bluuebunny/crossref_metadata_2025 huggingface dataset:
Defect formation and structural alternation in modified SiO2 glasses by irradiation with F2 laser or ArF excimer laser
Authors: Ikuta Yoshiaki , Kikugawa Shinya , Hirano Masahiro , Hosono Hideo
Published: July 2002

The formation and restoration of defects by F2 laser irradiation with high laser fluence were investigated for modified silica glasses, and the results were compared with those by ArF excimer laser irradiation. F2 laser irradiation induced oxygen deficient centers (ODCs) and E′ centers via one-photon-absorption processes, while ODC and E′ defects are generated by two-photon-absorption processes by an ArF excimer laser. As-doped SiOHs and photoinduced SiOHs enhanced the formation of defects markedly in the case of F2 laser irradiation. F2 laser light transformed isolated SiOH bonds into hydrogen-bonded SiOHs, while such a process did not occur under ArF excimer laser light. These results suggest that silica glass networks were dissociated by two types of processes. The dominant process is the formation of pairs of E′ centers and NBOHCs, followed by conversion to the SiHs and SiOHs as a result of chemical reactions with hydrogen molecules in silica glass at room temperature. The other is the generation of ODC defects accompanied by interstitial oxygen molecules, which are also decomposed partly into E′ centers with the aid of F2 laser light.
Behavior of ultrathin Al2O3 films in very high electric fields: Scanning tunneling microscope-induced void formation and dielectric breakdown
Authors: Niu C. , Magtoto N. P. , Kelber J. A.
Published: July 2002

We report on the use of high electric fields applied via scanning tunneling microscopy (STM) under ultrahigh vacuum conditions to induce voids and dielectric breakdown in ultrathin γ′-Al2O3 films (∼7 Å thick) grown on Ni3Al (111) substrates. Voltage pulses (bias voltages of 0.1–6 V, either polarity) are applied to a specific location on the oxide surface with the feedback current loop operative to prevent tip/sample physical contact. Subsequent STM constant current imaging reveals the effects of high field on surface composition and topography. The results show that dielectric breakdown occurs at a field of 12.3±1.0 MV/cm. Breakdown is marked by the creation of features with apparent size of 8–25 nm high and 100–250 nm wide in the constant current STM images, and by the loss of the insulating nature of the oxide as deduced from current/voltage spectroscopy. Constant height scanning indicates that these features are caused by electronic changes in the oxide and not by mass transport. At lower electric fields, small voids that are 0.2–0.8 nm deep can be created. STM images taken at a 2 vs 0.1 V gap voltage show that these voids are located at the oxide/metal interface, where they grow into the metal. Repeated application of a lower field within the void region leads to dielectric breakdown, even though the same field does not induce breakdown in regions away from the void. The results provide direct evidence of the ability of localized defects to decrease the barrier to dielectric breakdown in an ordered oxide film.
Nanolithography using ultrasonically assisted development of calixarene negative electron beam resist
Authors: Yasin Shazia , Hasko D. G. , Carecenac F.
Published: July 2002

Negative resist image distortion is caused by resist swelling during development and is a major problem in ultrahigh resolution electron beam lithography. This problem has been overcome through the use of ultrasonically assisted development. In addition, exposure dose latitude is increased by 50% compared to conventional dip development, due to the improvement in contrast. These advantages have been exploited in order to realize ∼6 nm wide lines in calixarene resist.
Nanoscale optical imaging on an electroluminescent polymer by conducting atomic force microscopy
Authors: Lin Heh-Nan , Chen Sy-Hann , Lee Yuh-Zheng , Chen Show-An
Published: July 2002

We demonstrate optical imaging with a resolution of around 50 nm on an electroluminescent polymer by conducting atomic force microscopy. The results indicate that brighter light emission occurs from asperities on the polymer surface. By comparing surface morphologies of the polymer and the indium tin oxide substrate, it is found that similar asperities exist on both surfaces and the polymer becomes thinner on these locations. Therefore, stronger luminescence intensity from asperities is caused by higher electric field due to reduced polymer thickness. The present method can also be extended to obtain simultaneous optical and electrical transport properties.
Effect of implantation energy on the microstructure evolution of low dose separation of implanted oxygen wafers
Authors: Chen M. , Chen J. , Zheng W. , Li L. , Mu H. C. , Lin Z. X. , Yu Y. H. , Wang X. , Wang G. Y.
Published: July 2002

The structure development of buried oxide in low-dose separation of implanted oxygen wafers implanted at acceleration energies of 160, 130, and 100 keV was investigated by cross-section and high resolution transmission electron microscopy. The threading dislocation density in the superficial silicon layer was determined by Secco etching. The results indicate that the thickness of superficial silicon, the buried oxide (BOX) integrity, effective BOX thickness, Si/SiO2 interface, and threading dislocation density have a strong energy dependence. For the samples implanted at a dose of 5.5×1017 cm−2, the optimum energy is 160 keV, while at a dose of 4.5×1017 cm−2, it is 130 keV. The mechanism was discussed.
Electron field emission characteristics of textured silicon surface
Authors: Fung Y. M. , Cheung W. Y. , Wilson I. H. , Chen Dihu , Xu J. B. , Wong S. P. , Kwok R. W. M.
Published: July 2002

