bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of the sputtering ambient contamination on the microstructure of Al–Si films
Authors: Queirolo G. , Dellagiovanna M. , De Santi G.
Published: July 2002

In this work we report the results of a study on the effects of the deposition parameters on the microstructure of sputtered Al–1% Si thin films, performed using x-ray diffraction techniques. In particular, preferred growth and texture were evaluated for films deposited with controlled amounts of contaminating gases in the sputtering ambient. Films deposited without any addition of contaminants show both a preferred growth along {111} planes and a strong texture, which appears to be a function of the deposition temperature. On the contrary, films deposited in an atmosphere containing contaminants like N2, CO2, O2 and H2O, appear to be more ‘‘powderlike,’’ with less—if any—preferred growth and texture. Electromigration tests show a better electromigration resistance for films grown in cleaner ambient. An interpretation of the results is given, which involves the different nucleation and growth processes for clean and contaminated films.
Structure of submonolayers of tin on Si(111) studied by scanning tunneling microscopy
Authors: Nogami J. , Park Sang-il , Quate C. F.
Published: July 2002

The structure of different reconstructions of Sn on Si(111) has been studied by scanning tunneling microscopy. For less than a monolayer (ML) of Sn, three reconstructions are seen with 7×7, 7/8 × 7/8 , and 2 7/8 ×2 7/8 periodicities. The 7×7 structure is similar to that of the clean surface. The 7/8 × 7/8 phase is a (1)/(3) ML array of adatoms similar to that of Al, Ga, or In on Si(111). The 2 7/8 ×2 7/8 structure is twofold symmetric with three possible orientations on the surface giving the threefold symmetry apparent in the low-energy electron diffraction pattern. All three surface phases coexist above 0.3 ML.
Ion beam milling effect on electrical properties of Hg1−xCdxTe
Authors: Bahir G. , Finkman E.
Published: July 2002

Changes induced near the surface of Hg1−xCdxTe crystals due to irradiation caused by low-energy ion beam milling have been investigated. The milling induces a thick n-type layer near the surface, more than 10 μm thick, within 2–3 min. Most of this layer is well-behaved n type with carrier concentration on the order of 1016 cm−3, electron mobility higher than 105 cm2/V s at 77 K, and relatively large lifetime. The temperature dependence is characteristic of uncompensated material, and compensation in highly compensated materials is reduced considerably. The sidewall effect is small; the direction of propagation obeys probably a cosine law. A three-step mechanism is proposed to account for these phenomena, which consists of creation of extended defects, fast propagation of metal ions along them, accompanied by annihilation of metal vacancies, and recombination of defects.
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u laser diagnostic studies of plasma-generated particulate contamination
Authors: Selwyn G. S. , Singh J. , Bennett R. S.
Published: July 2002

Laser light scattering measurements show that certain silicon etching plasmas produce a significant amount of in situ, particulate contamination. The particles are suspended at the sheath boundaries. Simultaneous measurement of plasma negative ions by the use of two-photon laser-induced fluorescence technique suggests that the particles are negatively charged and so are electrostatically trapped at the sheath boundaries. The parametric conditions for particle formation and growth in the plasma are identified. A mechanism for nucleation and growth is suggested involving formation of plasma negative ions from etch products, ion clustering with plasma species, and cluster growth into particles with electrostatic suspension and trapping. The particles drop onto the wafer when the rf is turned off. Implications for dry process technology are discussed.
Beta heating driven deuterium–tritium ice redistribution, modeling studies
Authors: Martin Alfred J. , Simms Richard J. , Wineberg Steve B.
Published: July 2002

We have previously demonstrated, based upon a one-dimensional analysis, that beta heating could cause a redistribution of nonuniform deuterium–tritium (DT) ice within a cryogenic target at an ideal rate that would decrease nonuniformity by a factor of 10 every hour. Our analysis was extended to address two pertinent questions: for a spherical target, where will the DT ice finally go and how quickly will it get there? This analysis is a two-dimensional heat and mass transfer problem. We have used PLTMG, a state-of-the-art multigrid computer code for the analysis. For the ‘‘tent’’ mount method of positioning a target in a cryogenic enclosure, an ice layer nonuniformity of <1% can be achieved. We have evaluated the rate of ice redistribution and report its variation as a function of 3He content within the target, the target temperature, target geometry, and thermal conductivity of the shell wall.
Aluminum deposition on polyimides: The effect of i
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u ion bombardment
Authors: Vasile M. J. , Bachman B. J.
Published: July 2002

The chemistry of the Al polyimide interface is examined by x-ray photoelectron spectroscopy sputter profiling. Al deposited on polyimide films without an in situ Ar backsputter shows a clearly defined 50-Å Al2O3 layer just prior to the polyimide. This layer is identified by the O/Al atom ratio at 1.5, and the binding energy of the Al 2p transition. There is a clear separation of the Al/Al2O3/polyimide layers in the sputter profiles. Deposition of Al on polyimide surfaces after Argon backsputtering produces a diffuse Al/polyimide interface with no Al2O3 present. There is evidence in the Al 2p spectra for Al–C or Al–O–C type bonds, while the C 1s spectrum clearly has a metal carbide component. Increased adhesion of Al to polyimide surfaces with Ar backsputtering may be due to the differences in chemistry observed in these two instances.
Morphology and charge capacity of sputtered iridium oxide films
Authors: Klein J. D. , Clauson S. L. , Cogan S. F.
Published: July 2002

