bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling a Cement Degradation Experiment by a Hydraulic Transport and Chemical Equilibrium Coupled Code
Authors: Pfingsten W. , Shiotsuki M.
Published: April 2011

An experiment degrading a porous cement disc by pure water was modelled by a reactive transport model including chemical reactions, mineral precipitation/dissolution reactions and changing hydraulic properties of the cement. For the early cement degradation or high pH phase, an equilibrium sorption approach is used for the release of alkali metals. Porosity changes of the porous cement disc during degradation induce conductivity changes that are taken into account in the modelling by coupling back transport to geochemical parameters.
Laboratory Measurement of Low-Permeability Rocks With a New Flow Pump System
Authors: Zhang Ming , Takahashi Manabu , Esaki Tetsuro
Published: April 2011

Nearly impermeable host rocks have been recognized as favorable media for many kinds of underground utilization such as radioactive nuclear waste disposal, storage of oil and LP gas, and CAES. To properly evaluate the ability of a geologic medium to retard transmission of fluids, it is necessary to accurately measure its hydraulic properties, most notably the permeability and specific storage. This paper presents a new flow pump permeability test system capable of testing low-permeability rocks under high confining and high pore pressure conditions, which simulate ground pressures at large depths. The new system was used to test the Inada Granite from Japan. The results of present study show that: 1) both permeability and specific storage of the rock are dependent not only on the confining pressure but also on the pore pressure. They decrease with the increment of the effective confining pressure, i.e., the difference between confining and pore pressures; 2) the permeability and specific storage of Inada Granite range from 10−11 to 10−12 cm/s and 10−6 to 10−7 1/cm, respectively. The flow pump technique with its rigorous theoretical analysis can be used to effectively obtain such low permeabilities within several tens of hours; 3) the storage capacity of flow pump system itself decreases with the increment of fluid pressure within the permeating system.
pH-Dependency of HLW Glass Dissolution and Sorption Behavior of Eu, Th, and U on Glass Corrosion Products
Authors: Luckscheiter B. , Grambow B.
Published: April 2011

Radionuclide release rates of HLW glasses in brines are normally orders of magnitude lower than glass corrosion rates. Various mechanisms were invoked to explain the experimental release; they may be controlled by the glass dissolution rate, solubility, sorption, coprecipitation, etc.. Glass matrix corrosion kinetics is described by a first order equation, where pH, S/V ratio, an initial constant rate and affinity term based on orthosilic acid activity are the key parameters. The dissolution rate decreases significantly as dissolved silica accumulates in solution
Characteristics of Materials Produced by Plasma Treatment of Radioactive Wastes
Authors: Hoffelner W. , Haefeli V. , Burkhard R.
Published: April 2011

Plasma processes become more and more attractive for the treatment of radioactive low/medium level waste. Plants with throughput rates ranging from 20 kilograms to several hundred kilograms per hour are under construction or under evaluation in different countries. One major installation is under construction at the ZWILAG-site in Wurenlingen (Switzerland). ZWILAG (Zwischenlager Wurenlingen AG) is a company being responsible for treatment and intermediate storage of all radioactive wastes occurring in Switzerland. Thermal destruction (pyrolysis) of organic material and melting of the inorganic residuals and inorganic feed stock can be done simultaneously in a plasma heated vessel. The following output materials are obtained: Metal, glassy slag, off-gas. Depending on feed stock and storage requirements these outputs can have different properties. The distribution of the activity is of particular importance. Isotopes like cobalt-60 (as a metal) partition almost quantitatively to the metal phase. Volatile isotopes like cesium-137 partition to some extent to the off-gas, they can however be retained in the slag to a high extent by employing a two stage process. For some applications the activity in the metal can be kept below the activity tolerance limits making the metal suitable for even non nuclear applications. The most important property of the slag is its leaching behaviour. Mechanical properties can be of importance, too. The paper will present examples from different types of radioactive waste: typical low level mixed waste, ion exchange resins and zeolites, mixtures of concrete and metal, contaminated soil, material contaminated with natural activity and others. Composition of the materials, activity distributions, data on leaching behaviour and some mechanical properties are presented
Effects of Band Offsets on a-Sic:H/c-Si Heterojunction Solar Cell Performance
Authors: Cleef M. W. M. Van , Rubinelli F. A. , Schropp R. E. I.
Published: April 2011

We used the internal photoemission technique to determine the exact valence and conduction band offsets at the a-SiC:H/c-Si interface and investigated with numerical simulations their effects on the photocarrier collection in p+a-SiC:H/n c-Si heterojunction solar cells. The valence and conduction band offsets were found to be 0.60 eV and 0.55 eV, respectively. Simulation results show that a high valence band offset increases the open circuit voltage (higher built-in potential) but on the other hand can decrease the fill factor (by blocking the collection of photogenerated holes at the front contact). Interestingly, despite having a large barrier inside the valence band (ΔEv = 0.6 eV), our highly doped p+a-SiC:H/n c-Si heterojunction solar cells show no collection problems (FF= 0.73). Both IPE measurements and simulation results indicate that tunneling of holes through this barrier in the valence band can explain this effect. For thin highly doped (Eact = 0.33 eV) p+a-SiC:H layers, the tunnel barrier becomes very narrow (< 70 Å) and the tunneling probability is strongly enhanced.
Stable Solar Cells Prepared from Dichlorosilane
Authors: Yamamoto Y. , Futako W. , Fukutani K. , Hagino M. , Sugawara T. , Kamiya T. , Fortmann C.M. , Shimizu I.
Published: April 2011

