bluuebunny/crossref_metadata_2025 huggingface dataset:
Fractoemission from the failure of metal/epoxy interfaces
Authors: Dickinson J. T. , Jensen L. C. , Bhattacharya S. K.
Published: July 2002

We examine the electron emission, photon emission, and long wavelength electromagnetic radiation accompanying the failure of interfaces between aluminum and epoxy. Experimental evidence is given in support of a previously presented model involving fracture induced microdischarges which excite the fracture surfaces by particle bombardment. We also examine the influence of an applied potential across the fracture surface at an Al/epoxy interface and present evidence for electrical breakdown in vacuum caused by fractoemission.
Deconvolution of concentration depth profiles from angle resolved x-ray photoelectron spectroscopy data
Authors: Bussing T. D. , Holloway P. H.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) can be made more surface sensitive by analysis of photoelectrons at small take-off angles relative to the sample surface. The intensity distribution of these angle-resolved data (ARXPS) has the potential for yielding nondestructively a depth profile of concentration in an extremely narrow surface region. Efforts to quantify ARXPS profiles have had limited success due to problems in deconvolution of the depth-concentration function from the exponential electron flux attenuation function. A new solution is shown based on inverse Laplace transforms. This approach will be compared to other approaches such as matrix inversion, iterative error reduction, and finite-layer analysis. Limitations on the quantitative accuracy of the recovered profiles are shown to be intrinsic to the numerical data reduction itself, thus compounding the effects of experimental imprecision. Examples of deconvoluted profiles from both simulated and actual experimental data sets are presented as illustrations of the potential for recovering a composition depth profile by this method.
Dissociative attachment in electron-stimulated desorption from condensed NO and N2O
Authors: Sanche L. , Parenteau L.
Published: July 2002

We have measured the intensity of O− ions produced by low-energy electrons (1–20 eV) impinging on NO and N2O molecules condensed on a polycrystalline platinum surface held at 17 and 40 K. In condensed NO (i.e., in the dimerized form N2O2), the energy dependence of the O− yield exhibits four broad peaks within the range 5–20 eV whereas in condensed N2O two peaks are observed at 9.4 and 16.4 eV. The linearity of O− production near the peak energies with coverage indicates the presence of a first-order mechanism which we ascribe to the decay of transient anion states (i.e., electron resonances) into the dissociative attachment channel.
Microstructure evolution in TiN films reactively sputter deposited on multiphase substrates
Authors: Helmersson U. , Sundgren J.-E. , Greene J. E.
Published: July 2002

Cross-sectional transmission electron microscopy (X-TEM) has been used to investigate the microstructure of TiN films deposited by reactive magnetron sputtering onto ASP 30 high speed steel (HSS) substrates. ASP 30 is a multiphase material consisting of a martensitic matrix with MC and M6C transition–metal particles embedded in it. The TiN films were ∼4 μm thick and were grown at substrate temperatures Ts between 200 and 550 °C. The X-TEM results showed that the film microstructure was very nonhomogeneous. A dense columnar morphology was observed above both the martensitic and M6C substrate phases. The average column diameter 〈d〉 ranged from 15 nm (Ts=200 °C) to 50 nm (Ts=550 °C) near the film/substrate interface over the martensitic phase and was in a factor of 2 less in the film regions adjacent to the M6C phase. 〈d〉 increased in both regions to 100 nm (Ts=200 °C) to 150 nm (Ts=550 °C) near the surface of the films. TiN grew epitaxially on MC particles but contained a high dislocation density which (except at 550 °C where some of the epitaxial grains extended throughout the entire film thickness) eventually coalesced to form low-angle grain boundaries and, finally, high-angle boundaries. Thus the nucleation and initial growth kinetics were strongly influenced by the local substrate structure while the growth temperature had relatively little effect other than to increase adatom surface diffusivities, and hence the average column size above the martensitic and M6C phases, and to decrease the extended defect concentration in the epitaxial regions. Grain boundary migration and secondary recrystallization were not observed even at the highest growth temperatures investigated.
Effect of oxygen on fluorine-based remote plasma etching of silicon and silicon dioxide
Authors: Loewenstein Lee M.
Published: July 2002

The addition of oxygen to a fluorine-containing gas in a remote microwave discharge significantly affects the etch rates of SiO2 and Si, and the selectivity of the etching. For a F2/He etchant mixture, the addition of O2 drops the etch ratio to 1:1, from a value of 40:1 without O2. For CF4, the ratio is reversed to less than 1:3, from an initial 10:1. A mechanism for this behavior is proposed, based on simultaneous etching and oxidation of the silicon surface by atomic F and O, respectively. When CF4 or C2F6 is the source of F, the selective deposition of a fluorocarbon polymer on Si strongly affects the etching behavior. Auger and x-ray photoelectron spectroscopy analysis supports these interpretations. The control of selectivity may be useful for an isotropic deglaze process.
Stress modification of Ni–Fe films by ion bombardment concurrent with film growth by alloy evaporation
Authors: Wojciechowski P. H.
Published: July 2002

