films were successfully explained. It is suggested that the roles of atomic H on the growing surface are a termination of dangling bonds on the surface and an extraction of SiH3 radicals from the growing surface. Since the role of atomic H competes with the deposition of Si, the supply balance between the atomic H and the SiH3 radicals is essential to determine the properties of Si thin films.
Effects of Stimulus Waveforms on the Magnetic Stimulation of Cardiac Muscle
Authors: Suzaki Takayuki , Maita Soichiro , Yamamoto Isao , Yamaguchi Masuhiro , Andoh Tomio , Okumura Fukuichiro
Published: October 2002

We analytically and experimentally studied how the stimulation threshold depended on the waveforms of magnetic fields for magnetic heart stimulation. The stimulation threshold was calculated for the magnetic fields of rectangular, damped sinusoidal and crowbar pulses on the basis of a cell membrane model for the ventricular muscle. In the experiment, premature contractions of canine hearts were induced by pulsed magnetic fields with different waveforms. The observed stimulation threshold for single pulses did not show the systematic waveform dependence which was obtained in the analysis. Applying double crowbar pulses to the canine hearts resulted in a lowering in the stimulation threshold, which corresponded to the analytical result.
Role of Superconductor-Normal Metal-Superconductor Proximity Junctions in Governing the Intergranular Flux Pinning in Electrophoretically Deposited Y–Ba–Cu–O Films
Authors: Bhattacharya Dipten , Das Himadri S. Maiti
Published: October 2002

Within a low-field limit, the magnetic critical current density (J
c) is found to have dropped drastically in case of thinner Y–Ba–Cu–O films ( ≤20 µm), deposited electrophoretically on silver substrates. In this low-field limit, the current loops scale the entire sample volume consisting of grain-grain-boundary networks. Due to the presence of uniformly distributed silver at the grain boundaries within the entire network (in case of these thinner films), the pinning potential (U
0) of the grain boundary Josephson vortices is small as it depends on random variation in Josephson coupling energy (E
J) of the grain boundaries. In case of thicker films, of course, U
0 can be high as no silver penetration is possible up to the top layers and hence, U
0 varies as ∼d
0.4 (d=film thickness) and ranges from 45 to 135 meV over a thickness regime of 3–65 µm. Consequently, the magnetic J
c too, follows an anomalous trend of variation with film thickness.
Silicon Oxynitride Waveguides for Optoelectronic Integrated Circuits
Authors: Agnihotri O. P. , Tyagi Rajeev , Kato Isamu
Published: October 2002

Planar optical waveguides on p-type Si wafers have been fabricated by a photo-induced deposition process. Silicon oxynitride was deposited using a gaseous mixture of SiH4 (2% in Ar), NH3 and N2O under 253.7 nm UV radiation. The oxynitride composition was varied by changing N2O: ( N2O+NH3) ratio while keeping N2O+NH3 and SiH4 flow rates constant. The refractive index varied from 1.46 to 1.95. The optical energy gap increased from 4.8 to 5.7 as the flow rate ratio varied from 0 to 0.25. Si–N bond shifts to higher energy owing to the incorporation of oxygen. A planar waveguide structure was fabricated using thermally grown SiO2 buffer layer of 1.1 µ m thickness. The loss was estimated to be 1.1 dB/cm for TE0 mode at 632.8 nm. The accuracy of measurements is 0.02 dB/cm.
Deposition of Tantalum Oxide Films by UV Laser Reactive Ablation in O3 Ambient
Authors: Zhengwen Fu , Mingfei Zhou , Qizong Qin , Shenkun Zhang , Fang Lu
Published: October 2002

