bluuebunny/crossref_metadata_2025 huggingface dataset:
Multilevel Damascene Interconnection in Integration of MOCVD Cu and Low-k Fluorinated Amorphous Carbon
Authors: Yang Hongning , Evans David R. , Nguyen Tue , Stecker Lisa H. , Ulrich Bruce , Hsu S.-T.
Published: April 2011

In this paper, we present studies on the integration process of CVD Cu with low-k fluorinated amorphous carbon (a-F:C) in single level and multilevel damascene structure. A thin layer of adhesion promoter material, SiC:H, was utilized to enhance the adhesion and mechanical properties of the damascene stacking layers. The SiC:H layer could also serve as a barrier to contain fluorine atoms from diffusion. The improved a-F:C damascene stacking layers are able to sustain the process of CMP, heat treatment, patterning and plasma etching. The fabrication of single and multi-level damascene structures is proved to be feasible. Some of the electrical performance data evaluated on the Cu/a-F:C damascene structure will be also presented in this paper.
Integration Challenges of Inorganic Low-K (K≤2.5) Materials with CU for Sub-0.25μm Multilevel Interconnects
Authors: Yu K. C. , Defilippi J. , Tiwari R. , Sparks T. , Smith D. , Olivares M. , Selinidis S. , Zhang J. , Junker K. , Braekelmann G. , Farkas J. , Lee K. S. , Filipiak S. , Lindell M. , Watanabe J. K. , Wetzel J. T. , Jawarani D. , Herrick M. T. , Cave N. G. , Hobbs C. C. , Stankus J. J. , Mora R. , Freeman M. , Van Gompel T. , Denning D. , Fowler B. W. , Garcia S. , Newton T. , Pena D. , Keyes C. , Nguyen T. , Kirksey S. , Neil T. , Conner J. , Lee J. J. , Fox R. , Hershey R. , Crabtree P. , Sieloff D. D. , Blumenthal R. , Weitzman E. J.
Published: April 2011

The recent introduction of dual inlaid Cu and oxide based interconnects within sub-0.25μm CMOS technology has delivered higher performance and lower power devices. Further speed improvements and power reduction may be achieved by reducing the interconnect parasitic capacitance through integration of low-k interlevel dielectric (ILD) materials with Cu. This paper demonstrates successful multi-level dual inlaid Cu/low-k interconnects with ILD permittivities ranging from 2.0 to 2.5. Integration challenges specific to inorganic low-k and Cu based structures are discussed. Through advanced CMP process development, multi-level integration of porous oxide materials with moduli less than 0.5 GPa is demonstrated. Parametric data and isothermal annealing of these Cu/ low-k structures show results with yield comparable to Cu/oxide based interconnects.
Integration Issues for Low Dielectric Constant Materials in each Generation of ULSI'S
Authors: Gomi Hideki , Kishimoto Koji , Usami Tatsuya , Koyanagi Ken-ichi , Yokoyama Takashi , Oda Noriaki , Matsubara Yoshihisa
Published: April 2011

The technologies utilizing Fluorinated Silicon Oxide (FSG, k=3.6) and Hydrogen Silsesquioxane (HSQ, k=3.0) have been established for 0.25-μm and 0.18-μm generation ULSIs. However, low-k materials for the next generation ULSIs, which have a dielectric constant of less than 3.0, have not become mature yet. In this paper, we review process integration issues in applying FSG and HSQ, and describe integration results and device performance using Fluorinated Amorphous Carbon (a-C:F, k=2.5) as one of the promising low-k materials for the next generation ULSIs.
Rapid Thermal Processing of Hydrogen Silsesquioxane for Low Dielectric Constant Performance
Authors: Bremmer J. N. , Gray D. , Liu Y. , Gruszynski K. , Marcus S.
Published: April 2011

Low dielectric constant hydrogen silsesquioxane films were achieved by rapid thermal cure processing with production viable equipment. A reduced dielectric constant of k = 2.5–2.6 is demonstrated by optimizing rapid thermal cure process conditions to produce low density hydrogen silsesquioxane thin films. This is a significant reduction relative to production proven furnace cure processed hydrogen silsesquioxane with k = 2.9. Concurrent with reduced k performance is a characteristic film expansion which contributes to formation of a low density structure. A mechanism for film expansion and relevance to low k performance is described; and issues relative to integration of rapid thermal processed low k hydrogen silsesquioxane are discussed.
Amorphous Carbon Nitride Films as a Candidate for Low Dielectric Constant Materials
Authors: Aono M. , Nitta S. , Iwasaki T. , Yokoi H. , Itoh T. , Nonomura S.
Published: April 2011

We have succeeded to prepare high resistivity and rather low dielectric constant amorphous carbon nitride films a-CNx (0.52<x<0.86) by the reactive radio frequency magnetron sputtering of a graphite target using nitrogen molecules as a sputter gas.

The resistivity of a-CNx are 5×1016 to 1017 Ω-cm and be estimated to 1020 Ω-cm, when the ratio of the carbon and nitrogen becomes chemically stoichiometry 3 to 4, i.e. C3N4. The resistivity of a-CNx films prepared by a layer-by-layer method, LL-a-CNx, is 1018 Ω -cm for x=0.6. The layer-by-layer method is a cyclic process of a deposition by the sputtering and an etching by atomic hydrogen. The sample LL-a-CNx made by a layer-by-layer method are compared with that of usual method a-CNx. The dielectric constant of a-CNx films calculated from the refractive index n are 3.6 to 2.8 corresponds to nitrogen contents, 0.52<x<0.86. The dielectric constants ε of a-CNx films decrease with the content of nitrogen x. At an ultimate component of a-CNx, at x=4/3, the dielectric constant is estimated to 1.8.
Mechanisms of Mound Coarsening in Unstable Epitaxial Growth
Authors: Amar Jacques G.
Published: April 2011