A technique is described for selectively modifying, by ion bombardment during film growth, the state of internal stress of thin films on flexible polymer substrates. A laser-monitoring system is used to measure strain-induced deflections of the simply supported substrate prior to, during, and after the deposition without disturbing the film–substrate system. Sensitivity of the in situ measured bending force per unit width is ∼130 dyn/cm. The result is a composite view of the ‘‘frozen-in’’ thin-film internal stress including postdeposition relaxation. Permalloy (83% Ni–17% Fe) is deposited on Kapton at room temperature by electron beam evaporation simultaneous with Ar+ bombardment of current densities j=10 to 1000 μA/cm2 and ion energies E=150, 300, 750, and 1500 eV/ion. In the absence of ion bombardment, the average internal stress is tensile with a value of 11 Gdyn/cm2 for deposition rate =0.5 nm/s. Transition from tensile to compressive stress is a strong function of j and a rather weak function of E.
Chemically bonded diamondlike films from ion-beam deposition
Authors: Kasi Srinandan R. , Kang Heon , Rabalais J. Wayne
Published: July 2002

Low-energy mass-selected C+ ion beams are used to deposit thin carbon films on surfaces of Si(100) and Ni(111) in an UHV environment at room temperature. The films are characterized by Auger electron spectroscopy, x-ray and UV photoelectron spectroscopy, valence level electron energy-loss spectroscopy, K-shell ionization loss spectroscopy, and ellipsometry. The initial monolayer of the deposited film is in the form of a carbide layer which is chemically bonded to the substrate atoms. Over the next several layers deposited, the film evolves gradually through intermediate structures into a diamondlike structure. A phase diagram, prepared as C+ ion dose versus C+ kinetic energy Ek, shows the regions of the different structures. The optimum C+ energy range for formation of the diamondlike structure is 30–175 eV. Below 10 eV the final diamondlike structure has not been attained and above 180 eV there is a sharp increase in the dose required to attain this final structure. Properties of the film, measured in situ, are mentioned.
X-ray photoelectron spectroscopy investigation on the chemical structure of amorphous silicon nitride (a-SiNx)
Authors: Ingo G. M. , Zacchetti N. , della Sala D. , Coluzza C.
Published: July 2002

Amorphous silicon nitride a-SiNx (0<x<1.7) thin films, prepared by dual ion beam sputtering, were investigated by means of high-energy resolution photoelectron spectroscopy using an x-ray monochromatized radiation. The variation of the position, width and line shape of the Si 2p photoemission peak, as a function of the alloy composition, was explained in terms of an overlapping of five chemically shifted unresolved components corresponding to the five tetrahedral silicon bonding configurations Si–Si4−nNn (n=0,1,...,4). Considering each component as a convolution of the spin-orbit doublet Si 2p1/2–Si 2p3/2, we experimentally determined their binding energy and full width at half-maximum. We thus obtained, by a curve-fitting process, the Si–Si4−nNn distribution as a function of atomic composition and compared it with the predictions of the most used growth models: the random bonding model and stoichiometric statistical model. These two models were in disagreement with the experimental data, thus a third model was proposed based on the invariant coordination of nitrogen to three silicon neighbors, and includes also a nucleation of possible stoichiometric clusters in the a-SiNx films. Moreover, methodological aspects such as artifacts induced by ion sputtering, used to clean the sample surface before x-ray photoelectron spectroscopy measurements, were taken into account.
Localized charge force microscopy
Authors: Terris B. D. , Stern J. E. , Rugar D. , Mamin H. J.
Published: July 2002

A force microscope has been used to deposit and image localized charge on insulating surfaces. The charge is deposited either by applying a voltage pulse to the microscope tip or by contact charging the insulator surface with the tip. An improved mode of charge imaging is presented, which distinguishes between charge and topography and allows the sign of the charge to be determined in a single scan.
Imaging bacteriorhodopsin lattices in purple membranes with atomic force microscopy
Authors: Worcester D. L. , Kim H. S. , Miller R. G. , Bryant P. J.
Published: July 2002

Surface images of the membrane protein bacteriorhodopsin have been obtained using atomic force microscopy. Trigonal lattices formed by trimers of bacteriorhodopsin are observed, but details of the protein surface structure have not yet been resolved. Grey scale oscilloscope images show that the surface features along one of the three equivalent axes in the plane of the membrane are more prominent than along the other two, resulting in parallel rows. This may result from anisotropic properties of the atomic force probe, substrate structure and membrane deformation, or differences of symmetry between the membrane interior and the membrane surface. Parallel rows have been obtained at several angles to the line scan direction, but not parallel to the scan. The measured spacings of the rows are in reasonably good agreement with the lattice constants of purple membranes determined by diffraction methods that are much more accurate.
Fundamentals of ion-beam-assisted deposition. I. Model of process and reproducibility of film composition
Authors: Van Vechten D. , Hubler G. K. , Donovan E. P. , Correll F. D.
Published: July 2002

An ion-beam-assisted-deposition (IBAD) system is under development to fabricate Si1−x Nx films for optical devices. Reproducible film composition requires characterization of the relationship between the incorporated nitrogen atom fraction x and the real time experimental measurable quantities. In this paper a simple model is presented which relates the film composition x to the measured beam current density JF , the vapor impingement rate Q, and the chamber pressure p. Effects included in the model are reflection of energetic particles, sputtering from the film surface, and charge exchange neutralization of the ions. Each term in the model is examined as a potential source of both systematic and random deviations of the data from the model. Data on film composition as a function of the nitrogen ion current to deposition rate ratio are presented for several sets of ion source voltages and chamber pressures. It is shown that by modifying the deposition system so as to minimize the identified sources of error, variation in composition can be reduced below 3 at. % nitrogen. Both the model and the discussion of the experimental sources of error are applicable to other IBAD systems.
An ultrahigh vacuum scanning tunneling microscope with a new inchworm mechanism
Authors: Shimizu N. , Kimura T. , Nakamura T. , Umebu I.
Published: July 2002

