bluuebunny/crossref_metadata_2025 huggingface dataset:
S-polarization photoemission extended x-ray absorption fine structure study of clean and adsorbate covered Si(100)2×1 surface
Authors: Mangat P. S. , Soukiassian P. , Schirm K. M. , Hurych Z.
Published: July 2002

This article presents a structural study of the clean and 1 monolayer Na covered Si(100)2×1 surface by s-polarization photoemission extended x-ray absorption fine structure and by core level and valence band photoemission spectroscopy using synchrotron radiation. The Na–Si and Si–Si distances are obtained by analyzing the extended x-ray absorption fine structure signal at the Na 2p and Si 2p core level lines. The results clearly indicate a single site of adsorption for the Na atoms, the cave, with a single layer chain at saturation coverage, and no Na–Na distance consistent with ‘‘double layer’’ models. The existence and growth of an additional overlayer are related to the presence of impurities which, even at very low levels, enhance the sticking coefficient of an alkali atom. We also measure the Si–Si dimer bond length for clean Si(100)2×1 and Na/Si(100)2×1 surfaces. The experimental Na–Si and Si–Si bond lengths are found to be in excellent agreement with the recent results obtained by ab initio total energy DMol calculations.
Computer calculation of neutral–radical densities in a CF4 electron cyclotron resonance plasma processing system
Authors: Ashtiani K. A. , Shohet J. L. , Harvey R. E. P.
Published: July 2002

The steady-state densities of neutral–radical species in a CF4 electron-cyclotron-resonance (ECR) plasma were calculated based on the following drift-diffusion equation: Kni(r,t)/∂t=−ℏ⋅(uin)+Di∇2ni+ ∑jnkijnj +∑j,mnjkijmnm− ni(∑jnekji +∑j,mkj imnm), where ni is the density, ui is the drift velocity, and Di is the diffusion coefficient of species i, and ne is the electron density, and k’s are the chemical rate coefficients. The above equation was solved in cylindrical coordinates using finite differences assuming symmetry in the azimuthal direction. The densities of the radical species were obtained for pressures between 1.0 and 2.5 mTorr in increments of 0.5 mTorr and the ECR power in a range between 500 and 900 W. The chemical rate coefficients were calculated directly from the convolution of electron-impact cross sections with the electron energy distribution function, and experimental plasma parameters, otherwise the best available chemical reaction rates were taken from the literature.

Diffusion coefficients were calculated from the Lennard–Jones parameters of intermolecular potential. The boundary conditions at the walls were based on available heterogeneous reactions and sticking coefficients. The electron densities entered the drift-diffusion equation directly. Results for the chemically dominant radical species such as F, CF3, and CF2 were obtained and compared with experimental measurements. The absolute magnitudes of the radical densities as predicted by the code are within an order of magnitude of the experimental measurements and in almost all cases follow the same trends as parameters are varied.
X-ray photoelectron spectroscopic study of the interactions of CF+ ions with gallium arsenide
Authors: Williston L. R. , Bello I. , Lau W. M.
Published: July 2002

Chemical modifications in the surface of gallium arsenide bombarded with low energy, 3–300 eV CF+ ions have been investigated using x-ray photoelectron spectroscopy (XPS). The effect of temperature on the modified surface was studied by annealing in a vacuum of 1×10−6 Pa prior to further XPS analysis. It was found that CF+ ion bombardment deposited an overlayer containing both carbon and fluorine on the GaAs surface. At 3 eV CF+ ion exposures, the overlayer consists primarily of CF and CC bonds whereas at experimental energies greater than the dissociation energy of the CF bond, there are appreciable amounts of CF2 and CF3 indicated. The GaAs surface itself is modified slightly, to include some gallium and arsenic fluorides, and perhaps some carbides as well. The levels of these components are limited, however, by the presence of the CF overlayer which upon forming encapsulates the GaAs surface, shielding it from subsequent CF+ bombardment. The overlayer also retains gallium and arsenic fluorides in the GaAs surface at temperatures higher than they would appear in the unencapsulated case. Heating in vacuum at 1×10−6 Pa releases some fluorine from the overlayer at and above 350 °C but is ineffective in removing the carbon. Fluorine was still present at low levels after heating to 450 °C but could not be found at higher temperatures.
Growth and characterization of laser-deposited superconducting Bi–Sr–Ca–Cu–O thin films
Authors: Kung P. J. , Muenchausen R. E.
Published: July 2002

Superconducting Bi–Sr–Ca–Cu–O thin films with thickness 400–3500 Å have been deposited on (100) MgO and (100) LaAlO3 by a pulsed excimer XeCl laser (λ=308 nm, τ=20 ns, and energy density=4–5 J/cm2). The oxygen pressure during deposition and the substrate temperature are in the range of 0.1–100 mTorr and 350–750 °C, respectively. The as-deposited films were annealed either inside (in situ) or outside (ex situ) the deposition chamber to improve the crystallinity and the superconducting transition of the films. The formation of 2212 and 2223 phases was controlled by tailoring the deposition and annealing parameters. The corresponding transition temperatures (Tc’s) of these phases in the ex situ films measured by zero-field cooled diamagnetic transition at 10 Oe are 80 and 110 K; however, the in situ mirrorlike shiny films with 2223 phase only exhibit Tc=81 K (or 98 K in an ac field of 0.1 Oe at 125 Hz). These films were also characterized by scanning electron microscopy, transmission electron microscopy, superconducting quantum interference device magnetometer, and ac susceptometer to study their morphology, microstructure, and magnetic properties. The critical magnetization current density (Jc) of the ex situ films is of the order of 107–108 and 105–106 A/cm2 for H⊥c axis and H∥c axis, respectively, at 7 K up to 5 T. Jc of the in situ films is two orders of magnitude lower than that of the ex situ films, and further enhancement of Jc appears promising if better crystallinity of the in situ films can be achieved. A qualitative phase diagram with respect to the development of 2212 and 2223 phases is given and discussed.
Real-time determination of the direction of wafer temperature change by spatially resolved infrared laser interferometric thermometry
Authors: Donnelly V. M.
Published: July 2002