The effects of various island and mound relaxation mechanisms on the mound morphology and asymptotic mound coarsening exponent n are investigated for growth on fcc/bcc(001) and fcc (111) metal surfaces. While the strength of the diffusion bias (due for example to an Ehrlich-Schwoebel step barrier) affects the crossover time, the presence or absence of corner diffusion is found to play a crucial role in determining the asymptotic value of the coarsening exponent. In the absence of island-relaxation or in the case of island-relaxation without rapid corner diffusion the asymptotic exponent is found to satisfy n ≃ 1/4. However, when rapid corner-diffusion is allowed, the coarsening exponent is found to approach 1/3. For the case of reversible island growth a strong step-barrier leads to an effective corner diffusion so that a growth exponent of either 1/4 or 1/3 may be observed depending on the strength of the step-barrier. These results appear to account for recent experimental observations of a large coarsening exponent (n ≃ 0.33) in epitaxial growth of Rh/Rh(111) at high temperature as well as of a smaller coarsening exponent (n ≃ 1/4) observed in epitaxial growth of Fe/Fe(001) and Cu/Cu(001). An explanation for these results is also presented in terms of the effects of corner diffusion on the surface current and mound morphology.
MBE Grown Planar Doped Barrier Diodes
Authors: Tuyen Vo Van
Published: April 2011

The realization of Planar Doped Barrier Diode (PDBD) presented in this paper starts out from the limits of the MBE layer growth technology. The limitations due to the background doping concentration and the diffusion of the n and p type dopants during the epitaxial growth are considered. The next parameter is the height of the potential barrier. The choice of this value depends on the requirements of the application. It must take into consideration the current transport mechanisms and the current limitation appearing at higher bias levels.
Self-Organization of Surface Patterns during Clustering
Authors: Zinke–Allmang Martin , Hul'ko Oleksa , Brongersma Sywert , Carlow Graham
Published: April 2011

Ostwald ripening, early stage and late stage coalescence growth are well–characterized, fundamental late–stage processes in the phase separation of thin film deposits on surfaces. These processes have recently been studied in respect to ordering of the clustered phase. While late stage coalescence growth is associated with random positions of the growing clusters, partial ordering is observed for early stage coalescence and ripening

To obtain even higher order of clustering, additional physical driving forces must be included in the process. Two examples are discussed, one utilizing vertical correlation of clusters in super-lattice growth of coherent Stranski–Krastanov structures (coalescence based structures) and a novel concept based on preferential secondary clustering based on ripening morphologies.
Initial Strain Relaxation in S0.91Ge0.09/Si Superlattice Structures via Misfit-Dislocations
Authors: Leininger J. , U'ren G. D. , Goorsky M. S.
Published: April 2011

We addressed the initial strain relaxation of symmetric 95 Å period Si0.91Ge0.09/Si heterostructures grown by ultra-high vacuum chemical vapor deposition on vicinal substrates miscut 2.04° from (001) in a direction 36° from a [110]. Double-axis x-ray topography revealed misfit-dislocation sources in the as-grown samples with an average density of about 60 cm−2, although the distribution of these sites was not homogeneous. The progression of dislocation nucleation and growth was observed during subsequent rapid thermal annealing (800°C, 20s-320s). Physical heterogeneities were identified as dislocation sources, and they gave rise to orthogonal misfit dislocation bundles, which on a macroscopic scale resemble crosses. Upon longer annealing, a more homogeneous distribution of defects was observed without measurable relaxation. These original defects did propagate; however, they did not spur a cross-slip multiplication sequence.
Homoepitaxial Growth of Si at Low Temperature (325 °C)
Authors: Platen J. , Selle B. , Sieber I. , Zeimer U. , Fuhs W.
Published: April 2011

Electron cyclotron resonance chemical vapor deposition (ECR-CVD) is used to grow to prepare epitaxial films on Si(100), Si(111), and Si(311) at 325 °C with a growth rate of 10…12 nm/min. On Si(100) up to a layer thickness of more than 300 nm the films exhibit a well defined and smooth interface and a perfectly ordered lattice structure. Beyond a critical thickness of about 500 nm the formation of conically shaped, amorphous regions was observed. At a thickness of 1.6 µm only 10… 15 % of the surface consists of these amorphous cones. On Si(311), Si(111), and Si(011) the critical epitaxial thicknesses hepi depends on the crystallographic orientation of the substrate in the sequence hepi(311) > hepi(111) > hepi(011) with an abrupt change of the film structure from crystalline to amorphous
High Temperature Stable WSi2-Contacts on p-6H-Silicon Carbide
Authors: Erler Frank , Romanus Henry , Lindner Jörg K. N. , Spiess Lothar
Published: April 2011

Amorphous tungsten-silicon layers were deposited by DC co-sputtering and subsequently annealed in an argon atmosphere up to 1325 K to form tetragonal crystalline WSi2. Al-implanted p-6H-SiC exhibits a small depletion area forming an ohmic contact with low specific contact resistance. A modified Circular Transmission Line Model (CTLM), introduced by Marlow & Das [1] and Reeves [2], was used to characterize the electrical properties of the prepared contacts in the range between 300 K and 650 K. Deviations between calculated fieldemission contact resistances and measured contact resistances (ρc=2·10−2 Ωcm2, T=650 K) could be explained by TEM-cross section investigations. These deviations are caused by inhomogeneous contact interfaces originating from technological difficulties during contact preparation.
Oxidation Modelling for SiC
Authors: Wright N. G. , Johnson C. M. , O'neill A. G.
Published: April 2011

