bluuebunny/crossref_metadata_2025 huggingface dataset:
Functionalized Magnetic Nanoparticles for Selective Targeting of Cells
Authors: Tremel Wolfgang , Shukoor Mohammed Ibrahim , Natalio Filipe , Schladt Thomas , Barz Matthias , Tahir Muhammad Nawaz , Weber Stefan , Zentel Rudolf , Schreiber Laura Maria , Brieger Jürgen , Schröder Heinz Christoph , Müller Werner
Published: August 2010

Initiation of pathways that lead to proliferation and chemoresistance by Toll-like receptors (TLRs) is an important factor in cancer progression. Here, we show the response of human cancer cells to TLR signaling inevitably linked to tumor biology. The approach is based on tailored multifunctional magnetic nanoparticles equipped with pathogen-derived ligands (CpG) functioning as TLR agonists (molecular component) to investigate the impact of transcription factor immune activation on human cancer cells. Magnetic nanoparticles (MnO and bifunctional Au-MnO) particles were covalently coated with a multifunctional polymer, displaying no cytotoxicity, to being able to enter cells while carrying foreign DNA (unmethylated CpG) to recognize intracellular TLR 9. Both, the particle and the nucleic acid are tagged with fluorescent markers for simultaneous visualization inside the cell. Apart from optical imaging, the magnetism of the particles also allows magnetic resonance imaging of organisms.
Protocrystalline Silicon for Micromorph Tandem Cells on Gen. 5 Size
Authors: van Elzakker Gijs , Sixtensson Daniel , Papathanasiou Niklas , Neubeck Klaus , Sillmann Roland
Published: August 2010

Inventux Technologies AG is a high volume producer of Micromorph (a-Si:H/μc-Si:H) tandem modules. The light-induced degradation of hydrogenated amorphous silicon (a-Si:H), called Staebler-Wronski effect (SWE), limits the stabilized efficiency of a-Si:H-based solar cells. Several laboratories have reported on the development of a-Si:H with increased resistance against light-soaking. This so-called ‘protocrystalline' silicon can be grown with plasma-enhanced chemical vapor deposition (PECVD) by diluting the silane source gas with hydrogen.

The aim of the work presented in this paper was to scale-up the laboratory results on protocrystalline silicon to a size of 1.43 m2 (Gen. 5) using a process that is suitable for high volume production. We demonstrate that the strict boundary conditions regarding uniformity and growth rate, which are necessary for a production process, can be met. The reduced light-induced degradation of protocrystalline solar cells fabricated with the newly developed process is confirmed by a light-soaking experiment. As an outlook towards future work, we discuss issues related to the implementation of a protocrystalline top cell in the Micromorph tandem configuration. The challenge of choosing the right top-cell thickness is illustrated by experimental results on two tandem cells. The top cells of these tandems contain protocrystalline i-layers of different thicknesses.
High-efficiency Large-area Nanocrystalline Silicon Solar Cells Using MVHF Technology
Authors: Xu Xixiang , Su Tining , Ehlert Scott , Bobela David , Beglau Dave , Pietka Ginger , Li Yang , Zhang Jinyan , Yue Guozhen , Yan Baojie , DeMaggio Greg , Worrel Chris , Lord Ken , Banerjee Arindam , Yang Jeff , Guha Subhendu
Published: August 2010

We present the progress made in attaining high-efficiency large-area nc-Si:H based multi-junction solar cells using Modified Very High Frequency technology. We focused our effort on improving the spatial uniformity and homogeneity of nc-Si:H film growth and cell performance. We also conducted both indoor and outdoor light soaking studies and achieved 11.2% stabilized efficiency on large-area (≥400 cm2) encapsulated a-Si:H/nc-Si:H/nc-Si:H triple-junction cells.
Oxygenated Protocrystalline Silicon Thin Films for Wide Bandgap Solar Cells
Authors: Schropp Ruud E.I. , Schüttauf Jan Willem , van der Werf Karine
Published: August 2010

