bluuebunny/crossref_metadata_2025 huggingface dataset:
Systematic review of clinical trials comparing open and endovascular treatment of abdominal aortic aneurysm
Authors: Ho Pei , Yiu Wai Ki , Cheung Grace Chung‐Yan , Cheng Stephen Wing‐Keung , Ting Albert Chi‐Wai , Poon Jensen Tung‐Chung
Published: January 2006

Objective:  Endovascular repair (EVAR) using stent‐graft device is a new treatment for abdominal aortic aneurysm (AAA) that is gaining more and more popularity. This systematic review compares the new minimally invasive endovascular treatment with the conventional open repair aiming to provide more evidence for clinical decision on choice of treatment for aneurysm patients.

Methods:  Electronic search on MEDLINE, EMBASE and Cochrane Library and manual search on bibliographies was performed to identify studies published from 1991 to 2004 comparing clinical outcomes of patients who underwent EVAR and open repair. Quality of clinical studies was assessed by modified Evans and Pollok score and those scores below 50 were excluded. Systematic analysis was performed for short‐, mid‐ and long‐term clinical outcomes. The effect size of the clinical parameters was estimated by relative risk, weighted mean difference and standard mean difference.

Results:  27 clinical studies and 7226 patients were included in this systematic review. Three studies were randomized control studies and the rest were comparative studies. Systematic review showed patients after EVAR had significantly lower 30‐day mortality, shorter hospital and intensive care unit stay, less blood loss or blood transfusion, fewer cardiac and respiratory complications, less colonic ischaemia, and fewer overall operative morbidities. But EVAR carried a significant higher frequency of early secondary procedures and graft‐related complications. The 1–5‐year mortality between the two groups was similar. Patients receiving EVAR required more late secondary procedures and the cost related to EVAR was higher. Systematic review on quality of life could not be performed as there was a large variation on method of measurement.

Conclusions:  EVAR offers significant benefit to aneurysm patients in the early postoperative period. However, it does not show an advantage over open repair in mid‐ and long‐term outcome. Furthermore, EVAR might carry more morbidity and higher cost in the long term. Prospective randomized control studies focusing on long‐term outcome of EVAR and open repair aneurysm patients as well as on studies on newer generation devices are needed to provide more information for clinical decisions.
Go‐kart injuries of the abdominal cavity
Authors: Li Jimmy Chak‐Man , Leong Heng‐Tat
Published: January 2006

Go‐karting is one of the famous sporting activities in Hong Kong and southern China. Go‐karting is easily accessible to the general public and almost everyone can enjoy the excitement of the sport. Although karting has always been claimed to be safe, the risks and injuries of this fun sport should not be overlooked. From May 2001 to February 2004, we observed three serious intra‐abdominal injuries with go karts in the North District Hospital of Hong Kong. The injuries included hemoperitoneum caused by omental vessel tear, peritonitis caused by perforation of duodenojejunal flexure and peritonitis caused by perforation in the duodenum associated with liver laceration. A high index of clinical suspicion is essential in encountering such cases, as potential life‐threatening complications can occur.
Rectus sheath haematoma requiring laparotomy
Authors: Ma Wai‐Kit , Fung Terence Ming‐Kit , Lam Yuk‐Hoi , Lau James Yun‐Wong
Published: January 2006

Rectus sheath haematoma is a well‐documented but unusual cause of acute abdomen. Combination of clinical features and appropriate radiological investigations can make for a prompt diagnosis. Most authors advocate conservative management and it has been reported that patients were directly discharged from the emergency department. We report a case of rectus sheath haematoma which progressed with clinical deterioration and necessitated surgical intervention for clot evacuation. Causes, physical signs, radiological features and classification of rectus sheath haematoma are discussed. It may be necessary to continue close clinical monitoring after diagnosis of rectus sheath haematoma.
Liver retraction using a Kelly retractor and sutures
Authors: Yan‐Wah Mak Josephine , Leong Heng‐Tat
Published: January 2006

Adequate exposure enables an operation to be performed safely and with precision. In most of the upper abdominal operations, good retraction of the abdominal wall as well as the upper abdominal viscera is necessary. A simple but effective and inexpensive method of liver retraction is introduced.
Effects of through-focus symmetry in maskless lithography using micromirror arrays
Authors: Wang J.-S. , Hafeman S. , Neureuther A. R. , Solgaard O.
Published: January 2006

In this article we model and characterize the effects of the through-focus asymmetry induced by pixels with phases other than 0 and π in micromirror arrays for maskless lithography. Analytic models for several mirror configurations are provided and shown to result in small deviations (±1.5%) from simulation results. These models, together with full simulations, are used to compare multiple-tilt and multiple-piston mirrors. The results show that for comparable multiple-tilt and multiple-piston mirrors, the piston mirrors have better modulation characteristics. A test of off-grid printing is performed, suggesting that the four-piston mirror is the best configuration for maskless lithography.
High performance 100mm-in-diameter true zero-order waveplates fabricated by imprint lithography
Authors: Wang Jian Jim , Deng Xuegong , Liu Feng , Chen Lei , Nikolov Anguel , Liu Xiaoming , Deng Jiandong , Sciortino Paul
Published: January 2006

