bluuebunny/crossref_metadata_2025 huggingface dataset:
A Numerical Model for Hot-Wire Chemical Vapor Deposition of Amorphous Silicon
Authors: Goodwin D. G.
Published: April 2011

A Direct Simulation Monte Carlo numerical model for hot-wire CVD is described that includes detailed gas-phase chemistry and accurately models gas-phase transport, from the low-pressure ballistic regime to the high-pressure diffusive regime. Model predictions for an idealized reactor geometry are shown to agree qualitatively with experimental trends.
Dependence of Image Transient Behavior on Operating Parameters of Amorphous Silicon Image Sensors
Authors: Aflatooni Koorosh , Weisfield Richard , Zhong Fan , Bornstein Jon , Hack Mike , Gomcz Carlos
Published: April 2011

The growing interests for real-time applications of our amorphous silicon X-ray image sensors requires a better understanding of transient behavior in imaging characteristics. In our pixel structure, which consists of a p-i-n photodiode and an addressing thin film transistor (TFT), the image lag can stem from a number of mechanisms, including charge retention on the photodiode, TFT charge transfer efficiency, and data-line charge sharing. The exact prevailing mechanism depends on the array design and the operating conditions of the sensors. This paper describes the results of our systematic studies on image lag, and its dependence on various operating conditions of the image sensors, such as applied bias, light intensity, frame time, and applied gate voltages. We find that the charge retention in the intrinsic region of the photodiode is an important source of the image lag, and it is correlated to the forward transient characteristics of the diode. This correlation can be explained by the common underlying mechanisms leading to depletion region formation and charge transport through the diode. Furthermore, we notice that the time dependent decay of the image lag, originated mainly from charge retention in the diode, presents power-law time dependence, which is consistent with the release of trapped charges from a continuous distribution of defect states. We also find only a small variation in the image lag, <%3, for a wide range of gate on-periods, 10μs-80μs, and gate on-voltages, 15V- 30V, which indicates an efficient charge transfer by the switching TFT. These results demonstrate that in our devices, the image lag is controlled by the intrinsic defect levels in the a-Si:H photodiode.
Photoinduced Space Charge Effects in a-Si:H Solar Cells
Authors: Unold T. , Binnewies T. , Brüggemann R. , Bauer G.H.
Published: April 2011

We have investigated charge collection in thin amorphous silicon solar cells under light bias illumination, both experimentally and by numerical simulation. In such charge collection experiments, space charge due to trapped bias-light generated carriers leads to an enhancement of a small signal probe beam charge collection. It is found that this enhancement of the small signal charge collection is strongly dependent on the diode thickness and the defect density in the samples. In particular for thin diodes (d < 0.5 microns) the charge collection enhancement can be shown to increase with light-induced degradation of the devices. The effect of these material parameters as well as other experimental parameters, such as light bias and probe beam photon flux, will be demonstrated by means of numerical simulation.
Artificial Formation of Nucleation Seed in Excimer Laser Recrystallization Of Poly-Si
Authors: Jeon Jae-Hong , Park Kee-Chan , Kang Ji-Hoon , Lee Min-Cheol , Han Min-Koo
Published: April 2011

ABSTARCT

Excimer laser annealing method employing artificial nucleation seed is proposed to increase the grain size of polycrystalline silicon(poly-Si). We utilize Si component incorporated in aluminum(Al)-sputtering source for the nucleation seed. Si clusters which are to be used as nucleation seed are successfully formed on the substrate by deposition and etch-back of Si-incorporated Al layer. Irradiation of excimer laser on amorphous silicon(a-Si) film deposited on the substrate prepared by our method results in enlargement of poly-Si grains, compared with conventional laser recrystallization. Poly-Si thin film transistor also shows much improved electrical perfbrmance which directly reflects the quality of poly-Si film recrystallized by our method.
From A Reaction Mechanism to New PPV'S for High Performance Polymer-Leds
Authors: Spreitzer H. , Becker H. , Kreuder W. , Kluge E. , Schenk H.
Published: April 2011

Poly(p-phenylene vinylene)s (PPVs) are very promising materials for optoelectronic applications, especially for displays based on polymer light emitting diodes (PLEDs). We report here our findings concerning defect structures in this materials and the influence of the discovered irregularities on an important property of the materials, i.e. the operational life in a PLED. Recent improvements, which were deviated from this findings are presented: optimized PPVs with a lower amount of defects result in a strong increase of operational lifetime.
Jet Printing of Copper Lines at 200°C Maximum Process Temperature
Authors: Hong C.M. , Wagner S.
Published: April 2011

We describe a new technique for making copper lines by printing a precursor pattern that is converted to copper, at a maximum process temperature of 200°C. We formed copper metallization patterns on 80 μm thick Coming 0211 glass substrates by jet printing. Continuous lines of copper with resistivity of 10 μΩcm have been obtained. We successfully applied this technique to the direct printing of copper source and drain contacts for amorphous silicon thinfilm transistors. The TFTs are bottom gate back-channel etched structures, with the silicon stack made by RF excited PE-CVD. The TFT process uses only printing for all masking steps, by employing laser-printed toner etch masks, and using the printed copper as the mask for the back channel etch. The transistor ON/OFF current ratio is 105. The process for copper printing represents a further step toward an all-printed TFT technology.
Polymer Leds Based on N-Alkylsulfinyl Ppv Precursor Polymers
Authors: Kiebooms R. , Resel R. , Vanderzande D. , Leising G.
Published: April 2011

