bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evaluation of Copper Oxide to Copper Selectivity of Chemical Systems for BEOL Cleaning Through Electrochemical Investigations
Authors: Venkataraman Nandini , Muthukumaran Ashok Kumar , Raghavan Srini 
Published: April 2011

ABSTRACTBack End of Line (BEOL) cleaning of copper based structures requires chemical formulations that can remove copper oxide selectively without corroding copper and etching the dielectric. Many commercially available semi-aqueous and all aqueous formulations claim to meet these criteria. These include semi-aqueous fluoride strippers (SAF) and all- aqueous ammonium phosphate based chemical systems.This paper will report the results from a fundamental study undertaken to evaluate the performance of a semi-aqueous fluoride formulation in removing copper oxide films of controlled thickness grown on copper. The thickness and composition of the oxide films were determined electrochemically using cathodic reduction technique. Electrochemical impedance spectra of samples immersed in the formulation have been measured as a function of time to follow copper oxide dissolution and the data have been analyzed to detect the transition of copper oxide to copper.
Characterization of Atomic Layer Deposited Ultrathin HfO2 Film as a Diffusion Barrier in Cu Metallization
Authors: Majumder Prodyut , Katamreddy Rajesh , Takoudis Christos G 
Published: April 2011

ABSTRACTThermally stable, amorphous HfO2 thin films deposited using atomic layer deposition have been studied as a diffusion barrier between Cu and the Si substrate. 4 nm thick as-deposited HfO2 films deposited on Si are characterized with X-ray photoelectron spectroscopy. Cu/HfO2/<Si> samples are annealed at different temperatures, starting from 500 °C, in the presence of N2 atmosphere for 5 min and characterized using sheet resistance, X-ray diffraction and scanning electron microscopy. Ultrathin HfO2 films are found to be effective diffusion barrier between Cu and Si with a high failure temperature of about 750 °C.
Interface Stability of Metal Barrier and low K Dielectrics
Authors: Lu Toh-Ming , Ou Y. , Wang P.-I. 
Published: April 2011

ABSTRACTIt is known that the interface between a refractory metal barrier and a dielectric material is stable against thermal treatment at a conventional IC interconnect processing temperature. However, the interface may not be stable against thermal and electrical stress called the bias temperature stress (BTS) at moderate conditions of 150 °C and 0.5 MV/cm. Massive refractory metal ions are seen to drift into low K dielectric materials that contain a mixture of organic and inorganic elements. It is argued that the oxidation of the metal at the interface creates unstable metal ions that are ready to drift into the dielectric film under an electric filed during the BTS test. Dielectric or dielectric capping materials that do not contain oxygen can prevent metal oxidation and are desirable to create a stable metal and dielectric interface.
Study of Fatigue Behavior of 300 nm Damascene Interconnect Using High Amplitude AC Tests*
Authors: Read David T. , Geiss Roy , Alers Glenn 
Published: April 2011

ABSTRACTThe AC fatigue test technique, which uses cyclic joule heating to apply thermal cycles to thin-film structures, was applied to copper lines and vias in damascene dielectric structures on silicon substrates. Specimen chips with two different types of dielectric, oxide and low-k, were tested. The lines were 300 nm wide; various via widths were tested. At 100 Hz, cyclic temperature ranges from 400 to 900 °C produced line lifetimes between 10 and 1 million seconds. Similar lifetimes were reached in the vias for temperature ranges between 100 and 500 °C. The data were plotted as number of load reversals to failure against cyclic temperature range; the data trends for the two different types of dielectric were indistinguishable. When the line data were fit to the Basquin equation for mechanical fatigue, the temperature ranges for both dielectrics at the one1-reversal intercept were above 1000 °C. The via data were more scattered, but trended toward a lower intercept temperature.
Memory Effect in Organic Diodes Containing Self-assembled Gold Nanoparticles
Authors: Wang Hai Ping , Pigeon Sébastien , Izquierdo Ricardo , Martel Richard 
Published: April 2011

