bluuebunny/crossref_metadata_2025 huggingface dataset:
Velocity Fields of Nonpremixed Bluff-Body Stabilized Flames
Authors: Huang R. F. , Lin C. L.
Published: July 2002

The velocity fields of nonpremixed circular-disk stabilized flames are measured by a two-component laser Doppler velocimeter. The results are presented in different flow regimes: prepenetration, penetration, and large shear flow. The velocity-vector fields, streamline patterns, corresponding flame appearances, and axial length of recirculation bubble in different flow regimes are illustrated and compared. Mean velocity and turbulent stresses along the central axis are presented and discussed. The combustion characteristics in different characteristic flow regimes are presented through the discussion of entrainment, diffusion, mixing capabilities, flow patterns, and turbulence properties. The detached flames, particularly operating in the transition flow regime, offer a relatively efficient combustion situation. Operating the concentric-jets burner in the regime of high shear flow do not benefit mixing and flame stability through the bluff-body effect. [S0195-0738(00)00102-3]
A Numerical Study of Vortex Breakdown in Turbulent Swirling Flows
Authors: Spall Robert E. , Ashby Blake M.
Published: July 2002

Solutions to the incompressible Reynolds-averaged Navier–Stokes equations have been obtained for turbulent vortex breakdown within a slightly diverging tube. Inlet boundary conditions were derived from available experimental data for the mean flow and turbulence kinetic energy. The performance of both two-equation and full differential Reynolds stress models was evaluated. Axisymmetric results revealed that the initiation of vortex breakdown was reasonably well predicted by the differential Reynolds stress model. However, the standard K-ε model failed to predict the occurrence of breakdown. The differential Reynolds stress model also predicted satisfactorily the mean azimuthal and axial velocity profiles downstream of the breakdown, whereas results using the K-ε model were unsatisfactory. [S0098-2202(00)01601-1]
Flat-Ended Tool Swept Sections for Five-Axis NC Machining of Sculptured Surfaces
Authors: Sarma R.
Published: July 2002

The concept of swept sections for flat-ended tools is revisited with the goal of improving the accuracy of calculations in five-axis tool path generation. Firstly, the notions of partial and total swept sections (distinct from traditional swept sections) are introduced. It is shown that partial and total swept sections provide a more accurate representation of the geometry of the moving tool compared to traditional swept sections. Next, geometric and numerical methods focused on calculating partial swept sections are presented. These methods are based on calculating plane-circle intersections. Finally, the calculated partial swept sections are compared to the traditional swept sections. Variations from the traditional swept sections are characterized to provide guidelines to the tool path programmer. [S1087-1357(00)71101-4]
Optimizing the Smoothness and Temperatures of a Wet Clutch Engagement Through Control of the Normal Force and Drive Torque
Authors: Holgerson Mikael
Published: July 2002

Automatic transmission gear shifts are handled by wet clutches, which determine the smoothness. The clutch face temperatures during the engagements are often an important parameter for the total clutch life. A wet clutch test rig has been used to evaluate how a wet clutch engagement can be improved in terms of smoothness and temperature. This was performed with control based upon knowledge about friction characteristics and dynamic performance. The parameters used for control were the drive torque and the normal force on the clutch. By drive torque shut-off and reduced normal force the torque variations were greatly reduced and the temperature rise was decreased by 37%. [S0742-4787(00)01601-5]
Noise Reduction Using Finite-Length Flexible Segments
Authors: Chapnik Brian , Currie I. G.
Published: July 2002

In this work, the reduction of acoustic noise in piping systems through the installation of finite flexible segments is explored. A mathematical model describing the relevant parameters is developed. To verify the model, experimental work is undertaken using rubber hoses as flexible segments and air as the contained fluid. The effect of the segment on propagating acoustical energy is studied in terms of its insertion loss. Both theoretical and experimental results indicate that, for light fluid loading, the flexibility of the segment is only important when significant axial shell resonances exist, or when one or both acoustical termination impedances at the ends of the segment are much larger or smaller than the characteristic impedance of the medium. Further, the model indicates that for heavier fluid loading (i.e., when the compressibility of the flexible section is significant in relation to the bulk compliance of the fluid), in addition to higher associated insertion losses, the finite length resonances become more pronounced, and performance is less sensitive to small variations in the termination impedances. [S0739-3717(00)00402-5]
Er deposition in the submonolayer range on weakly boron-doped Si(111) surface
Authors: Palmino F. , Pelletier S. , Ehret E. , Gautier B. , Labrune J. C.
Published: July 2002

Erbium silicide growth on weakly boron-doped Si(111) was studied by scanning tunneling microscopy. The reactivity and the strain of this √3×√3R30° surface are different from those observed on Si(111) 7×7. These interesting features allow us to study the erbium silicide growth on a new interface. We have observed, in the submonolayer range, the formation of a metastable 2√3×2√3R30° reconstruction and the nucleation of two kinds of stable two-dimensional ErSi2.
Reflectance anisotropy spectroscopy of the growth of perylene-3,4,9,10-tetracarboxylic dianhydride on chalcogen passivated GaAs(001) surfaces
Authors: Kampen T. U. , Rossow U. , Schumann M. , Park S. , Zahn D. R. T.
Published: July 2002