Commercial quality high-performance true zero-order quarter waveplates based on artificial dielectric nanostructures were made by high throughput and low cost wafer-based nanofabrication processes. Both precise phase retardation (90°±2° across a 100mm-in-diameter glass wafer) and a high transmittance (>98.8%) were achieved. The quarter waveplates with different center wavelengths, such as, 780nm and 660nm, have been fabricated for optical pick-up (CD/DVD) applications. The nanostructure based true zero-order quarter waveplates are operational at a large wavelength and temperature range under a wide incident angle. The developed high quality true zero-order quarter waveplates have the potential for many cost-sensitive optical applications. Furthermore, it opens the potential for integrated optical applications thanks to the nanofabrication processes.
Dynamic chromatic aberration correction in low energy electron microscopes
Authors: Khursheed Anjam
Published: January 2006

This paper presents a method of dynamically correcting for the chromatic aberration in pulsed gun low energy electron microscope systems. The proposal is based upon the use of a drift tube in combination with electron lenses whose focal strengths can be rapidly modulated. Simulation results that use direct ray tracing of electrons are presented for specific drift tube/correction lens combinations.
Modeling and simulation for nanometrics
Authors: Neureuther Andrew R. , Ceperley Daniel
Published: January 2006

Nanoscale phenomena and especially surface plasmon-based optical devices are playing important roles in historical and emerging applications of photography, instrumentation, imaging, and signal processing. Simulation of these devices is synergistic with invention, and commercial computer-aided design infrastructure will eventually follow to cope with design and manufacturing. Devices based on source-free solutions to Maxwell’s equations, such as plasmons and guided waves, are emphasized. They include the Daguerrotype and plasmon scattering from topographical features. A more general survey of the applications of simulation to optical nanodevices is also included. For finite-difference time domain using up to 250 million nodes, the major computational challenges are associated with the nm-level detail of large distributed structures, the small real part of the refractive index, and the necessity to accurately compute phases.
Subpixel alignment for scanning-beam lithography using one-dimensional, phase-based mark detection
Authors: Krishnamurthy A. V. , Namepalli R. V. , Hastings J. T.
Published: January 2006

A phase-based alignment technique for scanning electron-beam lithography is proposed and evaluated. The approach uses a grid alignment mark rotated with respect to the beam deflection axes and requires only a single, one-dimensional (1D) line scan to perform subpixel registration in both the x and y directions. This 1D, phase-based method promises subpixel alignment without interpolation, faster mark signal acquisition, and more computationally efficient detection. Theoretical limits for alignment accuracy and a simple phase-estimation algorithm that approaches these limits are described. Monte Carlo simulations indicate that nanometer-level registration precision can be achieved with modest grid periods and signal to noise ratios (SNRs). Experimental measurements of registration variance as a function of SNR agree well with both theory and simulation. Registration errors of 3 nm (1-standard deviation) are observed using a 1μm grid period, 49 nm pixel size, and the highest observed SNR of 5.9.
Fabrication of a hard mask for InP based photonic crystals: Increasing the plasma-etch selectivity of poly(methyl methacrylate) versus SiO2 and SiNx
Authors: Wüest R. , Strasser P. , Robin F. , Erni D. , Jäckel H.
Published: January 2006

We introduce cyclic reactive ion etching processes for SiO2 and SiNx hard masks where the fluorine-based etch steps are interleaved with N2 flushing steps in order to improve the selectivity to electron-beam resists. For SiO2 etching an etch-step duration of 30s resulted in a doubled selectivity of almost 4:1 between SiO2 and poly(methyl methacrylate) (PMMA) due to a reduced thermal load. We established the pattern transfer from a 200nm thick PMMA resist into a 600nm thick SiO2 layer for 200nm diameter holes. For SiNx etching we demonstrate improved sidewall verticality, an enhanced etch rate, and suppressed redeposition of etch byproducts for a cyclic process. With the use of an additional 30nm titanium intermediate layer we show an excellent overall selectivity between SiNx and PMMA of almost 5:1. This process is applied to the fabrication of planar photonic-crystal devices with 3.5μm deep holes in an InP based slab waveguide with an initial PMMA layer thickness of 220nm.
Electrical characterization of multilayer masks for extreme ultraviolet lithography
Authors: Hartley J. G. , Raghunathan S. , Govindaraju A.
Published: January 2006

Voltage potentials on the surface of a mask blank form one of the mechanisms by which errors in mask patterning may be introduced. When electrical currents flow through the mask either from the patterning beam or induced through other means, it is the impedance to ground from the point being patterned on the mask that determines the potential developed. Ten multilayer coated mask blanks from four sources were provided by Sematech for electrical characterization. The initial purpose of this project is to experimentally determine the resistance between various points in the quality area to likely ground locations on the mask. The mask can be grounded on the top, side or bottom edges. Initial attempts to characterize the resistance with a variety of measurement tools proved to be inconsistent. A test fixture was then assembled to enable voltage-current (V-I) characteristic measurements to be made on the samples. Several key issues were observed. First, the behavior was not very stable—the V-I characteristics were observed to transition between several different resistance modes. Second, quite a few of the modes observed exhibited semiconductor-like behavior. We have included representative examples of the results. Details of the experimental setup and the results obtained from the samples are presented and the behavior is explained.
Ion implantation with scanning probe alignment
Authors: Persaud A. , Liddle J. A. , Schenkel T. , Bokor J. , Ivanov Tzv. , Rangelow I. W.
Published: January 2006

