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Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films

Issue 4 • Date Jul 2001

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Displaying Results 1 - 25 of 182
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Photovoltaic characteristics of BR/p-silicon heterostructures using surface photovoltage spectroscopy

    Page(s): 1037 - 1041
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    Purple membrane (PM) monolayers were deposited on hydrophilic or hydrophobic silicon substrates through the Langmuir–Blodgett (LB) technique. The photovoltaic features and interfacial charge separation of p-Si/PM/indium tin oxide (ITO) heterostructure were studied by surface photovoltage spectroscopy (SPS). The different photovoltaic response values were obtained due to the nonrandom orientation of PM in the LB films on the hydrophilic versus hydrophobic silicon substrates. The photovoltaic response value versus external potential of the p-Si/cytoplasmic-extracellular/ITO heterostructure showed an obviously rectifying behavior. Compared with the p-Si/ITO heterostructure, the response value of SPS increased more rapidly in the case of the positive external bias. © 2001 American Vacuum Society. View full abstract»

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  • Observation of the bone matrix structure of intact and regenerative zones of tibias by atomic force microscopy

    Page(s): 1042 - 1045
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    Atomic force microscopy (AFM) was used to comparatively study the structure of the bone matrix of rat tibia from an intact region with that from regions submitted to surgical injury. We used young male adult rats (Wistar), with corporal masses between 250 and 300 g. Each injury was provoked by drilling a 1.5-mm-diam hole in one cortical tibia surface. The healing course was monitored at 8 and 15 days after the injury. Atomic force microscopy images, at different magnifications, allowed the identification of the time dependence of the osteoblast activity, measured by the increase in the area of neoformed primary bone and in the organization of the collagen fibers of the bone matrix. Characterization of the natural recovery of the damaged bone tissue by AFM is potentially of great importance because it allows the comparison of natural recovery processes with those induced by medicines and other therapeutic procedures. © 2001 American Vacuum Society. View full abstract»

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  • Structural and electrical characteristics of chemical vapor deposited W/n-Si0.83Ge0.17/Si(001) and chemical vapor deposited WSix/n-Si0.83Ge0.17/Si(001)

    Page(s): 1046 - 1051
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    Structural and electrical properties of chemical vapor deposited (CVD) W/n-Si0.83Ge0.17/Si(001) and CVD–WSix/n-Si0.83Ge0.17/Si(001) were studied by structural, chemical, and electrical characterizations. W and WSix layers were deposited on n-Si0.83Ge0.17/Si(001) and n-Si(001) at the growth temperature Ts=350–550 °C by low-pressure chemical vapor deposition utilizing WF6 and SiH4 source gases. Structural and chemical properties of CVD–W/n-Si0.83Ge0.17(001) and CVD–WSix/n-Si0.83Ge0.17(001) interfaces were analyzed by x-ray diffraction, transmission electron microscopy, scanning electron microscopy, Rutherford backscattering spectroscopy, and Auger electron spectroscopy. Interfaces of CVD–WSix/n-Si0.83Ge0.17(001) were much sharper than those of CVD–W/n-Si0.83Ge0.17(001)- - . Interfaces of CVD–W/n-Si0.83Ge0.17(001) are very rough presumably due to encroachment of SiGe layers caused by etching reaction of SiGe layers by WF6. Electrical properties of the CVD–W/n-Si0.83Ge0.17(001) and CVD–WSix/n-Si0.83Ge0.17(001) Schottky diodes were characterized by the current–voltage measurements. The measured effective Schottky barrier heights Bn) of the CVD–W/n-Si0.83Ge0.17(001) Schottky contacts were 0.56±0.01 eV as the deposition temperature, Ts, of W layers increases from 350 to 550 °C, and CVD–WSix/n-Si0.83Ge0.17(001) Schottky contacts with CVD–WSix layers grown at Ts=350 °C showed the ϕBn values similar to those of CVD–W/n-Si0.83Ge0.17(001). © 2001 American Vacuum Society. View full abstract»