AbstractElectrical bistability is reported in metal-organic-metal diodes. The device consists of two Al electrodes separated by an organic layer that contains embedded Au nanoparticles (NPs) supported by parylene nanopillars. This paper presents results with two different organic materials: 2-amino-4, 5-imidazoledicarbonitrile (AIDCN) and aluminum tris(8-hydroxyquinoline) (Alq3). Electrical characterization of the diodes shows bistability with two well-defined states with high (OFF) and low (ON) resistances. The ON/OFF ratio is 104 and current-voltage (I-V) curves show a negative differential resistance (NDR). The diodes can be programmed in either the ON or the OFF state and maintained it for at least 8 months in air without any evidence of degradation. This conspicuous memory effect is rationalized in terms of charge storage mediated by the oxidation/reduction of the NPs. The fabrication method is general and provides a good control on both the size-uniformity and the position of the Au NPs embedded in the organic materials. The diode characteristics with different NP density are also addressed.
Electrical Properties of CuTCNQ Based Organic Memories Targeting Integration in the CMOS Back End-of-Line
Authors: Mueller Robert , Billen Joris , Naulaerts Rik , Rouault Olivier , Goux Ludovic , Wouters Dirk J , Genoe Jan , Heremans Paul 
Published: April 2011

AbstractCuTCNQ (TCNQ=7,7,8,8-tetracyanoquinodimethane) is a resistive switching charge-transfer complex which can be used for organic nonvolatile memories. In this contribution we report on a thorough investigation of the electrical switching of CuTCNQ memories. Our memories currently achieve an endurance of up to 10000 write/erase cycles with a clear distinction between ON and OFF reading currents. ON and OFF threshold voltages follow a Gaussian distribution. Temperature dependent measurements of CuTCNQ based organic memories show a semiconductor like behavior for the ON state. The retention time of the ON state exceeded 60 hours at room temperature. Electrical switching of CuTCNQ memories in air was virtually not affected by temperatures up to 80°C, but becomes erratic at 120°C. The CuTCNQ material itself already starts to decompose around 200°C in presence of oxygen as shown by thermogravimetric analysis.
Oxide-nitride-oxide Dielectric Stacks with Embedded Si-nanoparticles Fabricated by Low-energy Ion-beam-synthesis
Authors: Ioannou-Sougleridis Vassilis , Dimitrakis Panagiotis , Vamvakas Vassilios Em. , Normand Pascal , Bonafos Caroline , Schamm Sylvie , Ben Assayag Gerard 
Published: April 2011

AbstractThis work reports on the formation of Si-nanocrystals within silicon nitride layers by low-energy Si ion implantation. Electrical characterization of oxide/Si-nanocrystal-nitride/oxide dielectric stacks demonstrates regions of negative differential resistance at low-fields. In addition, the memory characteristics in terms of charge trapping, write/erase response and retention properties of the dielectric stacks were recorded. The results indicate the large potential of the low-energy ion beam synthesis method in nitride memory technology.
New Nonvolatile Memory Effect Showing Reproducible Large Resistance Ratio Employing Nano-gap Gold Junction
Authors: Naitoh Yasuhisa , Horikawa Masayo , Shimizu Tetsuo 
Published: April 2011

AbstractA large negative resistance is observed in the I-V characteristics of gold nanogap junction when high-bias voltages are applied. This phenomenon is characteristic behaviour on the nanometre scale; it only occurs for gap widths slightly under 13 nm. Furthermore, this junction exhibits a non-volatile resistance hysteresis when the bias voltage is reduced very rapidly from a high level to around 0 V, and when the bias voltage is reduced slowly. This non-volatile resistance change occurs as a result of changes in the gap width between the metal electrodes, brought about by the applied bias voltage.
Femtosecond Laser Structuring of As2S3 Glass for Erasable and Permanent Optical Memory
Authors: Juodkazis Saulius , Rode Andrei V. , Kondo Toshiaki , Misawa Hiroaki , Samoc Marek , Luther-Davies Barry 
Published: April 2011

AbstractThe nonlinear absorption coefficient of As2S3 glass has been measured to be 2.0 cm/GW for femtosecond pulses at 800 nm. Femtosecond laser structuring via two photon absorption in bulk As2S3 glass by erasable and permanent photo-darkening is demonstrated using both holographic and direct multi-beam laser writing.
Fabrication and Characterization of Cd1-xMgxTe Thin Films and Their Application in Solar Cells
Authors: Dhere Ramesh , Ramanathan Kannan , Scharf John , Young David , To Bobby , Duda Anna , Moutinho Helio , Noufi Rommel 
Published: April 2011