We describe a scanning probe instrument which integrates ion beams with the imaging and alignment function of a piezoresistive scanning probe in high vacuum. The beam passes through several apertures and is finally collimated by a hole in the cantilever of the scanning probe. The ion beam spot size is limited by the size of the last aperture. Highly charged ions are used to show hits of single ions in resist, and we discuss the issues for implantation of single ions.
Functionalized SU-8 patterned with x-ray lithography
Authors: Balslev S. , Romanato F.
Published: January 2006

In this work we demonstrate the feasibility of x-ray lithography on SU-8 photoresist doped with the laser dye Rhodamine 6G, while retaining the photoactive properties of the embedded dye. Two kinds of structures are fabricated via soft x-ray lithography and characterized: a laser and an amplified spontaneous emission light source that couples out light normal to the chip plane. In addition we examine the influence of the x-ray irradiation on the fluorescence of thin films of dye doped SU-8. The dye embedded in the SU-8 is optically excited during characterization by an external light source tuned to the absorption band of the dye.
Rapid prototyping of infrared bandpass filters using aperture array lithography
Authors: Han Keping , Morgan Mark , Ruiz Ariel , Vemula Sri C. , Ruchhoeft Paul
Published: January 2006

We demonstrate the prototyping of infrared bandpass filters, which consist of cross-shaped openings in a thin gold film, using ion beam aperture array lithography. In the lithography process, a stencil mask containing a periodic array of square apertures is irradiated by a broad beam of helium ions. The ions that pass through the openings expose the resist on a substrate that is placed in close proximity and cross-shaped filter structures are printed by moving the stage underneath the substrate, thus allowing for rapid formation of periodic patterns. We have fabricated filter patterns with peak transmittance ranging from 53% to 67% at wavelengths between 1.2 and 1.3μm that exhibit high reflectance for longer wavelength radiation. The prototyping throughput for masks with 2μm pitch patterns was about 2cm2∕h. The spectral performance of the prototyped filters was measured. Large-area, second-generation masks with 667nm pitch had a lithography throughput of 300cm2∕h and were used to print filter patterns of similar quality.
Overlay alignment using optical microscopy and arbitrary surface features
Authors: Picciotto Carl , Gao Jun , Hoarau Eric , Wu Wei , Jackson Warren , Tong William M.
Published: January 2006

In this article, we present our nanoscale displacement sensing and estimation (nDSE) theory,which describes the theoretical limitations of displacement-sensing and predicts thepracticality of measuring nanoscale displacements using optical microscopy, and indirect displacement-measurement-based alignment (IDMA), an application framework for achieving precision alignment using individual displacement sensing rather than directly comparing nominally identical alignment marks. We propose that IDMA may form the basis for low-cost overlay alignment metrology for emerging fabrication techniques such as nanoimprint lithography. As a first step in experimentally investigating IDMA on a nanoimprinting tool, we present a variation, direct displacement-measurement-based alignment (DDMA), and we describe proof-of-concept experiments performed using an in-house nanoimprinter. We demonstrate that DDMA, enabled by nDSE, can measure misalignments in the tens of microns to a precision easily better than 100nm. We maintain that in more optimized conditions DDMA should be expected to provide precisions in the 20nm range. More to the point, we expect that IDMA, the preferred application framework, will demonstrate even better results due to its inherent robustness against mismatched alignment targets, an inevitable issue faced in real-world application environments. For more background information please see the work presented by J. Gao, C. Picciotto, and W. Jackson [Appl. Phys. A 80, 1265 (2005)] and C. Picciotto, J. Gao, E. Hoarau, and W. Wu [Appl. Phys. A 80, 1287 (2005)].
Use of optical defocus components to investigate and improve pattern spatial frequency characteristics for more robust layouts
Authors: Melvin Lawrence S. , Shiely James P. , Yan Qiliang
Published: January 2006

As semiconductor manufacturing moves to smaller geometries, the existing methodologies for verifying the manufacturability of a design are increasingly cumbersome. Current practice is to use geometric “design rules”—such as minimum spacing and width constraints—to identify design configurations that are not manufacturable or likely to reduce yield. One manufacturing property that is particularly difficult to capture accurately with geometric rules is the robustness of the layout configuration with respect to variation through the lithographic process window. The nonlinear characteristics of optical partial coherence effects, particularly strong in modern exposure systems with off-axis illumination, are currently incorporated into the design rules through an exhaustive empirical process. The resulting design rules can be overly conservative to insure complete problem pattern capture, and this may result in unnecessary restrictions on the design that reduce the layout density or interfere with circuit performance. In this article a process model that has been designed to identify process sensitive layout configurations is presented. The model is a spatial filter constructed to select the diffraction components that are most sensitive to focus variation. This defocus model then may be applied to a layout pattern to find features that suffer with lithography focus variation. In addition, the technique may be employed once the optical components of a manufacturing process have been developed. Current results show a good correlation between patterns highlighted using the defocus filter and patterns which will be sensitive to process variations during simulated manufacturing. It is believed that this methodology integrated into physical verification techniques will help to identify yield-limiting layout configurations.
Fabrication of a Si∕SiO2 multiple-quantum-well light emitting diode using remote plasma enhanced chemical vapor deposition
Authors: Rölver R. , Brüninghoff S. , Först M. , Spangenberg B. , Kurz H.
Published: January 2006