Protocrystalline silicon, which is a material that has enhanced medium range order (MRO), can be prepared by using high hydrogen dilution in PECVD, or, alternatively, using high atomic H production from pure silane in HWCVD. We show that this material can accommodate percentage-level concentrations of oxygen without deleterious effects. The advantage of protocrystalline SiO:H for application in multijunction solar cells is not only that it has an increased band gap, providing a better match with the solar spectrum, but also that the solar cells incorporating this material have a reduced temperature coefficient. Further, protocrystalline materials have a reduced susceptibility to light-induced defect creation. We present the unique result in the PV field that these oxygenated protocrystalline silicon solar cells have an efficiency temperature coefficient (TCE) that is virtually zero (TCE is between -0.08%/°C and 0.0/°C). It is thus beneficial to make this cell the current limiting cell in multibandgap cells, which will lead to improved annual energy yield.
Plasmonic Light-trapping and Quantum Efficiency Measurements On Nanocrystalline Silicon Solar Cells and Silicon-On-Insulator Devices
Authors: Zhao Hui , Ozturk Birol , Schiff Eric A , Yan Baojie , Yang Jeff , Guha Subhendu
Published: August 2010

Quantum efficiency measurements in (nc-Si:H) solar cells deposited onto textured substrates indicate that these cells are close to the “stochastic light-trapping limit“ proposed by Yablonovitch in the 1980s. An interesting alternative to texturing is “plasmonic“ light-trapping based on non-textured cells and using an overlayer of metallic nanoparticles to produce light-trapping. While this type of light-trapping has not yet been demonstrated for nc-Si:H solar cells, significant photocurrent enhancements have been reported on silicon-on-insulator devices with similar optical properties to nc-Si:H. Here we report our work on the measurerements of quantum efficiencies in nc-Si:H solar cells and normalized photoconductance spectra in SOI photdetectors with and without silver nanoparticle layers. As was done previously, the silver nanoparticles were created by thermal annealing of evaporated silver thin films. We observed enhancement in the normalized photoconductance spectra of SOI photodetectors at longer wavelengths with the silver nanoparticles. For nc-Si:H solar cells, we have not yet observed significant improvement of the quantum efficiency with the addition of annealed silver films.
High Quality, Low Bandgap a-Si Films and Devices Produced Using Chemical Annealing
Authors: Dalal Vikram , Shyam Ashutosh , Congreve Dan , Noack Max
Published: August 2010

We report on the growth and properties of novel amorphous Silicon (a-Si:H) p-i-n devices prepared using chemical annealing with argon gas. The i layer in the p-i-n devices was grown using a layer by layer approach, where the growth of a very thin a-Si:H layer (7-30 angstroms) grown using a silane:argon mixture was followed by chemical anneal by argon ions. Repeated cycling of such growth/anneal cycles was used to produce the desired total thickness of the i layer. The thickness of the a-Si layer, and duration of the anneal time, were varied systematically. Pressure and power of the plasma discharge were also systematically varied. It was found that a thin a-Si layer, <10 angstroms, and low pressures which led to relatively high ion flux on the surface, gave rise to a significantly smaller bandgap in the device, as indicated by a significant lateral shift in the quantum efficiency vs. photon energy curve to lower energies. The smallest Tauc gap observed was in the range of 1.62 eV. Corresponding to this smaller bandgap, the current in the solar cell increased, and the voltage decreased. The Urbach energies of the valence band tail were also measured in the device, using the quantum efficiency vs. energy curve, and found to be in the range of45 meV, indicating high quality devices. Too much ion bombardment led to an increase in Urbach energy, and an increase in defect density in the material. Raman spectra of the device i layer indicated an amorphous structure. When hydrogen was added to argon during the annealing cycle, some materials turned microcrystalline, as indicated by the Raman spectrum, and confirmed using x-ray diffraction.
Equivalent-circuit Modeling of Microcrystalline Silicon pin Solar Cells prepared over a Wide Range of Absorber-layer Compositions
Authors: Reynolds Steve , Smirnov Vladimir
Published: August 2010

