bluuebunny/crossref_metadata_2025 huggingface dataset:
Laparoscopic Findings in Primary Sclerosing Cholangitis
Authors: KOMATSU Masafumi , HOSHINO Takao , ONO Tsuyoshi , GOTO Takashi , OHSHIMA Shigetoshi , YONEYAMA Kazuo , FUJII Tomoo , KURAMITSU Tomoyuki , NAKANE Kunio , MIKAMI Ken‐ichiro , YAGISAWA Hitoshi , MASAMUNE Osamu
Published: December 2007

Abstract: The laparoscopic appearance of the liver surface in patients with primary sclerosing cholangitis (PSC) has not been fully delineated. We examined 5 patients with PSC and reviewed 35 previously reported cases. Intense white markings in a mesh‐like pattern were characteristic of PSC. The findings varied depending on the histologic stage and affected site. Red patches which have also been seen in primary biliary cirrhosis (PBC), green patches indicating cholestasis, and dilatation of the terminal bile ducts were also observed. The red patches were wider than those in PBC. The white markings were less well defined in the red patches than in other areas. The severity of the fibrosis and histologic damage was judged to be mild at the red sites. The green patches were caused by localized cholestasis. This indicated that PSC unevenly affects the liver. Severe obstruction may be present between the interlobular bile ducts and the septal bile ducts in anicteric stages. (Dig Endosc 1999; 10: 37–41)
Hematoma with High Oxygen Partial Pressure Resulting from Injection Sclerotherapy for Esophageal Varices — Report of a Case
Authors: MURAKAMI Masato , HOSHIKA Akiko , YANO Harumi , ARAKI Katsuyuki , YANO Tetsuro , OHSHIMA Kanji , KOKUBU Shigehiro
Published: December 2007

Abstract: Endoscopic injection sclerotherapy (EIS) was performed on a 44‐year‐old Japanese male, who had been suffering from risky esophageal varices due to cirrhosis of the liver. Blood gas analysis at the beginning of therapy showed that the partial pressure of oxygen at the variceal (PO2) and arterial blood (PaO2) were 47.2 mmHg and 64.1 mmHg, respectively. Sclerosant with contrast medium was injected into the varices and the left gastric vein was embolized; this was always confirmed by endoscopic varicealography during injection scleorotherapy (EVIS). During the fifth EIS session, there was evidence of pooling of contrast medium with sclerosant and an intramural hematoma had developed, which could not be reduced by puncture. The blood gas analysis showed a drastic increase in PO2 (107.9 mmHg), whereas PaO2 remained mostly unchanged (58.8 mmHg). To our knowledge, this is the first report of blood gas analysis during hematoma and the high PO2 compared with PaO2 indicated that there was a substantial inflow of oxygen‐rich blood, possibly from the pulmonary vein into the varices. This inflow of blood into the varices may have contributed to the formation of the large hematoma in small varices following EIS. (Dig Endosc 1999; 11: 55–61)
Recent Advances in Light‐Induced Fluorescence Endoscopy (LIFE) of the Gastrointestinal Tract
Authors: DaCosta Ralph S. , Wilson Brian C. , Marcon Norman E.
Published: December 2007

Abstract: Gastrointestinal (GI) cancer continues to be a significant malignant disease. It is well recognized that early detection of dysplastic changes prior to invasive growth may have a pronounced effect on the clinical efficacy of treatment and subsequent patient survival. Standard white‐light endoscopic visualization of such early lesions is often difficult and many premalignant lesions remain undetected during routine screening procedures. Additionally, dysplastic lesions are usually not distinguished against surrounding normal tissue, and visible non‐adenomatous lesions such as hyperplastic polyps are often indistinguishable from adenomatous polyps. However, recent developments in endoscopic technology have led to the development of more sensitive endoscopic screening methods. Fluorescence‐based endoscopic imaging or spectroscopy of the gastrointestinal tract may offer a novel and alternative means of detecting and identifying premalignant and malignant lesions otherwise occult to conventional white‐light endoscopy. The purpose of this review is to present a general overview of the current developments and possible clinical roles of light‐induced fluorescence endoscopy (LIFE) as an adjunct to conventional diagnostic endoscopy for screening and surveillance for premaligant and malignant gastrointestinal lesions. (Dig Endosc 1999; 11: 108–118)
K‐ras Codon 12 Mutation and Horizontal Growth of Colorectal Cancer
Authors: SAITO Kenichi , OGAWA Akira , OHKI Ichiro , MORI Masatomo
Published: December 2007