Tantalum oxide films have been deposited on n-type silicon substrate by 355 nm laser ablation of Ta2O5 in the presence of O3. The dielectric and electrical properties of Ta2O5 films after annealing treatment have been studied. The results suggest that the film has dielectric constant of 28, and leakage current of 10-7 A/cm2 at an applied electric field of 500 kV/cm. The capacitance-voltage characteristics of the Al/Ta2O5/n+Si capacitors exhibit an interface trap density and border trap density of 3×1011 eV-1 cm-2 and 1.2×1011 cm-2, respectively. The effect of ambient gases during laser deposition on the border trap densities of annealed films are also discussed.
Physical Properties of CoFe/IrMn Spin-Valves Prepared Using Ion Beam Sputtering with an Xe-H2 Mixture Gas
Authors: Umemoto Takashi , Maeda Atsushi , Takahashi Seiichirou , Tanuma Toshio , Minoru Kume Minoru Kume
Published: October 2002

Co90Fe10/Cu/Co90Fe10/Ir25Mn75 spin-valves with a Ta seed layer were prepared by ion beam sputtering. Improvements in magnetoresistive (MR) and magnetic properties were obtained by adding H2 to Xe sputtering gas. Specifically, the coercivity in the free Co90Fe10 layer considerably decreased as the H2 flow rate was increased. Furthermore, exchange coupling between the Ir25Mn75 and pinned Co90Fe10 layers became stronger in the preparation under the higher H2 flow rate. X-ray diffraction, transmission electron microscopy, and secondary ion mass spectroscopy observations suggest that micro-crystallization of each layer is responsible for improving the MR and magnetic properties.
Near Band-gap Photoluminescence Peak of Ge-doped GaAs
Authors: Taketo Watanabe Taketo Watanabe , Masashi Suezawa Masashi Suezawa
Published: October 2002

The objective of our research was to clarify the origin of the peculiar shift of the photoluminescence (PL) peak near the band gap energy to low energy accompanied with the increase of Ge concentration in GaAs. Specimens of Ge-doped bulk GaAs were grown by the liquid-encapsulated Czochralski method. We measured the Hall effect at room temperature and PL spectrum at 4.2 K. Carrier concentrations were smaller than those of Ge by more than one order of magnitude which indicated high compensation. The PL peak near the band gap energy shifted to low energy as the Ge concentration increased. This PL peak shifted to low energy, as the excitation energy decreased, as the excitation intensity decreased and as the measurement temperature increased. This behavior was explained qualitatively by the model of recombination of carriers at donor-acceptor pairs in spatially separated potential wells which were built due to a fluctuation in the distribution of highly doped donors (Ge at Ga atom site) and acceptors (Ge at As atom site).
Relation between the Metastability and the Configuration of Iron-Acceptor Pairs in Silicon
Authors: Takahashi Hideki , Masashi Suezawa Masashi Suezawa , Koji Sumino Koji Sumino
Published: October 2002

To determine the energy differences between the first and second nearest-neighbor iron (Fe)-acceptor pairs in silicon, the generation and annihilation processes of these pairs were investigated by means of electron spin resonance (ESR). Isochronal annealing of the Fe-doped specimen revealed that the concentrations of iron-group III acceptor pairs attained maxima at about 100° C, and then decreased with increasing temperature. An isothermal annealing experiment showed that the concentrations of these pairs increased monotonically with annealing and approached constant values after a long duration of annealing. The temperature dependence of the ratio of the concentrations of these two atomic configurations at equilibrium showed that the pair with trigonal symmetry was stable and that with orthorhombic symmetry was metastable in the cases of Fe–Al and Fe–Ga pairs, in contrast, the pair with trigonal symmetry was metastable and that with orthorhombic symmetry was stable in the case of Fe–In pairs. The energy differences in the two configurations of these pairs were 0.07 eV, 0.03 eV and 0.09 eV for Fe–Al, Fe–Ga and Fe–In pairs, respectively.
Studies of Second Harmonic Generation in Liquid Crystal-Polymer Mixtures
Authors: Huang Andy Ying-Guey Fuh , Chien Cheuk-Wah Lau
Published: October 2002