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  • Fabrication of smooth diamond films on SiO2 by the addition of nitrogen to the gas feed in hot-filament chemical vapor deposition

    Page(s): 1052 - 1056
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    Diamond films of small roughness have been deposited onto thermally oxidized Si substrates by a process of anisotropic crystalline growth induced by nitrogen in a hot-filament chemical vapor deposition reactor. Ethanol (C2H5OH), diluted in hydrogen and nitrogen, was used as the source of carbon. At high concentrations, nitrogen tends to suppress the diamond growth in the <100> direction, which allows the growth of square mesoscopic-like crystals (“plates”) of large area in the directions parallel to the surface of the substrate. These plates stack upon each other, forming a thick diamond coating of uniform thickness. Analysis of the films made by micro-Raman spectroscopy and atomic force microscopy revealed that it is possible to obtain diamond coatings of high quality with a roughness comparable to that of the SiO2 at the diamond/SiO2 interface, and of nanometric roughness on the surface of the plates. A model to explain the morphology of the plates based on the microscopic mechanisms that involve the possible passivation of the (100) plane and an increase of vacancies by nitrogen is also discussed. © 2001 American Vacuum Society. View full abstract»

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  • Micro-crystalline diamond and nano-carbon structures produced using a high argon concentration in hot-filament chemical vapor deposition

    Page(s): 1057 - 1062
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    Micro-crystalline diamond films and nano-carbon structures in the form of wires have been grown by the introduction of argon at very high concentrations (60%–87.5% vol Ar) into the feed mixture (ethanol and hydrogen) of a hot-filament chemical vapor deposition reactor. The argon, in addition to acting as an inert diluent, also modified the kinetics of the carbon deposition process; its presence apparently minimized the deposition of intergranular hydrogenated species, induced an increase in the number of flaws between the diamond grains, increased the porosity of the films, and formed new carbon structures. Well-faceted diamond films, diamond-like carbon (DLC) balls, spongy-like wires, and multilayer structures were observed at different concentrations of Ar. Raman spectroscopy of the deposited material showed that structures of high quality diamond (60%–65% vol Ar) and carbon structures related to DLC, fullerenes and carbon nanotubes, may be deposited by this process. © 2001 American Vacuum Society. View full abstract»

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  • Damage in etching of (Ba, Sr)TiO3 thin films using inductively coupled plasma

    Page(s): 1063 - 1067
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    High dielectric (Ba, Sr)TiO3 thin films were etched in an inductively coupled plasma as a function of the Cl2/Ar gas mixing ratio. Under Cl2 (20)/Ar (80), the maximum etch rate of the BST film was 400 Å/min and the selectivities of BST to Pt and PR obtained were 0.4 and 0.2, respectively. Etching by-products remained on the surface of BST and resulted in varying the stochiometry. Therefore, we investigated the surface of the etched BST using x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and x-ray diffraction (XRD). From the results of XPS analysis, we found that metal (Ba or Sr) chloride compounds remained on the surface of the etched BST for high boiling points. The morphology of the etched surface was evaluated with AFM. The surface roughness decreased as the Cl2 increased in the Cl2/Ar plasma. From the results of XRD analysis, the crystallinity of etched BST films under Ar only and under Cl2 (20)/Ar (80) was similar to that of as-deposited BST. However, the (100) diffraction peak abruptly decreased at the Cl2 only plasma. It was assumed that metal (Ba or Sr) chloride compounds remained on the etched BST surface and changed the stoichiometry, resulting in crystallinity of the BST film during the etch process. © 2001 American Vacuum Society. View full abstract»

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  • Etch characteristics of CeO2 thin films as a buffer layer for the application of ferroelectric random access memory

