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

Issue 2 • Date Mar 2014

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Displaying Results 1 - 25 of 62
  • Phase transition characteristics under vacuum of 9,10-di(2-naphthyl)anthracene for organic light-emitting diodes

    Page(s): 020601 - 020601-4
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    The phase transition characteristics of 9,10-di(2-naphthyl)anthracene (ADN), an organic light emitting diode (OLED) material, are evaluated under vacuum. The phase transition is indicated by a plateau in the temperature curve of the ADN upon heating to its melting or sublimation temperature under pressure in a vacuum chamber. The melting temperature of the ADN at 1 atm pressure is verified by differential scanning calorimetry. The boiling temperature decreases by a few degrees as the vacuum chamber is evacuated from 1 atmosphere, and the material sublimes below 1 Torr. The sublimation temperature also decreases slightly as the pressure is lowered. Our results provide not only the optimal evaporation conditions for ADN but also information on the thermal stability of ADN and other types of organic materials for OLEDs under high vacuum. View full abstract»

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  • On the possibility to grow zinc oxide-based transparent conducting oxide films by hot-wire chemical vapor deposition

    Page(s): 020602 - 020602-5
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    Hot-wire chemical vapor deposition (HW-CVD) was applied to grow zinc oxide (ZnO)-based transparent conducting oxide (TCO) films. Indium (In)-doped ZnO films were deposited using a cold wall pulsed liquid injection CVD system with three nichrome wires installed at a distance of 2 cm from the substrate holder. The wires were heated by an AC current in the range of 0–10 A. Zn and In 2,2,6,6-tetramethyl-3,5-heptanedionates dissolved in 1,2-dimethoxyethane were used as precursors. The hot wires had a marked effect on the growth rates of ZnO, In-doped ZnO, and In2O3 films; at a current of 6–10 A, growth rates were increased by a factor of ≈10–20 compared with those of traditional CVD at the same substrate temperature (400 °C). In-doped ZnO films with thickness of ≈150 nm deposited on sapphire-R grown at a wire current of 9 A exhibited a resistivity of ≈2 × 10−3 Ωcm and transparency of >90% in the visible spectral range. These initial results reveal the potential of HW-CVD for the growth of TCOs. View full abstract»

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  • Fluorocarbon assisted atomic layer etching of SiO2 using cyclic Ar/C4F8 plasma

    Page(s): 020603 - 020603-4
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    The authors demonstrate atomic layer etching of SiO2 using a steady-state Ar plasma, periodic injection of a defined number of C4F8 molecules, and synchronized plasma-based Ar+ ion bombardment. C4F8 injection enables control of the deposited fluorocarbon (FC) layer thickness in the one to several Ångstrom range and chemical modification of the SiO2 surface. For low energy Ar+ ion bombardment conditions, the physical sputter rate of SiO2 vanishes, whereas SiO2 can be etched when FC reactants are present at the surface. The authors have measured for the first time the temporal variation of the chemically enhanced etch rate of SiO2 for Ar+ ion energies below 30 eV as a function of fluorocarbon surface coverage. This approach enables controlled removal of Ångstrom-thick SiO2 layers. Our results demonstrate that development of atomic layer etching processes even for complex materials is feasible. View full abstract»

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  • Evolution of morphology and structure of Pb thin films grown by pulsed laser deposition at different substrate temperatures

    Page(s): 020604 - 020604-5
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    Pb thin films were prepared by pulsed laser deposition on a Si (100) substrate at different growth temperatures to investigate their morphology and structure. The morphological analysis of the thin metal films showed the formation of spherical submicrometer grains whose average size decreased with temperature. X-ray diffraction measurements confirmed that growth temperature influences the Pb polycrystalline film structure. A preferred orientation of Pb (111) normal to the substrate was achieved at 30 °C and became increasingly pronounced along the Pb (200) plane as the substrate temperature increased. These thin films could be used to synthesize innovative materials, such as metallic photocathodes, with improved photoemission performances. View full abstract»

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  • Development of atomic layer deposition-activated microchannel plates for single particle detection at cryogenic temperatures

