bluuebunny/crossref_metadata_2025 huggingface dataset:
Subharmonic and Chaotic Motions of a Hybrid Squeeze-Film Damper-Mounted Rigid Rotor With Active Control
Authors: Chen Chieh-Li , Yau Her-Terng , Li Yunhua
Published: July 2002

The hybrid squeeze-film damper bearing with active control is proposed in this paper. The pressure distribution and the dynamics of a rigid rotor supported by such bearing are studied. A PD (proportional-plus-derivative) controller is used to stabilize the rotor-bearing system. Numerical results show that, due to the nonlinear factors of oil film force, the trajectory of the rotor demonstrates a complex dynamics with rotational speed ratio s. Poincare´ maps, bifurcation diagrams, and power spectra are used to analyze the behavior of the rotor trajectory in the horizontal and vertical directions under different operating conditions. The maximum Lyapunov exponent and fractal dimension concepts are used to determine if the system is in a state of chaotic motion. Numerical results show that the maximum Lyapunov exponent of this system is positive and the dimension of the rotor trajectory is fractal at the nondimensional speed ratio s=3.0, which indicate that the rotor trajectory is chaotic under such operation condition. In order to avoid the nonsynchronous chaotic vibrations, an increased proportional gain is applied to control this system. It is shown that the rotor trajectory will leave chaotic motion to periodic motion in the steady state under control action.
Design of Reconfigurable Machine Tools
Authors: Moon , Yong-Mo , Kota, Sridhar
Published: July 2002

In this paper, we present a systematic methodology for designing Reconfigurable Machine Tools (RMTs). The synthesis methodology takes as input a set of functional requirements—a set of process plans and generates a set of kinematically viable reconfigurable machine tools that meet the given design specifications. We present a mathematical framework for synthesis of machine tools using a library of building blocks. The framework is rooted in (a) graph theoretic methods of enumeration of alternate structural configurations and (b) screw theory that enables us to manipulate matrix representations of motions to identify appropriate kinematic building blocks.
Microstructure Integrated Modeling of Multiscan Laser Forming
Authors: Cheng Jin , Yao Y. Lawrence
Published: July 2002

Laser forming of steel is a hot forming process with high heating and cooling rate, during which strain hardening, dynamic recrystallization, and phase transformation take place. Numerical models considering strain rate and temperature effects only usually give unsatisfactory results when applied to multiscan laser forming operations. This is mainly due to the inadequate constitutive models employed to describe the hot flow behavior. In this work, this limitation is overcome by considering the effects of microstructure change on the flow stress in laser forming processes of low carbon steel. The incorporation of such flow stress models with thermal mechanical FEM simulation increases numerical model accuracy in predicting geometry change and mechanical properties.
Two-Dimensional Simulations of Enhanced Heat Transfer in an
Intermittently Grooved Channel
Authors: Greiner M. , Fischer P. F. , Tufo H. M.
Published: July 2002

Two-dimensional Navier-Stokes simulations of heat and momentum transport in an intermittently grooved passage are performed using the spectral element technique for the Reynolds number range 600⩽Re⩽1800. The computational domain has seven contiguous transverse grooves cut symmetrically into opposite walls, followed by a flat section with the same length. Periodic inflow/outflow boundary conditions are employed. The development and decay of unsteady flow is observed in the grooved and flat sections, respectively. The axial variation of the unsteady component of velocity is compared to the local heat transfer, shear stress and pressure gradient. The results suggest that intermittently grooved passages may offer even higher heat transfer for a given pumping power than the levels observed in fully grooved passages.
A Theoretical Analysis of Alternate Blade Cavitation in Inducers
Authors: Horiguchi Hironori , Watanabe Satoshi , Tsujimoto Yoshinobu , Aoki Masanori
Published: July 2002

An analysis of alternate blade cavitation on flat plate cascade is made using a singularity method based on a closed cavity model. In the steady flow analysis, it was found that two kinds of steady cavitation patterns exist. One is equal length cavitation in which the cavity lengths of all blades are the same. The other is alternate blade cavitation in which the cavity length changes alternately from blade to blade. Although the present model fails to predict the range of cavitation number where alternate blade cavitation occurs, it predicts alternate blade cavitation fairly well in terms of cavity length. A parameter study shows that the development of alternate blade cavitation is quite different depending on the solidity of cascade. The stability of equal length and alternate blade cavitation is then examined allowing the cavity length freely to change. It was found that alternate blade cavitation is stable for the cascades with larger solidity and unstable for the cascades with smaller solidity. The equal length cavitation is stable in both cases only in the region of cavitation number larger than that where the alternate blade cavitation solution separates from the equal length cavitation. [S0098-2202(00)01301-8]
A Panel-Fourier Method for Free-Surface Flows
Authors: D’Elı´a Jorge , Storti Mario A. , Idelsohn Sergio R.
Published: July 2002

A panel-Fourier method for ship-wave flow problems is considered here. It is based on a three-dimensional potential flow model with a linearized free surface condition, and it is implemented by means of a low order panel method coupled to a Fourier-series. The wave-resistance is computed by pressure integration over the static wet hull and the wave-pattern is obtained by a post-processing procedure. The strategy avoids the use of numerical viscosity, in contrast with the Dawson-like methods, widely used in naval-panel codes, therefore a second centered scheme can be used for the discrete operator on the free surface. Numerical results including the wave-pattern for a ferry along fifteen ship-lengths are presented. [S0098-2202(00)01402-4]
Diagnostic Feature Extraction From Stamping Tonnage Signals Based on Design of Experiments
Authors: Jin Jionghua , Shi Jianjun
Published: July 2002