Interferometric thermometry is a noncontact method of directly measuring the temperature of a semiconductor wafer. Periodic modulation in the intensity of reflected laser light is detected as the temperature-dependent change in the optical pathlength causes transitions from constructive to destructive interference between the front and back surfaces of the wafer. In its simplest implementation, only a temperature change is detected; heating and cooling are indistinguishable. In this article, a simple method for determining the direction of temperature change is described and demonstrated, based on sensing phase differences in periodic signal intensity detected from two regions of slightly different thickness. A statistical analysis reveals that this method will have an extremely high probability of correctly determining the direction of temperature change in almost all instances.
X-ray photoelectron spectroscopy study of growth of thin cerium films on polypropylene
Authors: Heuberger M. , Dietler G. , Nowak S. , Schlapbach L.
Published: July 2002

From x-ray photoelectron spectroscopy (XPS) measurements of thermally evaporated cerium films on polypropylene (PP) we conclude that an ion bombardment pretreatment of the substrate significantly improves the deposited amount of cerium. The metal–polymer interface state is dependent upon the ion bombardment of the PP substrate. For a mild bombardment (Ar+ ions of kinetic energy less than 500 eV and doses less than 1015 ions/cm2) we observed the formation of Ce–C bonds, which are not observed if we apply a more energetic ion bombardment (ions kinetic energy 3 keV, doses≳1016 ions/cm2). The effect of the ion bombardment on the cerium film formation can be summarized in an increased coverage of the polymeric substrate for the same thickness of the cerium film. We find that the cerium film grows with a Volmer–Weber mechanism and the difference between treated and untreated samples consists in an increased coverage of the substrate by cerium for the treated samples. A new kind of plot of the XPS data is used to discriminate between different surface coverages. The XPS measurements have also shown that an oxidation of the cerium films takes place during the XPS measurements. Mass spectrometry of the residual gas composition of the ultrahigh vacuum system, where the XPS measurements are performed, shows that the x-rays induce an outgas of H2, water, OH, CO, and CO2 originating from the polypropylene substrate. Water in the PP is dissociated by x-ray influence and therefore is responsible for the oxidation of the cerium film.
Investigation of a laser soldering process for the interconnection of thin film sensors with sputtered multilayer metallizations
Authors: Chabicovsky R. , Nicolics J. , Musiejovsky L.
Published: July 2002

Miniaturized thin film sensor elements can be simply carried by their lead-in wires. Laser soldering seems to be a favorable technique for attaching relatively thick wires to thin film metallizations. Work described in this paper concerns soldering experiments carried out with a Nd:YAG laser. We have investigated two types of metallizations (NiCr–Au and Al–NiCr–Au) deposited on glass, alumina, and silicon substrates by rf–magnetron sputtering. Special test patterns with integrated thin film thermocouples were developed to analyse temperature dependent dynamic effects of the laser soldering process. The thermocouples formed by NiCr and W tracks were placed below the solderable metallization and electrically insulated by silicon nitride and silicon oxide layers. We show temperature versus time curves recorded during soldering processes. A further part of this paper is focused on the dependence of solder joint quality on soldering parameters, type of metallization, and substrate material. Solder joint quality has been evaluated by means of visual inspection of solder formation and mechanical strength testing. We have established the lower limits of the range of parameter settings (laser power and pulse duration) leading to an acceptable bonding quality. Results of strength tests are correlated to metallization type and substrate material.
Passivation with SiO2 on HgCdTe by direct photochemical-vapor deposition*
Authors: Lin J. D. , Su Y. K. , Chang S. J. , Yokoyama M. , Juang F. Y.
Published: July 2002

For the first time, SiO2 layers, prepared by direct photochemical-vapor deposition, were passivated onto HgCdTe substrates using a deuterium (D2) lamp as the ultraviolet and vacuum-ultraviolet light source. It was found that the refractive index of the SiO2 films, grown at 60 °C and 0.5 Torr for a mixture of SiH4 and O2, is close to 1.462 (the refractive index of thermal silicon dioxide) when the gas ratio (SiH4/O2) is adjusted to 0.2. Various characterization techniques, such as x-ray photoemission, Auger-electron, and Fourier-transform spectroscopies were used to give a detailed study of the physical and chemical properties of the SiO2 thin films. The electrical properties of these SiO2 layers were investigated by performing high frequency (1 MHz) capacitance–voltage (C–V) and current–voltage (I–V) measurements, at 77 K. The C–V measurement shows that the minimum interface state density is 5×1010 cm−2 eV−1 with a hysteresis smaller than 0.2 V. The maximum dielectric strength observed from I–V measurement is around 580 kV/cm.
Nature of super-lubricating MoS2 physical vapor deposition coatings
Authors: Le Mogne T. , Donnet C. , Martin J. M. , Tonck A. , Millard-Pinard N. , Fayeulle S. , Moncoffre N.
Published: July 2002