    Page(s): 1068 - 1071
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    Cerium oxide (CeO2) thin film has been proposed as a buffer layer between the ferroelectric film and the Si substrate in metal–ferroelectric–insulator–silicon structures for ferroelectric random access memory applications. In this study, CeO2 thin films were etched with a Cl2/Ar gas combination in an inductively coupled plasma. The etch properties were measured for different gas mixing ratios of Cl2/(Cl2+Ar) while the other process conditions were fixed at rf power (600 W), dc bias voltage (-200 V), and chamber pressure (15 mTorr). The highest etch rate of the CeO2 thin film was 230 Å/min and the selectivity of CeO2 to YMnO3 was 1.83 at a Cl2/(Cl2+Ar) gas mixing ratio of 0.2. The surface reaction of the etched CeO2 thin films was investigated using x-ray photoelectron spectroscopy (XPS) analysis. There is a Ce–Cl bonding by chemical reaction between Ce and Cl. The results of secondary ion mass spectrometer analysis were compared with the results of XPS analysis and the Ce–Cl bonding was discovered at 176.15 (amu). These results confirm that the Ce atoms of the CeO2 thin films react with chlorine and a compound such as CeCl remains on the surface of the etched CeO2 thin films. These products can be removed by Ar-ion bombardment. © 2001 American Vacuum Society. View full abstract»

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  • Chemical interaction and adhesion characteristics at the interface of metals (Cu, Ta) and low-k cyclohexane-based plasma polymer (CHexPP) films

    Page(s): 1072 - 1077
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    Chemical interaction and adhesion characteristics between metals (Cu, Ta) and low-k plasma-treated cyclohexane-based plasma polymer (CHexPP) films were studied. In order to generate new functional groups that may contribute to the improvement of adhesion between metal and plasma polymer, we performed O2, N2, and H2/He mixture plasma treatment on the surfaces of CHexPP films. Chemical interactions at the interface between metals (Cu, Ta) and plasma-treated CHexPP films were analyzed by x-ray photoelectron spectroscopy. The effect of plasma treatment and thermal annealing on the adhesion characteristics was measured by a tape test and scratch test. The formation of new binding states on the surface of plasma-treated CHexPP films improved adhesion characteristics between metals and CHexPP films. Thermal annealing improves the adhesion property of Cu/CHexPP films, but degrades the adhesion property of Ta/CHexPP films. © 2001 American Vacuum Society. View full abstract»

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  • Low temperature deposition and characterization of polycrystalline Si films on polymer substrates

    Page(s): 1078 - 1082
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    Polycrystalline Si films were deposited on poly(ethyleneterephthalate) (PET-Mylar®) and glass (7059 Corning) substrates at 140 and 200 °C, respectively. X-ray diffraction and Raman spectroscopy were used to confirm the polycrystalline nature of the films. The largest grain size obtained was 95 nm. Raman spectroscopy also showed a simultaneous presence of an amorphous phase. The relative fraction of this amorphous phase was controllable by adjusting the composition of the sputtering gas. Films deposited with only Ar or Ar+H2 sputtering gas show a very small polycrystalline Si peak. With the addition of up to 10% Kr to the gas mixture, a very strong polycrystalline peak appears in the Raman spectra. X-ray diffraction also confirmed the polycrystalline nature of the films. The Kr effect was related to the energetic condensation. The presence of Kr increased the energy of the sputtered atoms. Even after collision with the sputtering gas, these atoms impinge on the substrate surface with enough residual energy that the ad-atoms experience enhanced diffusion, which leads to polycrystalline film formation. For our system, the final energy of the ad-atoms was calculated to be 1.92 eV, which is more than the activation energy for surface self-diffusion for Si. © 2001 American Vacuum Society. View full abstract»

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  • Cross-sectional transmission electron microscopy investigation of the dead layer of ZnS:Ag,Al phosphors in field emission displays

