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

Issue 1 • Date Jan 1994

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Displaying Results 1 - 25 of 49
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • In situ x‐ray photoemission spectroscopic studies of Al/SiO2 interface formation

    Page(s): 1 - 6
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    A structural model for the Al/SiO2 interface system after an oxidation–reduction reaction is proposed. Thermal dependence of the initial stages of the Al/SiO2 interface formation process is investigated by in situ x‐ray photoemission spectroscopy analysis and secondary ion mass spectrometry measurements of depth profiles. An abrupt interface without any reaction is confirmed when the interface is formed at room temperature. During Al deposition on SiO2 at substrate temperatures beyond 300 °C, oxidation–reduction reaction occurs that produces Al2O3 and reduces metallic Si at the interface. The reduced Si spreads throughout the entire Al layer uniformly and the thin Al2O3 layer acts as a diffusion barrier that limits the reaction in the very vicinity of the interface. This suggests a distinct layer ordering of the reacted system, Al(Si)/Al2O3/SiO2.   View full abstract»

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  • Passivation with SiO2 on HgCdTe by direct photochemical‐vapor deposition

    Page(s): 7 - 11
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    For the first time, SiO2 layers, prepared by direct photochemical‐vapor deposition, were passivated onto HgCdTe substrates using a deuterium (D2) lamp as the ultraviolet and vacuum‐ultraviolet light source. It was found that the refractive index of the SiO2 films, grown at 60 °C and 0.5 Torr for a mixture of SiH4 and O2, is close to 1.462 (the refractive index of thermal silicon dioxide) when the gas ratio (SiH4/O2) is adjusted to 0.2. Various characterization techniques, such as x‐ray photoemission, Auger‐electron, and Fourier‐transform spectroscopies were used to give a detailed study of the physical and chemical properties of the SiO2 thin films. The electrical properties of these SiO2 layers were investigated by performing high frequency (1 MHz) capacitance–voltage (C–V) and current–voltage (I–V) measurements, at 77 K. The C–V measurement shows that the minimum interface state density is 5×1010 cm-2 eV-1 with a hysteresis smaller than 0.2 V. The maximum dielectric strength observed from I–V measurement is around 580 kV/cm. View full abstract»

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  • Thickness determination of thin oxide layers at the bottom of contact holes of semiconductor devices by Auger electron spectroscopy

    Page(s): 12 - 18
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    Fabrication of electrical contacts in semiconductor device technology can be hampered by the presence of thin oxide layers that may form at the bottom of the contact or via holes as a consequence of the reactive ion etching process. In order to achieve low contact resistances after metallization this oxide thickness must be below some critical value. This article describes a method based upon Auger electron spectroscopy for the thickness determination of such thin oxide films at the bottom of micron‐sized contact holes prior to metallization. In this technique, the different Si KLL line shapes of elemental and oxidized silicon are utilized for fitting the measured spectrum with a superposition of Si and SiO2 spectra; the oxide thickness follows from the fitting coefficients. The method is applicable to oxide thicknesses up to ∼10 nm and to contact holes with aspect ratios below ∼1. Systematic errors due to scattering and shadowing effects, and to electron‐beam induced damaging are discussed. The method has proven to be extremely important in optimizing reactive ion etching processes. View full abstract»

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  • Aligned Au–Si eutectic bonding of silicon structures

    Page(s): 19 - 22
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    A technique for precisely aligning structures before a Au–Si eutectic bond has been developed. A (100) silicon wafer is anisotropically etched to create v grooves around the periphery of the structure to be bonded. Gold is then deposited onto one of the wafers prior to dicing into individual die. Optical fibers are used as precision locating keys and align the structure when it is assembled. The entire structure is then placed onto a hot chuck at 400 °C. An ultrasonic transducer is used to aid the Au–Si bond. The fibers may be removed after bonding. Current results have shown a maximum misalignment of 5 μm for a 1 cm×1 cm die. This accuracy is achieved with the entire assembly being done by hand without the aid of a microscope or micropositioners. This technique allows a sensor die to be precisely bonded to an electronics die. View full abstract»

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  • Pb preadsorption facilitates island formation during Ge growth on Si(111)