Iridium oxide films deposited on stimulation electrode wires by rf sputtering exhibit markedly different surface morphologies and charge capacities in response to variations in deposition conditions. The films sputtered on the composite wire specimens are comprised of closely packed ellipsoidal platelets in varying degrees of alignment. The film appearance and electrochemical properties are strongly dependent on the water-to-oxygen ratio in the sputter gas. Increasing this ratio from 0 to 0.22 results in a marked rotation of the direction of net alignment of the sputtered iridium oxide film (SIROF) platelets and reduced anodic and cathodic charge capacities. The anodic charge capacities of the SIROF films were remarkably linear with respect to the logarithm of the cyclic voltammetry sweep rate.
Electronic states of an amorphous semiconductor cluster system: Ge on C
Authors: Yu R. Q. , Fortner J. , Lannin J. S.
Published: July 2002

Ultraviolet photoelectron (UPS) and Auger electron (AES) spectroscopies have been applied to study the semiconductor cluster system of Ge on disordered C films. Both UPS and AES reveal that sputtered Ge deposited at 300 K has island growth character. Substantial changes were observed in the valence p states of Ge clusters as the cluster size decreases: the leading edge p-band slope is reduced, the centroid shifts to higher binding energy, and the half-width narrows. These changes are attributed to size effects and an increasing fraction of dangling bonds in the Ge clusters. The form of the UPS spectra suggest amorphous-like order in clusters.
Surface characterization of a poly(styrene/p-hydroxystyrene) copolymer series using x-ray photoelectron spectroscopy, static secondary ion mass spectrometry, and chemical derivatization techniques
Authors: Chilkoti Ashutosh , Castner David G. , Ratner Buddy D. , Briggs David
Published: July 2002

A series of poly(styrene/p-hydroxystyrene) copolymers was examined by x-ray photoelectron spectroscopy (XPS), static secondary ion mass spectrometry (SIMS), and chemical derivatization. Static SIMS distinguished polystyrene (PS) and poly(p-hydroxystyrene) (PHS) on the basis of fragments, 107 D (C7H7O+) and 119–121 D {[M–H]+,, [M]+, and [M+H]+, where M is the hydroxystyrene (HS) monomer}, that were present in the positive ion spectrum of PHS. The negative ion spectrum of PHS was structurally less informative (C− –C−4, CH−–C4H−, O−, OH−), with the exception of a peak at 119 D [M–H]−. While fluorinated fragments characteristic of trifluoroacetic anhydride (TFAA) (CF+3, CF−3, CF3 CO−2 ) were observed in both the positive and negative ion spectra of TFAA-derivatized PHS, fragments characteristic of the derivatized polymer (C7H6F+ , C7H6CO2CF+3 ) were observed only in the positive ion spectrum of TFAA-derivatized PHS. The quantitative relationship of positive ion intensities to XPS oxygen concentration for these copolymers was complicated by the absence of peaks unique to the styrene component. Quantitation based on normalization of unique hydroxystyrene peaks to total ion yield and peak ratio normalization of selected peaks was successful. Similarly, quantitative trends were observed for the TFAA-derivatized copolymer series when the peak intensity of the C7H6CO2CF+3 ion was normalized to the total ion yield.
Area selective metalorganic chemical vapor deposition of gold on tungsten patterned on silicon
Authors: Colgate Samuel O. , Palenik Gus J. , House V. Evan , Schoenfeld Dean W.
Published: July 2002

Metalorganic chemical vapor deposition was used to deposit gold thin films selectively on tungsten patterned on n-doped silicon wafers. Gold on tungsten is one possible replacement metallization for aluminum in future high speed high density integrated circuits. The gold thin films from the decomposition of (C2 H5 )3 PAuCl show excellent selectivity and tungsten feature resolution as shown by scanning Auger analysis. Results suggest that decomposition inhibition on silicon is a function of the native oxide structure while deposition on tungsten is autocatalytic.
Model studies of tunneling time
Authors: Huang Z. H. , Cutler P. H. , Feuchtwang T. E. , Kazes E. , Nguyen H. Q. , Sullivan T. E.
Published: July 2002

The precise definition and physical interpretation of a tunneling time is a fundamental problem in quantum mechanics. The lack of a well-defined time operator in quantum theory precludes the calculation of time in terms of an expectation value. Consequently, model calculations and simulation studies have been proposed and used to determine the time for a particle to traverse a quantum-mechanical barrier. The results offer both qualitatively and quantitatively, disparate predictions. One of the more commonly used approaches is the phase method, which we have applied to several one-dimensional model potentials to show that the tunneling time is characterized by the ratio of the typical decay length in the barrier to the incident velocity, τ∼(1/κ)/v0. We also show that the phase and the spin precession methods are equivalent when the magnetic field is applied throughout the space containing the particle wave function and the tunneling barrier. In principle, the spin precession method can be regarded as an operational definition of the tunneling time. It also has been shown that a tunneling time can be defined operationally for a time-dependent barrier, for which the model calculations predict a tunneling time given by the mean barrier width divided by the magnitude of the imaginary velocity of the particle in the barrier, τ∼d/‖v‖. This pseudokinematic result has been inferred by magnetic field dependent tunneling through heterostructures and computer simulation of wave packet tunneling through one-dimensional square barriers. Other tunneling time theories predict one or the other of the above mentioned characteristic times; several theories predict both. We interpret these different results for τ to mean that a tunneling time is not uniquely defined as a function of particle energy and the barrier shape unless the process in which the tunneling is involved is also specified. That is, the tunneling time is a meaningful and unique concept only for particular tunneling processes or definite operational procedures.
Initial stage deposition of Ag on the Si(100)2×1 surface studied by scanning tunneling microscopy
Authors: Hashizume T. , Hamers R. J. , Demuth J. E. , Markert K. , Sakurai T.
Published: July 2002