An ultrahigh vacuum scanning tunneling microscope (STM) with a new piezo-driven inchworm for coarse positioning has been designed and constructed. The inchworm consists of five piezoelectric stacks and moves, being pressed from the side by a spring. This structure makes it durable to bakeout of the vacuum chamber. The tip and the sample set in the tunneling unit are exchangable without breaking vacuum. The STM chamber is attached to a conventional molecular beam epitaxy chamber equipped with surface analysis instruments without external vibration isolation. We have ascertained that the STM has an atomic-order resolution even under poor conditions, where much acoustic noise and mechanical vibration are produced by vacuum pumps and cooling water in the main chamber.
High rate sputter deposition of wear resistant tantalum coatings
Authors: Matson D. W. , Merz M. D. , McClanahan E. D.
Published: July 2002

The refractory nature and high ductility of body centered cubic (bcc) phase tantalum makes it a suitable material for corrosion- and wear-resistant coatings on surfaces that are subjected to high stresses and harsh chemical and erosive environments. Sputter deposition can produce thick tantalum films but is prone to forming the brittle tetragonal beta phase of this material. Efforts aimed at forming thick bcc phase tantalum coatings in both flat plate and cylindrical geometries by high-rate triode sputtering methods are discussed. In addition to substrate temperature, the bcc-to-beta phase ratio in sputtered tantalum coatings is shown to be sensitive to other substrate surface effects.
Characterization of a radio frequency plasma source for molecular beam epitaxial growth of high-T
c superconductor films
Authors: Locquet Jean-Pierre , Mächler Erich
Published: July 2002

The growth of superconducting oxides in vacuum conditions compatible with molecular beam epitaxy (MBE) requires a form of activated oxygen. The activated oxygen species can be either atomic oxygen (O) or ozone (O3). Here we characterize a rf plasma source by measuring the oxidation rate of a silver film on a quartz crystal deposition monitor as a function of the oxygen flow. The initial oxidation rate provides a lower limit for the actual atomic oxygen flux. If the frequency change of the quartz signal is entirely due to the oxidation of silver by atomic oxygen and we assume a detection efficiency of one, then the total cracking efficiency of the source is estimated to be around 30%. The source was used in a MBE machine to deposit thin (200 Å) high-Tc films of DyBa2Cu3O7 on SrTiO3 with a Tonsetc of 88 K and a Tzeroc of 86 K.
Scanning tunneling microscopy study of the adsorption and recombinative desorption of hydrogen from the Si(100)-2×1 surface
Authors: Boland John J.
Published: July 2002

A scanning tunneling microscopy and spectroscopy study of the adsorption and recombinative desorption of hydrogen from the Si(100)-2×1 surface is presented. Initially at room temperature, hydrogen atoms singly occupy the Si dimer units resulting in the formation of isolated Si–H bonds and unpaired dangling bonds. At higher temperatures (∼630 K) these hydrogen atoms tend to pair up on the dimer units. Thus there is a thermodynamic preference for the hydrogen atoms to occupy the dimers in pairs. This pairing phenomenon is due to a π interaction between the dangling bonds on the Si(100)-2×1 surface which favors pairing the unpaired dangling bonds on the dimer units. This pairing of dangling bonds in turn forces the hydrogen atoms to pair. Following desorption from the saturated surface, pairs of dangling bonds are found localized on the Si dimer units, suggesting that desorption involves the direct recombination of hydrogen atoms from the dimers units of the monohydride surface. The implications of this desorption mechanism are discussed and compared to earlier models.
Influence of vacuum gauges on outgassing rate measurements
Authors: Saitoh M. , Shimura K. , Iwata T. , Momose T. , Ishimaru H.
Published: July 2002

When the outgassing rates from eighteen chamber samples with different surface treatments for ultrahigh vacuum were measured by the throughput method, the minimum specific outgassing rate measured was limited to about 10−13 Torr ℓ/s/cm2 due to the outgassing of a Bayard–Alpert gauge (BAG), about 10−9 Torr ℓ/s. A measurement of outgassing rates with a BAG and an extractor gauge (EG) showed that the outgassing rate of the EG is lower than that of the BAG and that outgassing due to thermal desorption from the wall surrounding of the gauges cannot be neglected in seeking to obtain correct outgassing rates for the gauges, especially for the case after baking. A new type of quadrupole mass spectrometer (QMS) and an extractor gauge (EG) showed an outgassing rate of 6–7×10−11 Torr ℓ/s. Using the QMS and EG, a minimum specific outgassing rate from the sample chambers was measured on the order of 10−14 Torr ℓ/s/cm2 from the total pressure. The measurement showed that the main residual gas species are H2O, before baking, and H2, after baking. Therefore, the outgassing rate (q) must be described using the partial pressures of the residual gases and was 2.0×10−10 Torr ℓ/s/cm2 for water (qH2O) and 1.4×10−13 Torr ℓ/s/cm2 for hydrogen (qH2) from an A6063 EX mirror-finished sample.
Vacuum pumpdown model for long outgassing tubes
Authors: Ernst Michael J. , Hemond Harold F.
Published: July 2002