The properties of organic molecular layers grown from perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) on GaAs(001) substrates were investigated using reflectance anisotropy spectroscopy/reflectance difference spectroscopy (RAS/RDS). In an attempt to grow ordered organic layers GaAs(001) surfaces were modified with sulfur prior to the evaporation of PTCDA under ultrahigh vacuum conditions. The chalcogen modification results in a gallium sulfide-like surface layer terminated by S dimers, which shows a (2×1) low-energy electron diffraction pattern. The lines shapes of the RAS spectra of S modified surfaces show sharp derivative-like features at the E1 gap and broad spectral features at higher energies likely related to E0′ and E2 gaps of bulk GaAs. For low PTCDA coverages the shape of the spectra in the energy range of the GaAs bulk features is unchanged which indicates a low interaction between substrate and organic layer. Additional features appear in the spectra for PTCDA coverages even below 0.3 nm which can be attributed to transitions between the highest occupied molecular orbital and the lowest unoccupied molecular orbital at 2.23 eV. While the sharp feature due to the E1 gap of GaAs is essentially unaffected, the optical anisotropy at higher energies is increasing strongly with increasing PTCDA layer thickness which is due to interference effects as shown by a model calculation.
Change in surface roughness with the thickness of TiO2 film grown on MgO(001) by Ar-ion beam sputtering
Authors: Uchitani Takeshi , Maki Kunisuke
Published: July 2002

The surface roughness, Ra, and the crystallinity are studied for the rutile-type TiO2 films at their thickness, d, above 10 nm deposited on the air-cleaved MgO(001) held at 630 °C at 3.1×10−3 Pa in the partial pressure of O2 by sputtering the Ti target by Ar-ion beam accelerated with 1.2 kV. The amount of Ra estimated by observing the surface morphology with an AFM is the order of nanometers and changes with d according to d1/2. The linear relationship between the intensity ratio of the (110) peak for the TiO2 to the (004) peak for the MgO in x-ray diffraction pattern and d2 is also confirmed which is evidence of little change in the film crystallinity during growth. These mean that the surface morphology of the TiO2 films at d>10 nm keeping their crystallinity is determined from the statistical fluctuation in the impinging vapor flux.
High-temperature strength stability of three forms of chemically vapor deposited tungsten
Authors: Bryant W. A.
Published: July 2002

Three types of CVD tungsten (fluoride-produced, chloride-produced, and a layered composite of the two-termed duplex) were evaluated to determine their high-temperature strength and microstructural stability following 5000-h exposure to temperatures of 1540 and 1700 °C. At the highest temperatures investigated (1540 and 1700 °C) the tensile strengths of the two basic materials were essentially equal. At lower temperatures, chloride tungsten possessed lower yield strength but higher ultimate strength than fluoride tungsten while the behavior of the duplex material was generally intermediate. Apparent anomalies in high-temperature elongation behavior are explained on the basis of grain boundary cavity formation and recrystallization. The grain size of fluoride tungsten changed only slightly following 5000-h treatment at 1700 °C. In contrast, chloride tungsten possessed both poor resistance to grain growth and an accompanying relatively high ductile–brittle transition temperature.
Supercritical drying for water-rinsed resist systems
Authors: Namatsu Hideo
Published: July 2002

Two methods of supercritical resist drying (SRD) using CO2 have been developed for water-rinsed resist patterns. The key to their effectiveness is the use of a surfactant. In indirect SRD, a solution of n-hexane, a CO2-philic liquid, and a surfactant, sorbitan fatty acid ether, first replaces the water, and is in turn replaced with liquid CO2 before SRD is performed. The addition of a compound with a high hydrophilic-lipophilic balance to the surfactant compensates for the poor miscibility of water in a solution of n-hexane and sorbitan fatty acid ether. In direct SRD, which does not require a CO2-philic liquid, the water is replaced directly with liquid CO2 containing a surfactant, fluoroether carboxylate, which makes water miscible in CO2; and then SRD is performed. The excellent results obtained by both methods demonstrate that there is no inherent barrier to the use of SRD on water-rinsed resist patterns.
Beam steering system and spatial filtering applied to interference lithography
Authors: Konkola Paul T. , Chen Carl G. , Heilmann Ralf K. , Schattenburg Mark L.
Published: July 2002

Production of metrologically accurate interference patterns with subnanometer fidelity requires precise control of beam position and angle. We consider the beam stability requirements for the cases of interference by plane and spherical waves. Interferometers using beamsplitter cubes and diffraction gratings are among the analyzed topologies. The limitations of spatial filtering to remove angular variations are also discussed. We present a beam steering system that uses position sensing detectors, tip-tilt actuators, and digital control to lock the beam position and angle at the interference lithography system. We describe the prototype’s performance and limitations of this approach. This beam steering system allows us to locate the laser far (∼10 m) from the sensor assembly, thereby reducing the thermal and mechanical disturbances at the lithography station and allowing sharing of the laser between different lithography tools.
Thick Epitaxial Films of Cubic Zinc Sulfide Deposited by a Hot Wall Technique
Authors: Behrndt Marianne E. , Moreno Salvatore C.
Published: July 2002

A vacuum technique is described which permits the deposition of epitaxial films of ZnS in thicknesses up to 100 μ. Results of electron diffraction and observations of the surface morphology are described. The films can be used in devices which are based upon electro-optic effects.
Kinetics and Thermodynamics in Continuous Electron-Beam Evaporation of Binary Alloys
Authors: Santala Teuvo , Adams C. M.
Published: July 2002