Photoluminescence (PL) and electroluminescence (EL) measurements are performed on Si∕SiO2 multiple quantum wells fabricated by using a combination of remote plasma enhanced chemical vapor deposition (RPECVD) and rapid thermal annealing (RTA). A significant enhancement of light emission is observed from nanocrystalline Si wells embedded in a SiO2 matrix. The enhancement depends critically on additional annealing processes carried out after the RPECVD deposition.
Magnetoplasmons in a pair of armchair carbon nanotubes
Authors: Lee C. H. , Chiu C. W. , Shyu F. L. , Lin M. F.
Published: January 2006

The low-frequency magnetoelectronic excitations in a pair of armchair carbon nanotubes are studied within the self-consistent-field approach. The intertube Coulomb interactions would induce the coherent and incoherent plasmon modes. Their existence, intensity, frequency, and group velocity are investigated in detail. They are dominated by the transferred momentum, the intertube distance, the magnitude, and the direction of the magnetic field.
Co-gas impact of B2H6 plasma diluted with helium on the plasma doping process in a pulsed glow-discharge system
Authors: Qin Shu , McTeer Allen , Hu Y. Jeff
Published: January 2006

It has been reported that helium dilution of B2H6 in the plasma doping (PLAD) process can be used to control and minimize deposition phenomenon. In this article we quantify the impact of such dilution on boron doping and deposition under PLAD conditions appropriate for ultrashallow junction formation. The sheet resistance (RS) of the implanted wafers remains nearly constant when B2H6 is diluted with He up to 95%, although the retained B dose is reduced. Secondary ion mass spectroscopy profiles indicate that B profiles are deeper for higher dilution than for lower dilution due to less B deposition. The deeper B profiles contribute to a higher activation fraction during annealing due to the B solid solubility limit. This higher activation compensates for the reduction of the retained B dose. The plasma doping process of a pulsed glow-discharge system by using B2H6 diluted with 95% provides optimal conditions for minimizing deposition. This results in a higher doping rate and then higher throughput.
Self-assembled tungsten nanocrystals in high-k dielectric for nonvolatile memory application
Authors: Samanta S. K. , Tan Zerlinda Y. L. , Yoo Won Jong , Samudra Ganesh , Lee Sungjoo , Bera L. K. , Balasubramanian N.
Published: January 2006

Discrete midgap tungsten nanocrystals (W-NCs) embedded in atomic layer deposited hafnium aluminate (HfAlO) film were fabricated by a self-assembly method using sputtering followed by rapid thermal annealing and integrated into transistors for nonvolatile memory application. Transmission electron microscopy and single electron diffraction analysis revealed the formation of crystalline W-NCs (∼5nm) embedded in an amorphous HfAlO matrix. Effects of deposition of thin Al2O3 on the formation of W-NCs were investigated. Al2O3 was found to be effective to retain the amorphous property of the underlying HfAlO, assisting to form uniformly distributed and small W-NCs. Electrical characterization of the Si∕HfAlO∕W-NCs∕HfAlO structure based memory device showed that clear memory effects (1.8 V memory window at operating bias of 7 V) and good retention properties (50mV∕dec threshold voltage decay rate) originate from the charge storage of electrons in W-NDs and deep quantum well of W-NDs embedded in the HfAlO+Al2O3 high-k structure.
Tip characterization and surface reconstruction of complex structures with critical dimension atomic force microscopy
Authors: Dahlen G. , Osborn M. , Okulan N. , Foreman W. , Chand A. , Foucher J.
Published: January 2006

This paper presents the first known image reconstruction of complex probe tip shapes and the removal of those shapes from reentrant topologies that are encountered in critical dimension (CD) measurements. Algorithm improvements are described that enable reentrant image reconstruction. In addition, a solution is presented which eliminates image artifacts that result from noise when using Legendre transform or “slope-matching” reconstruction techniques. The new methods are compared to existing technology and demonstrated on reentrant features. Although demonstrated with two-dimensional profiles, the methods are readily extendable to three-dimensional morphologies. Tip wear effects on CD measurement are investigated and compared with the previous state-of-the-art method (“tip width subtraction”) and fully reconstructed images, clearly showing superior measurement stability for the image reconstruction method. Finally, CD measurements derived from reconstructed images are compared directly with Hitachi S4000 and S5000 cross-section SEM (X-SEM) data. The results show a close match between the SEM and CD AFM data.
Study of the buffer-layer and annealing-temperature impact on fabrication of polycrystalline Fe3O4 film for the application of spintronic devices
Authors: Tang Xiao-Li , Zhang Huai-Wu , Su Hua , Zhong Zhi-Yong
Published: January 2006

Polycrystalline Fe3O4 film grown directly on a Si(100) substrate and on a tantalum (Ta) buffer layer have been prepared by direct current (dc) magnetron-reactive sputtering and vacuum annealing under an infrared-lamp furnace system. The Fe3O4 quality was examined by x-ray diffraction (XRD). The results showed that the polycrystalline Fe3O4 films fabricated on a Ta buffer layer were better than directly sputtering the film on a Si substrate after annealing. The annealing temperatures were also investigated carefully. The optimum annealing temperature was found at 300°C. The negative magnetoresistance was tested in polycrystalline Fe3O4, and showed a very weak saturation trend in the magnetic field up to 400Oe.
Effect of a thin W interlayer on the thermal stability and electrical characteristics of NiSi film
Authors: Huang Wei , Zhang Li-Chun , Gao Yu-Zhi , Jin Han-Yan , Ning Bao-Jun , Zhang Guang-Qin
Published: January 2006

