bluuebunny/crossref_metadata_2025 huggingface dataset:
Cholesteric Thermo-reversible Liquid-Crystal Gels: Phase Behaviour and Electro-optical Response
Authors: Janssen Rob H. C. , Teunissen Jean-Pierre , Picken Stephen J. , Bastiaansen Cees W. M. , Broer Dirk J. , Tervoort Theo A. , Smith Paul
Published: October 2002

Thermo-reversible gels of a chiral nematic liquid-crystal (LC) with 12-hydroxyoctadecanoic acid (HOA) were cast in a light-reflecting planar configuration by choosing a processing temperature higher than the sol–gel temperature but lower than the onset-temperature for the chiral nematic-isotropic transition in the gel. The choice of processing temperature is dictated by the quasi-ternary phase diagram of the system, which displays a 3-phase region at which an isotropic liquid is in equilibrium with a fibrillar solid and a chiral nematic mesophase. Planar configurations of the gels produced show a significant broadening of the reflection band with respect to the neat LC-material indicating a distribution of the cholesteric pitch within the gel. Visco-elasticity, electro-optical activity and zero electric field bistability of gelled films has been utilized in building a reflective bistable chiral nematic cell with improved shock-resistance that holds the promise of being produced via a continuous processing route.
Thermal Nitridation and Oxygen-induced Etching Reactions: A Comparative Study on Si(100) and (111) Surfaces by Scanning Tunneling Microscopy
Authors: Ha Jeong Sook , Park Kang-Ho , Yun Wan Soo , Ko Young-Jo
Published: October 2002

Comparative studies of the thermal nitridation and subsequent oxygen-induced etching reactions on Si(100) and Si(111) surfaces were done using a scanning tunneling microscope. Both surfaces were thermally nitrided by exposure to nitrogen gas at 700°C and subsequently reacted with oxygen under an oxygen partial pressure of 1×10-7 Torr. Silicon nano-structures were formed via selective local oxygen etching of silicon using the silicon nitrides as masks against the oxygen exposure. Resultant silicon nano-structures showed distinct differences between the two surfaces. Very narrow size distribution of silicon dots with an average size of ∼5 nm was obtained on the Si(100) surface, whereas a broad size distribution of silicon protrusions ranging from 5 to 20 nm was obtained on the Si(111) surface. We discuss the observed differences between Si(111) and (100) surfaces considering the thermal mobility of nitrogen species and the lattice and symmetry mismatches between the silicon nitride layer and Si.
Observation of Nematic Liquid Crystal Director Reorientation at the Interface between Substrate and Liquid Crystal Layer by Total Reflection Ellipsometry
Authors: Satoshi Okutani Satoshi Okutani , Munehiro Kimura Munehiro Kimura , Hirokazu Toriumi Hirokazu Toriumi , Kenichi Akao Kenichi Akao , Toshiyasu Tadokoro Toshiyasu Tadokoro , Tadashi Akahane Tadashi Akahane
Published: October 2002

The liquid crystal (LC) director reorientation near the interface between the substrate and the LC layer was studied using total reflection ellipsometry (TRE). The dynamic and static responses of the ellipsometric angles to the electric field were measured by TRE. It was experimentally confirmed that total reflection occurs in the LC cell. The reflected light is dominantly modified by the interfacial LC director reorientation. The polar anchoring strength of the cell was estimated by analyzing the electrical response of the phase difference response. We confirm that the TRE is useful for studying the LC director reorientation near the interface between the substrate and the LC layer.
Effects of Sr/Ti Ratio on the Step Coverage of SrTiO3 Thin Films Fabricated Using Electron Cyclotron Resonance Plasma Enhanced Metal Organic Chemical Vapor Deposition
Authors: Park Soon Yon , Choi Jongwan , No Kwangsoo
Published: October 2002

SrTiO3 thin films were deposited on Si(p-type 100), Pt(1000 Å)/SiO2/Si and stepped Pt(800 Å)/SiO2/Si substrates using electron cyclotron resonance plasma enhanced metal organic chemical vapor deposition (ECR-PEMOCVD) to study the effects of deposition temperature and composition on the properties of SrTiO3 thin films. The crystallinity and dielectric properties of SrTiO3 thin films were improved as the deposition temperature increased. We observed a distinct correlation, not between step coverage and deposition temperature, but between the step coverage and the composition. The composition of the film was changed by changing the flow rate of one of the carrier gas but fixing that of the other, with the deposition temperature fixed at 550°C. The step coverage was improved as the composition (Sr/Ti ratio) increased up to the stoichiometric composition and showed a saturated value of about 55% as the Sr/Ti ratio increased beyond the stoichiometric composition. This correlation was speculated based on the sticking coefficients of the precursor vapors.
Plasma Source Ion Implantation for Ultrashallow Junctions: Low Energy and High Dose Rate
Authors: Cho Jeonghee , Han Seunghee , Lee Yeonhee , Kim Ok Kyung , Kim Gon-Ho , Kim Young-Woo , Lim Hyuneui , Jung Hye Sun
Published: October 2002

Ultrashallow p+/n junctions fabricated by plasma source ion implantation (PSII) were studied. After as-implanted samples were spike-annealed at 1000°C and annealed for 5 s at 1000°C, for samples with a background doping concentration of 6×1017 #/cm3, ultrashallow junction depths of 548 Å and 745 Å, respectively, could be obtained with an implant energy of 0.5 keV. Also, sheet resistances of 330 Ω/\Box and 228 Ω/\Box were acquired, respectively. These junction depths and sheet resistances obtained by the PSII process were found to satisfy 0.15 µm metal oxide semiconductor field effect transistor (MOSFET) applications.
Hyperfine Structure Measurement of LaII by Collinear Fast Ion-Beam-Laser Spectroscopy
Authors: Li Guang-Wu , Zhang Xue-Mei , Lu Fu-Quan , Peng Xian-Jue , Yang Fu-Jia
Published: October 2002