The initial stage deposition of Ag on the Si(100)2×1 surface at room temperature has been studied by scanning tunneling microscopy/spectroscopy. A thermal evaporation source made of a high-purity Ag coiled around a 10 mil tungsten wire was used. The three types of Ag clusters were observed: (1) Single Ag atom adsorbs on the hollow site between two dimers in the adjacent dimer rows, which is in agreement with the result derived by Hanbucken and Neddermeyer, Surf. Sci. 114, 563 (1982). (2) The Ag atoms form linear chains perpendicular to the dimer rows. (3) Two-dimensional islands of Ag atoms are formed. The absorption site is same as the single Ag adsorption; the local p(2×2) structure was observed for the two-dimensional islands. The STS on one-dimensional and two-dimensional islands showed nonmetallic I-V characteristics, which is consistent with the long distance (7.7 A) between each Ag atom. The stability of two-dimensional islands will be discussed.
Local stress relaxation phenomena in thin aluminum films
Authors: Smith Ulf , Kristensen Nils , Ericson Fredric , Schweitz Jan-Åke
Published: July 2002

This article reports a systematic study of local stress relaxation effects in thin Al films, deposited on silicon substrates by sputtering or electron beam evaporation. The stresses were induced thermally during an annealing cycle, as well as thermomechanically by micromechanical technique. The latter experiments were performed in situ in the vacuum chamber of a scanning electron microscope (SEM), which made it possible to monitor the reconstruction of the film surface as it happened, and simultaneously register applied forces, strains, and temperatures. Three fundamental, local stress relaxation phenomena were observed. Compressive film stresses were, at elevated temperature, relaxed by hillock formation. The in situ experiments in the SEM, combined with cross-sectional transmission electron microscopy of hillock structures, provided important information on the growth mechanism of hillocks. Tensional film stresses at elevated temperature were relaxed by two modes of local stress relief. One mode of tensional stress relief occurred in films of thickness 1 μm or more. Singular Al grains were observed to ‘‘collapse’’ and become wider and thinner than neighboring grains. Such grain collapses are scarcely reported by previous workers, and were in the present investigation seen to occur very suddenly, in a second or less, as the strain and the temperature reached critical levels. A collapse mechanism, based on local plastic yield and interfacial slip, is suggested. Films of submicron thickness relaxed by a second mode: hole formation. Essentially two types of holes were observed: small, circular holes and large branched-out holes. A hole formation mechanism, based on creep cavitation and interfacial slip, is suggested. The observed holes resemble the ‘‘voids’’ many other workers have reported in narrow, passivated Al lines. The present results show that passivation coatings and narrow geometries are not necessary prerequisites for holes in Al films; a high tensional film stress is enough.
Perfluoroalkylether reactions on iron and oxygen covered iron surfaces studied using x-ray photoelectron spectroscopy and secondary ion mass spectrometry
Authors: Napier Mary E. , Stair Peter C.
Published: July 2002

X-ray photoelectron spectroscopy and secondary ion mass spectrometry have been used to investigate the reaction of a model perfluoroalkylether (PFAE), CF3 OCF2 CF2 OCF2 CF3, with clean iron, oxygen modified iron and clean gold surfaces. These studies revealed an unexpected low temperature decomposition reaction on clean iron surfaces. The decomposition appeared to proceed through a defluorination of the carbon backbone, followed by a dissociation of the entire molecule. The clean gold and oxygen covered iron surfaces were essentially unreactive toward the PFAE.
The measurement of cathode evaporation rate by quartz crystal microbalance
Authors: Cheng Zhang-qi , Wu Chong-rou , Ni Ming-sheng
Published: July 2002

The quartz crystal microbalance (QCM) is used to measure the thickness of deposited materials in vacuum. This paper presents a method for measuring cathode evaporation rate by the QCM. The cathode and quartz crystals are mounted in a vacuum tube which is evacuated to 1×10−5 Pa. To overcome thermal frequency shifts, a thermistor is used to control the heater current to maintain a constant temperature. The frequency stability of the QCM is better than 0.3 Hz, so that the detectable mass of the evaporated material is 3.5×10−9 g/cm2, which corresponds to 3×10−2 monolayer of barium. The evaporation rates for (Ba, Sr, Ca) O cathodes and scandate cathodes were measured by this QCM. The measured rates were about 2×10−7 g/cm2 min (at 1210 K) and 1.5×10−8 g/cm2 min (at 1273 K) respectively, which are in agreement with the data by other authors. Calculation of the evaporation rate for small flat cathodes and cylindical cathodes are also given.
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u native oxide clean followed by chemical vapor deposition of tungsten silicide on polysilicon in a cluster tool
Authors: Nowicki Ronald S. , Geraghty Patrice , Harris David , Lux Gayle , Johnson David J.
Published: July 2002