Films of liquid crystal (LC)-polymer dispersion materials having various chiral dopant and monomer concentrations were fabricated. Using a mode-locking Nd:YAG laser, we observed second harmonic generation (SHG) in these mixtures which is due to the dielectric gradient across the interfaces between the LC/polymer network and those between adjacent cholesteric domains having a different helical axis. The results showed that UV curing intensity, polarization of incident light and frequency of driving voltage affected SHG intensity significantly. Chiral dopant concentration was also found to affect not only the threshold voltage, but the SHG intensity of the cell. Finally, two experiments that highlighted the applications of SHG measurements in LC-polymer mixtures were conducted. Polarization-dependent SHG measurement can be used to determine the dielectric constant of the polymer dispersed in LC cells, and SHG change on polymerization can be used to monitor the polymerization of LC-polymer mixtures.
Effect of Deposition Temperature on the Crystallization Mechanism of Amorphous Silicon Films on Glass
Authors: Lee Jeong No , Lee Bum Joo , Dae Gyu Moon Dae Gyu Moon , Byung Tae Ahn Byung Tae Ahn
Published: October 2002

The crystallization mechanism of amorphous Si films deposited on glass substrates by plasma enhanced chemical vapor deposition method was investigated. The deposition temperature varied from 200 to 400° C and the films were crystallized at 600° C in nitrogen. As the deposition temperature increased the nucleation rate was increased, but the nucleation activation energy was independent of the deposition temperature with a value of 3.8 eV. The results suggest that the pre-exponential factor in Arrhenius equation is dependent on the deposition temperature. The dependence of nucleation rate on deposition temperature was mainly due to the increased structural disorder during hydrogen evolution. The grain size was increased by introducing a double-layer structure of amorphous Si film, where the nucleation occurred other than at the Si/SiO2 interface.
Reduction of the Number of Parameters for the Simulation of Impurity Diffusion
Authors: Masashi Uematsu Masashi Uematsu
Published: October 2002

This paper shows that the binding energy and the rate constants for the kick-out reaction are not essential parameters for the simulation of impurity diffusion, which leads to a reduction of the number of parameters. We have found that transient enhanced B diffusion will be underestimated due to the self-interstitial undersaturation if a large binding energy value is assumed. However, the simulated results are fairly insensitive to the variations of the energy values as long as these values are small enough. In addition, it is concluded that the kick-out reaction is fast enough to achieve the local equilibrium even in a short time at a low temperature. In the simulation, as long as the values of the rate constant of the kick-out reaction are large enough, the local equilibrium is found to be satisfactorily achieved, and the simulated results are almost totally independent of the parameter values.
Magnetooptic Waveguide with SiO2 Cladding Layer Integrated on InP Substrate by Wafer Direct Bonding
Authors: Hideki Yokoi Hideki Yokoi , Tetsuya Mizumoto Tetsuya Mizumoto
Published: October 2002

Magnetooptic waveguides with a SiO2 cladding layer were fabricated on an InP substrate by the wafer direct bonding technique for the purpose of integrating a laser diode and an optical isolator. First, direct bonding between InP and sputter-deposited SiO2 on a Gd3Ga5O12 substrate was investigated. Bonding was achieved by surface treatment of both wafers and subsequent heat treatment in H2 ambient. By applying heat treatment in H2 ambient at temperatures ranging between 110 and 220° C, the magnetooptic waveguides were bonded to the InP substrate without deterioration of their optical properties.
Variation of the Preferred Orientation with Thickness in Barium Titanate Thin Films Prepared by Pulsed Laser Deposition
Authors: Kim Dong-Young , Lee Soon-Gul , Park Yong-Ki , Soon Ja Park Soon Ja Park
Published: October 2002

In the deposition of BaTiO3 thin films by pulsed laser deposition, the variation of the preferred orientation with thickness was studied. The preferred orientation of the films deposited below 1 mTorr was (100), and did not change with variations in the thickness due to the high adatom mobilities. The preferred orientation of the films deposited above 200 mTorr was (110) which has the highest growth rate in the BaTiO3 perovskite structure, and it did not also change with variations in thickness. During the deposition between 50–100 mTorr, the preferred orientation varied in the order of (111)–(110)–(111) with an increase in the thickness of the film. For this orientation change to occur, the film surface should be rough. This preferred orientation change was thought to be related to the (111) twins of BaTiO3.
Charging Damages to Gate Oxides in a Helicon O2 Plasma
Authors: Lin Wendy , Kang Tzong-Kuei , Perng Yean-Chyi , Dai Bau-Tong , Huang-Chung Cheng Huang-Chung Cheng
Published: October 2002