A textured silicon surface was prepared by chemical etching. The textured surface was covered with small silicon tips. The base diameter of the tips is random and the size is from less than 1–10 μm. A field emission emitter that shows a lower turn-on voltage has been fabricated by using aqueous potassium-hydroxide solutions with isopropyl alcohol added as a complexing agent. The silicon wafers were (100) monocrystalline n-type with a resistivity of 0.01 Ω cm. A texturing process using dilute inorganic alkaline in isopropyl alcohol solution is investigated. This causes the formation of randomly distributed pyramids on the (100) cyrstallographic plane without any masking pattern. Dilute alkaline solutions show a low-etching rate of typically 0.5 μm/min. The anisotropy arises from hydrogen bubbles which are able to stay on the silicon surface for a short time during etching. The diameter of the bubbles, their density, and the rate of the etching reaction define the geometry of the textured silicon surface. The silicon tip size and the density is affected by the concentration of isopropyl alcohol, potassium hydroxide, pretreatment of silicon substrate, and the temperature of the etchant. The turn-on voltage of the textured silicon surface was approximately at 25 V/μm when the emission current density reaches 1 μA/cm2. This compared with the turn-on field about 35 V/μm on a silicon tip array fabricated by using an isotropic etching solution of nitric acid. A silicon carbide layer was formed on the textured silicon surface by using metal vapor vacuum arc ion implantation. The turn-on voltage can be lowered to approximately 9 V/μm when the emission current density reaches 1 μA/cm2.
Field emission characteristics of boron nitride films deposited on Si substrates with cubic boron nitride crystal grains
Authors: Kimura Chiharu , Yamamoto Tomohide , Sugino Takashi
Published: July 2002

Field emission characteristics are investigated for boron nitride (BN) films deposited on Si substrates with cubic (c-)BN crystal grains. A comparative study of field emission characteristics is performed for the BN samples with and without c-BN grains. The turn-on electric fields are 7 and 18 V/μm for the BN samples with and without c-BN grains, respectively. A significant reduction in the turn-on electric field of the electron emission is found for the sample with c-BN grains. Fowler–Nordheim plots of the field emission characteristics suggest a variation in the field enhancement factor between the BN samples with and without c-BN crystal grains. It is also found that c-BN crystal grains are effective in increasing electron emission area.
Thermal model of Knudsen cells for organic molecular beam deposition
Authors: Pinotti E. , Sassella A. , Borghesi A.
Published: July 2002

Knudsen cells used for molecular beam deposition of organic materials are usually derived from the ones employed for conventional epitaxy of inorganic semiconductors. However, organic molecular materials need rather low evaporation temperatures and a very precise temperature control in the range from 100 to 400 °C. Therefore, a thermal model of the cell is needed, which, taking into account the peculiarity of organic molecular beam deposition, gives the thermal dynamics of the cell and can be used for developing accurate algorithms for thermal programming and control. In this article such a model is developed and fully assessed through a comparison with experimental results; on this basis, all information necessary for precisely controlling and programming Knudsen cells for organics is obtained.
Pressure change characteristics of a field emission display panel in operation
Authors: Oh J. Y. , Woo K. J. , Kim K. S. , Lee D. Y. , Choi J. O.
Published: July 2002

Pressure change characteristics of a field emission display (FED) panel in operation was studied with various operating conditions. For this study, low anode voltage FED samples with a vacuum gap of 0.2 mm were fabricated using unique process technologies of cathode, anode, spacers, and packages. With the FED samples, real-time pressure measurements were carried out during operation of the FED panel with a forced increase of an anode current and/or an anode voltage. Results from the experiment suggest that the pressure buildup of the panel in operation is mainly affected by an electron flux density rather than an electron energy in the low anode voltage FED.
Characterization of Hafnium Diboride, HfB2 (0001), by XPS
Authors: Perkins C. L. , Singh R. , Tanaka T. , Trenary M.
Published: July 2002

X-ray photoelectron spectra of a clean, well-ordered HfB2 (0001) single crystal surface are reported. A survey spectrum covering a binding energy range of 0 to 1000 eV is shown, which reveals the presence of minor amounts of oxygen and zirconium. Spectra over narrower binding energy ranges are also shown for the Hf 4f, B 1s, and Hf 4s/O 1s regions. A comparison of the Hf 4s/O 1s region before and after oxygen exposure provides for unambiguous assignment of the overlapping O 1s and Hf 4s peaks at binding energies of 531 and 534 eV, respectively.
Role of molecular beam epitaxy parameters on InGaAs surface roughness
Authors: Deng X. , Liu W. , Lin M. E. , Zhang Jie
Published: July 2002

The effects of various growth parameters such as growth temperature (410–560 °C), indium composition (18%–36%), and growth front (GaAs or AlGaAs) on the InGaAs layer surface morphology, the room-mean-squared surface roughness (rrms value), and the microstructure are systematically reported. Atomic force microscopy (AFM) analysis of 12 nm thick In0.2Ga0.8As grwon on GaAs demonstrates a vey smooth surface with average rrms of ∼3.5 Å. Within the temperature range of 410–440 °C, there is no trend or rrms change observed, which indicates that the growth temperature in this range is not a sensitive factor to the formation of In0.2Ga0.8As surface roughness. AFM images of 12 nm thick In0.2Ga0.8As grown on Al0.2Ga0.8As clearly show the initial formation of the InGaAs surface waves on GaAs at high resolution x-ray diffraction (HRXRD) analysis of the In0.23Ga0.77As grwon on GaAs at 520 °C indicates a nice crystal lattice match of the InGaAs to the GaAs surface. InGaAs with nominal 36% indium grown at 560 °C results in the disappearance of the InGaAs peak from HRXRD.
General rule for predicting surface segregation of substrate metal on film surface
Authors: Yoshitake Michiko , Aparna Yarrama-Reddy , Yoshihara Kazuhiro
Published: July 2002