    Page(s): 23 - 28
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    On a clean Si(111)‐7×7 surface, Ge grows in the Stranski–Krastanov mode. At 300–450 °C, relaxed islands begin to form when the Ge growth is 6 monolayers (ML) thick. When Ge is grown on a Pb/Si(111)‐√3×√3 surface, Pb segregates on the surface and agglomerates into two‐dimensional islands. And the critical thickness for the formation of relaxed island becomes 4 ML. This change in critical thickness is explained by Pb reducing the surface energy or by an improved crystallinity of Ge layers (due to a simplified substrate surface reconstruction), or by both. View full abstract»

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  • Metallization of Teflon PFA. I. Interactions of evaporated Cr and Al measured by x‐ray photoelectron spectroscopy

    Page(s): 29 - 34
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    Cr and Al were evaporated onto Teflon PFA (polytetrafluoroethylene-co‐perfluoroalkoxy vinyl ether) substrates by electron beam evaporation. In situ x‐ray photoelectron spectroscopy revealed that Cr deposition leads to defluorination and the formation of fluoride and carbide species. The concentrations of fluoride and carbide increased with deposited Cr thickness, slowly at the initial stages of deposition but more rapidly afterwards. Al deposition was qualitatively similar to that of Cr, although the concentrations of fluoride and carbide formed were much lower. The sticking coefficients of both metals, low at the outset of metal deposition, were enhanced after initial deposition, with simultaneous increases in interfacial reactions. Oxygen contaminants in the form of metal oxides were observed, particularly in the case of Al. View full abstract»

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  • Correlation of x‐ray photoelectron spectroscopy and Rutherford backscattering spectroscopy depth profiles on Hg1-xCdxTe native oxides

    Page(s): 35 - 43
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    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. View full abstract»

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  • X‐ray photoelectron spectroscopy study of x‐ray irradiated metal/fluoropolymer interfaces

    Page(s): 44 - 50
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    Interaction of Cr, Ti, Al, Ag, Au, and Cu with Teflon PFA (polytetrafluoroethylene‐ co‐perfluoroalkoxy vinyl ether) and FEP (fluoroethylene propylene), and the effect of x‐ray irradiation on the metal/polymer interfaces, were studied using in situ x‐ray photoelectron spectroscopy (XPS) and mass spectrometry. Cr, Ti, and Al were found to react with both PFA and FEP, leading to polymer surface graphitization and formation of carbide and fluoride species, which are enhanced at higher metal thicknesses. On the other hand, evaporation of Au, Ag and Cu causes only a slight loss of fluorine, but no chemical interaction occurs. Post‐deposition x‐ray irradiation does not promote metal–polymer interactions, but it leads, in the case of reactive metals, to a pronounced increase of the C–CFn peak intensity, which rises with the metal thickness. A mechanism based on radical recombination reaction and accumulation of the small fragments, inside the metal film and/or near the metal/polymer interface, is proposed to explain this behavior. The metal XPS signal decreases upon x‐ray exposure, which is interpreted by diffusion of metals into the polymer matrix. The relative change in XPS signal is enhanced at longer x‐ray irradiations, but decreases at a higher metal thickness. This effect is most pronounced for Cu, Cr, and FEP. View full abstract»

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  • Photoemission study of evaporated CuInS2 thin films. I. Surface stoichiometry and phase segregation

    Page(s): 51 - 55
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    The surfaces of evaporated CuInS2 films were investigated by photoelectron spectroscopy (XPS) with respect to stoichiometry dependent features. The surface composition of In‐rich CuInS2 films drastically exceeds the respective bulk value determined by energy dispersive x‐ray fluorescence and displays the formation of an In‐rich surface layer with a cation ratio of In/(In+Cu)=0.75(2). Sputter profiles obtained by Auger electron spectroscopy confirm the effect of In enrichment and Cu depletion on the surface. The altered surface region is estimated to extend approximately 0.1μm into the film. Films with a Cu‐rich bulk composition also exhibited In‐rich surfaces, but in addition the segregation of a CuS phase is concluded from XPS investigations. The interrelation of these observations is discussed using simple model considerations. View full abstract»