MoS2 is a well-known solid lubricant used for space applications. Radio frequency (rf) magnetron sputtered MoS2 films are being used increasingly, due to an ultra-low friction behavior in high vacuum (friction coefficient: ∼0.01). MoS2 coatings with a super-low friction behavior (friction coefficient: ∼0.001) have been recently synthesized in an ultra-high vacuum tribometer equipped with a rf magnetron sputtering device. Physicochemical and structural characterizations of the thin films have been carried out using XPS (x-ray photoelectron spectroscopy) and AES (Auger electron spectroscopy) to determine the extreme surface composition, HRTEM (high-resolution transmission electron microscopy), GXRD (grazing-angle x-ray diffraction) for structural investigations, RBS (Rutherford backscattering spectrometry) for thickness and stoichiometry determination, and NBS (nuclear backscattering spectrometry) for quantitative analysis of oxygen contamination. Indentation tests at nanometric scale have also been performed to compare the mechanical constants (Young modulus, hardness) of the sputtered MoS2 films with the characteristics of molybdenite and to confirm the overall data. The coatings are made of highly pure, stoichiometric MoS2, with a polycrystalline microstructure (grain size on the order of 10 nm). The stoichiometry is MoS1.97±0.10O0.10±0.01. Most of the grains are ‘‘edge-oriented’’ on the substrate surface [relative to their (002) basal planes], with an azimuthal disorder of the other crystallographic directions [(100) and (110)]. Consequently, and by comparison with already published data, the super-low friction regime is found to be associated with the purity and microstructure of the coating.
Study of cleaning agents for stainless steel for ultrahigh vacuum use
Authors: Herbert J. D. , Groome A. E. , Reid R. J.
Published: July 2002

Satisfactory operation of the synchrotron radiation source (SRS) at Daresbury Laboratory depends upon effective cleaning of the stainless steel vacuum vessels and other components. Pursuant to the Montreal protocol, current and proposed changes to European community environmental protection legislation require a reappraisal of all cleaning processes, since many involve chemicals that have been identified as environmentally unfriendly. This article reviews work carried out at Daresbury to establish replacement cleaning recipes for the preparation of stainless steel surfaces for ultrahigh vacuum systems. The importance of achieving clean ultrahigh vacuum for the Daresbury SRS, and environmental considerations in reaching the required level of cleanliness are discussed. Suitable criteria for comparing various cleaning agents are established, based on outgassing rates and stimulated desorption coefficients. Outgassing rates and some partial pressure comparisons are presented here. These demonstrate that the standard procedure used at Daresbury has been chosen with some care in the past. Further work is required before a fully satisfactory alternative procedure can be determined.
Modeling the electromagnetic excitation of a microwave cavity plasma reactor
Authors: Tan W. , Grotjohn T. A.
Published: July 2002

The electromagnetic excitation of a discharge-loaded microwave cavity plasma reactor used for diamond thin film deposition has been numerically modeled in the time domain. This reactor model simulates a three-dimensional, cylindrical, single-mode excited cavity including the input power coupling probe. The time-varying electromagnetic fields inside the resonant cavity, both inside and outside the discharge region, are obtained by applying a finite-difference time-domain method to solve Maxwell’s equations. The boundary conditions and electromagnetic field excitation methods of this model are discussed. The microwave electric field interactions with the plasma discharge are described using a finite-difference solution of the electron momentum transport equation. The spatial electric field patterns, power deposition patterns, stored energy, and quality factor of a cavity loaded with hydrogen discharges at various pressures (20–70 Torr) are simulated and compared with experimental data.
One-point numerical modeling of microwave plasma chemical vapor deposition diamond deposition reactors
Authors: Hyman E. , Tsang K. , Drobot A. , Lane B. , Casey J. , Post R.
Published: July 2002

As a first step to carrying out two-dimensional simulations of microwave reactors we have performed very detailed one-point calculations using a Boltzmann code to determine the distribution of electron energy, detailed time dependent ion chemistry, and detailed neutral time dependent hydrocarbon chemistry. Modeling a microwave chemical vapor deposition reactor requires accurate determination of the electron energy distribution generated by the microwave electromagnetic fields and their interaction with the neutral gas because the distribution is highly nonthermal and the important dissociation and ionization rates are determined by the small fraction of high energy electrons. The electrons lose most of their energy to vibrational excitation of the gas which heats it through vibrational–translational energy exchange. The one-point model takes account in an approximate way of the effects of mass diffusion and thermal conduction to the reactor substrate and walls. We show time dependent calculations of the rise in gas temperature, the evolution of ion species, and the neutral species development in the pressure range of 40–110 Torr characteristic of conditions in an ASTeX reactor. We vary the input power and the input methane and oxygen fractions and compare with experimental measurements in the reactor.
Optimized magnetic field shape for low pressure magnetron sputtering
Authors: Kadlec S. , Musil J.
Published: July 2002