As process complexities increase, the need has also increased for control of the cleanliness of film/film interfaces by the use of cluster processing tools which are capable of in vacuo wafer transport and predeposition removal of the thin (10–30 Å) oxide (‘‘native oxide’’) layer on a silicon surface prior to the deposition of another film. The presence of this oxide layer can adversely affect subsequent device processing steps, e.g., contact metallization and high-temperature annealing or oxidation. Thus, the in vacuo process capability of native oxide removal affords an advantage over the conventional method of aqueous hydrofluoric acid cleaning prior to a film deposition step. This study describes such a predeposition clean, in which reactive ion etching (RIE) with C2F6 prior to tungsten silicide deposition is employed. This technique yields silicide films which can easily withstand post-silicide deposition high-temperature heat treatment and wet oxidation without loss of film adhesion or other obvious degradative effects. Additionally, the extensive use of the secondary ion mass spectrometry (SIMS) analytical technique to show the effectiveness of native oxide removal and provide thorough characterization of the polysilicon/silicide film interface is reported.
Si(111)–(2√3×2√3)Sn reconstruction studied by ion scattering spectrometry and scanning tunneling microscopy
Authors: Worthington M. S. , Stevens J. L. , Chang C. S. , Tsong I. S. T.
Published: July 2002

The techniques of impact collision ion scattering spectrometry (ICISS) and scanning tunneling microscopy (STM) were used to study the (2√3×2√3)R30° reconstruction of Sn on the Si(111) surface. Our STM results show that the 2√3×2√3 structure has three equivalent orientations and that the electronic structure is onefold symmetric. ICISS polar-angle scans, using lithium ions (Li+) backscattered from Sn, establish that Sn atoms are located on top of the Si(111) surface. These scans, which reflect the relative positions of the Sn atoms with respect to each other, are compared with computer simulations of two models of the surface. Reasonable agreement is obtained with a model which contains two layers of Sn atoms.
Inelastic peak shape method applied to quantitative surface analysis of inhomogeneous samples
Authors: Hansen H. S. , Jansson C. , Tougaard S.
Published: July 2002

The validity of the peak shape analysis method for quantitative determination of the surface composition by electron spectroscopy is studied. To this end, inhomogeneous samples were produced by evaporating Ag and Au in varying amounts onto the (111) surface of a Ni single crystal. The amounts of deposits were monitored by a quartz crystal microbalance (QCM). The spectra from major x-ray excited core level peaks from the substrate and adsorbate were analyzed quantitatively using the ‘‘universal’’ inelastic scattering cross section. The data were analyzed by a three parameter model for the in-depth concentration profile corresponding to a layer-by-layer plus island (Stranski–Krastanov) growth model. By adjusting the three structural parameters, the intensity as well as the shape of all background corrected peaks from both substrate and adsorbate were found to fit exceptionally well with those of pure elemental samples. For both the Ag/Ni and the Au/Ni system, the total amount of evaporated material determined by the peak shape analysis method was found to be proportional to the observed QCM frequency shift to within ∼10% and the deviation is slightly larger for the highest amounts of evaporated adsorbate. Possible effects of elastic electron scattering are discussed.
Chemical interaction of thin Cr films with the MoS2(0001) surface studied by x-ray photoelectron spectroscopy and scanning Auger microscopy
Authors: Durbin Thomas D. , Lince Jeffrey R. , Yarmoff Jory A.
Published: July 2002

The growth of chromium films on the MoS2(0001) surface has been studied with core-level x-ray photoelectron spectroscopy and scanning Auger microscopy. The films grown on room temperature surfaces result in a limited chemical reaction to produce metallic Mo and chromium sulfide(s). The surfaces of the films are relatively S-rich, while the bulk of the films contains smaller amounts of S. Mo is found only at the film/MoS2 interface and is not incorporated into the bulk of the overlayer. Annealing the Cr covered sample to 650 °C and higher further drives the reaction between Cr and MoS2, and causes partial coalescence of the film.
Interferometric thermometry measurements of silicon wafer temperatures during plasma processing
Authors: Donnelly V. M. , Ibbotson D. E. , Chang C.-P.
Published: July 2002

This article reports the application of interferometric thermometry to the measurement of silicon wafer temperatures during exposure to low-pressure (1 mTorr), high-density (ne= 1 × 1011 cm3) helical resonator plasmas. This technique measures the temperature-dependent optical pathlength from the front to the back of a wafer polished on both sides. The measurement does not perturb the plasma, nor does it suffer from interference from the plasma, problems which often plague other techniques. Nonetching N2 plasmas heat the wafer to 140 °C in the first 3 min, and 200 °C after 10 min when the wafer is simply placed on the platen with no provisions for heat dissipation. When the wafer is clamped to an o-ring seal on the platen and a small gap between the wafer and platen is pressurized with helium (so-called helium backside cooling), the wafer temperature rise is reduced. With a helium pressure of 10 Torr between the wafer and platen, the temperature was 40 °C after 2 min and 70 °C after 10 min. When silicon wafers are etched in a Cl2 plasma, the interferometric signal contains contributions from both heating and etching, which respectively increase and decrease the optical pathlength within the wafer. A deconvolution of this signal using the known etch rate indicates that plasma-induced heating in a Cl2 plasma is approximately the same as in a N2 plasma of about the same power, indicating that any contributions from heating due to chemical reactions in the etching process are negligible compared to heating from the plasma.
Correlation of x-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy depth profiles on Hg1−xCdxTe native oxides
Authors: Winton G. H. , Faraone L. , Lamb R.
Published: July 2002