Abstract: K‐ras codon 12 mutations and horizontal growth were examined in 121 colorectal cancers to clarify genetic contributions to tumorigenesis. Invasion was submucosal [SMCa] in 61 cases and to the muscularis propria [PMCa] in 60. Growth patterns were further classified into polypoid [PG] and nonpolypoid [NPG] types. Horizontal growth cancers were defined as lesions associated with horizontally aligned cancerous glands. The K‐ras codon 12 mutation frequency was higher in PG SMCa than in NPG SMCa (49% versus 0%, respectively), and in PG PMCa compared to NPG PMCa (60% versus 24%, respectively). The K‐ras codon 12 mutation was less frequent in horizontal growth SMCa than in nonhorizontal growth SMCa (0% versus 49%, respectively), and in horizontal growth PMCa compared to nonhorizontal growth PMCa (0% versus 64%, respectively). The frequency of horizontal growth was higher in NPG SMCa than in PG SMCa (100% versus 0%, respectively), and in NPG PMCa compared to PG PMCa (76% versus O%, respectively). The frequencies of NPG carcinoma with horizontal growth and with wild type K‐ras in SMCa were both 26%. NPG carcinoma with horizontal growth and with wild type K‐ras in PMCa both occurred at a frequency of 22%. Our results suggest that NPG type carcinomas with horizontal growth do not result from K‐ras codon 12 mutations, and may arise through very different genetic pathways and histologic processes. At least 22% of early colorectal cancers may progress to advanced cancer of superficial origin. (Dig Endosc 1999; 11: 125–131)
Laparoscopic Microwave Coagulation for the Treatment of Hepatocellular Carcinoma
Authors: ITO Toshio , NIIYAMA Gouichi , KAWANAKA Miwa , ONOGI Toshiya , IWKUBE Satoshi , YOSHIDA Nobuhiro , SHO Akiko , KIMURA Tetsuya , KINOYAMA Shingo , YAMADA Gotaro
Published: December 2007

Abstract: Laparoscopic microwave coagulation (LMC) has recently been indicated for hepatocellular carcinoma (HCC). LMC was performed in 14 patients with a total of 22 HCCs in the 18‐month period from November 1996 to April 1998. The size of HCCs ranged from 10 mm to 100 mm, with an average diameter of 29.3 mm. The duration of microwave emission ranged from 8 min to 54 min; average 26.4 mm. Sufficient microwave emission was possible even in cases of multiple HCC large HCC, and HCC located deep within the liver, with the aid of laparoscopy and intraperitoneal ultrasound. Recurrence was observed in 4 out of 22 HCCs, and was treated by transcatheter arterial embolization (TAE) or percutaneous ethanol injection (PEI). LMC facilitates local control of HCC, and is a promising new therapeutic modality for HCC. (Dig Endosc 1999; 11: 137–143)
Possible Application of Microwave Coagulation Therapy for Recanalising Tumor‐occluded Self‐expandable Metallic Stents
Authors: MAETANI Iruru , OGAWA Satoshi , SATO Masahiro , ICARASHI Yoshinori , SAKAI Yoshihiro
Published: December 2007

Abstract: There is no consensus regarding optimal management of tumor ingrowth through self‐expandable metallic stents in the biliary system. We investigated the possibility that microwave therapy could be used to treat stent occlusion. We evaluated the thermal properties of a muscle equivalent phantom subjected to microwave energy. The temperature of the phantom was continuously monitored using the probe sensor of a fiberoptic thermometer embedded into the phantom model at different distances from a microwave electrode with and without a stent in place. The temperature of the phantom increased incrementally as the power increased from 30 to 50 watts at distances 2 and 5 mm from the electrode (p<0.01). With the goal of achieving adequate local heating without excessive distant heating, the most effective power was 40 watts. There was a significantly lower rise in temperature with stent in place than that without stent at 2 and 5 mm from the electrode at 40 watts. The temperature increase when the tip of the electrode was kept in contact with the stent was significantly smaller than when the conductor tip was kept apart from the stent (p<0.05). Using this method, the microwave energy did not induce destruction of the stent filament. In a muscle equivalent phantom model, the temperature changes induced by microwave energy were consistent with possible safe and effective application of this modality to recanalization of occluded metallic stents. (Dig Endosc 1999; 11: 158–164)
Flow‐mediated dilatation in the superficial femoral artery is nitric oxide mediated in humans
Authors: Kooijman M. , Thijssen D. H. J. , De Groot P. C. E. , Bleeker M. W. P. , Van Kuppevelt H. J. M. , Green D. J. , Rongen G. A. , Smits P. , Hopman M. T. E.
Published: December 2007

Flow‐mediated dilatation (FMD) of the brachial and radial arteries is an important research tool for assessment of endothelial function in vivo, and is nitric oxide (NO) dependent. The leg skeletal muscle vascular bed is an important territory for studies in exercise physiology. However, the role of endothelial NO in the FMD response of lower limb arteries has never been investigated. The purpose of this study was to examine the contribution of NO to FMD in the superficial femoral artery in healthy subjects. Since physical inactivity may affect endothelial function, and therefore NO availability, spinal cord‐injured (SCI) individuals were included as a model of extreme deconditioning. In eight healthy men (34 ± 13 years) and six SCI individuals (37 ± 10 years), the 5 min FMD response in the superficial femoral artery was assessed by echo‐Doppler, both during infusion of saline and during infusion of the NO synthase blocker NG‐monomethyl‐l‐arginine (l‐NMMA). In a subset of the controls (n= 6), the 10 min FMD response was also examined using the same procedure. The 5 min FMD response in controls (4.2 ± 0.3%) was significantly diminished during l‐NMMA infusion (1.0 ± 0.2%, P < 0.001). In SCI, l‐NMMA also significantly decreased the FMD response (from 8.2 ± 0.4% during saline to 2.4 ± 0.5% during l‐NMMA infusion). The hyperaemic flow response during the first 45 s after cuff deflation was lower in both groups during infusion of l‐NMMA, but the effect of l‐NMMA on FMD persisted in both groups after correction for the shear stress stimulus. The 10 min FMD was not affected by l‐NMMA (saline: 5.4 ± 1.6%, l‐NMMA: 5.6 ± 1.5%). Superficial femoral artery FMD in response to distal arterial occlusion for a period of 5 min is predominantly mediated by NO in healthy men and in the extremely deconditioned legs of SCI individuals.
Efficient and Robust Approaches to the Stability Analysis of Large Multibody Systems
Authors: Bauchau Olivier A. , Wang Jielong
Published: December 2007

