bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance of Poly-Si Tfts with Double Gate Oxide Layers
Authors: Min Byung-Hyuk , Park Cheol-Min , Jun Jae-Hong , Bae Byung-Sung , Han Min-Koo
Published: April 2011

We have fabricated a poly-Si TFT with double gate insulator composed of ECR oxide and APCVD oxide to improved the performance of poly-Si TFTs. The poly-Si TFT with double gate oxide exhibits the remarkable enhancement of the electrical parameters compared with the conventional poly-Si TFTs which has APCVD gate oxide, such as improvement of the subthreshold swing and the low threshold voltage. The proposed poly-Si TFT has a higher oxide breakdown electrical field and the device characteristics are not degraded significantly after an electrical stress. It is found that the ECR oxide plays a key role to improve the device performances and prevent the poly-Si TFTs from degradation due to the electrical stress.
Novel N2O Plasma Passivation on Polycrystalline Silicon Thin-Film Transistors
Authors: Wang Fang-Shing , Huang Chun-Yao , Cheng Huang-Chung
Published: April 2011

A novel defect passivation process of polycrystalline silicon thin-film transistors (poly-Si TFT's) utilizing nitrous oxide (N2O) plasma was investigated. In terms of the gas flow rate, chamber pressure, and plasma exposure time, the optimum plasma condition has been found to significantly improve the electrical characteristics of poly-Si TFTs. The performance is even better than those passivated with conventional hydrogen plasma. It is believed that the nitrogen radicals from the N2O gas as well as the hydrogen ones from the residual H2O both can diffuse into the gate-oxide/poly-Si interface and the channel poly-Si layer to passivate the defect-states. Furthermore, the gate-oxide leakage current significantly decreases and the oxide breakdown voltage slightly increases after applying N2O-plasma treatment. This novel process is promising for the applications of TFT/liquid crystal displays and TET/static random access memories.
Solution Grown Polysilicon for Flat Panel Displays
Authors: Wallace R. L. , Anderson W. A.
Published: April 2011

Thin-film poly-Si on low-cost substrates is useful for thin-film transistors in flat panel displays or for photovoltaics. The films reported herein were formed at 600°C by d.c. magnetron sputtering from a Si-target onto a SiO2/Mo substrate, pre-coated with Sn or In/Ti to give a liquid phase growth. Poly-Si films have given a preferred (111) orientation, grain size up to 20μm, a carrier mobility exceeding 100cm2/Vs and carrier lifetime of 8μs when using the Sn pre-layer. The Sn pre-layer typically gave smaller grain size than did the In/Ti solvent but the latter gave lower carrier lifetime from Ti incorporation in the film. The film from the Sn pre-layer gave carrier mobility of 140cm2/V-s after hydrogenation by microwave electron cyclotron resonance. Properties of the Si thin-film can be controlled by type of pre-layer, doping of the target, substrate temperature and deposition environment.
Amorphous Silicon Tfts and Flat Panel Displays
Authors: Tsukada T.
Published: April 2011

The current status and next-generation technologies for liquid-crystal displays based on amorphous silicon TFTs are described. Panel size, resolution, design rule, and viewing angle are discussed from the standpoint of panel performance, productivity, and product application. The material properties for future TFT/LCDs are specified based on the discussions of design rule.
Cr/Cr Compound Bilayered Thin Film Black Matrix For Lcd Color Filter
Authors: Lee Byung Hak , Kim Lee Gon , Lee Si-Hyun
Published: April 2011

The effect of process parameters on the optical property of the chromium/chromium compound multilayered thin film black matrix for liquid crystal display color filter has been investigated. A chromium compound layer was deposited reactively by DC magnetron sputtering, using gas mixture of Ar, CO2, and N2 on soda-lime glass substrate. Metallic chromium layer deposition was followed to enhance the light obstruction of the black matrix. X-Ray diffraction and transmission electron microscopy study showed that CrN is the major phase with unidentifiable oxides and carbides present as minor phases, in chromium compound layer, with nanocrystalline structure. Metallic chromium layer showed columnar growth structure. The ratio of CO2 in the reactive sputtering gas greatly affected the optical property of the multilayer, despite that N2 is the gas which contributes to the formation of the major phase. Delicate change of optical property is due to compositional variation of the compound layer, caused by reaction due to environmental changes. When processed with 10.28% of CO2 and 4.88% of N2 in 3.3 mTorr pressure, film with optical reflectivity of 3.31% at 655 nm of photon wavelength was obtained.
Improved Growth Of Srga2s4 Thin Film Electroluminescence Phosphors
Authors: Braunger D. , Oberacker T. A. , Troppenz U. , Schock H.-W.
Published: April 2011

Cerium activated ternary strontium thiogallate phosphor thin films have been deposited by multi-source evaporation of elemental strontium, gallium and sulfur as source materials. Cerium chloride (CeCI3) has been used as activator starting material. In order to avoid SrS as well as Ga phase segregations elemental In as well as compounds, such as LiF, NaF, LiCl, and SrCI2, have been investigated as possible growth enhancing agents.

Coevaporation of indium resulted in an improved crystallization with the drawback of an increased reabsorption of the cerium emission. The other additives lead to improved crystal quality combined with true-blue cathodoluminescence (CL) performance (C.I.E. color coordinates of up to 0. 14/0.12) which proves phosphor layers without any SrS phase segregations.