A new class of precursor polymers, as first described by Louwet et al. [1], was used to make organic LEDs. Device properties are relatively independent from the side chain to be eliminated. However introduction of two methyl groups onto the phenyl ring introduces significant changes in absorption, photoluminescence (PL) emission, PL quantum efficiency and electroluminescence spectra. From XRD there is an indication that this effect might be related to a different packing of the polymer chains.
Improved electroluminescence lifetime and efficiency of polymer light- emitting diodes with plasma-treated indium tin oxide anodes
Authors: Kim J. S. , Friend R. H. , Cacialli F.
Published: April 2011

We studied the influence of various surface treatments of indium-tin oxide anodes on the operational stability of high-efficiency green-emitting polymer light-emitting diodes, fabilicated with a doped poly(3,4-ethylene dioxythiophene) PEDOT hole transport layer, a polyfluorene-based emissive layer, and Ca-Al cathodes. The anodes were modified by physical (oxygen-plasma), chemical (aquaregia), or combined treatments. Oxygen-plasma improves the stability under constant current over all the other anodes, with half-brightness lifetimes (initial brightness, 200 cd/m2) two to five times longer than for untreated samples, and 1000 times longer than for aquaregia ones. We derive two major indications for optimisation of PLEDs. First, thermal management of the diode is of the uppermost importance. Second, the ITO anode and in general the electrical properties of the hole-injecting contact are crucial to device operation, even in the presence of a hole transport layer.
Energy Level Alignment at Tpd/Etal Interfaces Studied by Kelvin Method
Authors: Hayashi N. , Ito E. , Ishii H. , Ouchi Y. , Seki K.
Published: April 2011

The vacuum level shift A was determined by Kelvin probe method for TPD/metal systems prepared in ultrahigh vacuum (TPD: N, N'-bis(3-methylphenyl)-N, N'-diphenyl-[1, 1'-biphenyl]-4,4'-diamine). The energy of the vacuum level sharply changed at the initial stage of depositing TPD on the metal substrates, and further bending was not observed up to 100 nm thickness of TPD. This result is consistent with our previous studies of ultraviolet photoelectron spectroscopy. These results indicate the invalidity of traditional model with a common vacuum level at organic/metal interface. We discussed the dependence of the vacuum level shift on the work function Φm of the metal substrate (Au, Cu, Ag, Mg, and Ca). A liner correlation between Δ and Φm was observed only in the region of 3.8 eV < Φm < 4.5 eV, indicating that Fermi level alignment is not achieved at least for some interfaces. We found that Δ for TPD film on the air-exposed metal substrate is smaller than that of TPD on clean metals and was observed a liner relation between Φm and Δ except for the Cu substrate.
1.5 μm Luminescence from ErQ Based Organic Light Emitting Diodes
Authors: Curry R.J. , Gillin W.P.
Published: April 2011

Organic light emitting diodes have been fabricated using erbium tris(8-hydroxy-quinoline) as the emitting layer and N, N'-diphenyl-N, N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) as the hole transporting layer. Room temperature electroluminescence was observed at 1.5 μm due to intra-atomic transitions between the 4I13/2 and 4I15/2 levels in the Er3+, ion. These results make the possibility of producing silicon compatible 1.5 μm technology based on such devices a reality.
Frequency Resolved Photoluminescence (PL), Delayed Fluorescence and Triplet-Triplet Annihilation in Φ-Conjugated Polymers
Authors: Partee J. , Frankevich E. L. , Uhlhorn B. , Shinar J. , Ding Y. , Barton T. J.
Published: April 2011

The delayed fluorescence of poly(p-phenylene vinylene) (PPV) and poly(p-phenylene ethynylene) (PPE) derivative solids and frozen solutions at 20 K is described. It provides strong evidence for triplet-triplet annihilation to singlets excitons accounting for up to ∼3% of the total emission in PPV films and ∼1.5% in PPE powder. It also yields triplet lifetimes of 70 and 110 μs in PPV films and frozen solutions, and ∼200 and ∼500 μs in PPE powder and frozen solutions, respectively.
The Physics of Organic Light-Emitting Devices
Authors: Scott J. Campbell , Malliaras George G. , Bozano Luisa , Carter Sue A. , Ramos Sergio
Published: April 2011

Qualitatively, the basic principles behind the operation of OLEDs are well established. In order to optimize device parameters such as power efficiency and operating voltage, to explore the limits of performance and to understand changes in the electrical properties as diodes age, it is necessary to develop a quantitative understanding of each of the relevant processes: injection of electrons and holes at the cathode and anode, charge transport, recombination and exciton formation, and emission. In this paper, we summarize our experimental, theoretical and numerical studies to address these issues.
Properties of Si/Cs/O nanocluster thin films with negative electron affinity
Authors: Dinh L. N. , McLean W. , Schildbach M. A. , Balooch M.
Published: April 2011

Thin films of Si/Cs/O nanoclusters have been synthesized by the technique of supersaturated thermal vaporization of Si and Cs in an oxygen background gas. These films, which were deposited onto conducting or semiconducting substrates, exhibit negative electron affinity (NEA) as evidenced by ultraviolet photoemission spectroscopy (UPS). Photo and field electron emission properties of these nanocluster films were investigated with photo-electron emission microscopy (PEEM), field electron emission microscopy (FEEM), and current-voltage measurements. Flat cathodes covered with thin films of Si/Cs/O nanoclusters exhibited high current outputs and low turn-on fields. The films' NEA is unaffected by air exposure and is stable to high temperature annealing (550 TC). A field emission display unit with a simple diode structure containing a flat cathode coated with a patterned thin film of Si/Cs/O nanoclusters has also been built to demonstrate the potential application of this material in cold cathode electron emitting devices, particularly field emission flat panel displays.
High Current Field Emission from ZrC with Differing Cone Angles
Authors: Mackie W. A. , Xie Tianbao , Lee K.S. , McCalluma A.T. , Kirby M.J. , Davis P. R.
Published: April 2011

