bluuebunny/crossref_metadata_2025 huggingface dataset:
Automatic Fairing of Two-Parameter Rational B-Spline Motion
Authors: Purwar Anurag , Chi Xiaoyi , Ge Qiaode Jeffrey
Published: December 2007

This paper deals with the problem of automatic fairing (or fine-tuning) of two-parameter rational B-spline spherical and spatial motions. The results presented in this paper extend the previous results on fine-tuning of one-parameter rational B-spline motions. A dual quaternion representation of spatial displacements is employed and the problem of fairing two-parameter motions is studied as a surface fairing problem in the space of dual quaternions. By combining surface fairing techniques from the field of computer aided geometric design with the computer aided synthesis of freeform rational motions, smoother (C3 continuous) two-parameter rational B-spline motions are generated. Several examples are presented to illustrate the effectiveness of the proposed method. Techniques for motion smoothing have important applications in the Cartesian motion planning, camera motion synthesis, and spatial navigation in virtual reality systems. In particular, smoother two-parameter freeform motions have applications in the development of a kinematic based approach to geometric shape design and in five-axis NC tool path planning.
Review of Contemporary Approaches for Constraint Enforcement in Multibody Systems
Authors: Bauchau Olivier A. , Laulusa André
Published: December 2007

A hallmark of multibody dynamics is that most formulations involve a number of constraints. Typically, when redundant generalized coordinates are used, equations of motion are simpler to derive but constraint equations are present. Approaches to dealing with high index differential algebraic equations, based on index reduction techniques, are reviewed and discussed. Constraint violation stabilization techniques that have been developed to control constraint drift are also reviewed. These techniques are used in conjunction with algorithms that do not exactly enforce the constraints. Control theory forms the basis for a number of these methods. Penalty based techniques have also been developed, but the augmented Lagrangian formulation presents a more solid theoretical foundation. In contrast to constraint violation stabilization techniques, constraint violation elimination techniques enforce exact satisfaction of the constraints, at least to machine accuracy. Finally, as the finite element method has gained popularity for the solution of multibody systems, new techniques for the enforcement of constraints have been developed in that framework. The goal of this paper is to review the features of these methods, assess their accuracy and efficiency, underline the relationship among the methods, and recommend approaches that seem to perform better than others.
V-groove plasmonic waveguides fabricated by nanoimprint lithography
Authors: Fernandez-Cuesta Irene , Nielsen Rasmus Bundgaard , Boltasseva Alexandra , Borrisé Xavier , Pérez-Murano Francesc , Kristensen Anders
Published: December 2007

Propagation of channel plasmon-polariton modes in the bottom of a metal V groove has been recently demonstrated. It provides a unique way of manipulating light at nanometer length scale. In this work, we present a method based on nanoimprint lithography that allows parallel fabrication of integrated optical devices composed of metal V grooves. This method represents an improvement with respect to previous works, where the V grooves were fabricated by direct milling of the metal, in terms of robustness and throughput.
Evaluation of hybrid lithography and mix and match scenarios for electron beam direct write applications
Authors: Hohle C. , Arndt C. , Choi K.-H. , Kretz J. , Lutz T. , Thrum F. , Keil K.
Published: December 2007

An overview about process window evaluation and characteristic features of photoresists for e-beam/optical hybrid lithography as well as mix and match applications and implementation into new integration concepts is given. For that, several commercially available deep ultraviolet (DUV) (248nm), ArF (193nm), and e-beam resist samples from various suppliers were exposed at Qimonda’s dynamic random access memory pilot line environment using both e-beam and optical exposure. Due to the diverse, sometimes contradictory requirements and properties of the different material platforms (e.g., resolution, sensitivity, vacuum stability, etch resistance, etc.), a unique material for true hybrid lithography is difficult to find. At least the tested DUV resist is limited applicable for e-beam exposures putting up with low e-beam sensitivity.
Photolithography using an optical microscope
Authors: Gonski Ron , Melngailis John
Published: December 2007

The authors propose and demonstrate how to use an ordinary optical microscope as a flexible optical lithography tool. Until the advent of digital cameras, most high power optical microscopes had a vertical cone shaped fixture with a Polaroid film holder to record optical micrographs on the film. For conversion to lithography, the Polaroid film holder is simply removed and a vu-graph transparency, which serves as a mask, is substituted in the plane of the film. The transparency has the desired pattern printed on it by a laser printer or a copier. Ideally, the transparency has to be backlighted by a converging light source such that (ignoring diffraction) a pinhole anywhere in the transparency illuminates the entire lens at the base of the cone shaped fixture. The authors used a 11.4cm diameter, 12.7cm focal length Fresnel lens and a fiber light to generate the appropriately converging mask illumination. With the highest magnification, 100× lens the image on the mask was demagnified approximately by 700× on the sample. With this lens, the authors could expose lines of slightly less than 1μm width.
Membrane folding by helium ion implantation for three-dimensional device fabrication
Authors: Arora William J. , Sijbrandij Sybren , Stern Lewis , Notte John , Smith Henry I. , Barbastathis George
Published: December 2007