After the exposure of metal oxide semiconductor (MOS) capacitors with antenna structures to the helicon O2 plasma, the leakage current, charge-to-breakdown (Q
bd) and capacitance–voltage ( C–V ) curves have been characterized to realize the charging damages. The results indicate that the quasi static C–V (QSCV) distortion and Q
bd depend on the exposure time rather than the antenna ratio. The QSCV and Q
bd show a two stage degradation as the exposure time increases. The leakage current increases slightly for the specimens exposed to the plasma for less than 120 s, and increases considerably for the ones with the exposure time of 300 s. Based on these results, the degradation mechanism of gate oxides under the helicon O2 plasma is established.
Luminescence Study of Copper Halides in Oxygen Discharge Flow Containing Chlorine
Authors: Kobayashi Takaomi , Ikehara Eiji , Hirotaka Nagoya Hirotaka Nagoya , Nobuyuki Fujii Nobuyuki Fujii
Published: October 2002

Copper halide luminescence was measured when CuBr heated at 500 K was vaporized into oxygen discharge flow in the absence and presence of chlorine ( Cl2). With a slight Cl2 addition, emission peaks for CuCl transitions were detected instead of the CuBr transitions. As Cl2 was added in the range of 0.24–6.7 mmol/min, the blue luminescence for CuCl transitions was gradually changed to a red color for the CuCl2 transition. Evidence of the excitation process for CuBr and CuCl2 was shown by the observation of NO2 chemiluminescence and O2(1Δ) emission in the discharged flow. The results indicated that atomic oxygen and singlet oxygen species are responsible for the excitation of CuBr and CuCl2, respectively.
Fabrication of 0.1 µm Patterns Using an Alternating Phase Shift Mask in ArF Excimer Laser Lithography
Authors: Keisuke Nakazawa Keisuke Nakazawa , Masaya Uematsu Masaya Uematsu , Toshio Onodera Toshio Onodera , Kazuya Kamon Kazuya Kamon , Tohru Ogawa Tohru Ogawa , Shigeyasu Mori Shigeyasu Mori , Makoto Takahashi Makoto Takahashi , Takeshi Ohfuji Takeshi Ohfuji , Hiroshi Ohtsuka Hiroshi Ohtsuka , Masaru Sasago Masaru Sasago
Published: October 2002

We demonstrate applications of alternating phase shift mask (Alt-PSM) techniques to ArF excimer laser lithography with a numerical aperture of 0.6 and a coherence factor of 0.3. A 0.10 µm line-&-space (L/S) pattern was fabricated using a single-layer resist and a 0.09 µm L/S pattern was fabricated using a silylation resist. However, the process window was smaller for the silylation resist than for the single-layer resist over the 0.10–0.13 µm L/S range. The maximum depth of focus (DOF) values were approximately 0.3, 0.5, and 0.9 µm for 0.10, 0.11, and 0.13 µm L/S patterns, respectively, for the single-layer resist. From exposure dose-DOF-tree analysis, we estimated the inclusive process margin including the critical dimension difference, the DOF, the dose margin, and the phase error. Assuming that the usable DOF is larger than 0.5 and 0.6 µm for 0.11 and 0.13 µm L/S patterns, respectively, the inclusive process margin for the single-layer resist is poor in comparison with future predictions.
Novel Optimization of Total Alignment Error Factors
Authors: Kawamura Eiichi , Yasuhiko Konno Yasuhiko Konno , Teruyoshi Yao Teruyoshi Yao
Published: October 2002