Discharge characteristics at low pressures (<0.1 Pa) of an unbalanced magnetron with two electromagnets have been studied. The discharge extinction and ignition pressures are a function of the currents I1 and I2 in both electromagnet coils. Minimum pressure is obtained for a particular ratio I2/I1. Extinction pressures range down to 1.5×10−2 Pa. The magnetic field of the magnetron was measured. Its shape was fitted using Bessel functions and the field line pattern solved using Runge–Kutta method. The magnetic field for the minimum extinction and ignition pressures features maximum area of the target covered with the tunnel of magnetic field lines.
Mechanism of surface charging during CO2 jet spray cleaning
Authors: Hills M. M.
Published: July 2002

The mechanism by which surfaces are electrostatically charged during CO2 gas/solid jet spray cleaning has been investigated. The dominant mechanism of surface charging is the transfer of electrons between solid CO2 particles and the surface being cleaned. This transfer is driven by the mismatch in the Fermi levels of the CO2 particles and the substrate; hence, the direction of transfer (sign of the charge on the substrate) is determined by the work function of the material being cleaned. Materials with high work functions charge negatively, with the exception of ferromagnetic materials such as nickel and cobalt. Materials with low work functions initially charge positively, but some of these were observed to then charge negatively after several seconds of exposure to the spray. The magnitude of the steady-state charge (typically 0.1 to several kV) depended upon parameters other than the Fermi level, including substrate thickness, conductivity, and dielectric constant, and jet spray design. When the jet spray is operated in air, the charge is strongly affected by the relative humidity. Under these conditions, transients in the charge may occur; the magnitude of these transients will depend on nozzle design as well as the environment. The ramifications of these observations are several. The extent of charging will depend upon the nozzle design, which controls the CO2 particle velocity among other parameters. The effect of contaminant films on the work function of materials effectively prohibits tuning the charge on the CO2 particles to match the CO2 Fermi level with that of a substrate to eliminate charging. When cleaning under conditions of moderate to high relative humidity, one should expect transients in the charge to occur. These results indicate that, for at least some high-velocity CO2 jet spray gun designs, it would be prudent to avoid cleaning charge-sensitive materials or systems with the jet spray.
Charge separation in an electron cyclotron resonance plasma
Authors: Inoue M. , Nakamura S.
Published: July 2002

Separation of an electron cyclotron resonance (ECR) plasma flux into an ion flux and an electron flux during plasma extraction has been investigated. The phenomenon is explained by the difference between ion current distribution and electron current distribution in the ECR plasma. When magnetic force lines cross the direction of the electron flux at a larger angle, the charged particle flux separation is enhanced. Also, evaluation of the flux diffusion equation for a magnetoplasma indicates that the diffusion coefficient of the electron flux across the force lines is much smaller than that of the ion flux. The ion flux diffuses isotropically compared to the electron flux confined by the magnetic field, resulting in charged particle flux separation. The potential distribution within a wafer exposed to the ECR plasma was evaluated by the flat band voltage (Vfb) shifts in metal–nitride–oxide semiconductor capacitors. The separation of the charged particle flux causes a nonuniform potential distribution within the wafer.
Metal overlayers on organic functional groups of self-assembled monolayers. VI. X-ray photoelectron spectroscopy of Cr/COOH on 16-mercaptohexadecanoic acid
Authors: Jung D. R. , Czanderna A. W.
Published: July 2002

The interaction of Cr with the COOH groups of a self-assembled monolayer (SAM) of 16-mercaptohexadecanoic acid [HS(CH2)15COOH] on gold was studied by x-ray photoelectron spectroscopy (XPS). For each Cr overlayer thickness, a freshly prepared SAM was exposed to the evaporative deposition of Cr at ≤1×10−8 Torr and then transferred immediately in situ to a surface analysis chamber held at ≤5×10−10 Torr. Metallic Cr is deposited as evidenced by a Cr 2p3/2–2p1/2 splitting of 9.2 eV for 1 nm thick Cr films on Au. The C 1s and O 1s binding energies and intensities for the initial COOH-terminated SAM are consistent with the presence of the O=C—OH end group at the surface. For Cr overlayers of 0.04–1 nm average thickness, we identify Cr–COOH interactions primarily by changes in the O 1s level. For 0.04 nm Cr/COOH, the O 1s peak is narrowed and fitted by a single component at 532.9 eV that is between the O—C (533.9 eV) and O=C (532.5 eV) components of the bare SAM. The narrow width of this peak is evidence that the two oxygens of a single COOH end group interacting with Cr are indistinguishable by our instrument. For 0.07–1 nm average overlayer thickness, a low binding energy component (531.0–530.3 eV), assigned to a Cr(III) oxide, is of gradually increasing intensity. For coverages below 0.6 nm, analysis of XPS peak intensities indicates that adsorption of an adventitious oxygen-containing species has little effect on the results.
Microstructures of sputtered PbTiO3 thin films
Authors: Satoh Toshifumi , Wasa Kiyotaka , Tabata Kenji , Adachi Hideaki , Ichikawa Yo , Setsune Kentaro
Published: July 2002