We briefly report on progress in forming field emitter array (FEA) cones from zirconium carbide. The major advances are on high current emission from single carbide emitters. These unique carbide materials have electron emission properties making them attractive for several applications. These could include video displays, microwave applications, high current and small spot electron sources (accelerators and FELs) and for operation at tube pressures or in poor vacuums (FEAs, vacuum detectors, neutralizing beams for ion thrusters, and charge dissipation on spacecraft).

The significant recent outcomes are in high current electron emission from single emitters with and without extraction apertures. A new processing technique has been developed to allow in-situ sharpening of arced emitters. This method also yields large emitter-cone half angles yet preserves the small emitter radii of electrochemically etched emitters. So far, this geometry translates into currents as high as 15 mA dc, the highest yet measured from single emitters, and enhanced beam confinement. This geometry may also lead to new considerations in forming transition metal carbide emitter cones for FEAs.
Defect and Raman Spectroscopy of Chemical Vapor Deposition Grown Diamond Films
Authors: Perez J.M. , Stallcup R.E. , Akwani I.A.
Published: April 2011

Using photoelectron emission and Raman spectroscopy, we characterize normally unoccupied states that have an energy 2.41-2.71 eV below the conduction band of polycrystalline diamond films. The films are grown using chemical vapor deposition with methane to hydrogen gas concentrations of 0.10%, 0.20%, 0.30%, 0.45%, 0.60% and 0.70%. Photoelectron emission is performed using visible light from an argon laser. The light is focussed on a 5-10 µm diameter area of the sample. The emitted electrons are collected with high efficiency using a microchannel plate detector. Raman spectroscopy is performed simultaneously with photoelectron emission to determine the morphology and diamond versus graphite content of the photoelectron emission area. The photoelectron emission rate is observed to have a quadratic dependence on the incident light power showing that the photoelectron emission process is a two-photon process involving the excitation of electrons from normally unoccupied states. The photoelectric yield versus incident photon energy, and the photoelectric yield as a function of methane concentration are presented.
Analysis of Measured I(V) Relations for Electron Emission from Insulating Diamond Films on Various SI Substrates
Authors: Jensen K. L. , Göhl A. , Müller G.
Published: April 2011

In this work, we shall analyze the performance of a geometrical interface roughness model to estimate current from p-type silicon into insulating diamond and compare the performance of that model to experimental data. A minimum number of adjustable parameters are invoked. While the model qualitatively accounts for trends in the experimental data, in particular, the shift from negative to positive slope on a Fowler Nordheim plot of the I(V) data, it does so at the expense of demanding ellipsoid parameters that appear to be unreasonable. We therefore conclude that a simple geometrical field enhancement model of interface roughness is insufficient to account for the current observed, and thus the theory must be augmented by a more comprehensive electron transport model at the interface.
Intense UV-Visible-IR Adjustable Photoluminescence from Silicon-rich Oxynitride Layers Prepared by Plasma Enhanced Chemical Vapor Deposition
Authors: Pei Zingway , Chung Y.J. , Hsiao H.L. , Hwang H.L.
Published: April 2011

The intense UV-visible-IR adjustable light emissions from silicon-rich oxynitride thin films without any thermal annealing were observed at room temperature under a 325 nm He-Cd laser excitation. The silicon-rich oxynitride thin films were deposited by plasma enhanced chemical vapor deposition (PECVD) with the mixture of 5% Ar diluted silane and nitrous oxide gases. The strong naked-eye recognizable photoluminescence (blue-white-red) could be adjusted by changing the process gas flow ratio τ =([SiH4]/[N20]). To the best of our knowledge, intense and adjustable UV-blue light emissions in the as-deposited thin films are first reported in this work. The Fourier Transform infrared (FTIR) spectroscopy was applied to investigate the microstructure-bonding configurations, in which silicon polysilane related bonding at 830-890 cm' present that silicon complex, exists along with the Si-O-Si bonding. X-ray photoelectron spectroscopy was used to investigate the binding configuration, the binding energy of Si 2p appearing at 99.3 eV was indicative of formation of the silicon clusters. As a consequence, we suppose that the visible-IR lights emissions might possible be strongly related to silicon clusters formation in the films and the intense UV emissions might come from the oxygen-related defects.
Photoconductivity and Luminescence Efficiency of Rare Earth Activated Insulating Materials
Authors: Yen William M.
Published: April 2011

In this article, we discuss the nature of the high lying states in rare earth activated systems and their effect on the luminescence efficiency of these systems. We show that by comparing the optical spectra of these materials with complementary measurements such as photoconductivity (PC), the absolute energy level structure of the ions with respect ot the intrinsic bands of the host can be determined. We propose new measurements which will provide insight on the manner in which energy delocalizes in activated solids.
Cathodoluminescence of Quartz, Silica and Thin Amorphous SiO2 Layers
Authors: Barfels T. , Fitting H.-J. , von Czarnowski A.
Published: April 2011