Amorphous silicon films and solar cell i-layers were prepared from dichlorosilane(DCS) by ECR- and VHF-CVD. The hydrogen content, the chlorine content and the band gap could be controlled by varying argon and hydrogen dilution. The interaction of energetic and reactive plasma species with substrates and other previously deposited layers was studied. DCS, ECR-CVD causes darkening of TCO substrates even when buffer layers and/or doped layers were previously deposited by RF-CVD. Therefore n-i-p solar cell structures were prepared on NiCr and subsequent p-i-n solar cells were prepared with VHF-CVD which did not causeTCO reduction or other reactions in previously deposited amorphous layers. Preliminary results indicate that the VHF-CVD solar cells are at least as stable as standard amorphous silicon solar cells.
Narrow Band Gap Amorphous Silicon-Based Solar Cells Prepared by High Temperature Processing
Authors: Kambe M. , Yamamoto Y. , Fukutani K. , Kamiya T. , Fortmann C.M. , Shimizu I.
Published: April 2011

Generally higher depositions temperatures are required to prepare solar cells with narrow band gap amorphous silicon intrinsic layers. High processing temperatures require that diffusion resistant substrates and doped layer materials be developed. In the case of p-i-n solar cells both a new Ga-doped ZnO and/or semi-transparent Cr over-coated standard commercially available TCO show increased resistance to high temperature processing and it is possible to prepare efficient solar cells on these substrates at temperatures over 280 C. In most amorphous silicon i-layer cases a-SiC:H p-layers offer better diffusion resistance than microcrystalline players. However, in the case of narrow band gap amorphous silicon prepared at high temperatures using the argon treatment process [2] micro-crystalline p-layers offer significantly improved solar cell performance. Another promising approach involves the n-i-p deposition sequence, however, this case too can suffer from diffusion related problems.
Extremely Narrow Band Gap,∼1·50Ev, Amorphous Silicon
Authors: Fukutani K. , Sugawara T. , Futako W , Kamiya T. , Fortmann C.M. , Shimizu I.
Published: April 2011

Hydrogenated amorphous silicon (a-Si:H) films were prepared by a layer-by-layer (LBL) argon treatment technique. Thin amorphous silicon layers are first deposited and then treated by Ar. Thick films are built up by repeatedly the process many times. By reducing the deposition rate during deposition time (T, sec), a-Si:H with the gaps narrower than 1·55eV were prepared at substrate temperature lower than 300°C. These narrow-gap films contained less than 2 at.% hydrogen and had rigid Si network. Also, these narrow gap films exhibited good light soaking stability.
Programmable 3-Dimensional Memories Based on Current Induced Conductivity in Hydrogenated Amorphous Silicon Nitride
Authors: Shannon J.M. , Lau S.P. , Sealy B.J.
Published: April 2011

Changes of several orders of magnitude in the low field conductivity of hydrogenated amorphous silicon alloy metal-semiconductor-metal MSM devices can be obtained by current stressing. This feature is suitable for memory applications, since the device can be programmed from an unstressed state to a stressed state with a ratio greater than 104. The change in conductivity is attributed to the creation of a large concentration of silicon dangling bond states during current stressing which form a defect band with a low activation energy for current transport. In this paper, we consider the use of current induced conductivity in hydrogenated amorphous silicon nitride (a-SiNx:H) multi-layer structures and show that, in principle, highly complex three dimensional circuits could be made. In particular, the potential of this approach is illustrated by using a simple MSMSM device with two silicon rich silicon nitride layers. An array with lxi0 elements has been fabricated and programmed to store 28 bits of binary information with three outputs per input.
Wide Band Gap a-Si:H Based Ihgh Gain Vidicon Devices Prepared by Chemical Anniealing
Authors: Futako W. , Sugawara T. , Kamiya T. , Fortmann C.M. , Shimizu I.
Published: April 2011

Previously it was shown that high quality wide gap hydrogenated amorphous silicon material could be prepared by a layer-by-layer technique involving hydrogen chemical annealing. Using this wide gap material, high electric field, n-i-p diode devices were fabricated. Reverse bias dark current was suppressed by optimization of the n-layer doping level (250ppm) and the thickness (2000Å). Working vidicon type device were prepared, tested, and optimized by further reduction in the high reverse bias leakage current. Vidicon devices showed very promising performance; however, at the present stage of development some point defects were observable at the highest reverse bias voltages probed (∼-6×105 V/cm).
Nucleation of p-Type Microcrystalline Silicon on Amorphous Silicon for n-i-p Solar Cells Using B(CH3)3 And BF3 Dopant Source Gases
Authors: Koh Joohyun , Fujiwara H. , Koval R. J. , Wronski C. R. , Collins R. W. , Claflin B. , Lucovsky G.
Published: April 2011

Real time spectroscopic ellipsometry (RTSE) has been applied to identify optimal conditions for the nucleation and growth of 120 Å microcrystalline silicon (μc-Si:H) p-layers by rf plasma-enhanced chemical vapor deposition (PECVD) at 200°C on amorphous silicon (a-Si:H) i-layers in the n-i-p solar cell configuration. Analysis of the RTSE data provide the bulk p-layer dielectric function (2.5-4.3 eV), whose amplitude and shape yield insights into the structural quality and crystallinity of the p-layer. Among the deposition parameters varied include the underlying i-layer surface treatment, the p-layer plasma power flux, and the p-layer dopant source gas and flow ratio. Here we focus on the differences between p-layer deposition using trimethyl boron, B(CH3)3, and boron trifluoride, BF3, source gases. We find significant differences attributed to the differing effects of F and CH3radicals in the plasma on silicon crystallite growth.
Stability Improvement of a-Si:H Films Deposited in Sqwm-55 kHz Glow Discharge Plasma
Authors: Budaguan B.G. , Aivazov A.A.
Published: April 2011