Diagnostic feature extraction with consideration of interactions between variables is very important, but has been neglected in most diagnostic research. In this paper, a new feature extraction methodology is developed to consider variable interactions by using a fractional factorial design of experiments (DOE). In this methodology, features are extracted by using principal component analysis (PCA) to represent variation patterns of tonnage signals. Regression analyses are performed to model the relationship between features and process variables. Hierarchical classifiers and the cross-validation method are used for root-cause determination and diagnostic performance evaluation. A real-world example is used to illustrate the new methodology. [S1087-1357(00)00302-6]
MgO(100) by XPS
Authors: Vasquez Richard P.
Published: July 2002

XPS measurements of the core levels, including energy losses, and the valence band of a MgO(100) crystal are presented.
Si by XPS
Authors: Nakajima Kazuhiro , McGinnis Sean P. , Kelly Michael A.
Published: July 2002

X-ray photoemission spectra from Si which has been chemically etched in HF (hydrofluoric acid) are presented. The data include measurements of the valence band region, Si 2p region, Si 2s region, and O 1s region. These data are useful for comparison to the oxidized Si.
Chloropyromorphite (Pb5(PO4)3Cl) by XPS: An Environmentally Important Secondary Mineral
Authors: Eighmy T. Taylor , Shaw Elisabeth L. , Eusden J. Dykstra , Francis Carl A.
Published: July 2002

The ability to identify chloropyromorphite (Pb5(PO4)3Cl) using surface-sensitive spectroscopies such as x-ray photoelectron spectroscopy (XPS) is important in understanding lead and phosphate geochemistry in natural and engineered systems. We have used XPS to study the binding energy of primary photoelectrons from an air-exposed fracture surface of a well-formed hexagonal crystal sample from Kanderbach, Germany. General survey and high resolution spectra were collected using a Perkin Elmer Physical Electronics 5200 C spectrometer. Adventitious carbon was used for energy referencing. Charge corrected binding energies for the Pb 4f7/2, Pb 4f5/2, P 2p3/2, P 2p1/2, P 2s, O 1s, Cl 2p3/2, and Cl 2p1/2 photoelectrons are reported. These spectra are useful in identifying environmentally important lead phosphate minerals such as chloropyromorphite in ore bodies, soils, and phosphate-stabilized waste systems.
Analysis of a Glass-filled Poly(ethylene terephthalate) Polymer by XPS
Authors: Lannon John M. , Meng Qingru
Published: July 2002

We report x-ray photoemission spectra for a poly(ethylene terephthalate) (PET) polymer. XPS spectra were acquired with a SSI model SSX-100 instrument using monochromated Al Kα x-rays. We present the survey spectrum (binding energy 0–1000 eV) and a narrow spectrum of the C 1s and O 1s photoelectron peaks.
Hydroxylapatite (Ca5(PO4)3OH) Characterization by XPS: An Environmentally Important Secondary Mineral
Authors: Eighmy T. Taylor , Kinner Amy E. , Shaw Elisabeth L. , Eusden J. Dykstra , Francis Carl A.
Published: July 2002

Hydroxylapatite (Ca5(PO4)3OH) is an environmentally important secondary phosphate mineral, one of the apatite family of minerals. It is of significance geochemically around ore bodies and in soil, sedimentary, and waste systems. It is also a major inorganic component of vertebrate bone. We have used XPS to study the binding energy of primary photoelectrons from an air-exposed fracture surface of small hydroxylapatite grains exhibiting well-developed conchoidal fracture and vitreous luster. The sample is from Holly Springs, Georgia and is part of the Harvard University Mineralogical Museum’s collection. General survey and high-resolution spectra were collected using a Perkin Elmer Physical Electronics 5200C spectrometer. Adventitious carbon was used for energy referencing. Charge corrected binding energies for the photoelectrons of hydroxylapatite (Ca 2p3/2, Ca 2p1/2, P 2p 3/2, P2p1/2, P 2s, O 1s) are reported. The charge corrected binding energies of photoelectrons for other elements present in the natural sample (F 1s, S 2p3/2, and S 2p1/2) are also reported. The F and the S (as sulfate) are likely isomorphic substitutions for hydroxyl groups and phosphate in the mineral. A potential mineral formula of Ca5(PO4)1.5(SO4)1.5(OH)0.5F0.5 is proposed. The binding energies for hydroxylapatite are useful in identifying environmentally important calcium phosphate minerals such as hydroxylapatite in ore bodies, soils, sediments, and phosphate-stabilized waste systems.
Scanning probe metrology in the presence of surface charge
Authors: Griffith J. E. , Kneedler E. M. , Ningen S. , Berghaus A. , Bryson C. E. , Pau S. , Houge E. , Shofner T.
Published: July 2002

Surface charge on insulating samples can be a significant source of error for scanning probe microscopes. We have found that it is possible to operate a scanning force microscope in a manner that makes it relatively immune to charge-induced forces while still allowing the probe tip to nondestructively follow the surface topography. The need to maintain close charge balance on the sample is thus obviated. We have used this strategy to perform critical dimension measurements on optical photomasks with the Surface/Interface Stylus NanoProfilometer. This instrument incorporates a servoed force-balance sensor. Surface topography is determined by touching the surface with contact forces between 0.1 and 1 μN.
Mechanical analysis of the PLASMAX particle removal process for optical and next-generation lithography masks
Authors: Semke W. H. , Weisbrod E. J. , Engelstad R. L. , Lovell E. G. , Festa J. J. , Bailey J. B.
Published: July 2002