The composition of photochemical native oxides grown on Hg1−xCdxTe (x=0.3) has been studied using x-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectroscopy (RBS). By analyzing and comparing the results of the XPS and RBS depth profiles, a simple method of multiplying the XPS raw counts has enabled a realistic XPS depth profile to be obtained without having to directly account for sensitivity factors or preferential sputtering of elements. Photochemical oxides grown in O2 ambients were found to have a Hg rich surface layer in addition to a higher Hg concentration throughout the oxide film when compared to layers grown in an N2O ambient. For both growth processes, the bulk oxide regions had Cd/Te ratios in excess of that for the underlying mercury cadmium telluride (MCT) substrate and concomitantly lower Hg/Te ratios. Comparisons with other work indicate that the photochemically grown oxides are quite similar to anodically grown oxides in terms of oxide /MCT interface widths and oxide compositions.
Effect of surface excitations in determining the inelastic mean free path by elastic peak electron spectroscopy
Authors: Chen Y. F.
Published: July 2002

Elastic peak electron spectroscopy (EPES) has been widely used to determine the electron inelastic mean free paths (IMFPs) in solids. In this work the influence of surface excitations in determining the IMFP by EPES is investigated. An extended Drude dielectric function is employed to estimate the probability of surface excitations for incident and reflected electrons by including the recoil effect without the small scattering-angle approximation. Elastic scattering differential cross sections are calculated using phase-shift analysis and the finite difference method for solid atoms with the Hartree–Fock–Wigner–Seitz potential in the Dirac equation. Results of Monte Carlo simulations on the determination of IMFPs from experimental elastic reflection coefficients are presented for Ag and Cu. Our results show that the relative difference between the IMFPs obtained with and without surface excitation may reach 40% for low-energy electrons (∼250 eV). The experimental results, with corrections for surface excitations, are in better agreement with the theoretical data.
Anionic clusters in dusty hydrocarbon and silane plasmas
Authors: Hollenstein Ch. , Schwarzenbach W. , Howling A. A. , Courteille C. , Dorier J.-L. , Sansonnens L.
Published: July 2002

Measurements of anions and cations are reported for hydrocarbon and silane radio frequency capacitive glow discharges. Series of anions were observed by quadrupole mass spectrometry using power-modulated plasmas, and their structures are interpreted from the form of the mass spectra. Various experiments in silane plasmas show that anion confinement results in particles and conversely, anion detrapping can inhibit particle formation. In contrast, the polymerized neutral flux magnitudes, mass spectra and dynamics are independent of the powder formation. Powder is known to form readily in deposition plasmas containing electronegative free radicals, and the general role of anions in particle formation is discussed in the light of these experiments.
A study of Si compounds by Zr Lα photoelectron spectroscopy
Authors: Chourasia A. R. , Hood S. J. , Chopra D. R.
Published: July 2002

Zirconium Lα radiation has been utilized to investigate the chemical bonding in silicon compounds by x-ray photoelectron spectroscopy. The compounds studied in the present investigation are SiO2, SiO, SiC, Si3N4, and silicon-oxynitrides. The spectra in the Si 1s and KLL Auger regions were recorded for these compounds and compared with the elemental spectra. In order to estimate the change in chemical environment of Si in these compounds, the Auger parameter was determined in each case as the difference between the binding energies for the 1s and the KLL peaks. The trend in the value of the Auger parameter is correlated with the degree of atomic relaxation due to the increasing neutralization of charge around the Si cations in these compounds. A good agreement was found between the change in the Auger parameter and the bond ionicity calculated for the Si cation in these compounds. Using this plot, the bond ionicities were determined for the oxynitrides. A model is also developed to estimate these ionicities from the concentrations of oxygen and nitrogen present in these compounds. The values of the ionicities obtained by these two different methods give a satisfactory agreement. We have shown that the plot between the change in the Auger parameter and the bond ionicity could be used to estimate the bond ionicities.
Film properties of ZnO:Al prepared by cosputtering of ZnO:Al and either Zn or Al targets
Authors: Tominaga Kikuo , Manabe Haruhiko , Umezu Norio , Mori Ichiro , Ushiro Tomoko , Nakabayashi Ichiro
Published: July 2002

ZnO:Al and ZnO with oxygen vacancies (ZnO:OV) films were prepared by co-sputtering Zn and either ZnO:Al (Al2O3 2 wt %) or ZnO. The influence of the additional Zn supply on ZnO:Al film properties was investigated and compared with the data of ZnO:OV films. The additional Zn supply improved the film crystallinity and reduced the film resistivity. This was ascribed to the decrease of defects in ZnO:Al films due to the improvement of crystallinity, because the maximum carrier concentration in a ZnO:OV film was much smaller than that in a ZnO:Al film where the carrier concentration was created by Al donors. ZnO:Al films prepared by co-sputtering of ZnO:Al (2 wt %) and either ZnO:Al (6 wt %) or Al targets were also investigated. The doping of Al donors, in the first case, decreased the carrier mobility and increased the carrier concentration, in the second case, the carrier mobility increased with further doping.
Rectifying behavior of silicon–phthalocyanine junctions investigated with scanning tunneling microscopy/spectroscopy
Authors: Ottaviano L. , Santucci S. , Di Nardo S. , Lozzi L. , Passacantando M. , Picozzi P.
Published: July 2002