The spectra of singly ionized lanthanum have been measured by means of collinear fast ion-beam-laser spectroscopy (CFIBLS). The hyperfine structures (HFSs) in the 570.33 nm, 587.40 nm and 612.96 nm lines of LaII were resolved and the HFS constants A and B of the involved levels are given.
Refractive Index Change of an Amorphous Bisbenzothienylethene
Authors: Chauvin Jérôme , Kawai Tsuyoshi , Irie Masahiro
Published: October 2002

A bisbenzothieneylethene exhibiting a photochromic behavior in the amorphous bulk solid state was synthesized. Upon alternate ultraviolet (UV) and visible light irradiation the amorphous thin film underwent a reversible color change and modulation of the refractive index. The refractive index change was determined at 632.8 nm and 817 nm using a prism coupling method. The difference in the refractive index value between the open- and closed-ring isomers was as high as 0.064 at 817 nm.
Energy-filtered Electron Interferometry in Reflection Electron Microscopy
Authors: Suzuki Takayuki , Tanishiro Yasumasa , Ishiguro Nami , Minoda Hiroki , Yagi Katsumichi
Published: October 2002

We studied energy-filtered interferometry in reflection electron microscopy (REM) geometry for the first time. An ultra-high vacuum electron microscope (UHV-EM) equipped with a field emission gun (FEG), a Möllenstedt-type electron biprism and an omega-type energy-filter was used. The specimen was a well-defined Si(111) 7×7 clean surface. Single and multiple surface plasmon excitation is significant in a reflection electron energy loss spectrum (REELS) taken from the surface. The following was found in the REM geometry for the first time. Visibility of carrier fringes in the interference region formed by no-plasmon-loss electrons is higher than that in an unfiltered one. The carrier fringes are also visible in the interferograms formed by electrons exciting the surface plasmon once or twice. The lateral coherent length of the electrons exciting the surface plasmon once is narrower (about 45 nm) than that of the no-plasmon-loss electrons (about 90 nm).
Site Occupancy of Rare-Earth Cations in BaTiO3
Authors: Tsur Yoed , Hitomi Atsushi , Scrymgeour Ian , Randall Clive A.
Published: October 2002

A systematic study on the site occupancy of rare-earth cations in Ba-rich and Ti-rich BaTiO3 fired in reducing atmosphere is performed. The corresponding lattice relaxation is used as an indicator of site occupancy and, to a lesser extent, defect structures. Accurate lattice parameters are obtained from X-ray diffraction data that is analyzed with the maximum likelihood method to account for correlated errors in the c and a lattice parameters. Comparisons of lattice volume as a function of ionic radius of the dopant reveals three regimes, with the intermediate sized cations (0.087 nm \leqslantr \leqslant0.094 nm where r is the ionic radius in six-fold coordination) demonstrating amphoteric behavior (occupying A- or B-sites). Defect chemistry analysis of site occupancy links the importance of metal vacancy ratios and oxygen vacancy concentrations with site occupancy. The trends predicted from the defect chemistry analysis are consistent with the observed lattice relaxations.
Influence of Irradiation Wavelength on Atomic Emission Spectroscopy Using Laser Ablation
Authors: Kyu Kim Min , Takashi Higotani Takashi Higotani , Takayuki Takao Takayuki Takao , Yuji Oki Yuji Oki , Mitsuo Maeda Mitsuo Maeda
Published: October 2002

In this study, the influence of laser wavelengths on atomic emission spectroscopy using laser ablation for samples (glass, polymer, Si, and Cu) has been investigated using 1064 nm and 266 nm pulses of a Q-switched Nd:YAG laser. The threshold fluence is decreased and the emission intensity is increased for UV laser ablation, compared with IR laser ablation. Simultaneous irradiation by both IR and UV pulses has also been found in decreasing the threshold and increasing the emission intensity.
Optimization of a 118 MHz Resonant Cavity Shape for Damping of Higher Order Modes by SiC Material
Authors: Haß Klaus , Ishii Takehiko
Published: October 2002

The rf cavity of the storage ring of the Siam Photon Source at National Synchrotron Research Center (NSRC) in Thailand is modified for the purpose of suppression of higher order modes (HOM) by insertion of SiC material inside the nose cone part. For this purpose, the shape of the nose cone part must be changed. The effect on the modes by the change in shape and the use of SiC is presented and discussed. It is shown that the fields of HOM can be absorbed significantly by SiC, which leads to a marked reduction of their Q-values and shunt impedances. This work has been carried out in collaboration with the Photon Factory at KEK in Tsukuba, Japan.
Flexible Processor Based on Full-Adder/D-Flip-Flop Merged Module (FDMM)
Authors: Sakaidani Satoshi , Miyamoto Naoto , Ohmi Tadahiro
Published: October 2002

A flexible processor based on the full-adder/D-flip-flop merged module (FDMM) has been proposed and fabricated. The developed FDMM has a unique ability to perform both logic and flip-flop functions with a small number of transistors by merging the common parts of both circuits, which will improve hardware efficiency. We have also developed a context memory block (CMB) to reconfigure the hardware dynamically. It enables us to write the next configuration in parallel into the flexible processor during processing, which reduces the overhead of actual reconfiguration time and improves the performance.
A νMOS Vision Chip Based on Cellular-Automaton Processing
Authors: Tetsuya Asai Tetsuya Asai , Tatsuhiko Sunayama Tatsuhiko Sunayama , Yoshihito Amemiya Yoshihito Amemiya , Masayuki Ikebe Masayuki Ikebe
Published: October 2002

A neuron MOS (νMOS) vision chip was designed and fabricated for developing high-speed parallel image-processing systems based on cellular-automaton processing. The chip consists of cellular νMOS circuits that implement two fundamental functions in digital image processing: i) cleaning up noise in binary images and ii) detecting edges in the images, in addition to photosensing and image quantizing. Experimental results reveal that the fabricated chip successfully extracted edges from noisy inputs, which demonstrates the great potential of the νMOS vision chip in future image-processing applications.
Positron-Annihilation Studies of Frank-Kasper-Type Quasicrystals of the Mg–Zn–Ga–Al and the Mg–Zn–Rare-Earth System
Authors: Hamada Eisaku , Sato Kiminori , Takahashi Yasufumi , Uchiyama Hidefumi , Kanazawa Ikuzo , Oshima Nagayasu , Suzuki Takenori , Nakata Masataka , Yoshida Tomoyoshi , Takeuchi Shin
Published: October 2002