The authors demonstrate that silicon nitride membranes can be folded out of plane into three-dimensional structures by helium ion implantation. The folds have a radius of 1μm and can be directed both up or down by varying implant energy.
Hydrogen plasma-enhanced atomic layer deposition of copper thin films
Authors: Wu Liqi , Eisenbraun Eric
Published: December 2007

The growth of plasma-enhanced atomic layer deposition (PEALD) grown copper films appropriate for nanoscale electronics applications is reported. Self-limiting PEALD copper growth behavior, employing copper(II) acetylacetonate and atomic hydrogen as reactants, was observed. Deposition of continuous layers as thin as 10 nm was achieved on TaN, Ru, and SiO2 substrates in a temperature range between 85 and 135 °C. A copper purity greater than 95 at. %, as measured by Auger electron spectroscopy, was observed. For a 30 nm thick film, PEALD copper resistivity was 5.3 μΩ cm on TaN and 8.8 μΩ cm on Ru. Conformal depositions have been achieved over high aspect ratio (∼5:1) structures.
Advanced resist testing using the SEMATECH Berkeley extreme ultraviolet microfield exposure tool
Authors: Naulleau Patrick P. , Anderson Christopher N. , Dean Kim , Denham Paul , Goldberg Kenneth A. , Hoef Brian , Niakoula Dimitra , La Fontaine Bruno , Wallow Tom
Published: December 2007

Recent upgrades made to the SEMATECH Berkeley microfield exposure tool are summarized and some of the latest resist characterization results are presented. Tool illumination uniformity covering the full 200×600μm2 wafer-side field of view is demonstrated and intrawafer focus control of 1.8nm is shown. Printing results demonstrate chemically amplified resist resolution of 28nm dense and 22.7nm semi-isolated. Moreover, contact printing results show that shot noise is not a dominant issue in current 35nm contact printing performance.
Study of process contributions to total overlay error budget for sub-60-nm memory devices
Authors: Shin Jangho , Kang Hyunjae , Choi SungWon , Woo Seoukhoon , Kim Hochul , Lee SukJoo , Lee Junghyeon , Kang Chang-Jin
Published: December 2007

According to the 2006 International Technology Roadmap for Semiconductors, the overlay budget of 60nm memory devices is 11nm. To meet such a tight requirement, the total overlay error budget should be controlled carefully. There are many ways to analyze overlay budget; here, however, a simple but accurate methodology is introduced. In this study, total overlay error budget consists of four major contribution categories: scanner, process, metrology, and mask contributions. Scanner contributions are evaluated by measuring machine-to-machine overlay errors in the conventional way. Process contributions are estimated by inverse reactive-ion etch (RIE) lag and chemical mechanical polishing (CMP) erosion. Metrology contributions are evaluated by overlay metrology tools. Finally, mask contributions represent mask-to-mask misregistration. By applying this methodology to 60nm memory devices, it turns out that process contributions are more than 30% of the total overlay error budget for a contact layer. In this article, the optimum process window is investigated so that process effects can be minimized.
Dissolution characteristics and reaction kinetics of molecular resists for extreme-ultraviolet lithography
Authors: Toriumi Minoru , Santillan Julius , Itani Toshiro , Kozawa Takahiro , Tagawa Seiichi
Published: December 2007

Molecular resist of polyphenol was evaluated as an extreme-ultraviolet resist compared with a polymer resist of p(tert-butoxycarbonyl-hydroxystyrene). The molecular resist shows higher sensitivity than the polymer resist. The dissolution behavior was studied by quartz crystal microbalance method. The molecular resist shows thinner swelling layer than the polymer resist. The deprotection mechanism was approximated by simple reaction equations, and Fourier-transform infrared spectra were interpreted to give the products of a quantum yield and a deprotection rate constant as 6.2×10−8 and 6.0×10−8cm3∕moleculess for molecular and polymer resists. Both deprotection efficiencies are almost same. The higher sensitivity of the molecular resist is due to the dissolution behavior not the reaction mechanism.
Estimation of diffusion lengths of acid and quencher in chemically amplified resist on the basis of extreme ultraviolet exposure results
Authors: Tanaka Yuusuke , Kikuchi Yukiko , Goo DooHoon , Oizumi Hiroaki , Nishiyama Iwao
Published: December 2007

Line- and space-type patterns with a half pitch (hp) of 32–65nm were printed with the extreme ultraviolet microexposure tool at the Lawrence Berkeley National Laboratory using the positive-tone chemically amplified resist MET-1K, and the diffusion lengths of the acid and quencher in the resist were estimated by fitting the calculated shapes of resist patterns to the experimental results. Simulations of the resist process employed an acid/quencher mutual-diffusion model. It was found that not only acid diffusion but also quencher diffusion had a considerable effect on the fidelity of hp 32–45nm patterns. When the diffusion lengths were assumed to be 40nm for the acid and 30nm for the quencher, the calculated shapes of resist patterns agreed well with the experimental results for both line- and space-type patterns. If quencher diffusion were not considered, the acid diffusion length would be underestimated, which would make it difficult to explain the shapes of various types of resist patterns using the same acid diffusion length. In order to fabricate various types of hp 32nm patterns, the diffusion lengths of both the acid and the quencher should be less than 10nm.
Resolution in focused electron- and ion-beam induced processing
Authors: Utke Ivo , Friedli Vinzenz , Purrucker Martin , Michler Johann
Published: December 2007

