bluuebunny/crossref_metadata_2025 huggingface dataset:
Long‐Term Outcomes After Cryoablation for Ventricular Tachycardia During Surgical Treatment of Anterior Ventricular Aneurysms
Authors: DEMARIA ROLAND G. , MUKADDIROV MIRDAVRON , ROUVIÈRE PHILIPPE , BARBOTTE ERIC , CELTON BEATRICE , ALBAT BERNARD , FRAPIER JEAN‐MARC
Published: January 2005

Intraoperative map‐guided procedures have been widely advocated as the best surgical strategy for the treatment of ventricular tachycardia (VT), though favorable results have been reported with subendocardial resection without mapping. This study examined the very long‐term results of encircling cryoablation without mapping during surgery for anterior left ventricular aneurysm complicated by VT. Between 1985 and 2003, this procedure was performed in 52 patients, 7 of whom (13.7%) were operated within 1 month of anterior myocardial infarction. Their mean age was 64.4 ± 8.3 years and mean left ventricular ejection fraction was 31.7%± 9.5%. The overall hospital mortality was 1.9%. At 14 years, 86% of patients (95% CI: 75.4–96.6) were free from VT or sudden death. An implantable defibrillator was implanted in five patients (9.6%) during follow‐up. The 14‐year overall survival was 51.4% (95% CI: 33.8–72.4), and two patients (3.8%) underwent cardiac transplantation during follow‐up. The main cause of late death was congestive heart failure in eight patients (40.0%). Favorable long‐term results can be achieved with encircling cryoablation without mapping in patients undergoing surgery for anterior left ventricular aneurysm complicated by VT.
Melatonin prevents hydrogen peroxide‐induced Bax expression in cultured rat astrocytes
Authors: Juknat Adela Ana , Méndez María del Valle Armanino , Quaglino Ana , Fameli Cecilia Irene , Mena Marcela , Kotler Mónica Lidia
Published: January 2005

Abstract:  During oxidative stress, cell apoptosis is promoted through the mitochondrial death pathway. Increased reactive oxygen species (ROS) are linked to excess cell loss and mediate the induction of apoptosis in various cell types. However, the role of ROS in the apoptotic pathway has not been clearly established. The aims of this study were to investigate the biochemical and morphological responses of rat astrocytes to hydrogen peroxide‐mediated cell death and to define the role that melatonin might play in the apoptotic cascade. Hydrogen peroxide (H2O2; 0.1–1.0 mm) significantly reduced cell viability. Astrocyte death was associated with enhanced ROS production in a dose‐dependent manner, as measured by 2′,7′‐dichloro‐fluorescein fluorescence. H2O2‐induced cell death was found to be mediated through an apoptotic pathway as treated cells exhibited cell shrinkage, nuclear condensation and marked DNA fragmentation. H2O2 also triggered caspase‐3 activation and Bax expression. The ability of different antioxidants to prevent H2O2‐induced apoptosis was examined by pre‐incubating rat astrocytes with N‐acetylcysteine (10 mm), glutathione (0.5 mm) or melatonin (0.1 mm and 10 nm). Results showed that N‐acetylcysteine and glutathion can protect astrocytes against ROS accumulation and caspase‐3 activation, whereas 0.1 mm melatonin can inhibit H2O2‐induced apoptosis by regulating Bax expression and by inhibiting caspase‐3 activation. Antiapoptotic effect of 10 nm melatonin associated to inhibition of Bax expression, give rise to new therapeutic approaches.
Melatonin prevents the free radical and MADD metabolic profiles induced by antituberculosis drugs in an animal model
Authors: Loots Du Toit , Wiid Ian J. , Page Benedict J. , Mienie Lodewyk J. , van Helden Paul D.
Published: January 2005

Abstract:  The objective was to determine the effect of combined antituberculosis (anti‐TB) drug therapy and an antioxidant, melatonin, on the free radical and organic acid profiles in an experimental rat model. A combined anti‐TB drug, Rifater, consisting of 12.0 mg rifampicin, 0.8 mg isoniazid, and 23.0 mg pyrazinamide and 18.56 μg melatonin/kg body weight per day (corresponding to average physiological human intake) were orally administered to Sprague–Dawley rats. Hydroxyl radical production was monitored by quantifying 2,3‐dihydroxybenzoic acid produced after intraperitonial sodium salicylate injections. Organic acid extractions and gas chromatography‐coupled mass spectrometry analyses were performed on collected urine samples. The results show hydroxyl radicals (P = 0.0019) and organic acids (P‐value range: 0.037 to <0.001), characteristic of a multiple acyl‐CoA dehydrogenase defect (MADD), were elevated with Rifater treatment and these elevations were significantly lowered with melatonin pretreatment (P‐value range: 0.031 to <0.001), probably because of its inherent antioxidant activity. We conclude that hydroxyl radical production and an increased organic acid profile induced by anti‐TB medication indicates inhibition of the electron transport chain. We also conclude that free radicals leading to clinical symptoms associated with an MADD metabolic profile induced by anti‐TB treatment could be alleviated by melatonin intervention.
Melatonin as an organoprotector in the stomach and the pancreas
Authors: Jaworek Jolanta , Brzozowski Tomasz , Konturek Stanislaw Jan
Published: January 2005