We have performed positron-annihilation experiments for a Frank-Kasper (F-K)-type icosahedral quasicrystal, 2/1 and 1/1 approximant crystals of Mg–Zn–Ga–Al, and the stable F-K-type icosahedral quasicrystals of Mg–Zn–RE (RE=rare-earth metal, Y, Ho and Gd) alloys. It is shown that a high density of vacant centers in triacontahedral clusters exists in both icosahedral and approximant phases of Mg–Zn–Ga–Al. Furthermore, in the present study, we report a very interesting finding that stable non-Al-based quasicrystals such as the icosahedral quasicrystal Mg–Zn–RE system also contain a high density of structural vacancies, similar to the stable Al-based quasicrystals. In particular, it is estimated experimentally that the structural vacancy densities for icosahedral quasicrystal Mg34Zn58Y8 and Mg40Zn52Ho8 are 3 ×1020 and 4 ×1020 cm-3, respectively. These results provide important information on the structural modeling of the stable icosahedral quasicrystal Mg–Zn–RE, which is a recent research topic of the icosahedral quasicrystals.
A Dual-Gate Complementary Metal-Oxide-Semiconductor Technology with Novel Self-Aligned Pocket Implantation which Takes Advantage of Elevated Source/Drain Configurations
Authors: Sugihara Kohei , Miura Naruhisa , Furukawa Taisuke , Nakahata Takumi , Oishi Toshiyuki , Maruno Shigemitsu , Abe Yuji , Tokuda Yasunori
Published: October 2002

A dual-gate complementary metal-oxide-semiconductor technology with novel self-aligned pocket implantation is demonstrated which takes advantage of the elevated source/drain (S/D) configurations. Using the present procedure, S/D junction capacitance and leakage current were significantly suppressed for p-channel metal-oxide-semiconductor field-effect-transistors (MOSFETs) as well as for n-channel MOSFETs without degradation of the short channel characteristics. These results are interpreted in terms of the fact that the pocket impurity profiles shift to the upper positions in the deep S/D regions, though the impurity distribution at the gate edges was hardly varied. Furthermore, the suppression effects were more marked for a higher pocket implantation dosage, which will be required to suppress the short channel effects in future MOSFETs. In addition, improvement of drivability due to the reduction of the parasitic S/D resistance, an original benefit of the elevated S/D engineering, is maintained by the present technique. The present self-aligned pocket procedure is very promising as a key technology beyond the 0.1 µm node.
Comparison of Sub-Bandgap Impact Ionization in Sub-100 nm Conventional and Lateral Asymmetrical Channel nMOSFETs
Authors: Ramgopal Rao Kottantharayil Anil , Ignaz Eisele Ignaz Eisele
Published: October 2002

Sub-bandgap impact ionization is compared in 100 nm channel length conventional channel and laterally asymmetrical n-channel metal oxide semiconductor field effect transistor (MOSFET). An abnormal increase of the gate voltage at which the substrate current peaks is reported. The effect is enhanced in the case of laterally asymmetric channel devices. Experimental and simulation results are presented that suggest the role of inversion layer quantization as an energy gain mechanism.
Impact of Strained-Si Channel on Complementary Metal Oxide Semiconductor Circuit Performance under the Sub-100 nm Regime
Authors: Tetsuo Hatakeyama Tetsuo Hatakeyama , Kazuya Matsuzawa Kazuya Matsuzawa , Shin-ichi Takagi Shin-ichi Takagi
Published: October 2002

The impact of the enhanced mobility of a strained-Si channel on the performance of sub-100 nm complementary metal oxide semiconductor (CMOS) circuits is investigated by the combination of device and circuit simulations, considering both velocity saturation and velocity overshoot effects. It is found that higher mobilities of strained Si become more advantageous with reducing the channel length. It is also pointed out that the increase in energy relaxation time in strained Si, in addition to higher mobility, is effective for the enhancement of the circuit performance. The evaluated performance of 50 nm strained-Si CMOS amounts to around 1.7 times that of bulk-Si CMOS.
Wide Viewing Angle of Nematic Liquid Crystal Using the Vertical-Alignment-1/6π Cell on a Rubbed Polyimide Surfaces
Authors: Hwang Jeoung-Yeon , Seo Dae-Shik , Kim Jae-Hyung
Published: October 2002

The wide viewing angle characteristics of negative dielectric anisotropy nematic liquid crystal (NLC) using the vertical-alignment (VA)-1/6π cell on a homeotropic rubbed polyimide (PI) surface were investigated. Good voltage-transmittance characteristics using the VA-1/6π cell without a negative compensation films were obtained. The iso-viewing angle characteristics using the VA-1/6π cell without a negative compensation film can be achieved.
Characterization of Tungsten Carbide as Diffusion Barrier for Cu Metallization
Authors: Wang Shui Jinn , Tsai Hao Yi , Sun Shi Chung
Published: October 2002

In this paper, the physical and electrical properties as well as thermal stability of the sputter-deposited tungsten carbide (WC
x
) film used as a diffusion barrier layer for copper metallization were investigated for the first time. It is found that the as-deposited WC
x
film has a nanocrystalline structure and a low electrical resistivity of approximately 227 µΩ·cm. According to the four-point probe technique, X-ray diffraction (XRD) and secondary ion mass spectroscopy (SIMS) measurements, it is found that WC
x
film can preserve the integrity of the Cu(2000 Å)/WC
x
(600 Å)/n-Si structure without the formation of Cu3Si up to 600°C annealing in N2 for 30 min. A more sensitive diode leakage current measurement of the Cu(2000 Å)/WC
x
(600 Å)/p+n-Si structure shows that WC
x
film is effective against Cu diffusion into Si substrate up to 550°C. The failure of WC
x
film in preventing Cu diffusion is attributed to the Cu diffusion into the Si substrate through local defects of the WC
x
barrier layer. It is found that Cu diffusion is strongly enhanced by the formation of W5Si3 at the WC
x
/Si interface after high-temperature annealing.
Conformality of Chemical-Vapor-Deposited Tungsten on TiN Prepared by Metal-organic Chemical Vapor Deposition via Cyclic Plasma Treatment
Authors: Whang Soon-Hong , Kim Jun Ki , Park Jin Won , Kim Do-Heyoung , Cho Dong-Lyun , Lee Wan-Jin
Published: October 2002