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  • Photoemission study of evaporated CuInS2 thin films. II. Electronic surface structure

    Page(s): 56 - 60
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    The electronic surface structure of evaporated CuInS2 films with different stoichiometries was investigated by photoelectron spectroscopy [x‐ray and ultraviolet (XPS and UPS, respectively)]. The Fermi level position is observed to vary from EF-EV=1.3 eV for the In‐rich to EF-EV=0.0 eV for the Cu‐rich films. Valence band spectra of In‐rich films can be interpreted according to theoretical band structure calculations in the literature. The electronic surface structure of Cu‐rich films is determined by a CuS phase segregation which is displayed by an additional valence band emission structure. This phase is responsible for the semimetallic character of the Cu‐rich films. A comparison of the energy level positions of Cu‐rich and In‐rich films is given according to a simple model. The removal of CuS by a KCN treatment is indicated by the complete recovery of the CuInS2 valence band structure. As a consequence highly efficient solar‐to‐energy conversion can be obtained from CuInS2 films of a wide as‐deposited Cu‐rich composition range. View full abstract»

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  • Three‐dimensional simulation of surface evolution during growth and erosion

    Page(s): 61 - 68
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    A concise review of the basic ideas of the generalized kinematic model of surface evolution during growth and erosion is presented. Interpretation of the main results of this model as well as some specific rules and advice as to how this model is applied in practical simulations are also presented. It is concluded that three‐dimensional (3D) computer simulation of surface evolution is only possible by the use of adequate, theoretically motivated numerical methods. As a demonstration, 3D topography simulations during broad and focused ion beam bombardment, chemical vapor deposition, and reactive ion etching using the 3D code dinese are also presented. View full abstract»

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  • Dependence of etch characteristics on charge particles as measured by Langmuir probe in a multipolar electron cyclotron resonance source

    Page(s): 69 - 74
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    A multipolar electron cyclotron resonance (ECR) plasma source was characterized by Langmuir probe measurements and the charged particle energy and density are related to photoresist etch rate. Ion density was found to increase with microwave power but decrease with source distance, and is independent of rf power and flow rate. Among the different gases investigated, Ar plasma was found to have higher ion density compared to O2, N2, and Cl2 discharge. Ion density peaked at 5 mTorr for Ar and 2 mTorr for O2 plasma. For a N2 plasma, the maximum ion density was found to occur at 10 mTorr at 3 cm and 2 mTorr at 23 cm below the ECR source. Electron temperature is ∼3 eV for pressure ranging from 1 to 5 mTorr but decreases to 2 eV at 20 mTorr. Photoresist etch rate follows the same trend as ion density. It increases with microwave power and decreases with source distance. On the other hand, photoresist etch rate increases with rf power and flow rate, even though the ion density remains constant. This suggests that photoresist etching also depends on ion energy and concentrations of neutral species. Ion density uniformity of ±1% for a N2 plasma was measured across the central 24 cm along the stage at 23 cm below the source. For a source distance between 3 and 23 cm, uniformity of ±3% was obtained over a 12 cm diam region on the stage. In an O2 plasma, photoresist etch rate uniformity of ±2% was measured for a 10 cm diam wafer and the corresponding ion density uniformity was ±1%. View full abstract»

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  • Comparing reactive ion etching of III–V compounds in Cl2/BCl3/Ar and CCl2F2/BCl3/Ar discharges

    Page(s): 75 - 82
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    The reactive ion etching (RIE) of GaAs, AlGaAs, InP, InGaAs, InGaAsP in Cl2/BCl3/Ar or CCl2F2/BCl3/Ar discharges is investigated as a function of the plasma parameters: power, pressure, and relative composition as well as etching time. For the reason of In‐based fluoride with high boiling point, the etching rates of all of these materials are faster in Cl2/BCl3/Ar in comparison to CCl2F2/BCl3/Ar. The In‐based compounds show a similar dependence on power density and discharge composition, but it is quite different from GaAs. When discharges containing CCl2F2 are used, the surface morphologies are quite rough after the treatment of RIE with either type of discharge, although smooth etching surfaces can be obtained under appropriate conditions. Using BCl3 containing gas discharges will enhance smooth surface and maintain high etching rate. For selective etching of GaAs on AlGaAs, gas mixtures containing CCl2F2 are used. High performance and high selective etching can be obtained by using CCl2F2/BCl3/Ar gases mixtures. Photoresist or SiO2 were used as etching masks. Silicon dioxide is better than the photoresist mask for its low etching rate and sputtering to III–V compounds, and it could be in situ removed by CF4 plasma. The photoluminescence measurements show high performance of etched results when the power density was maintained at less than 0.6 W/cm2. View full abstract»