Thin film electroluminescent (TFEL) devices with SrGa2S4:CeCl3 phosphor layers prepared with LiF as additive exhibit highest ever reported L40 luminances of 78 cd/m2 and luminous efficiencies of 0.017 lm/W at a transferred charge of 1 μ;C/cm2 with 1 kHz / 50 μs bipolar square wave excitation.
Synthesis of CdSe/ZnS Quantum Dot Composites for Electroluminescent Devices
Authors: Rodriguez-Viejo J. , Dabbousi B. O. , Bawendi M. G. , Jensen K. F.
Published: April 2011

Quantum dot composite films, consisting of II-VI nanocrystals imbedded in a ZnS matrix, are candidate phosphor materials for electroluminescent flat panel displays. The optical properties of such composites can be tailored across the visible spectral region by selecting the composition and size of the nanocrystals. We present combined solution chemistry and electrospray organometallic chemical vapor deposition (ES-OMCVD) methods for realizing such composites. Size selected, CdSe quantum dots with an overlayer of ZnS are synthesized in solution. This surface derivatization produces a large enhancement of the photoluminescence efficiency. The quantum dot composites are subsequently formed by introducing the quantum dot solution by electrospray into an OMCVD ZnS thin film process. Photoluminescence and cathodoluminescence properties of the quantum dot composites are reported.
Electron Injection Effects in Electroluminescent Devices Using Polymer Blend Thin Films
Authors: Wu C. C. , Sturm J. C. , Register R. A. , Suponeva L. , Thompson M. E.
Published: April 2011

In this paper, we discuss the effects of electron injection on electroluminescence (EL) efficiency in single-layer EL devices using blends of poly(N-vinylcarbazole) (PVK) and poly(3-nbutyl- p-pyridyl vinylene) (Bu-PPyV). Pure Bu-PPyV thin films suffer from formation of excimers due to the strong interchain interaction. Diluting Bu-PPyV with the high-energy-gap and holetransporting polymer PVK suppresses excimer formation and substantially raises both photoluminescence (PL) and EL efficiencies. The emission color is converted from red to green, indicating a transition from excimer emission to monomer emission of Bu-PPyV. The electron injection and EL efficiency can be fluther improved by adding small-molecule oxadiazoles into the blends as electron-transport materials. In optimized devices, an external EL quantum efficiency (backside emission only) as high as 0.8% photon/electron and practical brightnesses of 100 cd/m2 and 1000 cd/m2 can be achieved at ∼9V and ∼13.5V, respectively.
Poly(bithiazole)s: A New Class of Conjugated Polymers for Polymer-Based Light-Emitting Diodes
Authors: Politis J. K. , Nanos J. , He Yi , Kanicki J. , Curtis M. D.
Published: April 2011

A new class of conjugated polymers have been synthesized based on the bithiazole moiety. The photoluminescence (PL) of these polymers ranges throughout the visible, from blue-green to red. These materials also show high stability, both thermal and oxidative. Therefore, it appears that this class of polymers are good candidates for polymer-based light emitting diodes.
Optical Studies of Znse Nanocrystals In Potassium Borosilicate Glass Matrices
Authors: Smith Christine A. , Risbud Subhash H. , Lee Howard W. H. , Cooke J. Diane
Published: April 2011

We have prepared ZnSe nanocrystals embedded in potassium borosilicate glass matrices in concentrations up to 14 wt%. The optical and electronic properties of these nanocrystals as a function of the fabrication process were investigated with High Resolution Transmission Electron Microscopy (HRTEM) and various optical techniques including absorption, photoluminescence, and excitation spectroscopy, and photoluminescence lifetime measurements. HRTEM confirms the presence of nanocrystals and indicates an average diameter size of 50 Å. The majority of the photoluminescence extends throughout the visible and is highly red-shifted from the absorptionedge, indicating emission from trap states such as Se vacancies. Contributions from the ZnSe nanocrystals as well as the borosilicate glass matrix are also observed. Exponential and biexponential photoluminescence decays are observed with decay times ranging from a few nanoseconds to a few hundred nanoseconds. The significance of these results to the optical and electronic properties of the ZnSe nanocrystals and their relevance as luminescent materials for light emitting applications will be discussed.
The True Liquid Crystal Approach to Mesoporous Silica
Authors: Attard George S. , Edgar Mark , Emsley James W. , Göltner Christine G.
Published: April 2011

Liquid crystalline phases, consisting of nonionic surfactant and water, are exploited as templates for the synthesis of inorganic nanostructures In this approach the aqueous domains of a lyotropic liquid crystal phase function as a confining medium, in which the polymerisation of a watersoluble precursor takes place without destroying the nanostructure. Conducting the prepration of mesoporous silica in a lyotropic liquid crystal phase has considerable advantages over previous routes towards mesoporous ceramic oxides. (i) The nanostructure of the solid can be predicted a priori by knowing the phase structure of the liquid crystal before solidification, (ii) this approach allows the use of nonionic surfactants as templates, (iii) the progress of the reaction can be observed by a variety of methods, such as polarised light optical microscopy, X-ray diffraction, and deuterium NMR spectroscopy, all of which are noninvasive. The synthesis and a new way of monitoring the temporal evolution of the inorganic nanostructure using deuterium NMR spectroscopy are described. The results show unambiguously that the lyotropic liquid crystal phase acts as a template for the nanostructure.
Polymerization Effects on the Electro-Optic Properties of a Polymer Stabilized Ferroelectric Liquid Crystal
Authors: Guymon C. Allan , Dougan Lisa A. , Hoggan Erik N. , Bowman Christopher N.
Published: April 2011