Linearized stability analysis methodologies that are applicable to large scale, multiphysics problems are presented in this paper. Two classes of closely related algorithms based on a partial Floquet and on an autoregressive approach, respectively, are presented in common framework that underlines their similarity and their relationship to other methods. The robustness of the proposed approach is improved by using optimized signals that are derived from the proper orthogonal modes of the system. Finally, a signal synthesis procedure based on the identified frequencies and damping rates is shown to be an important tool for assessing the accuracy of the identified parameters; furthermore, it provides a means of resolving the frequency indeterminacy associated with the eigenvalues of the transition matrix for periodic systems. The proposed approaches are computationally inexpensive and consist of purely post processing steps that can be used with any multiphysics computational tool or with experimental data. Unlike classical stability analysis methodologies, it does not require the linearization of the equations of motion of the system.
Saddlepoint Approximation for Sequential Optimization and Reliability Analysis
Authors: Du Xiaoping
Published: December 2007

A good balance between accuracy and efficiency is essential for reliability-based design (RBD). For this reason, sequential-loops formulations combined with the first-order reliability method (FORM) are usually used. FORM requires a nonlinear non-normal-to-normal transformation, which may increase the nonlinearity of a probabilistic constraint function significantly. The increased nonlinearity may lead to an increased error in reliability estimation. In order to improve accuracy and maintain high efficiency, the proposed method uses the accurate saddlepoint approximation for reliability analysis. The overall RBD is conducted in a sequence of cycles of deterministic optimization and reliability analysis. The reliability analysis is performed in the original random space without any nonlinear transformation. As a result, the proposed method provides an alternative approach to RBD with higher accuracy when the non-normal-to-normal transformation increases the nonlinearity of probabilistic constraint functions.
On Nonlinear Dynamics and an Optimal Control Design to a Longitudinal Flight
Authors: Pereira Danilo Carlos , Balthazar José Manoel , Chavarette Fábio Roberto , Rafikov Marat
Published: December 2007

In this work, we analyzed a bifurcational behavior of a longitudinal flight nonlinear dynamics, taking as an example the F-8 aircraft “Crusader.” We deal with an analysis of high angles of attack in order to stabilize the oscillations; those were close to the critical angle of the aircraft, in the flight conditions, established. We proposed a linear optimal control design applied to the considered nonlinear aircraft model below angle of stall, taking into account regions of Hopf and saddled noddle bifurcations.
The Kinematics of Wheeled Mobile Robots With Dual-Wheel Transmission Units
Authors: Chen Chao , Ostrovskaya Svetlana , Angeles Jorge
Published: December 2007

The dual-wheel transmission unit, an innovative driving mechanism for wheeled mobile robots, was introduced elsewhere. In this paper, we discuss wheeled mobile robots with such units, supplied with a novel suspension to keep the wheel-ground contact in spite of the irregularities of the floor. We derive closed-form solutions and constraints pertaining to the direct and inverse-kinematics problems of these robots; the constraints reveal the mobility of the robots at hand. Furthermore, we provide an algorithm for the trajectory tracking of the same robots that relies on a novel technique, which is termed the companion-curve method.
Research on Position Analysis of a Kind of Nine-Link Barranov Truss
Authors: Wang Pin , Liao Qizheng , Zhuang Yufeng , Wei Shimin
Published: December 2007

The position analysis of a nine-link Barranov truss is finished by using Dixon resultants together with Sylvester resultants. Above all, using vector method in complex plane to construct four constraint equations and transform them into complex exponential form, then three constraint equations are used to construct a 6×6 Dixon matrix, which contains two variables to be eliminated. We extract the greatest common divisor (GCD) of two columns of Dixon matrix and compute its determinant to obtain a new equation. This equation together with the fourth constraint equation can be used to construct a Sylvester resultant. A 50deg univariate polynomial equation is obtained from the determinant of Sylvester resultant. Other variables can be computed by Euclidean algorithm and Gaussian elimination. Lastly, a numerical example confirms that the analytical solution number of the Barranov truss is 50. It is the first time to complete analytical solutions of this kind of Barranov truss.
Analysis of a Gravity Compensated Four-Bar Linkage Mechanism With Linear Spring Suspension
Authors: Wongratanaphisan Theeraphong , Cole Matthew O. T.
Published: December 2007