A silicide method was for the first time studied to improve the thermal stability of nickel monosilicide by adding a thin W interlayer within the nickel film. The results show that after rapid thermal annealing (RTA) at temperatures ranging from 650°Cto800°C, the sheet resistance of formed Ni(W)Si samples was lower than that of nickel monosilicide without the interlayer. X-ray diffraction (XRD) and raman spectra results both reveal that only the NiSi phase exists in these samples, but the high resistance NiSi2 phase does not. According to the Gibbs free energy theory, the incorporation of a 7.3 atomic ratio of the W element in the ternary silicide can delay the appearance of the high resistivity NiSi2 phase, and thus enhance the thermal stability of the NiSi film. Fabricated Ni(W)Si∕Si Schottky barrier diodes displayed good quality, with the barrier height being located generally between 0.64eV and 0.66eV and the ideality factor approaching unity. This further shows that the presence of the W interlayer in nickel silicide is effective in promoting the thermal stability and electrical characteristics of nickel monosilicide.
Spatially selective immobilization of ferritin using solid–solution interfacial interactions
Authors: Manning Edward , Yau Siu-Tung
Published: January 2006

Spatially selective immobilization of ferritin, an iron-storage protein, on a silicon surface using a Si–SiO2 template is demonstrated. The material-specific immobilization of the protein is achieved by controlling physical forces at the solution–solid interface between a ferritin solution and the template. The electrostatic interaction and hydrophobic interaction between ferritin molecules and the two kinds of materials of the template can be tuned to achieve adsorption of ferritin only on Si. This method was used to generate spatially confined assemblies of ferritin on the nanoscale and on the micron scale.
Maximum achievable aspect ratio in deep reactive ion etching of silicon due to aspect ratio dependent transport and the microloading effect
Authors: Yeom Junghoon , Wu Yan , Selby John C. , Shannon Mark A.
Published: January 2006

When etching high-aspect-ratio silicon features using deep reactive ion etching (DRIE), researchers find that there is a maximum achievable aspect ratio, which we define as the critical aspect ratio, of an etched silicon trench using a DRIE process. At this critical aspect ratio, the apparent etch rate (defined as the total depth etched divided by the total elapsed time) no longer monotonically decreases as the aspect ratio increases, but abruptly drops to zero. In this paper, we propose a theoretical model to predict the critical aspect ratio and reveal its causal mechanism. The model considers aspect ratio dependent transport mechanisms specific to each of the reactant species in the three subprocesses of a time-multiplexed etch cycle: deposition of a fluorocarbon passivation layer, etching of the fluorocarbon polymer at the bottom of the trench, and the subsequent etching of the underlying silicon. The model predicts that the critical aspect ratio is defined by the aspect ratio at which the polymer etch rate equals the product of the deposition rate and the set time ratio between the deposition and etching phases for the time-multiplexed process. Several DRIE experiments were performed to qualitatively validate the model. Both model simulations and experimental results demonstrate that the magnitude of the critical aspect ratio primarily depends on (i) the relative flux of neutral species at the trench opening, i.e., the microloading effect, and (ii) aspect ratio dependent transport of ions during the polymer etching subprocess of a DRIE cycle.
Direct patterning of spin-on glass with 157nm lithography: Application to nanoscale crystal growth
Authors: Bloomstein T. M. , Juodawlkis P. W. , Swint R. B. , Cann S. G. , Deneault S. J. , Efremow N. N. , Hardy D. E. , Marchant M. F. , Napoleone A. , Oakley D. C. , Rothschild M.
Published: January 2006

Selective area homoepitaxial growth of InP in 50nm scale dense features has been demonstrated using hydrogen silsesquioxane (HSQ) as the growth mask. The HSQ growth mask was patterned lithographically using high resolution interference lithography at 157nm. Lithographic process conditions were optimized, including postapplication bake temperature, developer normality, and oxygen levels during exposure.
Narrow cone emission from negative electron affinity photocathodes
Authors: Liu Zhi , Sun Yun , Pianetta P. , Pease R. F. W.
Published: January 2006

The need for high brightness (e.g., 106Acm−2str−1 at 10keV) electron sources is well established. Negative electron affinity (NEA) semiconductor structures have been studied for this application for several years. It has been argued that one advantage of these materials, particularly GaAs, is that the low effective mass, m*, of electrons in the semiconductor would lead to a narrow cone of emission, and hence increased brightness for a given current density, as a result of Snell’s Law. However this advantage would only apply if the electrons were emitted directly from the Γ-valley (with low m*) rather than indirectly, that is via scattering into the L-valley. We present here a direct experimental confirmation of this narrow cone of emission (semiangle 15°) and describe a quantitative model to account for the results. In photocathodes based on group III-nitride materials, the cone is predicted to be about twice as wide because of the larger values of m*.
Growth and simulation of high-aspect ratio nanopillars by primary and secondary electron-induced deposition
Authors: Fowlkes J. D. , Randolph S. J. , Rack P. D.
Published: January 2006