    Page(s): 1083 - 1089
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    The dead surface layer of blue-emitting ZnS:Ag,Al phosphor with Al metallized thin film in high-voltage field emission displays (FEDs) has been investigated by means of cross-sectional transmission electron microscopy. From these observations, it was found that electron irradiation at 6 keV excitation causes the decomposition of ZnS and the subsequent evolution of sulfur in the topmost surface layer ∼30 nm, and also causes the formation of lattice defects within the electron penetration depth of ∼300 nm in a life-end stage. When this evidence was taken into account, it was estimated that the decomposition rate of ZnS and the formation rate of lattice defects depend mainly on the degree of crystallinity and the atomic-scale surface roughness of ZnS phosphor particles. Necessary characteristics of ZnS:Ag,Al phosphors for longer luminescence lifetime in FEDs were suggested in this work. © 2001 American Vacuum Society. View full abstract»

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  • Optical filters for plasma display panels using organic dyes and sputtered multilayer coatings

    Page(s): 1090 - 1094
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    Optical filters for plasma display panels (PDPs) have been studied. We obtained the sputtered seven-layer coatings (comprising alternate layers of silver and indium–tin–oxide) on substrates of polyethylene terephthalate by a roll-to-roll process. The coatings were designed in order to minimize interfacial reflectance between the coatings and the adjacent layer to it. The coatings have a surface resistance of 2.2 Ω/sq, a transmittance of 1%∼12% in the near-infrared region of 800–1200 nm, and visible-light transmittance of approximately 70%. In combination with these multilayer coatings working as shields of electromagnetic wave and near-infrared light, organic dyes were also applied to control transmission properties of the optical filters and to improve PDPs picture quality. © 2001 American Vacuum Society. View full abstract»

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  • Effects of ZnO buffer layer on the luminous properties of thin-film phosphors deposited on ZnO/ITO/glass substrates

    Page(s): 1095 - 1098
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    ZnGa2O4:Mn and CaTiO3:Pr thin-film phosphors which emit green and red light, respectively, were deposited on ZnO/ITO/glass and ITO/glass substrates by a rf reactive magnetron-sputtering method. To improve photo- and cathodoluminescent properties of the thin-film phosphors, ZnO buffer layers were deposited between the thin-film phosphor and the ITO-coated glass substrate. A transparent c-axis preferentially oriented ZnO thin-film buffer layer could be obtained on the ITO film, while ITO had an amorphous-like structure. ZnGa2O4:Mn and CaTiO3:Pr thin-film phosphors were used to evaluate the effects of the ZnO buffer layer. The crystal structures of thin-film phosphors deposited on ZnO/ITO/glass substrates were developed better than those on ITO/glass, consequently, the former showed photo- and cathodoluminescent intensity at least twice as high as the latter. © 2001 American Vacuum Society. View full abstract»

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  • Investigation of the outgassing characteristics of the materials comprising a plasma display panel

    Page(s): 1099 - 1104
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    Long gas evacuation time before the introduction of the discharge gases into the panel is one of the major problems in the production of a plasma display panel (PDP). In this study, the outgassing characteristics during the panel evacuation stage were investigated using a quadrupole mass spectrometer. The origin of the impurity gas was studied by measuring the outgassed species from each layer comprising the PDP. Dominant species observed during the evacuation of the panel were H2, H2O, N2, O2, and CO2 and water vapor was the most abundant species. When the outgassing characteristics of the panel were compared with the outgassing characteristics from each layer comprising the panel, the material most responsible for the water vapor turned out to be a MgO layer. The outgassing experiments of single panels have also shown that the long outgassing time of PDP is mostly related to the MgO layer and possibly also to red, green, and blue layers and white dielectric material coated on the each single panel. Therefore to reduce the gas evacuation time, controlled atmosphere appears to be required during the deposition of these materials and the storage of those deposited panels. © 2001 American Vacuum Society. View full abstract»

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  • In situ analysis of perfluoro compounds in semiconductor process exhaust: Use of Li+ ion-attachment mass spectrometry