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  • Low temperature radio frequency sputter deposition of TiN thin films using optical emission spectroscopy as process monitor

    Page(s): 83 - 89
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    TiN films were deposited onto various substrates including InP by rf sputtering in an N2/Ar ambient at room temperature. The rf power, the ratio of gas flows, and the total pressure were systematically varied. To optimize the deposition conditions, the plasma excitation processes were examined by optical emission spectroscopy using a calibrated crystal thickness monitor to determine the corresponding deposition rates. At pressures below 15×10-3 mbar, the deposition rate is linearly proportional to the intensity of the optical emission at 364.2 nm, I(Ti), associated with excited Ti. Although I(Ti) increases with the total pressure, at a given rf power, the resulting deposition rate decreases at pressures above 20×10-3 mbar due to greater gas‐phase scattering. The [N]/[Ti] ratio in the deposited films, as determined by Rutherford backscattering and Auger electron spectroscopy, is found to be linearly correlated with the ratio of the optical emission intensities of excited N+2(391.4 nm) and Ti at 364.2 nm, I(N+2)/I(Ti). View full abstract»

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  • Plasma‐enhanced chemical vapor deposition of a‐SiC:H films from organosilicon precursors

    Page(s): 90 - 96
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    A study of the growth of a‐SiC:H films by plasma‐enhanced chemical vapor deposition (PECVD) from two organosilicon precursors, silacyclobutane (H2CH2SiCH2CH2 or SCB) and methylsilane (CH3SiH3), is described. A capacitively coupled, parallel plate PECVD system was used to grow films at 250 °C and deposition pressure of 2.0 Torr. Standard (13.56 MHz) and low frequency (0.125 MHz) rf sources were used to generate the deposition plasma. Depositions were performed with and without argon dilution (neat) of the precursor. We report some of the first process/property relationships for organosilicon based a‐SiC:H films grown using a fixed, controlled set of deposition conditions. Included are data on film composition, structure, dielectric constant and stress. Films deposited from silacyclobutane had much higher carbon concentrations than those deposited from methylsilane, but in both cases the carbon fraction in the film was lower than that in the precursor. It is found that the plasma drive frequency has a stronger influence on film composition than argon dilution of the precursor during deposition. The low frequency plasma significantly increases the film growth rate for the neat precursor process. Depending on the growth process, the relative dielectric constants of the a‐SiC:H films ranged from 3.6 to 8.7. The variation of the dielectric constant over the frequency range 0.1–1000 kHz was negligible. All measured film stress was compressive and ranged from 0.1 to 1.0 GPa depending on precursor and plasma frequency. Films deposited from a 10% organosilicon/90% argon mixture showed higher dielectric constants, higher refractive indices and less bound hydrogen when compared to neat organosilicon precursor depositions. The films exhibited excellent oxidation resistance and could not be etched in 6:1 buffered HF solutions. The properties of the a‐SiC- - :H films are compared to PECVD hydrogenated silicon nitride and discussed in the context of applications requiring low temperature deposited protective dielectric coatings.   View full abstract»

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  • Angular impact energy distributions of argon ions at the powered electrode of a helicon plasma source