A novel optimization method has been developed for reducing total alignment error. We have investigated alignment errors induced by the interaction between the exposure tool and the wafer process, including measurement methodologies. We discovered that the chromatic image shift (CIS) in image processing alignment sensors has a strong effect on the alignment offset in processed wafers. The minimization of alignment offsets between various layers has been achieved. This improvement is realized by: (1) measuring the CIS as a measurement offset between two different illumination wavelengths on an alignment mark of an etched silicon step whose height is λ/8, where λ is the averaged illumination wavelength; (2) adopting electrical measurement to verify alignment accuracy; (3) clarifying the relationship between the CIS and alignment offsets of actual devices to obtain the tolerance of CIS; (4) adjusting optical elements of the alignment system to suppress CIS within tolerance; and (5) determining which alignment marks will induce the smallest alignment offset. This methodology contributes significantly to process automation and the elimination of the need for a send-ahead wafer.
Novel Proximity Effect Including Pattern-Dependent Resist Development in Electron Beam Nanolithography
Authors: Kenji Yamazaki Kenji Yamazaki , Kenji Kurihara Kenji Kurihara , Toru Yamaguchi Toru Yamaguchi , Hideo Namatsu Hideo Namatsu , Masao Nagase Masao Nagase
Published: October 2002

A novel proximity effect, which includes the effect due to secondary electron scattering to a range of less than a micron and the pattern dependence of resist development, has been found and investigated to develop a precise dose control method in electron beam nanolithography. Experiments and simulations including secondary electron scattering were performed for precise evaluation of the proximity effect. This result revealed that the proximity effect caused by secondary electron scattering to the range between 30 nm and a micron is not negligible for nano-patterns. In addition, from experimental estimation of the rate of development of patterns of various sizes, a significant decrease of the rate was found for patterns less than 30-nm wide. The difference of the rate is also modified by the background deposited energy due to surrounding patterns. Therefore, we have to be very careful about how we determine the proper dose for a given nano-pattern.
An Ultralow Stress Ta4B Absorber for X-Ray Masks
Authors: Shoki Tsutomu , Ohkubo Ryo , Sakurai Tadashi , Kawahara Takamitsu , Annaka Norimichi , Yabe Hideki , Aya Sunao
Published: October 2002

The stress controllability, stress uniformity, stress stability and dry etching characteristics of Ta4B films deposited by an in-line type sputtering system were investigated in detail. Low average stress Ta4B films within ±10 MPa have been fabricated on polished SiC films that demonstrate excellent reproducibility by step annealing. Stress uniformity of the film showed an approximate range of 7 MPa on a Si wafer in a 30 mm square area when the deposition conditions were modified. The Ta4B film demonstrated long-term stress stability and excellent resistance to the acid and water used in the cleaning process. The Ta4B film also ensures fine pattern formations below 0.2 µ m.
Roles of Surface Functional Groups on TiN and SiN Substrates in Resist Pattern Deformations
Authors: Yamanaka Ryoko , Mine Toshiyuki , Toshihiko Tanaka Toshihiko Tanaka , Tsuneo Terasawa Tsuneo Terasawa
Published: October 2002

Resist pattern deformations on a bottom anti-reflective layer (BARL) are a serious problem for deep UV lithography. To clarify the mechanism of these pattern deformations, we analyzed SiN and TiN substrates (candidates of BARL materials) by Auger electron spectroscopy (AES) and thermal desorption (TDS). We also applied N2 annealing and thermal oxidation to the substrates. To examine the reactivity of the substrates to the acid generated in the resist, the potential energy and partial charges of model compounds were calculated using the molecular orbital method. By comparing experimental and calculational results, it was found that the Si–OH group neighboring N atoms on SiN substrates was a stronger base than the Si–OH group neighboring O atoms. We also found that NH

x

groups can easily react with the acid. The oxidation of SiN, which eliminates NH

x

and N–Si–OH, prevented pattern deformation. In the case of TiN, on the other hand, oxidation was not effective because Ti–O–Ti can be decomposed by the acid.
Dependence of Electron Energy Distributions on Discharge Pressure in Ultrahigh-Frequency and Inductive-Coupled Cl2 Plasmas
Authors: Tsukada Seiji Samukawa
Published: October 2002