Continuous electron-beam evaporation of binary alloys was studied. Silver-copper wires with 5, 10, 20, and 30 at.% of silver were fed into an evaporation source which was heated by an electron beam. Beam powers up to 4.5 kW were used and evaporation temperatures from 1625–1960 K were obtained. Methods were developed to study mass and composition distribution of the vapor flux, the transient period, and the steady-state conditions. Prediction of the transient and the steady-state relationships among the compositions of the feed wire, the evaporant bath, and the vapor deposit, based on (a) published thermodynamic properties of silver-copper alloys, and (b) the assumption that the Langmuir equation correctly relates the evaporation rate of a particular component from solution to the equilibrium partial pressure of that component, agrees closely with experimental results. This means that transport within the liquid phase by diffusion or convection is not a significant rate-controlling factor.
Codeposition on diamond film surface during reactive ion etching in SF6 and O2 plasmas
Authors: Teii K. , Hori M. , Goto T.
Published: July 2002

The surface of polycrystalline diamond films during reactive ion etching in electron cyclotron resonance SF6 and O2 plasmas has been examined by scanning electron microscopy, Raman spectroscopy, and x-ray photoelectron spectroscopy. A SF6 plasma required a high voltage in negative substrate biasing in order to achieve an equivalent etching rate to an O2 plasma. This was ascribed to the codeposition effects and the low mean energy of ions upon impact in a SF6 plasma. The elemental composition of the amorphous layer formed at the etched film surface in the two plasmas was almost equivalent and mainly composed of carbon and oxygen, except a low concentration (⩽1%) of sulfur and fluorine in the case of a SF6 plasma. The significant codeposition on diamond surface was the most likely the result of plasma–wall interactions induced by the fragments from SF6, and highly responsible for suppressing the ratio of lateral to vertical etching rate leading to anisotropic etching in a SF6 plasma, in contrast with the little or no codeposition leading to isotropic etching in an O2 plasma. The results give the substantial implications for the etching process in practical SF6/O2 plasmas utilized in device fabrication.
The Use of Diffusion Pumps for Obtaining Ultraclean Vacuum Environments
Authors: Santeler Donald J.
Published: July 2002

Most of the vacuum systems in the world are contaminated with hydrocarbons. In some instances, it has become popular to blame this contamination on oil-diffusion pumps. This paper will first analyze the various other sources of hydrocarbons which are frequently present in vacuum systems in terms of their magnitude and elimination. The effectiveness of different types of traps will be considered in terms of their ability to stop different types of pump-generated gases. As a result of this analysis, it will be shown that properly designed and properly operated oil-diffusion-pumped systems can produce ultraclean vacuum environments as demonstrated by base pressures in the 10−14 Torr range.
Control of Film Properties by rf-Sputtering Techniques
Authors: Vossen J. L.
Published: July 2002

The versatility of rf sputtering and related processes often allows one to tailor the properties of thin films in ways not always available with other methods of film deposition. Effects that occur at the target, in the gas discharge, and at the substrate are reviewed in the context of their over-all effect on the physical and chemical properties of thin films. Special emphasis is placed on the effects of substrate temperature and the bombardment of substrates by various energetic species. Techniques involving controlled bombardment of substrates (deposition with rf-induced substrate bias) are considered in detail.
Adsorption of Mixed Gases on a Pyrex Glass Surface at Very Low Pressures
Authors: Tuzi Y. , Kobayashi M. , Asao K.
Published: July 2002

The physical adsorption of mixed gases, N2–CO, Kr–CO, and Kr–Xe, on a Pyrex glass surface was studied at the pressure range of 10−6–10−8 Torr and at the temperature of 77.4 K. The amounts of adsorption for component gases were obtained from the partial pressure variation after rapid cooling of the adsorbent. The amounts were also measured using the thermal desorption method. The component gases with lower activation energy of desorption seem to be replaced by the gases with higher activation energy of desorption. The replacement of gases physisorbed at 77.4 K and low coverages suggests the existence of heterogeneity on a Pyrex glass surface. The accuracy of residual gas analysis by the physical desorption spectrometer is likely to be limited by the replacement phenomena of physisorbed gases.
The Deposition of Multicomponent Phases by Ion Plating
Authors: Harker Howard R. , Hill Russell J.
Published: July 2002

Some preliminary results obtained using electron beam evaporation of multicomponent phases are presented. The combination of ion plating and the use of a rod-fed electron beam source allows coatings to be made with both alloy and compound materials on substrates which have been very difficult in the past. The results include both metallic and nonmetallic coatings on dielectric substrates.
Mass Spectrometric Analysis of the Sputter Gas Atmosphere without Pressure Reduction System
Authors: Visser J.
Published: July 2002