We studied surface segregation of substrate metal on the top of a deposited film in a vacuum. A metallic polycrystalline film of submicron or micrometer thickness was deposited on a substrate and heated in an Auger electron spectroscopy (AES) or x-ray photoelectron spectroscopy (XPS) apparatus. The surface composition was monitored during heating. The specimen was heated until the substrate metal was observed on the surface of the deposited film and the surface concentration of the substrate metal became saturated. The depth profile of the heated specimen was obtained by measuring AES/XPS with Ar ion etching. Al, Ti, Cr, Ni, Cu, Nb, and Fe were used as substrate materials and Al, Ti, Cr, Cu, Zr, Nb, and Fe were used as film materials. More than 25 combinations of film–substrate materials have been investigated. For some film–substrate combinations, substrate metal was observed on the surface by heating at rather low temperature and substrate metal was only observed at the surface (i.e., surface segregation). The substrate metal is considered to diffuse through grain boundaries of the film to reach the surface. Not all film–substrate combinations show surface segregation of substrate metal. By considering the migration of substrate atom to the grain boundary of a film at the film–substrate interface, the general rule to predict segregation of substrate metal to the film surface is proposed. The rule is that segregation of a substrate atom occurs if the adsorption energy of a substrate atom on a film is larger than that on the substrate itself. As experimental values of adsorption energy for many metals are not available, the adsorption energy is estimated from heat of solution, surface energy, and vaporization energy, and those estimated values are used to predict the segregation behavior.
Chemical effects on F KLL Auger spectra in fluorides
Authors: Kövér L. , Uda M. , Cserny I. , Tóth J. , Végh J. , Varga D. , Ogasawara K. , Adachi H.
Published: July 2002

Considerable chemical effects have been found on the satellite structures of F KLL Auger spectra in fluorides recently, which could be important for surface chemical identification and could provide information on the origin and the atomic or molecular character of particular Auger satellite lines. In the case of alkali fluorides unassigned satellites were found and interpreted on the basis of a new concept, resonant orbital rearrangement. In the present work we study the structure of the Auger satellites induced from rutile-type fluorides. F KLL Auger spectra were excited by Al Kα and Cu Lα x-rays from polycrystalline powder samples of MgF2, ZnF2, NiF2, and CoF2 and measured by a high luminosity electron spectrometer. Excitation by Cu Lα increased the peak to background ratio in the spectra significantly. Similar to the alkali fluorides, a satellite has been found in the high kinetic energy part of the measured F KLL spectra. From the satellite intensities the fluorescence yield for the doubly ionized states in MgF2 has been determined. An inverse proportionality has been found between the satellite/diagram x ray and the corresponding Auger intensity ratios, while the latter ratios have been found to be proportional to the linewidth of the new Auger satellites. These observations indicate the resonant nature of the Auger transition identified. For determining the energy difference between the molecular orbitals in resonance, discrete variational Xα cluster molecular orbital calculations have been performed and the experimental results have been interpreted on the basis of the resonant orbital rearrangement model. Multiplet structure calculations for K6F clusters indicate that multiplet splitting cannot explain the origin of the above satellite peak in the F KLL spectrum of solid KF.
Fabrication of photonic quantum ring laser using chemically assisted ion beam etching
Authors: Kim Jun-Youn , Kwak Kyu Sub , Kim Jong Sam , Kang Bongkoo , Kwon O’Dae
Published: July 2002

This article presents an etching process to fabricate a high-quality vertical facet for the photonic quantum ring (PQR) laser. The presented process uses the chemically assisted ion beam etching (CAIBE) method with a gas mixture of Ar:Cl2:BCl3=5:2:3 sccm, and uses a single-layer photoresist etch mask to reduce the process complexity of etching GaAs/AlGaAs structures for the PQR laser. The angle θ between the incident beam and the normal direction of the substrate has been adjusted to achieve a high-quality vertical facet. Distortions on the mask pattern are not transferred to the etched side wall for θ⩾25°, and a vertical facet is obtained at θ∼25°. The fabricated PQR lasers with the CAIBE process in this article show a sharp linewidth of ∼0.06 nm.
Plasma immersion ion cleaning of oxidized steel surfaces using hexafluoroethane and argon plasmas
Authors: Peters A. M. , Nastasi M.
Published: July 2002

For many years it has been known that cleaning of substrates using plasma techniques prior to physical vapor deposition processes can significantly improve coating adhesion. This article investigates the use of hexafluoroethane and argon plasmas in a pulsed glow discharge cleaning process. Applied voltages varied from −2 to −8 kV with a constant chamber pressure of 10 mTorr and etching times ranged from 15 to 120 min. Results indicate that in most cases, the hexafluoroethane plasmas removed 25% more oxygen atoms than the argon plasmas at similar applied voltages. Most of the oxygen removal was observed within the first 15 min with diminishing removal with increased cleaning time beyond 30 min. Plasma analysis revealed that the principal plasma specie was CF3 and reaction products for oxygen removal were carbon dioxide and carbon monoxide. The hexafluoroethane plasmas were determined to clean through a chemically enhanced sputtering while argon plasmas cleaned by physical sputtering only.
New photon detector for device analysis: Superconducting single-photon detector based on a hot electron effect
Authors: Somani Seema , Kasapi Steven , Wilsher Kenneth , Lo William , Sobolewski Roman , Gol’tsman Gregory
Published: July 2002