A simple mechanistic model of the oxidation of SiC is presented and analysed using Monte- Carlo simulation techniques. The model explains the observed anisotropic oxidation rate of SiC in terms of the effect of weakening/strengthening of Si-C bonds arising from the ongoing incorporation of highly electronegative oxygen atoms into the crystal lattice. The extraction of key process metrics (such as oxide thickness, interface roughness and oxide defect density) from the Monte-Carlo simulations is discussed.
Effect of Ge on SiC Film Morphology in SiC/Si Films Grown by MOCVD
Authors: Samey W. L. , Salamanca-Riba L. , Zhou P. , Spencer M. G. , Taylor C. , Sharma R. P. , Jones K. A.
Published: April 2011

SiC/Si films generally contain stacking faults and amorphous regions near the interface. High quality SiC/Si films are especially difficult to obtain since the temperatures usually required to grow high quality SiC are above the Si melting point. We added Ge in the form of GeH2 to the reactant gases to promote two-dimensional CVD growth of SiC films on (111) Si substrates at 1000°C. The films grown with no Ge are essentially amorphous with very small crystalline regions, whereas those films grown with GeH2 flow rates of 10 and 15 sccm are polycrystalline with the 3C structure. Increasing the flow rate to 20 sccm improves the crystallinity and induces growth of 6H SiC over an initial 3C layer. This study presents the first observation of spontaneous polytype transformation in SiC grown on Si by MOCVD.
Properties of Heteroepitaxial 3C-SiC Layer on Si Using Si2(CH3)6 by CVD
Authors: Chen Y. , Masuda Y. , Nishlo Y. , Matsumoto K. , Nishino S.
Published: April 2011

Single crystal cubic silicon carbide ( 3C-SiC ) has been deposited on Si(100) by atmospheric CVD at 1350°C using Si2(CH3)6. The 3C-SiC epilayers were characterized by XRD, Raman scattering and photoluminescence (PL). The 3C-SiC distinct TO near 796 cm−1 and LO near 973 cm−1 were recorded by Raman measurement. The PL spectra of SiC films at 11K included the nitrogen-bound exciton (N-BE) lines, the ‘defect-related’ W band near 2.15eV, and 2.13eV peak corresponding to D-A pair recombination as well as the ‘divacancy-related’ D 1 peak at 1.97eV. The thickness dependences of Raman and PL measurement were made and it was observed that tensile stress and strain in films decrease with increasing film thickness. Electrical properties of the films were measured by making schottky diodes and using Van der Pauw method. Above 300K, the electron mobility changed as μH ∼ T−1.45 ∼ −1.56 and the highest mobility was about 400 cm2V−1s−1 at room temperature. In 3C-SiC the scattering processes are affected prominently by acoustic scattering in this temperature range.
Characterization of Vanadium-Doped 4H-SiC Using Optical Admittance Spectroscopy
Authors: Smith S. R. , Evwaraye A. O. , Mitchel W. C. , Solomon J. S. , Goldstein J.
Published: April 2011

Vanadium is an important dopant in SiC because it gives rise to donor levels near the middle of the bandgap which can be used to make the material semi-insulating, and semiinsulating material has many applications as a substrate material for high-power electronics. However, conventional means of characterizing electronic levels in the bandgap of the material require very high temperatures, in the neighborhood of 650–800 °C, in order to move the Fermi level to midgap and cause ionization of the V donors. The technique of Optical Admittance Spectroscopy permits the ionization of the midgap donors using light of the appropriate energy, and thus avoids the need for high temperatures. Using this technique we have examined several specimens of V-doped and high-resistivity 4H-SiC. We have identified levels previously associated with V, and new levels we attribute to Ti. Pinning of the Fermi level in some specimens was verified by high-temperature Hall effect measurements. SIMS measurements were used to determine impurity concentrations. IR absorption measurements were correlated with the Ti, V, and Cr concentrations determined by SIMS.
Online Monitoring of PVT SiC Bulk Crystal Growth Using Digital X-Ray Imaging
Authors: Wellmann P. J. , Bickermann M. , Grau M. , Hofmann D. , Straubinger T. L. , Winnacker A.
Published: April 2011

An advanced method based on x-ray imaging is presented which allows us to visualize the ongoing processes during physical vapor transport (PVT) growth of SiC. Using a high resolution and high speed x-ray imaging detector based on image plates and digital recording we are able to follow the SiC bulk single crystal growth as well as the evolution of the SiC powder source inside the inductively heated graphite crucible on-line and quasi-continuously.
Pendeo-Epitaxial Growth of GaN on SiC and Silicon Substrates via Metalorganic Chemical Vapor Deposition
Authors: Linthicum K. J. , Gehrke T. , Thomson D. , Ronning C. , Carlson E. P. , Zorman C. A. , Mehregany M. , Davis R. F.
Published: April 2011

Pendeo-epitaxial lateral growth (PE) of GaN epilayers on (0001) 6H-silicon carbide and (011) Si substrates has been achieved. Growth on the latter substrate was accomplished through the use of a 3C-SiC transition layer. The coalesced PE GaN epilayers were characterized using scanning electron diffraction, x-ray diffraction and photoluminescence spectroscopy. The regions of lateral growth exhibited ∼0.2° crystallographic tilt relative to the seed layer. The GaN seed and PE epilayers grown on the 3C-SiC/Si substrates exhibited comparable optical characteristics to the GaN seed and PE grown on 6H-SiC substrates. The near band-edge emission of the GaN/3C-SiC/Si seed was 3.450 eV (FWHM ∼ 19 meV) and the GaN/6H-SiC seed was 3.466 eV (FWHM ∼ 4 meV).
Maskless Lateral Epitaxial Overgrowth of GaN on Sapphire
Authors: Fini P. , Marchand H. , Ibbetson J. P. , Moran B. , Zhao L. , Denbaars S. P. , Speck J. S. , Mishra U. K.
Published: April 2011