The pressure reduction method commonly used in monitoring gas composition at relatively high pressures is not adequate for application to sputter gas analysis. Desorption phenomena in the ion source of the spectrometer and adsorption phenomena in other parts of the reduction stage cause extraneous errors in the partial pressure measurement of most of the gases of interest. A successful attempt has been made to perform gas analysis without a reduction stage. Analysis of the influence of ion-atom (molecule) scattering on the performance of ionizer, extractor, and analyzer for different types of residual gas analyzers shows that a miniquadrupole offers the best prospects for this special purpose. Comparative data for a quadrupole and cycloidal mass spectrometer operating at an argon pressure of 2.10−3 Torr are given. Resolution, sensitivity, and linearity of the quadrupole have been determined at sputtering pressures (10−3–10−2 Torr). The resolution remains quite satisfactory (M/ΔM = 2.5 M when ΔM is measured at 50% peak height). The sensitivity decreases with increasing pressure. However, at 5.10−3 Torr nitrogen partial pressures of 10−8 Torr can still be detected. Simultaneous measurement of the sputter gas atmosphere by the pressure reduction method and the quadrupole during the deposition of gold in a planar rf sputtering system shows that the quadrupole which is directly connected to the sputter chamber allows a more accurate identification of the background gases.
Some Special Pumping Problems Associated with the Sputtering Application
Authors: Lamont Lawrence T.
Published: July 2002

The sputtering environment imposes special requirements upon a vacuum system. Not only does the operator face the dual requirements of UHV cleanliness and high pressure operation, but the gas discharge present during the deposition may greatly increase the reaction rate of surface contaminants. This is shown to modify certain conclusions regarding backstreaming and trapping otherwise valid. Further, it is shown that the system “base pressure” may be a grossly misleading parameter and that the critical properties of a vacuum system for sputtering are cleanliness during the initial pumpdown to high vacuum and the maximum usable throughput at the sputtering pressure.
Characteristics, advantages, and possible applications of condensation cryopumping
Authors: Benvenuti C.
Published: July 2002

A few years ago, serious doubts were raised about the possibility of obtaining very low pressures by means of condensation cryopumping. In fact, the equilibrium pressure of condensed H2 was found, in various laboratories, to deviate from the Clausius–Clapeyron law below about 3 K and to reach a temperature independent value ranging from 10−11 to 10−9 Torr. This phenomenon has since been investigated and clarified such that H2 saturation pressures as low as 10−14 Torr have been obtained in our laboratories. In parallel, a drastic improvement of the cryogenic aspect of cryopumping has made it possible to achieve the very high pumping speeds characterizing this pumping technique while still keeping the operating cost very low. The performance of a few cryopumps made at CERN will be presented and critically compared to those of pumps of different types. Although developed for extremely low pressures (below 10−11 Torr), we will show that these cryopumps could be advantageously used for higher pressure applications.
Switching Phenomena in Thin Films
Authors: Adler David
Published: July 2002

Of the two types of switching phenomena which characterize thin films of amorphous semiconductors, it is now generally acknowledged that memory switching is basically well understood, not only in principle, but in detail. On the other hand, threshold switching has been a subject of some controversy, and a plethora of mechanisms has been proposed. In this paper, equilibrium and high-field characteristics as well as switching properties of threshold-type material are reviewed, and the suggested mechanisms are critically analyzed in the light of recent experimental results.
Gas Desorption Temperatures of Two Molecular Sieves
Authors: Miller H. Craig
Published: July 2002

This paper considers the problem of finding the temperatures of the desorption maxima for various gases absorbed on 5A and 13X molecular sieves at pressures of the order of 100μ. The desorption temperatures were not found to be strong functions of pressure. The measured desorption temperatures (in K) were, for 5A molecular sieve, Ar-110, O2-108, N2-145, CH4-151, CO-187, CO2-249, and H2O-410/430, and for 13X molecular sieve, Ar-103, O2-108, N2-137, CH4-137, CO2-255/285, and H2O-400/425. These temperatures were measured with rates-of-rise of temperature low enough to minimize errors caused by the actual sieve temperature lagging the measured temperature.
High-resolution residual gas analysis (HRRGA)
Authors: Fite Wade L. , Irving Philip
Published: July 2002

Analysis of residual gases in a typical oil-diffusion pumped and LN2-trapped vacuum system in the 10−7 Torr range under high resolution (greater than 3000) has yielded a number of surprise. It is found, among other things, that the mass 28 peak is a triplet with CO+ dominating both the N2+ and C2H4+ components. Mass 16 is primarily O+ but the remainder of the triplet is primarily NH2+ rather than CH4+ as commonly believed. Mass 44 is primarily CO2+ but two other ions are also present. Alkanes (e.g., C7H15+) and what are believed to be polystyrene fragments are major components near mass 100. Examination of a mercury-pumped vacuum system was made for comparison with the oil-pumped system, and a comparison of the results at several mass peaks is presented.
Step coverage in the vacuum deposition of thin metal films
Authors: Tisone T. C. , Bindell J. B.
Published: July 2002

In the vacuum deposition of thin metal films the details of the film coverage over surface steps are an important consideration in many technological applications. A theory is presented which describes the relationship between the target (or emitter) and receiver (or substrate) geometry, which allows for the calculation of geometric shadowing effects between points on the receiver plane. The theory is used to formulate a computer simulation of the deposition of a film over a step on the receiver surface. The simulation has been applied to a particular case of low-voltage triode sputtering. The results are discussed in terms of the step geometry, position on the receiver table, and receiver-to-target distance. The calculations are compared with experimental observations. A generalization of the theory to other types of vacuum deposition is considered which includes extended target systems (such as conventional sputtering systems) and small target systems with substrate motion (such as electron beam deposition with planetary motion). The effects of substrate temperature are discussed.
Influence of underlying interlevel dielectric films on extrusion formation in aluminum interconnects
Authors: Chen Fen , Li Baozhen , Sullivan Timothy D. , Gonzalez Clara L. , Muzzy Christopher D. , Lee H. K. , Levy Mark D. , Dashiell Michael W. , Kolodzey James
Published: July 2002