This paper presents the analysis of a gravity compensated four-bar linkage mechanism with zero-free-length linear spring suspension. The objective of the study is to seek the possibility of employing the four-bar linkage or similar mechanisms for assisting vertical planar motion of a load mass in a gravitational field. The analysis is based on the system potential energy framework. Firstly, an arrangement of springs for gravity compensation in a four-bar linkage mechanism is proposed. It is then shown that for a four-bar linkage with symmetric geometric and mass properties the potential energy of the system has interesting and useful characteristics near the configuration at which the middle link is horizontal: an ideal operating configuration. The study also covers more practical cases where there is asymmetry in the mass distribution. The potential use of the mechanism in these cases is validated through a study of the sensitivity of the system potential energy function around the equilibrium point. Finally, based on the results obtained a novel mechanism is proposed for achieving gravity compensated vertical plane motion of a load mass. The proposed mechanism can have a wide range of travel and has significant potential for use not only in low-speed mechanical systems but also in high-speed heavy automated systems, where operating accelerations are of the order of 1g or less.
Causes of Microslip in a Continuously Variable Transmission
Authors: Kim Songho , Moore Carl , Peshkin Michael , Colgate J. Edward
Published: December 2007

The continuously variable transmission (CVT) is a type of transmission that can adopt any arbitrary gear ratio. Whereas typical transmissions utilize toothed gears, the CVT employs a sphere in rolling contact with a set of rollers; loads applied to the CVT are supported across these rolling contacts, resulting in microslips of varying amounts at each contact area. In this paper, we describe the causes of microslips in the CVT and ways to lessen them through an alternative CVT design.
A Modular Modeling Approach to Simulate Interactively Multibody Systems With a Baumgarte/Uzawa Formulation
Authors: Joli Pierre , Séguy Nicolas , Feng Zhi-Qiang
Published: December 2007

In this paper, a modular modeling approach of multibody systems adapted to interactive simulation is presented. This work is based on the study of the stability of two differential algebraic equation solvers. The first one is based on the acceleration-based augmented Lagrangian formulation and the second one on the Baumgarte formulation. We show that these two solvers give the same results and have to satisfy the same criteria to stabilize the algebraic constraint acceleration error. For a modular modeling approach, we propose to use the Baumgarte formulation and an iterative Uzawa algorithm to solve external constraint forces. This work is also the first step to validate the concept of two types of numerical components for object-oriented programming.
Stability Analysis of an Articulated Loading Platform in Regular Sea
Authors: Banik A. K. , Datta T. K.
Published: December 2007

Stability of the response of an articulated loading platform under regular wave, modeled as a SDOF nonlinear oscillator, is investigated. Relative velocity square drag force for harmonic wave appearing in the right hand side of the equation of motion is mathematically treated to bring the velocity dependent nonlinear hydrodynamic damping term to the left hand side of the equation of motion. Use of these two techniques makes the equation of motion amenable to the application of method IHBC. In order to trace different branches of the response curve and investigate different instability phenomena that may exist, the commonly used incremental harmonic balance method (IHB) is modified and integrated with an arc-length continuation technique to develop into incremental harmonic balance continuation (IHBC) method. Further, a technique for treating the nonlinear hydrodynamic damping term using a concept of distribution theory has been developed. The stability of the solution is investigated by the Floquet theory using Hsu’s scheme. The stable solutions obtained by the IHBC method are compared with those obtained by the numerical integration of equation of motion wherever applicable.
In situ x-ray absorption near-edge structure analysis for extreme ultraviolet lithography projection optics contamination
Authors: Niibe Masahito , Kakutani Yukinobu , Koida Keigo , Matsunari Shuichi , Aoki Takashi , Terashima Shigeru , Takase Hiromitsu , Murakami Katsuhiko , Fukuda Yasuaki
Published: December 2007

A contamination evaluation system for extreme ultraviolet (EUV) lithography projection optics was developed in the NewSUBARU SR facility, in which in situ surface analysis and elemental concentration mapping were carried out with the use of the x-ray absorption near-edge structure (XANES) method. For concentration mapping, the linearity between the x-ray absorption intensity and contamination thickness was confirmed by examining standard samples. The problem of quantitativity, which was caused by the antagonistic reaction of carbon deposition and surface oxidation on the mirror surface, was successfully solved by taking the ratio of intensities of the upper and lower sides of the absorption edge. Very useful information for protecting the surface of EUV lithography optics was obtained when the in situ XANES analysis was applied to the experiment of EUV irradiation with the introduction of ethanol gas to the vacuum atmosphere.
Extreme ultraviolet lithography at IMEC: Shadowing compensation and flare mitigation strategy
Authors: Lorusso G. F. , Goethals A. M. , Jonckheere R. , Hermans J. , Ronse K. , Myers A. M. , Kim I. , Niroomand A. , Iwamoto F. , Ritter D.
Published: December 2007

The extreme ultraviolet lithography (EUVL) program at IMEC is aimed to tackle many unsolved critical issues of EUV lithography as the technology moves towards production, by focusing specifically on tool, resist, and mask projects. Here, the authors describe the structure of the IMEC EUVL program and the status of the EUV alpha demo tool. In particular, they discuss their proposed strategies for flare mitigation and shadowing effect correction. They demonstrate how it is possible to implement an effective rule-based flare mitigation strategy. In addition, they propose a relatively simple methodology to fully compensate for shadowing pattern placement error and critical dimension bias.
Real-time spatial-phase locking for vector-scan electron beam lithography
Authors: Yang Yugu , Hastings J. T.
Published: December 2007