    Page(s): 1105 - 1110
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    Ion-attachment mass spectrometry is capable of accurate and in situ analysis of multicomponent gases that may even include unknown components. We developed a compact apparatus that uses this method and examined its performance for perfluoro compounds, a class of greenhouse gases, using typical standard gases, and subsequently applied the method to the in situ analysis of exhaust gases from a dry-etching machine, where c-C4F8/O2/Ar plasma is generated. Perfluoro compounds of low concentration can be detected as quasimolecules without any fragmentation. In the exhaust gases, many components that are not considered in the current measurement protocol [J. Meyers, D. Green, P. Maroulis, and W. Reagen, Equipment Environmental Characterization Guidelines, Rev. 3.0 (INTEL, 1999)] are measured, as well as components already reported. © 2001 American Vacuum Society. View full abstract»

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  • Quantitative comparison between Auger electron spectroscopy and secondary ion mass spectroscopy depth profiles of a double layer structure of AlAs in GaAs using the mixing-roughness-information depth model

    Page(s): 1111 - 1115
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    Application of the so called mixing-roughness-information (MRI) depth model to quantitative reconstruction of the in-depth distribution of the composition is demonstrated by comparing secondary ion mass spectroscopy (SIMS) and Auger electron spectroscopy (AES) depth profiles. A GaAs/AlAs reference sample consisting of two layers of AlAs [1 and 36 monolayer (ML)] separated by 44 ML of a GaAs matrix was depth profiled using almost identical sputtering conditions: Ar+ ions of 3 keV impact energy and 52° (SIMS: CAMECA 4f ) and 58° (AES: VG Microlab 310F) incidence angle. Both the Al+ intensity of the SIMS profile and the Al (LVV) intensity of the AES profile were quantified by fitting the measured profiles with those calculated with the MRI model, resulting in the same mixing length of 3.0±0.3 nm, similar roughness parameter (1.4–2 nm), and negligible information depth (0.4 nm). Whereas practically no matrix effect was observed for AES as well as for Al+ in the SIMS profile, quantification using dimer (Al2+) and trimer (Al3+) ions shows a marked nonlinearity between concentration and intensity, with the main effect caused by the simple mass action law probability of cluster ion formation. © 2001 American Vacuum Society. View full abstract»

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  • Surface characterization of IM7/5260 composites by x-ray photoelectron spectroscopy

    Page(s): 1116 - 1120
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    Surfaces of high-performance carbon fiber/bismeleimide (BMI) composites (IM7/5260) have been characterized by x-ray photoelectron spectroscopy. An experimental technique to separately examine the chemical natures of the carbon fibers and BMI resin in the composite form was developed. This technique uses a flood gun to establish differential charging conditions on the BMI resin. The binding energies from the BMI resin were shifted by an amount of voltage applied to the flood gun, whereas those from the carbon fibers were uniquely determined due to their electrically conducting nature. By adding external bias voltage to the sample, the binding energies for conducting fibers were further shifted from those of the BMI resin, thereby separating the IM7 phase completely from the BMI phase in the binding energy scale, allowing independent measurement of the chemical changes associated with those peaks. Using this technique, the effects of thermal aging and surface plasma treatment on the IM7/5260 composite were studied. © 2001 American Vacuum Society. View full abstract»

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  • Pt–metal oxide aerogel catalysts: X-ray photoemission investigation

    Page(s): 1121 - 1125
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    X-ray photoemission spectroscopy was used to study Pt–metal oxide aerogel catalysts that have been developed to respond to increased NOx emissions of lean-burn engines. Lean-burn engines, critical components of low and zero emission vehicles, produce much higher levels of engine-out NOx and current three-way catalytic converters are not sufficient to meet Clean Air Act standards. Platinum catalysts were formed by the reaction of modified Pt coordination compounds with selected transition–metal alkoxides through sol–gel techniques into aerogels. Photoemission measurements of the Pt 4f, Si 2p, Ti 2p, O 1s, and C 1s core lines were used to evaluate the chemistry of the material after each processing step. Results indicate Pt–O bonding and reduced Pt disbursed in the aerogel. In addition, Si 2p, Ti 2p, and O 1s binding energies indicate an oxo-bridged network structure. © 2001 American Vacuum Society. View full abstract»