The conformality of the chemical-vapor-deposited (CVD) W films is investigated with TiN films prepared by chemical vapor deposition using tetrakis-dimethylamino-titanium (TDMAT). Plasma treatment of TDMAT-TiN films is shown to be unsuccessful at removing volatile impurities from side-wall films. The conformality of CVD W films is improved with thinner TDMAT-TiN films and with a low contact aspect ratio. Based on the results of chemical analysis and annealing experiments, we deduce that outgassing from the TiN film on the side wall of holes strongly affects the conformality of CVD W films. Volatile impurities in the TiN film lead to slower growth of W films on the side-wall than on the top of the holes, which results in the deterioration of the conformality of W films.
Copper Electrodeposition: Principles and Recent Progress
Authors: Reid Jonathan
Published: October 2002

The capability of copper electroplating to produce void free filling of sub-micron high aspect ratio features has made it the process of choice for copper interconnect formation. Several aspects of copper electrodeposition including the basic electrochemistry and electrochemical kinetics, mass transport phenomena, potential gradients in solution, electrolyte composition, and the influence of various organic additives have been studied for over 50 years. Much of this basic understanding can be applied to development of integrated circuit (IC) copper electroplating processes. Other aspects of copper electroplating are unique to IC applications. These include the interactions of very thin seed layers with the electroplating process, the basic “bottom-up” filling mechanism necessary for seam free filling, and the metallurgical properties of sub-micron scale deposits. The dependence of IC filling processes upon plating bath chemistry and polarization characteristics are discussed in this paper.
Light Emission Analysis of Dielectric Breakdown in Stressed Damascene Copper Interconnection
Authors: Takeda Ken-ichi , Hinode Kenji , Noguchi Junji , Yamaguchi Hizuru
Published: October 2002

Visible light emission observed in biased comb-type capacitors with a copper (Cu) damascene structure appears to be caused by electroluminescence. Photon emission probably occurs via energy states related to dangling bonds formed at a chemical-mechanical polished (CMP) surface. These energy states also appear to degrade the time-dependent dielectric breakdown (TDDB) characteristics and to increase line-to-line leakage currents. Ammonia (NH3) plasma treatment of a Cu-CMP surface dramatically improved TDDB and decreased the leakage currents. We attribute this to a reduced energy-state density through the termination of dangling bonds by hydrogen generated from the NH3 plasma.
Low Dielectric Constant 3MS α-SiC:H as Cu Diffusion Barrier Layer in Cu Dual Damascene Process
Authors: Lee Soo Geun , Kim Yun Jun , Lee Seung Pae , Oh Hyeok-Sang , Lee Seung Jae , Kim Min , Kim Il-Goo , Kim Jae-Hak , Shin Hong-Jae , Hong Jin-Gi , Lee Hyeon-Deok , Kang Ho-Kyu
Published: October 2002

The primary candidate for the barrier/etch stop layer in damascene process is silicon nitride. However, silicon nitride has a high dielectric constant. To reduce the effective dielectric constant in the copper damascene structure, silicon carbide, which is prepared by plasma enhanced chemical vapor deposition (PECVD) using 3 methyl silane source (Z3MS), is studied for the dielectric copper diffusion barrier. The dielectric constant of PECVD α-SiC:H is varied from 4.0 to 7.0 and the fourier transform infrared (FTIR) spectra peak intensity ratio of Si–CH3 bond to Si–C is also examined. The reduction in dielectric constant of α-SiC:H using 3MS gas seems to be related to the decreased density upon incorporation of Si–CH3 groups. The value of capacitance with α-SiC is 8–10% lower than that with PECVD SiN. The leakage current with α-SiC:H barrier is lower by 1 order of magnitude than that with PECVD SiN barrier.
Atomic Layer Deposition- and Chemical Vapor Deposition-TiN Top Electrode Optimization for the Reliability of Ta2O5 and Al2O3 Metal Insulator Silicon Capacitor for 0.13 µm Technology and Beyond
Authors: Lim Hyun Seok , Kang Sang Bom , Jeon In Sang , Choi Gil Heyun , Park Young Wook , Lee Sang In , Moon Joo Tae
Published: October 2002

TiCl4-based atomic layer deposition (ALD)- and chemical vapor deposition (CVD)-TiN films are applied as the metal top electrode for Ta2O5 and Al2O3 metal insulator silicon (MIS) capacitor. The effects of factors such as Cl content, step coverage, deposition temperature of the TiN top electrode processes and pre-NH3 flushing on the electrical properties and reliability of the Ta2O5 and Al2O3 MIS capacitor are studied. Among these factors, poor step coverage shows distinctly degraded electrical properties of MIS capacitor, and high deposition temperature of TiN processes also degraded electrical properties, particularly those of Ta2O5. Although similar capacitance and leakage characteristics are measured with high chlorine content and pre-NH3 flushing TiN processes, a difference in the orders of magnitude is observed in time dependent dielectric breakdown (TDDB) measurements. Regarding the deposition temperature and pre-NH3 flushing effect, the electrical and TDDB characteristics of Ta2O5 degrade even more severely than those of Al2O3. Degradation of TDDB in TiN films with NH3 flushing prior to deposition is attributed to the reduction effect of the dielectric material by NH3 gas. Based on the X-ray photoelectron spectroscopy (XPS) analysis results, Al2O3 is chemically more inert than Ta2O5. In addition, the degradation of TDDB characteristics is directly correlated to the early generation of V
p-dependent solid “0” fail bit counts. Due to the relatively low deposition temperature as well as to the excellent step coverage and low resistivity, the ALD-TiN process is ideal for enhancing the reliability of a MIS capacitor.
Dual-Thickness Gate Oxidation Technology with Halogen/Xenon Implantation for Embedded Dynamic Random Access Memories
Authors: Sugizaki Taro , Murakoshi Atsushi , Ozawa Yoshio , Nakanishi Toshiro , Suguro Kyoichi
Published: October 2002