    Page(s): 020605 - 020605-5
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    Atomic layer deposition (ALD) technology is used to nanoengineer functional films inside the pores of microchannel plate (MCP) electron multipliers, enabling a novel MCP manufacturing technology that substantially improves performance and opens novel applications. The authors have developed custom tools and recipes for the growth of conformal films, with optimized conductance and secondary electron emission inside very long channels (∼6–20 μm diameter and >600 μm length, with tens of millions of channels per single MCP) by ALD. The unique ability to tune the characteristics of these ALD films enables their optimization to applications where time-resolved single particle imaging can be performed in extreme conditions, such as high counting rates at cryogenic temperatures. Adhesion of the conductive and emissive nanofilms to the 20 μm pore MCP glass substrates and their mechanical stability over a very wide range of temperatures (10–700 K) were confirmed experimentally. Resistance of ALD MCPs was reproducible during multiple cool-down cycles with no film degradation observed. Optimizing resistance of novel MCPs for operation at cryogenic temperature should enable high count rate event detection at temperatures below 20 K. View full abstract»

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  • Low-temperature CVD of iron, cobalt, and nickel nitride thin films from bis[di(tert-butyl)amido]metal(II) precursors and ammonia

    Page(s): 020606 - 020606-7
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    Thin films of late transition metal nitrides (where the metal is iron, cobalt, or nickel) are grown by low-pressure metalorganic chemical vapor deposition from bis[di(tert-butyl)amido]metal(II) precursors and ammonia. These metal nitrides are known to have useful mechanical and magnetic properties, but there are few thin film growth techniques to produce them based on a single precursor family. The authors report the deposition of metal nitride thin films below 300 °C from three recently synthesized M[N(t-Bu)2]2 precursors, where M = Fe, Co, and Ni, with growth onset as low as room temperature. Metal-rich phases are obtained with constant nitrogen content from growth onset to 200 °C over a range of feedstock partial pressures. Carbon contamination in the films is minimal for iron and cobalt nitride, but similar to the nitrogen concentration for nickel nitride. X-ray photoelectron spectroscopy indicates that the incorporated nitrogen is present as metal nitride, even for films grown at the reaction onset temperature. Deposition rates of up to 18 nm/min are observed. The film morphologies, growth rates, and compositions are consistent with a gas-phase transamination reaction that produces precursor species with high sticking coefficients and low surface mobilities. View full abstract»

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  • Critical review: Effects of complex interactions on structure and dynamics of supported metal catalysts

    Page(s): 020801 - 020801-17
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    This review article takes a new look at the problem of characterization of structural properties and reaction dynamics of supported metal catalysts. Such catalysts exhibit an inherent complexity, particularly due to interactions with the support and the adsorbate molecules, which can be highly sensitive to environmental conditions such as pressure and temperature. Recent reports demonstrate that finite size effects such as negative thermal expansion and large bond length disorder are directly caused by these complex interactions. To uncover the atomistic features underlying the reaction mechanisms and kinetics of metal catalysts, experimental characterization must accommodate the challenging operation conditions of catalytic processes and provide insights into system attributes. The combined application of x-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM) for this type of investigations will be examined, and the individual strengths and limitations of these methods will be discussed. Furthermore, spatial and temporal heterogeneities that describe real catalytic systems and can hinder their investigation by either averaging (such as XAS) or local (such as TEM) techniques alone will be addressed by conjoined, multiscale, ab initio density functional theory/molecular dynamics modeling of metal catalysts that can both support and guide experimental studies. When taken together, a new analysis scheme emerges, in which different forms of structure and dynamics can be fully characterized by combining information obtained experimentally by in situ XAS and electron microscopy as well as theoretically via modeling. View full abstract»

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  • Controlled ambient and temperature treatment of InGaZnO thin film transistors for improved bias-illumination stress reliability