    Page(s): 97 - 105
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    A radio frequency excited helicon plasma is generated by coupling externally generated electric and magnetic fields into the plasma confined by an axial magnetic field. The 13.56 MHz rf power provided via an antenna is varied between 100 and 500 W. The axial magnetic field strength is varied between 25 and 150 G. The substrate electrode is independently powered with 13.56 MHz radio frequency. A 100 μm orifice in the substrate electrode allows a small sample of argon ions bombarding the substrate electrode to enter a detection chamber. In the detection chamber a quadrupole mass spectrometer equipped with an energy filter is used to measure mass selected ion energy distributions and by tilting the quadrupole analyzer with the vertex lying in the orifice ion angular distributions are investigated. The ion energy distributions at the powered electrode mainly consist of either a single peak or they consist of the well known bimodal structure caused by rf splitting. For some source parameter a continuous energy distribution is detected for lower bombardment energies, which is interpreted as the result of scattering of ions with the background gas during their transport to the substrate electrode. The variation of the total flux intensities, the dc bias potentials, and the plasma potentials are evaluated and are interpreted as a result of mode transitions of the helicon plasma. The ion angular distributions are unstructured and show angular widths in the range between 2° and 3° full width at half‐maximum. Some aspects concerning the application of the source for semiconductor etching processes are discussed.   View full abstract»

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  • Metastable argon beam source using a surface wave sustained plasma

    Page(s): 106 - 113
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    A new source of metastable argon atoms in the thermal energy range is reported. The source is based on expanding a plasma sustained by electromagnetic surface waves in a quartz tube through a converging nozzle and extracting a beam from the supersonic free‐expansion jet. The beam was characterized by time‐of‐flight measurements which yielded the absolute intensity and velocity distribution of the argon metastables. The source produced a maximum intensity of 6.2×1014 metastables per second per steradian, the highest time‐averaged intensity of thermal argon metastables of any source reported to date. A simple picture of an expanding plasma in a recombination regime is used to explain the dependence of the metastable intensity on absorbed power. View full abstract»

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  • Characterization of electron cyclotyron resonance microwave plasma under critical configuration of magnetic field

    Page(s): 114 - 119
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    We have constructed a chemical vapor deposition/etching system consisting of a 2.45 GHz microwave generator (ASTeX S‐1000) and two movable coaxial magnetic coils. A unique rotatable planar Langmuir probe was designed to characterize the plasma. The Langmuir probe measurements showed an anisotropic character of the plasma which was mainly a result of the magnetic field gradient and propagation direction of the microwaves. By placing the coils at certain distances from the microwave window and adjusting the current through the coils, a critical condition was established, known as ‘‘high mode plasma.’’ In this high mode, the plasma ion density was more than four times that in the normal mode. The physical basis of the high mode involved placing the electron cyclotron resonance critical field (875 G) just in front of the microwave window with a positive magnetic field gradient toward the direction of microwave propagation. This condition produced a high absorption of microwave power and also prevented charged particles from escaping from the plasma. View full abstract»

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  • Deposition of gallium oxide and indium oxide on GaAs for in situ process use by alternating supply of TEGa, TMIn, and H2O2 as surge pulses

    Page(s): 120 - 124
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    Deposition of gallium oxide and indium oxide on GaAs (001) was investigated by the alternating supply of triethylgallium (TEGa) or trimethylindium (TMIn), and hydrogen peroxide (H2O2). A pressure‐control method was newly developed to produce precisely controlled surge pulses of source gases. Strong temperature dependence of the growth rate per source cycle obtained for the oxide deposition was caused by the decomposition of metalorganics, and by the thermal desorption of the oxide during the deposition. A critical thickness of 20 nm for the thermal desorption of gallium oxide was observed, which gives the upper limit of the promotive effect of underlying GaAs on thermal desorption of gallium oxide. With implications for in situ process use, deposition of GaAs on gallium oxides and on indium oxides was performed by chemical beam epitaxy, and the differences between the two oxides were discussed from the viewpoint of gallium‐atom‐induced desorption and selectivity for GaAs deposition. View full abstract»

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  • Improved heteroepitaxial growth of layered NbSe2 on GaAs (111)B

    Page(s): 125 - 129
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    Growth of layered NbSe2 has been carried out on a GaAs (111)B surface by molecular beam epitaxy (MBE). The optimum growth conditions to obtain high quality films were investigated by use of reflection high energy electron diffraction. Single crystalline films as thick as 100 nm were obtained when suitable surface treatment of the GaAs substrate was made with the interruption of the Nb beam or the use of a cracked Se beam. The factors determining the MBE growth of layered NbSe2 are also discussed.   View full abstract»