In this work we have used square-wave-modulated (SQWM) low frequency (55kHz) glow discharge plasma for deposition of a-Si:H films and observed a significant stability improvement. To investigate the origin of stability improvement the relation between growth mechanism, film microstructure and metastability was analyzed. It was shown that the use of SQWM-plasma decreases the concentration and average size of inhomogeneities calculated from AFM data while photoconductivity under He-Ne laser illumination (Staebler-Wronski effects) didn't degrade during standard time of experiments. Differential scanning calorimetry (DSC) measurements were carried out and it was found that in SQWM samples hydrogen effusion occurs at higher temperatures than in cw a-Si:H which is connected with increased structural stability of films deposited in SQWM-plasma. Taking into account the high photoconductivity and low defect density of SQWM samples it is concluded that modulating of LF plasma is a perspective method for deposition of stable a-Si:H films and its alloys.
Comparison of VHF, RF and Dc Plasma Excitation for a-Si:H Deposition with Hydrogen Dilution
Authors: Platz R. , Hof C. , Wieder S. , Rech B. , Fischer D. , Shah A. , Payne A. , Wagner S.
Published: April 2011

A comparative study of DC, RF and VHF excitation for the plasma enhanced chemical vapor deposition (PECVD) of intrinsic layers of a-Si:H is presented, with special emphasis on the effects of hydrogen dilution. Growth rates at comparable plasma power, for substrate temperatures between 100°C and 300°C and for various H2 dilution ratios are presented, along with optical bandgap, H content, and electronic transport properties in the light-soaked state.

H2 strongly reduces the growth rate for all techniques. The growth rate for the highest H2 dilution ratio is approximately four times higher for VHF than for DC or RF excitation. In all three cases increasing the substrate temperature reduces the optical gap and the H content CH. Raising the substrate temperature slightly enhances the stability of undiluted films. H2 dilution increases the optical gap for all three techniques. The H content of RF- and VHF-deposited samples increases with increasing H2 dilution ratio, while in DC deposition it produces an initial drop of the H content, followed by an increase.

In all three cases, H2 dilution improves the electronic transport properties of the material by roughly a factor of two. The gain in stability is most pronounced for relatively small dilution; in the case of DC deposition, too strong a dilution even has an adverse effect on stability.
Electrode Interdependence and Hole Capacitance in the Capacitance -Voltage Characteristics of Hydrogenated Amorphous Silicon Thin-Film Transistors
Authors: Park Hyuk-Ryeol , Cohen J. David
Published: April 2011

The inter-electrode capacitance - voltage (C-V) characteristics of back-channel etched inverted-staggered hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) were investigated. It is demonstrated that this simple measurement can be used to diagnose TFT parameters such as the fabricated channel length, the channel resistance, and the error in the mask alignment of the source and drain overlap lengths. The C-V characteristics associated with the hole accumulation in a-Si:H TFTs with n+-type source/drain contacts were also examined. We observed that the a.c. capacitance increases for low frequencies and/or moderately high measurement temperatures provided the gate voltage is sufficiently negative.
Microcrystalline Silicon-Germanium Alloys for Absorption Layers in Thin Film Solar Cells
Authors: Carius R. , Fölsch J. , Lundszien D. , Houben L. , Finger F.
Published: April 2011

Thin microcrystalline silicon-germanium films (μ-Sil.xGex:H) prepared by PECVD at 95 MHz have been investigated. The optical absorption of these films increases in the infrared spectral region with increasing germanium content. In addition to the shift of the indirect gap an increase of the absorption coefficient above the band edge is observed. The material shows high crystallinity and exhibits good structural quality similar to pure μ-Si:H films. The films are homogeneous on a macroscopic to a microscopic scale as confirmed by Raman spectroscopy and Electron Microscopy methods. p-i-n solar cells with pc-Sil-xGex:H i-layers have been prepared for the first time. An efficiency of η = 3.1 % under AM1.5 has been obtained for a cell with 150 nm thin i-layer.
How do Impurities Affect the Growth of μc-Si:H?
Authors: Kamei Toshihiro , Fukawa Makoto , Nishimiya Tatsuyuki , Isomura Masao , Kondo Michio , Matsuda Akihisa , Claflin B. , Lucovsky G.
Published: April 2011

Ultra clean plasma CVD process opens the doorway to clarify the role of impurities in the growth process of μc-Si:H. A reduction of impurity levels during the growth extends the temperature range for crystalline formation to lower side, i.e., high-crystallinity μc-Si:H formation even at room temperature, substantially reduces midgap defect density at 200°C, and enlarges crystalline grain size at 350°C. These results imply that impurities disrupt crystalline formation even on hydrogen covered surface. The crystalline-to-amorphous transition is induced by a loss of surface hydrogen coverage due to thermal hydrogen desorption at higher temperature of ∼450°C irrespective of the effect of oxygen impurity. Light-soaking experiments for the series of the films from a-Si:H to μc-Si:H films with different crystalline volume fraction indicate that the presence of small volume fraction of crystallite significantly suppresses light induced defect creation under the present light soaking condition of 3SUN 60°C 6hr. These results are explained in terms of preferential recombination of photo-excited carriers in the crystallite.
Hot-Wire CVD Poly-Silicon Films for Thin Film Devices
Authors: Rath J.K. , Tichelaar F.D. , Meiling H. , Schropp R.E.I.
Published: April 2011