An equivalent-circuit electrical model is used to simulate the photovoltaic properties of mixed-phase thin-film silicon solar cells. Microcrystalline and amorphous phases are represented as separate parallel-connected photodiode equivalent circuits, scaled by assuming that the photodiode area is directly proportional to the volume fraction of each phase. A reasonable correspondence between experiment and simulation is obtained for short-circuit current and open-circuit voltage vs. volume fraction. However the large dip in fill-factor and reduced PV efficiency measured for cells prepared in the low-crystalline region is inadequately reproduced. It is concluded that poor PV performance in this region is not due solely to shunting by more highly-crystalline filaments, which supports the view that the low-crystalline material has transport properties inferior to either microcrystalline or amorphous silicon.
Photonic Crystal Back Reflectors for Enhanced Absorption in Amorphous Silicon Solar Cells
Authors: Curtin Benjamin , Biswas Rana , Dalal Vikram
Published: August 2010

Photonic crystal back reflectors offer enhanced optical absorption in thin-film solar cells, without undesirable losses. Rigorous simulations of photonic crystal back reflectors predicted maximized light absorption in amorphous silicon solar cells for a pitch of 700-800 nm. Simulations also predict that for typical 250 nm i-layer cells, the periodic photonic crystal back reflector can improve absorption over the ideal randomly roughened back reflector (or the ‘4n2classical limit') at wavelengths near the band edge. The PC back reflector provides even higher enhancement than roughened back reflectors for cells with even thinner i-layers. Using these simulated designs, we fabricated metallic photonic crystal back reflectors with different etch depths and i-layer thicknesses. The photonic crystals had a pitch of 760 nm and triangular lattice symmetry. The average light absorption increased with the PC back reflectors, but the greatest improvement (7-8%) in short circuit current was found for thinner i-layers. We have studied the dependence of cell performance on the etch depth of the photonic crystal. The photonic crystal back reflector strongly diffracts light and increases optical path lengths of solar photons.
On The Mechanism of Nucleation in Pulsed-laser Quenched Si Films on SiO2
Authors: Deng Yikang , Hu Qiongying , Chung Ui-Jin , Chitu Adrian , Limanov Alexander , Im James
Published: August 2010

We have investigated the solid nucleation mechanism in laser-quenched Si films on SiO2. Previously neglected experimental steps, consisting of BHF-etching and irradiation in vacuum, were implemented to reduce potential extrinsic influences. The resulting experimental findings and computational analysis lead us to conclude that solid nucleation consistently takes place heterogeneously at, and only at, the bottom liquid Si-SiO2 interface.
Investigation of Near-IR Emission from Hydrogenated Nanocrystalline Silicon – The Oxygen Defect Band
Authors: Fields Jeremy David , Taylor Craig , Bobela David , Yan Baojie , Yue Guozhen
Published: August 2010

Hydrogenated nanocrystalline silicon (nc-Si:H), a mixture of nanometer sized crystallites and amorphous silicon tissue, demonstrates a photoluminescence band centered at ∼ 0.7 eV, which emerges in response to annealing at an onset temperature of ∼ 200–300 °C. This temperature range correlates well with hydrogen effusion spectroscopy studies, and evidence suggests thermal liberation of hydrogen from grain boundary regions allows oxidation of crystallite surfaces during annealing. We tentatively attribute the 0.7 eV PL in nc-Si:H to deep donor defect states related to oxygen precipitates, and argue for the possible involvement of dislocations inside of crystallites to accompany these precipitates.
Assignment of High Wave-number Absorption and Raman Scattering Peaks in Microcrystalline Silicon
Authors: Johnson Erik V. , Kroely Laurent , Roca i Cabarrocas Pere
Published: August 2010