We investigated the enhanced oxidation effect of using silicon (Si) implanted with fluorine (F), iodine (I), and xenon (Xe) before gate oxidation. I and Xe, which result in shallower implants because of their higher mass numbers, were expected to be less damaging to the Si substrate. The resultant increase in oxide thickness was found to be 20%, 80%, and 50% under F, I, and Xe implantations with a dose of 5×1014 cm-2, respectively. We found that F atoms outdiffuse to their ambient through SiO2, and that I implantation causes the greatest increase in oxide thickness. In addition, F implantation shows highly reliable dielectric characteristics, low contact resistance, and a low junction leakage current. Consequently, the F implantation process is capable of providing reliable dual-thickness gate oxide for embedded dynamic random access memories (DRAMs).
Boron Diffusion in SiO2 Involving High-Concentration Effects
Authors: Aoyama Takayuki , Arimoto Hiroshi , Horiuchi Kei
Published: October 2002

The diffusivity of boron in gate SiO2 increases with the concentration of boron in the polysilicon gates. A model is described that can explain both the thickness and annealing-time dependencies of the boron penetration in p-channel metal-oxide-semiconductor devices.
Application of a Two-Step Growth to the Formation of Epitaxial CoSi2 Films on Si(001) Surfaces: Comparative Study using Reactive Deposition Epitaxy
Authors: Yukihiro Hayashi Yukihiro Hayashi , Tamiyu Katoh Tamiyu Katoh , Hiroya Ikeda Hiroya Ikeda , Akira Sakai Akira Sakai , Shigeaki Zaima Shigeaki Zaima , Yukio Yasuda Yukio Yasuda
Published: October 2002

Epitaxial growth of 20-nm-thick CoSi2 films on Si(001) surfaces has been investigated for a two-step growth and reactive deposition epitaxy (RDE) at growth temperatures of 320–680°C using in-situ reflection high-energy electron diffraction and scanning tunneling microscopy, and ex-situ X-ray diffraction and atomic force microscopy. For the RDE, three-dimensional CoSi2 islands with a {115}-faceted structure grow along the <110 > directions and pinholes or channels with depths over ∼20 nm are formed. However, for the two-step growth, no {115}-faceted islands exist and the depth of pinholes or channels decreases greatly. In the two-step growth, cobalt is solely deposited at an elevated substrate temperature on an epitaxial CoSi2(001) film formed by solid-phase epitaxy of 0.23-nm-thick Co as the first step. The first-step CoSi2 film has effects on restraining the Si diffusion from the substrate at the pinhole sites and promoting the layer-by-layer growth at the second step. The original two-step growth technique will be highly suitable for the realization of high-quality epitaxial CoSi2 contacts in the future ULSI technology.
Phosphorus Doping in Si1-x-yGexCyEpitaxial Growth by Low-Pressure Chemical Vapor Deposition Using a SiH4–GeH4–CH3SiH3–PH3–H2Gas System
Authors: Lee Doohwan , Noda Takaaki , Shim Hyunyoung , Sakuraba Masao , Matsuura Takashi , Murota Junichi
Published: October 2002

Phosphorus doping in Si1-x-yGexCy(0≦x≦0.78, 0≦y≦0.016) epitaxial growth on Si(100) at 550°C by ultraclean hot-wall low-pressure chemical vapor deposition using a SiH4–GeH4–CH3SiH3–PH3–H2gas system is investigated. The relationship among the Ge, the C fraction, the P concentration (CP), the deposition rate, and the deposition conditions in the P-doped Si1-x-yGexCyepitaxial growth under the surface reaction-limited regime is experimentally obtained, and is explained by the modified Langmuir-type adsorption and reaction scheme. The relationships among the carrier concentration, theCP, and the resistivity in the P-doped Si1-x-yGexCyfor various Ge and C fractions are also presented. The carrier concentration of the P-doped Si1-x-yGexCywith low Ge and C fractions (x≦0.48 andy≦0.0046) is nearly equal toCPbelow approximately 2×1020cm-3. With increasing Ge and C fractions, the film has electrically inactive P atoms independent ofCP. The existence of C (y≧0.0048) in the film reduces the Hall mobility.
Formation of Al Clusters Grown on the Hydrogenated Diamond Surfaces
Authors: Hoshino Tadatsugu , Murata Katsumi , Mizutani Kyoko , Hata Masayuki , Tsuda Minoru
Published: October 2002

Stable structures of Al clusters grown on completely or incompletely H-terminated diamond (111) surfaces have been determined by first principles quantum chemical calculations. When Al atoms are deposited on the completely H-terminated diamond surface, planar stable structures are possibly formed as well as nonplanar ones. On the other hand, only nonplanar type Al clusters are grown on the partly H-removed surface losing three H atoms from the complete H-termination, and those nonplanar Al clusters have the structure of a single Al crystal. The result suggests the possibility of an epitaxial growth of Al metals on the diamond (111) substrate.
Vertical High Quality Mirrorlike Facet of GaN-Based Device by Reactive Ion Etching
Authors: Chen Chin Hsiang , Chang Shoou Jinn , Su Yan Kuin , Chi Gou Chung , Sheu Jinn Kong , Lin I Chao
Published: October 2002