Solar cell using profiled poly-Si:H by HWCVD as i-layer in the configuration SS/n-µSi:H(PECVD)/i-poly-Si:H(HWCVD)/p-µc-Si:H(PECVD)/ITO showed 3.7% efficiency. A current of 23.6 mA/cm2 was generated in only 1.5 µm thick poly-Si:H i-layer grown at ∼5Å/s. TFTs made with the poly-Si:H films (grown at ≥ 9Å/s) exhibited remarkable stability to long duration of 23 hours of gate bias stress of ∼lMV/cm. A saturation mobility of 1.5 cm2/Vs for the TFT has been achieved. Films made at low hydrogen dilution (Poly2) showed device quality (purely intrinsic nature, ambipolar diffusion length of 568 nm, only (220) oriented growth and low ESR defect density of <1017/cm3with complete absence of signal due to conduction electrons) but with an incubation phase of amorphous initial growth, whereas the films made at high hydrogen dilution (Polyl) had a polycrystalline initial growth, though with higher defect density, incorporated oxygen and randomly oriented grains. Poly2 films are compact and hydrogen bonding is at compact Si-H sites manifested as 2000 cm−1IR vibration and high temperature hydrogen evolution peak. Exchange interaction of spins and spin pairing are observed while increasing defects in such a compact structure. A new approach has been used to integrate these two regimes of growth to make profiled poly-Si:H layers. The new layers show good electronic properties as well as complete elimination of incubation phase.
Growth and Properties of Micro-Crystalline (Si,Ge):H Films
Authors: Erickson Karl , Dalal Vikram L. , Chumanov George
Published: April 2011

This paper reports on the growth and characterization of micro-crystalline (Si,Ge) films deposited on glass and polyimide substrates. The films were grown using a hydrogen diluted remote ECR plasma process. The feedstock gases were silane and germane. The entire range of composition from 100% Si to 100% Ge was studied. A low-pressure, low-substrate temperature, and high-power environment was used to change the morphology from amorphous to micro-crystalline. The films deposited at 5 mT pressure are generally micro-crystalline. The film's structure was studied using Raman spectroscopy. Raman spectra show clear, sharp crystalline-type Si and Ge peaks. Electronic properties of the films, such as activation energy and absorption constant down to α = 1 cm−1 were also measured. The sub-gap absorption data also show crystalline absorption behavior, with the absorption shifting to lower energies as the Ge content is increased. This absorption data shows that the materials have low defect densities.
Novel Dichroic Polarizing Materials and Approaches to Large-Area Processing
Authors: Bobrov Yuri. A. , Casey Sean M. , Ignatov Leonid. Y. , Lazarev Pavel I. , Phillips Daniel , Tam-Chang Suk-Wah
Published: April 2011

We have developed new polarizing coating materials and processes which enable the fabrication of polarizers for large-area liquid-crystal displays. The polarizing materials are novel discotic surfactants which self-assemble in aqueous solutions to provide a stable liquid-crystalline phase within a wide range of concentrations and temperatures. These lyotropic liquid crystals in an aqueous medium can be spread on a substrate surface by a variety of techniques including a knife-like doctor blade, a rolling cylinder, or a roll-to-roll method. Under the shearing force applied during deposition, the liquid crystals align on the substrate forming a dichroic polarizer. This alignment process allows continuous production of large-area polarizing films at low cost compared with the current technology that requires stretching of the films. Thin coatings can be applied to flexible plastic films, glass, or rigid plastic substrates. Direct coating of the polarizing material on glass eliminates several process steps in liquid-crystal display production since lamination of the polarizing film is no longer required. These new polarizing films have a high optical performance including a polarizing efficiency of above 98% and a dichroic ratio as high as 7.7.
Synthesis and Characterization of Luminescent ZnO Powders Produced by Thermally-Induced Doping
Authors: Allieri B. , Depero L. E. , Sangaletti L. , Antonini L. , Bettinelli M.
Published: April 2011

A low cost and efficient method of doping pure zinc oxide powders for luminescence applications is presented. The powders have been obtained from pure, non-luminescent ZnO by thermally induced doping under a nitrogen flux and in the presence of ZnS powders. Structural characterization has been carried out by X-ray diffraction analysis (XRD), while luminescence properties have been studied with both a spectrofluorimeter and microraman spectrometer. Emission spectra have shown an increase of the luminescence with treatment temperature. The XRD patterns of all samples showed, along with reflections of the hexagonal phase of ZnO, other reflections ascribed to the hexagonal phase of ZnS. Upon further annealing in air at 800°C, the ZnS reflections disappear even though the luminescence still persists with a comparable intensity. Luminescence is ascribed to ZnO reduction due to the interaction of S with ZnO. It has also been observed that excitation with a He-Ne laser beam (λ=633 nm) with a high specific power (5×10−3 W·µm−2) yielded blue-green luminescence in spite of excitation below the band-to-band absorption threshold.
Luminescence Properties of Thin-Film SrS:Cu Phosphors for Electroluminescent Displays
Authors: Jones T.C. , Park W. , Mohammed E. , Wagner B.K. , Summers C.J. , Sun S.S.
Published: April 2011