This article describes the development and application of a numerical model of vacuum flow with outgassing. The mass conservation equation for a vacuum tube is formed with three outgassing terms: a 1/t term, a 1/t0.5 term, and a constant term. Each term arises from a distinct sorption process at the walls of the containing vessel. All of these outgassing terms include a linear pressure dependence for a more realistic characterization during the initial stages of pumpdown. Specific conductance equations for the entire range of vacuum flow, from viscous to molecular, are combined with the mass conservation equation to obtain a nonlinear partial differential equation for the pressure in a vacuum system. The resulting equation is then solved using an iterative finite difference scheme to give the pressures as a function of time and location. Pressure measurements from several pumpdowns of a long outgassing tube are then compared to the model results to evaluate outgassing rate parameters. The 1/t type outgassing was found to depend strongly on the humidity levels to which the tubes were exposed before evacuation.
Fabrication of thin films with highly porous microstructures
Authors: Robbie K. , Friedrich L. J. , Dew S. K. , Smy T. , Brett M. J.
Published: July 2002

An evaporation process has been developed for depositing highly porous insulator or metal films with densities as low as 15% of bulk. The process utilizes either multiple evaporation sources or substrate movement to provide a symmetrical but very oblique (≳80%) flux incident on the substrate. Extreme self-shadowing produced a vertical columnar microstructure consisting of isolated and evenly spaced columns including a unique zigzag structure in a number of insulator films. Features of the film are often anisotropic, leading to conductivity differences of as much as a factor of two along perpendicular axes in the plane of the film surface. The direction of anisotropic growth was observed to switch orientation as the incident flux angle was increased to very oblique, beyond approximately 80°. A line segment simulator incorporating ballistic deposition and minimization of chemical potential has been used to aid in the understanding of the growth mechanisms of these films and to optimize the evaporation process. The simulator helped to confirm that self-shadowing was the dominant mechanism in this porous structure formation.
Measurements of electron temperature, electron density, and neutral density in a radio-frequency inductively coupled plasma
Authors: Hori T. , Bowden M. D. , Uchino K. , Muraoka K. , Maeda M.
Published: July 2002

Electron temperature, electron density, and neutral atom density were measured in a radio-frequency (rf) inductively coupled plasma using Thomson and Rayleigh scattering of laser radiation. Measurements were made in an argon discharge for pressures from 1 to 20 mTorr and input rf powers from 100 to 500 W. Spatial distribution profiles were measured for discharges with different aspect ratios. Electron temperature was found to depend on pressure but only weakly on power. Electron density depended strongly on both pressure and power. The neutral density was found to be significantly depleted in the plasma center and this depletion was attributed to heating of the neutrals by charged particle collisions. These results were compared to a simple model of inductively coupled plasmas.
Particle simulation of two dimensional dust crystal formation in a mesothermal plasma flow
Authors: Melandso/ F. , Goree J.
Published: July 2002

A two-dimensional simulation is used to study the crystallization of strongly coupled dusty plasmas. The dust grains are simulated as particles, while the electrons and ion solutions are obtained from fluid equations. We model gas discharges with dust particles confined in the sheath and at the sheath edge. In these regions the ions flow past the dust grains at a velocity v0 that typically is mesothermal, vTi≪v0≪vTe. A negative charged dust particle will under these conditions focus the ions, creating a local maximum in the plasma potential on the downstream side of the particle. This maximum means that there is an anisotropic interparticle interaction, which can be manifested as an attractive interparticle force along the axis of the plasma flow. Our simulation shows that the equilibrium configuration of a dust crystal structure can be profoundly influenced by this asymmetry in the ion flow and plasma potential for certain charge to mass ratios for the dust particles. We initially distribute dust particles randomly in space with zero velocity and integrate their equations of motion, tracking their orbits as they settle into equilibrium positions. We show that there are several stable final equilibria, although they do not all have the same potential energy or probability of occurring. The most likely crystal configuration depends on the charge-to-mass ratio and the horizontal particle spacing of the grains. The vertically aligned columns of particles that have been observed in plasma crystal experiments are shown to be most likely for large dust charge-to-mass ratios.
Diagnostic of dusty plasma conditions by the observation of Mach cones caused by dust acoustic waves
Authors: Havnes O. , Li F. , Melandso/ F. , Aslaksen T. , Hartquist T. W. , Morfill G. E. , Nitter T. , Tsytovich V.
Published: July 2002

The theory of dust acoustic waves in dusty plasmas is well developed for conditions with monosized dust particles. It was proposed [O. Havnes et al., J. Geophys. Res. 100, 1731 (1995)] that such waves may be generated in planetary dust rings by boulders moving through the dust at a velocity that is somewhat higher than the dust acoustic velocity. In this manner Mach cones can form with an opening angle that is dependent on the boulder velocity and the local dust acoustic velocity. Measurements of this opening angle will therefore provide additional information on dusty plasma conditions since the dust acoustic velocity can be determined when the boulder velocity is known. We suggest that this method may also be applied under laboratory conditions if a suitable controlled disturbance can be made and we discuss how the dust acoustic velocity and resulting Mach cones are affected if the dusty plasma have a distribution of dust sizes.
Fluorine atom induced decreases to the contribution of infrared vibrations to the static dielectric constant of Si–O–F alloy films
Authors: Lucovsky G. , Yang H.
Published: July 2002