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  • Scanning Auger microscopy studies of an ancient bronze

    Page(s): 1126 - 1133
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    Scanning Auger microscopy (SAM) has been used to study the surface and interface microchemistry of a sheet bronze belt from the Urartian kingdom in NE Syria of the early first millennium B.C. We find that the patina contains no copper species at all (decuprification), whereas carbonaceous species, Ca-silicates and N-bearing species are detected, the last being tentatively identified as organic (primarily amine-like) residues deriving from the soil. A textured grain, which we qualify as a second phase of bronze originated by an imperfect alloying of the two major metals (i.e., consisting of Cu-rich and Sn-rich domains) is observed on the metallic side lying beneath the patina. SAM imaging with a submicron spatial resolution highlights the presence of SnO2 oxide inside what appears to be the hollow veins of the grain, whereas a Cu2O-like oxide is confined exclusively to the flat regions of the grain. We explain these results by noting that the hollow veins, offering a higher exposure to external fluids, are likely to have promoted preferential formation of the more stable tin oxide over copper oxide. In another region of the metal side we studied the chemistry of grain boundaries and their surrounding areas. We find that S species lie exclusively inside the grain boundaries, whereas Sn and Zn species accumulate just outside the boundary channels, and this lateral chemical inhomogeneity is highlighted with a ∼200 nm spatial resolution. Lateral segregation of Cu and Sn domains is imaged in another region with a spatial resolution of ∼15 nm. This result marks the best spatial resolution any analytical method has yet achieved in highlighting chemical heterogeneities of ancient bronzes. Although archaeomaterials lie outside the mainstream applications of Auger techniques, this study provides convincing evidence that SAM can greatly advance- - our understanding of these materials, as it provides clues relating to corrosion and patination phenomena, as well as manufacturing processes that are not easily reachable by other microscopies or microanalytical techniques. © 2001 American Vacuum Society. View full abstract»

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  • Comparative ion yields by secondary ion mass spectrometry from microelectronic films

    Page(s): 1134 - 1138
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    Secondary ion mass spectrometry (SIMS) is reported from multiple-element multiple-matrix ion implants. The implants include a thirteen element metal set and a six element gas set implanted into films of interest for microelectronics (silicon, silicides, wiring layers, liner metals, inorganic dielectrics, and polymer dielectrics.) Using these standards, this study performs a broad comparison of ion yields using a metric defined as the normalized useful yield. We find that the yield of K+ with O2+ primaries is constant for almost all matrices, in keeping with a concept of ion yield saturation. The yield of Cl- with Cs+ primaries approaches a yield saturation limit for titanium but the ion yield falls for materials with higher sputter yields, becoming 3.5× lower from copper. The variations in negative ion yields from matrix to matrix are much larger, with anomalies more pronounced, for weaker-yielding ions, becoming 50× for C- from Ti to Cu. In this article we document sets of ion implants, show some of the SIMS profiles, and note trends in ion yields and implications for SIMS analysis. © 2001 American Vacuum Society. View full abstract»

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  • Surface potential measurement with high spatial resolution using a scanning Auger electron microscope

    Page(s): 1139 - 1142
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    The microscopic surface potential distributions were measured from the onset energies of secondary electron spectra using a scanning Auger electron microscope. The spatial resolution is several tens of nanometers and a sensitivity of the surface potential measurement is 0.05 eV. We demonstrated the calibration of the instrument for local surface potential analysis based on the onset energy measurement of the secondary electron spectrum. Several applications of this technique for Ni polycrystal grains of different orientations, and a potential profile along the p–n junction of a light-emitting diode were demonstrated. © 2001 American Vacuum Society. View full abstract»

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  • Chemical effects on F KLL Auger spectra in fluorides

    Page(s): 1143 - 1149
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    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 and Cu x-rays from polycrystalline powder samples of MgF2, ZnF2, NiF2, and CoF2 and measured by a high luminosity electron spectrometer. Excitation by Cu 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 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. © 2001 American Vacuum Society. View full abstract»