The origin of the electronic fine structure in thin-film SrS:Cu has been interpreted in terms of the several possible perturbations including spin-obit coupling, the Jahn-Teller effect and low symmetry splittings. Photoluminescence excitation measurements showed that the peak position of the excitation bands were independent of temperature suggesting that the electronic fine structure in our system was not due to the Jahn-Teller effect. Selective excitation measurements revealed that no peak shift occurs with changing excitation wavelength, indicating that Cu+ pairs or aggregates and Cu+-defect coupled centers were not existent in our system. Finally, several models were proposed for off-center displacements of Cu in SrS, since a rigorous treatment of these displacements is difficult. Both the tetragonal and trigonal distortion models for a <111> displacement yielded reasonable distortions parameters of 0. 16Å and 0.11Å, respectively. However, crystal field analysis showed that a <110> displacement was more likely since the energy level splitting scheme more closely resembled the observed data.
Al-RE-TM (RE = Rare-Earth Metals, TM = Transition Metals) Ternary Alloy Films for TFT-LCD Electrodes
Authors: Takayama Shinji
Published: April 2011

The effects of adding a third transition metal element, Co, Cu, Zr, or Ta, to Al-Nd (or Gd) alloy thin films were studied in order to investigate the changes in the film's microstructure and resistivity, and also their tendency to form hillocks or whiskers at high temperatures. The addition of Zr (or Ta), which has repulsive interactions with both Nd and Gd, to the Al-RE binary alloy films causes an increase of residual resistivity and enhances the formation of hillocks or whiskers at high temperatures. On the other hand, the addition of Cu or Co, which has attractive interactions with both Nd and Gd, results in a resistivity of less than 6 µωcm (depending on the content of added elements). Addition of either of these elements largely suppresses the growth of thermal defects after annealing at over 350 °C. The above results were explained by employing a theory of grain boundary segregation based on a chemical interaction between constituent elements of an alloy.
Mechanisms of Field Emission from Cubic Boron Nitride Coated Molybdenum Emitters
Authors: Schlesser R. , Mccarson B.L. , Sitar Z.
Published: April 2011

A combination of classical I-V characterization and voltage-dependent field emission energy distribution (V-FEED) analysis was employed to investigate the mechanisms that dominate field emission from tip-shaped Mo emitters electrophoretically coated with nominally intrinsic, cubic boron nitride (c-BN) powders. I-V characterization of Mo emitters before and after coating showed that the c-BN coating enhanced the field emission current by 2 orders of magnitude. V-FEED analysis revealed a voltage drop proportional to the applied voltage across the c-BN coating due to field penetration. This voltage drop was typically in the order of several Volts for applied voltages of several 100 Volts, and a cathode-to-anode distance of 500 μm. Extrapolation of V-FEED data to flat band condition identified the conduction band minimum of c-BN as the origin of field emitted electrons. At larger field emission currents, an additional voltage drop was observed and was found to be proportional to the emission current. This observation was interpreted in terms of an ohmic resistance at the Mo/c-BN interface and was estimated to be in the order of 10 MΩ.
Structural and Electronic Properties of Negative Electron Affinity Epitaxial Diamond (110) Films Studied Using Atomic Resolution UHV STM
Authors: Lim S.C. , Stallcup R.E. , Akwani I. , Perez J.M.
Published: April 2011

We report ultrahigh vacuum (UHV) scanning tunneling microscopy (STM) studies of the structural and electronic properties of epitaxial diamond (110) films. We observe that epitaxial diamond (110) films grow very rough due to striations. The striations are found to be due to the appearance of(111) faces and contain (100) steps. UHV STM atomic resolution images of the diamond (110) films show a (lxi) zigzag structure that measures 1.5 ± 0.1 Å × 1.5 ± 0.1 Å, in agreement with theoretical predictions for the hydrogen terminated diamond (110) surface. Ultraviolet spectroscopy shows that the epitaxial films have a photoelectric threshold of 5.3 ± 0.1 eV, providing evidence that the films have a negative electron affinity surface.
Electron Emission from Nano-Structured Diamond
Authors: Zhu W. , Kochanski G. P. , Jin S.
Published: April 2011

Strong and sustained electron emission at low electric fields has been observed in undoped, nano-structured diamond. The cold cathode emitters consist of a layer of nanometer-size diamond particulates coated on a silicon substrate which is subsequently heat treated in a hydrogen plasma for activation. Electron emission for a current density of 10 mA/cm2is observed at an applied field of 3-5 V/μm. We attribute this excellent emission property to the high defect density in the nano-structured diamond particles and the low electron affinity associated with the diamond surface. The emitters are useful for applications such as flat panel displays as, in addition to the very low fields required, they can easily be deposited on large area substrates by low-cost coating techniques and do not require complicated microtip fabrication processes.
Porous Silica: A Potential Material for Low Dielectric Constant Applications
Authors: Birdsell Edward D. , Gerhardt Rosario A.
Published: April 2011