Reactive ion etching (RIE) of GaN has been performed using BCl3 and additives Ar, CH4, and N2 to BCl3 plasma. The etching rate, surface roughness and the etch profile have been investigated. When BCl3/Ar was used as the RIE plasma source with 200 W RF power and 60 mTorr pressure, the highest etching rates of 505 Å/min and 448 Å/min were obtained for n- and p-GaN, respectively. It was found that the addition of CH4 and N2 to the BCl3 plasma would result in significant changes of the etching results, such as the etching rate and surface morphology. It was also found that with the proper etching parameter, the mirrorlike facet of GaN can be obtained using BCl3/Ar/CH4/N2 by RIE.
Nitrogen Doping into Cu2O Thin Films Deposited by Reactive Radio-Frequency Magnetron Sputtering
Authors: Ishizuka Shogo , Kato Shinya , Maruyama Takahiro , Akimoto Katsuhiro
Published: October 2002

The effects of nitrogen doping into Cu2O thin films deposited by reactive radio-frequency magnetron sputtering were studied. It was found that nitrogen is an effective p-type dopant for Cu2O and the hole density can be controlled from 1×1015 cm-3 to approximately 1017 cm-3. The acceptor level of nitrogen was estimated to be about 0.14 eV by temperature-dependent Hall effect measurements and this value roughly agrees with that obtained by the effective mass theory. No significant degradation of structural and optical properties induced by nitrogen doping were observed. The resistivity of 15.2 Ωcm was obtained for a relatively high nitrogen flow rate, which is the lowest value reported to date for Cu2O thin films.
High-Performance MOS Tunneling Cathode with CoSi2 Gate Electrode
Authors: Taizoh Sadoh Taizoh Sadoh , Yi-Qun Zhang Yi-Qun Zhang , Hiroki Yasunaga Hiroki Yasunaga , Atsushi Kenjo Atsushi Kenjo , Toshio Tsurushima Toshio Tsurushima , Masanobu Miyao Masanobu Miyao
Published: October 2002

The high performance of metal-oxide-semiconductor (MOS) tunneling cathodes with CoSi2 gates was demonstrated. First, the deposition process of CoSi2 was optimized. Stoichiometric CoSi2 films were formed by codeposition with Co and Si. The electrical measurement suggested that deposition above 300°C was necessary to obtain low-resistivity silicide films. Second, operation characteristics were evaluated for MOS tunneling cathodes with CoSi2 gates formed at 400°C. The emission efficiency increased with decreasing gate thickness and became as high as 1.5 ×10-3 for the 5 nm CoSi2 cathode. The efficiency did not depend on the electric field above 8.5 MV cm-1. Thus, the CoSi2 gates were deemed suitable for operation at higher electric fields to obtain larger emission currents. The lifetime of the cathodes corresponded to 500 h for operation at 8.5 MV cm-1.
Properties of a Monolithic Electroacoustic Device Geometry Using GaAs Resonant Tunnelling Structures
Authors: B. Hutchinson Alexander , I. Talyanskii Valery , H. Harrell Ruth , H. Linfield Michael Pepper
Published: October 2002

We present experimental and theoretical work on a monolithic electroacoustic system which exploits the interaction between a 1 GHz surface acoustic wave and electrons in a GaAs-AlGaAs resonant tunnelling structure. Non-annealed Ohmic contacts usingin situgrown Al are employed to obtain stable dc operation. The microwave response of the system is explained, with features attributed to charge accumulation in the spacer layer adjacent to the quantum well. The influence of screening of the surface acoustic wave potential by the highly-doped substrate is also investigated, showing the need for a wide depletion layer. Potential applications for this system in signal processing and power microwave devices are discussed, along with a suggested mechanism for a non-dispersive surface acoustic wave transducer which relies on the nonlinear properties of the system.
Novel Single Electron Memory Device Using Metal Nano-Dots and Schottky In-Plane Gate Quantum Wire Transistors
Authors: Hiroshi Okada Hiroshi Okada , Hideki Hasegawa Hideki Hasegawa
Published: October 2002

We report on the successful realization of a novel single electron memory device utilizing a Schottky in-plane gate (IPG) quantum wire transistor (QWTr) with nano Schottky metal dots whose position and size can be precisely controlled.
Current–voltage (I–V) characteristics of the nano-metal dot formed on n-GaAs showed clear hysteresis which suggests charging of the nano-metal dot.
A fabricated single electron memory device utilizing nano-metal dots showed clear threshold voltage shift once the bias was applied to the charging control gate of the nano-metal dot.
This indicates successful memory operation of the fabricated device.
X-Ray Diffraction Measurements on Lattice Mismatch of InTlAs Grown on InAs Substrates
Authors: Kajikawa Yasutomo , Asahina Shuuichi , Kanayama Nobuyuki
Published: October 2002

InTlAs layers were grown by molecular-beam epitaxy on InAs(001) substrates, and their lattice mismatch to the substrate was characterized by X-ray diffraction measurements. In each X-ray rocking curve, a distinct peak of InTlAs was observed at a higher diffraction angle than the substrate peak, indicating a smaller lattice constant of InTlAs than InAs. The lattice mismatch, δ=(a
epi-a
sub)/a
sub, was estimated to be -0.08% for a sample whose thallium composition x of In1-x
Tl
x
As was determined to be 0.12(±0.02)% by Rutherford backscattering spectrometry.
Degradation of Ta2O5 Gate Dielectric by TiCl4-Based Chemically Vapor Deposited TiN Film in W/TiN/Ta2O5/Si System
Authors: Lee JooWan , Han Chang Hee , Park Ji-Soo , Park Jin Won
Published: October 2002