Ultrathin stoichiometric PbTiO3 films, 10–100 nm thick, were deposited on (001) SrTiO3 substrate at 600 °C by rf planar magnetron sputtering to understand the microstructure of initial film growth. The electron microscopy and x-ray diffraction analysis suggested epitaxial growth of (001) PbTiO3/(001) SrTiO3 with three-dimensional crystal orientation; however, the PbTiO3 films still included crystal boundaries. Miscut (001) SrTiO3 substrates reduced the crystal boundaries and provided continuous ultrathin films of single crystal PbTiO3. Rapid thermal annealing at 600 °C for 10 s further improved their crystallinity.
Attaining a solar energy economy with active thin film structures
Authors: Goldner R. B.
Published: July 2002

First, quantitative arguments are presented which support the conclusion that the probability is high for the United States to attain a solar energy economy in the relatively near future. The basis of the arguments is the use of four active thin film structures: (a) electrochromic windows for energy conservation; (ii) thin film photovoltaic cells for energy conversion; (iii) thin film batteries; and (iv) thin film fuel cells for portable energy storage and delivery. The second part of the article focuses on the pivotal role for thin film deposition processes, and particular attention is paid to some of the deposition challenges presented by two of the structures, thin film electrochromic windows and batteries.
Identification of plasma induced failure modes in the development of a bipolar-complementary metal–oxide–semiconductor process
Authors: Hackenberg J. J. , Dion M. J. , Hemmenway D. F. , Pearce L. G. , Werner J. W.
Published: July 2002

Development of a bipolar-complementary metal–oxide–semiconductor process encountered metal–oxide–semiconductor (MOS) device failure behaviors that were traced to a single processing plasma source. Despite the fact that the process employed relatively thick 500 Å MOS gate oxides and was made in a manufacturing line that also produces a complementary metal–oxide–semiconductor product with gates below 200 Å, significant plasma damage effects were identified. Four distinct failure signatures were observed: shorted n-channel metal–oxide–semiconductor transistor (NMOS) gates, leaky NMOS gates with functioning channels, parasitic depletion mode conduction at the ends of the enhancement NMOS device channel, and p-channel metal–oxide–semiconductor transistor (PMOS) threshold shift as observed in a differential amplifier input offset. Test devices were specifically designed to monitor plasma damage through various gate antenna configurations. Device protection fuses were also employed to identify the cause of the failures as electrical damage induced during the backend of wafer processing. Although the methodology was successful, the experience points toward significant improvements that can be made and will be employed in future development and characterization efforts on a routine basis. Sequential characterization of device performance from the first metal out quickly identified the plasma enhanced chemical vapor deposition tool used for final passivation deposition as the primary contributor to the plasma damage. Subsequent process flow changes did eliminate this source of plasma damage.
Scanning tunneling microscopy observation of hydrogen-induced Ag cluster formation on the Si(111) surfaces
Authors: Ohnishi Hideaki , Yamamoto Yasuji , Oura Kenjiro , Katayama Itsuo , Ohba Yasuyuki
Published: July 2002

Using a scanning tunneling microscopy (STM) we have studied the nucleation and growth process of Ag clusters induced by the atomic hydrogen adsorption on the Si(111) √3×√3(R30°)-Ag (simply √3-Ag) surface. Size distributions of the clusters have been investigated as a function of the exposure of atomic hydrogen, and it is strongly suggested that the surface migration of Ag atoms over the hydrogen-reacted regions is largely suppressed compared with that on the √3-Ag surface. The size of Ag clusters is less than 150 Å and their average height is estimated to be 3.1 atomic layers, consistent with previous ion scattering results. We have proposed the model of nucleation and growth process of hydrogen-induced Ag clustering in which the broadened H/√3-Ag regions suppress the migration of expelled Ag atoms and lead to the formation of many small clusters.
Force modulation imaging of protein membranes
Authors: Yamada Hirofumi , Hirata Yoshiki , Miyake Jun
Published: July 2002

The force modulation technique in atomic force microscopy (AFM) provides new information about the local mechanical properties of samples using modulation of the applied load by vertical vibration of the sample at a frequency exceeding the feedback bandwidth of the AFM. This technique is expected to detect the difference in composition and/or conformation of organic molecular films. Using both the AFM and the force modulation technique, we have investigated Langmuir–Blodgett films of the photosynthetic protein membranes, chromatophores, obtained from photosynthetic bacteria Rhodopseudomonas viridis deposited on glass substrates. Chromatophores with various sizes ranging from 50 nm to 1 μm are composed of lipids and transmembrane proteins, known as photoreaction units (PRUs). The modulation frequency used here was 25 kHz and the amplitude was about 0.5–1 nm. The modulation images show a remarkable contrast between the glass substrate and the membrane. The hexagonally packed structure of PRUs with an average spacing of 10 nm can be clearly observed in the frequency modulation images even when the corresponding structure cannot be found in the normal topography images obtained simultaneously. In addition, the modulation images reveal that some membranes do not contain PRUs, while the topography data show no difference between these membranes and the other.
Adaptive extensions to a multibranch run-to-run controller for plasma etching
Authors: Moyne James R. , Chaudhry Nauman , Telfeyan Ronald
Published: July 2002