The ability to clean advanced lithographic masks in a cost-effective manner is becoming increasingly important as the semiconductor industry continues integrated circuit development with ever-decreasing feature sizes. The plasma mechanical activation and extraction of particle contamination (PLASMAX) particle removal process, under development by Beta Squared, Inc., provides a means to achieve the industry’s needs for both the current optical and next-generation lithography (NGL) masks. This cleaning procedure is imperative since all NGL technologies are unable to use a conventional protective pellicle. The cleaning process implements a charged plasma flow in conjunction with mechanical excitation. This article presents the results of research to identify the optimal procedures to mechanically oscillate 6 in. fused silica reticles and electron-beam projection lithography masks. Using both numerical and experimental methods, the analysis characterizes the dynamic response of lithographic masks to quantify and optimize the mechanical force delivered to a surface contaminant in the PLASMAX process. These modeling and simulation efforts are essential to support the experimental program and facilitate development of the cleaning process for advanced optical reticles and NGL masks.
Pattern generators and microcolumns for ion beam lithography
Authors: Scott K. L. , King T.-J. , Lieberman M. A. , Leung K.-N.
Published: July 2002

A self-aligned microfabrication process has been developed for micron-sized extraction systems, which can be used for pattern generators or microcolumns in ion beam lithography. The extraction of ions from a plasma source through micron-sized apertures is shown not to follow traditional design rules, and the governing equations of interest for meeting design parameters are presented. First order focal properties of the pattern generator and microcolumn are described using Davisson and Calbick’s derivation [C. J. Davisson and C. J. Calbick, Phys. Rev. 38, 558 (1931); 42, 580 (1932)] for an aperture lens. A second order refinement of the focal properties is characterized and explained with computer simulations using MEBS©.
Quantum interference in a vacuum nanotriode
Authors: Driskill-Smith A. A. G. , Hasko D. G. , Ahmed H.
Published: July 2002

The current–voltage and noise characteristics of vacuum nanoelectronic devices, including nanoscale field-emission diodes and vacuum nanotriodes, are presented. The turn-on voltage for field emission in these devices is about 8 V, independent of ambient temperature, and currents of up to 10 nA are obtained. Time-independent fluctuations are observed in the current–voltage characteristics of the vacuum nanoelectronic devices that persist down to 20 K. In the case of the nanotriode, these fluctuations are repeatable in different sweeps performed both at the same and at different temperatures. These measurements, coupled with a model of the nanotriode, which includes an analysis of the electrostatic field within the nanochamber, the electron trajectories, and the role of field-emission resonances, suggest that the origin of the time-independent fluctuations is a quantum-interference effect between the electron wave function in the tip of the nanopillar field emitter and the anode.
Carbon Monoxide Oxidation on a Pt(110) Single Crystal Surface
Authors: Bonzel H. P. , Ku R.
Published: July 2002

The catalytic reaction between CO and O2 on a Pt (110) surface is investigated by residual gas analysis for different partial pressures of CO and O2 and various temperatures. The surface cleanliness of the Pt crystal is monitored by Auger electron spectroscopy. The results of the reaction study are generally in agreement with previous studies for polycrystalline Pt catalysts. The temperature dependence of the formation rate of CO2 exhibits a maximum whose position depends on the composition of the gas phase. At T=215°C two different rate laws are valid. For PO2>PCO the rate of CO2 formation is proportional to PO21.1PCO−0.6, while for PO2>PCO it is proportional to PO20.25 PCO0.75. These observations support the idea that the reaction obeys an Eley-Rideal mechanism in the pressure and temperature range investigated, and the results are evaluated accordingly. The influence of segregated Si on the CO oxidation reaction is investigated and found to be small.
Thickness analysis of silicon membranes for stencil masks
Authors: Sossna E. , Kassing R. , Rangelow I. W. , Herzinger C. M. , Tiwald T. E. , Woollam J. A. , Wagner Th.
Published: July 2002

Stencil masks are key to charged particle projection lithography, in particular for ion projection lithography. To fulfill pattern printing requirements in the sub-70 nm regime, excellent thickness uniformity and thermal emissivity control are critical parameters for high quality stencil mask fabrication. We propose and demonstrate a technique based on infrared variable angle spectroscopic ellipsometry (IR-VASE) to measure these parameters with adequate accuracy and precision. The refractive index of the Si membrane was evaluated using a Sellmeier dispersion model combined with a Drude model. Because of its spectral range from 2 to 33 μm, the IR-VASE method is sensitive to the thickness of layers as well as to the concentration and profile of Si membrane doping.
Computer aided design and analysis of imaging energy filters with inhomogeneous bending magnets
Authors: Munro Eric , Rouse John
Published: July 2002

Software has been written to analyze and design magnetic imaging energy filters. The filters can be composed of any number of bending magnets of homogeneous or inhomogeneous type. The sharp cut-off fringing field approximation is used initially to evaluate quickly many possible designs. Promising designs are then analyzed taking the real fringing fields at the edges of the bending magnets into account, including the full three-dimensional field distributions in conical bending magnets. Graphical postprocessing software displays the optical properties in the energy selection plane and the image plane in the form of spot diagrams and current density contours.
Optimal strategy for controlling linewidth on spherical focal surface arrays
Authors: Ruchhoeft P. , Wolfe J. C.
Published: July 2002