Highly porous (15% dense) silica thin films with k < 2.2 have been produced using a colloidal sol-gel process. This process uses relatively inexpensive, commercially available colloidal silica and potassium silicate. These films were deposited by spin coating. The parameters for spin coating (spin speed, gelation time, gel composition, etc.) have been optimized and coherent films with thicknesses ranging from 0.7–2.0 μm can be reproducibly fabricated. Preliminary work shows that the porosity of these films ranges from a few rn to < 1 μm. The dielectric properties were examined for frequencies up to 1 MHz. Compatibility of the films with IC processing was also investigated.
Fundamental Aspects Of Polymer Metallization
Authors: Faupel F. , Strunskus T. , Kiene M. , Thran A. , Bechtolsheim C. V. , Zaporojtchenko V.
Published: April 2011

Valuable information on the structure and formation of metal-polymer interfaces originates from radiotracer measurements of metal diffusion at the interface, structural investigations by means of transmission electron microscopy, and computer simulations on the interplay of atomic metal diffusion and aggregation. Moreover, X-ray photoemission spectroscopy has largely contributed to our present understanding of the interfacial chemistry and the early stages of interface formation. While reactive metals always form relatively sharp interfaces with polymers, metals of lower reactivity diffuse into polymers at elevated temperatures and have a very strong tendency to agglomerate. The extent of diffusion appears to be determined by the initial stage of the deposition process. Here sticking coefficients recently measured for metals on virgin polymer surfaces deviate markedly from unity. Diffusion into the polymer increases strongly at low deposition rates. No significant diffusion is expected from a continuous metal film unless metal ions are formed at the interface. Metal ions are highly mobile and do not aggregate due to electrostatic repulsion. The model emerging from these observations allows us to predict the salient features of interface formation between metals and polymers in general and particularly with respect to the new low-k polymers.
Stress-Corrosion Cracking of Spin-on Glass Thin Films
Authors: Cook Robert F , Liniger Eric G
Published: April 2011

The crack-velocity behavior of silsesqioxane spin-on glass thin films exposed to moist environments is examined. An absolute reaction-rate model is used to predict crack velocity using a deleted-bond model and fused silica as a basis, and compared with observed steady-state crack velocities as a function of film thickness and variations in the curing process. An implication is that, on curing, the driving force for film fracture, determined by thermal expansion mismatch, increases less rapidly than the fracture resistance, determined by polymerization.
Low Dielectric Constant Materials Integration Challenges
Authors: Ray Gary W.
Published: April 2011

Considerable effort has been expended in recent years in the development, evaluation, and integration of new low Kc dielectric materials for IC applications. Many film properties must be measured before a film can be selected for integration into an interconnect process flow. Among them are glass transition temperature, thermal stability, Young's modulus, adhesion, stress, coefficient of thermal expansion, dielectric constant, breakdown voltage, solvent resistance, dry etch characteristics, and gap fill performance. These properties must in turn be considered when developing interconnect process modules and selecting the associated equipment set. The properties of these materials differ from those of the commonly used (PE)CVD silicon dioxides to varying extents, depending upon the nature of their composition and structure. This has often resulted in substantial modifications to the modules that comprise interconnect process flows, sometimes compromising manufacturability. This paper will address some of the issues associated with the integration of low K materials into interconnect process flows and how they are related to the properties of these materials.
Chemical-Mechanical Planarization of the Polymer Interlayer Dielectrics
Authors: Murarka S. P.
Published: April 2011

Low dielectric constant polymers are being investigated for application as interlayer dielectrics with copper as the metal in a multilevel interconnect scheme. Processing of such structures willrequire the use of chemical-mechanical planarization (CMP) technologies for both the metal and the dielectric. Polymers are comparatively quite soft. They are not readily attacked by chemicals thus requiring more mechanical component dependency compared to the chemical component in the CMP. Polymers are thus prone to scratching during CMP which may lead to reliability problems both from materials and electrical points of view. In this presentation we will discuss the use of chemical engineering and chemistry principles to optimize the polishing process to minimize or eliminate the scratching and other mechanical damages. The role of CMP parameters such as velocity, pressure, particle size, viscosity, and chemistry will be discussed to elucidate the emerging “scratch-free”-CMP-concept.
Overview Of Process Integration Issues For Low K Dielectrics
Authors: Havemann R. H. , Jain M. K. , List R. S. , Ralston A. R. , Shih W-Y. , Jin C. , Chang M. C. , Zielinski E. M. , Dixit G. A. , Singh A. , Russell S. W. , Gaynor J. F. , McKerrow A. J. , Lee W. W.
Published: April 2011

The era of silicon Ultra-Large-Scale-Integration (ULSI) has spurred an everincreasing level of functional integration on-chip, driving a need for greater circuit density and higher performance. While traditional transistor scaling has thus far met this challenge, interconnect scaling has become the performance-limiting factor for new designs. Both interconnect resistance and capacitance play key roles in overall performance, but modeling simulations have highlighted the importance of reducing parasitic capacitance to manage crosstalk, power dissipation and RC delay. New dielectric materials with lower permittivity (k) are needed to meet this challenge. This paper summarizes the process integration and reliability issues associated with the use of novel low k materials in multilevel interconnects.
Reliability and Copper Interconnections with Low Dielectric Constant Materials
Authors: Hu C-K.
Published: April 2011