The key physical processes governing resolution of gas-assisted focused electron-beam and ion-beam induced deposition and etching are analyzed via an adsorption rate model. The authors quantify how the balance of molecule depletion and replenishment determines the resolution inside the locally irradiated area. Scaling laws are derived relating the resolution of the deposits to molecule dissociation, surface diffusion, adsorption, and desorption. Supporting results from deposition experiments with a copper metalorganic precursor gas on a silicon substrate are presented and discussed.
Development of chemical-mechanical polished high-resolution zone plates
Authors: Rehbein Stefan , Guttmann Peter , Werner Stephan , Schneider Gerd
Published: December 2007

State-of-the-art zone plates for soft and hard x rays are commonly fabricated in nickel or gold by electroplating. The most critical fabrication step is the controlled filling of the plating mold, which directly affects the performance of the diffractive optics. One problem is that the electroplating rate depends on the actual zone width resulting in an inhomogeneous height profile across the optics. Another problem is the measurement of the actual zone height during the electroplating process to fill exactly the plating mold. In practice, underplating the mold results in a low diffraction efficiency of the zone plate. Overplating yields in unemployable optics. In this article, the authors apply a chemical-mechanical polishing (CMP) process to overcome the described problems. In the new processing step, the zone plate is planarized after overplating. The authors demonstrate for the first time that nickel zone plates with an outermost zone width down to 25 nm can be polished by applying a CMP process. This new step leads to a much better reproducibility in zone plate fabrication and their performance. In addition, to overcome the technical limit of the current aspect ratios of zone plates the authors propose to superimpose polished zone plate layers on top of each other. The authors assume that the introduced CMP process paves the way toward the development of future volume zone plates with ultrahigh aspect ratios for soft and hard x-ray applications.
Electrical properties and deep traps in ZnO films grown by molecular beam epitaxy
Authors: Polyakov A. Y. , Smirnov N. B. , Belogorokhov A. I. , Govorkov A. V. , Kozhukhova E. A. , Osinsky A. V. , Xie J. Q. , Hertog B. , Pearton S. J.
Published: December 2007

Capacitance-voltage (C-V), capacitance-frequency (C-f), admittance spectroscopy, deep trap spectra, and far infrared reflectance measurements were performed on undoped and N-doped ZnO films deposited on sapphire by molecular beam epitaxy. The results show existence of a heavily doped n+ layer near the interface with the substrate. The presence of these layers explains the large difference between the electron concentrations measured in the films by Hall effect and C-V profiling or calculated from the plasma minimum frequency in reflectance. C-V data obtained at low temperatures show a prominent persistent photocapacitance in the films. Admittance spectra were dominated by electron traps with ionization level EC−0.3eV commonly observed in ZnO crystals grown by all techniques.
Proposed single layer composite film used as high transmission phase shifting masks for the 32, 45, and 65nm technology nodes
Authors: Lai Fu-Der , Huang Jian Long
Published: December 2007

The optical constants of composite films are linearly dependent on their mole fraction. The (Al2O3)x–(TiO2)1−x composite films prepared by using rf unbalanced magnetron sputtering are completely oxidized using an O2∕Ar flow rate ratio of 2.0. By tuning the Al2O3 mole fraction of (Al2O3)x–(TiO2)1−x composite films, the optical constants can be made to meet the optical requirements for a high transmittance attenuated phase shifting mask (HT-AttPSM) blank. It can be seen that the Al2O3 mole fraction in (Al2O3)x–(TiO2)1−x composite films which would best meet the optical requirements of a HT-AttPSM blank in ArF (immersion) lithography is calculated to be between 78% and 86%. In order to obtain a HT-AttPSM blank with an optimized transmittance of 20%, one Al2O3–TiO2 composite film is fabricated. All the films meet the requirements of the adhesion test and surface roughness for HT-AttPSM applications. Therefore, a single layer composite film of Al2O3–TiO2 could be applied to HT-AttPSM blanks, which can be utilized to design fine patterns with dimensions as small as 65, 45, and 32nm.
Critical parameter determination of sonic flow controller diamond microtubes and micronozzles
Authors: Mammana S. S. , Degasperi F. T. , Salvadori M. C. , Sparapani D. C. , Laino M. F. , Rangel R. C. , Teixeira F. S. , Cattani M.
Published: December 2007

In this article, the authors measure throughput of sonic diamond microtubes and micronozzles that can work as passive gas flow controllers and flow meters under choking conditions. The behavior of the outlet pressure through the microdevices using an experimental setup with constant volume and constant temperature was determined in order to obtain the critical throughput, the critical mass flow rate, and the discharge coefficients of the diamond sonic microdevices.
Growth of ZnSe nanowires by pulsed-laser deposition
Authors: Zhang Tinwei , Shen Yiqun , Hu Wei , Sun Jian , Wu Jiada , Ying Zhifeng , Xu Ning
Published: December 2007