Spatial-phase locked electron beam lithography (SPLEBL) provides feedback control of electron beam position by monitoring the signal from a fiducial grid on the substrate. Continuous, or “real-time,” spatial-phase locking has been investigated for raster-scan Gaussian beam and for shaped-beam systems. Discontinuous feedback, or “look-then-write,” techniques have been implemented for vector-scan systems. However, it would be advantageous to provide real-time spatial-phase locking for vector-scan systems because of their wide adoption for research, prototyping, and specialty device production. Here, the authors present a phase locking algorithm, performance simulations, and initial experimental results for real-time, vector-scan SPLEBL. The authors demonstrate that real-time, vector-scan SPLEBL can provide subnanometer precision phase locking for different feature filling strategies, exposure parameters, and pattern geometries using reasonable data lengths and practical grid signal-to-noise ratios.
Accurate control of remaining resist depth for nanoscale three-dimensional structures in electron-beam grayscale lithography
Authors: Lee S.-Y. , Anbumony K.
Published: December 2007

In electron-beam (e-beam) grayscale lithography, a three-dimensional (3D) structure is transferred onto the resist or substrate. In either case, accurate control of the remaining resist depth and, accordingly, profile is critical for successful fabrication of the structure. Usually, the remaining resist depth control is guided by the empirically derived dose (or exposure)-depth relationship using a two-dimensional model. However, such an approach may require multiple calibrations and also lead to significant dimensional errors for nanoscale structures due to the depth-dependent variation of exposure and the nonlinearity between exposure and developing rate. In this study, a resist developing model is incorporated into e-beam dose control schemes in order to take the exposure variation and nonlinearity into account. Through computer simulation, it has been demonstrated that significant improvement in dimensional accuracy may be achieved by including the 3D resist developing model in the e-beam dose control for fabricating nanoscale 3D structures.
Creation of sub-20-nm contact using diblock copolymer on a 300mm wafer for complementary metal oxide semiconductor applications
Authors: Li Wai-kin , Yang Sam
Published: December 2007

The authors have demonstrated a method to form 20nm contact features of uniform size over a large area by integrating a self-assembling diblock copolymer with optical lithography. The diblock copolymer contacts are formed in topographical placers which are patterned with using optical lithography. A diblock copolymer pattern can only be formed in a placer and not in the narrower trenches that connect to the placer. This concept can be applied to form local interconnects using a single mask dual damascene process, where vias are self-aligned to the line. Some design rule restrictions must be applied to certain structures to enable patterning with diblock copolymer. They also observed that diblock copolymer contact formation was strongly influenced by the shape of the placer and the size of the cylindrical contact hole could be varied by the molecular weight of the block copolymer.
Atomic-force lithography with interferometric tip-to-substrate position metrology
Authors: Moon Euclid E. , Kupec Jan , Mondol Mark K. , Smith Henry I. , Berggren Karl K.
Published: December 2007

Inadequacies in lateral tip stability and registration presently limit lithographic applications of scanning probes. The authors describe a tool they constructed to write sub-10-nm features with 1nm pattern registration. The tool utilizes an interferometric metrology technique called interferometric-spatial-phase imaging (ISPI) to continuously measure tip position relative to a substrate. Direct tip-to-substrate position measurement permits correction for the multitude of error sources encountered in the long mechanical path between a tip and a substrate. Experimental results indicate that the lateral tip position is stabilized by ISPI to 3σ=0.3nm, and pattern placement accuracy in a two-dimensional (2D) grid array is 3σ=0.2nm. According to ISPI measurements, 2D closed figures written in a polymer are overlaid to <1nm. Analysis of patterns written by the tip while under ISPI control provides an error bound that is in good agreement with the ISPI measurements.
Are extreme ultraviolet resists ready for the 32nm node?
Authors: Petrillo Karen , Wei Yayi , Brainard R. , Denbeaux G. , Goldfarb Dario , Koay C.-S. , Mackey J. , Montgomery Warren , Pierson W. , Wallow T. , Wood Obert
Published: December 2007

The International Technology Roadmap for Semiconductors (ITRS) insertion point of extreme ultraviolet (EUV) lithography is the 32nm half-pitch node, and significant worldwide effort is being focused toward this goal. Potential road blocks have been identified and are being addressed. Readiness of EUV photoresists is one of the risk areas. According to the ITRS (www.itrs.net), a production-worthy EUV resist at 32nm half-pitch has to have a photospeed of ∼5mJ∕cm2 and line edge roughness (3σ) of 1.4nm. Toward this goal, the joint INVENT activity (AMD, CNSE, IBM, Micron, and Qimonda) at Albany has evaluated a broad range of EUV photoresists on various EUV exposure tools worldwide, including EUV MET at Lawrence Berkeley National Laboratory, EUV MET at SEMATECH Albany, and EUV interferometer at the Paul Scherrer Institute, Switzerland. This article will give a survey of the results, assessing the strengths and weaknesses of current materials.
Optimization of hydrogen silsesquioxane for photonic applications
Authors: Holzwarth C. W. , Barwicz T. , Smith Henry I.
Published: December 2007