The introduction of polymeric materials into liquid crystal (LC) matrices has been the focus of much interest in recent years. When a small percentage of polymer network is introduced, the mechanical strength of an LC system increases dramatically without significantly altering the electro-optic properties of the LC. One particular group of LCs, namely, ferroelectric liquid crystals (FLCs), are excellent candidates for such stabilization. FLCs, despite showing great potential for use in electro-optic and display technology due to inherently fast switching times and bistability, have found limited use as they are extremely susceptible to mechanical shock. This study examines the effects of polymerization conditions of a diacrylate monomer in an FLC on its inherent electro-optic properties. The LC phase in which polymerization occurs has a dramatic effect on the polymerization behavior and formation of the polymer network. Such effects have interesting implications on the ferroelectric polarization and switching speed of the FLC. As the temperature of polymerization increases and thus the order of the LC phase decreases, the ferroelectric polarization and the switching time increase.
Use of Glass-Forming Liquid Crystal Materials for Electroluminescent Diodes
Authors: Tsutsui T. , Lin C. P. , Saito S. , Chen S. H. , Shi H. , Mastrangelo J. C.
Published: April 2011

Spin-coated thin films of cyclohexane-based liquid crystalline materials were used for the fabrication of electroluminescent diodes. Electroluminescence from single-component films of cyclohexane-based liquid crystalline materials was observed. Double component films composed of a cyclohexane-based liquid crystalline material and a conventional hole transport dye were shown to give improved electroluminescence performances, but emission was due to exciplexes composed of two components. Use of cyclohexane-based dye molecules was effective for suppressing the formation of inter-molecular complexes. The highest external quantum efficiency observed was 0.17%.
Phase-Separation Behavior and Electro-Optical Properties for (Polymer/Liquid Crystal) Composite Films
Authors: Kikuchi Hirotsugu , Jeong Hwan-Kyeong , Kajiyama Tisato
Published: April 2011

Dominant factors that control the aggregation structure and electro-optical properties were presented for (polymer/liquid crystal) composite films prepared by a solvent cast method from homogeneous solutions. Phase-separation behavior of the composite films consisting of a three dimensional polymer network and low molecular weight liquid crystals (LCs) embedded in the network was studied by evaluating the development of optical heterogeneity in the casting solution during film formation and by observing the morphology of the polymer networks. It was confirmed from light scattering studies of the casting solution during solvent evaporation that the phase-separated structure of polymer and LC was formed through spinodal decomposition. The resultant size of the LC domain in the composite film was controlled by regulating the solvent evaporation rate. The morphology of the polymer network in the composite film was also strongly influenced by the solubility between the polymer and the casting solvent. The electro-optical properties based on field controlled light scattering of the composite film were strongly dependent on the size of the LC domain. Though the rise response time decreased, the decay response time increased with an increase in the size of LC domains in the composite film. When poly(diisopropyl fumarate), which is not compatible with the LC, was used as the matrix polymer, no electro-optical hysteresis was observed, while considerable electro-optical hysteresis was observed for the composite film consisting of poly(methyl methacrylate), which shows a certain compatibility with the LC.
Studies of polymer ball type polymer dispersed liquid crystal films
Authors: Chang S. J. , Yin Y. C. , Lin C. M. , Fuh A. Y. G.
Published: April 2011

Polymer dispersed liquid crystals ( PDLC ) are potentially useful as new types of display devices. By applying an electric field, one can switch the PDLC cell from a highly scattering opaque state to a transparent state. Normal PDLC cells consist of liquid crystal droplets, having sizes on the order of micrometers, embedded in a transparent polymer matrix. In this paper, we report the development of a new kind of PDLC cell with a distinct type of polymer morphology, teferred to as “reverse ” or “polymer ball ” type. The electro-optical behavior and the micro structure of the PDLC films were investigated by a He-Ne laser and the scanning electron microscopy ( SEA ) respectively.
Advances in Liquid Crystals for Am-Lcd
Authors: Kenji Furukawa , Etsuo Nakagawa , Yasuyuki Goto
Published: April 2011

Physical properties of mono-, di- and tri- fluorobenzenc derivatives with different core structures consisting of 3-ring system were measured. By introduction of fluorine atoms, phase change telnperaturcs decreased, nematic temperature range narrowed, optical anisotropy and elastic constant decreased, and dielectric anisotropy increased. From a calculation with MOPAC ver. 6.0, it is clear that elastic constants depend upon shapes of molecules under a restricted condition.