Cathodoluminescence and its temperature-dose behaviour of different modifications of SiO2 are presented. The detected luminescence bands are attributed to three optical active luminescence centers: the twofold coordinated silicon center (=Si:), the non-bridging oxygen hole center (NBOHC) and the self-trapped exciton (STE). The experiments are correlated with infrared absorption measurements. Existing structural models are discussed with reference to our results.
Optical Properties and Characterization of Eu3+ Activated Pmma:Paac Copolymer Samples: Eu Concentration Effects
Authors: F. R. Sosa , Flores M. , Rodríguez T. R. , Munoz F. A.
Published: April 2011

Samples of Eu3+ -activated PMMA:PAAc copolymers were prepared in order to investigate their spectroscopic properties. The densities, refractive indices, UV-Visible absorption and emission spectra and fluorescence decay times were obtained experimentally. These data were used in conjunction with Judd-Ofelt theory to calculate the spontaneous emission probabilities and branching ratios, as a function of the europium content. The range of the concentration was 0.1 to 2.5 % mol. Our results are combined with previous information on the optical properties of rare-earth activated polymers in order to get a better understanding of the role played by the Eu3+ ions on the polymerization process in our samples.
Effect of Co-Doping on the Photoluminescent Behavior and Electronic Structure of Zinc Silicate Phosphors
Authors: Park H.D. , Sohn K.-S. , Cho B. , Chang H.
Published: April 2011

The present study aims at investigating the effect of co-doping on the photoluminescence(PL) property of Zn2SiO4:Mn phosphor. Experimental data were interpreted by the first principles embedded-cluster discrete variational (DV)-Xα method.
Host Excitation and Luminescence in Large Band Gap Oxides
Authors: Schmidt P.C. , Sticht J. , Eyert V. , Mishra K.C.
Published: April 2011

A good understanding of the electronic states near the band gap of large gap materials is essential for designing phosphors when the energy of exciting radiation exceeds the band gap. This is particularly true when phosphors are designed for application in rare gas discharges with vacuum UV (VUV) radiation. Using density functional ab initio methods (augmented spherical waves and full potential linear muffin-tin orbitals), we have analyzed the nature of host excitations near the band gap energy for a number of complex oxides: LaPO4, AIPO4, BaB2O4, YBO3 and LuBO3 and the common trends in the optical transitions in borates and phosphates and the corresponding binary oxides La2O3, Lu2O3, Y2O3, BaO, B2O3 and P2O5. We have also studied the nature of impurity states of Eu3+ and Pr substituting y3+, in large gap oxides. The studies show how the relative ordering of the one-electron states of activator ions with respect to band states of the host lattice may affect their luminescence properties under host excitation.
Luminescence of Cds Nanoparticles Doped and Activated With Foreign Ions
Authors: Huang J. M. , Murphy C. J.
Published: April 2011

Nanoparticles of CdS (5.0 nm diameter) are prepared in aqueous solution, and copper or silver ions are incorporated into the nanoparticle lattice (doped) or adsorbed to the nanoparticle surface (activated). The materials are characterized by ultraviolet-visible spectroscopy, photoluminescence spectroscopy, transmission electron microscopy and electron diffraction. The photoluminescence efficiency of the materials is affected by the concentration of the foreign ion. The effect of spatial location (doped vs. activated) on the spectral distribution of the emission are modest. Photodecomposition of copper-doped CdS is suppressed compared to CdS alone.
Theoretical Description of Luminescent Effects in β,β-Di(4'-formylphenylethynyl)-4-ethynylstyrene
Authors: Salcedo R. , Guadarrama P. , Sansores L.E. , Fomine S. , Fomina L.
Published: April 2011

Theoretical calculations at HF/6-31G(d) level were carried out on a series of fully conjugated compounds (4-ethynylbenzaldehyde, β,β-dibromo-4-ethynylstyrene, β,β-Di(4'-formylphenylethynyl)-4-ethynylstyrene and its dimmer) to understand the source of blue emission observed in oligomers of the first and second generation in chloroform solutions. The frontier orbitals are distributed through the framework of the molecules (benzene rings, double and triple bonds and chromophores). Additionally, a configuration interaction approach was applied over β,β-Di(4'-formylphenylethynyl)-4-ethynylstyrene (compound 3) at CIS/6-31G(d) level to modeling excited states and simulate the UV-VIS spectrum experimentally obtained. Calculated transitions corresponded to S0→S1 which are, presumably, responsible for the fluorescence observed.
Design and Optimization of Chromophores for Liquid Crystal and Photorefractive Applications
Authors: Twieg R. J. , He M. , Sukhomlinova L. , You F. , Moerner W.E. , Diaz-Garcia M.A. , Wright D. , Casperson J.D. , Wortmann R. , Glania C. , Krämer P. , Lukaszuk K. , Matschiner R. , Singer K. D. , Ostoverkhov V. , Petschek R.
Published: April 2011

Organic chromophores have been exploited for a wide range of discrete optical and electronic functions as well as a growing number of combined opto-electronic functions. We are pursuing development of organic and polymer materials for a range of applications that require properties including liquid crystallinity, second order optical nonlinearity, photorefractivity and, more recently, special nonlinear optical behavior involving molecular chirality.
Photorefractive Polymers With High Speed
Authors: Peyghambarian N. , Ferrio K. B. , Herlocker J. A. , Hendrick E. , Guenther B. D. , Mery S. , Zhang Y. , Kippelen B.
Published: April 2011