Abstract:  Melatonin was thought to originate primarily from the pineal gland and to be secreted during the night, but recent studies revealed that gastrointestinal (GI) tract presents another, many times larger, source of melatonin that contributes significantly to the circulating concentration of this indole. Melatonin may exert a direct effect on GI tissues but its major influence on GI organs seems to occur indirectly, via the brain–gut axis including peripheral receptors, sensory afferent (vagal or sympathetic) pathways and central nervous system (CNS) acting on these organs via autonomic efferents and neuromediators. This article reviews and updates our experience with the fascinating molecule, as related to GI organs, with special focus on secretory activity of the stomach and pancreas and the maintenance of their tissue integrity. In addition to being released into the circulation, melatonin is also discharged into the gut lumen and this appears to be implicated in the postprandial stimulation of pancreatic enzyme secretion, mediated by melatonin‐induced release of cholecystokinin, acting through entero‐gastro‐pancreatic reflexes. Although exerting certain differences in the mechanism of action on gastric and pancreatic secretory activities, melatonin derived from its precursor l‐tryptophan, exhibits similar highly protective actions against the damage of both the stomach and the pancreas and accelerates the healing of chronic gastric ulcerations by stimulating the microcirculation and cooperating with arachidonate metabolites such as prostaglandins, with nitric oxide released from vascular endothelium, and/or sensory nerves and with their neuropeptides such as calcitonin gene related peptide. The beneficial effects of melatonin results in gastro‐ and pancreato‐protection, prevents various forms of gastritis and pancreatitis through the activation of specific MT2‐receptors and scavenges reactive oxygen species (ROS). Melatonin counteracts the increase in the ROS‐induced lipid peroxidation and preserves, at least in part, the activity of key anti‐oxidizing enzymes such as superoxide dismutase. It is proposed that melatonin should be considered as the agent exerting an important role in prevention of gastric and pancreatic damage and in accelerating healing of gastric ulcers.
Demonstration of PACAP‐immunoreactive intrapineal nerve fibers in the golden hamster (Mesocricetus auratus) originating from the trigeminal ganglion
Authors: Baeres Florian Martin Moesgaard , Møller Morten
Published: January 2005

Abstract:  By using immunohistochemistry, a network of nerve fibers containing pituitary adenylate‐cyclase activating polypeptide (PACAP) was demonstrated in the pineal gland of the golden hamster, a photoperiodic species often used in pineal and circadian rhythm research. The nerve fibers are present in the capsule from where they permeate into the pineal perivascular spaces and parenchyma. Immuno‐electron microscopy showed the PACAPergic nerve terminals, with clear transmitter vesicles, to terminate in the interstitial spaces between the pinealocytes or in the perivascular spaces. Some of the PACAPergic nerve terminals made synapse‐like contacts with the pinealocytes. The origin of the PACAP‐containing nerve fibers innervating the pineal gland of the hamster was investigated by combined retrograde tracing with fluorogold and immunohistochemistry for PACAP. A 2% fluorogold solution was injected iontophoretically into the superficial pineal gland and the animals were allowed to survive for 1 wk. After perfusion fixation of the rats, the location of the tracer was investigated in the brain, the parasympathetic sphenopalatine, and otic ganglia, as well as in the sensory trigeminal ganglia. The tracer was found in perikarya of all the investigated ganglia. However, co‐localization with PACAP was found only in the trigeminal ganglion.
Melatonin modulates aromatase activity in MCF‐7 human breast cancer cells
Authors: Cos Samuel , Martínez‐Campa Carlos , Mediavilla Maria D. , Sánchez‐Barceló Emilio J.
Published: January 2005

Abstract:  Most of the current knowledge about the mechanisms by which melatonin inhibits the growth of breast cancer cells point to an interaction of melatonin with estrogen‐responsive pathways, thus behaving as an antiestrogenic hormone. However, a possible effect of melatonin on the local synthesis of estrogens had not been examined. The objective of this work was to study whether melatonin may modify the aromatase activity in MCF‐7 breast cancer cells thus modulating the local estrogen biosynthesis. In MCF‐7 cells cultured with testosterone in estradiol‐free media, melatonin (1 nm) counteracts the testosterone‐induced cell proliferation dependent on the local biosynthesis of estrogens from testosterone by the aromatase activity of the cells. We found that melatonin reduces the aromatase activity (measured by the tritiated water release assay) of MCF‐7 cells both at basal conditions and when aromatase activity was stimulated by cAMP or cortisol. The greatest inhibition of the aromatase activity was obtained with 1 nm melatonin, the same concentration that gives the highest antiproliferative and anti‐invasive effects of MCF‐7 cells. Finally, by RT‐PCR, we found that melatonin downregulates aromatase expression at the transcriptional level in the MCF‐7 cells. We conclude that melatonin, at physiological concentrations, decreases aromatase activity and expression in MCF‐7 cells. This aromatase inhibitory effect of melatonin, together with its already known antiestrogenic properties interacting with the estrogen‐receptor, makes this indoleamine an interesting tool to be considered in the prevention and treatment of hormone‐dependent mammary neoplasias.
Low temperature crystallization of high permittivity Ta oxide using an Nb oxide thin film for metal/insulator/metal capacitors in dynamic random access memory applications
Authors: Ma Dongjoon , Park Sungho , Seo Bum-Seok , Choi SangJun , Lee Naesung , Lee Jung-Hyun
Published: January 2005

( Ta 1 − x Nb x ) 2 O 5 as the dielectric for metal/insulator/metal capacitors with Ru electrodes were investigated. Deposition was performed by ALD using tantalum ethoxide, niobium ethoxide, and ozone as source materials. The high-κ dielectric layer was synthesized from a binary layer (Ta2O5∕Nb2O5) with self-diffusion of the seed layer, Nb2O5. The seed layer becomes effective at a thickness of over 60 Å. The dielectric deposited with 60 Å Nb2O5 crystallized at 575 °C, the lowest processing temperature required to achieve good step-coverage (86%) for future generation dynamic random access memory. A capacitance density of about 23.0fF∕μm2 was observed for seed layers of 20 and 35 Å. Capacitors with a Nb2O5 seed layer of 60 Å achieved a capacitance density as high as 44.2fF∕μm2. The reason for this disparity is that the thicker insulator crystallizes at a post-annealing temperature of 575 °C. The leakage current measured at 1 V was moderately low, near 1×10−7A∕cm2.
Deposition of silica-silver nanocomposites by magnetron cosputtering
Authors: Boscarino Diego , Vomiero Alberto , Mattei Giovanni , Quaranta Alberto , Mazzoldi Paolo , Della Mea Gianantonio
Published: January 2005