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  • Effects of plasma enhancement on the carrier‐gas‐free metalorganic chemical‐vapor deposition of oxide superconducting thin films

    Page(s): 130 - 134
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    The effect of plasma enhancement on carrier‐gas‐free metalorganic chemical vapor deposition of superconducting YBa2Cu3Ox films has been investigated based on crystallographic studies, plasma diagnosis, and composition analysis of the gas phase. With plasma enhancement, the oxygen pressure needed for growing thin films with YBa2Cu3Ox structure is reduced from 4.0×10-2 to 2.0×10-2 Pa. YBa2Cu3Ox films grown with plasma‐enhancement at oxygen pressure of 4.0×10-2 Pa showed zero resistivity at 86 K and a critical current density of 2×105 A/cm2 at 77 K. Plasma enhancement also was found to increase oxidizing activity by three orders of magnitude during the cooling process. Plasma diagnosis indicated that superconducting properties of grown films are related to plasma density, which can in turn be related to the concentration of active oxygen. Composition analysis of the gas phase indicated that plasma enhancement increases reaction between oxygen and metalorganic sources or their derivatives. The effect of plasma enhancement on oxidizing activity clearly differs between growth and the cooling process, and this difference may be due to the consumption of activated oxygen by metalorganic sources or their derivatives. View full abstract»

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  • Structural and morphological characterization of Nb2O5 thin films deposited by reactive sputtering

    Page(s): 135 - 139
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    Amorphous Nb2O5 thin films of three different thicknesses (10, 100, 400 nm) were deposited onto SiO2/Si substrates by reactive sputtering in an Ar–O2 plasma. Thermal treatments were performed at different temperatures between 500 and 1100 °C. The structural and morphological evolution with temperature is shown to be dependent on the film thickness. At 600 °C, the films essentially crystallize in the TT phase. On the thickest films, the T phase also appears. Annealing at higher temperature progressively increases the concentration of the T phase. The films show large flat grains extending over the whole film thickness. In addition, a large number of polyhedral bubbles is present in the 100 and 400 nm films due to Ar atoms trapped during sputtering. After annealing at 1100 °C the Ar bubbles are no longer present and partial diffusion of the films into the substrate is observed. The modification at high temperature, explained either by the M or the H phase, is favored on the thickest films and leads to plate shaped grains. View full abstract»

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  • Surface reconstructions of (001) CdTe and their role in the dynamics of evaporation and molecular‐beam epitaxy growth

    Page(s): 140 - 147
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    We present studies of the surface reconstruction and chemical analysis of the uppermost atomic layer of thick and thin (001) CdTe layers grown on (001) CdTe and ZnTe by (MBE). Techniques include reflection high energy electron diffraction and x‐ray photoelectron spectroscopy (XPS). All the surfaces obtained in the temperature range used (220–300 °C) in MBE are Cd covered with about 50% of undimerized Cd atoms; the peak of the Cd surface is clearly identified by XPS on thin CdTe layers. The surfaces can be (2×1), c(2×2) or (2×1)+c(2×2) reconstructed. Heating these surfaces above 300 °C leads to a (2×1) Te‐stabilized surface. A reversible transition occurs between this last surface and the mixed (2×1)+c(2×2) structure: thermal cycling between these two reconstructed surfaces induces the evaporation of half a monolayer per cycle. Tentative models to account for the results are presented and correlation between these results and the properties of the MBE layers is discussed. View full abstract»

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  • Mo–Si multilayer as soft x‐ray mirrors for the wavelengths around 20 nm region

    Page(s): 148 - 152
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    Molybdenum–silicon multilayer soft x‐ray mirrors have been fabricated using a magnetron sputtering system. Their structures have been characterized by x‐ray diffraction and reflectivities at normal incidence have been measured by using monochromatized synchrotron radiation in the 18–24 nm region. A normal incidence reflectivity as high as 40% at 20.8 nm was achieved. 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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G. Lucovsky
North Carolina State University