While several studies have suggested that secondary electrons dominate electron beam induced deposition (EBID), we demonstrate that primary electrons (PE’s) contribute significantly to the deposition for nanoscale EBID over the electron beam energy range (500–20keV). High-aspect ratio pillar growth is a signature of EBID; W nanopillar growth on SiO2 substrate yielded a growth rate of 6nms−1 and a nanopillar aspect ratio of ∼50. A simple integration of the primary, secondary, and backscattered electron distributions versus a dissociation cross section for WF6 suggests that all three electron species should contribute to the total volume of the deposited nanopillar, contrary to reports that suggest that secondary electrons dominate the process. A three-dimensional, Monte Carlo simulation including time correlated gas dynamics and species specific deposition was developed to help elucidate which of the relevant electron species, primary (PE’s), secondary (SE’s), and/or backscattered electrons (BSE’s), induce the dissociation of precursor gas and lead to nanopillar growth. PE’s and secondary electrons produced from the incident beam (SEI’s) were found to induce the vertical nanopillar growth component relative to secondary electrons induced from backscattered electrons (SEII’s) and BSE’s.
Negative charging-up contrast formation of multilayered structures with a nonpenetrating electron beam in scanning-electron microscope
Authors: Miyoshi Motosuke , Ura Katsumi
Published: January 2006

In this article, we explain the contrast-formation mechanisms of the scanning-electron microscope for insulating samples under a nonpenetrating irradiation condition. Our fundamental point is that the detected secondary-electron signal current is only modified by the surface potential distribution. We propose a semiempirical model to explain the image contrast caused by excess negative-charge buildup on the surface of the insulating samples. The model treats the redistribution of secondary electrons and the contribution of tertiary electrons. The image-contrast formation mechanism of two typical examples is explained.
Predicting the dynamic response of an extreme ultraviolet reticle during exposure scanning
Authors: Dicks G. , Mikkelson A. , Engelstad R. , Lovell E.
Published: January 2006

Extreme ultraviolet (EUV) masks are expected to experience up to 6g’s of acceleration and achieve speeds as high as 500mm∕s while mounted in the exposure tool. Therefore, it is critical that the mounting technique employed to hold the mask in position prevents the mask from slipping under these conditions. An electrostatic pin chuck must generate adequate pressure between the mask and chuck, as well as a sufficient amount of friction. To ensure the success of such a mount design, three-dimensional finite element (FE) models have been created to predict the conditions necessary to prevent mask slippage during exposure scanning. The FE modeling is used to predict the influence of the initial substrate backside surface shape on mask flatness when mounted in the chuck, as well as the effects of friction on the relative displacement between the reticle and chuck. Simulation results indicate that for typical EUV mask substrates, coefficients of friction greater than 0.2 are necessary to prevent bulk displacement of the mask during the acceleration duty cycle. Larger coefficients may be required to limit local in-plane displacements, depending upon the initial backside shape.
Electron-electron interaction induced beam displacement in a multiple electron beam system
Authors: Yu Ming L. , Coyle Steven T. , DeVore William , Shamoun Bassam
Published: January 2006

We have studied electron-electron (e-e) interaction induced beam displacement in multiple electron beam systems both experimentally and using trajectory simulation. A prototype 32-beam lithography system was used to record the beam displacements on chrome mask plates and the latter were directly measured by electron microscopy. Both experimental data and simulation results of demagnifying columns were consistent with a demagnification of the electron beam array with increasing current. While the simulation matched qualitatively the experimental data well, it predicted a smaller effect than measured. The overall demagnification was underestimated by 20%–30%. In an attempt to understand the underlying physical reason, we used a phenomenological model for the e-e induced beam displacement to fit the acquired data. The analysis suggested that the trajectory simulation underestimated the defocusing lens effect of the interacting electrons by about 1.5. The parametric expression derived from this model may be used to correct for global space charge effects during multi-electron beam lithography.
Proximity effect correction using blur map in electron projection lithography
Authors: Yamashita Hiroshi , Yamamoto Jiro , Koba Fumihiro , Arimoto Hiroshi
Published: January 2006

We demonstrate and evaluate proximity effect correction using blur map at a compromised focal plane in electron projection lithography. Critical dimension (CD) accuracy was improved from 12to5nm for 100nm L∕S pattern with 34% pattern area density by using blur maps calculated by space charge effect correction (SCEC) program, which is provided with the electron beam stepper NSR-EB1A by Nikon. CD error due to the SCEC was estimated to be 4nm, corresponding to 6nm in terms of blur for the resist process; this is substantiated by comparing the calculated and measured blurs that ranged from 6.3to−4.3nm.
Passivation effects on the stability of pentacene thin-film transistors with SnO2 prepared by ion-beam-assisted deposition
Authors: Kim Woo Jin , Koo Won Hoe , Jo Sung Jin , Kim Chang Su , Baik Hong Koo , Lee Jiyoul , Im Seongil
Published: January 2006