We present ultrahigh vacuum (UHV) scanning tunneling microscopy/spectroscopy (STM/STS) and ultraviolet photoemission spectroscopy (UPS) measurements on ultrathin films of nickel–phthalocyanine (Ni–PC) deposited onto clean Si(111)7×7 substrates. STS spectra refer to a sample with 5 Å of Ni–PC nominal thickness. The current-voltage (I-V) measurements were taken at constant tip-sample separation showing high reproducibility at different nanometer size topographical features of the sample. In particular, three typical spectra have been repeatedly observed: (i) I-V curves with a slow increase of the current up to +1.9 eV (I < 5 nA) where the current steeply increases (I>50 nA), (ii) highly noisy I-V curves symmetric with respect to the applied bias and, (iii) curves which show a marked rectifying behavior with negligible current (I<10 pA) at negative (sample to tip) voltages and steeply increasing current by applying a positive bias (I>50 nA for V>0.5 V). We explain the different electronic behaviors in terms of the different morphological features observed by means of simultaneous STM imaging (different Ni–PC crystallites height, and different Ni–PC molecular plane orientation with respect to the substrate) and starting from the density of states below the Fermi energy of the Ni–PC/Si(111)7×7 interface as measured with UPS. The diodelike behavior observed is explained in terms of resonant tunneling of electrons from the tip through the PC layer to the silicon substrate, and also in terms of the intrinsic asymmetry of the tip/vacuum gap/Ni–PC/Si(111)7×7 junction.
Electrostatically actuated micromechanical switches
Authors: Majumder S. , McGruer N. E. , Zavracky P. M.
Published: July 2002

Micromechanical switches and relays realized by a simple surface micromachining process are presented. The devices use a nickel cantilever beam and gold-to-gold electrical contact, and are electrostatically actuated. They have lifetimes exceeding 109 cycles, and a current handling capability of 150 mA.
Interactions between sulfur and platinum in bimetallic surfaces: Reaction of S2 with Pt–Al alloys
Authors: Rodriguez José A. , Kuhn Markus
Published: July 2002

The reaction of S2 with Pt–Al alloys has been investigated using core- and valence-level photoemission. The Pt–Al alloys display a Pt 5d band that appears at much higher binding energy (1.8–2.1 eV) than in metallic Pt. This is accompanied by positive shifts in the Pt 4f (0.3–1.3 eV) and Al 2s (0.1–0.3 eV) core levels. The electronic perturbations in Pt do not increase the reactivity of this metal toward sulfur. After exposing Pt–Al alloys to S2 gas, aluminum is extensively sulfided, while platinum remains in a metallic state. The Pt↔AlSx interactions are much weaker than Pt↔Al interactions. The chemisorption of S2 induces the segregation of aluminum toward the surface of the alloys. The behavior observed for the PtAlx surfaces in the presence of sulfur is different from that seen for Cu/Pt (111) and Ag/Pt (111) surfaces, where the admetals promote Pt↔S interactions and the formation of several layers of platinum sulfide. Changes in the nature of the bimetallic bond and in the relative stability of the metal sulfides are responsible for this difference in behavior.
Patterning of Cu, Co, Fe, and Ag for magnetic nanostructures
Authors: Jung K. B. , Lee J. W. , Park Y. D. , Caballero J. A. , Childress J. R. , Pearton S. J. , Ren F.
Published: July 2002

Wet and dry etching of thin metallic multilayer structures is necessary for the development of sensitive magnetic field sensors and memory devices based on spin–valve giant magnetoresistance elements. While it is well established that Cu, Co, and Fe are soluble in HNO3 and H3PO4 at room temperature, little effort has been made to investigate selective wet and dry etch chemistries. For example, we find Ag is not etched in H2SO4, HCl, or H3PO4 under conditions where etch rates for the other metals are in the range of 2000–60 000 Å/min. Electron cyclotron resonance (ECR) SF6/Ar plasmas provide etch selectivities of ⩾5:1 for Ag over Cu, Co, and Fe, while lower selectivities are obtained with CH4/H2/Ar. Cl2-based plasma chemistries leave significant metal–chlorine surface residues, which can be removed in situ by low ion energy H2 or Ar plasma treatments that eliminate corrosion problems. Cu etch rates in excess of 3000 Å/min at 25 °C can be obtained in ECR Cl2/Ar discharges because the high ion flux prevents formation of a CuClX-rich selvedge layer, which normally only is volatile for etch temperatures ⩾220 °C in conventional reactive ion etch systems. Photoresist masks suffer severe reticulation under ECR conditions, at least for microwave powers >400 W, and SiO2 or SiNX thin films offer much better etch resistance.
Pseudo spin valve magnetoresistive random access memory
Authors: Everitt B. A. , Pohm A. V.
Published: July 2002