    Page(s): 021101 - 021101-6
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    The failure mechanisms arising from the instability in operation of indium gallium zinc oxide based thin film transistors (TFTs) upon prolonged real application stresses (bias and illumination) have been extensively studied and reported. Positive and negative gate bias conditions, along with high photonic energy wavelengths within visible light spectrum are used as stress conditions. The increased carrier concentration due to photonic excitation of defects within bandgap and ionization of deep level vacancies is compensated by the reduction in off currents under illumination due to the trapping of carriers in the intermetal dielectric. Band lowering at the source-channel junction due to accumulation of negative carriers repelled due to negative gate bias stress further causes high carrier flow into the channel and drives the devices into failure. The defect identification during failure and degradation assisted in proposing suitable low temperature post processing in specific ambients. Reliability tests after specific anneals in oxygen, vacuum, and forming gas ambients confirm the correlation of the defect type with anneal ambient. Annealed TFTs demonstrate high stabilities under illumination stresses and do not fail when subjected to combined stresses that cause failure in as-fabricated TFTs. Oxygen and forming gas anneals are impactful on the reliability and opens an area of study on donor and vacancy behavior in amorphous mixed oxide based TFTs. The subthreshold swing, field-effect mobilities, and off currents provide knowledge on best anneal practices by understanding role of hydrogen and oxygen in vacancy annihilation and transistor switching properties. View full abstract»

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  • Novel method for the prediction of an interface bonding species at alumina/metal interfaces

    Page(s): 021102 - 021102-8
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    Interface bonding between alumina and various metals is discussed from the viewpoint of chemical thermodynamics. A method to predict the interface bonding species at an alumina/metal interface under equilibrium conditions is proposed by using the concept of chemical equilibrium for interface termination. The originality of this method is in the way a simple estimation of the interface binding energy, which is generally applicable to most metals, is developed. The effectiveness of this method is confirmed by careful examination of the experimental results. Comparison of the predicted and experimentally observed interface terminations reveals that the proposed method agrees well with the reported results. The method uses only basic quantities of pure elements and the formation enthalpy of oxides. Therefore, it can be applied to most metals in the periodic table and is useful for screening materials in the quest to develop interfaces with particular functions. View full abstract»

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  • Second-harmonic intensity and phase spectroscopy as a sensitive method to probe the space-charge field in Si(100) covered with charged dielectrics

    Page(s): 021103 - 021103-9
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    A space-charge region (SCR) can develop in silicon due to the presence of built-in charges in dielectric thin films that are used in silicon-based device architectures. To study both the strength and polarity of the electric field in such a SCR, the authors performed second-harmonic (SH) generation spectroscopy in the vicinity of the E1 critical point (2.7–3.5 eV) of silicon. As multiple contributions add coherently to SH intensity spectra, the electric-field-induced contribution cannot always be distinguished unambiguously from the intensity data in the absence of complementary phase information. Combined SH intensity and phase measurements were therefore performed to resolve this ambiguity. Using a coherent superposition of critical-point-like resonances with excitonic line shapes, the intensity and phase spectra of several SiO2- and Al2O3-based samples were simultaneously modeled. This analysis reveals that not only the polarity of the space-charge field can be determined unambiguously but also that the sensitivity to the electric field strength is significantly enhanced. View full abstract»

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  • Determination of subband energies and 2DEG characteristics of AlxGa1−xN/GaN heterojunctions using variational method

    Page(s): 021104 - 021104-8
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    A physics-based model based on the variational method for analyzing the two dimensional electron gas (2DEG) characteristics of polar AlGaN/GaN heterojunctions is developed. The 2DEG carrier concentration, the first and second energy subbands, and the position of the Fermi energy level are calculated for various barrier thicknesses, Al mole fractions, background dopant concentrations, and gate voltages for gated AlGaN/GaN heterojunctions. The results are in good agreement with the data reported based on self-consistent method. Whereas the aforementioned report has dealt with specific values of Al mole fraction, barrier thickness, and unintentional doping level, the present work provides a basis for calculating the 2DEG characteristics for the full range of these parameters. Furthermore, according to the proposed model, the applicability of the triangular approximation of the quantum well in AlGaN/GaN heterojunctions is evaluated. View full abstract»

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  • Self limiting deposition of pyrite absorbers by pulsed PECVD

    Page(s): 021201 - 021201-9
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    Self-limiting growth of pyrite thin films was accomplished by pulsed plasma-enhanced chemical vapor deposition (PECVD) with continuous delivery of iron pentacarbonyl diluted in a mixture of H2S and argon. The growth rate per cycle was controlled between 0.1 and 1 Å/pulse by adjusting the duty cycle and/or plasma power. The onset of thermal chemical vapor deposition was identified at ∼300  °C, and this process resulted in films containing substoichiometric pyrrhotite. In contrast, pulsed PECVD produced stoichiometric FeS2 films without the need for postdeposition sulfurization. Films contained a mixture of pyrite and marcasite, though the latter could be attenuated using a combination of high duty cycle, low temperature, and low plasma power. Pulsed PECVD films displayed similar optical properties with a band gap of ∼1 eV and an absorption coefficient of ∼105 cm−1, regardless of the pyrite:marcasite ratio. View full abstract»