By blending the investigated compounds as main components, different nematic mixtures, having
low threshold voltage low viscosity, large optical anisotropy or wide nematic range, which are suitable for specific applications for AM-LCD, were obtained
Synthesis and Physical Properties of π -Conjugated Polymers Containing Mesogenic Group
Authors: Watanabe Y. , Koide N.
Published: April 2011

Novel side chain type liquid crystalline polymers, polythiophene and poly(aryleneethynylene) [PAE], containing a mesogenic group in the side chain were synthesized. Polythiophene derivatives were obtained by dehalogenative polycondensation with zero-valence nickel complex under mild condition. PAE type polymers were obtained by coupling dihalo aromatic compound with diethynyl aromatic compound. Their thermal properties were examined by differential scanning calorimetry, optical microscopy and X-ray diffractometry. All polymers exhibited a smectic or nematic mesophase depending upon the polymer backbone and pendant mesogenic group. Polythiophene derivatives exhibited electrochemical activity. Annealing polythiophene derivatives led to a lower oxidation potential and a higher conductivity. The degree of the orientation of the polymer backbone was supported by polarized UV-vis measurement. An effective conjugated length became longer by introducing thiophene rings into the polymer backbone. A high quantum yield of fluorescence was observed for PAE type polymers.
Electronic Structures of P-Type Doped CuInS2
Authors: Yamamoto T. , Katayama-Yoshida H.
Published: April 2011

We have studied the electronic structures of CuIn(S0.875X0.125)2 (X=B, C, N, Si or P) based on the ab-initio electronic band structure calculations using the augmented spherical wave (ASW) method. We have clarified that the physical characteristics of the p-type doped CuInS2 crystals are mainly determined by a change in the strength of interactions between Cu and S atoms. On the basis of the calculated results, we discussed the material design considerations, such as controlling the strength of resistivity for p-type doped CulnS2 materials and converting the conduction type, from n-type to p-type by a codoping method.
Defect Distribution And Metastability in Chalcopyrite Semiconductors
Authors: Walter T. , Herberholz R. , Müller C. , Schock H. W.
Published: April 2011

Deep levels in chalcopyrite based heterojunctions are investigated by capacitance techniques. A method is presented which allows the determination of defect distributions from admittance measurements. For CuInSe2 a defect level at 280 meV above the valence band with an attempt to escape frequency of about 1011 s-1 is detected. A characteristic defect structure consisting of a shallow defect level and a broad deep structure is observed for Cu(In, Ga)Se2. The depth of the shallow defect is affected by annealing treatments which are necessary to achieve the optimum performance of the devices. CulnS2grown under an excess of CuS exhibits a high density of shallow defects whereas for Cu-poor CuInS2 defects close to midgap position with a large capture cross section are observed. These defects are metastable with respect to current injection and illumination relaxing to the equilibrium state around room temperature. The increase of the defect density after illumination results in a reduced bucking current. CV measurements can be interpreted in terms of a high density of deep states.
Effect of CdCl2 Treatment of CdS Films on CdTe/CdS Solar Cells
Authors: Song W. , Mao D. , Feng L. , Zhu Y. , Aslan M. H. , Collins R. T. , Trefny J. U.
Published: April 2011

We investigated the effect of CdCl2 treatment of CdS films on the photovoltaic performance of polycrystalline CdTe/CdS solar cells. X-ray diffraction studies indicated that the diffusion of S into CdTe is qualitatively the same for CdTe/CdS films fabricated with both as-deposited and CdCl2-treated CdS. A major difference was observed in the extent of Te diffusion into CdS for the two types of CdS films. Full conversion of CdS into CdS1-yTey; was observed for films prepared with asdeposited CdS, while the formation of the ternary phase was below the detection limit for films prepared with CdCl2-treated CdS. Photoluminescence measurements confirmed this result. The difference in interdiffusion leads to differences in optical transmission of CdS films and spectral response of CdTe/CdS solar cells. An increase of 2.7 mA/cm2 in short-circuit current density was observed as a result of improved spectral response in the wavelength range of 500–600 nm for the CdCl2-treated CdS.
Comparison Between Al- and B-Doped Zno Window Layers For CuInSe2Thin Film Solar Cells
Authors: Nakada T. , Murakami N. , Kunioka A.
Published: April 2011

A comparative study of several properties of ZnO:Al and ZnO:B films grown by magnetron sputtering has been performed. The influence of these window layers on device performance has also been investigated. Sputter-deposited ZnO:B films were used for the first time as a window material of CIS thin film solar cells. The short circuit current was improved by replacing ZnO:Al with ZnO:B window layers. A discussion of the issues relating to ZnO window layers for improving cell performance is presented.
Structure Effect on Electrical Properties of Ito Films Prepared by Rf Reactive Magnetron Sputtering
Authors: Meng Li-Jian , Santos M. P. dos
Published: April 2011

ITO films have been deposited onto glass substrates by rf reactive magnetron sputtering using In-Sn (90–10) alloy target. After the deposition, the films were annealed in air at 500 °C for 30, 60, 90 and 180 min respectively. The film structure varies as the annealing time is changed. The film electrical properties show a strongly dependence on the film structure. Although all the films show a preferred orientation along the (400) direction, the film which has high (222) diffraction peak intensity, has high carrier mobility and low resistivity.
Amorphous Silicon Films From Dichlorosilane and SiH4 For Solar Cells
Authors: Payne A. M. , Wagner S.
Published: April 2011

We have deposited amorphous silicon films from mixtures of dichlorosilane (SiH2CI2, DCS), and silane (SiH4) and made the first p-i-n solar cells using i-layers of this material. We measured optical and electronic transport properties of the DCS-derived films and relate them to the solar cell performance. The DCS cells are compared to standard cells made with SiH4.
Cost Impacts of Anti-Reflection Coatings on Silicon Solar Cells
Authors: Wong David C. , Waugh Art
Published: April 2011