Tantalum pentoxide was adopted as a gate dielectric for obtaining gate oxide with less than 3.0 nm SiO2 equivalent thickness and low leakage current. Physical vapor deposited (PVD) TiN or TiCl4-based chemical-vapor-deposited (CVD) TiN was used as the barrier material between the W electrode and Ta2O5 layer. The thermal stability and electrical property of each barrier were evaluated at an elevated temperature of 900°C. In the as-deposited condition and after annealing at 800°C, PVD and CVD TiN show similar electrical properties. However, after annealing at 900°C, CVD TiN barriers show much lower breakdown fields and higher leakage current compared with PVD TiN, indicating that CVD TiN has worse barrier performance than PVD TiN. Microvoids are formed in the Ta2O5 layer along the PVD TiN/Ta2O5 interface after annealing at 900°C. It is found that Ta diffuses into the TiN layer leaving microvoids behind. Ta2O5 is more severely damaged in the CVD TiN system after annealing. The high content of residual Cl in CVD TiN was found to reduce Ta2O5 and generate free Ta and O. Free Ta and O atoms that are generated from the reduction of Ta2O5 diffuse into the TiN layer and hence produce macrovoids and disconnected areas in the Ta2O5 layer. The transmission electron microscopy (TEM) images and secondary ion mass spectrometry (SIMS) depth profiles are in good agreement with the electrical properties of W/TiN/Ta2O5/Si gate devices.
Characteristics of TaOxNy Gate Dielectric with Improved Thermal Stability
Authors: Cho Heung-Jae , Park Dae-Gyu , Yeo In-Seok , Roh Jae-Sung , Park Jin Won
Published: October 2002

We report the properties of novel gate dielectric TaO
x
N
y
prepared by low-pressure chemical vapor deposition using Ta(OC2H5)5 and NH3. The metal-oxide-semiconductor (MOS) characteristics of TaO
x
N
y
/SiO2 gate dielectric are compared with those of Ta2O5/SiO2 stack gated with a W/WN electrode. The flat-band voltage shift (ΔV
fb) of TaO
x
N
y
in comparison with Ta2O5 is -0.17 V due to the nitrogen-induced positive charges accumulated at the SiO2/Si interface. The interface state density of W/WN/TaO
x
N
y
/SiO2/p-Si nMOS capacitors as determined by the conductance method is in the 0.85–1.5×1011 eV-1 cm-2 range near the Si midgap. The leakage current level of the TaO
x
N
y
/SiO2/p-Si MOS capacitor is ∼-10 nA/cm2 at -2.5 V at the effective oxide thickness (T
eff) of 31 Å. The leakage current is four to five orders of magnitude lower than that of poly-Si-gated SiO2 in the -2–-3 V range. The reliable characteristics of TaO
x
N
y
over Ta2O5 in terms of a smaller increase in T
eff and excellent breakdown field against selective oxidation at 950°C allow us to maintain the standard complementary metal-oxide-semiconductor fabrication process and technology.
Reliability of Thin Gate Oxides Irradiated under X-Ray Lithography Conditions
Authors: Cho Byung Jin , Kim Sun Jung , Ang Chew Hoe , Ling Chung Ho , Joo Moon Sig , Yeo In Seok
Published: October 2002

The effect of X-ray lithography (XRL) process on the reliability of thin gate oxide has been investigated. A large increase in the low-field excess leakage current was observed on irradiated oxides, which was very similar to the electrical stress-induced leakage currents. However, it has been found that the long-term reliability of ultra-thin gate oxide is not affected by XRL process. The excess leakage current could be eliminated by thermal annealing at 400°C and above and no residual damages in the oxide were observed after the annealing.
Microscopic Observation of X-Ray Irradiation Damage in Ultra-Thin SiO2 Films
Authors: Ohmori Kenji , Goto Tomokazu , Ikeda Hiroya , Sakai Akira , Zaima Shigeaki , Yasuda Yukio
Published: October 2002

X-ray irradiation damage in ultra-thin SiO2 films has been investigated on an atomic scale using scanning tunneling microscopy (STM). From the X-ray photoelectron spectroscopy time-dependent measurement, the creation of hole traps and the successive electron trapping are observed with increasing irradiation time. In both cases, bright spots are observed in the STM images. We conclude that the bright spots which appeared in the hole trapping duration correspond to the hole traps in the SiO2 film. The bright spots which appeared in the electron trapping duration are larger in height and diameter in the STM images than those that appeared in the hole trapping duration. Although most of the bright spots in the hole trapping duration vanish with annealing at 600°C, the larger bright spots remain after the annealing. It is considered that the larger bright spots in the electron trapping duration correspond to leakage sites in the ultra-thin SiO2 films. Moreover, these trap sites are considered to originate from surface defects pre-existing on a clean Si(100) surface.
Quantum Chemical Calculations of Sulfur Doping Reactions in Diamond CVD
Authors: Zhou Hui , Yokoi Yasuto , Tamura Hiroyuki , Takami Seiichi , Kubo Momoji , Miyamoto Akira , N.-Gamo Mikka , Ando Toshihiro
Published: October 2002

Recently, n-type semiconducting diamond was successfully obtained by sulfur doping using CH4/H2S/H2 plasma chemical vapor deposition (CVD). It was reported that the crystal quality too was improved by the sulfur doping. In this study, the equilibrium geometry and the band structure of S- and O-doped diamond have been investigated using density function theory (DFT) calculations. Moreover, the sulfur incorporation mechanisms have been investigated by the semi-empirical molecular orbital (MO) calculations. Our calculations revealed that the sulfur atoms are spontaneously incorporated into the diamond (100) surface, while the incorporation of the oxygen atoms is unfavorable.
Hot Carrier Effects in Low-Temperature Polysilicon Thin-Film Transistors
Authors: Yukiharu Uraoka Yukiharu Uraoka , Tomoaki Hatayama Tomoaki Hatayama , Takashi Fuyuki Takashi Fuyuki , Tetsuya Kawamura Tetsuya Kawamura , Yuji Tsuchihashi Yuji Tsuchihashi
Published: October 2002

We have studied the reliability of a low-temperature polysilicon (poly-Si) thin-film transistor (TFT). The drain avalanche hot electron effect was characterized by changing the stress gate and drain voltage dependence. Generation of hot carriers was confirmed using an emission microscope. It was found that the degradation was improved by the lightly doped drain (LDD) structure. A degradation model was proposed and analyzed along with a two-dimensional device simulator. Reasonable agreement with the experimental results was successfully obtained. It was found that the density of state (DOS) of poly-Si was increased by the hot carrier effect locally around the drain region.
Spin-Dependent Trap-Assisted Tunneling Current in Ultra-Thin Gate Dielectrics
Authors: Miura Yoshinao , Fujieda Shinji
Published: October 2002