Magnetoresistive random access memory has many desirable characteristics compared to other nonvolatile memory technologies. These include no inherent wear-out mechanism, very fast switching capability, and relatively few mask layers required for fabrication. We have investigated sub-micron memory cells patterned from asymmetric giant magnetoresistance (GMR) sandwich materials that have 6%–7.5% signal levels, exhibit sharp single-domain-like switching thresholds, and are sensed in a mode that yields a differential output signal effectively twice the intrinsic GMR of the material. The cell is designed so that the thinner of the two magnetic layers reverses freely in a read operation, while the bit state is stored in the thicker magnetic layer whose magnetization switches only upon writing the bit. Due to the high signal level and similarity in transfer characteristic to that of pinned spin valve material, we have labeled this cell structure and mode of operation pseudo spin valve (PSV). Experimental PSV memory cells and test structures approximately 0.3 μm in width were patterned and tested, and yielded GMR values of up to about 7.5%. Dependence of the write thresholds on sense line current as well as word and bias line fields was studied and confirmed that two-dimensional cell selection may be used in an array. Single bits exhibited sharp, single-domain-like write threshold characteristics, if properly shaped. Using a single domain model that takes into account static torques on the magnetic layers in a bit, as well as coupling between these layers, transfer curves and switching characteristics that qualitatively match the experimental data were generated. Using the model, properties of conceptual double pseudo spin valve (DPSV) cells were also studied. A DPSV cell is comprised of GMR material with three magnetic layers, where either the center layer or one of the two outer layers acts as the storage film. Advantages of DPSV cells include nearly twice the GMR compared with a PSV cell of similar area, as well as lower write thresholds.
Growth of
c
-axis oriented aluminum nitride films on GaAs substrates by reactive rf magnetron sputtering
Authors: Cheng Chien-Chuan , Chen Ying-Chung , Horng Rong-Chang , Wang Horng-Jwo , Chen Wen-Rong , Lai Erh-Kun
Published: July 2002

c-axis oriented aluminum nitride (AlN) films deposited on GaAs substrates by reactive rf magnetron sputtering were fabricated. The structural and morphological characterizations were found to be sensitive to the deposition conditions including rf power, N2 concentration, sputtering pressure and substrate temperature. A highly c-axis oriented AlN film was identified as low as 350 °C by x-ray diffraction. The crystallization of the AlN film with (002) preferred orientation tended to improve with increased rf power and N2 concentration within the experimental range. A densely pebble-like surface texture of the c-axis oriented AlN films with an average grain size of about 80 nm was observed by scanning electron microscopy (SEM). The film showed a high degree of alignment of the columnar structure as was indicated by the cross-sectional SEM photograph. The selected area diffraction pattern showed that the deposited films exhibited a polycrystalline microstructure.
Chemical sensing using nonoptical microelectromechanical systems
Authors: Freidhoff C. B. , Young R. M. , Sriram S. , Braggins T. T. , O'Keefe T. W. , Adam J. D. , Nathanson H. C. , Syms R. R. A. , Tate T. J. , Ahmad M. M. , Taylor S. , Tunstall J.
Published: July 2002

Micromachining is a technology that miniaturizes mechanical sensors and actuators through the use of tools and materials commonly used in the integrated circuit industry. The physics of the devices formed in this way are sometimes similar and sometimes different to achieve the same functionality of current macroscopic devices, but in sizes that are hundreds or thousands of times smaller. This article will discuss a few chemical detectors being developed as examples of the application of microelectromechanical systems (MEMS) for nonoptical laboratory instruments. In this article, we will report on the development and demonstration of two approaches (quadrupole and magnetic Lorentz) to fabricate a mass filter as part of a mass spectrometer. This article is not meant as a review of the field of MEMS chemical sensors, but rather a tutorial on how miniaturization is achievable through the use of MEMS fabrication techniques for mass spectrometers.
Rarefied gas flow through a long rectangular channel
Authors: Sharipov Felix
Published: July 2002

The mass flow rate of a rarefied gas through a long channel with a rectangular cross section has been calculated based on the model kinetic equation for the whole range of the Knudsen number and in the wide range of the height-to-width ratio. First, the reduced flow rate through a cross section has been calculated as a function of the local rarefaction parameter assuming the pressure gradient to be small. A criterion of the lateral wall influence on the flow rate has been given. Then, the mass flow rate has been calculated as a function of the rarefaction parameters on the channel ends. The last result is obtained for any pressure ratio even if the flow varies along the channel from the hydrodynamic regime to the free molecular one.
Microstructural evolution during tempering of arc-evaporated Cr–N coatings
Authors: Almer J. , Odén M. , Hultman L. , Håkansson G.
Published: July 2002

The thermal stability of arc-evaporated Cr–N coatings has been investigated as a function of incident ion energy via tempering experiments. Coatings were grown onto high-speed steel substrates at two bias voltages, 50 and 300 V, and examined using x-ray diffraction, transmission electron microscopy, and Auger electron spectroscopy. A significant reduction in the as-deposited lattice defect density, accompanied by the formation of equiaxed grains, was observed after tempering the coatings slightly above the deposition temperatures. Phase evolution was also observed during tempering, characterized by β-Cr2N phase formation above a time-dependent temperature, which suggests that a nonequilibrium excess of CrN1−x(x≈0.17) was formed during growth. The apparent activation energy, Q, for defect relaxation was determined to be approximately 2.7±0.3 eV in the 50 V coating, which is in good agreement with published values for bulk diffusion of N in CrN. In the 300 V coating, however, Q was found to increase from 1.7±0.3 to 3.1±0.3 eV with decreasing defect concentration. These results are discussed in terms of different defect populations formed as a function of incident ion energy during deposition, and corresponding defect-mediated diffusion.
Channeling effects during focused-ion-beam micromachining of copper
Authors: Phillips J. R. , Griffis D. P. , Russell P. E.
Published: July 2002