Fuzzy logic and database learning mechanisms have been incorporated into a generic plasma etching run-to-run controller, resulting in a very dynamic, adaptable, and robust system. The system features an Applied 8300 reactive ion etcher controlled by a Techware II equipment controller. A TCP/IP connection links this equipment controller to the run-to-run controller residing on a SUN. The run-to-run control environment is generic in that the basic control framework and controller development results are applicable to very large scale integrated manufacturing in general. The controller is multibranch as it utilizes multiple algorithms in complementary fashion to achieve process optimization and control. The current implementation utilizes three branches: (1) a linear approximation control algorithm, (2) an optimization algorithm that utilizes (real-time) data collected in situ to determine optimal run-to-run process parameter settings, and (3) a statistical optimization algorithm that utilizes run-to-run data. We have extended the controller to accommodate an automated branch selection process that utilizes fuzzy logic to incorporate a process engineer as well as optimization and control algorithmic knowledge. We have also extended the controller to adapt to unforeseen events through utilization of a learning mechanism; this mechanism detects these unforeseen events, intelligently queries the process engineer, guides the engineer through the development of an event servicing scheme, and incorporates this new knowledge into its control knowledge base so that the event may be serviced automatically in the future. Implementation results of the controller (in the control of the etcher) confirm the robust control capabilities in the face of process shift and drift, and recipe change.
Interfacial properties of metal–insulator–semiconductor capacitors on GaAs(110)
Authors: Huang L. J. , Rajesh K. , Lau W. M. , Ingrey S. , Landheer D. , Noël J.-P. , Lu Z. H.
Published: July 2002

Passivation of both cleaved GaAs(110) facets and wafers (both n and p types) was performed with different surface treatments including HF-etch of native oxide, passivation with an ammonium sulfide solution, passivation with hydrogen polysulfide, and passivation with a Si/S, Ge/S, or Si/Ge/S interface control layer. The interface state density was measured with capacitance–voltage (CV) measurements of metal–insulator–semiconductor capacitors fabricated on the passivated surfaces using remote plasma deposited silicon nitride as gate insulator. The interface structures of the capacitors were analyzed by x-ray absorption near-edge structure spectroscopy and x-ray photoemission spectroscopy. It was found that, while the passivation procedures with the sulfur compounds or a Si/S interface control layer did improve the CV data when compared with the HF oxide etch, the Si/Ge/S multilayer passivation technique led to the best CV results. By comparing the quasistatic and high frequency (1 MHz) CV data, we found that the minimum interface state density of the fabricated capacitors was about 1012 eV−1 cm−2. The results were compared with those obtained from GaAs(100) and the difference was addressed with respect to the surface geometry and the electronic structures.
Surface diffusion of In on Si(111): Evidence for surface ionization effects
Authors: Allen C. E. , Ditchfield R. , Seebauer E. G.
Published: July 2002

Second harmonic microscopy has been used to quantify the surface diffusion of In on Si(111). At temperatures near 50% of the bulk melting temperature and in the coverage range 0<θ<0.7, the activation energy Ediff and pre-exponential factor D0 lie at 42±0.5 kcal/mol and 3×103±0.3 cm2/s, respectively. These parameters, which are quite large, are explained semiquantitatively by reference to an adatom–vacancy model recently developed for related systems. The present work, when compared with the results of these other systems, offers significant evidence for the effects of adatom–vacancy ionization.
Use of a Cu/Ag/Au alloy as a reference material for the calibration of x-ray photoelectron spectrometers
Authors: Strohmeier Brian R.
Published: July 2002

The use of a sputter-cleaned copper/silver/gold (Cu/Ag/Au) alloy for calibrating the energy scale and instrument resolution as full width at half-maximum (FWHM) of x-ray photoelectron spectrometers is described. The Cu 3p3/2, Cu 2p3/2, Cu L3M4,5M4,5, Ag 3d5/2, Ag M4NN, and Au 4f7/2 lines have been recommended in the literature for calibrating x-ray photoelectron spectroscopy (XPS) instruments. The three-component alloy material is a convenient alternative to the common practice of using three separate sputter-cleaned reference materials (i.e., Cu, Ag, and Au foils) to obtain these measurements. Results indicate that the Cu/Ag/Au alloy yields XPS binding energies within reasonable experimental error (i.e., ±0.2 eV or less) of the values obtained for pure Cu, Ag, and Au materials. In addition, the FWHM values obtained for the major XPS peaks of the Cu/Ag/Au alloy were essentially equivalent (i.e., within ±0.03 eV or less) to the values obtained for pure Cu, Ag, and Au metal foils. This material, however, is not suitable as a standard reference material for calibrating the intensity scale of XPS instruments because of localized variations in composition across the alloy surface.
Mapping of radio frequency plasma potential throughout a particle trapping region using an emissive probe
Authors: Kang Jungwon , Carlile Robert N. , O’Hanlon John F. , Collins Sean M.
Published: July 2002

This article describes the use of an emissive probe to map the time-invariant plasma potential in a rf generated plasma in a GEC Reference Cell. The mapping has been done throughout a region expected to trap contamination particles for four different geometric configurations of materials on the powered electrode of the GEC Cell. For one case, there is a potential maximum which is a trap for negatively charged particles. For the other three cases, trapping can occur if a second force besides the electrostatic force is present. We postulate that this is the ion drag force. When particles are present in the system, the resulting particle clouds are observed using laser light scattering, and are superimposed of the maps. These clouds occur just where one would expect them to, given the electromagnetic force configuration exhibited by the maps plus the supposition of the existence of an ion drag force. It is shown that, at the location of a cloud, the ion drag force is of the right magnitude relative to the electrostatic force to permit trapping of particles.
Adsorption isotherms of H2 and mixtures of H2, CH4, CO, and CO2 on copper plated stainless steel at 4.2 K
Authors: Wallén E.
Published: July 2002