Stoichiometric ZnSe nanowires have been grown by pulsed-laser deposition on GaAs (100) substrates coated with gold layers. The gold layer plays a key role as catalyst in the deposition of ZnSe nanowires. The thickness of the gold film greatly affected the density of the ZnSe nanowires synthesized on the substrate. No ZnSe nanowires were synthesized on the bare GaAs (100) substrate. The microstructures and the chemical compositions of the as-synthesized nanowires were investigated by scanning electron microscopy, x-ray diffraction, and Raman spectroscopy. The results reveal that the as-grown thin films consist of ZnSe nanowires with diameters ranging from 20to40nm, and the nanowires appear to be randomly oriented on the Au-coated substrate. The as-grown nanowires were also observed to be elongated along different crystallographic directions.
Progress in extreme ultraviolet interferometric and holographic lithography
Authors: Isoyan A. , Cheng Y.-C. , Jiang F. , Wallace J. , Cerrina F. , Bollepalli S.
Published: December 2007

The Center for Nanotechnology has developed an advanced beamline dedicated to nanopatterning using the radiation from a new undulator on the Aladdin storage ring at the Synchrotron Radiation Center of the University of Wisconsin-Madison. Computer generated holograms and transmission interferometric gratings were fabricated and tested on the new extreme ultraviolet (EUV) exposure system. The authors have developed an accurate model, based on Fresnel-Kirchhoff integral diffraction theory, to analyze performance of real EUV interferometric and holographic lithography systems.
Improving electron beam resist sensitivity by preexposure to deep ultraviolet radiation
Authors: Murali Raghunath , Brown Devin , Martin Kevin P. , Meindl James D.
Published: December 2007

Electron beam lithography, when combined with optical lithography, is a promising approach to obtain good throughput. A bottleneck for this is resist sensitivity and the concomitant shot-noise limit for resolution. It is possible to obtain increased sensitivity without reducing resolution by preexposing electron beam resist to deep ultraviolet radiation before electron beam patterning. Results show that up to a 30% reduction in required dosage is obtained with this method; the associated trade off in dissolution of unexposed areas and critical dimension sensitivity is minimal. Resolution is also maintained and sub-50nm lines with good aspect ratio have been demonstrated.
Viscosity measurement of nanoimprint lithography resists with a rheological nanoindenter
Authors: Svintsov A. A. , Trofimov O. V. , Zaitsev S. I.
Published: December 2007

Considering Navier-Stokes equation, penetration of a tip in viscous film was considered allowing acquisition of viscosity from experimental data. Viscosity of thin (<500nm) films as a function of temperature in the range of 25–200°C was measured with the rheological indenter for thermoplastic polymers and (as a function of annealing temperature and annealing time) for thermocurable polymers with submicron spatial resolution. The approach could be used in design, tailoring, and optimization of soft materials for different applications.
Image contrast slope and line edge roughness of chemically amplified resists for postoptical lithography
Authors: Kozawa Takahiro , Tagawa Seiichi , Santillan Julius Joseph , Toriumi Minoru , Itani Toshiro
Published: December 2007

The reduction of line edge roughness (LER) or linewidth roughness is the most challenging issue associated with the development of resist processes for the next generation lithography. The extent of LER has been reported to correlate with the image contrast slope. Although the postoptical lithography such as electron beam and extreme ultraviolet lithographies can create high contrast images, low-energy electrons degrade image contrasts in these lithographies. The precise prediction of image contrasts requires the incorporation of the effects of low-energy electrons into process simulators. For the reduction of LER, better understanding of LER formation is needed. In this work, the authors proposed a simulation method for the calculation of latent images for postoptical lithographies on the basis of the sensitization mechanisms of chemically amplified resists.
Deposition of carbonaceous structures using focused Au and Si ion-beam-induced chemical vapor deposition methods
Authors: Okada Ryo , Yo Takuma , Yanagisawa Junichi , Matsui Shinji
Published: December 2007

Focused ion-beam-induced chemical vapor deposition (FIB-CVD) using Au or Si ions and phenanthrene as a precursor gas was performed to obtain carbon-related materials containing no Ga elements. It was confirmed that narrow wires were deposited on a substrate by 15 keV Au and 30 keV Si FIB irradiations under the phenanthrene gas atmosphere. The shape of the deposited materials was, however, strongly affected by the FIB scanning speed, which might be subject to the supply of the phenanthrene gas molecules on the surface during the time interval between each FIB scan. The height of the deposited materials using the 15 keV Au FIB was three to eight times higher than that using the 30 keV Si FIB, although the other FIB parameters were almost the same. This might be explained by the difference in the electronic energy loss of those ions in the deposited materials. From Auger electron spectroscopy, the composition of the deposited material using the Au FIB was found to be a carbon-related material with no Ga but Au atoms inside.
Pattern matching, simulation, and metrology of complex layouts fabricated by electron beam lithography
Authors: Tsikrikas N. , Drygiannakis D. , Patsis G. P. , Raptis I. , Gerardino A. , Stavroulakis S. , Voyiatzis E.
Published: December 2007