Knowledge of the mechanical properties of interlevel dielectric films and their impact on submicron interconnect reliability is becoming more and more important as critical dimensions in ultralarge scale integrated circuits are scaled down. For example, lateral aluminum (Al) extrusions into spaces between metal lines, which become more of a concern as the pitches shrink, appear to depend partially on properties of SiO2 underlayers. In this article nanoindentation, wafer curvature, and infrared absorbance techniques have been used to study the mechanical properties of several common interlevel dielectric SiO2 films such as undoped silica glass using a silane (SiH4) precursor, undoped silica glass using a tetraethylorthosilicate precursor, phosphosilicate glass deposited by plasma-enhanced chemical vapor deposition and borophosphosilicate glass (BPSG) deposited by subatmosphere chemical vapor deposition. The elastic modulus E and hardness H of the as-deposited and densified SiO2 layers are measured by nanoindentation. The coefficients of thermal expansion (CTE) of the densified layers are estimated by temperature-dependent wafer curvature measurements. Fourier transform infrared spectroscopy is used to obtain the chemical structures of all SiO2 layers. Among the four common interlevel layers, BPSG exhibits the smallest modulus/hardness and a relatively small amount of moisture loss during anneal. The BPSG shows the highest CTE, which generates the smallest thermal stress due to a closer match in the CTE between Al and SiO2. BPSG again has the lowest as-deposited compressive stress and the lowest local Si–O–Si strain before annealing. The center frequency of the Si–O bond stretching vibration exhibits a linear dependence on total film stress. The shifts of Si–O peaks for all the SiO2 layers also correlate well with the stress hysteresis obtained from wafer curvature measurements. Stress interactions between the various SiO2 underlayers and the Al metal film are also investigated. The impact of dielectric elastic properties on interconnect reliability during thermal cycles is proposed.
Nanofabrication and diffractive optics for high-resolution x-ray applications
Authors: Anderson Erik H. , Olynick Deirdre L. , Harteneck Bruce , Veklerov Eugene , Denbeaux Gregory , Chao Weilun , Lucero Angelic , Johnson Lewis , Attwood David
Published: July 2002

Short wavelength x-ray radiation microscopy is well suited for a number of material and life science studies. The x-ray microscope (XM1) at the Advanced Light Source Synchrotron in Berkeley, California uses two diffractive Fresnel zone plate lenses. The first is a large condenser lens, which collects soft x-ray radiation from a bending magnet, focuses it, and serves as a linear monochromator. The second is the objective zone plate lens, which magnifies the image of the specimen onto a high-efficiency charge coupled device detector. The objective lens determines the numerical aperture and ultimate resolution. New objective lens zone plates with a minimum linewidth of 25 nm and excellent linewidth control have been fabricated using Berkeley Lab’s 100 keV Nanowriter electron beam lithography tool, a calixarene high-resolution negative resist, and gold electroplating. Although the condenser zone plate is less critical to the resolution of the instrument, its efficiency determines the flux on the sample and ultimately the exposure time. A new condenser zone plate was fabricated and has a 9 mm diameter, 44 000 zones, and a minimum zone width of 54 nm (optimally the condenser and objective should have the same zone width). It is also fabricated with the Nanowriter at 100 keV using poly(methylmethacrylate) resist and nickel electroplating. The phase shift through the nickel absorber material enhances the diffraction efficiency over an amplitude only zone plate. To evaluate the microscope’s performance transmission test patterns have been made and imaged. Lineout data show modulation for 30 nm lines and 60 (1:2) spaces to be almost 100%. These new diffractive optical elements represent a significant advancement in the field of high-resolution soft x-ray microscopy. Diffractive optical elements have been used to measure the wave front error of an extreme ultraviolet projection optical system. The reference wave is generated by the spherical wave generated by diffraction from a small freestanding pinhole.
Proposal for a 50 nm proximity x-ray lithography system and extension to 35 nm by resist material selection
Authors: Kitayama Toyoki , Itoga Kenji , Watanabe Yutaka , Uzawa Shunichi
Published: July 2002

In this article, a 50 nm generation proximity x-ray lithography (PXRL) system is proposed using shorter wavelengths of exposure light down to around 3 Å. The illumination system uses a mirror at 1° incidence angle such as in the Canon stepper XRA-1000, which can be realized by coating with a fourth or fifth period metal such as Co or Rh. The resist containing chemical elements such as Cl, S, P, Si, and Br whose x-ray absorption edge lies in the wavelength band of the exposure light can yield a strong absorption using this system. Therefore, a resist material containing such elements is highly sensitive when applied to the 50 nm system. The average wavelength of power absorbed by the resist depends on the elements contained in the resist. This suggests that the resolution limits also depend on the resist material even for the same exposure system. Therefore, this system should be extendible down to the 35 nm generation by using such a resist and a thick diamond mask membrane. The system described assumes that the mask–wafer gap is the currently available 10 μm. In the future, an additional gain in resolution can be expected from a narrower gap. With these improvements, it is foreseeable that PXRL technology can be applied to the 20 nm regime, down to the operational limits of silicon devices at room temperature.
Laser reflectometryin situmonitoring structural and growth effects on the electron cyclotron resonance etching of In0.49Ga0.51P layers in Al-free laser structures
Authors: Mestanza S. N. M. , Frateschi N. C.
Published: July 2002