We demonstrate a technique of lateral epitaxial overgrowth (LEO) of GaN, termed 'maskless' LEO, in which no mask is deposited prior to LEO regrowth. Instead, a bulk (> 2 μm) GaN layer on sapphire is selectively dry etched, leaving ∼5 μm-wide stripe mesas oriented in the <1010>GaN direction, with a 20 μm period. These stripes serve as seeds for LEO GaN growth, which proceeds from the tops of the stripes and expands laterally, resulting in a ‘T’, or overhang, morphology. As for LEO over an SiO2 mask, significant defect reduction (from ∼109 cm−2 to ∼106 cm−2 ) is observed in cross-sectional transmission electron microscopy (TEM). Atomic force microscopy of the top surface of the LEO GaN reveals that no threading dislocations with screw component terminate at the surfaces of laterally overgrown regions. X-ray diffraction measurements reveal that the wings exhibit a crystallographic tilt away from the seed regions in an azimuth perpendicular to the stripe direction; the tilt angle (∼0.4 – 0.5°) is relatively independent of growth temperature and wing aspect ratio.
Ca Dopant Site Within Ion Implanted GaN Lattice
Authors: Kobayashi H. , Gibson W. M.
Published: April 2011

We have investigated the Ca dopant site within the GaN lattice using ion channeling in combination with Rutherford backscattering spectrometry (RBS), particle induced x ray emission (PIXE) and nuclear reaction analysis (NRA). Metalorganic chemical vapor deposition (MOCVD) grown GaN on c-plane sapphire substrates implanted with 40Ca at a dose of 1×1015 cm−2 with post-implant annealing were investigated. The channeling results indicate that more than 80% of Ca are near Ga sites even in as-implanted samples, however, they are displaced by ∼ 0.2 Å from the Ga sites and that the Ca goes to the exact Ga sites after annealing at 1100°C. We think that the displaced Ca in the as-implanted samples are electrically compensated due to formation of complex defects with donor like point defects, such as CaGa-VN and/or CaGa-GaN, and that CaGa becomes electrically active when these complex defects are broken and the point defects diffuse away with annealing at 1100°C.
Characterization of SiO2/SiC Samples Using Photoelectron Spectroscopy
Authors: Johansson L. I. , Glans P- A. , Wahab Q. , Grehk T. M. , Eickhoff T. H. , Drube W.
Published: April 2011

The results of photoemission studies of SiO2/SiC samples for the purpose of revealing presence of any carbon containing by-products at the interface are reported. Two components could be identified in recorded Si 2p and C ls core level spectra. For Si 2p these were identified to originate from SiO2 and SiC while for C ls they were interpreted to originate from graphite like carbon and SiC. The variation in relative intensity of these components with emission angle was first investigated. Thereafter the intensity of the different components were studied after successive Ar+-sputtering cycles. Both experiments showed contribution from graphite like carbon on top of the oxide but not at the interface.
SIMS and Cl Characterization of Manganese-Doped Aluminum Nitride Films
Authors: Tucceri R. C. , Bland C. D. , Caldwell M. L. , Ervin M. H. , Magtoto N. P. , Spalding C. M. , Wood M. A. , Richardson H. H.
Published: April 2011

We have recently carried out MOCVD experiments that showed for the first time the doping of AlN thin films with manganese. Films of AlN that were doped with less than 0.1% of manganese showed emission bands at 427 nm, 488 nm and 600 nm in accordance with previous published excitation and emission spectra of manganese incorporated in bulk A1N. A film with a higher percentage of manganese (1.7%) grown on top of a pure A1N layer (underlayer) showed weak emission at 601 nm. A portion of the underlayer not covered during growth of the overlayer has a very strong emission band at 408 nm and a weaker band at 605 nm. SIMS and EDX analyses of this film revealed both carbon and oxygen contamination as well as diffusion of manganese into the A1N underlayer. The band at 408 nm is associated with direct gap emission from oxygen contaminated A1N and the band at 605 nm is from manganese incorporated by diffusion into the A1N underlayer.
Disorder Induced IR Anomaly in Hexagonal AlGaN Short-Period Superlattices and Alloys
Authors: Mintairov A. M. , Vlasov A. S. , Merz J. L. , Korakakis D. , Moustakas T. D. , Osinsky A. O. , Gaska R. , Smirnov M. B.
Published: April 2011

We report an experimental (infrared reflectance spectroscopy) and theoretical study of the polar optical phonons in hexagonal ternary nitride compounds: AlNm/GaNn (n=2-8, m=4, 8) superlattices (SL) and spontaneously ordered AlxGa1−xN (x=0.08–0.55) alloys. In infrared (IR) reflectivity spectra we revealed two modes having strong LO-TO splitting (20–150 cm−1), and several modes, having a small (1–3 cm−1) LO-TO splitting. All modes have a very high damping parameter ≥20 cm−1. The unusual observation is the negative value of the oscillator strength for the weak IR mode at ∼690 cm−1, suggesting possible lattice instability, consistent with high damping observed. We found from lattice dynamical calculations that weak IR active modes correspond to modes localized at GaN-AlN interfaces. Our analysis has shown that an anomalous mode is induced by the disorder effects and arises due to strong overlapping of the LO-TO phonon branches of the bulk GaN and AlN. In SL samples the anomalous mode corresponds to phonons localized on interface inhomogenities.
Study of Near-Threshold Gain Mechanisms in MOCVD-Grown GaN Epilayers and InGaN/GaN Heterostructures
Authors: Bidnyk S. , Schmidt T. J. , Little B. D. , Song J. J.
Published: April 2011