AbstractWe present our work on development of Cd1-xMgxTe (CMT) polycrystalline thin film for solar cells for tandem cell applications. CMT thin films were fabricated by co-evaporation of CdTe and Mg at a substrate temperature of 400˚C. The spatial separation of the two sources resulted in a compositional gradient, which allowed the deposition of a wide range of compositions from fewer runs. Stable films for compositions up to x=0.73 were fabricated. The structural analysis showed that the as-deposited films have a sphalerite structure and are preferentially oriented in the <111> direction, and the lattice constant varies linearly with composition. Optical analysis of the samples shows that the optical bandgap varies linearly with composition. The optical absorption coefficient of the alloy films for the entire composition range (up to x=0.73) is over 6×104/cm-1 for energies above the bandgap, indicating a direct-gap semiconductor. We have fabricated solar cells using these films with the following structure: glass / SnO2 / CdS / CMT / back contact. Using the same processing conditions used for CdTe solar cells, the device efficiency was less than 2%. With modified contact processing, we were able to improve efficiencies to over 5%. Post-deposition chloride heat-treatment in oxygen ambient resulted in partial dissociation of the CMT alloy and loss of Mg. With modified chloride processing, we were able to reduce alloy decomposition and further improve the efficiencies. We have obtained devices with open-circuit voltages of up to 845 mV and efficiencies of 8% for CMT devices with a bandgap in the range of 1.6-1.62 eV which are highest reported values for CMT alloys.
In-situ Characterization of As-grown Surface of CIGS Films
Authors: Kashiwabara Hirotake , Teshima Shimpei , Kikunaga Kazuya , Takeshita Kazunori , Okuda Tetsuji , Obara Kozo , Sakurai Keiichiro , Ishizuka Shogo , Yamada Akimasa , Matsubara Koji , Niki Shigeru , Terada Norio 
Published: April 2011

AbstractIn-situ characterization of composition, electronic structure and their depth profiles of surface of Cu(In1-xGax)Se2 (CIGS) film grown by three stage co-evaporation has been carried out by means of photoemission and inverse photoemission spectroscopy (PES/IPES), for the purpose of investigating the formation mechanism of the CIGS-side wide band-gap region adjacent to CBD-CdS/CIGS interface in cell structure. Sample-transportation in vacuum below 1 x 10-8 Torr yielded almost contamination-free feature of the CIGS surface. The as-transferred surface of Cu0.93(In0.65Ga0.35)Se2 grown at the identical condition for the high performance solar cell exhibited seriously Cu and Ga deficient composition. Chemical formula of this region was inbetween Cu : (In+Ga): Se = 1 : 3 : 5 and 1 : 5 : 8. In-situ UPS/IPES measurements CIGS showed that the as-grown surface region of the CIGS already had expanded band gap energy up to 1.4 eV and n-type character. A gradual decrease of band energy and a rise of valence band maximum as a function of depth from the original surface were observed. These results have revealed that the surface of CIGS by the three stage method already has the wide band gap, which might originate in so-called Cu-vacancy ordered phase.
Study of Band Alignment at the Interface between CBD-CdS and CIGS grown by H2O-introduced co-evaporation
Authors: Terada Norio , Kashiwabara Hirotake , Kikunaga Kazuya , Teshima Shimpei , Okuda Tetsuji , Niki Shigeru , Sakurai Keiichiro , Yamada Akimasa , Matsubara Koji , Ishizuka Shogo 
Published: April 2011

AbstractFor understanding the origin of the improvements of properties in the CIGS-based cells, of which the CIGS absorber has been fabricated by H2O-introduced co-evaporation [CIGS-H2O], band alignment at the interfaces between chemical bath deposited CdS and CIGS-H2O with Ga substitution ratio ~ 40 % has been studied by photoemission and inverse photoemission spectroscopy. The CdS layer over the CIGS-H2O showed an identical electronic structure with that of CdS on the conventionally grown CIGS; band gap energy of 2.3 ~ 2.4 and a location of conduction band minimum (CBM) and valence band maximum (VBM) relative to Fermi level were + 0.75 eV and -1.6 ~ -1.7 eV, respectively. In the interface region, decreases of CBM and a rise of VBM were observed. Total amount of the decrease of CBM over the interface was 0.2 ~ 0.3 eV. XPS measurements of the core-level signals over the interface showed a small upward bend bending of 0.1 ~ 0.2 eV. Consequently, the conduction band offset (CBO) and valence bad offset (VBO) at the CBD-interface over the CIGS-H2O (Ga~40%) are about +0.1, and 0.9 ~ 1.1 eV, respectively. This positive CBO is contrast with a slightly negative CBO at the interface between CBD-CdS/conventionally grown CIGS with Ga ~ 40 % measured previously. These results indicate that the H2O introduction is effective to extend the upper limit of the Ga substitution ratio where the Type-I conduction band alignment is maintained. The observed band alignments are consistent with the rise of Voc and efficiency in the CIGS-H2O based cells.
On Coincidence Site Lattice Modelling of Twins in the Sphalerite and Chalcopyrite Structures
Authors: Durose Ken 
Published: April 2011