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  • Highly transparent Nb-doped indium oxide electrodes for organic solar cells

    Page(s): 021202 - 021202-7
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    The authors investigated the characteristics of Nb-doped In2O3 (INbO) films prepared by co-sputtering of Nb2O5 and In2O3 for use in transparent anodes for organic solar cells (OSCs). To optimize the Nb dopant composition in the In2O3 matrix, the effect of the Nb doping power on the resistivity and transparency of the INbO films were examined. The electronic structure and microstructure of the INbO films were also investigated using synchrotron x-ray absorption spectroscopy and x-ray diffraction examinations in detail. At the optimized Nb co-sputtering power of 30 W, the INbO film exhibited a sheet resistance of 15 Ω/sq, and an optical transmittance of 86.04% at 550 nm, which are highly acceptable for the use as transparent electrodes in the fabrication of OSCs. More importantly, the comparable power conversion efficiency (3.34%) of the OSC with an INbO anode with that (3.31%) of an OSC with a commercial ITO anode indicates that INbO films are promising as a transparent electrode for high performance OSCs. View full abstract»

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  • MD simulations of low energy Clx+ ions interaction with ultrathin silicon layers for advanced etch processes

    Page(s): 021301 - 021301-7
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    Molecular dynamics simulations of low-energy (5–100 eV) Cl+ and Cl2+ bombardment on (100) Si surfaces are performed to investigate the impact of plasma dissociation and very low-energy ions (5–10 eV) in chlorine pulsed plasmas used for silicon etch applications. Ion bombardment leads to an initial rapid chlorination of the Si surface followed by the formation of a stable SiClx mixed layer and a constant etch yield at steady state. The SiClx layer thickness increases with ion energy (from 0.7 ± 0.2 nm at 5 eV to 4 ± 0.5 nm at 100 eV) but decreases for Cl2+ bombardment (compared to Cl+), due to the fragmentation of Cl2+ molecular ions into atomic Cl species with reduced energies [one X eV Cl + <−> two 2X eV Cl2+]. The Si etch yield is larger for Cl2+ than Cl+ bombardment at high-energy (Ei > 25 eV) but larger for Cl+ than Cl2+ bombardment at low-energy (Ei < 25 eV) due to threshold effects. And the higher the ion energy, the less saturated the etch products. Results suggest that weakly dissociated chlorine plasmas (containing more Cl2+ than Cl+ ions) should lead to thinner SiClx mixed layers and lower Si etch yields if ion energies remains below 25 eV, which confirms the potential of pulsed plasmas to address etching challenges of ultrathin films transistors, in which slow etch rates and very controlled processes are required. View full abstract»

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  • Plasma damage mechanisms in low k organosilicate glass and their inhibition by Ar ion bombardment

    Page(s): 021302 - 021302-7
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    In-situ x-ray photoelectron spectroscopy and ex-situ Fourier transform infrared spectroscopy studies of vacuum ultraviolet (VUV) photons with or without O2, and O radicals point to distinct mechanisms of carbon abstraction in nanoporous organosilicate glass (OSG) films. VUV alone in the absence of O2 results in Si-CH3 bond scission and recombination preferentially at silicon monomethyl sites, obeying diffusion kinetics. In contrast, the presence of O2 interferes with recombination, resulting in diffusion-dominated carbon loss kinetics, enhanced Si oxidation, and greatly accelerating the rate of carbon loss in both the near surface and bulk regions of the OSG, at both monomethyl and dimethyl sites. Carbon abstraction due to exposure to (O(3P)) does not follow diffusion kinetics, and such interactions yield a SiO2-like surface layer inhibiting further O diffusion. Results indicate that diffusion-dominated carbon abstraction kinetics previously observed for OSG exposure to O2 plasma damage is primarily attributable to the diffusion of O2 down OSG nanopores, reacting at photoactivated sites, rather than the diffusion of O radicals. OSG pretreatment by 900 eV Ar+ bombardment effectively inhibits both VUV + O2 and O damage mechanisms by formation of ∼1 nm thick SiO2-like surface region that inhibits both O and O2 diffusion. View full abstract»