Thin films have been grown on silicon and silica substrates by cosputtering of silica and silver in Ar, Ar+2.5%O2, and Ar+5%O2 gas mixtures. Rutherford backscattering spectrometry showed that the films have Ag atomic fractions xAg in the range of ∼1to∼10at.%, and, by valence considerations, that the fraction of oxidized Ag in the films deposited in presence of oxygen is limited. Transmission electron microscopy images revealed the presence of Ag nanoclusters, with a mean size diameter not larger than 5nm. The clusters are preferentially arranged along columns. It is suggested that the columns are regions with diameter in the nanometer range in which the density of the dielectric matrix is lower, thus favoring the formation of metal clusters. In presence of O2, the clusters were observed to have a more regular spherical shape. The optical absorption spectra of films grown in presence of O2 are distinguished from those grown in Ar by specific features, which are attributed to oxidation at the cluster surface.
Local pressure in the proximity of a field emitter
Authors: Žumer Marko , Nemanič Vincenc , Zajec Bojan
Published: January 2005

A basic characterization of field emitters is usually realized in a standard UHV chamber equipped with appropriate pumps. Their high pumping speed and the remote location of the vacuum gauge prevents the monitoring of small pressure changes during the operation of a field emitter. In most potential applications, the field emitter is supposed to run in a small sealed device, where the local pressure is frequently unknown and its influence on the device’s lifetime is often underestimated. A small glass envelope equipped with a miniature ion-getter (IG) pump, spinning rotor gauge (SRG), and a cathodoluminescent screen, was prepared to study the influence of the field emitter on the residual atmosphere. This was monitored via the discharge current of the miniature IG pump, previously calibrated in situ by the SRG. Single-crystalline nanoparticles deposited onto molybdenum needles were used as field emitters. The initial pressure in a well outgassed envelope was in the UHV range, but its increase for almost three orders of magnitude was detected when the field-emission current from a few emission sites reached the one microampere range at 1 kV. A good correlation between the power of the generated e-beam and the discharge current of the miniature IG pump was observed.
Analysis of stress and composition of silicon nitride thin films deposited by electron cyclotron resonance plasma-enhanced chemical vapor deposition for microfabrication processes
Authors: Cianci E. , Pirola F. , Foglietti V.
Published: January 2005

We investigated the influence of process parameters in electron cyclotron resonance plasma-enhanced chemical-vapor deposition (ECR-PECVD) of silicon nitride on the intrinsic stress of thin SiNx films and on their composition, to obtain SiNx films suitable for micromechanical applications. The silane-to-nitrogen gas flow ratio R, along with the addition of helium to the gas mixture, was found to be a critical parameter for the tuning of intrinsic stress in ECR-PECVD SiNx films, from compressive to tensile stress within a large window of R from 0.3 to 0.7, with a maximum related to the largest Si–N bond density in the film.
Characterization of prototype silicon pitch artifacts fabricated by scanning probe lithography and anisotropic wet etching
Authors: Chien F. S.-S. , Hsieh W.-F. , Gwo S. , Jun J. , Silver R. M. , Vladár A. E. , Dagata J. A.
Published: January 2005

Scanning probe lithography (SPL) and anisotropic tetra-methyl ammonium hydroxide (TMAH) etching (SPL+TMAH) were used to fabricate a series of one-dimensional prototype pitch structures on (110)-oriented silicon substrates. Overall lateral dimensions of the test structure are 20μm×80μm. Line scales, consisting of 10-μm-long, 100-nm-tall, and 40-nm-wide lines, are observable by optical and scanning electron microscopy (SEM). Etched features were produced with pitches varying from 100 nm to 8 μm. Large-scale pattern placement errors of the SPL tool have been evaluated by analysis of optical image data obtained with a calibrated optical metrology instrument. Small-scale errors were analyzed in the range of 100 nm to 2 μm using SEM. Sources of placement error are discussed and possible methods for minimizing them are presented. The SPL+TMAH process in conjunction with a closed-loop scan control has the precision necessary for repeatable device prototyping in the nanoscale regime.
High-temperature self-grown ZrO2 layer against Cu diffusion at Cu(2.5at.%Zr)∕SiO2 interface
Authors: Liu C. J. , Chen J. S.
Published: January 2005

Films of pure Cu and of Cu alloy containing 2.5at.% of Zr [abbreviated as Cu(2.5at.%Zr)] were deposited on SiO2∕Si substrates by magnetron sputtering. Samples were subsequently annealed at temperatures ranging from 500to800°C in vacuum (2×10−5Torr) for 30min and analyzed by Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy, and glancing incident angle x-ray diffraction. Resistivity of both pure Cu and Cu alloy films, before and after annealing, was measured at room temperature by using a standard four-point probe technique. Upon annealing, the added Zr atoms in Cu(2.5at.%Zr) diffuse to both the free surface and the alloy∕SiO2 interface and react with the residual oxygen in the vacuum system and with the SiO2 to form a ZrO2 layer. At the interface, a self-grown ZrO2 layer forms upon annealing at 700°C that hinders Cu from diffusion into the SiO2, while Cu diffusion into SiO2 is apparent for pure Cu on SiO2 at this temperature. The room-temperature resistivity of the as-deposited Cu(2.5at.%Zr) film is 21.8μΩcm and decreases to about 6.2μΩcm upon vacuum annealing at 700°C for 30min. This value is still thrice that of the pure Cu film similarly treated. The relation between the diffusion of the added Zr and the characteristics of Cu(2.5at.%Zr)∕SiO2 interface, self-formed surface layer, and the resistivity change, is discussed.
Chamber maintenance and fault detection technique for a gate etch process via self-excited electron resonance spectroscopy
Authors: Baek Kye Hyun , Jung Youngjae , Min Gyung Jin , Kang Changjin , Cho Han Ku , Moon Joo Tae
Published: January 2005