Despite the early discovery of the Photovoltaic effect by Bechquerel almost 107 years ago, its commercial value had never been seriously considered because of its high cost in production and low in energy conversion efficiency. A familiar predicament has restrained demand for photovoltaic application: People won't use them until they are affordable, but they won't get affordable until there is a mass market for them. As has happened in other expensive markets, businesses are desperate to crack the conundrum. Since the oil shortage in the 70s, crystalline solar cell efficiency has increased from 8% to over 13% to date on 100 mm2 commercial silicon cells by refining the process with advanced device technologies. Together with increased production volume, the cost per watt has been reduced from over $ 8 in the 80's to as low as $3 to day. However, the cost is still considered too high to compete with fossil fuel energy. Further cost reduction is necessary by improving the cell and module conversion efficiency. The increase in cell efficiency and the process to achieve the goal, however, have to follow the golden rule of economics that the operational cost is a fraction of the profit in return. It is shown numerically in this paper that Anti Reflection (AR) coating on silicon solar cells by Atmospheric Pressure Chemical Vapor Deposition (APCVD) technique for large volume production could have over 650% profit return.
More Insights Into the ZnO/a-SiC:H(B) Interface - An Improved TCO/p Contact
Authors: Böhmer E. , Siebke F. , Rech B. , Beneking C. , Wagner H.
Published: April 2011

Solar cells based on amorphous silicon (a-Si:H) exhibit a decreased fill factor if ZnO is used as front electrode instead of SnO2. This is due to a poor electric contact between the ZnO and the p-type a-SiC:H(B) layer. To gain a deeper understanding of the chemical and electronic properties of the ZnO/p interface, in-situ XPS measurements were applied to thin a-SiC:H(B) films deposited on ZnO. The effects of CO2 and H2 plasma pretreatments on clean ZnO surfaces and the influence of deposition conditions on the ZnO/a-SiC:H interface were investigated. Upon H2 plasma treatment the formation of SiOx by chemical transport of Si from the reactor walls is observed. Furthermore, a shift of all core levels towards higher binding energies indicates the formation of an accumulation layer. CO2 plasma treatments show no effects on ZnO. Depth profiling across the ZnO/a-SiC:H interface indicates SiO2 formation on ZnO. The depth profile of ZnO related core levels exhibits two features: a reduction of the ZnO at the interface, and, after longer sputter times, a core level shift towards higher binding energy due to an hydrogen induced accumulation layer in the n-type ZnO. The latter causes a depletion of the p-layer resulting in an enhanced series resistance and diminished fill factor. To reduce the depletion layer thin highly conductive microcrystalline layers were introduced, increasing the fill factor up to 74%.
A Learning Curve Approach to Projecting Cost and Performance in Thin Film Photovoltaics
Authors: Cody George , Tiedje Thomas
Published: April 2011

The current cost of electricity generated by PV power is still extremely high with respect to utility power and there remain questions as to whether PV power can ever be competitive with electricity generated by fossil fuels. A previous paper by the authors supplied an objective framework for considering this important question and introduced analytical tools to define and project the technical/economic status of PV power through the year 2010. In this paper, we update this previous work in the context of the recent announcements by Amoco/Enron Solar of projected sales of PV power in 1997 at rates considerably less than the US average.
Optimization Of Porous Silicon Reflectance For Solar Cell Applications
Authors: Coles A. X. , Gerhardt R. A. , Rohatgi A.
Published: April 2011

The potential use of porous silicon as an antireflective coating on solar cells has recently been recognized. This study investigates the effect of current density, anodization time, and surface conditions on the reflectance of porous silicon which was fabricated by anodizing (100) float zone single crystal Si wafers. The wafers were coated on one side with Al prior to anodization, and a HFbased solution was used as the electrolyte. Current densities of 5 – 100 mA/cm2 were used to anodize both polished and unpolished wafers over time intervals ranging from 2sec - 30 minutes. Reflectance properties were tested over the 400 - 1100 nm range, and minimum reflectances of 3 – 5% were achieved. The reflectance of the best porous Si sample normalized with respect to the sun's spectrum compares favorably with the reflectance of a double layer ZnS/ MgF2 with prior texturing.
Contamination Problems of Amorphous Silicon N-I-P Solar Cells on Metal Substrates
Authors: Goetz M. , Keppner H. , Pernet P. , Hotz W. , Shah A.
Published: April 2011

Commercial aluminium and stainless steel sheets were used as substrates for thin film silicon solar cell deposition. The influence of elemental contamination and disturbed film growth on solar cell performance and yield were studied. Diffusion during film growth was found to be more pronounced than thermally activated interdiffusion of existing films. Surface irregularities of the substrate are shown to reduce the fill factor of the solar cell. Initial efficiencies of 8.5% with single-junction amorphous silicon solar cells on both types of metal sheets were reached.
Establishing a Quantitative Relationship Between Harmonic Signals and Damage in Interconnects
Authors: Wen Qingzhe , Clarke David R.
Published: April 2011