Rapid progress in photorefractive polymers includes new materials with improved response rates. We briefly review recent developments in this rapidly evolving area and report grating formation with a 2-millisecond time-constant, the fastest reported to date in any photorefractive polymer.
1.5 νm Luminescence from ErQ based Organic Light Emitting Diodes
Authors: Curry R.J. , Gillin W.P.
Published: April 2011

Organic light emitting diodes have been fabricated using erbium tris(8-hydroxy-quinoline) as the emitting layer and N, N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) as the hole transporting layer. Room temperature electroluminescence was observed at 1.5 νdue to intra-atomic transitions between the 4I13/2; and 4I15/2; levels in the Er3+, ion. These results make the possibility of producing silicon compatible 1.5 νm technology based on such devices a reality.
Frequency Resolved Photoluminescence (PL), Delayed Fluorescence and Triplet-Triplet Annihilation In 7Φ-Conjugated Polymers
Authors: Partee J. , Frankevich E. L. , Uhlhom B. , Shinar J. , Ding Y. , Barton T. J.
Published: April 2011

The delayed fluorescence of poly(p-phenylene vinylene) (PPV) and poly(p-phenylene ethynylene) (PPE) derivative solids and frozen solutions at 20 K is described. It provides strong evidence for triplet-triplet annihilation to singlets excitons accounting for up to ∼3% of the total emission in PPV films and ∼1.5% in PPE powder. It also yields triplet lifetimes of 70 and 110 μs in PPV films and frozen solutions, and ∼200 and ∼500 μs in PPE powder and frozen solutions, respectively.
Second Order Nonlinear Optical Thin Films Fabricated from Electric Field-Assisted Electrostatic Self-Assembled Monolayer Method
Authors: Liu Y. , Claus R.O. , Marciu D. , Figura C. , Heflin J.R.
Published: April 2011

A new method for the build-up of non-centrosymmetric multilayer thin films has been developed for the first time using an electric field-assisted electrostatic self-assembled monolayer (EF-ESAM) technique. An increase by 116% of the second-harmonic intensity of the films has been observed in comparison with that of ESAM film.
Structure-Property Relationships in Organic Nonlinear Optical Materials
Authors: Breitung Eric M. , McMahon Robert J.
Published: April 2011

Tuning the degree of bond-length alternation in organic nonlinear optical materials is a powerful paradigm for the design of organic materials with large molecular hyperpolarizabilities (β). Several research groups have employed this paradigm in the design and synthesis of NLO materials incorporating donor-acceptor polyenes. Increased bond-length alternation in polyenes leads to decreased barriers to rotation about C=C bonds and, hence, increased conformational flexibility. Since the degree of bond-length alternation is solvent dependent, so is the degree of conformational flexibility. In an effort to probe the influence of conformational flexibility on NLO response, we synthesized a series of simple donor-acceptor polyenes that are either conformationally flexible (la, 2a, 3a) or rigid (1b, 2b, 3b). For each pair of molecules ZINDO sum-over-states calculations predict a larger value of βμ, for the conformationally flexible isomer, but EFISH measurements (CHCl3) display mixed results. Various explanations for this behavior will be considered.
Optical Nonlinear Properties of Self-Assembled J-Aggregates Cyanine Molecules Doped in Spin-Casted Silicate Films
Authors: Honma I. , Watanabe T. , Zhou H.S. , Mito A. , Asai K. , Ishigure K.
Published: April 2011

J aggregates cyanine dyes have been successfully doped directly in sol-gel derived silicate thin films. The films are transparent, homogeneous and stable at room temperature. The J aggregates successfully incorporated in rigid SiO2 framework were characterized by absorption spectroscopy and fluorescence microscopy. The films are expected to be useful for non-linear optical devices, multiple photon recording and photoelectric cell.
Electromigration Reliability Study of a GMR Spin Valve Device
Authors: Shingubara S. , Takeda Y. , Sakue H. , Takahagi T. , Verbruggen A. H.
Published: April 2011

Electromigration reliability of a GMR spin valve device has been investigated at elevated temperatures at various DC current densities. Significant degradation of the magnetoresistance was observed when the current density was higher than 20 MA/cm2. Either the electromigration induced damage or the rotation of the magnetization vector of the Mnlr anti-ferromagnetic layer are possible mechanisms of degradation. Furthermore, significant voiding caused by electromigration and thermal gradient induced atomic motion was observed at current densities higher than 35 MA/cm2. High-resolution temperature distribution measurements by scanning thermal probe microscopy revealed the existence of a huge temperature gradient of 106°C/cm, which is a strong driving force for atomic diffusion.
Fracture of a Lead-Tin and a Tin-Silver Solder Under Combined Tensile Shear Loading
Authors: Manoharan M. , Siow K. S.
Published: April 2011

The increasing demands on solder joints have made it imperative that they perform not only their traditional role of electrical connection but also possess good mechanical integrity. One such key mechanical property is the shear strength of the solder. A number of specimen geometries can be used to evaluate the shear strength of solders, each with its advantages and limitations. However, these geometries do not provide information about the notched fracture strength of the solder under shear. Studies on a number of ductile materials have indicated that in many of these materials shear is the preferential mode of fracture even when the imposed load is a combination of tensile and shear. This study, which is part of a larger project on the failure of materials under combined tensile-shear loading, uses a modified compact tension specimen to measure the appropriate failure criterion. It is shown that the fracture of solders under these conditions follows the general principles of a mixedmode fracture mechanism map and shear is the preferred mode of failure.
Effects of Thickness and Oxygen Content on Thermomechanical Behavior of Thin Cu Films Passivated with Ain
Authors: Shu J. , Clyburn S. , Mates T. , Baker S. P.
Published: April 2011