With the introduction of 300mm wafer and sub-100nm technology processes, semiconductor manufacturers are gradually paying attention to efficient methods for process and equipment control, which is conventionally called advanced process control (APC) and advanced equipment control (AEC). As a potential strategy, an APC∕AEC technique by self-excited electron resonance spectroscopy (SEERS) was evaluated in a dynamic random access memory gate etch process, in terms of chamber maintenance and process control. Small changes in the chamber conditions after wet cleaning, which could not be detected under conventional monitoring methods, were identified by analyzing the electron collision rate of plasma. This event justifies that plasma monitoring is inevitable in chamber maintenance, especially considering that process results gradually tend to be affected by even small chamber changes in sub-100nm technology process era. Also, the first wafer effect, one of the most serious process drifts in an etch process, could be clearly detected by comparing average electron collision rates of plasma during each wafer process. In addition, a strong correlation between average electron collision rate and remaining oxide thickness enables us to control the gate etch process more tightly. Consequently, the APC∕AEC technique by SEERS is expected to be a potent strategy for plasma etch processes in semiconductor manufacturing.
Tapered sidewall dry etching process for GaN and its applications in device fabrication
Authors: Choi H. W. , Jeon C. W. , Dawson M. D.
Published: January 2005

A method of etching which allows the direct interconnection of multiple GaN-based devices is introduced. The mesa structures of devices are etched using an isotropic recipe which produces tapered sidewalls. The degree of inclination can be readily controlled through various etching parameters, which include the inductively coupled plasma power, plate power, and pressure, thus modifying the vertical and lateral etch components. This approach has been successfully adopted in the fabrication of interconnected and matrix-addressable microlight-emitting diodes, and offers superior optical and electrical performance and a high degree of uniformity compared to similar devices fabricated using conventional processes.
Mass spectrometry studies of resist trimming processes in HBr∕O2 and Cl2∕O2 chemistries
Authors: Pargon E. , Joubert O. , Chevolleau T. , Cunge G. , Xu Songlin , Lill Thorsten
Published: January 2005

In a previous article, a parametric study of HBr∕O2 and Cl2∕O2 resist trimming processes correlated to x-ray photoelectron spectroscopy (XPS) analyses has been performed. The present article confirms the preliminary results obtained by XPS. Mass spectrometry experiments have established that the slow resist erosion rate measured in Cl2∕O2 trim chemistries is attributed to a competitive etching of the resist by atomic chlorine and oxygen, while in HBr∕O2 trim chemistries, atomic oxygen is the main etching species, bromine playing only a minor role. The etching of the resist by the oxygen species originating from the dissociation of HBr∕O2 and Cl2∕O2 plasmas generates the formation of volatile resist-etch-by-products such as CO and CO2, while the etching of the resist by halogen (bromine or chlorine) generates less volatile and heavier resist-etch-by-products such as CxHyBrz with bromine and CxHyClz with chlorine. Mass spectrometry has also shown that plasma conditions leading to a higher concentration of halogen-resist-etch-by-products in the plasma gas phase are also the conditions inducing the lower trim rates. This confirms the assumption that the deposition of heavy resist-etch-by-products on the resist sidewalls controls the trim rates.
High-temperature electrostatic chuck for nonvolatile materials dry etch
Authors: Kanno S. , Edamura M. , Yoshioka K. , Nishio R. , Kanai S. , Kihara H. , Shimada T.
Published: January 2005

A high-temperature electrostatic chuck (HT-ESC) for nonvolatile materials dry etch was developed and applied for etching nonvolatile materials used in ferroelectric random-access memory or magnetic random-access memory. The HT-ESC can be heated up to 400°C from room temperature within 40min, and the temperature distribution across a 200mm wafer during chucking is 407±9°C. The HT-ESC generates a clamping pressure of over 1kPa in the temperature range from 250to400°C. According to the results of etching platinum with a standard inductively coupled plasma etcher equipped with the HT-ESC, a measured etching time can be reduced by 41% by heating the sample up to 300°C compared with etching at 40°C. It can thus be concluded that this HT-ESC is suitable for etching nonvolatile materials.
Use of lateral film structure for ultrathin diffusion barrier thermal stability study
Authors: Lim Boon Kiat , Park Hun-Sub , Tan Valuina , See Alex K. H. , Seet Chim-Seng , Lee Tae-Jong , Yakovlev Nikolai L.
Published: January 2005

There are studies in which Si3N4 is used as a passivation layer on Cu to simulate the vertical stack structure in interconnect systems. However, these studies are only applicable to barrier studies involving metal lines. In this study, a passivated “sandwich” film stack is used to simulate the lateral structure found in dual damascene vias and trenches. X-ray diffraction analysis shows that an ultrathin Ta barrier remains robust up to 850°C, at which the Ta barrier fails upon a β-to-α phase transformation. Time-of-flight secondary-ion mass spectrometry depth profiling and scanning electron microscopy analysis provide supporting evidence in the assessment of the thermal stability of the lateral film stack. The passivation provided by the lateral structure improves the thermal stability. However, the stability of the film stack was found to be dependent on the crystallography of the Ta barrier.
Effect of self-patterned Si1−xGex template layer on the structural and optical properties of Ge dots
Authors: Ismail B. , Descoins M. , Ronda A. , Bassani F. , Brémond G. , Maaref H. , Berbezier I.
Published: January 2005