Electron cyclotron resonance (ECR) plasma etching of p- and n-In0.49Ga0.51P layers in Al-free laser structures is studied based on BCl3/N2 gas mixture. Laser reflectometry is used for the in situ etching analysis. Strong etching rate discrepancies are found for the same material whether inserted in multilayer laser structures or in single calibration layers. Strong etching dependence with growth conditions and beryllium concentration is found. Great reduction in etching rate is observed near p++GaAs/p++In0.49Ga0.51P interfaces depending on growth conditions. These results are explained by a 200 Å beryllium diffusion in the In0.49Ga0.51P material with subsequent formation of Be3P2 clusters in p-In0.49Ga0.51P during growth.
Friction force microscopy study on photodegradation of organosilane self-assembled monolayers irradiated with a vacuum ultraviolet light at 172 nm
Authors: Sugimura Hiroyuki , Hayashi Kazuyuki , Amano Yukihiro , Takai Osamu , Hozumi Atsushi
Published: July 2002

An alkylsilane self-assembled monolayer (SAM) has been micropatterned by the use of vacuum ultraviolet (VUV) light at 172 nm in wavelength radiated from an excimer lamp. By a chemical vapor deposition method, the SAM was prepared on Si substrates covered with native oxide from a precursor molecule of octadecyltrimethoxysilane. Micropatterning of the SAM was demonstrated based on a simple photomask-contacting method. Due to a distinct difference in friction coefficient between the VUV-irradiated and unirradiated regions, the photoprinted pattern was clearly imaged in friction force microscopy. The VUV-irradiated region showed stronger friction force than the unirradiated SAM surface. As confirmed by friction force microscopy, water contact angle measurements, and x-ray photoelectron spectroscopy, the SAM was found to be decomposed and removed due to the VUV irradiation. This photodegradation mechanism is ascribed to dissociative excitation of C–C and C–H bondings in the organosilane molecules and to subsequently proceeded oxidation with atomic oxygen radicals generated simultaneously through VUV excitation of atmospheric oxygen molecules. Microlines whose width was less than 1 μm could be fabricated based on this VUV lithography.
Microstructural investigation of α-Al2O3-epitaxially coated cemented carbide cutting tools
Authors: Ishii Toshio , Shima Nobuhiko , Ueda Hiroshi , Okayama Shirou , Gonda Masayuki
Published: July 2002

Cemented carbide cutting tools coated with a TiN layer, a Ti(C,N) layer, a bonding layer, and an α-Al2O3 layer by a chemical vapor deposition method have been developed. Epitaxial growth among the Ti(C,N) grains, the bonding layer grains, and the α-Al2O3 grains were observed by cross section transmission electron microscopy. X-ray diffraction results indicate that the epitaxial growth could be realized in many areas of the coating. This epitaxial growth can be considered as the origin for the improved close adherence of the layers and prolonged life of the developed cutting tools. It was also concluded that stepped surfaces of many vertical-plane shape protrusions in the bonding layer had promoted the epitaxial growth of the α-Al2O3 grains.
Influence of the different operations of gas in the large microwave plasmas
Authors: Wu Cong-Feng , Huang Wei-Dong , Zhan Ru-Juan
Published: July 2002

The study of discharge performance was performed for argon, nitrogen, and the H2–C2H5OH gas mixture in a power range from 250 to 1000 W, and a pressure range from 10 to 1000 Pa. With argon, a surface wave at the plasma-quartz interface can be excited above 250 W. The surface wave modes can be identified as m=4 and m=6 with pressures of 10 and 230 Pa. With nitrogen, surface waves propagate in two or more modes superposed with a different value of m below the pressure of 133 Pa. In contrast to the above gases, the H2–C2H5OH gas mixture showed no surface wave generation for power levels up to 1000 W; only a hemisphere plasma with a diameter of 8 cm was observed just above the substrate. The plasma, having a diameter of 160 mm, is uniform below the pressure of 133 Pa in nitrogen discharges, but the plasma density is lower than in argon discharges. The radial distributions of electron density in the quartz tube also prove the existence of surface waves for argon and nitrogen. In addition, the axial distributions of electron density prove that the traveling and standing surface waves can be excited by argon discharges in each case: with or without the short plunger at the top of the setup.
Near edge x-ray absorption fine structure spectroscopy study of atomic nitrogen implanted in Al2O3 by low energy N2+ bombardment
Authors: Barranco A. , Holgado J. P. , Yubero F. , Espinós J. P. , Martı́n A. , González-Elipe A. R.
Published: July 2002

N 2 + bombardment of Al2O3 has been investigated by near edge x-ray absorption fine structure spectroscopy. Two kinds of species were detected and were attributed to implanted nitrogen atoms and nitride species. These results are discussed in relation to previous attributions in the literature of these species to AlNO and AlN.
Structure, stability, and mechanical properties of epitaxial W/NbN superlattices
Authors: Madan A. , Barnett S. A. , Misra A. , Kung H. , Nastasi M.
Published: July 2002