A novel superconducting single-photon detector (SSPD), intrinsically capable of high quantum efficiency (up to 20%) over a wide spectral range (ultraviolet to infrared), with low dark counts (<1 cps), and fast (<40 ps) timing resolution, is described. This SSPD has been used to perform timing measurements on complementary metal–oxide–semiconductor integrated circuits (ICs) by detecting the infrared light emission from switching transistors. Measurements performed from the backside of a 0.13 μm geometry flip–chip IC are presented. Other potential applications for this detector are in telecommunications, quantum cryptography, biofluorescence, and chemical kinetics.
Characterization of multicusp-plasma ion source brightness using micron-scale apertures
Authors: Scott K. L. , King T.-J. , Leung K.-N. , Pease R. F.
Published: July 2002

The brightness of a multicusp-plasma ion source was characterized to determine its suitability for a proposed maskless ion-beam lithography system. In order to be competitive with similar systems utilizing electron sources, the brightness requirement must be met to satisfy throughput demands. For this requirement, 1 nA into each beam diameter of 50 nm is needed at the target plane; this implies a brightness of about 1000 A/cm2/sr at the entrance to the objective lens. The brightness of the source has been characterized using 5-μm-diam extraction apertures under two different extraction configurations: (1) with the apertures directly illuminated by the source and (2) with the apertures flooded using an extraction system. The maximum brightness achieved for either configuration was 15 A/cm2/sr at 3 keV beam energy, He+ ions, and continuous wave operation. Although this configuration falls short of the requirement for high-throughput exposures, it is also possible to operate the multicusp-plasma ion source in pulsed mode. This would give higher current densities, which may also give adequate brightness as well.
Double-gated Spindt emitters with stacked focusing electrode
Authors: Dvorson Leonard , Akinwande Akintunde I.
Published: July 2002

Arrays of molybdenum field emission cones with integrated focusing electrode (IFE-FEA) were studied as a potential device structure for field emission displays (FEDs) that achieve high brightness, high luminous efficiency, and longer lifetime, without loss of resolution. Device operation and optimization were examined both qualitatively and analytically. Double-gated devices were fabricated using the Spindt cone process. Extensive electrical characterization of IFE-FEAs was conducted. Preliminary optical measurements demonstrated the desired focusing effect.
Effects of temperature on electronic properties of nickel phthalocyanine thin sandwich film structures
Authors: Anthopoulos T. D. , Shafai T. S.
Published: July 2002

The effects of temperature on electronic properties of thin sandwich film structures of Au/NiPc/Au were investigated for both freshly prepared and heat-treated sample devices at a pressure of 10−4 Pa. Current density–voltage characteristics at room temperature for both types of sample indicate ohmic conduction at low voltages, followed by space charge limited conduction in the higher voltage range. The latter has been found to be controlled by an exponential trap distribution above the valence band edge. Experimental results indicate that conductivity is critically dependent upon the film annealing history. Hole and trapping parameters for both the fresh and heat-treated sample were also evaluated yielding the following values: Trap concentration per unit energy range P0=1.03×1044 J−1 m−3, total concentration of traps Nt(e)=1.70×1024 m−3, concentration of thermally generated holes p0=1.30×1014 m−3, for the freshly prepared sample, and P0=2.50×1044 J−1 m−3, Nt(e)=4.10×1024 m−3, p0=5.60×1012 m−3, for the heat-treated sample. Measurements of current density over a temperature range of 250–430 K were also performed yielding a hole mobility value of μ=7×10−5 m2 V−1 s−1.
Effect of annealing on structural and electrical properties of laser ablated Sr0.8Ba0.2Bi2Ta2O9 thin films
Authors: Das Rasmi R. , Bhattacharya P. , Pérez W. , Katiyar Ram S.
Published: July 2002

Ferroelectric thin films of Sr0.8Ba0.2Bi2Ta2O9 were grown on Pt/TiO2/SiO2/Si substrates by using the pulsed laser deposition technique and the effect of annealing on structural and electrical properties of the films has been investigated. The films deposited at 500 °C substrate temperature and 200 mTorr oxygen pressure showed amorphous nature. Perfect crystalline films were obtained after annealing at 750 °C. Increase in grain size with increasing annealing temperature was observed by atomic force microscopy. Good hysteretic behavior with remanent polarization (2Pr) of 11 and 25 μC/cm2 and coercive field (Ec) of 32 and 34 kV/cm with fatigue endurance of up to 1010 switching cycles were obtained with the films annealed at 750 and 800 °C. Moreover, the films annealed at 800 °C had a maximum dielectric constant of ∼375. Increase in dielectric constant with increasing annealing temperature is attributed to the increased grain size, whereas the lower dielectric constant and higher dissipation factor of the 850 °C annealed film is attributed to the presence of the secondary phase, which resulted from the loss of Bi due to evaporation and/or interdiffusion of metallic Bi into the platinum substrate at higher annealing temperature.
Effect of the interface on the local structure of Ge–Si nanostructures
Authors: Kolobov A. V. , Oyanagi H. , Brunner K. , Abstreiter G. , Maeda Y. , Shklyaev A. A. , Yamasaki S. , Ichikawa M. , Tanaka K.
Published: July 2002