Increasingly complex electronic-photonic integrated circuits, based on strong confinement of photons, has increased the importance of low-refractive-index overcladding materials. In addition to providing high optical transparency and sufficient thickness for adequate optical insulation, overcladding materials must also fill in high-aspect-ratio gaps, withstand high temperatures, and provide acceptable thermal conductivity. Previously, all of these qualities were simultaneously achievable only through tetraethylorthosilicate (TEOS)-based deposition of SiO2. Here, the authors demonstrate how hydrogen silsesquioxane (HSQ) can be used as a lower-cost alternative to TEOS, with superior gap-filling and self-planarization properties. HSQ is a spin-on dielectric designed for low-k applications. The standard curing process for HSQ results in a low-k porous film that is not adequate for photonic applications. It shows very low thermal conductivity, optical absorption due to Si–H bonds, and high intrinsic tensile stress, which limits the achievable layer thickness. By optimizing the HSQ curing process, they eliminate these shortcomings while maintaining HSQ’s excellent gap-filling and self-planarization properties. They demonstrate that HSQ layers can be made almost arbitrary thick, with no detectable Si–H bonds while easily filling sub-100-nm gaps. They demonstrate Si3N4 optical microring resonators with quality factor of 240 000, consistent with the best published values using TEOS as an overcladding.
Submicron aligned wafer bonding via capillary forces
Authors: Tupek Michael R. , Turner Kevin T.
Published: December 2007

Submicron wafer-to-wafer alignment is critical in wafer bonding for the fabrication of three-dimensional integrated circuits. In this work, the authors examine the sources of misalignment in traditional alignment methods and then examine the capabilities of an alternative alignment approach that uses capillary forces. A multiscale model was developed to investigate the potential of capillary assisted alignment. The model consists of a local model of a confined liquid droplet and a finite element model that predicts wafer-level distortions and misalignment. Using the model, the effect of pattern error and wafer nonflatness on misalignment in bonding was examined for both the traditional and capillary assisted methods. The results indicate that capillary assisted alignment has several distinct advantages over traditional methods that result primarily from the ability to align the wafers at many locations across the wafer.
Defects in HgTe grown by molecular beam epitaxy on (211)B-oriented CdZnTe substrates
Authors: Selvig E. , Tonheim C. R. , Kongshaug K. O. , Skauli T. , Lorentzen T. , Haakenaasen R.
Published: December 2007

The authors present a systematic study showing the evolution of the defect morphology and crystalline quality in molecular beam epitaxially grown HgTe epilayers with substrate temperature. The authors have characterized the layers using optical microscopy, atomic force microscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy, and high-resolution x-ray diffraction. Four types of defects (microvoids, circular voids, hillocks, and high-temperature voids) have been characterized on epilayers grown in the substrate temperature range of 183.3–201.3 °C. The authors find that there is a minimum in the area covered by defects at a temperature just below the onset of Te precipitation, and they define this temperature as the optimal growth temperature. Above the optimal growth temperature the authors observe the appearance of high-temperature voids. By determining the onset of Te precipitation in HgTe, and performing thermodynamic calculations, the authors can also successfully predict the onset of Te precipitation in CdHgTe, which again is related to the optimal growth temperature in CdHgTe. Furthermore, the authors have found that the shape and density of the microvoids are particularly sensitive to the substrate temperature, and that these properties can be used to determine the deviation from the optimal growth temperature. From the shape and density of microvoids in one growth of HgTe, the authors can therefore determine the temperature correction needed to reach the optimal growth temperature for CdHgTe. The authors also suggest a mechanism for the formation of the microvoids based on the assumption of impurities on the substrate combined with a preferential Te diffusion in the [1 ¯11] direction across the steps.
Nanofabrication of high aspect ratio 24nm x-ray zone plates for x-ray imaging applications
Authors: Feng Yan , Feser Michael , Lyon Alan , Rishton Steve , Zeng Xianghui , Chen Sharon , Sassolini Simone , Yun Wenbing
Published: December 2007

Building high-performance zone plate is a critical step for achieving nanometer resolution in advanced x-ray imaging and microscopy. Zone plates with smaller outmost zone width and higher aspect ratio are increasingly in demand, simply because the resolution and efficiency of an x-ray microscope are ultimately determined by these two features. In this paper, we will present detailed discussion of achieving high aspect ratio and high resolution x-ray zone plate through electron beam lithography, trilevel resist process and gold plating, fabrication problems, and limitations. We will also present the technique to double the aspect ratio of the zone plate and measure the results of x-ray diffraction efficiency of single and aspect ratio doubled zone plates.
Study of the assist features effect on the through focus behavior in isoline with an innovative method
Authors: Li Jianliang , Yan Qiliang , Melvin Lawrence S.
Published: December 2007

Driven by the ever shrinking feature size in the chip design and the complexity of the heuristic subresolution assist feature (SRAF) placement rules, more wafer data for calibration and more effort on the part of design engineers are necessary for each process node. The main purpose of placing assist features around the main feature is to improve the through focus robustness on the target edge of the main feature. Therefore, it is desirable to study the effect of assist feature placement on the main feature in terms of the focus sensitivity with a quick and accurate method. In this paper, an innovative way of calculating the signal dependence on the locations of the SRAF placed in the isoline pattern is proposed. The results indicated that the optimal location for the assist feature placement to increase the depth of focus is about 380nm from the isoline center and is independent of the isoline structure for an annular illumination system. The results are verified by using independent tools and measured before and after optical proximity correction. Consistency of the optimal assist feature location is observed, and a qualitative explanation of the observations is presented.
On-wafer monitoring of charge accumulation and sidewall conductivity in high-aspect-ratio contact holes during SiO2 etching process
Authors: Jinnai Butsurin , Orita Toshiyuki , Konishi Mamoru , Hashimoto Jun , Ichihashi Yoshinari , Nishitani Akito , Kadomura Shingo , Ohtake Hiroto , Samukawa Seiji
Published: December 2007