In the ultrahigh frequency (UHF) plasma, a high ion density and a high energy tail in the electron energy distributions can be maintained in a wide pressure range from 3 to 20 mTorr, whereas in the inductively coupled plasma (ICP) these characteristics are drastically reduced when the gas pressure is increased. This indicates that the ionization in the UHF plasma does not depend significantly on the gas pressure from 3 to 20 mTorr because the discharge frequency is higher than the electron collision frequency in the UHF plasma. As a result, the UHF plasma possesses a wider process window for highly-selective polycrystalline silicon etching than the ICP.
Advanced Trench and Local Oxidation of Silicon (LOCOS) Isolation Technology for Ultra-Low-Power Bulk Dynamic Threshold Metal Oxide Semiconductor Field Effect Transistor (B-DTMOS)
Authors: Hiroshi Kotaki Hiroshi Kotaki , Kouichirou Adachi Kouichirou Adachi , Kazuo Sugimoto Kazuo Sugimoto , Masayuki Nakano Masayuki Nakano , Seizou Kakimoto Seizou Kakimoto , Takashi Fukushima Takashi Fukushima
Published: October 2002

We have developed a novel deep trench and local oxidation of silicon (LOCOS) isolation technology termed SITOS II in order to isolate the shallow-well regions necessary for realizing a high speed dynamic threshold metal oxide semiconductor field effect transistor (MOSFET) in a bulk wafer. Using this simple isolation technology, suppression of birds-beak formation, low junction leakage current, high punch-through voltage between shallow-wells, and sub-threshold transistor characteristics without kinks were achieved.
Surface Analysis by Imaging of H + on Si Device Surface
Authors: Kazuyuki Ueda Kazuyuki Ueda , Ken'ichi Ishikawa Ken'ichi Ishikawa , Masamichi Yoshimura Masamichi Yoshimura
Published: October 2002

The technique of imaging hydrogen concentration on solid surface by scanning electron-stimulated desorption spectroscopy has been reported. Improvement of an electron gun makes it possible to realize higher resolution imaging of H+ ions from copper mesh compared to that of our previous work. Although primary current is lower than 1 nA due to a thermal field emission gun, it produces a fine beam 300 nm in diameter at primary energy of 800 eV. Here, we show two-dimensional images of hydrogen ions of which the lateral resolution is less than 1 µm on copper mesh and on an integrated circuit.
In Situ Observation of Photon-Stimulated Hydrogen Removal on a HF-Passivated Si(111) Surface by Ultraviolet Photoelectron Spectroscopy Using Synchrotron Radiation
Authors: Takakuwa Yuji , Nogawa Masafumi , Ishida Hiroyuki , Niwano Michio , Kato Hiroo , Miyamoto Nobuo
Published: October 2002

Photon-stimulated hydrogen removal on a HF-passivated Si(111) surface has been investigated by ultraviolet photoelectron spectroscopy (UPS) using synchrotron radiation (SR). Vacuum ultraviolet (VUV) light, which was tuned to a photon energy of ∼23 eV and an incidence angle of ∼45° to maximize the efficiency of hydrogen removal due to irradiation, was employed as a light source for UPS measurement as well as for irradiation. This enabled us to observe in situ the changes in the adsorption state and the amount of surface hydrogen during irradiation without probe-beam induced disturbance of hydrides and the need to position a probe beam within an irradiated area on the surface. UPS spectra for the HF-passivated Si(111) surface, which was composed primarily of trihydride with a small amount of dihydride and monohydride prior to irradiation, showed that the amount of each kind of hydride varied with irradiation time in a different manner. The variation is interpreted in terms of a kinetics model proposed for the photon-stimulated hydrogen removal reaction, in which monohydride and dihydride are produced via photon-stimulated hydrogen removal in dihydride and trihydride, respectively. Based on the reaction kinetics model, it was clarified that the order of magnitude in the rate of photon-stimulated hydrogen removal R is R(monohydride)>R(dihydride)>R(trihydride).