We report the results of an experimental study on near-threshold gain mechanisms in optically pumped GaN epilayers and InGaN/GaN heterostructures at temperatures as high as 700 K. We show that the dominant near-threshold gain mechanism in GaN epilayers is inelastic excitonexciton scattering for temperatures below ∼ 150 K, characterized by band-filling phenomena and a relatively low stimulated emission (SE) threshold. An analysis of both the temperature dependence of the SE threshold and the relative shift between stimulated and band-edge related emission indicates electron-hole plasma is the dominant gain mechanism for temperatures exceeding 150 K. The dominant mechanism for SE in InGaN epilayers and InGaN/GaN multiple quantum wells was found to be the recombination of carriers localized at potential fluctuations resulting from nonuniform indium incorporation. The SE spectra from InGaN epilayers and multiple quantum wells were comprised of extremely narrow emission lines and no spectral broadening of the lines was observed as the temperature was raised from 10 K to over 550 K. Based on the presented results, we suggest a method for significantly reducing the carrier densities needed to achieve population inversion in GaN, allowing for the development of GaNactive-medium laser diodes.
Annealing of Ion Implantation Damage in SiC Using a Graphite Mask
Authors: Thomas Chris , Taylor Crawford , Griffin James , Rose William L. , Spencer M. G. , Capano Mike , Rendakova S. , Kornegay Kevin
Published: April 2011

For p-type ion implanted SiC, temperatures in excess of 1600 °C are required to activate the dopant atoms and to reduce the crystal damage inherent in the implantation process. At these high temperatures, however, macrosteps (periodic welts) develop on the SiC surface. In this work, we investigate the use of a graphite mask as an anneal cap to eliminate the formation of macrosteps. N-type 4H- and 6H-SiC epilayers, both ion implanted with low energy (keV) Boron (B) schedules at 600 °C, and 6H-SiC substrates, ion implanted with Aluminum (Al), were annealed using a Graphite mask as a cap. The anneals were done at 1660 °C for 20 and 40 minutes. Atomic force microscopy (AFM), capacitance-voltage (C-V) and secondary ion mass spectrometry (SIMS) measurements were then taken to investigate the effects of the anneal on the surface morphology and the substitutional activation of the samples. It is shown that, by using the Graphite cap for the 1660 °C anneals, neither polytype developed macrosteps for any of the dopant elements or anneal times. The substitutional activation of Boron in 6H-SiC was about 15%.
Photo-Assisted RIE of GaN in BCl3/Cl2/N2
Authors: Medelci N. , Tempez A. , Berishev I. , Starikov D. , Bensaoula A.
Published: April 2011

Gallium nitride (GaN) has been under intense investigation due to its unique qualities (wide band gap, chemical and temperature stability) for optoelectronic and high temperature/high power applications. To this end, reactive ion etching (RIE) experiments were performed on GaN thin films using BCl3/Cl2/Ar. These resulted in etch rates of 1400 Å/min at −400 V dc bias. However, rough etched surfaces, nitrogen surface depletion and high chlorine content were observed. In order to remedy these shortcomings, a photo-assisted RIE process using a filtered Xe lamp beam was developed, resulting in higher etch rates but again in nitrogen depleted surfaces. Preliminary results on using nitrogen instead of argon in the process chemistry show a big improvement in photo-asssisted etch rates (50%) and Ga/N ratio (0.78 versus 1.25). In this paper, the effects of epilayer doping, dc bias, nitrogen flow rate and photo-irradiation flux on GaN etch rates, surface morphology and composition are presented. Finally, preliminary results on the use of a KrF excimer laser beam in the GaN photo-assisted RIE process are presented.
Full Band Monte Carlo Simulation of Short Channel MOSFETs in 4H and 6H-SiC
Authors: Hjelm M. , Nilssoni H-E. , Dubaric E. , Persson C. , Käckell P. , Petersson C. S.
Published: April 2011

This is a presentation of a full band Monte Carlo (MC) study, which compares electron transport and device performance for 4H and 6H-SiC 100 nm n-channel MOSFETs. The model used for the electrons is based on data from a full potential band structure calculation using the Local Density Approximation (LDA) to the Density Functional Theory (DFT). For the holes the transport is based on a three band k-p model including spin orbit interaction. The two polytypes are compared regarding surface mobilities obtained with the program, as well as transconductance, unit current gain frequency, carrier velocity, I-V characteristics and energy distribution in the channel for the MOSFETs.
Selective Dry Etching of the GaN/InN/AlN, GaAs/AlGaAs and GaAs/InGaP Systems
Authors: Hays D. C. , Abernathy C. R. , Hobson W. S. , Pearton S. J. , Han J. , Shul R. J. , Cho H. , Jung K. B. , Ren F. , Hahn Y. B.
Published: April 2011

Selective etching of InN over GaN and AlN, and of GaAs over both AlGaAs and InGaP was examined with a number of different plasma chemistries under inductively coupled plasma conditions. Selectivities up to 55 for InN/GaN and 20 for InN/AlN were achieved in IC1/Ar discharges. For GaAs/AlGaAs, maximum selectivities of 75(with BCl3/SF6) were obtained while for GaAs/InGaP values of 80(with BCl3/SF6) and 25(with BCl3/NF3) were achieved. Selective etching of InGaP over GaAs is possible with either CH4/H2 or BI3. The selectivity is a strong function of ion flux and ion energy, and can result from two factors – either formation of a nonvolatile etch product, or a difference in bond strength between the two materials.
A Novel Surface Pivation Structure for III-V Compound Semiconductors Utilizing a Silicon Interface Control Layer and its Application
Authors: Hashizume Tamotsu , Hasegawa Hideki
Published: April 2011