The rapid introduction of copper metallization for semiconductor devices has prompted increased research into focused-ion-beam micromachining of copper. Studies with the aim of increasing the material removal rate of Cu by focused-ion-beam micromachining have been complicated by variable micromachining behavior apparently resulting from differing Cu film morphologies produced by the various Cu deposition procedures. This work examined the micromachining behavior of thin copper films produced by physical-vapor deposition (PVD) and electroplating, as well as single-crystal copper samples. PVD copper films were found to be preferentially textured along 〈111〉, with a columnar grain structure. Channeling effects within this type of grain structure provide a geometric enhancement of the material removal rate of 30% when the sample normal is tilted 12° from the incident ion beam, regardless of sample rotation. Single-crystal (111) copper was found to exhibit similar material removal rate enhancement (averaged over 360° rotation) when tilted 12°, verifying that the etching enhancement observed in the PVD films is directly related to their 〈111〉 texture. Compared to the PVD film, electroplated (EP) copper thin films contained a significantly more random grain orientation. Consequently, the EP films did not exhibit any appreciable variation in material removal rate beyond the expected cosine dependence when tilted with respect to the incident Ga+ beam normal. Micromachining of the electroplated films, which have larger randomly oriented grains, results in grain decoration due to preferential etching producing severe micromachining-induced topography.
Real time control of plasma deposited optical filters by multiwavelength ellipsometry
Authors: Heitz T. , Hofrichter A. , Bulkin P. , Drevillon B.
Published: July 2002

Real time control of optical filters by multiwavelength ellipsometry is presented. The filters consist of SiO2/Si3N4 multilayers deposited on transparent substrates by a microwave plasma technique at room temperature. Using four-wavelength kinetic ellipsometry measurements and standard dispersion laws, efficient algorithms have been developed to determine in real time the current refractive index (n) and deposition rate (Rd) of the different layers. The program is based on minimizing square differences between calculated and experimental ellipsometry data. From the (n, Rd) calculation, which takes less than 200 ms, a control process operating the gas flows has been implemented which allows the deposition of high quality optical filters. As an illustration, the growth of a 11-layer Bragg reflector has been controlled in real time. The deposited filter has been characterized by comparing experimental and target spectral response, both in ellipsometry and spectrophotometry modes. Transmission measurements show excellent agreement in peak position and bandwidth, with less than 2% error.
Surface structure of MnO/Rh(100) studied by scanning tunneling microscopy and low-energy electron diffraction
Authors: Nishimura H. , Tashiro T. , Fujitani T. , Nakamura J.
Published: July 2002

The atomic structure of a MnO-deposited Rh(100) surface was studied using scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). The STM image of MnO/Rh(100) at a Mn coverage of 0.80 showed two hexagonal domains rotated by 90° with respect to each other. One of the unit vectors for these hexagonal domains had the same direction as the unit vector of the Rh(100) substrate, suggesting that these hexagonal domains grow in the [011] or [011̄] direction of Rh(100). An averaged spacing of 3.1 Å was obtained by the STM for the nearest-neighbor atoms of the hexagonal layer. The LEED pattern supported the presence of two hexagonal domains rotated by 90° by 12 extra spots in addition to the spots of the Rh(100) substrate. A lattice constant of 3.1 Å for the hexagonal domain measured by LEED coincided with that measured by STM. The hexagonal layer was found to be stable at 800 K. Although the Mn/Rh(100) surface showed no hexagonal LEED pattern or hexagonal STM image, the oxidation of the Mn/Rh(100) surface resulted in the appearance of a hexagonal pattern identical to those observed for the MnO/Rh(100) surfaces. The stable hexagonal domains were thus attributed to the monolayer of MnO species covering the Rh(100) surface.
Monte Carlo derived diffusion parameters for Ga on the GaAs(001)- (2×4) surface: A molecular beam epitaxy–scanning tunneling microscopy study
Authors: LaBella V. P. , Bullock D. W. , Ding Z. , Emery C. , Harter W. G. , Thibado P. M.
Published: July 2002

The migration of individual Ga atoms on the technologically important GaAs(001)-(2×4) reconstructed surface has been studied as a function of substrate temperature and As4 pressure using a combined molecular beam epitaxy and scanning tunneling microscope ultrahigh vacuum multichamber facility. We have deposited 10% of a plane of Ga onto a GaAs(001) surface with a low defect density (<1% ) and with large terraces (>0.5 μm) to avoid the influence of surface defects like step edges and vacancies. Both the island number density and the geometry are measured and compared to Monte Carlo solid-on-solid simulations. Basic diffusion parameters, such as the activation energy, directional hopping-rate ratio, directional sticking-probability ratio, etc., are reported.
Insertion process and electrical conduction of conjugated molecules in n-alkanethiol self-assembled monolayers on Au(111)
Authors: Ishida Takao , Mizutani Wataru , Tokumoto Hiroshi , Choi Nami , Akiba Uichi , Fujihira Masamichi
Published: July 2002

We have investigated an insertion process of conjugated molecules, 4-biphenylmethanethiol (BP) and [1,1′:4′,1″-terphenyl]-4-methanethiol (TP) into preassembled n-alkanethiol self-assembled monolayers on Au(111) using scanning tunneling microscopy (STM). Ex situ STM observation revealed that the insertion process is dependent on an organic solvent in which the conjugated molecules dissolve. The insertion of conjugated molecules with three phenyl rings (TP) was faster than that with two phenyl rings (BP). By analyzing the STM images, the lower limits of resistances for single BP and TP molecules were obtained as 22±5 and 36±5 GΩ, respectively.