Validation of design rules taking into account fine details such as line-edge roughness, and full chip layout simulation for design inconsistencies, before actual fabrication, are among the main objectives of current software assisted metrology tools. Line-edge roughness quantification should accompany critical dimension (CD) measurements since it could be a large fraction of the total CD budget. A detailed simulation and metrology approach of line-edge roughness quantification versus the length scales in a layout are presented in this work using a combination of electron beam simulation for the exposure part, and stochastic simulations for the modeling of resist film, postexposure bake, and resist dissolution. The method is applied also on a test layout with critical dimension of 200nm and the resulted simulation and scanning electron microscopy images are compared with the aid of a pattern matching algorithm which enables the identification of the desired layout for metrology on a complex layout containing many printed features.
Ultrastiff stage for imprint lithography
Authors: Jeon Y. , Feldman M. , Jiang L.
Published: December 2007

The high-resolution capabilities of imprinting and step and flash make these techniques strong contenders for the next generation lithography. Unfortunately, alignment remains an area of concern for imprinting because it must be completed before the template is moved into contact with the wafer. The large forces on the template during the process, even for step and flash, place additional demands on the stiffness as well as the reproducibility of the template stage. A prototype flexure stage has been developed to meet these demands. A compressive load, slightly below the Euler limit, is used to produce relatively free motion in the vertical direction while maintaining extremely high horizontal stiffness. In addition, the horizontal stage position is viewed by an optical system based on a microscope objective with a central stop. With it, the horizontal position of a diffraction grating fixed to the stage has been measured to a few nanometers, over a vertical range of several hundred microns. Consequently, not only does the high transverse stiffness of the stage minimize unwanted horizontal motions but also any that occur are measured over the entire required range of motion.
Zero-dimensional analysis for discharge characteristics
Authors: Park Wontaek
Published: December 2007

A volume-averaged, zero-dimensional numerical simulator for ac discharge of plasma display panel (PDP) is developed. The vacuum-ultraviolet photons such as 147 and 173nm are treated as particles that cannot be stored. The surface charge on the dielectric layer is introduced in this study. Solving particle continuity and electron energy balance equations simultaneously, the characteristics of ac-discharge phenomena, such as the temporal evolution of surface charge, electric field, and particle densities, are analyzed. This numerical simulation result shows that the increment of the percentage of xenon atoms in a neon-xenon mixture of PDP improves the luminous efficiency of the ac-discharge gas by raising the intensity of 173nm vacuum-ultraviolet photons from xenon excimers.
Sub-30-nm hybrid lithography (electron beam∕deep ultraviolet) and etch process for fully depleted metal oxide semiconductor transistors
Authors: Pauliac-Vaujour S. , Brianceau P. , Landis S. , Chiaroni J. , Faynot O.
Published: December 2007

Fully depleted silicon on insulator (FDSOI) devices with high-k dielectrics and metal gate are promising candidates for sub-45-nm complementary metal oxide semiconductor technologies. At present, the gate length reduction becomes more and more difficult due to resist thickness diminution induced by critical dimension downscaling. In order to suppress resist thickness limitations, we have added a carbon layer with a SiO2 capping onto the conventional dielectric hard mask (SiO2 or Si3N4). In this study, FDSOI transistors with hafnium dielectric (HfO2), titanium nitride (TiN) metal gate were patterned by combining high resolution hybrid lithography (electron beam∕deep ultraviolet) and amorphous carbon hard mask. Full three-dimensional (3D) characterizations were carried out by using 3D atomic force microscope (CD-AFM from Veeco) to determine the best process window. Finally, after carbon hard mask trimming, sub-30-nm gate length transistors were achieved and successfully electrically tested.
Nanometer-scale gaps in hydrogen silsesquioxane resist for T-gate fabrication
Authors: Jin Niu , Choi Sookyung , Wang Liang , Chen Guang , Kim DongHyun , Kumar Vipan , Adesida Ilesanmi
Published: December 2007

The authors present a novel T-gate fabrication process which takes advantage of the unique high-resolution property of the low-k dielectric material, hydrogen silsesquioxane (HSQ), as a negative tone electron beam resist. By optimizing layout design and process parameters, the authors demonstrate ∼30nm gap between two HSQ rectangular geometries, which is then used to define the T-gate footprint and support the T gate. An InGaAs∕InAlAs∕InP high electron mobility transistor with 80nm gate length was fabricated using this HSQ-based resist technique. Excellent dc and rf performances are presented.
Metal-semiconductor-metal electron detectors
Authors: Aldana Rafael , Pease R. Fabian
Published: December 2007

Metal-semiconductor-metal (MSM) junctions are a standard photon detector for high-speed applications due to fast response time (subpicosecond) and long device lifetime, high gain (QE>100%), small device area, and reduced capacitance per area. Here, the authors characterize how such devices perform as electron detectors, performing preliminary gain and frequency response experiments on MSM illuminated by an electron beam. Experiments were performed on both a Hitachi scanning electron microscope SEM 2500, and in a custom-made vacuum system used as a testbed for analog to digital conversion. The experiments demonstrated a gain of 300× at 5 kV acceleration voltage and frequency response up to 0.85 GHz, which complied with the specifications required by the analog to digital converter. Using other semiconductor materials (GaAs) as well as e-beam lithography to define smaller fingers will lead to faster response times.
Structural and optical characterization of WO3 nanorods/films prepared by oblique angle deposition
Authors: Smith W. , Zhang Z.-Y. , Zhao Y.-P.
Published: December 2007