We first discuss the limitations of Raman scattering as applied to Ge/Si nanostructures. We further summarize our recent efforts to investigate the local structure of various Ge nanostructures, namely, Ge quantum dots grown by molecular beam epitaxy (MBE) on bare Si(100), on Si(111) with a 0.3 nm SiO2 coverage, and nanocrystals embedded in SiO2, by x-ray absorption fine structure spectroscopy. In particular, the MBE growth of Ge dots on bare Si(100) has been studied as a function of the growth conditions: in most cases strong alloying with Si takes place. Ge nanoislands on Si(111) with SiO2 coverage, on the other hand, may retain the local structure of bulk Ge and be very stable against oxidation. The Ge nanocrystals embedded in SiO2 possess the structure of relaxed bulk Ge without any Ge–Si bonding. The latter two kinds of Ge nanostructures possess visible photoluminescence.
Growth and characterization of ultrahigh vacuum/chemical vapor deposition SiGe epitaxial layers on bulk single-crystal SiGe and Si substrates
Authors: Sheng S. R. , Dion M. , McAlister S. P. , Rowell N. L.
Published: July 2002

High-quality SiGe epitaxial layers have been grown on low-defect-density bulk single-crystal SiGe substrates using low-temperature ultrahigh vacuum chemical vapor deposition (UHV/CVD). The layers were simultaneously grown on Si substrates for comparison. Various techniques, including high-resolution x-ray diffraction (HRXRD), photoluminescence (PL), Auger electron spectroscopy, atomic force microscopy (AFM), and cross-sectional transmission electron microscopy (XTEM) were used to characterize the structural quality of the materials. There is good agreement between different techniques for the determination of the composition and thickness of the layers. HRXRD, PL, and XTEM results confirm that the materials deposited are high-quality single-crystal epilayers. The surface root-mean-square roughness measured by AFM is less than 0.4 nm, indicating very smooth surfaces. A thin undoped Si buffer layer was found to improve the structural quality of the layers. The bulk crystal SiGe substrates are useful for the growth of thick lattice-matched and strained SiGe epilayers.
Development of a microwave microelectromechanical systems switch
Authors: Qiu S. N. , Qiu C. X. , Shih I. , Yu M. , Brassard G. , Séguin G.
Published: July 2002

A novel microwave microelectromechanical systems switch with a coplanar waveguide structure has been developed. The switch consists of a freestanding metallic cantilever and an electromagnet. A permanent magnetic film was deposited on top of the cantilever. By supplying a dc current to the electromagnet, the magnetic field generated would attract or repel the permanent magnetic film on top of the cantilever, causing it to make or break contact with a bottom electrode. An all-electrodeposition method has been used to improve the mechanical properties of the cantilever. The deposition process of the cantilevers has been optimized to improve the adhesion of the cantilever to the substrate and to minimize the switching dc power. Using commercially available electromagnet, a voltage of 2 V (dc power of about 15 mW), is sufficient to actuate the switches. Similar switching power was observed using an improved hand wound electromagnet. The on-state dc resistance of the switches is generally less than 2 Ω. At 10 GHz, the on state insertion loss due purely to the switches is about 0.1 dB and off state isolation is greater than 20 dB. Repeated operations of the switches showed no sign of performance degradation in a conventional room environment.
Photoelectron spectroscopy by time−of−flight technique using synchrotron radiation
Authors: Bachrach R. Z. , Brown F. C. , Hagström S. B. M.
Published: July 2002

A time−of−flight spectrometer for photoelectron spectroscopy is described. It is based on the pulsed structure of the synchrotron radiation emitted from the storage ring (SPEAR) at SLAC with a pulse width of 1.5 nsec and a repetition period of 780 nsec. The sample is irradiated with monochromatic light from a soft x−ray grazing incidence monochromator which works in the photon energy range of 25−1500 eV. The time−of−flight spectrometer consists of a 6 in. mu−metal drift tube which can be pivoted around the sample making angularly resolved photoelectron spectroscopy feasible in both the horizontal and vertical direction. On the sample side of the drift tube a retardation sector is attached and on the other side, a fast channelplate detector. The design parameters are 100 MeV energy resolution at 5 eV at 1° angular resolution. Some preliminary results on single crystals are described.
Interactions in adsorbed layers
Authors: Ertl G.
Published: July 2002

This paper is concerned with various factors which may influence the chemisorption bond on metal surfaces. Its localized character is demonstrated by a comparison of the cluster compound Rh6(CO)16 with CO adsorbed on an extended Pd(111) surface. The influence of the position of the adsorbed particle within the unit cell of the substrate lattice is discussed with the system CO/Pt(111). Distortions of the perfect periodicity of low-index single-crystal planes may act ’’active sites’’ whose atomistic properties are illustrated by the interaction of hydrogen with ’’flat’’ and stepped Pt(111) surfaces. Direct or indirect interactions between neighboring adsorbed particles responsible for their geometric configuration on the surface and may cause variations of the bond energies and of the electonic properties as outlined by several examples.
Recent progress on the electron image projector
Authors: Scott J. P.
Published: July 2002