Si–O–F alloy films deposited by chemical vapor deposition have static dielectric constants, εs, significantly reduced with respect to those of similarly prepared SiO2, ∼3.2 to 3.4 as compared to 4.0 to 4.2. Infrared absorption spectra provide a basis modeling the molecular structure of these alloys, as well as helping to identify microscopic mechanisms responsible for static dielectric constant reductions. Contributions of electronic and vibrational transitions to εs are discussed in terms of an empirical chemical bonding model. Ab initio calculations are then used to identify inductive effects of Si–F bonds on the properties of Si–O–Si groups that are back-bonded to the Si atom of that Si–F group. The ab initio calculations provide a theoretical framework for understanding why relatively low concentrations of F atoms; ∼10–12 at. %, produce significant decreases in εs, ∼22%, as reported for the Si–O–F alloys.
Modeling of SiO2 deposition in high density plasma reactors and comparisons of model predictions with experimental measurements
Authors: Meeks Ellen , Larson Richard S. , Ho Pauline , Apblett Christopher , Han Sang M. , Edelberg Erik , Aydil Eray S.
Published: July 2002

High-density-plasma deposition of SiO2 is an important process in integrated circuit manufacturing. A list of gas-phase and surface reactions has been compiled for modeling plasma-enhanced chemical vapor deposition of SiO2 from SiH4, O2, and Ar gas mixtures in high-density-plasma reactors. The gas-phase reactions include electron impact, neutral–neutral, ion–ion, and ion–neutral reactions. The surface reactions and deposition mechanism is based on insights gained from attenuated total reflection Fourier transform infrared spectroscopy experiments and includes radical adsorption onto the SiO2 surface, ion-enhanced desorption from the surface layer, radical abstractions, as well as direct ion-energy-dependent sputtering of the oxide film. A well-mixed reactor model that consists of mass and energy conservation equations averaged across the reactor volume was used to model three different kinds of high-density plasma deposition chambers. Experimental measurements of total ion densities, relative radical densities, and net deposition rate, as functions of plasma operating conditions, have been compared to model predictions. The results show good quantitative agreement between model predictions and experimental measurements. The compiled reaction set and surface reaction network description was thus validated and can be employed in more sophisticated two- or three-dimensional plasma simulations.
Multiple bonding geometries and binding state conversion of benzene/Si(100)
Authors: Lopinski G. P. , Fortier T. M. , Moffatt D. J. , Wolkow R. A.
Published: July 2002

Scanning tunneling microscopy (STM), Fourier-transform infrared spectroscopy and semiempirical quantum cluster calculations have been used to investigate the chemisorption of benzene on the Si(100)(2×1) surface. Room temperature adsorption results in the occupation of multiple bonding configurations including on-top of a single Si dimer and two different bridging geometries involving interaction with two Si dimers. While the single dimer state is populated preferentially upon adsorption, it is observed to be metastable with respect to the bridging configuration. The single dimer to bridge conversion is activated, with a barrier of 0.94 eV. The single dimer geometry can be repopulated via a process assisted by the STM tip.
Knudsen compressor as a micro- and macroscale vacuum pump without moving parts or fluids
Authors: Vargo S. E. , Muntz E. P. , Shiflett G. R. , Tang W. C.
Published: July 2002

Applications of Knudsen compressors as both microscale and macroscale vacuum pumps have been investigated. The study is based on a cascade analysis incorporating available transitional thermal transpiration and Poiseuille flow results for slender channels. It was found that the Knudsen compressor is an attractive possibility for microscale pumps down to a pressure of about 1 mTorr and for macroscale pumps to about 0.1 mTorr. A microscale pump for a micromass spectrometer providing a molecule flow rate of 5×1014 molecules/s results in the following pump characteristics: energy use of 2.4 W, pump volume of 13.9 mℓ at an inlet pressure of 1 mTorr and an energy use of 28.5 mW, and pump volume of 0.16 mℓ at an inlet pressure of 10 mTorr. A macroscale pump providing a pumping speed of 103 ℓ/s results in a pump with an energy use of 1786 W, and pump volume of 1695 ℓ at an inlet pressure of 0.1 mTorr. Several Knudsen compressor characteristics such as pressure rise, pumping speed, volume, energy use and mass flow are presented.
X-ray photoelectron spectroscopy and Auger electron spectroscopy investigation on the oxidation resistance of plasma-treated copper leadframes
Authors: Wong A. S. W. , Krishnan R. Gopal , Sarkar G.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) have been employed in the investigation of the surface chemistry and oxidation-resistant property of the C-, N-, and Cu-containing films, formed by the plasma treatment of pristine copper. The copper oxidation process has been elucidated using realistic microelectronic packaging-assembly conditions, results of which are in agreement with established models. From the chemical shift in binding energy and change in full-width-half-maxima of the XPS core-level peaks, the heated copper has been observed to first form the monovalent cuprous oxide (Cu2O) followed by nucleation and growth of the divalent cupric oxide (CuO) above the Cu2O. The copper hydroxide [Cu(OH)2] has been observed to form on the Cu2O, CuO, and copper metal surfaces. This knowledge of copper oxidation has been used as a yardstick for the study of film decomposition and subsequent oxidation of exposed copper. Variation of the plasma treatment time produced two films of varied thickness [CuCxNy(A):15 nm and CuCxNy(B):75 nm], with the longer time producing the thicker films. AES results also suggest that the two films have the analogous film stoichiometry of 1:1:0.16 (Cu:C:N). Further XPS and AES analyses reveal the thickness dependence of the oxidation-resistant property, with the thicker film having the better oxidation resistance. A difference in film thickness of ∼5 times delayed the film decomposition temperature by 50 °C. AES depth profiles on the heated (250, 300, and 350 °C) films show the gradual decay of the film thickness with heating temperatures. Oxide growth predominates with the complete decomposition of the films. Present results suggest neither the presence of entrapped N2 gas in the copper oxide structure nor an oxide structure with the C and N decorations at the copper oxide grain boundaries. One possible film decomposition mechanism may be through the breaking of the Cu–N bonds under suitable heating conditions, thereby allowing the formation of the Cu–O bonds as the oxidation proceeds.
Methylated poly(4-hydroxystyrene): A new resin for deep-ultraviolet resist application
Authors: McKean Dennis R. , Hinsberg William D. , Sauer Thomas P. , Willson Grant , Vicari Richard , Gordon Douglas J.
Published: July 2002