The structural and optical properties of WO3 nanorods prepared by oblique angle depositions were studied and compared with WO3 thin films. The x-ray diffraction analysis revealed that both the thin films and nanorods annealed at temperatures of 400 and 500°C had an orthorhombic structure, while only the thin films showed a monoclinic phase when annealed at 300°C. The band gap energies of the thin films and nanorods all decreased with increasing annealing temperature. The polarized optical absorbance spectra of the as-deposited nanorod samples initially showed anisotropy, but after annealing at temperatures above 400°C, they became isotropic. This is believed to result from the changes in morphology, crystal structure, and orientation of the nanorod arrays after annealing.
Imaging layers for the directed assembly of block copolymer films: Dependence of the physical and chemical properties of patterned polymer brushes on brush molecular weight
Authors: Stuen K. O. , In I. , Han E. , Streifer J. A. , Hamers R. J. , Nealey P. F. , Gopalan P.
Published: December 2007

The directed assembly of polystyrene-block-poly(methyl methacrylate) films using chemically nanopatterned polymer brush surfaces with various molecular weights was investigated. The brushes (3–10nm in thickness) were made from polystyrene that was end grafted to silicon wafers and patterned to have 40–60nm period stripes consisting of unmodified polymer and polymer that was subjected to brief oxygen plasma. The best assembly of block copolymer films was achieved using brushes with molecular weights of 3kg∕mol or less. The brushes were analyzed by goniometry, infrared reflection-absorption spectroscopy, x-ray photoelectron spectroscopy, and ellipsometry. The brush thickness increased nonlinearly with molecular weight and the high molecular weight brushes reconstructed under solvent and thermal annealing. The lower molecular weight brushes form the best imaging layers due to their optimum thickness that provides uniform surface coverage and prevents reconstruction of the film surface. The thin brushes ensure contact between the block copolymer and the hydrophilic groups in the modified regions of the brush during annealing, maximizing the effective interfacial energy contrast and the driving force for perfect directed assembly.
Production of noble gas ion beams in a focused ion beam machine using an electron beam ion trap
Authors: Ullmann Falk , Grossmann Frank , Ovsyannikov Vladimir P. , Gierak Jacques , Bourhis Eric , Ferré Jacques , Jamet Jean Pierre , Mougin Alexandra , Zschornack Günter
Published: December 2007

The aim of this article is to report on preliminary investigations in evaluating a new kind of focused ion beam (FIB) instrument realized by coupling an advanced FIB “nanowriter” with a compact electron beam ion trap. The authors demonstrate the possibility to produce noble gas ion beams (He, Ar, Xe, and Kr) in a FIB machine using an electron beam ion trap. Preliminary results obtained using highly charged ions as projectiles are presented.
Optimal temperature for development of poly(methylmethacrylate)
Authors: Cord Bryan , Lutkenhaus Jodie , Berggren Karl K.
Published: December 2007

The authors have investigated a range of poly(methylmethacrylate) (PMMA) development temperatures as low as −70°C and characterized their effect on the resolution of PMMA as an electron resist. The results show that cooling, in addition to reducing the sensitivity of the commonly used positive-tone mode of PMMA, also increases the sensitivity of its less commonly used negative-tone mode. They have shown that the resolution-enhancing properties of cold development peak at approximately −15°C as a result of these competing sensitivity changes. At lower temperatures, the high doses required to expose the resist produce significant cross-linking of the polymer, altering its solubility properties and sharply degrading the contrast. If the correct development temperature is used, however, sub-10nm features are readily achievable in PMMA-based scanning electron-beam lithography.
Experimental demonstration of dark field illumination using contact hole features
Authors: Crouse Michael M. , Schmitt-Weaver Emil , Hansen Steven G. , Routh Robert
Published: December 2007

The use of off-axis illumination in present lithography processes has enabled patterning to push below k1<0.40. This continual drive toward printing smaller feature sizes at the 193nm wavelength has led to the investigation and successful implementation of a number of new resolution enhancement technique (RET) approaches. In this work, the application of dark field imaging as a RET for low-k1 contact hole features was examined using both simulation and experiment on a standard lithography tool set. Here dark field imaging is defined as imaging where a portion of the illumination source is placed outside of the projection optics. This approach is similar to standard off-axis illumination approaches using the familiar two-beam imaging but at greater incident angle where the zeroth diffraction order is not captured and image modulation is created by higher diffraction orders. This approach creates a number of “unexpected” effects and the authors show these for contact hole patterns using ASML Twinscan lithography tools operationally modified to operate in dark field mode. They demonstrate the following new dark field effects for contact holes: reduced and negative mask error enhancement factor, inverted develop critical dimension as a function of pitch, and image tone reversal at phase edges. Additionally, experimentally relevant items such as stray light and dark field exposure energy requirements are discussed.
UV-nanoimprint with the assistance of gas condensation at atmospheric environmental pressure
Authors: Hiroshima Hiroshi , Komuro Masanori
Published: December 2007