The authors investigated charge accumulation in high-aspect-ratio contact-hole structures by using the new on-wafer monitoring device they fabricated on a Si substrate of 8in. in diameter by using a conventional production process for semiconductor devices. The device has high-aspect-ratio contact-hole structures that are comparable with the practical interconnect structures of recent dynamic random access memory devices. In this article they discuss charge accumulation and the electric conductivity of fluorocarbon polymer deposited on the sidewall in high-aspect-ratio contact holes during plasma etching processes. They also monitored the charge accumulation during pulse-time-modulated (TM) plasma etching of high-aspect-ratio SiO2 contact-hole structures and found that the charge accumulation potential between the top and bottom of the contact-hole structures increased with the aspect ratio of the contact holes. Even in high-aspect-ratio contact holes the charge accumulated during TM plasma exposure was less than that accumulated during the conventional continuous-wave plasma exposure. The electrical conductivity of the fluorocarbon polymer deposited on the sidewall was increased by ion bombardment and was lower in high-aspect-ratio contact holes than in low-aspect-ratio contact holes. The new on-wafer monitoring device is a very effective tool for investigating local charge accumulation during the etching of device structures.
Influence of RuO2 nanoparticles on electron emission from carbon nanotubes
Authors: Liu Huarong , Noguchi Tsuneyuki , Kato Shigeki
Published: December 2007

The authors studied the influence of RuO2 nanoparticles attached to multiwalled carbon nanotube (MWCNT) emitters on field emission. The threshold field, corresponding to 10mA∕cm2, was reduced 30% to ∼0.90V∕μm after attaching the particles. However, the particles deteriorated the stability of field emitters to some extent, especially in the high emission-current-density region of several A∕cm2. The maximum emission-current density was limited to a lower current region compared with field emitters without RuO2. This can be explained reasonably by considering the vaporization of RuO2 particles that frequently causes significant self-ion-sputtering during strong emission because of the large contact resistance between the particles and MWCNTs. This explanation was experimentally proved by measuring the reduction of field-enhancement factor with the elapsed-emission time. This reduction is quicker for emitters with RuO2 than for emitters without RuO2. Experimental data also show that the standard deviation of Fowler-Nordheim plots for field emitters can be used to judge their stability and lifetime—a value of ∼5×10−3 suggests stable performance for our emitters.
Fabrication of periodic microstructures on flexible polyimide membranes
Authors: Shelton D. J. , Tharp J. S. , Zummo G. , Folks W. R. , Boreman G. D.
Published: December 2007

Periodic metallic microstructures were fabricated on polyimide membranes. Techniques were developed to maintain flatness of the membrane during processing while still allowing for flexibility in the final structure. For proper functionality of the structures, it was necessary to first fabricate a continuous metallic film and a continuous dielectric layer on top of the flexible substrate, which underlaid the periodic microstructure. Flexibility of the overall structure was maintained by using a polymer as the dielectric layer, which was constrained to have high optical transmission over the infrared wavelength range of 6–14μm. Three candidate polymers were evaluated, and their measured optical properties are presented. Benzocyclobutene was found to be the best choice for this application. The final structure fully populated a 10cm (4in.) diameter flexible membrane with microstructures of excellent uniformity.
Evolution of surface morphology of GaN thin films during photoelectrochemical etching
Authors: Leach J. H. , Özgür Ü. , Morkoç H.
Published: December 2007

The evolution of the surface morphology of unintentionally doped and Si-doped GaN samples subjected to photoelectrochemical (PEC) etching in the carrier-limited regime in aqueous KOH is reported. It was found that a nanoporous structure precedes whisker formation in samples in which high densities of whiskers ultimately form. Increasing the light intensity accelerated the rate of change of the surface morphology, but increasing the molarity of the KOH had no effect on the etching. The surface morphology in this regime tends to only depend on parameters of the starting layers, as well as how much etching in total has occurred. The identification of variations in surface morphology at different times during PEC etching of GaN may have utility in that assorted nanopatterning of the GaN surface can be intentionally achieved in a controllable, large-scale, and inexpensive manner.
Extreme ultraviolet lithography: From research to manufacturing
Authors: La Fontaine Bruno , Deng Yunfei , Kim Ryoung-han , Levinson Harry J. , Okoroanyanwu Uzodinma , Sandberg Richard , Wallow Tom , Wood Obert
Published: December 2007