Positive photoresists which function on the basis of dissolution inhibition are the mainstay of optical lithographic technology at long wavelength. Described in this paper is a new type of material which permits the dissolution inhibition mechanism to be extended to deep-UV wavelengths. Methylated poly(4-hydroxystyrene) resins are prepared by a copolymerization reaction which results in a final product whose dissolution properties can be defined by the ratio of the two monomers used in the reaction. The deep-UV optical absorbance of the methylated resin is about one-half the absorbance of novolac at 248 nm which makes these materials attractive for application in deep-UV resist formulations. Binary photoresists using diazo compounds as dissolution inhibitors have been prepared with the methylated poly(4-hydroxystyrene) as the host resin. These materials function very similarly to the familiar diazonaphthoquinone/novolac photoresists at long wavelength. For deep-UV application, both binary and three component resists have been evaluated. The three component system has high sensitivity (<5 mJ/cm2 ) and contrast (γ>3). The high contrast is due in part to the induction effect observed from dissolution data. Projection printed images have steep wall profiles indicative of high contrast photoresists.
Determination of acid diffusion in chemical amplification positive deep ultraviolet resists
Authors: Schlegel Leo , Ueno Takumi , Hayashi Nobuaki , Iwayanagi Takao
Published: July 2002

A new method was developed to study the diffusion of photogenerated acid in chemical amplification resist systems which allowed an estimation of the diffusion range by simple means. The acid mobility was investigated for two different resist systems under various process conditions. It was found that solvent traces in the film cause a very strong increase of the acid mobility. In order to control the diffusion range, the post-exposure-bake temperature must be below the glass transition temperature. For one resist system, the increase in resist sensitivity with increasing baking temperature was much smaller than the corresponding increase in diffusion range. The results corresponded well with those obtained by lithography with the same resist.
High-temperature superconducting thin films in strong electric fields
Authors: Shkuratov Sergei I.
Published: July 2002

The article is devoted to some important, from the point of view of search of practical applications of new materials, physical aspects of the behavior of high-temperature superconducting (HTSC) thin films in strong electric fields. An analysis is made of factors limiting the superconducting cathode current. A review is given of HTSC emissive properties. The results of the investigation of switching of YBa2Cu3Ox thin films from the superconducting over to the normal state by field electron emission current are presented. It is shown that the time required for switching over to the normal state may attain a value of 10−9 s. A comparative analysis of switching of HTSC films by various methods (magnetic, current, thermal) shows that field electron emission current control of HTSC film switching devices is preferable in some technical applications. The feasibility of formation of nanostructures on HTSC film is discussed.
Subnanometer alignment system for x-ray lithography
Authors: Zhou H. , Feldman M. , Bass R.
Published: July 2002

Proximity printing with soft x rays is a leading contender for very large scale integrated circuit lithography below 0.25 μm. It will require overlay accuracy far below the 100 nm (3σ) typical of today’s systems. In addition, it should use wafer marks which permit planar resist flow, so their apparent position is not distorted. We report an alignment system which uses a linear zone plate on the mask to focus laser light into a line on the wafer. The wafer mark is the boundary between two adjacent fine pitch gratings. These gratings diffract the light into photodiodes. The gratings either differ slightly in pitch or by 180° in phase. This configuration minimizes the disturbance to the resist as it flows over the alignment mark. In the case of gratings with slightly different pitch the light from each grating is detected by one-half of a split photodiode. This arrangement has good sensitivity and a very wide capture range. The phase shift gratings have reduced capture range but enhanced sensitivity because of the improved resolution from the phase shift. We observe that the full width at half-maximum (FWHM) of the alignment signal is 0.6 μm when the FWHM of the zone plate focus is 1.0 μm. By collecting all of the light focused by the zone plate and diffracted by the gratings we obtain strong alignment signals with signal to noise ratios of more than 1000:1. We routinely obtain a reproducibility in a bench setup equivalent to less than 1 nm (3σ). This alignment technique is currently undergoing installation in a commercially available x-ray exposure tool.
Fabrication of column-based silicon field emitter arrays for enhanced performance and yield
Authors: Temple D. , Ball C. A. , Palmer W. D. , Yadon L. N. , Vellenga D. , Mancusi J. , McGuire G. E. , Gray H. F.
Published: July 2002