Nanoimprint should be carried out in an ordinary environment from the standpoint of cost-performance. However, bubble defects arise when the process is done in air and the problem can become worse with large patterns and thin resin films. UV-nanoimprint using resin droplets reduces air capture by expelling air during resin spreading and, in some cases, achieves bubble free UV-nanoimprint by air dissolution in resin. When the authors simulated the smooth spreading of a large resin droplet in wafer warping, resin spreading occurred on mold plateaus but hardly reached into mold recesses where a significant amount of air was sealed and the air in a mold recess was not completely dissolved in resin within 10 min under an imprint pressure of 0.5 MPa. In contrast, a captured gas of concentrated pentafluoropropane (CHF2CH2CF3, 1,1,1,3,3-pentafluoropropane, HFC-245fa, CAS No. 460-3-1) whose vapor pressure is 0.15 MPa at room temperature was completely condensed and dissolved within 2 s, leaving no trace of bubble defects in UV-nanoimprint. UV-nanoimprint with the assistance of gas condensation at atmospheric pressure thus handles spin coat resin film and dramatically improves throughput by quickly eliminating bubble defects. The authors confirmed that the process is applicable to thin resin film whose resulting residual layer is 25 nm thick.
Graphoepitaxial cylindrical block copolymer nanodomains evaluated as bit patterned media template
Authors: Xiao Shuaigang , Yang XiaoMin
Published: December 2007

To utilize self-assembled block copolymer structures to fabricate the template of bit patterned media, two basic issues of block copolymer nanodomains need to be considered: (a) size uniformity and (b) position accuracy. The manipulation of domain position was achieved here by graphoepitaxy of cylindrical block copolymer domains in a topographic trench pattern. Trench surface may be neutralized to guarantee the perpendicular orientation of cylindrical domains on the trench bottom surface and domain alignment along the trench sidewall. The size distributions of cylindrical domains on both flat surface and topographically patterned surface have been analyzed and the correlation between the size distribution and the local-range order is addressed. The distributions of the domain size and domain position-related parameters, such as the dot spacing along the axis (parallel to the trench edge) and across the axis, have been investigated as a function of the number of domain rows in the trench. Qualitatively, line edge roughness or linewidth roughness of trenches attributes to the larger variation of spacing across the axis. Finally, a surface trench without neutralization pretreatment was found to enable the graphoepitaxy of block copolymer domains with an areal density >1 Tdot/in.2.
Effects of photoacid generator incorporation into the polymer main chain on 193nm chemically amplified resist behavior and lithographic performance
Authors: Lee Cheng-Tsung , Henderson Clifford L. , Wang Mingxing , Gonsalves Kenneth E. , Yueh Wang
Published: December 2007

The need for chemically amplified resists (CARs) that can resolve sub-65-nm node features with sufficient linewidth roughness (LWR) control and sensitivity to meet the requirements outlined in the International Technology Roadmap for Semiconductors has placed a significant and daunting challenge for the design of resist materials that can achieve these goals. In this article, the ability to improve the performance of CARs designed for 193nm lithography via the direct bonding of a photoacid generator (PAG) anion into the resist polymer main chain has been investigated. The bound-PAG anion resist is shown to achieve higher sensitivity and resolution with smaller LWR than their blended-PAG resist analog. Binding of the PAG anion provides reduced photoacid diffusivity, higher maximum PAG loadings, and more homogeneous PAG distributions that help achieve these three critical resist requirements.
Pattern transfer using poly(styrene-block-methyl methacrylate) copolymer films and reactive ion etching
Authors: Liu Chi-Chun , Nealey Paul F. , Ting Yuk-Hong , Wendt Amy E.
Published: December 2007

Self-assembly block copolymers have drawn a lot of attention for its great potential on critical dimension (CD) control and line-edge roughness (LER) reduction, which become more and more crucial as the CD of transistors is only tens of nanometers nowadays. In this study, lamellar-forming poly(styrene-b-methyl methacrylate) copolymer which fabricates line patterns was chosen for its ability to provide higher aspect ratio and vertical sidewall profile in template stage, thus more suitable for the following etching process to substrate. A dry plasma etching process using pure oxygen and pure argon plasma as example chemical etching gas and physical etching gas, respectively, was studied. Etching selectivity and lateral etch rate, which are responsible for the final template height and CD loss, had been characterized on a capacitive reactive ion etching tool. The templates formed by the proposed process had high aspect ratios, excellent pattern fidelity, and low LER values. The PS lateral etch rate was small enough to provide a wide process window for retaining the CD of the pattern during the template forming process. Subsequent silicon etching using the PS template made by dry etching process yielded a steep and smooth sidewall profile.
Ion energy control at substrates during plasma etching of patterned structures
Authors: Silapunt R. , Wendt A. E. , Kirmse K. H. R.
Published: December 2007