The materials, process integration, and reliability issues in the development of multilevel electroplated Cu/polyimide on-chip interconnections are described. A combination of: good diffusion/adhesion barrier layers consisting of a metal liner plus the insulator Si3N4, and W stud/Si contacts resulted in a highly reliable IC chip. Electromigration of Cu damascene lines in both SiO2 and polyimide structures was investigated. Similar void growth was observed at the cathode ends of both the interconnect systems. However, the shapes of protrusions at the anode ends of the lines were different. Although the activation energies for both near bamboo-like Cu/SiO2 and Cu/polyimide were both 1.1 eV, the electromigration lifetime of the former was significantly longer. The difference is largely attributable to the poorer thermal conductivity of polyimide.
Aluminum Wiring Reliability of Fluorinated Amorphous Carbon Interlayer
Authors: Iguchi M. , Matsubara Y. , Ito S. , Endo K. , Koyanagi K. , Kishimoto K. , Gomi H. , Tatsumi T. , Horiuchi T.
Published: April 2011

We investigated the aluminum wiring reliability of fluorinated amorphous carbon (a-C:F) interlayer dielectrics (ILD) using electromigration tests at the wafer level under accelerated stress conditions with current density ranging from 25–32 MA/cm2 and a the substrate temperature of 300 K. The a-C:F film is one of the low-k organic materials with a dielectric constant of 2.5. The thermal conductivity of the a-C:F film (0.108 W/m·K) is about one order lower than that of SiO2 (1.2 W/m.K). We found that joule heating effect is enhanced by the lower thermal conductivity of a-C:F and that the wiring lifetime for a-C:F ILD is about one order lower than that for SiO2 ILD under high current stress. However, when the wiring lifetime is plotted as a function of the wiring temperature, the wiring lifetimes for both a-C:F ILD and SiO2 ILD became almost the same. The degradation of the wiring lifetime for a-C:F ILD is explained by the increase of the wiring temperature which is caused from joule heating. Moreover, the activation energy of the electromigration for a-C:F ILD has the same value as that of SiO2 LD at a temperature.
Reliability of Cu/WN thin Films Deposited on Low Dielectric Constant SiOF ILD
Authors: Lee Seoghyeong , Kim Dong Joon , Yang Sung-Hoon , Park Jeongwon , Sohn Seil , Oh Kyunghui , Kim Yong-Tae , Park Jong-Wan
Published: April 2011

The effect of the post plasma treatment on the dielectric properties and reliability of fluorine doped silicon oxide (SiOF) films was studied. Also, the thermal stability of a Cu/WN interconnect system with SiOF intermetal dielectrics was examined by RTA. The surface roughness of SiOF films increased with the increasing plasma treatment power due to ion bombardment effect during the plasma treatment. As the plasma treatment power increased, the dielectric constant increased from 3.16 to 3.43, while the change in the relative dielectric constant of the plasma treated films by the boiling treatment was decreased in magnitude. Furthermore, the chemical properties of the plasma treated SiOF films near the top layer tend to resemble those of thermal oxides by the plasma treatment of sufficient power because of the reduction in the Si-F bonding in the films. In the case of Cu/WN/SiOF/Si multilayer structure, surface oxidation and densification due to the plasma treatment seemed to play an important role in protecting the interdiffusion between SiOF and metal interconnects.
Adhesion Study in Aluminum/Polyimide System
Authors: Yoo S. H. , Heo S. J. , Kim Y.-H. , Han B. J. , Yoon J. H.
Published: April 2011

The effects of RF plasma precleaning and polyimide curing conditions on the peel strength have been studied. polyimide precursors of BG-2480 (Toray) and PI-2611 (Du Pont) were spincoated and cured under the various conditions. Cured polyimide substrates were in-situ Ar+ RF plasma cleaned prior to metal deposition. Al-2%Si or Al-0.5%Cu-1%Si thin films were deposited onto polyimide substrates using DC magnetron sputtering.

The peel strength was enhanced by RF plasma treatment. The Al/modified PI specimen failed cohesively in the polyimide. The polyimide curing condition strongly affects the peel strength in the Al/modified PI system.
Newly Developed Low-K and Low-Stress Fluorinated Silicon Oxide Utilizing Temperature-Difference Liquid-Phase Deposition Technology
Authors: Yeh Ching-Fa , Lee Yueh-Chuan , Lee Su-Chen
Published: April 2011

To meet the requirements of low-K and low-stress intermetal dielectric (IMD) for future ULSI devices, a novel temperature-difference liquid-phase deposition (TD-LPD) method is proposed. The deposition solution of supersaturated silicic acid with high concentration of fluorine can be achieved by raising deposition temperature larger than 15 °C from dissolution temperature (0 °C). Because fluorine atoms can easily be incorporated with the technique, TDLPD fluorine-doped SiO2 (FSG) exhibits low-K (∼3.4) and low-stress (∼40MPa) property. In this paper, to study the interaction between TD-LPD FSG and moisture, the FSG is annealed and moisture stressed repeatedly as in a real process. Since K is sensitive to moisture absorption, and the stress is sensitive to the dehydration reaction between Si-OH's, the both are monitored as indices. A feasible mechanism is proposed to explain the variation in K/stress during annealing and boiling cycles.
The Origin of Nanopipes and Micropipes in Non-Cubic GaN and SiC
Authors: Pirouz P.
Published: April 2011