The long-term stability of pentacene thin-film transistors (TFTs) encapsulated with a transparent SnO2 thin-film prepared by ion-beam-assisted deposition (IBAD) was investigated. When a buffer layer of 100-nm SnO2 film had been thermally deposited to reduce ion-induced damage prior to the IBAD process, our encapsulated organic thin-film transistors (OTFTs) showed somewhat degraded field-effect mobility of 0.5cm2∕V that was initially 0.62cm2∕Vs, while the OTFTs without a buffer layer showed a 60% reduction in field-effect mobility after the IBAD process. However, surprisingly, the mobility was sustained up to one month and then gradually degraded down to 0.35cm2∕Vs, which was still three times higher than that of the OTFT without any encapsulation layer after 100 days in air. The encapsulated OTFTs also exhibited superior on/off current ratio of over 105 to that of the unprotected devices (∼104), which was reduced from ∼106 before aging. Therefore, the enhanced long-term stability of our encapsulated OTFTs should be attributed to good protection of permeation against H2O into the devices with the IBAD SnO2 thin film, which was identified as having a dense amorphous microstructure with lots of OH groups. Passivation effects on the electrical properties of OTFTs are discussed in terms of the physical and chemical properties of the barrier films.
Electromagnetic phenomena in advanced photomasks
Authors: Schellenberg F. M. , Adam K. , Matteo J. , Hesselink L.
Published: January 2006

The adoption of resolution enhancement techniques (RET) for subwavelength lithography relies on performing accurate simulation of mask effects. Although topography effects have been successfully used in RET flows, the impact of electromagnetic effects such as surface plasmons tend to be ignored. It is known, however, from the performance of “C-shaped” apertures that extraordinary transmission and opacity can be achieved using these electromagnetic effects. We have examined simulations for representative 45nm features using both conventional and novel finite difference time domain simulators. When the mask material is assumed to be conducting chromium, we found that electromagnetic effects appear to be significant and highly dependent on polarization. This may place additional constraints on the specification of mask material composition for these integrated circuit generations.
Spectral analysis of line-edge roughness in polyphenol EB-resists and its impact on transistor performance
Authors: Yamaguchi Atsuko , Fukuda Hiroshi , Arai Tadashi , Yamamoto Jiro , Hirayama Taku , Shiono Daiju , Hada Hideo , Onodera Junichi
Published: January 2006

Resists using polyphenol resin are introduced to reduce line-edge roughness (LER), and the spatial frequency characteristics of LER are evaluated. It is found that the long-period components of LER are suppressed in our low molecular-weight polyphenol resists. Device simulation using the measured LER shows that our polyphenol-based resist can drastically reduce the number of low-threshold-voltage (Vth) transistors compared with a conventional resist due to reduced long-period LER. Because LER impact is more serious as the transistor width shrinks, our results suggest that the use of the polyphenol-type resist will be more effective in improving device performance in future lithography process. In addition, it is shown that spectral analysis is a powerful tool for LER evaluation, especially from the viewpoint of device performance estimation.
Hybrid exposure strategy: Combining e-beam direct writing with optical lithography for magnetic recording heads
Authors: Yang XiaoMin
Published: January 2006

Hybrid exposure strategies have been implemented with commercially available chemically amplified resists for the fabrication of magnetic recording heads. This approach relies on splitting the pattern into high-resolution and low-resolution components at the same resist level. Two critical features of the thin-film head (TFH) device (write top pole and read sensor widths) are defined by e-beam direct writing for the high-resolution patterning, and all other, relatively large features, are patterned with optical lithography for high throughput. In this article we will present the results from the fabrication of sub-50nm magnetic write and read components with this hybrid exposure process. Key lessons from many aspects of the process development effort will be discussed in relation to TFH fabrication, including dual sensitive resist selection, exposure sequence, postexposure delay effect, e-beam process challenges, and overlay alignment issue. We demonstrate the capability of printing top pole structures with pole widths of sub-40nm in a 0.35-μm-thick resist film (aspect ratio>8:1), and electroplated top pole structures of 40nm with CoFe.
Effects of bonding materials in screen-printing paste on the field-emission properties of carbon nanotube cathodes
Authors: Shin Heo-Young , Chung Won-Sub , Kim Kwang Ho , Cho Young-Rae , Shin Byoung-Chul
Published: January 2006

The effects of bonding materials in screen-printing paste on field-emission properties were investigated with respect to high-efficient carbon nanotube (CNT) cathodes. The materials used to bond the CNTs to the cathode were composed of an insulating glass frit and a conducting Ag paste. The dependence of the electrical conductivity of the CNT paste, bonding material, and CNT ink on the field-enhancement factor was investigated using the Fowler–Nordheim equation. The emission current from the CNT cathode as the result of an electron tunneling effect was increased with increasing ratio of the dielectric glass-frit fraction in the CNT paste. The larger emission current of CNT cathode containing insulating-bonding materials can be attributed to a combination of the increased effective height of the CNTs, which protrude over the film in the cathode, and an increased field-enhancement factor.
Characterization of bulk GaN rectifiers for hydrogen gas sensing
Authors: Voss Lars , Gila B. P. , Pearton S. J. , Wang Hung-Ta , Ren F.
Published: January 2006