We report the structural and optical properties of Ge dots grown on self-patterned Si1−xGex template layers. The study focuses on the influence of a Si1−xGex template layer on Ge dot properties. Surface morphology is analyzed by atomic force microscopy and cross-sectional transmission electron microscopy. Optical properties are investigated by photoluminescence (PL) and Raman spectroscopy. The results show that increasing x in the Si1−xGex template layer from 0.3 to 0.5 induces a significant decrease of Ge island size and a dramatic reduction of Ge∕Si intermixing. The lower intermixing is evidenced by the larger Ge–Ge∕Si–Ge integrated intensity ratio of Raman peaks and by the island-related PL redshift. Moreover, the island-related PL signal is found to be highly dependent on the power excitation and temperature: from 10to30K, an anomalous increase of islands’ PL was accompanied by a rapid decrease of the wetting layer PL. Such a behavior results from the transfer of photon-induced carriers in the wetting layer into the neighboring islands. Significant PL signal at 1.55μm was obtained up to room temperature for Si(001)∕Si0.5Ge0.5∕7 monolayer Ge structures.
Performance of nanomanipulator fabricated on glass capillary by focused-ion-beam chemical vapor deposition
Authors: Kometani Reo , Hoshino Takayuki , Kondo Kazushige , Kanda Kazuhiro , Haruyama Yuichi , Kaito Takashi , Fujita Jun-ichi , Ishida Masahiko , Ochiai Yukinori , Matsui Shinji
Published: January 2005

An electrostatic 3D nanomanipulator that can perform inclusion of nano parts and cell operation has been developed by focused-ion-beam chemical vapor deposition (FIB-CVD). This 3D nanomanipulator has 4 fingers in order to catch the target of various shapes firmly. The movable principle is that an electric charge is accumulated in the structure by applying voltage to 4 fingers structure and it moves by repulsion of the electric charge. Furthermore, we succeeded to catch the microsphere (polystyrene latex with a diameter of 1μm) by using this 3D nanomanipulator with 4 fingers.
Subpicosecond jitter in picosecond electron bunches
Authors: Ioakeimidi K. , Gradinaru S. , Liu Z. , Machuca F. , Nielsen J. F. , Aldana R. , Bolton R. P. , Clendenin J. , Leheny R. , Pease R. F. W.
Published: January 2005

We have simulated and measured 60–120fs time jitter of photoelectron pulses emitted by a nitride photocathode at 100GHz rate as in order to evaluate the resolution performance of a previously proposed photonic analog to digital converter. Recently, there has been an increasing demand for high speed analog-to-digital converters (ADCs) for microwave bandwidth signals. State of the art electronic ADCs have reached 10Gigasamples∕second (GS/s), 6–12bit performance [P. W. Juodawlkis, J. C. Twichell, G. E. Betts, J. J. Hargreaves, R. D. Younger, J. L. Wasserman, F. J. O’Donnell, K. G. Ray, and R. C. Williamson, IEEE Microwave Theory Tech. 49, 1840 (2001)]. We have previously introduced a photoelectronic ADC implementation with measured performance of 3bits at 100GS∕s [K. Ioakeimidi, R. Leheny, S. Gradinaru, K. Ma, R. Aldana, J. Clendenin, J. S Harris, R. F. W. Pease, IEEE Trans. Microwave Theory Tech. (to be published); Conference on Lasers and Electro-Optics, Baltimore MD, 1–6 June 2003]. The basic operating principle of the ADC is based on a miniaturized cathode ray tube where a bunch of photoemitted electrons passing through an electric deflection system is directed to a specific detector whence a digital code word emanates. The electron bunch samples the analog deflecting voltage that is then quantized according to the position of the detector receiving the bunch. The fundamental limit of the number of distinguishable voltage levels is the ratio of the deflecting voltage to the energy spread due to diffraction of the electron beam. This allows for up to 12bits at 100GS∕s [R. F. Pease, K. Ioakeimidi, R. Aldana, and R. Leheny, J. Vac. Sci. Technol. B 21, 2826 (2003)]. At a more practical level, the bit resolution is primarily limited by the uncertainty in the emission of each electron bunch (temporal jitter). For 100fs time uncertainty 5bits of resolution are attainable with the nitride cathode for a 50GHz bandwidth analog signal.
Hydrogen silsesquioxane as a high resolution negative-tone resist for extreme ultraviolet lithography
Authors: Junarsa Ivan , Stoykovich Mark P. , Nealey Paul F. , Ma Yuansheng , Cerrina Franco , Solak Harun H.
Published: January 2005

Hydrogen silsesquioxane (HSQ) was evaluated as a high resolution negative-tone photoresist for extreme ultraviolet (EUV) lithography. The following imaging properties of HSQ were evaluated in EUV exposure: sensitivity, contrast, resolution, and line edge roughness (LER). In this article we report that HSQ has a sensitivity of 11.5mJ∕cm2 with a contrast of 1.64 in EUV exposure and is able to resolve 26nm dense lines (70nm thick film) with a LER of 5.1nm (3σ). These results, especially with regard to the sensitivity and low line edge roughness, imply that this class of materials may hold distinct advantages over traditional chemically amplified resists and should be further explored for application in EUV lithography.
On-wafer monitoring of plasma-induced electrical current in silicon dioxide to predict plasma radiation damage
Authors: Okigawa Mitsuru , Ishikawa Yasushi , Samukawa Seiji
Published: January 2005