In the optimization of high-growth rate hydrogenated microcrystalline silicon (μc-Si:H) for photovoltaics, the observation of the infrared (IR) absorption peaks around 2000 cm-1 - which originate from silicon hydrogen (Si-HX) bonds in the film bulk - can provide useful information about the properties of the film. If the films are deposited on IR transparent substrates, Fourier Transform infrared (FTIR) spectroscopy is the most commonly used technique to measure the absorption in this regime. The rich spectrum of Si-HX peaks that can be observed in this wavenumber region describes the distribution of the bonded hydrogen amongst the various possible SiHX configurations, and as well, the presence of a pair of narrow, twin peaks at 2085 and 2100 cm-1 is indicative of material that is porous and prone to oxidation upon exposure to air. Many of these high wavenumber peaks are also observable using Raman scattering spectroscopy, allowing one to observe films on substrates that are not IR transparent. As well, the different absorption/scattering cross sections of the two techniques provide a useful tool to understand the origins of the various peaks, and in particular, those of the twin narrow peaks. In this work, we examine the dynamics upon exposure to atmosphere of these twin peaks in μc-Si:H grown by Matrix Distributed Electron Cyclotron Resonance (MD-ECR) PECVD. This deposition technique is an extremely promising one for growing μc-Si:H thin films at high deposition rates, and has demonstrated μc-Si:H film deposition at up to 28Å/s. By using both FTIR and Raman spectroscopy to characterize these films, we examine the differences in the dynamics of each of the twin peaks according to the technique used. In addition, secondary ion mass spectrometry (SIMS) measurements on the films show the physical distribution of oxygen in the films after five months of air exposure, and XRD measurements correlate the presence of these twin peaks with a [111] preferential surface orientation. Using these observations, we assign these absorption and scattering features to specific configurations of Si-HX within the film, and explain both the dynamics of the peaks over time and the similarity of the peaks for a wide range of samples.
Standard Characterization of Multi-junction Thin-film Photovoltaic Modules: Spectral Mismatch Correction to Standard Test Conditions and Comparison with Outdoor Measurements
Authors: Pravettoni Mauro , Tzamalis Georgios , Anika Komlan , Polverini Davide , Müllejans Harald
Published: August 2010

Multi-junction thin-film devices have emerged as very promising PV materials due to reduced cost, manufacturing ease, efficiency and long term performance. The consequent growing interest of the PV community has lead to the development of new methods for the correction of indoor measurements to standard test conditions (STC), as presented in this paper. The experimental setup for spectral response measurement of multi-junction large-area thin-film modules is presented. A method for reliable corrections of indoor current-voltage characterization to STC is presented: results are compared with outdoor measurements where irradiance conditions are close to standard ones, highlighting ongoing challenges in standard characterization of such devices.
Optimization of the a-SiC p-layer in a-Si:H-based n-i-p Photodiodes
Authors: Vygranenko Yuri , Sazonov Andrei , Heiler Gregory , Tredwell Timothy , Vieira Manuela , Nathan Arokia
Published: August 2010

Our work is aimed at enhancing the external quantum efficiency (EQE) of n-i-p photodiodes by reducing the absorption losses in the p-layer and the recombination losses in the p-i interface. We have applied boron-doped and undoped hydrogenated amorphous silicon carbon alloy (a-SiC:H) grown in hydrogen-diluted, silane-methane plasma to both the p-layer and undoped buffer layer, thus tailoring the p-i interface. The current-voltage, capacitance-voltage, and spectral-response characteristics of fabricated photodiodes are correlated with the doping level, optical band gap, and deposition conditions for a-SiC:H layers. The optimized device exhibits a leakage current of about 110 pA/cm2 at the reverse bias of 5 V, and a peak value of 89% EQE at a wavelength of 530 nm. At shorter wavelengths, the EQE decreases down to 56% at a 400 nm wavelength. Calculations of transmission/reflection losses at the front of the photodiode show that observed short-wavelength sensitivity enhancement can be attributed to improved separation of electron-hole pairs in the p-layer depletion region.
Demultiplexer/Photodetector Integrated System Based on a-SiC:H Multilayered Structures
Authors: Louro Paula , Vieira Manuela , Vieira M. A. , Costa João , Fernandes Miguel , Barata Manuel
Published: August 2010

In this paper we present results on the use of multilayered a-SiC:H heterostructures as an integrated device for simultaneous wavelength-division demultiplexing and measurement of optical signals. These devices are useful in optical communications applications that use the wavelength division multiplexing technique to encode multiple signals into the same transmission medium.