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  • Modeling of inductively coupled plasma SF6/O2/Ar plasma discharge: Effect of O2 on the plasma kinetic properties

    Page(s): 021303 - 021303-10
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    A global model has been developed for low-pressure, inductively coupled plasma (ICP) SF6/O2/Ar mixtures. This model is based on a set of mass balance equations for all the considered species, coupled with the discharge power balance equation and the charge neutrality condition. The present study is an extension of the kinetic global model previously developed for SF6/Ar ICP plasma discharges [Lallement et al., Plasma Sources Sci. Technol. 18, 025001 (2009)]. It is focused on the study of the impact of the O2 addition to the SF6/Ar gas mixture on the plasma kinetic properties. The simulation results show that the electron density increases with the %O2, which is due to the decrease of the plasma electronegativity, while the electron temperature is almost constant in our pressure range. The density evolutions of atomic fluorine and oxygen versus %O2 have been analyzed. Those atomic radicals play an important role in the silicon etching process. The atomic fluorine density increases from 0 up to 40% O2 where it reaches a maximum. This is due to the enhancement of the SF6 dissociation processes and the production of fluorine through the reactions between SFx and O. This trend is experimentally confirmed. On the other hand, the simulation results show that O(3p) is the preponderant atomic oxygen. Its density increases with %O2 until reaching a maximum at almost 40% O2. Over this value, its diminution with O2% can be justified by the high increase in the loss frequency of O(3p) by electronic impact in comparison to its production frequency by electronic impact with O2. View full abstract»

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  • Comparison of surface vacuum ultraviolet emissions with resonance level number densities. I. Argon plasmas

    Page(s): 021304 - 021304-11
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    Vacuum ultraviolet (VUV) photons emitted from excited atomic states are ubiquitous in material processing plasmas. The highly energetic photons can induce surface damage by driving surface reactions, disordering surface regions, and affecting bonds in the bulk material. In argon plasmas, the VUV emissions are due to the decay of the 1s4 and 1s2 principal resonance levels with emission wavelengths of 104.8 and 106.7 nm, respectively. The authors have measured the number densities of atoms in the two resonance levels using both white light optical absorption spectroscopy and radiation-trapping induced changes in the 3p54p→3p54s branching fractions measured via visible/near-infrared optical emission spectroscopy in an argon inductively coupled plasma as a function of both pressure and power. An emission model that takes into account radiation trapping was used to calculate the VUV emission rate. The model results were compared to experimental measurements made with a National Institute of Standards and Technology-calibrated VUV photodiode. The photodiode and model results are in generally good accord and reveal a strong dependence on the neutral gas temperature. View full abstract»

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  • Fabrication of tapered graded-refractive-index micropillars using ion-implanted-photoresist as an etch mask

    Page(s): 021305 - 021305-5
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    Thermally reflowed photoresist is used as an etch mask in inductively coupled plasma reactive ion etching of dielectric graded-refractive-index (GRIN) coatings. The coatings have varying compositions of TiO2 and SiO2 and are used to fabricate GRIN micropillars with tapered sidewalls. The effects of ion implantation on the dry-etch-resistance of photoresist are investigated for Si, N, and Ar ion implantation. Compared with the unimplanted photoresist, the implanted photoresists show enhanced dry-etch-resistance under fluorine chemistry (CHF3 and O2). The etch rate of the Si-implanted photoresist is 72% lower than that of the unimplanted photoresist. The measured depth of modification of the photoresist is in good agreement with the trend predicted by ion-implantation-simulation software. Using Si-implanted photoresist as an etch mask, five-layer GRIN micropillars with tapered sidewalls are fabricated. View full abstract»

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  • Role of the blocking capacitor in control of ion energy distributions in pulsed capacitively coupled plasmas sustained in Ar/CF4/O2