A simple on-wafer monitoring device that we developed showed that the increase in electrical current in silicon dioxide film corresponded completely to the increase in interface states at the interface between silicon dioxide and silicon under plasma irradiation, as measured by a charge pumping current method in a metal-oxide-semiconductor transistor. Using an electron spin resonance spectrometer, we found that the E′ centers in the silicon dioxide also increase. An experiment using helium (He), argon (Ar), and oxygen (O2) plasmas showed that the electrical current, interface states, and E′ centers depend on the wavelength of vacuum ultraviolet protons in the plasma. Under the same plasma density, the plasma-induced current in He plasma is the largest of the three gas plasmas. In the same way, the interface states and E′ centers increased the most for He plasma. This strongly implies that the plasma-induced carriers (holes and electrons) that generate the electrical current in the insulator directly or indirectly affect the bonding of silicon to oxygen in SiO2 and the increase in the interface states at the boundary between SiO2 and Si in metal-oxide-semiconductor (MOS) devices. The simple on-wafer monitoring for plasma-induced current that we developed can predict the generation of SiO2–Si interface states as plasma-induced damage in MOS devices.
Photoluminescence properties of p-type InGaAsN grown by rf plasma-assisted molecular beam epitaxy
Authors: Xie S. Y. , Yoon S. F. , Wang S. Z.
Published: January 2005

We have investigated the temperature-dependent photoluminescence (PL) properties of p-type InGaAsN epilayers grown by a solid source molecular beam epitaxy system. The PL spectra were dominated by near-band-edge emission at high temperatures and localized excitonic (LE) emission plus a broad deep band at low temperatures. The deep PL band could originate from recombinations associated with N-related traps. The hole concentration dependence of the integrated intensity ratio of the LE emission peak to the deep PL band at 5K can be separated into two doping regimes. At light doping regime corresponding to nondegeneracy (1.0×1016cm−3<p<1.2×1018cm−3), this ratio is linearly proportional to the hole concentration and is explained in terms of excitons bound to neutral acceptors accompanied by N clusters. At high doping regime corresponding to degeneracy (2.1×1018cm−3<p<1.2×1019cm−3), this intensity ratio saturates and is explained in terms of excitons bound to N clusters.
Highly selective low-damage processes using advanced neutral beams for porous low-k films
Authors: Ohtake Hiroto , Inoue Nobuhiko , Ozaki Takuya , Samukawa Seiji , Soda Eiichi , Inukai Kazuaki
Published: January 2005

A highly selective and low-damage damascene process for porous methyl-silsesquioxane (porous MSQ, k-2.2) films has been realized using a neutral beam system we have developed. Use of a SF6 or CF4 neutral beam enables etching of porous MSQ with higher selectivity to the photoresist than what can be obtained in a conventional plasma. This is considered to be because the neutral beam eliminates exposure to ultraviolet (UV) light which enhances the resist etching. Anisotropic, low-dimension-shift damascene etching of porous MSQ is achieved through the neutral beam system. In addition, an O2 neutral beam reduces damage to the sidewall of porous MSQ during the resist ashing process. Also, a modified layer generated on porous MSQ during ashing using a H2 or H2∕N2 beam could prevent damage by UV light, which allows more effective resist ashing in a dual damascene structure of porous MSQ. Accordingly, this neutral beam system is a promising candidate for use in porous MSQ damascene processes.
Cleaning of extreme ultraviolet lithography optics and masks using 13.5nm and 172nm radiation
Authors: Hamamoto K. , Tanaka Y. , Watanabe T. , Sakaya N. , Hosoya M. , Shoki T. , Hada H. , Hishinuma N. , Sugahara H. , Kinoshita H.
Published: January 2005

Under extreme ultraviolet (EUV) exposure, the surfaces of the imaging optics and mask, which are coated with a Mo∕Si multilayer, become contaminated with organic compounds. Thus, an efficient method of removing carbon contamination from masks and the imaging optics is required. Then, we propose two methods as a removal method of contamination: one is in situ cleaning method without heating a sample by synchrotron radiation irradiation that is mainly targeted at the imaging optics, and another is cleaning method without heating a sample using by 172nm light irradiation that is targeted at an EUV lithography finished mask. For in situ cleaning so called online cleaning, the contamination removal rate is 0.24nm∕min in the condition of O2-rich-vacuum environment at a pressure of 5.0×10−2Pa and an electron beam current of 130mA of 1.0GeV electron storage ring. For offline cleaning using 172nm light, the contamination removal rate is 2nm∕min in the O2-rich-vacuum environment at the pressure of 2×10−3Pa. Both two methods restore the reflectivity of a Mo∕Si multilayer to its original level without causing any surface damage. The effectiveness of both in situ and offline contamination removal are confirmed.
Formation of GdSi2 film on Si(111) via phase transformation assisted by interfacial SiO2 layer
Authors: Chung K. B. , Choi Y. K. , Jang M. H. , Noh M. , Whang C. N. , Jang H. K. , Jung E. J. , Ko D.-H.
Published: January 2005

GdSi 2 film with almost perfect interface was grown on a Si(111) substrate via phase transformation assisted by interfacial SiO2 layer. The evolution of Gd silicide and the role of an oxide layer were investigated by using in situ reflection of high-energy electron diffraction, x-ray diffraction (XRD), atomic force microscopy (AFM), x-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy (HRTEM). The XRD and AFM results confirm structural transformation from the initial GdSi1.7 layer to the GdSi2 layer after the post-annealing at 900°C. The HRTEM image suggests that the formation of GdSi2 follows kinetic growth process, where the grain growth is dominated by the abundance of Si at the reacting surface. The thermally decomposed interfacial oxide initiates rapid phase transformation and finally results in almost perfect GdSi2∕Si interface without any residual oxide or mixed structure.
Schottky barrier height of TiN∕p-type Si(100) evaluated by forward current–voltage and capacitance
Authors: Pelleg Joshua , Douhin A.
Published: January 2005