We present a method for patterning concave spherical substrates based on ion beam proximity lithography. The approach overcomes both the distortion and radial dose variation that are inherent to projecting a flat mask pattern onto a sphere. We use a self-complementary mask (SCM) concept where an array of discrete ion beamlets is scanned across the substrate to expose the circuit pattern. This scanning is implemented by varying the inclination of the incident ion beam with respect to the mask. Pincushion distortion is corrected by applying a global transformation to the centers of the SCM openings while a local transformation, applied within each opening, ensures that the beamlets stitch together properly on the substrate and that the ion dose is uniform. We show that the linewidth variation for 1 μm features is less than ±80 nm over a 7.2 mm deep, spherical bowl with a 1.5 cm radius of curvature.
Quantitative factor analysis of resolution limit in electron beam lithography using the edge roughness evaluation method
Authors: Yoshizawa Masaki , Moriya Shigeru
Published: July 2002

Various factors influencing the resolution limit (RL) in electron beam (EB) lithography have been analyzed quantitatively using the edge roughness evaluation (ERE) method. The ERE method is based on the experimental finding that line edge roughness of a resist pattern is inversely proportional to the slope of the Gaussian-distributed quasi-beam-profile (QBP). The analysis reveals that beam blur and development process are primary factors of RL, that electron forward scattering is negligible with the resist thickness under 200 nm, and that the effect of aperture degradation on RL is as large as that of resist performance. A necessary and sufficient condition for realizing 50 nm patterns is following. Use of EB lithography instruments of which beam blur is under 31 nm, resist thickness of 200 nm, and 20% improvement of the resist performance accompanying optimum development condition.
Demonstration of multiblanker electron-beam technology
Authors: Winograd G. , Krishnamurthi V. , Garcia R. , Veneklasen L. H. , Mankos M. , Pease F.
Published: July 2002

A set of multiple electron-beam (e-beam) aperture/blanker chips have been fabricated using silicon microelectro-mechanical systems (MEMS) techniques. The aperture sizes range from 8 to 4 μm (nominal) squares, and the chip configurations feature either eight individually controlled monopolar blanker electrodes or four bipolar electrode pairs. The chips replace the shapers of a 20 kV AEBLE™ shaped e-beam lithography column. The apertures in the chips convert an incident 150 μm diameter e-beam into multiple beamlets. Each beamlet can be independently blanked off of a 100 μm aperture placed at the following beam crossover. Data are presented that demonstrates the ability to independently blank each beamlet by applying 10 V. Magnified images of the beamlets show square or rectangular shapes with sharp corners, indicating that the apertures were properly fabricated. The degree of electrostatic blanker crosstalk was measured and found to be up to 15% at the crossover plane for different pairs of beamlets, but no observable beam displacement occurred at the image plane. We compared the experimental results to a rough model that estimates the effect of the electrostatic field distribution of one excited blanker electrode on the unblanked beams. The results matched to within 20%.
Effects of smoothing on defect printability at extreme ultraviolet wavelengths
Authors: Cardinale G. F. , Ray-Chaudhuri A. K. , Fisher A. , Mangat P. S. J. , Wasson J. , Mirkarimi P. B. , Gullikson E.
Published: July 2002

Improvements in mask blank yield by the reduction in defects dramatically reduces the reticle cost of any lithography. Extreme ultraviolet lithography (EUVL) masks typically consist of a substrate coated with reflective multilayer (ML) materials (e.g., Mo and Si), followed by a sacrificial or “repair” layer (e.g., SiO2) and top absorber layer material (e.g., Cr or TaSiNx). Defects of the following two types exist: substrate and absorber defects. Substrate defects are generally below the absorber and buffer layers, i.e., at the substrate–ML interface or within the ML stack, whereas the absorber defects are located at the absorber layer. In addition, the printability of substrate-type defects may be reduced by coating the defects with a planarizing or smoothing layer. In this work, we discuss simulation and experimental results that compare the printability of programmed defect reticles with and without smoothing layers covering the programmed defect. We propose several criteria for smoothing layer specifications that are necessary to mitigate a size range of defects for an EUV imaging system.
Electron optical image correction subsystem in electron beam projection lithography
Authors: Kojima S. , Stickel W. , Rockrohr J. D. , Gordon M.
Published: July 2002

To obtain ultimate image fidelity in the PREVAIL electron beam projection lithography system (EB stepper) [Pfeiffer et al., J. Vac. Sci. Technol. B 17, 2840 (1999)], precise dynamic corrections [Zhu et al., Proc. SPIE 2522, 66 (1995)] of an exposed reticle subfield image on the wafer are required. The electron beam column for the EB stepper covers a large deflection area by a curvilinear variable axis lens (CVAL) [Stickel and Langner, J. Vac. Sci. Technol. B 17, 2847 (1999)] type deflection with high current, and very large 0.25 mm square beam. Because of these features together with tighter specifications for electron optics in below 70 nm node, aberrations which can be negligible in prior art electron beam lithography systems, can no longer be ignored. Therefore the electron optical image correction subsystem in the EB stepper is required to precisely correct the increased numbers of possible measurable aberrations caused by deflection as well as by space charge effects. In this article, a systematic overview of beam corrections is described.
Inter- and intramembrane resist critical dimension uniformity across a SCALPEL mask
Authors: Nordquist K. , Ainley E. , Resnick D. J. , Weisbrod E. , Martin C. , Engelstad R. , Masnyj Z. , Mangat P.
Published: July 2002