AbstractCoincidence site lattice (CSL) modelling has been applied to determine the orientations and atomic structures of first order twin boundaries in the chalcopyrite structure. A rotation of 250°32' about [110] generated a CSL similar to that for the Ó = 3 sphalerite boundary, but with one in two cation columns being metal-metal anti-sites. The models predict one coherent boundary type i.e. (112)M-(112)T, and four lateral types, (110)M-(118)T, (1110)M-(112)T, (114)M-(114)T, (001)M-(114)T. Un-relaxed atomic models for the boundaries have been constructed. The coherent boundary is shown to differ from that in sphalerite by the inclusion of one in two Se columns having alternate atoms with either three Cu and one In nearest neighbours or vice versa. All of the [110] tilt boundaries in chalcopyrite are expected to be electrically active. A tentative list of the boundaries ranked by energy, electrical and chemical activity is given, along with comments on the influence of preferred orientation in polycrystalline films in the context of solar cells.
All-Chemically Deposited Solar Cells with Antimony Sulfide-Selenide/Lead Sulfide Thin Film Absorbers
Authors: Messina Sarah , Nair M.T.S. , Nair P. K. 
Published: April 2011

AbstractSolar cell structures with Sb2SxSe3-x and PbS as absorber layers were fabricated by chemical deposition on commercial transparent conductive oxide coated glass. The solid solution here was prepared by heating at 250°C a Sb2S3 thin film in contact with a chemically deposited Se-thin film. It has a graded band gap of 1-1.8 eV. A PbS thin film deposited on this layer basically fulfils the role of a p+ layer; its role as an absorber is yet to be studied. Open circuit voltage of 560 mV and short circuit current density ¡Ö 1mA/cm2under 1-3 kW/m2 tungsten halogen radiation are characteristics of these cells. Optimization of the film thicknesses and heating may offer prospects for these materials toward alternate thin film solar cell technology.
Hg1-xCdxTe as the Bottom Cell Material in Tandem II-VI Solar Cells
Authors: Parikh Viral , Chen Jie , Marsillac Sylvain , Collins Robert W , Compaan Alvin D 
Published: April 2011

AbstractWe have measured the electrical, optical and morphological properties of as-grown Hg1-xCdxTe films prepared by r.f. sputtering. The Hg1-xCdxTe films were grown at substrate temperatures ranging from 25°C to 150°C. Films grown at temperatures lower than or equal to 70°C were highly resistive (≥105 Φ-cm) and were not measurable by our Hall apparatus. Optical transmission data show that the band gap of these films ranged from 0.8 eV-1.5 eV, satisfying the optimum band gap criteria. Plan view and cross sectional SEM studies indicate that the films grown at 85°C and 100°C have larger grains with compact grain boundaries and these films typically yield the best cell performance. Spectroscopic ellipsometry studies are being used to estimate the band-gap as a function of substrate temperature.We have also studied the effect of various back contacts and have fabricated complete solar cells. We found that Cu-Au serves as the best ohmic back contact to CdS/HgCdTe solar cell. Our preliminary results of J-V analyses on the complete solar cell show that the efficiency is mainly limited by the short-circuit current. Electrical-bias-dependent QE measurements indicate voltage-dependent current collection mainly in the long wavelength region. Further optimization of growth parameters and CdCl2 treatment needs to be carried out to improve the cell performance.
Confinement Effects of Hard Disk Lubricant Investigation by Atomic Force Microscopy
Authors: Caia George L , Buenviaje-Coggins Cynthia , Munoz Nicole , Faddis David , Florescu Doru I , Park Sung , Lee SungChang 
Published: April 2011

AbstractAs the critical design requirements decrease, we need to understand how confinement affects the performance of the materials we use. One example of this occurs with the lubricant used on magnetic recording disks to reduce wear between the disk and head reader during unexpected intermittent contact. Lubricants for use in hard drives need to have sufficient reflow and redistribution properties which are stable in a wide range of temperatures experienced in today's hard drive. Since the material properties of the confined system often differ from the bulk properties, the tools needed to properly investigate these systems need to be developed and understood. In this study, we utilized atomic force microscopy (AFM) techniques, to study the confinement effects on lubricant stability with temperature. Our studies have demonstrated distinct changes in adhesion force with changes in the thickness of the confining substrate layer. As adhesion is a component of friction, these changes in adhesion are directly related to lubricant performance and its ability to reduce wear between disk and reader.
Influence of Molecular Ordering on Surface Free Energy of Polymer Nanofibres using Scanning Probe Microscopy
Authors: Li Shuangwu , Wang Wei , Barber Asa H 
Published: April 2011