Schottky barrier height (ϕBp) of amorphous TiN (∼40nm) diode on p-type Si(100) obtained by reactive-sputtering was determined by forward current–voltage (I–Vf) and capacitance–voltage (C–V) measurements at room temperature and the effect of heat treatment was examined. The TiN remained amorphous following annealing. The zero-bias barrier heights evaluated by I–Vf of the as-deposited and annealed specimens were in the range of 0.53–0.64 V with an average of ∼0.58. The lower ϕBp values of 0.53–0.54 V are related to the as deposited and 673 K annealed specimens whereas the 0.62–0.64 V values refer to samples annealed at 773–873 K. Forward I–V measurements of as-deposited TiN∕Si diodes were performed over the temperature range of 220–285 K. The activation energy evaluated from the ln(Js∕T2) versus 1∕T plot exhibits a linear relation through the entire temperature range. From the slope of this plot, the barrier height was determined at the saturation current density resulting in ϕBp=0.58V, which is the same as the average value obtained from room temperature I–Vf measurements. Capacitance measurements at 1 MHz resulted in higher barrier heights than those obtained from I–Vf measurements in the range of 0.76–0.81 V. In the case of nonlinear C–V plots, an excess capacitance was taken into account for correcting the derived ϕBp values. Nonideal behavior was observed in some diodes, which was attributed to the effect of N on the interface.
LiNbO
3
thin film growth on (0001)-GaN
Authors: Hansen Peter J. , Terao Yutaka , Wu Yuan , York Robert A. , Mishra Umesh K. , Speck J. S.
Published: January 2005

LiNbO 3 thin films were grown by rf magnetron sputtering on (0001)-GaN templates and AlGaN∕GaN structures. The films were characterized by four-circle x-ray diffraction, atomic force microscopy (AFM), and transmission electron microscopy (TEM). No second phases, such as a Li-excess or Li-deficient phase, were detected by θ-2θ scans and the films were highly (0001) textured. LiNbO3{202¯4} φ-scans and the electron diffraction pattern show that the films were epitaxially grown on GaN with crystallographic registry. The LiNbO3 c-plane was parallel to the c-plane of the GaN, but there was a 30° in-plane rotation between the LiNbO3 and GaN so that [11¯00]LiNbO3‖[112¯0]GaN(AlGaN) and the LiNbO3 films had two variants of grains rotated 60° in-plane to each other. It was confirmed by high resolution TEM that there was a transition layer between LiNbO3 and GaN. The films were annealed to improve the crystallinity and following annealing investigated using convergent beam electron diffraction (CBED) to determine the polarity. The films grow with a spontaneous polarization vector opposite to that of the underlying GaN film.
Quantifying acid generation efficiency for photoresist applications
Authors: Tsiartas Pavlos C. , Schmid Gerard M. , Johnson Heather F. , Stewart Michael D. , Willson C. Grant
Published: January 2005

A direct analytical technique for measuring the solution quantum efficiencies of photoacid generators (PAGs) is presented. The technique is based on the nonaqueous potentiometric titration of the photogenerated acid and does not require separate calibrations, or the addition of sensing materials such as dyes or bases. Solutions of PAGs in acetonitrile were irradiated at 248 nm and subsequently titrated with known concentrations of triethanolamine base. The only quantities required for an accurate determination of the quantum efficiency are the incident radiation energy and the titration equivalence point. A mathematical analysis that enables this calculation is derived, and a table with calculated quantum efficiency values for three classes of PAGs having a variety of counterions is presented. The method is simple, accurate, and applicable to any class of PAG molecules.
Monitoring polarization and high-numerical aperture with phase shifting masks: Radial phase grating
Authors: McIntyre Gregory , Neureuther Andrew R.
Published: January 2005

A class of phase shifting test mask patterns is introduced for monitoring both linear and circular polarization balance of the illumination in high-numerical aperture (NA) and immersion projection printing systems. Four test mask patterns are constructed of periodic, alternating phase, radial arrays to scatter light into high angle spatial frequencies to create a central intensity dependent only on the local state of polarization. Two two-phase patterns measure the orthogonal linear polarization components while an additional two four-phase patterns determine the phase relationship between those components. When exposed in a dose matrix in photoresist, they can likely measure polarization imbalance to within a few percent. Based on these patterns, a technique is introduced for predicting image degradation in IC production due to polarization and high-NA effects.
Comparative study of polycrystalline Ti, amorphous Ti, and multiamorphous Ti as a barrier film for Cu interconnect
Authors: Ou Keng-Liang , Yu Ming-Sun , Hsu Ray-Quen , Lin Ming-Hong
Published: January 2005