The thermomechanical behavior of a Cu thin film can be dramatically influenced (“oxygen effect”) by exposing the film to a small amount of air or oxygen prior to passivation. Film exposure is accomplished by breaking vacuum at some point prior to passivation. When the top surface is exposed immediately before passivation, the oxygen effect is produced when the passivation material is Si3N4, but no effect is seen with AIN passivations. However, the effect is seen in AIN passivated films when the Cu film surface is exposed to air or O2 and additional Cu is deposited before passivation. This suggests that conditions at the film/passivation interface are an important factor in this anomalous plasticity effect. We have investigated the effects of film thickness and oxygen concentration on these behaviors by preparing films with different thicknesses and oxygen contents for thermomechanical analysis. The thermomechanical behavior is correlated with secondary ion mass spectrometry (SIMS) data that shows oxygen concentration vs. film depth. The presence of the “oxygen effect” in thermomechanical behavior is found to be correlated with an increased oxygen concentration near the film/passivation and film/barrier interfaces.
Environmental Effects on Cu/SiO2 and Cu/Ti/SiO2Thin Film Adhesion
Authors: Tymiak N. I. , Li M. , Volinsky A. A. , Katz Y. , Gerberich W. W.
Published: April 2011

For several microelectronics applications, Cu/dielectric adhesion is a key reliability issue. Either electroplating or local galvanic coupling under moist operating conditions may result in hydrogen induced interface weakening. The present study compared hydrogen effects on Cu/SiO2 adhesion for sputter deposited f'dms with and without Ti underlayers. Thin Cu and Cu/Ti films ranging from 80–3000 nm have been evaluated. Direct observations of the surface during electrolytic charging have shown no evidence of film/substrate debonding for Cu/Ti systems. In contrast, extensive delaminations have been observed for Cu films. Indentation testing immediately after charging indicated up to 100% decrease in the practical adhesion for Ti/Cu films. The observed effect resulted from a true interfacialfracture energy reduction from 4 to 2 J/m2, Plastic energy dissipation was assumed unaffected as no yield stress changes were detected after charging. Even with the deleterious effect of hydrogen, adhesion strength of Cu/Ti films remained higher than that of non-charged Cu films.
Reliability of Electroless Processed Thin Layered Solder Joints
Authors: Wang L. C. , Mei Z. , Dauskardt R. H.
Published: April 2011

There has recently been an increasing interest in using electroless processes to produce the metal thin film stacks that make up the bond pads in solder ball grid array (BGA) packages. Electroless processes produce a more uniform and better controlled film thickness, but the resulting metal stacks have exhibited less mechanical reliability than that of traditional electrolytic stacks. This paper addresses a layered system consisting of a eutectic Sn-Pb solder sandwiched between stacks of Cu, Ni, and Au thin films. The samples were tested to determine cyclic fatigue behavior and fracture toughness values using traditional linear elastic fracture mechanics techniques. Surprisingly, fatigue crack propagation occurred in the middle of the solder layer even though the electroless interface was expected to be very weak. In contrast, fracture tests did appear to cause failure near an interface, but not necessarily at the electroless interface. Fracture toughness values measured for these samples were much lower than those reported for bulk metals. These results are discussed in terms of the microstructures present in order to determine possible relationships between the microstructure of the solder joint and its fracture behavior.
Interconnect Failure Mechanism Maps for Different Metallization Materials and Processes
Authors: Andleigh V. K. , Park Y. J. , Thompson C. V.
Published: April 2011

A tool for simulation of electromigration and electromigration-induced damage, MIT/EmSim, has been used to investigate interconnect reliability, focusing on transitions in failure mechanisms associated with void nucleation, growth, and growth saturation. Conventional scaling of electromigration test results assume that the median time to electromigration-induced failure scales with the current density j to the power −n. The effects of transitions in failure mechanisms have been studied by characterizing the apparent current density exponent. When failure is limited by void nucleation, n=2 scaling is observed, and when failure requires substantial void growth, n=1 scaling is observed. When lines end at diffusion barriers such as W or liner-filled vias, void growth saturates in short lines at low current densities, and, depending on the failure criterion, lines under these conditions can be ‘immortal’. As growth saturates, apparent current density exponents increase above 2. Failure mechanism maps can be constructed to illustrate the failure mechanisms and scaling behavior as a function of line length and current density. Failure maps can be used in accurately scaling test results to service conditions, to suggest layout strategies for optimized circuit reliability, and to assess the reliability of new interconnect materials and structures.
Simulation of Electromigration Induced Atomic Transport in Al-Cu Alloys
Authors: Dekker J. P. , Elsässer C. , Gumbsch P.
Published: April 2011

To improve the fundamental understanding of alloying effects in electromigration, in particular of Cu addition to Al conductor lines, the electromigration process in the grain boundary of an Al-Cu alloy is simulated using a 2D kinetic Monte Carlo method. These simulations give the fluxes of Al and Cu from microscopic parameters, which determine the probability of each atomic jump. The parameters used in these simulations are the diffusion barriers, the attempt frequencies, the electromigration driving force, the temperature, the Cu concentration, and the binding energy of a Cu-vacancy pair. Values for the electromigration driving force on Al and Cu atoms are calculated ab initio. A very interesting result of the kinetic Monte Carlo studies is that the Al flux is reversed due to the addition of a small amount of Cu if the binding energy for the Cu-vacancy pair is larger than 0.12 eV. Such an Al back flux can explain the strongly inhibiting effect of Cu on electromigration damage initiation and transport in Al.
Strain Measurements in a Thermally-Cycled Flip-Chip PBGA Solderball
Authors: Drexler E. S.
Published: April 2011