    Page(s): 021306 - 021306-12
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    In plasma etching for microelectronics fabrication, the quality of the process is in large part determined by the ability to control the ion energy distribution (IED) onto the wafer. To achieve this control, dual frequency capacitively coupled plasmas (DF-CCPs) have been developed with the goal of separately controlling the magnitude of the fluxes of ions and radicals with the high frequency (HF) and the shape of the IED with the low frequency (LF). In steady state operation, plasma properties are determined by a real time balance between electron sources and losses. As such, for a given geometry, pressure, and frequency of operation, the latitude for controlling the IED may be limited. Pulsed power is one technique being investigated to provide additional degrees of freedom to control the IED. In one configuration of a DF-CCP, the HF power is applied to the upper electrode and LF power is applied to the lower electrode which is serially connected to a blocking capacitor (BC) which generates a self dc-bias. In the steady state, the value of the dc-bias is, in fact, constant. During pulsed operation, however, there may be time modulation of the dc-bias which provides an additional means to control the IED. In this paper, IEDs to the wafer in pulsed DF-CCPs sustained in Ar/CF4/O2 are discussed with results from a two-dimensional plasma hydrodynamics model. The IED can be manipulated depending on whether the LF or HF power is pulsed. The dynamic range of the control can be tuned by the dc-bias generated on the substrate, whose time variation depends on the size of the BC during pulsed operation. It was found that high energy ions can be preferentially produced when pulsing the HF power and low energy ions are preferentially produced when pulsing the LF power. A smaller BC value which allows the bias to follow the change in charged particle fluxes produces a larger dynamic range with which to control IEDs. View full abstract»

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  • Process monitoring during AlNxOy deposition by reactive magnetron sputtering and correlation with the film's properties

    Page(s): 021307 - 021307-10
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    In this work, AlNxOy thin films were deposited by reactive magnetron sputtering, using an aluminum target and an Ar/(N2+O2) atmosphere. The direct current magnetron discharge parameters during the deposition process were investigated by optical emission spectroscopy and a plasma floating probe was used. The discharge voltage, the electron temperature, the ion flux, and the optical emission lines were recorded for different reactive gas flows, near the target and close to the substrate. This information was correlated with the structural features of the deposits as a first step in the development of a system to control the structure and properties of the films during reactive magnetron sputtering. As the target becomes poisoned, the discharge voltage suffers an important variation, due to the modification of the secondary electron emission coefficient of the target, which is also supported by the evolution of the electron temperature and ion flux to the target. The sputtering yield of the target was also affected, leading to a reduction of the amount of Al atoms arriving to the substrate, according to optical emission spectroscopy results for Al emission line intensity. This behavior, together with the increase of nonmetallic elements in the films, allowed obtaining different microstructures, over a wide range of compositions, which induced different electrical and optical responses of films. View full abstract»

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  • TOF SIMS analysis and generation of white photoluminescence from strontium silicate codoped with europium and terbium

    Page(s): 021401 - 021401-6
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    White light emitting terbium (Tb3+) and europium (Eu3+) codoped strontium silicate (Sr2SiO4) phosphors were prepared by a solid state reaction process. The structure, particle morphology, chemical composition, ion distribution, photoluminescence (PL), and decay characteristics of the phosphors were analyzed by x-ray diffraction (XRD), scanning electron microscopy (SEM), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and PL spectroscopy, respectively. The XRD data showed that our Sr2SiO4 composed of two phases, namely, β-Sr2SiO4 and α′-Sr2SiO4, and the α′-Sr2SiO4 phase was more prominent than the β-Sr2SiO4 phase. The SEM micrographs showed that the particles were agglomerated together and they did not have definite shapes. All ions (i.e., negative and positive) present in our materials were identified by TOF-SIMS. In addition, the chemical imaging performed with the TOF-SIMS demonstrated how the individual ions including the dopants (Eu3+ and Tb3+) were distributed in the host lattice. White photoluminescence was observed when the Sr2SiO4:Tb3+, Eu3+ phosphor was excited at 239 nm using a monochromatized xenon lamp as the excitation source. The phosphor exhibited fast decay lifetimes implying that it is not a good candidate for long afterglow applications. View full abstract»

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  • Chemical mechanical planarization of gold