When a metal conductor is driven by an AC current of frequency ω, its resistance will vary at a frequency 2ω, and a third harmonic voltage will be generated. If the conductor is also under a DC bias, a second harmonic voltage will arise as well. The magnitude of these harmonic voltages increases with damage because of nonlinear increases in the resistance caused by localized Joule heating. We use the harmonic technique to evaluate the damage in metal lines. The correlation between deliberately introduced defects of different sizes and the amplitude of the harmonic voltages has been studied experimentally. The harmonic technique shows higher damage sensitivity than the commonly used resistance method. Additionally, it has a better rejection to noise and resistance drifting.
Electromigration in Thin Metal Films in the Presence of Two Stress-Relaxation Mechanisms
Authors: Katsman A. , Levin L.
Published: April 2011

Kinetics of mass transfer in thin metal films during electromigration was analyzed as a function of the generated internal stress. Stress evolution was considered for the case when two different stress relaxation mechanisms can operate simultaneously near the anode end of the strip: thresholdless diffusional creep through a fixed aperture, and diffusional creep with a threshold stress, σt, through the same aperture. Stress distribution and electromigration rate were found as explicit functions of the film length, the aperture size, and the current density. The apparent threshold length was analyzed. It was shown that an apparent threshold product can grow with the current density, in agreement with the experimental results.
Film Crystallographic Texture and Substrate Urface Roughness in Layered Aluminum Metallization
Authors: Rodbell K. P. , Svilan V. , Gignac L. M. , Dehaven P. W. , Murphy R. J. , Licata T. J.
Published: April 2011

Material anisotropy implies that many film properties are affected by crystallographic orientation in the growth direction (out-of-plane texture) and / or in the plane of growth (in-plane texture). Physical vapor deposited (PVD) Ti and Al-alloy films deposited on silicon dioxide substrates typically exhibit strong fiber textures in the growth direction with little in-plane-texture observed. The strength of these fiber textures has been found to vary substantially depending on the details of the deposition process(es) and, to a lesser degree, on any post-deposition anneals. In this paper the role of the substrate surface roughness in defining film texture is reported. It was found that the substrate surface roughness determines the overlying film crystallographic orientation for Ti and Ti/AlCu films deposited on various oxides. Furthermore, it was found that the texture of the initial metal “seed” layer defines the texture in subsequently deposited films (texture inheritance). Modifications to the oxide surface which decrease the surface roughness lead to an improved crystallographic texture in Ti, AlCu, Ti/AlCu and Ti/TiN/AlCu films. Film orientation was determined from crystallographic pole figures measured using x-ray diffraction (XRD). The oxide surface roughness was measured using atomic force microscopy (AFM), transmission electron microscopy (TEM) and glancing incidence x-ray reflectivity (GIXR).
Evaluation of Microstructure Evolution of Al-1%SI-0.5%CU Thin Film Induced By Post Deposition Processing
Authors: Zaccherini C. , Bacchetta M. , Pavia G. , Riva L. , Savoia C.
Published: April 2011

The evolution of grain structure of AI-1%Si-0.5%Cu film, deposited by sputtering at 150'C substrate temperature has been evaluated, comparing as deposited film microstructure and grain structure at the end of process, both on large metal areas and on narrow strips. Microstructure has been characterized by means of FIB, TEM and XRD analyses. Grain size evolution resulted to be strongly dependent from the type of substrate. In particular TiN substrate appeared to greatly inhibit AlSiCu grain growth. This behavior was attributed to the formation of Ti9AI23 intermetallic compound during the alloy thermal treatment, that pins grain boundaries thus limiting Al grain boundary mobility.
The Failure Mechanism of MOCVD TiN Diffusion Barrier at high Temperature
Authors: Lee Hoojeong , Sinclair Robert , Li Pamela , Roberts Bruce
Published: April 2011

By using TDEAT and ammonia gas, MOCVD TiN films were grown at 300°C and 30torr.After annealing in a vacuum furnace at 500°C, 550°C, and 600°C, the TiN films were investigated by transmission electron microscopy (TEM). After annealing at 550°C, both hexagonal and cubic AIN phase were found at the interface between Al and TiN films. A Ti rich phase such as Al3Ti was also found at Al side. The failure mechanism during high temperature annealing is discussed.
Reactive Plasma Sputter Deposition of Silicon Oxide
Authors: Vossough K. K. , Hunt C. E.
Published: April 2011

Silicon dioxide films were reactively sputter deposited in argon/oxygen ambient using RF magnetron sputter deposition techniques. A substantial drop in the deposition rate at high enough partial pressure of the oxygen which is typical in reactive sputtering was observed. The best quality silicon dioxide films were obtained at the lower deposition rate, close to the deposition rate transition point. Higher quality films were obtained at higher RF powers with higher deposition rates. However, at 800 Watts RF, the so called negative ion effect dominates and results in higher surface roughness of the films, as seen by AFM results. Various characterization techniques including ellipsometry and wet chemical etching were used to compare stoichiometry and film density, respectively. MOS capacitor characterization along with breakdown voltages were also measured as a means of qualifying the films.
Hot Carrier Reliability in Sub-0.1 μm nMOSFET Devices
Authors: Saha Samar K.
Published: April 2011