The use of chemically amplified (CA) resists in integrated circuit fabrication is accepted in semiconductor manufacturing as a way to achieve high resolution with excellent critical dimension (CD) control and etch selectivity. The use of CA resists for mask fabrication has not had as much favor due to resist storage stability issues and CD variations due to postexposure bake (PEB) sensitivities. One key component to the CD control on SCALPEL membrane masks is the thermal uniformity of the membranes and baking environment during the PEB process. This article discusses the numerical models created to predict temperature gradients within membranes and across membranes on a 200 mm SCALPEL mask. Verifications of the model by comparison of simulation results and actual CD data are also presented.
Structure of stochastic Coulomb interactions in electron beam columns
Authors: Wu Bo , Neureuther Andrew R.
Published: July 2002

The stochastic Coulomb interactions in a probe forming beam with a crossover show a strong symmetric structure with respect to the crossover region that can be utilized to reduce beam blur, especially in configurations in which all the beam angles are the same. The blur contribution is nearly constant with distance along the column even though the magnitude of the transverse forces increase nearly inversely with the distance from the crossover. A consequence is that to first order the blur only depends on the beam semiangle and column length. Simulations utilizing fast multipole accelerated techniques show that the blur is about 42 nm for 1 μA current in a 40 cm column with a 1.5 mR Gaussian semiangle. For beam projection systems such as SCAPEL simulation shows that an aperture near the crossover can increase the stochastic blur.
Focused ion beam patterning of III–V crystals at low temperature: A method for improving the ion-induced defect localization
Authors: Schneider M. , Gierak J. , Marzin J. Y. , Gayral B. , Gérard J. M.
Published: July 2002

In this study we have investigated the damage distribution induced by a focused ion beam irradiation on a GaAlAs/GaAs heterostructure. The samples were kept at various temperatures during ion bombardment: room temperature (RT), 80 and 22 K. The samples were then characterized, after being warmed up at RT, using photoluminescence (PL) experiments without any subsequent annealing. Stable, reproducible, and localized modulation of the PL characteristics of several GaAlAs/GaAs heterostructures are demonstrated. The defect localization is found to be considerably improved for a sample kept at 22 K during irradiation.
Fixed-bed microreactor for transient kinetic experiments with strongly adsorbing gases under high vacuum conditions
Authors: van Veen A. C. , Zanthoff H. W. , Hinrichsen O. , Muhler M.
Published: July 2002

The fixed-bed microreactor used for carrying out transient kinetic experiments in the temporal analysis of products (TAP-1) reactor was significantly modified, thus allowing investigations with strongly adsorbing gases. The design of this microreactor minimized side reactions and adsorption on the reactor walls in order to perform catalytic measurements over low surface area catalysts using very small pulses under high vacuum conditions. These enhancements were achieved by fitting an inert quartz insert into a metallic reactor body which was specially designed for isothermal operation. Furthermore, the gas feed system was rebuilt using glass-lined heated tubing allowing the calibration of strongly adsorbing gases (e.g., methanol and formaldehyde). The modified TAP-1 microreactor was used to study the kinetics of methanol oxidation to formaldehyde over an electrolytically prepared silver catalyst. The distinct modification of the microreactor and the feed system allowed a quantitative analysis of the experiments.
Development of procedures for obtaining clean, low-defect-density Ge(100) surfaces
Authors: Chan L. H. , Altman E. I. , Liang Y.
Published: July 2002

A repeatable, in situ process was developed for preparing clean, low-defect-density Ge(100) surfaces based on scanning tunneling microscopy (STM), Auger electron spectroscopy (AES), and x-ray photoelectron spectroscopy (XPS) measurements. Surfaces prepared by ion sputtering followed by annealing, wet chemical etching followed by oxidation and thermal desorption of the oxide layer, growth of a Ge buffer layer, and in situ plasma cleaning were compared. The first two methods produced surfaces with no impurities detectable by AES, however, STM images of the surfaces revealed numerous protrusions, vacancies, and other defects. Auger electron spectra and STM images recorded before and after annealing C contaminated surfaces suggested that the protrusions were three-dimensional C clusters formed at elevated temperatures. The low surface to volume ratio of the clusters makes them difficult to detect by either XPS or AES. Although XPS indicated that oxygen plasma treatment effectively removes C from Ge surfaces, images of the plasma treated surfaces still showed the protrusions attributed to C. In contrast, surfaces prepared by Ge buffer layer growth followed by annealing exhibited no protrusions, low-defect densities on the terraces (less than 2% of a monolayer), and evenly spaced terraces that reflect the misorientation of the crystal. Thus, the surfaces prepared by Ge buffer layer growth were determined to be the most suitable for atomic level nucleation and growth studies.
Complex roughening of Si under oblique bombardment by low-energy oxygen ions
Authors: Alkemade P. F. A. , Jiang Z. X.
Published: July 2002