Three main aspects of the 1:1 electron image projector are considered; the economics, the ultimate resolution, and an electrostatic chuck. It is shown that the image projector is economic if more than four exposures per mask can be made; the resolution limitation due to the system is shown to be 200–300 Å, but is in practive limited by electron scattering. The effect of electron scattering can be overcome by altering dimensions in patterns down to 1 μm, but isolated windows of 0.5 μm require ’two-mode’ masks. The electrostatic chuck is shown to provide an adequate pressure to hold slices flat, and adequate heat sinking.
Modeling ion milling
Authors: Neureuther A. R. , Liu C. Y. , Ting C. H.
Published: July 2002

A string segment motion algorithm is presented and used in conjunction with SEM observation of line edge profiles to study phenomena in ion milling which result from the angular dependence of etch rates. The algorithm allows samples to be rotated and includes shadowing, automatic faceting,and special boundary conditions at interior and exterior corners. The accuracy of the algorithm is demonstrated by comparison with known mathematical results. Simulation is used to study how the shape of the angular etch rate curve and the modification of the local etch rate at corners affect the line edge profiles. Comparisons with experimental results are made to check the algorithm assumptions and applicability. The comparisons include preferentially etched Si, a soft Au mask on a hard NiFe substrate and a hard Ti mask on a soft Au substrate.
Simulation of dry etched line edge profiles
Authors: Reynolds John L. , Neureuther Andrew R. , Oldham William G.
Published: July 2002

Computer simulation of dry etching is used to explore line edge profiles obtained in IC processing. The model divides the process into isotropic or chemically reactive etching and directional or ion illuminated etching. The algorithm simulates the time evolution of the two dimensional profile by advancing nodes on a string according to the local anisotropic and isotropic rates. The accuracy of the model and its applicability to IC processing are illustrated through comparison with known mathematical cases and experimental results. Experiment and simulation are used to explore the residue left at a step with anisotropic etching and the amount of under cut necessary in producing stepped arsenic implanted polysilicon layers.
Data compaction and vector scan e-beam system performance improvement using a novel algorithm for recognition of pattern step and repeats
Authors: Grobman W.D. , Studwell T.W.
Published: July 2002

Many classes of circuit pattern designs contain regular repeats of individual shapes. However, design manipulations (such as personalization), or electron-beam postprocessor functions (such as partitioning and dose assignment for proximity effect correction, overlap elimination, etc.) often destroy some of the pattern regularity, leaving smaller repetitive subpatterns. We describe a novel heuristic for efficiently ’’recognizing’’ these pattern repetitions at the end of design and postprocessing. Consequently, one can achieve pattern data compaction by large factors, using a hardware step-and-repeat function of the vector scan pattern generator, which is discussed in detail. In order for the step-and-repeat recognition and compaction to be useful, this pattern recognition problem must be solved by a very efficient algorithm, due to the large number of shapes involved. We have developed an algorithm which requires an amount of CPU time which is only linear in the number of shapes in the design, requiring less than one ms/shape on an IBM model 168 computer. We will describe the algorithm in detail and demonstrate its ability to economically compact data sets for LSI by up to an order of magnitude or more.
PMMA copolymers as high sensitivity electron resists
Authors: Hatzakis M.
Published: July 2002

Copolymers of methyl methacrylate and methacrylic acid have been shown to have higher sensitivity and thermal stability than PMMA as electron resists. A new method is presented which allows further sensitivity improvement through the use of multiple resist layers consisting of PMMA and copolymers of PMMA or entirely copolymers with different methacrylic acid content. Such combinations allow electron resist sensitivity as high as 2×10−6C/cm2 with temperature stability of over 160°C.
Simple ways to improve ’’flash desorption’’ measurements from single crystal surfaces
Authors: Feulner P. , Menzel D.
Published: July 2002

Flash desorption measurements from single crystal surfaces may be improved by following work function changes rather than parameters such as pressure.(AIP)
Anodic oxide composition and Hg depletion at the oxide–semiconductor interface of Hg1−xCdxTe
Authors: Davis G. D. , Sun T. S. , Buchner S. P. , Byer N. E.
Published: July 2002

The composition and chemical states of the oxide, interface, and bulk semiconductor regions of Hg0.8Cd0.2Te with anodic oxide films of 360, 1200, 1600, and 1600 Å chemically etched to 1200 Å were analyzed with x-ray photoelectron spectroscopy combined with ion sputterng. The near interface semiconductor exhibits 30%–40% less Hg than the bulk semiconductor. Detailed depth profiles were measured for this Hg depletion region. The maximum depletion is independent of the oxide thickness, but its spatial extent is a function of oxide thickness for thin films. For thick oxide films (≳1000 Å) the depletion width is constant at 150–200 Å. No significant change in the Cd concentration is seen. Line shape analysis of the Cd M45N45N45 Auger transition in the anodic oxide, CdO, Cd(OH)2, and CdTeO3 suggests that CdTeO3 rather than TeO2, CdO, or Cd(OH)2, is the major constituent of the anodic oxide. The oxide composition is interpreted to be 44% CdTeO3, 29% CdTe2O5, 17% HgTeO3, and 10% HgTe2O5.
Novel oxygen source for ultrahigh vacuum studies
Authors: Yang C. Y. , O’Grady W. E.
Published: July 2002