AbstractFibrous materials are used in a variety of applications due to their relatively high surface area to volume as well as anisotropic behavior. Electrospinning is a popular fabrication method which produces polymer nanofibres with a potentially high molecular alignment. In this work we examine the surface free energy of electrospun polyvinyl-alcohol nanofibres and its relation to molecular ordering using scanning probe microscopy adhesion measurements. Comparisons are made with bulk polymer material to show that a high degree of molecular orientation is present at least at the surface of the polymer nanofibre. As a result, the surface free energy of electrospun polymer nanofibres is greater than that of a bulk polymer. This effect indicates that the electrospinning process is effective at polymer alignment over a variety of experimental parameters.
Development of Homoepitaxially Grown GaN Thin Film Layers on Freestanding Bulk m-plane Substrates by Metalorganic Chemical Vapor Deposition (MOCVD)
Authors: Jindal Vibhu , Grandusky James , Tripathi Neeraj , Tungare Mihir , Shahedipour-Sandvik Fatemeh , Sandvik Peter , Tilak Vinayak 
Published: April 2011

AbstractHigh quality homoepitaxial growth of m-plane GaN films on freestanding m-plane HVPE GaN substrates has been performed using metalorganic chemical vapor deposition. For this a large growth space was studied. Large areas of no-nucleation along with presence of high density of defects were observed when layers were grown under growth conditions for c-plane GaN. It is believed that these structural defects were in large part due to the low lateral growth rates as well as unequal lateral growth rates in a- and c- crystallographic directions. To achieve high quality, fully coalesced epitaxial layers, growth conditions were optimized with respect to growth temperature, V/III ratios and reactor pressure. Higher growth temperatures led to smoother surfaces due to increased surface diffusion of adatoms. Overall, growth at higher temperature and lower V/III ratio decreased the surface roughness and resulted in better optical properties as observed by photoluminescence. Although optimization resulted in highly smooth layers, some macroscopic defects were still observed on the epi-surface as a result of contamination and subsurface damage remaining on bulk substrates possibly due to polishing. Addition of a step involving annealing of the bulk substrate under H2: N2 environment, prior to growth, drastically reduced such macroscopic defects.
Density functional calculations of the binding energies and adatom diffusion on strained AlN (0001) and GaN (0001) surfaces
Authors: Jindal Vibhu , Grandusky James , Tripathi Neeraj , Tungare Mihir , Shahedipour-Sandvik Fatemeh 
Published: April 2011

AbstractDensity functional theory calculations were carried out to study the binding energies and diffusion barriers for various adatoms on AlN and GaN (0001) surfaces. The binding energies and potential energy surfaces were investigated for Al, Ga, and N adatoms on both Al (Ga) terminated and N terminated (0001) surfaces of AlN (GaN). Calculations for the diffusion paths and diffusion energy barriers for Al, Ga, and N adatoms on AlN and GaN were performed. It was found that the N adatom on N terminated AlN and GaN surfaces faces a high diffusion barrier due to strong N-N bond. The Al and Ga adatom on Al (Ga) terminated AlN (GaN) surfaces showed lower diffusion barriers due to the weak metallic bonds. However, the diffusion barrier for an Al adatom was always larger than that of a Ga adatom on any surface. The surfaces were also subjected to a hydrostatic compressive and tensile strain in the range of 0 to 5% to investigate the effect of strain on diffusion barriers. The diffusion energy barrier for N adatom on N terminated AlN and GaN surfaces decreased when the strain state was changed from tensile to compressive. In contrast, Al and Ga adatoms show continuous increase in diffusion barriers from tensile to compressively strained Al (Ga) terminated AlN (GaN) surfaces.
Non-planar Corrugated Layered Heptazine-based Carbon Nitride: The Lowest Energy Modifications of C3N4
Authors: Kroll Peter , Gracia Jose 
Published: April 2011

AbstractWe investigate structure and energy of carbon nitride, C3N4, with a special focus on two-dimensional graphitic-type structures. Our density functional calculations indicate that structures comprising heptazine (C6N7) heterocycles are energetically more favorable than structures comprising triazine (C3N3) heterocycles. Lowest energy modifications exhibit corrugated sheets with a substantial gain in energy in comparison to planar structures. Our analysis indicates that nitrogen-nitrogen non-bonded interaction is the key to understand the corrugation.