This paper presents a systematic investigation of the hot-carrier effect in deep sub-micron silicon nMOSFET devices. A Hydrodynamic model for semiconductors was used to simulate the local carrier heating and the non-local transport phenomena in nMOSFETs of effective channel lengths 41, 66, 96, and 126 nrn under various biasing conditions. Test structures for device simulation were generated by using a super-steep retrograde channel profile with subsurface peak concentration of l×1018 cm−3, and a gate oxide thickness of 3 nm. Superb MOSFET device characteristics were obtained for all devices. The simulation results show a significant decrease in substrate current, electron impact ionization rate, and peak electron temperature near the drain end of the channel with the decrease in supply voltage. The distribution of electrons into the substrate due to local electron heating is shown to be responsible for hot-carrier reliability in ultra-short channel silicon nMOSFET devices.
Hot Carrier Effects in Deep Submicron Nmosfets
Authors: Phanse Abhijit , Saha Samar
Published: April 2011

This paper addresses hot-carrier related reliability issues in deep submicron silicon nMOSFET devices. In order to monitor the hot-carrier induced device degradation, the substrate current was measured for devices with varying channel lengths (20 um - 0.24 um) under various biasing conditions. Deep submicron devices experience velocity saturation of channel carriers due to extremely high lateral electric fields. To evaluate the effects of velocity saturation in the channel, the pinch-off length in the channel was extracted for all the devices of the target technology. It was observed that for very short channel devices, carriers in most of the channel experience velocity saturation and almost the entire channel gets pinched off. It is shown in this paper that for very short channel devices, the pinch-off length in the channel is limited by the effective channel length, and that velocity saturation effects are critical to the transport of channel carriers.
Low Temperature (850 °C) Two-Step N2O Annealed Thin Gate Oxides
Authors: Lai Chao Sung , Lee Chung Len , Lei Tan Fu , Chao Tien Sheng , Peng Chun Hung , Wang Han Ching
Published: April 2011

The electrical characteristics of thin gate dielectrics prepared by low temperature (850 °C) two-step N20 nitridation (LTN) process are presented. The gate oxides were grown by wet oxidation at 800 °C and then annealed in N2O at 850 °C. The oxide with N2O anneal, even for low temperature (850 °C), had nitrogen incorporation at oxide/silicon interface. The charge trapping phenomena and interface-state generation (ΔDitm) induced by constant current stressing were reduced and charge-to-breakdown (Qbd) under constant current stressing was increased. This LTN oxynitride was used as gate dielectric for N-channel MOSFET, whose hot-canrier immunity was shown improved and reverse short channel effect (RSCE) was suppressed.
A New, Real-Time Method for Measuring Mobile Charge and Injected Charge in SiO2 on Si
Authors: Edelman P. , Lagowski J. , Savchouk A. , Hoff A. , Jastrzebski L. , Persson E.
Published: April 2011

We present a new approach to measuring mobile charge in SiO2 without MOS test structures. The measurement is done in non-contact mode and offers a whole-wafer mapping capability of the mobile charge in single minutes. Determination of the mobile charge is based on monitoring the ion drift by measuring corresponding changes in the oxide voltage. The drift is induced on the whole wafer by corona charge deposited on SiO2 followed by 200°C annealing. Surface contamination is distinguished from bulk contamination by selecting the appropriate sequence of the corona-temperature-stress, which injects ions from the surface into the SiO2.
Finite Element Modeling Of Grain Aspect Ratio And Strain Energy Density In A Textured Copper Thin Film
Authors: Vinci R. P. , Bravman J. C.
Published: April 2011

We have modeled the effects of grain aspect ratio on strain energy density in (100)-oriented grains in a (111 )-textured Cu film on a Si substrate. Minimization of surface energy, interface energy, and strain energy density (SED) drives preferential growth of grains of certain crystallographic orientations in thin films. Under conditions in which the SED driving force exceeds the surface- and interface-energy driving forces, Cu films develop abnormally large (100) oriented grains during annealing. In the elastic regime the SED differences between the (100) grains and the film average arise from elastic anisotropy. Previous analyses indicate that several factors (e.g. elimination of grain boundaries during grain growth) may alter the magnitude of the SED driving force. We demonstrate, using finite element modeling of a single columnar (100) grain in a (111) film, that changes in grain aspect ratio can significantly affect the SED driving force. A minimum SED driving force is found for (100) Cu grains with diameters on the order of the film thickness. In the absence of other stagnation mechanisms, such behavior could cause small grains to grow abnormally and then stagnate while large grains continue to grow. This would lead to a bimodal grain size distribution in the (100) grains preferred by the SED minimization.
Thermal- And Electromigration- Induced Stresses In Passivated Al- And Alsicu-Interconnects
Authors: Beckers D. , Schroeder H. , Eppler I. , Schilling W.
Published: April 2011

Al and Al- alloys are commonly used as interconnect materials in integrated electronic devices. Stress induced voiding and degradation of metal lines by electromigration are closely related to the stresses in the lines.

We have studied the strain and stress evolution during thermal cycling, isothermal relaxation and due to electromigration in passivated Al and AlSi(1%)Cu(0.5%) lines by Xray diffraction with variation of experimental parameters such as the aspect ratio and the electrical current density. Furthermore the extent of voiding and plastic shear deformation has been determined from the experimental metal strains with the help of finite element calculations.