Surface roughening of Si under bombardment with oblique O2+ beams at energies between 0.5 and 2 keV was studied with atomic force microscopy and secondary ion mass spectrometry. At beam energies of 1 keV and below, the general features of the topography and the magnitude of the roughness depended critically on the incidence angle. In most cases there were two angular ranges where surface roughening was strong, in-between and at grazing incidence roughening was minimal. Apart from the known topographical features—ripples and irregular bumps—triangular elevations were observed. In many cases, the local angle of incidence at the beam-facing slopes of the ripples corresponded to the maximum in sputter rate. Furthermore, the average distance between adjacent ripples increased with depth until saturation. It is concluded that the complexity in the topographies is caused by a delicate balance between several roughening and smoothing mechanisms.
Immersion lithography at 157 nm
Authors: Switkes M. , Rothschild M.
Published: July 2002

We present a preliminary study on the feasibility of immersion lithography at 157 nm for patterning below 70 nm. This technology can enable an enhancement in resolution of ∼40% without radical changes in lasers, optics, or resist technology. We have identified a class of commercially available liquids, perfluoropolyethers, which are good candidates for use as immersion liquids. They are transparent (α≈10−3 μm−1 base 10), optically clean, chemically inert, and compatible with at least some current resist materials and with the semiconductor manufacturing environment. We have also constructed a high-resolution lensless interference immersion lithography system, preserving much of the design of a previous nonimmersion interference system. With this immersion interference tool, we have patterned resist with 30 nm dense features.
Room-temperature fabrication of hard AlN/TiN superlattice coatings by pulsed laser deposition
Authors: Pankov V. , Evstigneev M. , Prince R. H.
Published: July 2002

Factors affecting the stability of the deposition rate of TiN and AlN during pulsed laser deposition (PLD) were studied using a quartz crystal microbalance technique. Monitoring of optical emission of plasma generated during laser ablation proved effective for stabilizing the deposition rates during superlattice fabrication. As a result, high-quality AlN/TiN superlattices with a pronounced hardness enhancement effect have been fabricated for the first time by the PLD technique at room temperature. The coatings were studied by a nanoindentation technique based on a scanning probe microscope, low-angle x-ray diffraction, and atomic force microscopy. Drastic changes in the nanohardness and surface morphology were observed in AlN/TiN structures when the bilayer period was reduced below 3 nm. These changes were assigned to a hexagonal-to-cubic phase transformation in AlN.
Recent advances in resists for 157 nm microlithography
Authors: Trinque Brian C. , Chiba Takashi , Hung Raymond J. , Chambers Charles R. , Pinnow Matthew J. , Osborn Brian P. , Tran Hoang V. , Wunderlich Jennifer , Hsieh Yu-Tsai , Thomas Brian H. , Shafer Gregory , DesMarteau Darryl D. , Conley Will , Willson C. Grant
Published: July 2002

The synthesis and characterization of several new fluoropolymers designed for use in the formulation of photoresists for exposure at 157 nm will be described. The design of these platforms has in some cases been inspired by ab initio quantum mechanical calculations of excited state transition energies and by interpretation of gas phase VUV spectrophotometric data. We have explored anionic polymerizations, free radical polymerizations, metal-catalyzed addition polymerizations and metal-catalyzed copolymerizations with carbon monoxide in these studies. The polymers and resist formulations were characterized by VUV spectrometry and variable angle spectroscopic ellipsometry (VASE). Resist formulations based on these polymers were exposed at the 157 nm wavelength to produce high-resolution images that will be presented.
Low temperature wafer bonding by spin on glass
Authors: Lin H. C. , Chang K. L. , Pickrell G. W. , Hsieh K. C. , Cheng K. Y.
Published: July 2002

We report the development of a low temperature (∼400 °C) and low pressure (∼0.5 kg/cm2) spin-on-glass (SOG) wafer bonding technique that can bond compound semiconductors and silicon without using chemical-mechanical polishing, surface etching or other intermediate materials in the bonding process. The relation of bonding quality and applied bonding pressure was studied. Cross sectional transmission electron microscopy analysis shows that the bonding interface is smooth, uniform and did not generate dislocations. Using this SOG bonding method, simulated vertical-cavity surface-emitting laser (VCSEL) structures that consist of GaInAs and InP cavities sandwiched by Al–oxide/Si distributed Bragg reflectors (DBRs) were successfully bonded to a silicon substrate with the bonding interface located outside the bottom DBR away from the VCSEL cavity.
Multi-aperture ion source with a deflectable focused beam for compositional control in sputter deposition
Authors: Smits J. W.
Published: July 2002

Composition control in ion beam sputtering of thin films can be achieved by electrostatic deflection of a focused ion beam. The necessary adaptation of a multi-aperture ion source consists in using a spherically dished screen grid and an accelerator grid built up from bent deflection plates. At a total accelerating voltage of 2 kV, a focused Ar+ beam of ∠10 mA is obtained, which can be deflected up to 11° with deflection voltages not exceeding 120 V.
Optical information storage using explosive crystallization in amorphous films
Authors: Wickersham C. E. , Bajor G. , Greene J. E.
Published: July 2002

Optical information storage utilizing the explosive crystallization of amorphous In1−xGaxSb films is reported. Information encoding is accomplished using a low power, focused laser beam to crystallize local areas of the film by normal nucleation and grain growth. The remainder of the film is ‘‘developed’’ by spontaneously propagating an explosive crystallization (EC) front. The formation can be retrieved by rastering a low intensity laser beam across the storage media and detecting the difference in optical reflectivity between the roughened EC matrix and the smooth highly reflecting laser annealed regions. A 15:1 signal-to-noise ratio has been obtained in initial experiments with 5 μm diameter recorded spots. The spot temperature and laser power densities required for writing with this approach are expected to be lower than in comparable techniques where melting or vaporization is required.
Propagation of explosive crystallization in thin Rh–Si multilayer films
Authors: Floro J. A.
Published: July 2002