Adsorption isotherms in the pressure range 10−11–10−6 Torr have been measured for H2 and mixtures of H2 and CH4, CO, and CO2 on copper plated stainless steel at 4.2 K. The measurements have been focused on the behavior of the isotherms at low surface coverage, up to a few monolayers of adsorbed gas on the cold surface. The isotherms were measured in a static situation with a small amount of gas injected for each point on the isotherm. Coadsorption measurements of H2 with CH4, CO, and CO2 as well as adsorption of H2 on condensates of CH4, CO, and CO2 have been made. A cryotrapping effect of H2 is seen when coadsorbing the gas mixtures, which is especially strong for the mixture of H2 and CO2. The measurements show that CO2 condensed at 4.2 K may have a porous structure that H2 can penetrate, while CO and CH4 have rather dense structures when adsorbed at 4.2 K. The measurements have been done within the framework of the Large Hadron Collider project [The Large Hadron Collider Accelerator Project, CERN/AC/95-05 (LHC), 20 October 1995] at CERN, Geneva, Switzerland, where superconducting magnets will be used to produce a magnetic field of about 9 T around the arcs of the 27 km long quasicircular accelerator. Synchrotron radiation produced by the circulating proton beam in the superconducting magnets will induce desorption of neutral gas molecules, mainly H2, CH4, CO, and CO2, from the inner surface of the vacuum chamber. The desorbed gas molecules will be physisorbed on the cold surfaces in the vacuum chamber and they may induce vacuum instabilities in the accelerator. Hence, it is of importance to have knowledge of the mixed adsorption isotherms of these gases at low temperatures.
Chemical vapor deposition diamond for tips in nanoprobe experiments
Authors: Niedermann Ph. , Hänni W. , Blanc N. , Christoph R. , Burger J.
Published: July 2002

Diamond is the most suitable material for many experimental methods in nanoprobe microscopy and materials testing. The extreme hardness, the high Young’s modulus, the inert nature of the surface, and the electrical conductivity obtained through doping make this material particularly attractive. We have coated silicon atomic force microscope (AFM) levers with thin (100 nm) doped diamond layers by chemical vapor deposition (CVD). A continuous diamond coating was obtained, resulting in tips with 100–200 nm radii. Owing to their electrical conductivity, these tips were found to be adequate for conducting AFM and scanning tunneling microscope applications, some of which are briefly discussed and reviewed in this article. We have also demonstrated CVD diamond tips, microfabricated in a controlled fashion, that have a 20 nm apex radius. These tips are particularly promising for nanomechanics and general AFM use.
Thermally induced processes in thin layers, obtained by coevaporation of TeO2 and Sn
Authors: Podolesheva I. , Platikanova V. , Konstantinov I. , Dimov V. , Tarassov M.
Published: July 2002

Thin layers with controlled Sn/Te ratio (0÷2) and thickness are prepared by coevaporation of TeO2 and Sn. The structure and chemical composition of the as-deposited layers and the changes they undergo upon heating are studied by various transmission electron microscopy techniques and energy dispersive spectroscopic and electron spectroscopy for chemical analysis. It is shown that during the coevaporation a chemical reaction between TeO2 and Sn takes place resulting in the production of a finely dispersed phase of elemental Te. Upon annealing transport of the dispersed elemental Te to the free upper surface of the layer, particle growth and crystallization are observed. A strong correlation between the concentration of elemental Te in the layer and the rate of these processes is found. The reaction between TeO2 and Sn proceeds till the complete consumption of TeO2 or Sn; SnTe is formed only at excess amounts of Sn and after all TeO2 is consumed.
Plasma assisted chemical vapor deposition silicon oxynitride films grown from SiH4+NH3+O2 gas mixtures
Authors: Olivares-Roza J. , Sánchez O. , Albella J. M.
Published: July 2002

Silicon oxynitride films exhibiting refractive indexes in the 2.01–1.49 range have been deposited in a plasma assisted chemical vapor deposition system using SiH4+NH3+O2 gas mixtures. The O2/NH3 gas ratio was varied in order to obtain different oxynitride compositions, ranging from silicon nitride to nearly stoichiometric silicon oxide. A single peak, in contrast to two separate peaks normally associated with silicon oxide and silicon nitride, was observed in the IR spectra, indicating the formation of a unique oxynitride compound. The IR absorption spectra as well as the refractive indexes measured by ellipsometry were used to estimate the stoichiometry of the films, the results being well correlated to Auger analysis.
Growth and structural properties of hydrogenated silicon films deposited by pulsed laser ablation
Authors: Trusso Sebastiano , Vasi Cirino , Neri Fortunato
Published: July 2002

Hydrogenated silicon thin films have been deposited by means of pulsed laser ablation. Efficient hydrogenation was obtained by performing the ablation process in a controlled H2 atmosphere. Fluorescence spectroscopy characterization of the plume revealed the presence of both atomic hydrogen and highly ionized silicon atoms. The hydrogen content ranged from 2% to 15% as the H2 pressure was varied between 0.05 and 30 mbar. Infrared spectroscopy measurements showed a monohydride preferential incorporation at low hydrogen pressure. The films’ crystalline fraction, obtained by both Raman scattering and x-ray diffraction experiments, was found to show a maximum value of about 60% for H2 pressure values around 1 mbar. These results suggest that crystallinity and hydrogenation of the film, deposited at room temperature, can be properly adjusted as a function of the deposition parameters.
Interface matching in oxides of rocksalt/rocksalt(001) and rocksalt/perovskite(001)
Authors: Chern G. , Cheng C.
Published: July 2002