Main results are: 1) During thermal cycling the voiding is less than 2.10-3. The extent of plastic shear deformation increases with increasing line width and with decreasing flowstress. 2) During isothermal relaxation void growth occurs but no significant change in the plastic shear deformation. 3) An electric current in the lines causes no measurable additional change of the volume averaged stresses up to line failure.
Temperature Dependence Of Residual Stresses In Capped Blanket Cu Films Of Various Thicknesses
Authors: Langelaan G. , Saimoto S. , Moske M.
Published: April 2011

Residual strains in thin films of 1.0 μm, 0.5 μm and 0.25 μm Cu capped with 24 nm Ta and a 62 nm Ta diffusion barrier were measured using x-rays during continuous temperature ramping. Cycles up to 300°C and 400°C were performed. At ambient temperature, the flow stresses after heating to 400°C were found to increase wth decreasing film thickness. The stresses were sufficiently high below 100°C to cause plastic yielding. The diffracted intensities from the in-plane and out-of-plane (111) planes were recorded with temperature and the intensity changes were attributed to the necessary dislocation density and distribution variation to accomodate the mismatch strain due to thermal expansion differences.
Activation Energy of Electromigration in Copper Thin Film Conductor Lines
Authors: Gladkikh A. , Lereah Y. , Karpovski M. , Palevski A. , Kaganovskii Yu. S.
Published: April 2011

Activation energy of electromigration damage was determined as 1.2 eV for Cu
lines, indicating grain boundary paths for electromigrationo The surface diffusion was found to play a role during electromigration in Cu and impeded the failure process.
Residual Stress And Lattice Distortion Mapping Of Patterned Devices Which Failed Electromigration Testing Using The Microbeam X-Ray Diffraction (MXRD) Technique
Authors: York B. R. , Pfizenmayer H. L. , Lee C. H. , Carnes R. O.
Published: April 2011

Spatially resolved residual stress and lattice distortion measurements have been made or experimental RF NPN devices which failed electromigration testing. The experimental devices underwent a steady state long term life test for 38272 hours at a die temperature of 100 degrees Celsius and device emitter currents of 100 mA. Residual stress contour maps of the Au interconnect metallurgy of these patterned devices were constructed with spatial resolution approaching 13 microns. The stress contour maps clearly show areas of the Au interconnect emitter lines, approximately 17 microns wide, which buckled when the local stresses exceeded the adhesion limits of these films. A stress gradient was observed going along the Au line from the emitter to the wire bonded pad which went from slightly compressive near the emitter to tensile approaching the wire bonded lead, and consistent with electromigration failures. In addition, lattice distortions as determined by integral line breadths, which were least square fitted by a gaussian*orentzian convolution of the instrument function, show a large continuous increase along the Au interconnect line in going from the emitter to the wire bond pad. The data was acquired using a 4-circle x-ray diffractometer which was specifically constructed to study electromigration issues in-situ. The diffractometer has a very low sphere of confusion (< 5 microns) and is equipped with tapered glass capillary optics, a mechanical, electrical, and thermal stressing stage and various energy dispersive (EDX) or position sensitive (PSD) detectors.
Electromigration In Submicron Wide Copper Lines
Authors: Kononenko O. V. , Matveev V. N. , Koval Yu. I. , Dubonos S. V. , Volkov V. T.
Published: April 2011

Copper films were deposited onto oxidized silicon wafers by the self-ion assisted technique. A 0 and 6 kV bias was applied to the substrate during the deposition. The films were patterned into parallel line arrays of 20 lines 0.5 mm long, using electron lithography and dry etching. After patterning, the lines were covered by silicon oxide and annealed in vacuum for 1 hour at the temperature 450° C. Electromigration testing was performed in air in the temperature range from 280° to 350° C and at a current density 3.106 A/cm2.

It was found that the resistivities of the films deposited at 6 kV and without bias were 1.7 and 2.0 μΩ-cm, respectively. The median times to failure are 398.6 and 240 h and the deviations in the time to failure are 0.8 and 0.54 for 6 kV lines and 0 kV lines, respectively. An electromigration activation energy of 0.89 eV was found for 0 kV films.
Characterization of Electromigration Failures Using a Novel Test Structure
Authors: Gall Martin , Jawarani Dharmesh , Kawasaki Hisao
Published: April 2011

Electromigration failures occur at locations where Al mass transport flux divergences exhibit a maximum. In VLSI circuits, these locations correspond to tungsten plug contact / via areas. Characterizing and understanding electromigration failures at tungsten plug contact / via areas are essential in assuring the reliability of 0.5 μm and smaller devices. In this study, a novel test structure with four vias connecting metal 1 and metal 2 levels was used to separate two stages in the Al-Cu interconnect electromigration process. These stages are the incubation time during which Cu in the Al-Cu alloy is swept away from the via area and an Al drift time which leads to interconnect failure. By the use of this structure, a non-destructive method has been established to measure incubation times and Al drift times separately, monitoring discrete increases in line resistance corresponding to a sequential depletion of all four vias. Activation energies for both processes have been determined. The temperature dependence of the incubation time is characterized by a thermal activation energy of Q=1.08 ± 0.15 eV, indicative of Cu grain boundary diffusion through Al grains. Al depletion was found to occur with an activation energy of Q=0.72 ± 0.12 eV. We therefore conclude that Al self-grain boundary diffusion constitutes the Al depletion mechanism. The application of this novel test structure enables distinct determination of dominating failure mechanisms under operating conditions and therefore provides a realistic reliability assessment of actual on-chip interconnect structures.