The present status of surface passivation research for III-V compound semiconductors utilizing a novel unique structure including a silicon interface control layer (Si ICL) is presented and discussed. The basic principle of passivation is to insert an ultrathin MBE-grown Si layer between the III-V compound semiconductor and a Si-based thick insulator so as to terminate the surface bonds of the III-V material with Si atoms and then to transfer Si-bonds smoothly to those of the Si based insulator. Based on the calculation of quantized levels in strained Si ICL, the passivation structure was optimized. Such a structure was realized by partial nitridation of Si ICL surface. In-situ surface characterization techniques including newly developed UHV contactless C-V technique, were used for optimization of each passivation step. Surface reconstruction of initial semiconductor surface was found to have a great influence on passivation. In the case of GaAs, the c(4×4) surface is preferable to the (2×4) surface. The novel process has realized the oxide-free surface passivation of InP with a Nssmin value of 2 × 1010 cm−2 eV−1. Furthermore, the novel passivation technique has been successfully applied to the fabrication of MISFETs and IGHEMTs, and the passivation of quantum structures.
Degradation Reactions in SONY-Type Li-Ion Batteries
Authors: Roth E. Peter , Nagasubramanian G.
Published: April 2011

Thermal instabilities were identified in SONY-type lithium-ion cells and correlated with interactions of cell constituents and reaction products. Three temperature regions of interaction were identified and associated with the state of charge (degree of Li intercalation) of the cell. Anodes were shown to undergo exothermic reactions as low as 100°C involving the solid electrolyte interface (SEI) layer and the LiPF6 salt in the electrolyte (EC:PC:DEC/LiPF6). These reactions could account for the thermal runaway observed in these cells beginning at 100°C. Exothermic reactions were also observed in the 200°C-300°C region between the intercalated lithium anodes, the LiPF6 salt, and the PVDF. These reactions were followed by a hightemperature reaction region, 300°C-400°C, also involving the PVDF binder and the intercalated lithium anodes. The solvent was not directly involved in these reactions but served as a moderator and transport medium. Cathode exothermic reactions with the PVDF binder were observed above 200°C and increased with the state of charge (decreasing Li content). This offers an explanation for the observed lower thermal runaway temperatures for charged cells.
Development and Characterization of Nanostructure Tin alloys as Anodes in Lithium - Ion Batteries
Authors: Peled E. , Ulus A. , Rosenberga Y.
Published: April 2011

Several tin-antimony and tin-zinc nanostructure alloys were electroplated from an acid bath, on a copper foil, at current densities higher by an order of magnitude than the limiting current density. They have been characterized as potential high-capacity anodes for lithium-ion battery applications. SEM micrographs of the tin-based alloys reveal nanosize particles, which aggregate into larger agglomerates of fractal shapes. On the nanoscale, the zinc-tin alloys have house-of-cards or honeycomb morphology. The composition of one series of tin based alloys was Sn:Sb (atomic ratio) 1.4:1 to 9:1; another alloy consisted of Sn:Sb:Cu in the ratio 34:10:4. All contained about 5% carbon and about 20% oxygen. The zinc-rich tin alloys contain at least 80 atomic percent zinc (their electrochemical characterization will be reported elsewhere). Tin-based alloys with low antimony content, have high reversible capacity (up to 700mAh/g), low irreversible capacity (about 24%), a better rate capability, and a lower average working potential vs. Li. On the other hand, alloys rich in antimony have a longer cycle life, but poor rate capability and a high average working potential vs. Li. The addition of copper to the tin-based alloys improved cycle life and slightly reduced irreversible capacity.
Effect of Alloy Composition on the Structure of Zr Based Metal Alloys
Authors: Chao B. S. , YOUNG R. C. , Ovshinsky S. R. , Pawlik D. A. , Huang B. , Im J. S. , CHAKOUMAKOS B. C.
Published: April 2011

The structures of Ovonic multi-element, multi-phase Zr-based transition metal alloys for hydrogen storage are studied. The alloys are designed to be multi-phase materials. The hexagonal and diamond cubic structures, known as C14 and C15 Laves structures respectively, are the two major hydrogen storage phases in the alloys. In both C14 and C 15 structures, Zr and Ti are the elements typically occupying the hydride former (A) sites and V, Cr, Mn, Fe, Co and Ni the catalytic (B) sites. Based on the application of Ovshinsky's design principles for disordered materials, both A and B sites are compositionally disordered by the corresponding elements in cubic (C15) structure. However, the hexagonal (C14) structure has two distinct B sites, B(I) and B(Il) with a 1:3 ratio. Preliminary neutron diffraction studies indicate that the B(I) sites are predominantly occupied by Ni and the B(ll) sites are randomly mixed with V, Cr, Mn, Fe, and Ni. It is then proposed that the formula of the hexagonal structure should become A2B(I)IB(II) 3 in the current multi-element Zr-based alloys. Minor phases close to the structures of Zr7Ni10, Zr9Ni11, and ZrO2 are also present in some alloys. The average electron concentration factor (e/a) derived from the alloy composition dictates the alloy structures. The alloys with higher electron concentration factor (> 7.1) favor the diamond cubic structure. On the other hand, the hexagonal structure is associated with the alloys with lower electron concentration factor (< 6.5). The alloys having electron concentration factors in between are mixtures of the diamond cubic and hexagonal structures.
Lithium Nickelate with Cadmium Iodide Structure
Authors: Arai Hanime , Sakurai Yoji
Published: April 2011

We obtained a highly delithiated sample of Li0.04NiO2using acid leaching. The Rietveld analysis of its X-ray diffraction pattern indicated that the sample was a mixture of three phases. Two of them maintained the pristine structure with cubic close-packing layers while the other phase had a cadmium iodide structure with hexagonal close-packing layers. We examined the electrochemical behavior of this sample as a positive electrode material for lithium batteries. The discharge capacity was smaller than that of a Li0.10NiO2sample obtained by acid leaching, suggesting that the capacity loss is due to the formation of the phase with the cadmium iodide structure.
Porous Thin-Film Anode Materials for Solid-Oxide fuel Cells
Authors: Morse Jeffrey D. , Graff Robert T. , Hayes Jeffrey P. , Jankowski Alan F.
Published: April 2011