Alternating layers of Si (400–500 Å thick) and Rh (200 Å thick), up to 21 layers altogether, have been deposited by electron beam evaporation under high vacuum conditions on to thermally oxidized silicon substrates at room temperature. Many of the as-deposited samples exhibit varying degrees of surface roughness. RBS and AES profiles of these samples show that layer intermixing has occurred; the number of layers consumed in the reaction correlates with the degree of surface roughness. The compounds Rh4Si5 and Rh3Si4 have been identified by x-ray diffraction. Both compounds are known to form by nucleation-controlled kinetics at temperatures in excess of 800 °C. However, in this case it appears that reaction occurred via an explosive crystallization process initiated in situ by the arrival of hot Si microparticles. Propagation of the crystallization wave front around secondary Si microparticles results in the formation of a variety of striking geometric surface morphologies. These morphologies can be grouped into three distinct classes or types. Though individual morphologies arise from a random process, the emission of Si microparticles during evaporation, each class of morphologies is itself phenomenologically repeatable and relates to the energy balance governing the propagation of the explosive crystallization wave front. In addition, multilayer films left unreacted after deposition have been explosively crystallized at room temperature by tapping with a stylus or by pulse laser heating, with similar results.
Growth of ultrathin single-crystal NiSi2 layers on Si(111)
Authors: Tung R. T.
Published: July 2002

Reaction of monolayers of nickel with Si(111) toward the formation of single-crystal epitaxial NiSi2 layers is examined in detail. New results are presented to illustrate the dependence on the processing parameters. A model is shown to successfully account for the experimental results.
Catalytic hydrogenation activity of a ZrNi3 intermetallic alloy
Authors: Wright R. B. , Jolley J. G. , Owens M. S. , Cocke D. L.
Published: July 2002

The catalytic hydrogenation activity of a ZrNi3 intermetallic alloy has been determined and has been found to be more active than either pure Ni or Pt for the hydrogenation of ethylene to ethane. The ZrNi3, prepared by arc melting, was powdered and sieved (−200, +325 mesh) and tested in a microcatalytic reactor at atmospheric pressure from 30 to 200 °C using a reactant gas stream of composition He:H2:C2H4=78:20:2 at a total flowrate of 390.8 standard cm3/min. Pure, powdered Ni and Pt were also studied under the same conditions. The test results indicate that from 30 to 120 °C the relative hydrogenation activities are ZrNi3>Pt>Ni for this reaction. Over this temperature range the apparent activation energies were found to be ZrNi3=7.1 kcal/mol, Pt=11.5 kcal/mol, and Ni=7.0 kcal/mol. Above ∼100 °C the activity of the ZrNi3 begins to decline (as does that of Pt from previous studies). Upon pretreating the ZrNi3 in an O2/He stream at 400 °C for 2 h followed by a 2-h treatment in H2 at 400 °C the activity increased and the apparent activation energy decreased to 0.75 kcal/mol. A further treatment at 550 °C caused the apparent activation energy to decrease to 0.40 kcal/mol. Both of these O2 treatments also resulted in an enhanced stability of the alloy with regard to its time-on-stream activity and in its activity temperature maximum being extended to ∼140 °C. The catalytic activity of ZrNi3 is due to an O2 induced decomposition into a NiO/ZrO2 mixture residing on an inner core at ZrNi3 alloy. Upon reduction the active catalyst is reduced Ni dispersed on ZrO2 which, in turn, is present as a thin film on the ZrNi3 core.
A new theory for the anisotropic etching of silicon and some underdeveloped chemical micromachining concepts
Authors: Kendall Don L.
Published: July 2002

A new model for the anisotropic etching of Si predicts a maximum dissolution rate at 22 wt. % KOH:H2 O and a zero etch rate at the solubility limit of KOH in H2 O, which is in good agreement with experiments on {100} and {110} Si. However, the {111} etch rate may decrease continuously with OH− concentration (no peak) and appears to be blocked by OH:3H2 O or some other threefold complexes that attach themselves to every bond on this surface. The strong effects of organics on the etching of convex corners, groove bottoms, and the relative etch rates on the three major orientations are noted, as are the possible effects of Fe and other impurities on the etching velocity and geometry of misorientation steps. The ability to pass current preferentially down the face of these steps needs to be developed before several unique functions can be tested. These include the fabrication of atomic wires, chiral molecule filters, and a sort of flying carpet type of air foil; the functions of which are based on clockwise facing steps on all four walls of holes in single crystal wafers. Vertical thin studs containing controlled pore diameters ranging from 1 to 1000 nm can be formed easily into semipermeable membranes and other complex structures. These interdigitated three dimensional structures can be applied to desalinization, fuel cells, biological membrane and neuron simulation, chemical and nuclear reaction schemes, and much more. The fabrication of micromirrors and lenses is also discussed.
A hyperthermal (0.1–4 eV) F atom beam source suitable for surface etching investigations
Authors: Levis Robert J. , Waltman Curtis J. , Cousins Lisa M. , Copeland R. Guild , Leone Stephen R.
Published: July 2002