Epitaxial W/NbN superlattices with modulation wavelengths Λ ranging from 1.3 to 25 nm were grown on MgO(001) substrates by dc reactive magnetron sputtering in Ar/N2 mixtures. The epitaxial relationship between the layers is given by W(001)‖NbN(001) and W[110]‖NbN[100]. X-ray diffraction and Rutherford backscattering results fitted using simulations showed that the superlattices had well-defined planar layers with interface widths of ≈0.2 nm. Nanoindentation measurements showed superlattice hardnesses as high as 33 GPa compared to 8 for W and 20 for NbN. The superlattices showed little change in x-ray superlattice reflections or nanoindentation hardness after vacuum annealing up to the highest temperature tested, 1000 °C for 6 h. Thus, the layers remained intact during annealing, allowing the superlattice hardness enhancement to be retained.
Epitaxial ScN(001) Grown and Analyzed In situ by XPS and UPS. I. Analysis of As-deposited Layers
Authors: Haasch R. T. , Lee T. -Y. , Gall D. , Greene J. E. , Petrov I.
Published: July 2002

X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS) were used to characterize as-deposited ScN(001) layers grown in situ. The films were deposited by ultrahigh vacuum reactive magnetron sputtering on MgO(001) at 800 °C in pure N2 discharges maintained at a pressure of 5 mTorr (0.67 Pa). Mg Kα and monochromatic Al Kα x-ray sources were used to obtain the XPS spectra, while the UPS data were generated by He I and He II UV radiation. The spectra show that the ScN(001) surfaces are free of O and C. The films were found to have a slight excess of nitrogen, in agreement with Rutherford backscattering spectroscopy (RBS) results, yielding a N/Sc ratio of 1.11 ± 0.03.
Raman study of luminescent spark processed porous GaAs
Authors: Rojas-López M. , Gracia-Jiménez J. M. , Vidal M. A. , Navarro-Contreras H. , Silva-González R. , Gómez E.
Published: July 2002

We have analyzed spark-processed porous GaAs (spp-GaAs) samples prepared by the application of high-voltage discharges at low repetition rates (20 Hz) in different ambients, ranging from pure nitrogen to pure oxygen flow, using a microRaman probe and a scanning electron microscope in combination with an energy dispersive spectroscopy system (SEM-EDS). We found that for samples prepared in pure nitrogen, the resulting material is basically amorphous material, with amorphous-GaAs with some cubic phase of As2O3 also present. For samples prepared under even a low concentration of oxygen, 20:1, we find that the cubic phase of As2O3 is substituted by the monoclinic phase of As2O3 “claudetite.” SEM micrographs show the resultant morphologies obtained that exhibit a porous, granular, agglomerated granular appearance. EDS and Raman suggest that the claudetite phase of As2O3 and As2O5 play a contributing role in the green-blue photoluminescence emitted by spp-GaAs.
Selective ultrahigh vacuum dry etching process for ZnSe-based II–VI semiconductors
Authors: Legge M. , Bacher G. , Bader S. , Kümmell T. , Forchel A. , Nürnberger J. , Schumacher C. , Faschinger W. , Landwehr G.
Published: July 2002

A selective dry etching technique for II–VI semiconductors based on ZnSe has been developed by using thermally assisted electron cyclotron resonance etching with a gas mixture of Ar, Cl2, and BCl3. While the etching process is found to be almost nonselective between ZnSe and MgZnSSe at low (<100 °C) and high (>220 °C) substrate temperatures, a strong selectivity is obtained in the intermediate temperature range (e.g., 12:1 for Tsub=180 °C). Due to the ultrahigh vacuum (UHV) design of the etching chamber, a complete in situ fabrication of buried II–VI nanostructures should be accessible.
Highly selective photoelectrochemical etching of nitride materials for defect investigation and device fabrication
Authors: Visconti P. , Reshchikov M. A. , Jones K. M. , Wang D. F. , Cingolani R. , Morkoç̌ H. , Molnar R. J. , Smith D. J.
Published: July 2002

Photoenhanced electrochemical (PEC) etching in an unstirred KOH solution under He–Cd laser illumination was used for delineating extended defects in GaN films. When a low-excitation intensity was employed, the process yielded threading vertical features at dislocation sites. Application of an external voltage or a higher-illumination intensity led to high-etch rates with smooth surfaces. Some highly resistive samples, for which no etching was obtained under normal etching conditions, could be etched with the application of a single-polarity external voltage. Finally, in a GaN sample with an AlN/GaN superstructure inside, high selectivity between AlN and GaN was achieved; in this case, the PEC process stopped at the thin AlN stop layer.
Growth of NiO films on various GaAs faces via electron bombardment evaporation
Authors: Nishita K. , Koma A. , Saiki K.
Published: July 2002

Growth of NiO films was examined on various crystal faces of GaAs by using a single electron bombardment source. Use of alkali halide buffer layers achieved good quality of epitaxial growth on GaAs (001). Electron spectroscopies (Auger electron spectroscopy, ultraviolet photoelectron spectroscopy, electron energy loss spectroscopy) revealed that the grown NiO film has almost the same electronic structure as bulk NiO. This method helps integration of 3d transition-metal oxides on technologically important materials such as GaAs or Si.
Deep etching of silicon carbide for micromachining applications: Etch rates and etch mechanisms
Authors: Chabert P.
Published: July 2002