Thin film, solid-oxide fuel cells (TFSOFCs) synthesized from an electrolyte and conductive material are developed using photolithographic patterning and physical vapor deposition. The anode layer must enable combination of the reactive gases, be conductive to pass the electric current, and provide mechanical support to the electrolyte and cathode layers. The microstructure and morphology desired for the anode layer should facilitate generation of maximum current density from the fuel cell. For these purposes, the parameters of the deposition process and post-deposition patterning are developed to optimize a continuous porosity across the anode layer. The anode microstructure is characterized using scanning electron microscopy and the power ouput generated through current-voltage measurement.
A Study on Oxidized Glassy Carbon sheets for Bipolar Supercapacitor Electrodes
Authors: Braun A. , Bärtsch M. , Geiger F. , Schnyder B. , Kötz R. , Haas O. , Carlen M. , Christen T. , Ohler C. , Unterinahrer P. , Krause E.
Published: April 2011

Electrochemical Double Layer Capacitors (EDLC) for high energy and power density applications, based on glassy carbon (GO) electrodes, are being developed in our laboratory. In the context of this project, GC sheets were oxidized and investigated with Small Angle X-ray Scattering (SAXS), Electrochemical Impedance Spectroscopy (EIS) and Nitrogen Gas Adsorption (BET). During oxidation an active film with open pores is built on the surface of the GC. Upon oxidation, the internal volumetric surface area of the active film decreases, whereas the volumetric electrochemical double layer capacitance increases. We show that this effect is correlated with the opening, the growth and the coalescence of the pores.
New Conducting Polymers for Electrochemical Ultracapacitors
Authors: Naoi K. , SUEMATSU S.
Published: April 2011

Redox reactions and structural changes of a poly(2,2′-dithiodianiline) [poly(DTDA)], a conducting polymer interconnected with disulfide (S-S) bonds, in acid aqueous solution of various pH values are discussed. We proposed the poly(DTDA) as a proton-exchange type of energy storage material. The cyclic voltammograms (CVs) for poly(DTDA) showed a reproducible redox couples for repeated (10,3-104cycles. To investigate the structure of the poly(DTDA) for each potential and the pH value, a plot of E° vs. pH values obtained from the results of CVs (Pourbaix diagram) was formed and discussed.
Stability of Self-Assembled Organic-Inorganic Layered Perovskite
Authors: Kitazawa Nobuaki , Yamamoto Takafumi , Watanabe Yoshihisa , Nakamura Yoshikazu
Published: April 2011

Photo-stability of (C6H5C2H4NH3)2PbX4 (X; Br and I) films was studied and the degradation processes were discussed. The prepared films were not stable against the UV-light irradiation. The PhE-PbX4 films were readily oxidized by the UV-light irradiation in air. In vacuum, the PhE-PbI4 films changed to β-phenethylamine intercalated PbI2 due to the elimination of halogen species. On the contrary, no degradation was observed for the PhE-PbBr4 films. These results suggested that the photo-irradiation induced photochemical reaction was one of the possible reasons for the degradation. To suppress the oxidation and halogen elimination induced by the photochemical reaction, PMMA-coated PhE-PbX4 films were also fabricated and their photo-stability was examined.
Nanostructural Lithography via Photo-Initiated Phase Transformation of Silica-Surfactant Assemblies
Authors: Doshi D. A. , HÜsing N. , Fan H. , Hurd A. J. , Brinker C. J.
Published: April 2011

Cooperative self-assembly processes of inorganic species and amphiphilic molecules have experienced major advances over the past six years. The ability to design these materials with spatially controlled combinations of different mesophases or compositions, and therefore different properties, would greatly enhance their utility as nanofunctional surfaces.

We present a simple lithographic procedure, which allows a deliberate control of structure and properties of a meso-ordered silica film through optical mediation. This nanostructural lithography process exploits the pH sensitivity of supra-molecular self-assembly which allows spatial control over mesophases in the thin film and a selective etching capability. Through the addition of a photoacid generator in the coating sol along with surfactant and silica source, dip coating results in continuous, ordered photosensitive films. Exposure to UV light through a mask produces local pH changes, inducing mesostructural phase transitions and an increase in the acidcatalyzed siloxane condensation rate in the exposed regions. Two surfactant systems, CTAB (CH3(CH2)15N+(CH3)3Br–) and Brij 56 (CH3(CH2)15(OCH2CH2)10OH) have been studied. X-ray diffraction, transmission and scanning electron microscopy, optical microscopy, ellipsometry, MAS-NMR and atomic force microscopy are used to characterize the patterned nanostructured surfaces.
Storage Stability of Solvent-Free Condensates of Functionalized Trialkoxysilanes
Authors: Stein S. , Clausbruch St. Cramer V. , Moszner N. , Ag V. Rheinberger Ivoclar
Published: April 2011

The lack of storage stability of organic-inorganic solvent-free sols is a well-known problem. We investigated the influence of different solvents in the acid catalyzed hydrolysis of various sols on their storage stability. Our experiments were based on two different silanes, 3-methacryloxypropyltrimethoxysilane (MPTS) and 1,1,1-tris(allyloxymethyl)-l-[[[3-(triethoxysilyl)propyl]aminocarbonyl]oxymethyl]methane (silane 31), synthesized by reaction of pentaerythritol triallyl ether and 3-isocyanatopropyltriethoxysilane. The employed solvents were alcohol, tetrahydofuran and tert-butyl methyl ether in a range of 95 wt% to 30 wt% in solution. In order to get comparable chemical conditions the degree of condensation of the various sols were adjusted between 75% and 85%. Furthermore, the sols were modified by silylation with trimethylchlorosilane. A comparison of silylated and not silylated silane 31 clearly showed that a decrease in residual silanol groups increase the storage stability. The results of the investigations demonstrated that both the kind and the amount of solvent used in hydrolysis affects the initial viscosity of solvent-free condensates of silane 31 and MPTS.
Optical Characteristics Of Silica-Poly(Ethylene Oxide) Hybrid Thin Films
Authors: Park O. H. , Eo Y. J. , Choi Y. K. , Bae B. S.
Published: April 2011