Using laser vaporization of cryogenic films of XeF2, a beam of F atoms is produced with most probable kinetic energy variable from 0.3 to 1.1 eV. Fluorine atoms are observed with energies up to 4.3 eV. Also present in the beam are F2, Xe, XeF, XeF2, and impurity H and HF. The beams are produced by vaporizing thin films of XeF2 with 266 nm photons of a quadrupled Nd:YAG laser (∼0.5 J cm−2, 5 ns). The kinetic energy of the F atoms can be increased monotonically by decreasing the repetition rate of the vaporization laser from 1 to 0.1 Hz while the deposition rate of XeF2 is constant. The relative velocities of the heavier species are always less than that of the F atoms, but their most probable energies are greater than the energy of the F beam. This result suggests that a hydrodynamic flow of the lighter species propels the heavier F2, Xe, XeF, and XeF2 particles to higher velocities. Evidence is presented that complete desorption of the XeF2 film occurs within the vaporization area during each laser pulse, from which a desorption yield can be estimated. Such a source may be suitable for novel studies of anisotropic etching of semiconductor substrates with energetic reactive species.
Zirconia/pack-aluminized Co–29Cr–6Al–1Y thermal barrier coatings
Authors: Chang S. F. , Chao C. H. , Wu B. C. , Leu R. Q. , Chang E.
Published: July 2002

A modified two-layer thermal barrier coating (TBC) was studied. In this work, the vacuum plasma sprayed Co–29Cr–6Al–1Y bond coat (first layer) received a pack aluminizing treatment prior to deposition of the air plasma sprayed ZrO2–8-wt. %Y2O3 top coat (second layer). The effects of this treatment on the properties of plasma sprayed thermal barrier coatings were evaluated by thermal cycing tests in air within the temperature range from 1000 to 1150 °C. Results of experiments showed that the performance of TBC can be improved by the prior aluminizing treatment on Co–29Cr–6Al–1Y bond coat. This treatment was found to be very effective in reducing the oxidation rates of the bond coat. The fractographic analyses were also conducted on the spalled specimens to elucidate the performance improving mechanisms of TBC effected by the attempted prealuminizing treatment on the bond coat.
State-specific study of hydrogen desorption from Si(100)-(2×1): Comparison of disilane and hydrogen adsorption
Authors: Shane S. F. , Kolasinski K. W. , Zare R. N.
Published: July 2002

The desorption of hydrogen from the monohydride species on Si(100) has been studied state specifically using (2+1) resonance-enhanced multiphoton ionization. The monohydride phase was prepared by dosing the surface with either disilane (Si2H6) or atomic hydrogen. Adsorption of disilane with subsequent desorption of H2 leads to the growth of an epitaxial silicon film, based on evidence obtained with scanning electron microscopy and low energy electron diffraction. We report that the rovibrational-state distribution for hydrogen desorbed from Si(100) is the same after both disilane and atomic-H adsorption. Hydrogen desorbs with low average rotational energy but with a population in the v=1 state enhanced by roughly 20 times over a thermal distribution at the temperature of the surface. The agreement between internal-state distributions for both adsorption schemes indicates that the desorption of hydrogen during epitaxial growth of Si after Si2H6 adsorption proceeds in the same manner as that for a hydrogen-prepared Si(100)-(2×1):H surface.
Growth and morphology of partial and multilayer Fe thin films on Cu(100) and the effect of adsorbed gases studied by scanning tunneling microscopy
Authors: Johnson K. E. , Chambliss D. D. , Wilson R. J. , Chiang S.
Published: July 2002

Fe epitaxy on Cu(100) is investigated for Fe coverages θ≤3.0 ML. The layer filling statistics are quantitatively related to an evolving growth process, which includes intermixing at the substrate overlayer interface. The resulting inhomogeneous substrate surface and first layer affect the processes by which arriving Fe atoms add to the growth front. Our results explain the previously reported covering of initial Fe not as bilayer growth, but instead as the result of island growth on top of Fe incorporated in the top substrate layer. First layer composition and structure influence the nucleation and growth of the second layer. Island coalescence and formation of a first layer percolation network change the connected first layer area thereby changing the nucleation and growth behavior of the second layer. After both first and second layer growth are completed, images show additional growth is much more layer-by-layer in nature. Oxygen exposure after Fe deposition changes the layer filling by both promotion of step crossing and expansion of partially filled Fe layers.
Thin film properties of germanium oxide synthesized by pulsed laser sputtering in vacuum and oxygen environments
Authors: Wolf Paul J. , Christensen Thomas M. , Coit Nathan G. , Swinford Richard W.
Published: July 2002

Germanium oxide thin films were deposited on Si substrates at ambient temperature using pulsed laser sputtering of GeO2 targets in both vacuum and oxygen environments. The structure and composition of these films were deduced from infrared transmittance and Auger electron spectroscopy measurements. The film properties were strongly influenced by the pressure of the background reactive gas and the laser fluence during deposition with O2. The vacuum deposited films had a low oxygen content and the film’s stoichiometry varied from metal rich at the center to oxidelike near the edges of the film. The films deposited in oxygen appeared stoichiometric and they showed no content variation with radius. Ellipsometry studies indicated, however, that the oxygen grown films were porous. The trends observed in growing these films under various conditions are discussed with respect to potential reaction kinetics in the plume and gas expansion phenomena.