Ultrathin (10nm) Ti films with various structures were deposited by physical vapor deposition (PVD) and chemical vapor deposition (CVD) processes. CVD-Ti films with low-temperature(<500°C) plasma-enhanced chemical vapor deposition using TiCl4 and H2 as reactants is an amorphous structure. This result is different from PVD-Ti films deposited by magnetron sputtering, which have a columnar structure. Ammonia plasma was further employed to post-treat the CVD-Ti barrier layer to improve barrier properties. An amorphous Ti(N,H) layer was formed on the surface of the CVD-Ti layer after ammonia plasma post-treatment. The resultant films had a bilayered amorphous Ti(N,H)∕Ti structure. Furthermore, the effective resistivity of the resultant Ti(N,H)∕Ti film decreased to 122μΩcm. The thermal stability of Cu∕PVD-Ti∕Si and Cu∕CVD-Ti∕Si contact systems was evaluated by thermal stressing at various annealing temperatures. For the Cu∕PVD-Ti∕Si, the highly copper titanium compound was formed after 450°C annealing. The PVD Ti barrier failed initially due to the reaction of Cu and the Ti barrier, in which Cu atoms penetrated into the Si substrate after annealing at high temperature. However, no copper-titanium and copper-silicide compounds were found for amorphous Ti and plasma-treated Ti[Ti(N,H)∕Ti] barriers, even after annealing at 500 and 600°C, respectively. Improved barrier capability against Cu diffusion was found for the Ti(N,H)∕Ti barrier layer because the Cu∕Ti(N,H)∕Ti∕n+-p junction diodes retained low leakage current densities even after annealing at 500°C for 1h. Ti(N,H)∕Ti barrier layers present lengthened grain structures to effectively impede Cu diffusion, thus acting as much more effective barriers than conventional Ti and TiN films.
Selective growth of InAs quantum dots on patterned GaAs
Authors: Hsieh Tung-Po , Chiu Pei-Chin , Liu Yu-Chuan , Yeh Nien-Tze , Ho Wen-Jeng , Chyi Jen-Inn
Published: January 2005

We report selective growth of InAs self-assembled quantum dots (QDs) on nano-ridges (30–50nm) formed by wet chemical etching and epitaxial growth processes. The QDs formed on the ridges exhibit distinctive characteristics from those on the planar region between the ridges in terms of physical shape as well as optical property. The QDs, which align one by one on the top of the ridges, are of an asymmetric shape along the [011] and [01̱1] directions. By defining the width of ridge and the monolayers of QDs, we are able to control the height and the width of these QDs. Compared to the QDs on the planar region between the ridges, the luminescence from QDs on the ridges exhibits a shorter wavelength, which is attributed to higher compressive strain in these QDs.
Ideal delta doping of carbon in GaAs
Authors: Winking L. , Wenderoth M. , Reusch T. C. G. , Ulbrich R. G. , Wilbrandt P.-J. , Kirchheim R. , Malzer S. , Döhler G.
Published: January 2005

Delta doped carbon acceptors in molecular-beam-epitaxy-grown GaAs were investigated on the atomic scale with scanning-tunneling microscopy in cross-sectional configuration. Monolayer-sharp spatial distributions were found at the intended positions of the delta layers in a wide range of dopant concentrations from 3×1012∕cm2 up to 1×1014∕cm2. The carbon concentrations were checked independently with secondary-ion-mass spectroscopy. All distributions had full widths at half maximum around 0.85nm and were symmetric up to the highest concentration investigated. These results point out that even at the elevated growth temperature of 590°C, and for very high dopant concentrations, neither segregation nor diffusion plays an important role in delta doping of GaAs with carbon acceptors. The observed small spreading of the dopant distribution is attributed to the generic surface roughness during growth.
Diffusion-barrier properties of Ta1−xWx alloy films and silicidation-induced Cu penetration in Cu∕Si contacts
Authors: Noya Atsushi , Takeyama Mayumi B. , Sase Touko
Published: January 2005

Alloy films of Ta1−xWx were prepared by co-sputtering and their diffusion-barrier properties in Cu∕Si contacts were examined. The alloy films over 30at.% of the W composition were in a state of substitutional solid solution, and the resistivity of 100-nm-thick film was ∼45μΩcm, at most. In the Cu∕Ta1−xWx∕Si contacts, the silicidation temperature of 680°C was higher than that reported for the Cu∕Ta∕Si or Cu∕W∕Si contact. We confirmed for the Cu∕Ta0.5W0.5∕Si contact that Cu penetration into the Si substrate was completely suppressed by a thin amorphous interfacial layer upon annealing at temperatures below that of silicidation reaction. It was revealed that at more elevated temperatures, an extremely small amount of Cu atoms was incorporated into the silicide layer at the Ta0.5W0.5∕Si interface during reaction and penetrated into the Si substrate through the silicide layer.
Investigation of Ta∕Ti∕Al∕Ni∕Au ohmic contact to AlGaN∕GaN heterostructure field-effect transistor
Authors: Kim Ki Hong , Jeon Chang Min , Oh Sang Ho , Lee Jong-Lam , Park Chan Gyung , Lee Jung Hee , Lee Kyu Seok , Koo Yang Mo
Published: January 2005

An AlGaN∕GaN wide band-gap semiconductor with the Ta∕Ti∕Al∕Ni∕Au ohmic contact (7.5×10−7Ωcm2) was demonstrated by 700°C annealing for 1min. High-resolution electron microscopy and synchrotron-radiation x-ray diffraction showed that nitride phases were formed at the interface between the metal and the AlGaN layer. The thick formation of TaN∕TiN interfacial layers appears to be responsible for the good ohmic contact behavior in Ta∕Ti∕Al∕Ni∕Au metal scheme. The surface morphology of Ta-based contacts is superior to that of the Ti∕Al∕Ni∕Au metal scheme. The fabricated heterostructure field-effect transistor exhibited the saturation drain current density of 605mA∕mm and transconductance of 246mS∕mm.
Some comments on Sabine absorption coefficient (L)
Authors: Sum K. S.
Published: January 2005

The case of a nonzero reverberation time when all absorptive surfaces in a room have values of Sabine absorption coefficient of one, the existence of values of the coefficient that are larger than one, and the difference of the coefficient from the statistical absorption coefficient, are well known. So far, the reasons for these phenomena are still unclear. This letter provides a new perspective to the classical problem of sound absorption where physical interpretations of the Sabine absorption coefficient are given for different types of absorptive surface and conditions of the sound field in rooms.