    Page(s): 021402 - 021402-5
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    In this article, the authors investigate chemical mechanical planarization (CMP) of gold. Our experiments show that the oxidizer concentration, hardness of the adhesion layer, and surfactants added to stabilize the slurry are the main factors determining the outcome of the process. A combination of 30% H2O2 solution and an alumina based slurry in 1:3 volumetric ratio along with added sodium dodecyl sulfate and poly(vinyl pyrrolidone) was successfully used to pattern gold in a CMP Damascene process. After fabricating inlaid gold structures with CMP, the authors observed that pattern density, as opposed to feature size, is the major factor in determining the amount of metal thinning in inlaid features. 10 μm lines at 5% density were thinned down by 40 nm, while 150 μm pads at 75% density were recessed by 20 nm. The authors believe that in this process, metal recess, that is a chemical effect, outweighs dishing, a feature-size dependent factor, in controlling the severity of metal thinning. View full abstract»

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  • Reactive sputtering of substoichiometric Ta2Ox for resistive memory applications

    Page(s): 021501 - 021501-6
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    A major class of resistive memory devices is based on transition metal oxides, where mobile oxygen vacancies allow these devices to exhibit multiple resistance states. Ta2O5 based devices in particular have recently demonstrated impressive endurance and forming-free results. Deposition of substoichiometric Ta2Ox (x < 5) films is a critical process in order to produce the required oxygen vacancies in these devices. This paper describes a physical vapor deposition (PVD) reactive sputtering process to deposit substoichiometric Ta2Ox films. The desired film stoichiometry is achieved by feedback control of the oxygen partial pressure in the PVD chamber. A calibration procedure based on Rutherford backscattering spectroscopy is described for locating the optimum oxygen partial pressure. View full abstract»

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  • Properties of zinc oxide films grown on sapphire substrates using high-temperature H2O generated by a catalytic reaction on platinum nanoparticles

    Page(s): 021502 - 021502-5
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    The authors investigated the characteristics of ZnO films grown on a-plane (11-20) sapphire substrates at 773–873 K using a reaction between dimethylzinc and high-temperature H2O generated by a catalytic reaction on Pt nanoparticles. The growth rate was 0.02–0.07 μm min−1. The largest electron mobility and the smallest residual carrier concentration for the ZnO films were 169 cm2 V−1 s−1 and 1.6 × 1017 cm−3, respectively. X-ray diffraction patterns for the ZnO films exhibited intense (0002) and (0004) peaks associated with ZnO (0001) planes. The minimum full width at half maximum of the ω-rocking curve for ZnO (0002) was less than 0.1°. In a ZnO film with a high electron mobility, no rotational domains were identified using a ZnO (10-10) ϕ scan. From secondary ion mass spectroscopy, a hydrogen concentration of 3 × 1018 cm−3 and a boron concentration of 2–5 × 1017 cm−3 were determined. These were identified as extrinsic donor impurities. View full abstract»

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  • Mechanical and transparent conductive properties of ZnO and Ga-doped ZnO films sputtered using electron-cyclotron-resonance plasma on polyethylene naphtalate substrates

    Page(s): 021503 - 021503-7
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    Transparent conductive ZnO and Ga-doped ZnO (GZO) films were deposited on polyethylene naphtalate (PEN) sheet substrates using electron cyclotron resonance plasma sputtering. Both ZnO and GZO films were highly adhesive to the PEN substrates without inserting an intermediate layer in the interface. When compared at the same thickness, the transparent conductive properties of GZO films on PEN substrates were only slightly inferior to those on glass substrates. However, the carrier concentration of ZnO films on PEN substrates was 1.5 times that of those on glass substrates, whereas their Hall mobility was only 60% at a thickness of 300 nm. The depth profile of elements measured by secondary ion mass spectroscopy revealed the diffusion of hydrocarbons out of the PEN substrate into the ZnO film. Hence, doped carbons may act as donors to enhance carrier concentration, and the intermixing of elements at the interface may deteriorate the crystallinity, resulting in the lower Hall mobility. When the ZnO films were thicker than 400 nm, cracks became prevalent because of the lattice mismatch strain between the film and the substrate, whereas GZO films were free of cracks. The authors investigated how rolling the films around a cylindrical pipe surface affected their conductive properties. Degraded conductivity occurred at a threshold pipe radius of 10 mm when tensile stress was applied to the film, but it occurred at a pipe radius of 5 mm when compressive stress was applied. These values are guidelines for bending actual devices fabricated on PEN substrates. View full abstract»

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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