The mismatch between the coefficients of thermal expansion of silicon chips and their organic substrates has been mitigated through the practice of using underfill in flip-chip packages. Yet solder fatigue and package failures still occur. This is particularly true for flip-chips on organic substrates that are thermally cycled between low (−55 °C) and high temperatures (125 °C). In this study, I used electron-beam moir6 to measure displacements and calculate strains in a solderball contained in a flip-chip plastic-ball grid array package. A crossed-line grating with a pitch of 450 nm was used to allow detailed measurements of the local displacements from a cross section of a flip-chip package. Elastic displacements were observed and measured, and the v-field displacements, out of the plane of the chip, were more significant than the shear or u-field, in the plane of the chip, displacements. Larger v-field displacements were measured near the center of the silicon chip than at the edge of the chip.
Effect of Cu on Al Interfacial Mass Transport in Bamboo Rie and Damascene Al(Cu)
Authors: Proost J. , Li H. , Witvrouw A. , Maex K.
Published: April 2011

In this work, the electromigration (EM)-behaviour of bamboo RIE and damascene Al(Cu) interconnects has been studied by drift experiments. For RIE lines, both lattice and interface EM can be operative, depending on the Cu-distribution. Cu-alloying only retains its retarding effect for Al-diffusion at metallic interfaces, while the accompanying presence of an incubation time was found to become rate-controlling for the EM-performance at operating conditions. Contrary to the case of polycrystalline lines, the higher EM-threshold still observed for bamboo damascene relative to RIE is now insufficient to compensate for the significantly increased Cudepletion rate in bamboo damascene due to both geometrical and metallurgical reasons.
Silicide Contacts for Sub-0.25 μm Devices
Authors: Chen L. J. , Cheng S. L. , Chang S. M. , Peng Y. C. , Huang H. Y. , Cheng L. W.
Published: April 2011

Low resistivity TiSi2, CoSi2 and NiSi are the three primary candidates for metal contacts in sub-0.25 μ m devices. In the present paper, we review recent progress in the investigations of lowresistivity contacts, which include enhanced formation of C54-TiSi2 on (001)Si by tensile stress, high temperature sputtering, and interposing Mo or TiN layer, improved thermal stability of C54-TiSi2 by the addition of N2 during Ti sputtering or N implantation in (001)Si, self-aligned formation of CoSi2 on the selective epitaxial growth silicon layer on (001)Si, effects of stress on the epitaxial growth of CoSi2 on (001 )Si, improvement of thermal stability of CoSi2 by nitrogen ion implantation or high temperature sputtering, and improvement of thermal stability of NiSi by nitrogen ion implantation or compressive stress.
Diffusion Barriers for Mobile Ions in 256M DRAMs
Authors: Gambino J. P. , Parks C. C. , Hegde S. , Domenicucci A. G.
Published: April 2011

In this study, we investigate the diffusion of mobile ions through thin PSG or SiN layers using secondary ion mass spectrometry (SIMS). The diffusivity of Na through either layer is about 100,000X slower than through SiO2. Hence, thin layers of these materials are effective barriers for short anneals at 400°C. However, there is significant diffusion of both Na and K through these layers at 550°C. This suggests that improved cleans will be required to remove mobile ion contamination after interconnect processes.
Effects of Seeding Layers on Electroless Copper Deposition
Authors: Liu Kai Yu , Tse Man Siu , Goh Wang Ling
Published: April 2011

Copper has been actively pursued as the most promising candidate for replacing the current Al metallization for ULSI interconnection because of its higher electrical conductivity and resistance to electromigration. In this work, we present our experimental results on electroless copper deposition on various seeding layers from a formaldehyde-based solution with EDTA as a complexing agent. For electroless plating, a seeding layer is essential for the initiation of copper deposition. X-ray diffraction analysis revealed a variation in the crystallographic orientation of the electroless deposited copper with different underlying seeding layers. The seeding layer is the key factor affecting copper nucleation and grain growth. The initial nucleation behaviors of electroless copper deposition on palladium and copper seeding layers were investigated. The microstructure of electroless deposited copper blanket films was studied using both SEM and AFM, and the crystallinity was analyzed using XRD. The crystal orientation and surface texture of the electroless deposited copper films could be modified by thermal annealing in vacuum (10E-6 Torr) for 30 min at temperatures ranging from 200°C to 300°C. The ratio of crystal orientation, I(111)/I(200) increased with higher annealing temperature, indicating enhanced growth of the (111) crystal structure.
Stress Enhanced Arsenic Diffusion In Titanium Salicided Junctions By Implantation Into C49 TiSi2 and Rapid Thermal Annealing
Authors: Sohn Dong Kyun , Park Ji-Soo , Bae Jong-Uk , Hub Yun-Jun , Park Jin Won
Published: April 2011