Micro/nanopipes are linear defects along the c-axis of hexagonal polytypes of SiC and GaN that are currently the focus of much attention. It has been shown that these defects can be very detrimental to the electronic properties of devices manufactured from, at least, 6H-SiC. In this paper, the origin of these defects is discussed in terms of Frank's theory [1] that dislocations will have a hollow core when their Burgers vector is large. Two fundamental issues about such dislocations are addressed: their formation along the c-axis of the crystal, and their stability despite their large Burgers vectors [2]. The proposed model is based on the mosaic structure of sublimation-grown 6H- or 4H-SiC, and VPE-grown 2H-GaN on sapphire substrates. The presence of unit c-axis screw dislocations is attributed to the accommodation of low-angle twist boundaries in the mosaic structure. The formation of superscrew dislocations with large Burgers vector, which empty their cores to reduce the excessive strain energy there, is shown to be the result of 3c screw dislocations in the axis of triple junctions which “getter” the neighboring unit dislocations and simultaneously increase their diameter. The predictions of the model are compared with available data in the literature, and suggestions are made for the decrease of nano/micropipe density.
The Estimation and revision of barrier heights in 4H- SiC and 6H-sic Schottky Diodes
Authors: Lee You-Sang , Kim D.-Y. , Oh J.-K. , Han M.-K. , Choi Y.-I.
Published: April 2011

The barrier heights of various Schottky diodes in n-type 4H-SiC and 6H-SiC is estimated from published data at Si-face and C-face, respectively, employing the LSM (least square method). It is found that the barrier height in SiC Schottky diode is a linear function of metal work function as φB. =a φm + b. The a is about 0.63 ∼ 0.72. The already established analytic expression in [9] is compared with the estimated linear expression and revised by employing the empirical factor, α between the upper and lower boundary of interface state density, DIT. The values of a lie in 1.65 ∼ 32.1.
Turn-on Process in High Voltage 4H-SiC Thyristors
Authors: Dyakonova N. V. , Levinshtein M. E. , Palmour J. W. , Rumyantsev S. L. , Sing R.
Published: April 2011

The turn-on process and the steady state current-voltage characteristics have been investigated in 4H-SiC thyristors with a forward breakover voltage close to 700 V and pulse switch current density of 16 000 A/cm2. The rise current constant, τr, has been found to decrease monotonically with temperature: τr, ≈ 10.5 nsec at T = 300 K and τr ≈ 1.2 nsec at T = 500 K at high bias Uo ≥ 300 V. The value of τr ≈ 1.2 nsec is the lowest observed value for SiC thyristors. At very high current density, j ≥ 5 103 A/cm2, the residual voltage drop for 4H-SiC thyristors is lower than for identically rated Si thyristors. The voltage drop Udo decreases monotonically with temperature.
Deep Levels In High Resistivity AlGaN Films Grown By MOCVD
Authors: Polyakov A. Y. , Smirnov N. B. , Govorkov A. V. , Redwing J. M.
Published: April 2011

Deep levels in high resistivity layers of AlGaN grown by MOCVD on sapphire were studied by means of dark current and photocurrent versus temperature measurements and by photoinduced current relaxation spectroscopy (PICTS). Strong temperature quenching of photocurrent was observed and explained by the presence of hole traps with energies 0.2 eV, 0.3 eV and 0.35 eV for films with correspondingly 5%, 15% and 25% of Al. Two hole traps with activation energies of 0.27–0.35 eV and 0.85–1.05 eV depending on composition were detected in PICTS spectra. It is suggested that the former traps are the same as observed in temperature quenching of photocurrent while the latter traps are related to the yellow luminescence band in AlGaN. The photocurrent decay is shown to have a complex form with a rapid decrease followed by a long tail associated with detrapping of holes. It is argued that, at room temperature, the ∼1 eV hole traps are mainly responsible for the amplitude of the tail.
Vacancy-Type Defects in as-Grown and Proton-Irradiated 6H-SiC
Authors: Puff Werner , Mascher Peter , Balogh Adam G.
Published: April 2011

Annealing of defects in as-grown and proton irradiated bulk n- and p-type 6H-SiC has been investigated by positron lifetime spectroscopy and Doppler-broadening measurements. The grown-in defects do not anneal out until 1600 °C, whereas the radiation induced defects show three main annealing stages well below this temperature. During annealing, the formation of larger defect complexes can be observed.
Phonons and Holes in Magnesium Doped GaN
Authors: Demangeot F. , Frandon J. , Renucci M. A. , Smirnov D. , Létin J. , Grandjean N. , Beaumont B. , Kuball M. , Davies T. , Steeds J. W
Published: April 2011

P doping of gallium nitride by incorporation of magnesium in the layers was controlled recently. Only Popovici et al. [1] have published the results of a Raman study on p type GaN. In the present communication, we report on the interaction of the free hole gas with the axial A1(LO) or planar E1(LO) phonon modes, evidenced by Raman scattering: the observed coupled phononplasmon mode is found very different from the corresponding one evidenced in silicon doped (n type) GaN. We compare the experimental data with the lineshape calculated within a dielectric model, using the results of electrical measurements. These results are also compared with infrared reflectivity spectra.
Comparison of High Field Characteristics of SiO2 and AIN Gate Insulators in 6H SiC MOS Capacitors
Authors: Madangarli V. P. , Sudarshan T. S. , Tin C. C.
Published: April 2011

Using a fast ramp response technique, the high field characteristics, specifically the breakdown strength, of thermally grown silicon-dioxide (SiO2) and MOCVD grown aluminum-nitride (AIN), on n-type 6H-SiC epilayers is obtained as a function of three different processing conditions for the insulator growth. Significant improvement in the breakdown strength of thermally grown SiO2 after a 30 minute post annealing at 400°C in nitrogen ambient is reported. Further, the influence of temperature profile during the AIN growth on the breakdown strength is reported.