In this article, simulation, fabrication, and direct current (dc) characterization data are presented for column-based silicon field emitter array (FEA) devices, made using anisotropic or isotropic etching of silicon to form emitter tips. In the design of the fabrication process, we have attempted to minimize spatial nonuniformity of process parameters affecting the geometry of the device structure, and, where possible, counteract the nonuniformity through a proper choice of processing variables. FEA devices, with as many as 232 630 tips, on 4–10 μm centers, have been successfully fabricated. The highest electron emission current measured was over 18 mA at the gate voltage of 150 V for a 6648 tip array.
Structure and electronic states on reduced SrTiO3(110) surface observed by scanning tunneling microscopy and spectroscopy
Authors: Bando H. , Aiura Y. , Haruyama Y. , Shimizu T. , Nishihara Y.
Published: July 2002

The SrTiO3(110) surface, after annealing in ultrahigh vacuum (UHV) was observed by scanning tunneling microscopy/spectroscopy (STM/S). These observations were compared with the ultraviolet photoemission spectroscopy (UPS) and x-ray photoemission spectroscopy (XPS) data previously reported. The surface, after annealing at 800 °C, is dominated by flat regions where tunneling spectra are of metallic character, in agreement with the UPS data that showed a clear cutoff at the Fermi energy, EF. After annealing above 1000 °C, step edges along [11̄0] and rowlike structures along [001] with spacing ∼2.2 nm, close to 4√2a, are observed. The tunneling spectra showed an energy gap and an in-gap state ∼1 eV below EF, both of which are similar to those reported on the SrTiO3(100) surface after annealing in UHV. After 20 cycles of annealing above 1000 °C, a new ordering with c(2×6) periodicity is observed on the terraces. The STM/S results are explained by formation of (100) and (010) microfacets in the course of annealing in vacuum.
Real time investigation of nucleation and growth of silicon on silicon dioxide using silane and disilane in a rapid thermal processing system
Authors: Hu Y. Z. , Diehl D. J. , Zhao C. Y. , Wang C. L. , Liu Q. , Irene E. A. , Christensen K. N. , Venable D. , Maher D. M.
Published: July 2002

The kinetics of the nucleation and growth of Si films on amorphous SiO2-covered Si using rapid thermal chemical vapor deposition from SiH4 and Si2H6 (5% in He) were compared at temperatures between 600 and 800 °C and reactant gas pressures between 1 and 25 mTorr. Quantitative assessment of the nucleation parameters and the structures of the deposited Si films have been determined using in situ real time single wavelength and spectroscopic ellipsometry. In addition to ellipsometry, atomic force microscopy, scanning electron microscopy, and cross-sectional transmission electron microscopy were used ex situ to observe the nucleation stage and the microstructures of the films. This study compares the initial growth parameters for SiH4: nuclei density (6×108 cm−2), nuclei size (94 nm), incubation time (4.2 min), and degree of selectivity (42 nm) with those for Si2H6: 1.3×1010 cm−2, 31 nm, 0.4 min, and 10 nm, respectively. The incubation times for SiH4 and Si2H6 are different, as is the degree of selectivity, but they show similar activation energies of about 1 eV in the 600–800 °C range. The Si film quality in terms of surface roughness and grain structure was better for the Si film derived from Si2H6 than from SiH4.
Dynamical and mechanical study of immobilized microtubules with atomic force microscopy
Authors: Vinckier Anja , Dumortier Chantal , Engelborghs Yves , Hellemans Louis
Published: July 2002

The dynamics of the assembly/disassembly reaction play an important role in the study of microtubule (MT) polymers. The polymerization rate constant (2±1×10−3 s−1) of this process was determined on the basis of atomic force microscopy images of air-dried samples, taken at discrete time intervals. The decay of tubulin oligomers (rings) is ten times faster, and consequently is not a rate-limiting step. The time dependence of turbidity measurements is compared with atomic force microscopy results expressed as the average MT length and mass per unit surface. Further, the elastic behavior of microtubules under liquid is analyzed as a function of a cross-linking agent’s concentration (glutaraldehyde). Recording force–distance curves allows the indentation to be determined, from which Young’s modulus E is derived. Extrapolating these data provides the intrinsic stiffness of the MTs (E=3.1±0.9 MPa). MTs prepared in the presence of the drugs taxol and taxotere have values of, respectively, 1.3±0.6 and 2.7±1.2 MPa as Young’s modulus. Experimental MT heights are quantitatively explained by the indentation values found in this study, and a similar approach to determine true heights for any kind of soft sample is suggested.
Isolation of a lattice-mismatched AlInAs/GaInAs layer on InP using ion implantation for high energy mobility transistor realization
Authors: Fourré Hervé , Pesant Jean Claude , Schuler Olivier , Cappy Alain
Published: July 2002