Silica-PEO hybrid materials which have both silica network and polymer network are synthesized from hydrolysis, condensation and polymerization of γ -glycidoxypropyltrimethoxysilane(GPTS). Polymerization of the epoxy groups to poly(ethylene oxide) units is achieved by using mixed triarylsulfonium hexafluorophosphate salt as a UV curing agent. The structural change of the hybrid solution is investigated by using NMR spectroscopy. The microstructure of silica hybrid film can be changed according to the degree of polymerization controlled by the UV curing conditions. The epoxide polymerization is confirmed by using FT-IR. The hybrid material is densified due to the epoxide polymerization as well as silica condensation with UV curing. The optical properties such as optcial absorbance and refractive index of the silica hybrid thin films are measured as functions of curing conditions. These optical properties are then correlated to the epoxide polymerization.
Influence Of Hybridation With A Silicate Network On The Properties Of An Eu 3+ Complex Derived From Dipicolinic Acid
Authors: Franville A. C. , Zambon D. , Mahiou R. , Troin Y. , Cousseins J. C.
Published: April 2011

In this paper, the preparation, the characterization and the optical features of organicinorganic materials incorporating a trivalent europium organic chelate into a silicate network are described. The covalent grafting and the sol-gel process allow to obtain monophasic hybrid gels in which the structure and the activity of the organic molecules were retained. The Eu3+ coordination mode is not sensitive to the sol-gel processing conditions whereas the morphology of materials, their thermal resistance and their luminescence properties may be adjusted. Characteristics of hybrid compounds are compared to those of the corresponding organic species.
Thermosetting Mechanism Study of Organosilicon Polymer Containing Carborane by Solid-State NMR Spectroscopy
Authors: Kimura H. , Okita K. , Ichitani M. , Yonezawa M. , Sugimoto T.
Published: April 2011

The thermosetting mechanism of an organosilicon polymer containing carborane has been studied utilizing the 13and 29Si solid-state NMR method. The polymer having C≡C bonds in the main chain and CH═CH2, Si-H bonds, and carborane in the bulky side chain, shows a very highly thermal stability in air by curing. From 13C and 29Si NMR spectra of the polymer, it was found that the intermolecular cross-linking reactions of the polymer was due to (1) the diene reaction between Ph-C≡C and C≡C and (2) the addition reaction between side chain terminal and Ph-C≡C and between CH═CH2 and Si–H, and a very highly thermal stable structure is formed.
Magnetic Anisotropy in Rare-Earth - Transition Metal Intermetallic Compounds
Authors: Luong Nguyen Hoang , Thuy Nguyen Phu , Quang Pham Hong , Thang Pham Duc
Published: April 2011

In this work the rare-earth anisotropy in the rare-earth - transition metal intermetallic compounds is investigated by studying the temperature-induced spin reorientation phenomena on aligned powder samples and by analyzing the temperature dependence of the magnetization measured along different principal axes of single crystals. From such investigations the crystalline-electric-field parameters of the rare-earth ions in these compounds have been derived. The results on different hard magnetic materials of the compositions R2Fe14B, RFe11 and their substituted compounds as well as R2Co17 are summarized.
Novel Permanent Magnets and Their Uses
Authors: Constantinides S.
Published: April 2011

Two changes have gone hand in hand during the 20th century. First, applications were conceived that required new or greatly improved materials. Need being the mother of invention, materials were then developed to satisfy the application needs. Permanent magnets are today used in devices that could only have been dreamed about 25 years ago. Who could have foreseen, for example, the advances in data storage that have occurred over the last 15 years? Hard disk drives of under 10 megabytes in size and with random access times of over 65 milliseconds were the norm in 1984. Today, the standard drive is over 8 gigabytes, is smaller in size and costs less than a fourth of the old drives, with an access time of 10 milliseconds and more than 33 mbps burst throughput. Novel has two interpretations: first it may refer to the magnetic material or it may refer to the application of a material. Several examples of each are presented.
A Study on High Coercivity and L10Ordered Phase in CoPt and FePt Thin Films
Authors: Ristau R. A. , Barmak K. , Lewis L. H. , Coffey K. R. , Howard J. K.
Published: April 2011

This study relates the microstructure of equiatomic binary alloys of CoPt and FePt with their room-temperature hysteretic magnetic properties, particularly their high coercivity. A transformation from an atomically disordered, face-centered-cubic structure to the Li0ordered structure occurred during post-deposition annealing and was characterized using digital analysis of dark-field transmission electron microscopy (TEM) images. The transformation was observed to follow first-order nucleation and growth kinetics, and the ordered volume fraction transformed was quantified at numerous points during the transformation. The ordered volume fraction was then compared to the magnetic coercivity data obtained from a superconducting quantum interference device (SQUID) magnetometer. Although the relationship most commonly described in the literature is that the highest coercivity corresponds to a two phase ordered/disordered mixture, the maximum value for coercivity in this study was found to correspond to the fully ordered state. Furthermore, in samples that were less than fully ordered, a direct relationship between ordered volume fraction and coercivity was observed. The proposed mechanism for the high coercivity in these films is an increasing density of magnetic domain wall pinning sites concurrent with an increasing fraction of ordered phase.