Pd and Pt Schottky diodes were fabricated on free-standing 2-in.-diameter GaN substrates prepared by a combination of hydride vapor phase epitaxy of ∼350μm onto sapphire, substrate removal and subsequent growth of 3μm of epi GaN by metalorganic chemical vapor deposition. Vertical diodes with Ti∕Al∕Pt∕Au back contacts annealed at 850°C for 30s showed excellent rectification with an on/off ratio of ∼100 at 1.5V∕−10V. Both forward turn-on and reverse breakdown voltages showed negative temperature coefficients. Pd and Pt diodes showed detection of 10ppm H2 in N2 at 25°C, with fast (<10s) recovery times upon removal of hydrogen from the measurement ambient. The Pt showed higher detection sensitivity than Pd. Detection of C2H4 and C2H6 required much higher temperatures (∼450°C) and concentrations (10%) of the gases in N2 than hydrogen detection.
Sn
O
2
lithographic processing for nanopatterned gas sensors
Authors: Candeloro P. , Comini E. , Baratto C. , Faglia G. , Sberveglieri G. , Kumar R. , Carpentiero A. , Fabrizio E. Di
Published: January 2006

Tin dioxide (SnO2) is widely used as sensing material in metal-oxides gas sensors. In this work we present two lithographic approaches for SnO2 patterning, an additive process and a subtractive one. In the first case patterns of SnO2 nanowires are successfully fabricated and exploited as sensing element in working devices; responses to several testing gases are satisfactorily improved with respect to continuous film devices. Regarding the subtractive process, we present reactive ion etching of SnO2 based on CF4∕H2 gas mixture. Dependence of etch rate upon H2 concentration and effects due to Ar additions to plasma are investigated; results are discussed and a possible etching reaction is proposed, but further developments are required to increase the etch rate.
Development, installation, and performance of the x-ray stepper JSAL 5C
Authors: Leonard Q. , Malueg D. , Wallace J. , Taylor J. W. , Dhuey S. , Cerrina F. , Boerger B. , Selzer R. , Yu M. , Ma Y. , Myers K. , Trybendis M. , Moon E. , Smith H. I.
Published: January 2006

We show the first results from a newly-operation advanced x-ray stepper, and describe an improved type of x-ray mask for use on it. The Mod 5C is the newest x-ray stepper developed by JMAR (JSAL Nanolithography). It is configured for installation at the Center for NanoTechnology (CNTech) on a synchrotron radiation port of the Aladdin storage ring. The alignment system is based on a new IBBI detection system with demonstrated subnanometer resolution. For this system, three microscopes are used for detecting the misalignment between wafer and mask marks with the error signal fed back in the mask positioning stage with the mask locked to the wafer stage through the use of a high-resolution laser interferometer. Both field-by-field and global alignment techniques are possible, and multiple wafer sizes can be used with a NIST format mask held in a kinematic mount, with a gap setting capable of adjustment between 2 and 50microns. A novel beam scanning system was installed to deliver a uniform exposure over a field of 35×35mm2 field. The high power from the storage ring allows exposure times in chemically amplified resists of 5–10s for the CNTech-designed beamline; shorter exposure times could be achieved with a refocusing beamline, and the stepper can be configured for an x-ray point source. To achieve sub-35nm resolution requires very small gaps. A new type of mask had to be developed, on the basis of the mesa mask originally developed at MIT. A very high flatness is required to maintain a parallel mask-wafer exposure environment. Currently, for low cost and easy manufacturing, we employ gold-plated absorber masks with a silicon nitride membrane. From the initial exposures, the resolution achieved is below 50nm with exposure conditions described. The issues of the resolution of the exposure tool are addressed and compared to the outcomes from detailed modeling.
Polymer time constants during low temperature nanoimprint lithography
Authors: Scheer H.-C. , Bogdanski N. , Wissen M. , Konishi T. , Hirai Y.
Published: January 2006

We investigate low temperature nanoimprint into polymers, where adequate pressure choice helps to increase the imprint velocity of larger patterns und thus decreases pattern size effects by reduction of the effective viscosity. In order to make use of shear rate effects, the imprint has to be performed within the viscoelastic plateau region and not in the viscous flow regime of the polymer. Therefore elastic effects play an important role and may lead to shape recovery of the polymer after imprint. We address the counter play of elastic effects and viscous flow by conducting experiments very near to the glass transition temperature. The elastic behavior at the beginning of the imprint is simulated for different pattern sizes and thus different aspect ratios of the stamp. The investigations show, that a reduction of temperature has to be compensated by an increased imprint time and this time increase has to consider the reduction of viscosity on the one hand and the extension of the polymer flow time constants on the other hand. The experiments are suitable to define a lower limit for utilization of shear thinning effects.
Sealed three-dimensional nanochannels
Authors: Reano R. M. , Pang S. W.
Published: January 2006

A technique to create sealed three-dimensional nanochannel networks is developed using sequentially stacked thermal nanoimprint lithography on planarized self-supporting dielectric sealing material over polymer sacrificial layers. Void-free plasma enhanced chemical vapor deposited SiO2 encloses and seals nanochannels that are formed upon the removal of the sacrificial polymer. Planarization of the SiO2 surface allows the utilization of the vertical dimension to sequentially apply nanoimprint lithography for the formation of multiple-level nanochannel networks. Removal of the sacrificial polymer is performed with a high-power and high-pressure O2 plasma. Wet chemical processes using common solvents are found to be ineffective in removing the sacrificial polymer. Two level nanochannels with cross-sectional dimensions of 300nm×200nm and lengths of 65μm that are aligned offset from one another and aligned on top of one another are demonstrated.