In this communication, we present Ar+ implant isolation results of InGaAs/InAlAs/InP layers for high electron mobility transistor fabrication. Ar+ implantations were performed at 100 keV at room temperature with doses ranging from 5×1012 to 1015 at./cm2. A sheet resistance of about 30 MΩ was measured after 10 hours annealing at 300 °C. Using deep Auger analysis, we show that this high resistivity is due to the intermixing of InGaAs and InAlAs layers.
Nanomechanical surface characterization by atomic force acoustic microscopy
Authors: Rabe U. , Scherer V. , Hirsekorn S. , Arnold W.
Published: July 2002

We constructed an atomic force acoustic microscope that enables one to detect out-of-plane and in-plane sample surface vibrations in a wide frequency range from about 100 kHz to several MHz. From the point of view of acoustics, an AFM cantilever is a miniaturized elastic beam that can vibrate in different types of modes as, for example, flexural, torsional, and extensional. We present a method of how to calculate the vibrational behavior of a cantilever with its sensor tip in contact with or near a sample surface, and how to deduce surface properties like the Young’s modulus from the vibrations induced in the cantilever. Further, we present single-point measurements in which we compare ultrasonic cantilever vibration spectra where the tip is in contact with surface areas with different stiffnesses to force calibration curves. Finally, we present ultrasonic images taken with our microscope.
Chemically amplified resist processing with top coats for deep-ultraviolet and e-beam applications
Authors: Petrillo Karen , Bucchignano James , Angelopoulos Marie , Cornett Kathleen , Brunsvold William
Published: July 2002

Protective top coats and top antireflective coatings (ARCs) are frequently used in conjunction with chemically amplified resists. Top coats provide resistance to airborne contamination, and are particularly important where charcoal filtration is not available in the processing area. They are also useful in environments where delay times between process steps are not precisely controlled. Conductive top coats can be used for e-beam applications to reduce charging and image placement errors. Top ARCs are used to reduce reflections at the resist/air interface, thereby lowering the amplitude of the swing curve. All of these materials are applied on top of the photoresist after the postapply bake. In this article we report that depending on the subsequent processing conditions, top coatings can significantly impact the lithographic performance of the photoresist. Alterations in development rate, optical proximity effects, resist profile, and postexposure bake latitude have been observed as a result of processing with an additional top film. The primary mechanism responsible for these changes is an alteration of the diffusion characteristics of the photo acid generator during the deprotection step.
Sharp edged silicon structures generated using atom lithography with metastable helium atoms
Authors: Lu Weijian , Baldwin Kenneth G. H. , Hoogerland Maarten D. , Buckman Stephen J. , Senden T. J. , Sheridan T. E. , Boswell R. W.
Published: July 2002

By combining atom lithography and plasma etching technology in a two-step process, we demonstrate the transfer of sharp edged structures into silicon with a depth of 580 nm and an inclination of better than 86°. A self-assembled monolayer resist deposited on a Au-coated Si surface is damaged by a beam of metastable helium atoms through a physical mask. A wet etching process removes Au in the damaged regions, resulting in an intermediate mask of patterned Au on Si. Low-pressure plasma etching is then used to transfer the pattern of the Au mask into the Si. This plasma etching process shows a selectivity greater than 19 with respect to the Au mask.
Field emission: New theory for the derivation of emission area from a Fowler–Nordheim plot
Authors: Forbes Richard G.
Published: July 2002

This article takes a fresh look at the theoretical basis of methods for deriving emission area from the intercept of a Fowler–Nordheim (FN) plot. It sharpens the concepts involved, by defining a generalized FN equation, an intercept correction factor, and an emission-area extraction function. Some new general formulas are introduced. An improved version of the Charbonnier and Martin (CM) [F. M. Charbonnier and E. E. Martin, J. Appl. Phys. 33, 1897 (1962)] method for extracting emission area is discussed; this is numerically illustrated using formulas developed within the framework of Murphy and Good’s 1956 [E. L. Murphy and R. H. Good, Phys. Rev. 102, 1464 (1956)] treatment of the theory of cold field emission from metals at zero temperature. It is shown that uncertainties were underestimated in the methods introduced by CM and by Spindt and colleagues, [C. A. Spindt et al., J. Appl. Phys. 47, 5248 (1976)] but can be reduced by iterating the new method. Strictly, the numerical results presented apply only to field emission from materials that are, or behave like, metals. The numerical results are not exact in any absolute sense, but they are precise within the context of the formulation of FN theory normally used in technological contexts; further, they have been derived within the context of higher-level formulas of general validity, and are considered to be a well-defined and useful step towards future developments. Opportunity is taken to present the usual 1956 version of the FN equation in modern notation, employing quantity algebra, rmks equations, and precise up-to-date values of the relevant universal constants, and to give an equation that identifies the onset of field-induced ballistic emission.
Fundamental performance of state-of-the-art proximity effect correction methods
Authors: Hofmann Uli , Crandall Richard , Johnson Leslie
Published: July 2002

A framework is presented that allows for mathematical classification of most published proximity effect correction (PEC) algorithms. Most algorithms, such as GHOST and dose modulation methods, are first-order approximations to the problem of inverse diffusion. All of these algorithms show equivalent performances and limitations in regard to the lithographic quality terms. Understanding the similarities between the algorithms has allowed us to construct a new, higher-order PEC algorithm with better performance.