The matching configuration in an ionic interface is more stringent relative to metallic systems due to the polarity concern. This configuration has to satisfy both geometric and electrostatic requirements. We study the growth of several different thin films, including MgO, SrO, NiO, and Fe3O4 on single crystalline MgO(001) and SrTiO3(001) substrates by molecular beam epitaxy. These oxides have different structures (rocksalt, perovskite, and spinel) and lattice misfits (small, ∼1%, and large, ∼23%). Using high energy electron diffraction, we observed some specific orientation relations between these structures. The interface of a rocksalt/rocksalt only shows a direct matching configuration. However, the interface of rocksalt/perovskite shows two different matching configurations, direct on and 45° rotation of the film relative to the substrate. This difference results from the relative ionic arrangements of these materials. It further implies that a more general matching rule may exist in other ionic interfaces depending on the relative ionic symmetry. A calculation based on Ewald sum is also included.
Microscopic modeling of InP etching in CH4–H2 plasma
Authors: Houlet L. , Rhallabi A. , Turban G.
Published: July 2002

The Monte Carlo method has been applied to simulate the CH4–H2 reactive ion etching process for an atomic scale InP surface. Two neutral precursor types and one ionic precursor type have been considered in the surface etching process. CH3 and H adsorbed radicals are assumed to be bonded to the surface substrate leading to the ejection of indium and phosphorous sites, respectively, whereas energetic ions induce the In(CH3)x and P(H)x (x=0,1,2,3) ejection from the surface. The model takes into account precursor and site identities, physisorption, chemisorption, migration and desorption of etchant neutrals, chemical etching, and ion preferential sputtering of sites. The chemisorption probability effects of the neutral precursors on the rms roughness, the etching rate, and the phosphorus depletion are shown. On the other hand, the increase of the ion flux allows an increase in rms roughness. By setting the available experimental data, the simulation results confirm the existence of the phosphorus depleted surface layers, which were previously observed by x-ray photoelectron spectroscopy analyses.
Parameters of vacuum deposition of ZnS:Mn active layer for electroluminescent displays
Authors: Krasnov Alex N. , Hofstra Peter G. , McCullough Mike T.
Published: July 2002

In this article, x-ray diffraction measurements and scanning electron microscopy are employed to characterize the crystalline structure of the ZnS:Mn phosphor layers grown by thermal and electron-beam evaporation. The brightness–voltage and charge–voltage characteristics were used to estimate the efficiency of the active layer and to correlate it with the deposition conditions. The critical role of the preparation conditions and type of starting material is emphasized. Thermal deposition from a powder source has been found to favor the production of a smoother active layer. The use of specially prepared pellets has been found to be a key factor in the high-quality e-beam deposition of ZnS:Mn films. Peculiarities of both processes from the point of view of the evaporation kinetics are extensively discussed.
Transfer etching of bilayer resists in oxygen-based plasmas
Authors: Mahorowala A. P. , Babich K. , Lin Q. , Medeiros D. R. , Petrillo K. , Simons J. , Angelopoulos M. , Sooriyakumaran R. , Hofer D. , Reynolds G. W. , Taylor J. W.
Published: July 2002

Thin film imaging offers the possibility of extending 248 nm lithography to sub 150 nm resolution. We have been working on a 248 nm bilayer imaging scheme which utilizes a thin Si-containing resist on top of a thick, planarizing underlayer. The image is developed in the top layer and transferred to the underlayer via O2-based plasma etching. This article focuses on three aspects of the critical transfer etch process: etch resistance of the imaging resist, profile control and resist roughening. The imaging resist thickness loss is very fast during the first few seconds of the etch after which the rate diminishes. The relative importance of three phenomena that can explain this nonlinear behavior: oxidation of silicon, deprotection of resist moieties, and plasma etching of resist, are discussed. Fourier transform infrared studies on imaging resist films indicate minimal deprotection-related film thickness losses. X-ray photoelectron spectroscopy analyses of etched films indicate that the extent of surface oxidation increases initially and then becomes constant. Thus, the etching of this category of resists can be described as a combination of the oxidation of the silicon species and sputtering of the oxide-like layer formed. Post-transfer etch profiles using an O2 plasma are shown, and methods to reduce imaging resist faceting and thickness loss either by modifying the imaging layer silicon content or by using passivating plasma chemistries are discussed. The effect of different etching chemistries and processing conditions on imaging layer roughening and striation formation on underlayer sidewalls are explained with the aid of scanning electron microscopy micrographs and atomic force microscopy images of etched feature sidewalls. It is shown that the SO2–O2 etch significantly reduces the sidewall roughness from the postlithograpy values. The ∼3.5 nm rms sidewall roughness observed postetch is comparable to postdeveloped roughness values measured for mature single layer resists. The printing of 125 nm line/space patterns and 150 nm trench features with 10:1 aspect ratios in the underlayer is also demonstrated.