The etch rate of 4H–SiC in a SF6 helicon plasma has been investigated as a function of pressure, rf power, bias voltage and distance between the substrate holder and the helicon source. Very high etch rates of 1.35 μm/min were achieved when this distance is minimum. Good uniformity on 2 in. SiC substrates and smooth etched surfaces free of micromasking have been obtained when using a nickel mask. The selectivity SiC/Ni was found to be about 50 in high etch rate conditions. Via holes have been etched to a depth of 330 μm in 4H–SiC substrates. Etch mechanisms were also studied in a parallel-plate capacitively coupled reactor. We have detected by laser-induced fluorescence (LIF), the radicals SiF2, CF, and CF2 produced during the reactive ion etching of SiC in a pure SF6 plasma. Spatially and temporally resolved LIF measurements were used to distinguish between gas phase and etched surface production of these species. Whereas CF and CF2 are primary etch products (i.e., mainly produced at the etched surface), the SiF2 radicals are mainly produced in the gas phase (probably by electron impact dissociation of SiF4, the putative major etch product). We attribute this difference to the formation of a carbon-rich layer on the SiC substrate surface. The removal of this layer, which is a rate-limiting step, produces unsaturated CFx (x=1,2,3) radicals. The CF2 radical represents up to 20% of the total carbon etch products under our conditions.
Surface passivation of GaAs using an ultrathin cubic GaN interface control layer
Authors: Anantathanasarn Sanguan , Hasegawa Hideki
Published: July 2002

An attempt was made to passivate the GaAs surface by a Si3N4/c-GaN/GaAs passivation structure, having an ultrathin cubic GaN as an interface control layer (ICL) with a wide energy gap. The GaN ICL was formed by direct nitridation of GaAs with active nitrogen radical species in a molecular beam epitaxy (MBE) chamber. A detailed in situ x-ray photoelectron spectroscopy study confirmed formation of 1 or 2 monolayers of pseudomorphic cubic GaN layer. A remarkable increase of the quantum efficiency of photoluminescence (PL) by a factor of 30 was obtained by forming the passivation structure on the MBE grown clean (001) GaAs under optimum conditions. This indicates a large reduction of the surface recombination velocity. The increase of the PL intensity was extremely stable, maintaining its value even after leaving the sample in air for 2 months. Detailed ultrahigh vacuum contactless capacitance–voltage (C–V) measurements and usual metal–insulator–semiconductor C–V measurement indicated reduction of interface states, realizing a wide movement of the Fermi level within the midgap region.
Atomic structure and optical anisotropy of III–V(001) surfaces
Authors: Esser N. , Schmidt W. G. , Cobet C. , Fleischer K. , Shkrebtii A. I. , Fimland B. O. , Richter W.
Published: July 2002

The optical anisotropy of materials with isotropic bulk crystal structure depends to a large extent on the surface atomic structure. For instance, data obtained by reflectance anisotropy spectroscopy (RAS) on (001) surfaces of zinc blende semiconductors such as InP and GaAs, have a fingerprint character for the various surface reconstructions. Here we present RAS spectra for GaAs(001) and InP(001) recorded at room temperature and at low temperature. We show that by comparison with a theoretical analysis based on ab initio density functional theory in local-density approximation calculations the origin of characteristic spectral features can be identified and thus RAS spectra utilized to discriminate between different competing structural models. We identify contributions related to electronic transitions between surface states as well as features arising from surface perturbed bulk wave functions. We explain the high sensitivity of RAS to the surface structure and chemistry as due to the surface state related features.
Periodic submicrometer structures by sputtering
Authors: Dick B. , Brett M. J. , Smy T. , Belov M. , Freeman M. R.
Published: July 2002

It is known that glancing angle deposition (GLAD) utilizing extreme self-shadowing during film growth can produce periodic microstructures on a predefined seed layer using electron-beam evaporation. This deposition process has been applied to the fabrication of periodic arrays of magnetic pillars and has possible applications in optical devices. Critical to the production of these microstructures is adherence to a narrow angular flux distribution centered at an oblique incidence angle, and optimizing the seed pattern for the desired film characteristics. In this article, a low-pressure, long-throw collimated GLAD sputter deposition has been used to fabricate submicrometer scale periodic pillar and quasihelical microstructures over a range of seed separations (e.g., 150, 300, 600, 900, and 1200 nm) and deposition angles (82.5° and 86° with respect to the substrate normal). We have found that for fixed deposition parameters, periodic quasihelical growth degenerates into pillars as the seed separation increases, and that the transitional region over which this degeneration occurs shifts to high seed separations with increasing flux incidence angles. This and other growth trends are also observed and described using the three-dimensional (3D) ballistic simulator, 3D-FILMS, which has proven to be successful in simulating the growth of aperiodic and periodic GLAD films. The use of sputtering for periodic GLAD simplifies the process control, and should enable deposition of a broader range of materials for diverse applications including magnetics, optics, and sensors.
Plasma-induced damage study for n-GaN using inductively coupled plasma reactive ion etching
Authors: Khan F. A. , Zhou L. , Kumar V. , Adesida I.
Published: July 2002

In this article, we report a comprehensive study on plasma-induced damage for n-GaN using inductively coupled plasma (ICP) reactive ion etching. Effect of ICP coil power, etch duration and bias voltage on the electrical characteristics of n-GaN was investigated. It was observed that variation in ICP coil power and etch duration had minimal effect on varying the plasma-induced surface damage. Bias voltage was found to be the most significant cause of variation in plasma-induced damage to the surface of n-GaN. Therefore, low surface damage can be achieved by optimizing the bias voltage at which the sample is being etched. Auger electron spectroscopy analysis showed that the stoichiometry of the etched GaN surfaces was identical, independent of the etching conditions.