We have characterized the leakage current paths of ultra-thin gate dielectrics using spin-dependent tunneling (SDT) spectroscopy. A spin-dependent current was detected in metal-oxide-semiconductor diodes with chemical-vapor-deposition SiN gate films with thickness less than 3 nm. We examined the nature of the trap sites in terms of g-value, bias-dependent signal intensity, and magnetic-field orientation dependence. The main feature of the observed spectrum is attributed to a paramagnetic Si site in the SiN films. By using a quantitative model of electron spin-polarization, we were able to estimate the ratio of trap-assisted current to the total leakage current.
Nondestructive and Contactless Monitoring Technique of Si Surface Stress by Photoreflectance
Authors: Sohgawa Masayuki , Agata Masashi , Kanashima Takeshi , Yamashita Kaoru , Eriguchi Koji , Fujimoto Akira , Okuyama Masanori
Published: October 2002

Strain and stress at the Si surface have been studied by photoreflectance (PR) spectroscopy. A Si diaphragm structure has been fabricated in order to produce the surface strain caused by N2 gas pressure which changes the PR spectra of the Si diaphragm. The transition energy obtained from the PR peak energy of approximately 3.4 eV is proportional to the surface stress, which is calculated by elastic analysis. Additionally, PR spectroscopy was applied to measure stress at the interface between the Si and thermal oxide. As the SiO2 growth temperature increases, the interface stress decreases. From our experimental results, it is considered that PR spectroscopy is effective as a contactless and nondestructive monitoring technique for Si surface stress.
Plasma-Assisted Atomic Layer Growth of High-Quality Aluminum Oxide Thin Films
Authors: Jeong Chang-Wook , Lee Jang-Sik , Joo Seung-Ki
Published: October 2002

Thin aluminum oxide (Al2O3) films were grown by the plasma-assisted atomic layer controlled deposition (PAALD) method using Dimethylethylamine alane [(CH3)2(C2H5)N:AlH3] (DMEAA). Al was deposited by the PAALD method, then the Al films were oxidized into Al2O3 by plasma oxidation in the same chamber without breaking the vacuum. Al2O3 thin films of 15 nm thickness were prepared by repetition of this process. Thus prepared Al2O3 thin films exhibited a refractive index of 1.68. The thickness and the refractive index fluctuation of the film over a 4 inch wafer were ±2.3% and ±1.9%, respectively, for the deposited films. The leakage current density and breakdown field were measured to be about 10-8 A/cm2 at 1 MV/cm and 7 MV/cm, respectively. Considerable improvement of the electrical properties was realized by the post oxygen-plasma annealing at 200°C.
Novel FFT LSI for Orthogonal Frequency Division Multiplexing Using Current Mode Circuit
Authors: Kim Seong-Kweon , Cha Jae-Sang , Nakase Hiroyuki , Tsubouchi Kazuo
Published: October 2002

We propose a design method of fast Fourier transform (FFT) large-scaled integration (LSI) for an orthogonal frequency division multiplexing (OFDM) system. The proposed FFT LSI is designed with simple current mode circuits, wired-OR connection and gate-width-ratioed current mirror. For a low power consumption, two design methods are proposed, current-cut (CC) and rounding process. The CC operation is performed with on-off operation of a current source. The rounding process is adopted for the component of the FFT matrix. Bit error rate (BER) in the OFDM system is simulated from “0.1” rounding step to “1.0”. The BER performance of the FFT matrix with the “0.2” rounding step has little degradation from that of the original FFT matrix. The 8-point FFT LSI with the “0.2” rounding step is designed and implemented using a 0.8 µm complementary metal-oxide semiconductor (CMOS) technology. On the basis of measurement of the 8-point FFT LSI, the power consumption of the 64-point FFT LSI using CC can be estimated as being less than 10 mW.
A Novel Fabrication Technique of Ultrathin and Relaxed SiGe Buffer Layers with High Ge Fraction for Sub-100 nm Strained Silicon-on-Insulator MOSFETs
Authors: Tezuka Tsutomu , Sugiyama Naoharu , Mizuno Tomohisa , Suzuki Masamichi , Takagi Shin-ichi
Published: October 2002

A novel fabrication technique for relaxed and thin SiGe layers on buried oxide (BOX) layers, i.e., SiGe on insulator (SGOI), with a high Ge fraction is proposed and demonstrated for application to strained-Si metal-oxide-semiconductor field effect transistors (MOSFETs). This fabrication technique is based on the high-temperature oxidation of the SGOI layers with a lower Ge fraction. It is found that Ge atoms are rejected from the oxide and condensed in the SGOI layers. The conservation of the total amount of Ge atoms in the SGOI layer is confirmed by structural and compositional analyses of dry-oxidized SGOI layers at 1050°C of different initial thicknesses and oxidation times. Using this technique, a 16-nm-thick SGOI layer with the Ge fraction as high as 0.57 is successfully obtained. The Ge profiles across the SGOI layers are quite uniform and the layers are almost completely relaxed. Significant dislocation generation in the SGOI layer is not observed after the oxidation. This is a promising technique for application to sub-100 nm fully-depleted silicon-on-insulator (SOI) MOSFETs with strained-Si or SiGe channels.
A Partial-Ground-Plane (PGP) Silicon-on-Insulator (SOI) Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) for Deep Sub-0.1-µm Channel Regime
Authors: Yanagi Shin-ichiro , Nakakubo Atsushi , Omura Yasuhisa
Published: October 2002

Silicon-on-insulator (SOI) metal-oxide-semiconductor field-effect transistor (MOSFET) offers a number of advantages over conventional bulk silicon transistors. In this paper, we present a new SOI device structure called a “partial-ground-plane” SOI MOSFET down to 50 nm channel length. This new device shows good suppression of short-channel effect together with a small subthreshold swing and has a good driveability with a low leakage current.