High-temperature solid oxide electrolyte (e.g., yttria-stabilized zirconia) cells are compatible with ultrahigh vacuum systems. Since the oxygen activity at the electrode/electrolyte interface is controlled precisely by the applied potential, the cells are ideal as oxygen sources for UHV studies. A three-electrode oxide electrolyte cell has been constructed and incorporated into a UHV surface analysis chamber. The control of the cell is extremely sensitive, and it can be used either to maintain a constant oxygen pressure or to pulse oxygen similar to a molecular beam source in the UHV chamber.
Composition and electron stress effects in silicon nitride thin films made by thermal growth and chemical etching of LPCVD MNOS structures as studied by x-ray photoelectron spectroscopy (XPS)
Authors: Wurzbach J. A. , Grunthaner F. J. , Maserjian J.
Published: July 2002

XPS has been used in conjunction with stopped-flow chemical etching and angular resolution to obtain depth profies and interface structures of native oxide LPCVD MNOS structures and thermally-grown silicon nitride films. Depth profiling of LPCVD samples required stopped-flow etching with HF/H3PO4/ethanol (15:10:60). A uniform composition of nearly stoichiometric Si3N4 was found throughout the bulk; SiO2 was found intact at the interface along with a sharp Si3N4/SiO2 interface width of 8–10 Å. Another LPCVD sample was etched to ∠30 Å and subjected to a low-energy electron flux in an XPS investigation of degradation mechanisms of MNOS devices; cleavage of Si–H bonds was observed. Angle-resolved XPS on thin, thermally grown films showed a compositional gradient ranging from a high concentration of oxide at the surface to nearly pure Si3N4 at the interface. The results are related to interface state formation and mechanisms of MNOS memory degradation and film growth.
Schottky barrier modulation at metal contacts to CdS and CdSe
Authors: Brucker C. F. , Brillson L. J. , Katnani A. D. , Stoffel N. G. , Margaritondo G.
Published: July 2002

Soft x-ray photoemission spectroscopy measurements have been used to study the pinning position of the surface Fermi level as well as the nature of the electrostatic band bending for single and interlayer metal contacts to ultrahigh-vacuum-cleaved CdSe and CdS (101̄0) surfaces. Single metal (Al,Au) contacts are found to exhibit a one-to-one correspondence between the pinning position and the effective Schottky barrier height as measured by in situ C–V and I-V analyses. However, a fundamentally different mechanism of barrier modulation is indicated for interlayer contacts, i.e., contacts formed by interspersing an ultrathin reactive metal interlayer (Al) between the semiconductor and a noble metal contact (Au). Core level broadenings as a function of photon energy are interpreted in terms of sharp band bending at the surface, leading to the possibility of quantum mechanical tunneling through the barrier. This barrier narrowing effect is attributed to an indirect doping effect as a consequence of metal–semiconductor interfacial reaction.
Microanalysis needs for device and package fabrication
Authors: Ramsey J. N.
Published: July 2002

The semiconductor industry, or more generally microelectronics, has made enormous strides in performance, largely by miniaturizing all dimensions to decrease delays and increase function per area. This has been the result of advances not only in device physics/design, material/process, but increased process analysis and control based on increased analytical capability. This paper will show the need for improved analytical capability to continue this accelerating trend of ever-increasing performance. I will review several examples of ‘‘real world’’ problems in semiconductor and packaging development and manufacturing, with solutions made possible with state-of-the-art (and beyond) instruments and people, and show where new advances are required. The examples are roughly in the sequence of device fabrication and joining into packages with brief descriptions of the analytical techniques used. The many very important aspects of transmission electron microscopy of defects in silicon are omitted because they are covered in companion papers in this symposium (Petroff and Krivanek).
MO/Ti bilayer metallization for a self-aligned TiSi2 process
Authors: Park H. K. , Sachitano J. , Eiden G. , Lane E. , Yamaguchi T.
Published: July 2002

During the TiSi2 formation from Ti/Si couples, Ti is often found to oxidize appreciably by reacting with residual oxygen in annealing ambients. A bilayer of Mo/Ti replacing a single layer of Ti has been evaluated for application to a self-aligned process. Due to the presence of the thin overlayer Mo, a reduced internal oxidation of Ti increased the overall oxidation resistance during the silicide-formation cycle. We also found that the Mo/Ti bilayer was incorporating an appreciable amount of nitrogen along with the formation of TiSi2 layer in a flowing nitrogen forming-gas (N2+8–10% H2) ambient when the structure was subjected to heat treatment at 590 °C±10 °C. The thin-film rections of Mo/Ti/Si structures will be discussed and compared with that of Ti/Si couples. Due to the uniform TiSi2 formation with minimized oxidation, a very homogeneous etching across a wafer resulted during an excess-metal etch step. This bilayer was applied to fabricate MOSFET’s giving 3–4 Ω/⧠ of sheet resistance with good reproducibility.
Reactively sputtered ZrN used as an Al/Si diffusion barrier in a Zr contact to silicon
Authors: Östling M. , Nygren S. , Petersson C. S. , Norström H. , Wiklund P. , Buchta R. , Blom H-O. , Berg S.
Published: July 2002