The authors explore the critical issues remaining for the introduction of extreme ultraviolet lithography (EUVL) in semiconductor manufacturing. Among all technical issues, source power appears to be the most significant challenge that the technology is facing at this time. The lack of sufficiently high-power sources integrated in the first generation of full-field commercial scanners has profound implications on the remaining issues, and therefore on the risk associated with the insertion of EUVL technology. At the core of the problem is the cost of ownership of EUVL, which depends most heavily on source power. Moreover, the lifetime of the scanner mirrors and of the masks can only be tested properly with high-power sources on these first scanners. Without the ability to perform these tests, the technology might suffer unrecoverable delays. Fortunately, there has been good progress in the development of laser-produced plasma sources, which appear to be the most capable candidates for high-power scalability at this time. Furthermore, a booming new technology, fiber lasers, provides prospects of highly efficient and cost-effective EUV sources for high-volume manufacturing. Finally, significant progress has been made in the development of EUV resists to support the 32nm half-pitch node.
Benchmarking of 50nm features in thermal nanoimprint
Authors: Gourgon C. , Chaix N. , Schift H. , Tormen M. , Landis S. , Sotomayor Torres C. M. , Kristensen A. , Pedersen R. H. , Christiansen M. B. , Fernandez-Cuesta I. , Mendels D. , Montelius L. , Haatainen T.
Published: December 2007

The objective of this benchmarking is to establish a comparison of several tools and processes used in thermal NIL with Si stamps at the nanoscale among the authors’ laboratories. The Si stamps have large arrays of 50nm dense lines and were imprinted in all these laboratories in a ∼100nm thick mr-18010E film. Other materials, such as mr-17010E, were also tested. Good patterns were obtained and some limitations were identified. Reducing the pressure to 15bars enables the printing of 50nm structures without pulling them off. At higher pressures, some bending effects resulting in pattern deformation were observed. It was proven that a pressure of 1.5bars is sufficient to imprint perfect 50nm lines. The influence of the antiadhesive layer and mold design has been characterized by the demonstration of pulled off lines in some cases. Moreover, it has been shown that the scatterometry method is particularly useful for the characterization of 50nm lines and that the residual layer thickness corresponds to the theoretical estimate as long as the lines are well defined. One process was demonstrated which combines high reproducibility with high throughput, achieving a cycle time of 2min.
Economic approximate models for backscattered electrons
Authors: Baghaei Rad Leili , Downes Ian , Ye Jun , Adler David , Pease R. Fabian W.
Published: December 2007

The Monte Carlo method is widely used to simulate the signal from a scanning electron microscope. Although the results closely match the actual signal, the method is inherently slow due to the repeated calculation of random trajectories. The authors re-examine the alternative approach of using an approximate model to describe the signal. The authors develop a progressive approximate model which describes the spatial probability distribution of an electron along its entire path. The model also includes information about the angular and energy distribution of the electron. The model is compared to the Monte Carlo method by determining the yield of backscattered electrons as the beam is scanned across a step feature. For this simple feature the model-based approach computes the signal approximately two orders of magnitude faster.
Dry etch release processes for micromachining applications
Authors: Zhu Tongtong , Argyrakis Petros , Mastropaolo Enrico , Lee Kin Kiong , Cheung Rebecca
Published: December 2007

The authors report on the comparative study of two dry etch processes for polysilicon sacrificial layer release using vapor phase xenon difluoride (XeF2) continuous etching and inductively coupled plasma (ICP) etching with sulfur hexafluoride (SF6) gas. Test structures of 0.5μm thick polysilicon have been patterned and etch channels varying in widths from 1to500μm have been fabricated successfully for the purpose of comparison. The influence of etch pressure, aperture opening size, and ICP etch power on the undercut etching rate as well as selectivity between mask and substrate have been studied. It has been possible to achieve an undercut etch rate of up to 11.6μm∕min under a pressure of 3Torr in XeF2 etch gas, while for SF6 plasma, an undercut etch rate of 2.56μm∕min at 65mTorr is obtained. Moreover, the optimized process has been employed for the fabrication of silicon carbide (SiC) resonators.
Effects of developer temperature on electron-beam-exposed hydrogen silsesquioxane resist for ultradense silicon nanowire fabrication
Authors: Choi Sookyung , Jin Niu , Kumar Vipan , Adesida Ilesanmi , Shannon Mark
Published: December 2007

The effects of developer temperature on hydrogen silsesquioxane (HSQ) resist for the fabrication of ultradense silicon nanowires are reported. At higher developer temperatures, the contrast of HSQ significantly increased and sharply defined gratings were obtained. In addition, higher developer temperature provided larger processing windows for various grating periodicities. Pattern transfer with HSQ masks using both dry and wet etching processes to fabricate silicon nanowires on silicon-on-insulator substrates is demonstrated. 27-nm-period silicon nanowire arrays obtained using the high temperature development along with the two etching processes are presented and discussed.
Novel coexisted sol-gel derived poly-Si-oxide-nitride-oxide-silicon type memory
Authors: You Hsin-Chiang , Wu Chi-Chang , Ko Fu-Hsiang , Lei Tan-Fu , Yang Wen-Luh
Published: December 2007

The authors use a very simple sol-gel spin coating method at 900°C and 1min rapid thermal annealing to fabricate three different poly-Si-oxide-nitride-oxide-silicon-type flash memories. The memory windows estimated from the curve of drain current versus applied gate voltage are 3, 3.3, and 4V for (i) HfO2 thin film, (ii) hafnium silicate nanocrystal, and (iii) coexisted hafnium silicate and zirconium silicate nanocrystal memory, respectively. Together with the measurement from gate disturbance and drain disturbance on these fabricated devices, the coexisted nanocrystal devices exhibit better reliability than both the thin film type memory and single nanocrystal type memory.