In fluorocarbon-based plasma etching of dielectrics, deposition of fluorocarbon on the substrate contributes to a complex surface chemical structure that strongly affects etch rate and etch selectivity. Results reported herein demonstrate that the energy distribution of bombarding ions (IED) has a significant effect on this polymer layer, subsequently affecting etch rate and selectivity in submicron patterned structures. Specifically, we have narrowed the IED while keeping other process conditions unchanged by tailoring the shape of the rf voltage wave form used for substrate bias. Significant improvements in etch selectivity for organosilicate glass (OSG) over silicon carbide in a C4F8∕N2∕Ar plasma have been obtained by using a narrow IED compared to the broad IED resulting from the typical sinusoidal bias wave form. Trenches etched in OSG with the tailored bias voltage wave form show good feature profiles and high selectivity at feature bottoms. Slight differences in feature profiles between tailored and sinusoidal wave forms, as well as variations in etch selectivity with feature depth, are consistent with an enhancement in polymerization at the substrate in the case of the tailored bias voltage wave form.
Novel magnetic microstigmator for electron beam astigmatism correction in the electron beam microcolumn system
Authors: Rong Rong , Kim Ho Seob , Park Seong Soon , Hwang Nam Woo , Park Kyoung Wan , Jin Sang Won , Ahn Chong H.
Published: December 2007

A novel magnetic microstigmator was developed for the astigmatism correction in the electron beam microcolumn system. The magnetic microstigmator consists of eight magnetic poles coupled with micromachined solenoid-type coils that are divided into four pairs. The proposed magnetic microstigmator was fabricated using microelectromechamical system technology and was assembled in an electron beam microcolumn for testing. The preliminary experimental results show that the developed magnetic microstigmator can effectively correct the astigmatism of the electron beam in the electron beam microcolumn with a driving current of 300mA and low power.
Optimizing nanoimprint and transfer-bonding techniques for three-dimensional polymer microstructures
Authors: Park Hyunsoo , Li Huifeng , Cheng Xing
Published: December 2007

Successful fabrication of three-dimensional multilayer microstructures in thermoplastic polymers using optimized layer-transfer and transfer-bonding techniques are reported in this work. For successful multilayer fabrication, it is very important to control the adhesion between two polymer layers and between mold and polymer. The authors discuss two techniques, bonding with a thin adhesive layer and direct thermal bonding near glass transition temperature, to achieve good bonding between two polymer layers while maintaining the structural integrity of the bottom polymer layers. Bonding with an adhesive layer achieves near 100% yield and heterogeneous materials can be bonded by this method. Direct thermal bonding is a generic approach that is suitable for all thermoplastic polymers. It opens up the possibilities of creating 3D multilayer structures in functional polymers for advanced applications. The capability and flexibility of the techniques developed here are expected to have deep impact on the applications of soft materials such as polymers in micro- and nanofabricated devices and systems.
Design studies for a high brightness, energetic neutral atom source for proximity lithography
Authors: Guo Hong-jie , Craver Barry , Reynolds Jackson , Wolfe John C.
Published: December 2007

Line-edge roughness due to mask and wafer charging in ion beam proximity lithography can be simply and completely eliminated by neutralizing the ions before they reach the mask. This dramatically increases the usable depth of field and enables high quality imaging below 20nm. Neutralization is accomplished by charge transfer scattering in a high pressure cell, a process that preserves both the energy and direction of the parent ion with remarkable accuracy. In this article, the authors discuss the design of an energetic atom source and characterize an optimized helium ion injector based on a dc-multicusp ion source. The injector provides a crossover at a fixed position in the charge transfer cell over a design energy range from 30to50keV. For 100W discharge power, the full width at half maximum diameter and normalized brightness of the crossover are 95μm and 100A∕m2srV, respectively.
Mechanical nanostepping for atom beam lithography
Authors: Craver B. , Roy A. , Nounu H. , Wolfe J. C.
Published: December 2007

One solution to stencil mask density limitations in particle lithography is to print dense patterns using multiple offset exposures of a lower density mask. The goal of this article is to demonstrate the ability to make high accuracy stepped exposures in proximity lithography with energetic neutral atoms where magnetic or electrostatic deflection is impossible. The authors’ approach is to clamp the mask to the wafer, setting the proximity gap with a suitable spacer, and to mechanically incline the mask/wafer stack relative to the beam. This approach is remarkably insensitive to vibration and thermal drift; nanometer scale image offsets have been obtained with ±2nm placement accuracy for experiments lasting over 1h. The reported error may include significant contributions from shot noise, resist roughness, and metrology errors, not related to the stepping process itself. The authors also show that the standard deviation of Gaussian image blur is 4.4±1.4nm, about three times smaller than the secondary electron range limitation in electron beam lithography. Thus, the technology has the potential to form high density, periodic patterns with ∼10nm resolution.
Structural characteristics of single-crystal nanowires grown by self-catalytic chemical vapor deposition method
Authors: He Maoqi , Noor Mohammad S.
Published: December 2007

Physical characteristics of III-V nitride nanowires grown by the self-catalytic chemical vapor deposition method have been studied. The nanowire shape (uniform or tapered) and nanowire branching are found to depend on a number of parameters that influence the nanowire growth. Among them, the Gibbs-Thompson effect and the diffusivity of adatoms through liquid droplet dictate the length-to-diameter relationship of nanowires. The Raman scattering spectrum shows that the nanowires exist primarily in the hexagonal phase. Local modes, electronic transitions of dopant atoms, and impurity atoms contribute to unexpected peaks in this spectrum.