We studied reverse leakage current in n+/p titanium-salicided shallow junctions using C49 Ti-silicide as a diffusion source. After Ti deposition, rapid thermal annealing (RTA) was performed to form the C49 Ti-silicide. Subsequently, arsenic ions were implanted and a 2nd RTA was carried out at 850 °C to form the low resistivity C54 Ti-silicide. In spite of no drive-in process following the 2nd annealing, the implanted As diffused well into Si substrate and the reverse leakage current of the n+/p junctions was reduced to two orders of magnitude lower. Since the high chemical affinity of As to Ti-silicide trapped the dopant in the silicide, it has been known that Ti or Ti-silicide cannot be used as a diffusion source. However, in this work, we found that the C49 Ti-silicide acted as a diffusion source of As ions. The reason of fast diffusivity is attributed to the generation of high tensile stress induced by As implantation.
X-ray Photoelectron Spectroscopic Studies of Cu-AI alloy/SiO2 Interfaces
Authors: Wang Pei-I , Yang G. -R. , Murarka S. P. , Lu T. -M.
Published: April 2011

Cu-Al alloys have been recommended for application as the diffusion barriers/adhesion promoters for advanced copper based metallization schemes. In this study interfacial reaction between Cu-Al alloy/SiO2 is investigated by x-ray photoelectron spectroscopy (XPS). A set of thin Cu-Al alloy films, about 30Å in thickness, are deposited on SiO2 substrates. These were directly examined by XPS. This is followed by a study of the interface formation during bias temperature stressing (BTS) of metal/dielectric interfaces in Cu/Cu-5at.%AI/SiO2 subjected to the electrical testing. Core-level spectra of silicon and aluminum obtained indicate that the reduction of silicon dioxide initiates at room temperature when the aluminum concentration in the copper alloys reaches about 5 atomic percent. The silicon diffusion into metal or vice versa is found to be suppressed during the low temperature anneal (300°C) by the Al2O3 interfacial layer. Also, a difference is present in the observed chemical states and interfacial reaction progressing between sputter and electron-beam deposited films. The films of Cu doped with Al appear to act as a suitable diffusion barrier and adhesion promoter between SiO2 and Cu.
HDP-FSG Integration in Multilevel Interconnect Devices
Authors: M'saad Hichem , Vellaikal Manoj , Zhang Lin , Witty Derek
Published: April 2011

HDP-FSG has been integrated as an inter-metal dielectric in a multilevel interconnect scheme. Process regimes for obtaining stable HDP-FSG films were identified. Gap-fill of high aspect ratio structures was achieved for 0.18µm technology node. HDP-FSG film stability, homogeneity, and impurity content were evaluated. In addition to the development of the HDP-FSG process, integration of the interconnect module was investigated and optimized. Analysis of the AI/FSG interface integrity was tested for gap-fill and corrosion with SEM and for fluorine diffusion with SIMS. CMP rate of the FSG was determined and compared to HDP-USG. Al metallization integration approaches in conjunction with FSG were identified.
Integration Challenges of Inorganic Low-K (K≤2.5) Materials with Cu for Sub-0.25µm Multilevel Interconnects
Authors: Yu K. C. , Defilippi J. , Tiwari R. , Sparks T. , Smith D. , Olivares M. , Selinidis S. , Zhang J. , Junker K. , Braekelmann G. , Farkas J. , Lee K. S. , Filipiak S. , Lindell M. , Watanabe J. K. , Wetzel J. T. , Jawarani D. , Herrick M. T. , Cave N. G. , Hobbs C. C. , Stankus J. J. , Mora R. , Freeman M. , Van Gompel T. , Denning D. , Fowler B. W. , Garcia S. , Newton T. , Pena D. , Keyes C. , Nguyen T. , Kirksey S. , Neil T. , Conner J. , Lee J. J. , Fox R. , Hershey R. , Crabtree P. , Sieloff D. D. , Blumenthal R. , Weitzman E. J.
Published: April 2011

The recent introduction of dual inlaid Cu and oxide based interconnects within sub-0.25μm CMOS technology has delivered higher performance and lower power devices. Further speed improvements and power reduction may be achieved by reducing the interconnect parasitic capacitance through integration of low-k interlevel dielectric (ILD) materials with Cu. This paper demonstrates successful multi-level dual inlaid Cu/low-k interconnects with ILD permittivities ranging from 2.0 to 2.5. Integration challenges specific to inorganic low-k and Cu based structures are discussed. Through advanced CMP process development, multi-level integration of porous oxide materials with moduli less than 0.5 GPa is demonstrated. Parametric data and isothermal annealing of these Cu/ low-k structures show results with yield comparable to Cu/oxide based interconnects.
Low Dielectric Constant Sicoh Films As Potential Candidates for Interconnect Dielectrics
Authors: Grill A. , Perraud L. , Patel V. , Jahnes C. , Cohen S.
Published: April 2011

The quest to improve the high performance in ULSI circuits, is driving the search for new materials with low dielectric constants (k=2.5–3.0) for the back end of the line (BEOL) interconnect structures. Novel SiCOH films comprising Si, C, O and H, have been deposited by a PECVD deposition technique. The films have been characterized as-deposited and after anneals of up to 8 hours at 400°C. The atomic composition of the films has been determined by RBS and FRES analysis and their optical properties have been determined by FTIR and index of refraction measurements. The mechanical properties have been determined by measurements of stress and of crack development velocity in water. Metal insulator silicon structures have been used to test the electrical properties of the SiCOH films. After an initial stabilization anneal, the SiCOH films are thermally stable up to 400°C have low tensile stresses (<50 MPa), an extremely low crack propagation velocity, and a hydrophobic behavior. According to the deposition conditions the films have dielectric constants in the range of 2.8 to 3.5. These film properties, combined with an easy-to-integrate deposition process indicate that the material has a strong potential as an interconnect dielectric.