An evaluation of the processing of zirconium nitride and the usefulness of this nitride as a diffusion barrier between aluminum and silicon has been carried out. Reactive sputtering from an elemental zirconium target in a mixture of Ar/N2 makes it possible to change the nitrogen content in the deposited film. The composition variation with N2 concentration will be presented. Films have been prepared using rf-diode reactive sputtering. The as-deposited film resistivity dependence on bias voltage has also been studied. Zirconium deposited on silicon forms a silicide at 550–600 °C. We have found by Rutherford backscattering spectroscopy analysis that during this silicide formation on arsenic implanted silicon substrates, the arsenic is piled up at the silicon/silicide interface. This effect favors the formation of a low resistance Ohmic contact. Since the barrier height between the silicide and silicon is expected to be 0.55 eV we want to point out that this contact may be useful for both n- and p-type regions. It is confirmed by the RBS analysis that the zirconium nitride prevents Al/Si interreactions up to 550–600 °C. Evaluation of the following process that needs only one single pump down to form a complete contact metallization system will be presented: zirconium is sputtered on top of the silicon. Nitrogen is then mixed to the argon and zirconium nitride is formed by reactive sputtering on top of the zirconium layer. Finally, aluminum is deposited on top of the zirconium nitride. This multilayer structure is then annealed to form the silicide and simultaneously cure induced radiation damages from previous processing steps. The RBS analysis shows no interaction between the aluminum and the silicon after a heat treatment in 600 °C for 30 min.
Comparison of microwave and lower frequency plasmas for thin film deposition and etching
Authors: Wertheimer M. R. , Moisan M.
Published: July 2002

We review the literature on cold plasma chemistry, dealing with the plasma deposition of organic (plasma polymers) and inorganic thin films, and with plasma etching, in which the plasma excitation frequency is the principal variable. Based on recent theoretical results by Ferreira and Loureiro, we propose that some observed frequency effects should be interpreted as resulting from different electron energy distribution functions (EEDF), as the shapes of these EEDF depend upon the ratio ν/ω (ν being the electron-neutral collision frequency for momentum transfer and ω the angular frequency of the applied electromagnetic field) of the plasma under consideration. For gas pressures in the range 50–500 mTorr, this leads one to distinguish between low frequency (LF, ≤13.56 MHz, where ν/ω≥1) and microwave plasmas (>300 MHz, the microwave frequency range, for which ν/ω ≪ 1); the microwave plasmas have a comparatively higher population of very energetic electrons. We then present a selection of our own experimental data comparing LF and microwave (2.45 GHz) plasma deposition of organosilicon plasma polymers, and of plasma deposited silicon nitride. Deposition rates in microwave plasmas are found to be about ten times higher than in LF plasmas, and films tend to differ in their structures and physical properties. These results are tentatively attributed to differences in the EEDF, pending confirmation by selected plasma diagnostic experiments.
Characterization of electron-beam deposited tungsten films on sapphire and silicon
Authors: Souk J. H. , O’Hanlon J. F. , Angillelo J.
Published: July 2002

In this work, the electrical and structural properties of e-beam deposited tungsten films on sapphire are described. Tungsten thin films (200–400 nm) were evaporated on sapphire substrates at different substrate temperature Ts. Film resistivity varied from 95 μΩ cm deposited at room temperature to 5.5 μΩ cm deposited at Ts between 440 and 500 °C. The resistivity value of 5.5 μΩ cm is comparable to the bulk resistivity value of 5.50–5.65 μΩ cm. The crystalline structure of these films was characterized by x-ray diffraction and scanning transmission electron microscopy (STEM) (Kikuchi lines). The films show a distinct increase in the degree of crystal orientation as Ts approaches 400 °C. The films deposited at 400 °C and above shows (100) epitaxial growth on the (11̄02) plane or r plane of sapphire, which has a distorted fourfold symmetry. Film stresses which vary from tensile (7.3×109 dyn/cm2) to compressive (−4.4×109 dyn/cm2) between 100 and 500 °C were measured by the interference fringe technique. The intrinsic stress was determined to vary from 8.3×109 dyn/cm2 at Ts=100 °C to 2.4×109 dyn/cm2 at Ts=500 °C. The observed intrinsic stresses (tensile) in epitaxial films are regarded as produced by the lattice misfit at the film–substrate interface. The minimum total film stress was obtained between Ts=350 and 400 °C, where tensile intrinsic stress was compensated by the compressive thermal stress. The properties of tungsten films on silicon, silicon oxide, and polysilicon substrates are also discussed.
Aluminum/aluminum-nitride sputter deposition on the inertial fusion target using the pulsed-gas process
Authors: Noyes S. G. , Kim H.
Published: July 2002

Typical inertial confinement fusion targets consist of glass microballoons containing pressurized DT gas. They are often coated with organic and/or metal layers which should have variations of thickness and density of a few percent. Root mean square surface roughness should be less than 500 Å. We have utilized the pulsed nitrogen process during sputter coatings of aluminum onto the glass microballoons. Improvement of surface finish and density is substantial when compared with pure aluminum deposits. X-ray diffraction studies and energy dispersive analysis imply that a small amount of ionized nitrogen atoms are incorporated into growing crystallographic planes of the layer and effectively poison the surface to prevent further growth. Under such conditions, crystallization is limited to small crystallites or amorphous structure forms. The improved surface finish observed is due to the amorphous structure of the film.
Pressure controlled VPE growth of quaternary Hg1−x−yCdxMnyTe epitaxial layers
Authors: Becla P. , Wolff P. A. , Aggarwal R. L. , Yuen S. Y. , Galazka R. R.
Published: July 2002

Quaternary Hg1−x−yCdxMnyTe epitaxial layers were grown on Cd1−xMnxTe substrates by pressure controlled isothermal vapor phase epitaxy employing a two-zone configuration system. The interdiffusion of Cd and Mn from the solid was investigated. The optimum growth conditions (i.e., the highest growth rate and the best electronic properties) were determined. Desired values of x and y were obtained by varying the growth temperature T0, mercury pressure pHg, and substrate composition.