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  • X-ray photoelectron spectroscopy, x-ray absorption spectroscopy, and x-ray diffraction characterization of CuOTiO2CeO2 catalyst system

    Page(s): 1150 - 1157
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    X-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), and x-ray absorption spectroscopy (XAS) techniques have been applied to characterize the surface composition and structure of a series of CuO–TiO2–CeO2 catalysts. For a small loading of cerium, ceria was mainly dispersed on the titania surface and a minor amount of CeO2 crystallite appeared. At higher loading of cerium, the CeO2 phase increased and the atomic Ce/Ti ratio values were smaller than the nominal composition, as a consequence of cerium agglomeration. This result suggests that only a fraction of cerium can be spread on the titania surface. For titanium-based mixed oxide, we observed that cerium is found as Ce3+ uniquely on the surface. The atomic Cu/(Ce+Ti) ratio values showed no influence from cerium concentration on the dispersion of copper, although the copper on the surface was shown to be dependent on the cerium species. For samples with a high amount of cerium, XPS analysis indicated the raise of second titanium species due cerium with spin-orbit components at higher binding energies than those presented by Ti4+ in a tetragonal structure. The structural results obtained by XAS are consistent with those obtained by XRD and XPS. © 2001 American Vacuum Society. View full abstract»

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  • Chemical and structural characterization of V2O5/TiO2 catalysts

    Page(s): 1158 - 1163
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    A series of V2O5/TiO2 samples was synthesized by sol–gel and impregnation methods with different contents of vanadia. These samples were characterized by x-ray diffraction (XRD), Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), and electronic paramagnetic resonance (EPR). XRD detected rutile as the predominant phase for pure TiO2 prepared by the sol–gel method. The structure changed to anatase when the vanadia loading was increased. Also, anatase was the predominant phase for samples obtained by the impregnation method. Raman measurements identified two species of surface vanadium: monomeric vanadyl (V4+) and polymeric vanadates (V5+). XPS results indicated that Ti ions were in octahedral position surrounded by oxygen ions. The V/Ti atomic ratios showed that V ions were highly dispersed on the vanadia/titania surface obtained by the sol–gel method. EPR analysis detected three V4+ ion types: two of them were located in axially symmetric sites substituting for Ti4+ ions in the rutile structure, and the third one was characterized by magnetically interacting V4+ ions in the form of pairs or clusters. A partial oxidation of V4+ to V5+ was evident from EPR analysis for materials with higher concentrations of vanadium. © 2001 American Vacuum Society. View full abstract»

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  • Interface formation and electrical properties of a TiNx/SiO2/Si structure for application in gate electrodes

    Page(s): 1164 - 1169
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    In this work, we investigate the interface formation and electrical properties between TiNx and SiO2 for application of a gate electrode as a function of annealing temperature, TA. Auger electron spectroscopy (AES) and four-point probe measurement were performed to measure the chemical composition and sheet resistance, Rs, respectively, of TiNx/SiO2 films. Also, interface formation of TiNx/SiO2 films as a function of annealing temperature was investigated by x-ray photoemission spectroscopy (XPS) depth profiling. X-ray diffraction spectra showed an increase in the crystallinity of TiNx above TA=600 °C. AES and XPS data show that thermal annealing of the sample with TiNx deposited at an Ar/N2 gas flow ratio of 6/1 (QAr/QN2=6/1) above 600 °C increases the oxidation reaction of TiNx layers, resulting in the formation of TiO2 phases. The Rs values increased at elevated annealing temperatures above 600 °C for TiNx deposited with QAr/QN2=6/1, but the Rs values of TiNx deposited at an Ar/N<- - /roman>2 gas flow ratio of 6:3 continuously decreased up to TA=800 °C. © 2001 American Vacuum Society. View full abstract»

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Aims & Scope

The Journal of Vacuum Science and Technology A is devoted to reports of original research, review articles, and Critical Review articles.

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Editor
G. Lucovsky
North Carolina State University