The device is composed of two stacked p-i-n photodiodes, both optimized for the selective collection of photo generated carriers. Band gap engineering was used to adjust the photogeneration and recombination rates profiles of the intrinsic absorber regions of each photodiode to short and long wavelength absorption and carrier collection in the visible spectrum. The generated photocurrent signal using different input optical channels was analyzed at reverse and forward bias and under steady state illumination. A demux algorithm based on the voltage controlled sensitivity of the device was proposed and tested. An electrical model of the WDM device is presented and supported by the solution of the respective circuit equations. Other possible applications of the device in optical communication systems are also proposed.
A Full p-Type Poly-Si TFT Shift Register for Active Matrix Displays
Authors: Jung Myoung-Hoon , Chung Hoon-Ju , Park Young-Ju , Kim Ohyun
Published: August 2010

A new shift register using p-type poly-Si thin-film transistors (TFTs) for active matrix display is proposed. It utilizes only p-type TFTs to simplify the fabrication process, and provides time-shifted output signals with a voltage swing from VSS to VDD without signal-level loss. In the proposed shift register, output is structurally separated from carry and therefore has a high immunity to output signal distortion caused by output load capacitance. We also propose a new light emitting control method using this shift register for high image quality active-matrix organic light emitting diode (AMOLED) displays. The proposed shift register was verified by simulation and measurement.
Crystallization Kinetics in High-rate Electron Beam Evaporated Poly-Si Thin Film Solar Cells on ZnO:Al
Authors: Sontheimer Tobias , Becker Christiane , Klimm Carola , Gall Stefan , Rech Bernd
Published: August 2010

The microstructure and crystallization kinetics of electron beam evaporated Si on ZnO:Al coated glass for polycrystalline solar cells was studied by electron backscatter diffraction and optical microscopy at various deposition temperatures. A time dependent analysis of the dynamics of the crystallization allowed for the individual determination of growth and nucleation processes. The nucleation process of Si on ZnO:Al was found to be influenced by a variation of the deposition temperature of the amorphous Si in a critical temperature regime of 200 ˚C to 300 ˚C. The nucleation rate decreased significantly with decreasing deposition temperature, while the activation energy for nucleation increased from 2.9 eV at a deposition temperature of 300 ˚C to 5.1 eV at 200 ˚C, resulting in poly-Si which comprised grains with features sizes of several μm.
Study of Crystallinity in μc-Si:H Films Deposited by Cat-CVD for Thin Film Solar Cell Applications
Authors: Hsu Cheng-Hang , Hsu Yi-Peng , Yao Fang-Hong , Huang Yen-Tang , Tsai Chuang-Chuang , Zan Hsiao-Wen , Bi Chien-Chung , Lu Chun-Hsiung , Yeh Chih-Hung
Published: August 2010

The crystallinity of the hydrogenated microcrystalline silicon (μc-Si:H) film was known to influence the solar cell efficiency greatly. Also hydrogen was found to play a critical role in controlling the crystallinity. Instead of employing conventional plasma deposition techniques, this work focused on using catalytic chemical vapor deposition (Cat-CVD) to study the effect of hydrogen dilution and the filament-to-substrate distance on the crystallinity, deposition rate, microstructure factor and electrical property of the μc-Si:H film. We found that the substrate material and structure can affect the crystallinity of the μc-Si:H film and the incubation effect. Comparing bare glass, TCO-coated glass, a-Si:H-coated glass and μc-Si:H-coated glass, the microcrystalline phase grows the fastest onto μc-Si:H surface, but the slowest onto a-Si:H surface. Surprisingly, the template effect lasted for more than a thousand atomic layers of silicon.
Growth of Large Diameter 6H SI and 4H n+ SiC Single Crystals
Authors: Gupta Avinash , Wu Ping , Rengarajan Varatharajan , Xu Xueping , Yoganathan Murugesu , Martin Cristopher , Emorhokpor Ejiro , Souzis Andrew , Zwieback Ilya , Anderson Thomas
Published: August 2010

SiC single crystals are grown at II-VI by the seeded sublimation technique. The process has been scaled up and optimized to support commercial production of high-quality 100 mm diameter, Semi-Insulating (SI) 6H substrates and 100 mm 4H n+ substrates. The growth process incorporates special elements aimed at achieving uniform sublimation of the source, steady growth rate, uniform doping and reduced presence of background impurities.

Semi-insulating 6H substrates are produced using precise vanadium compensation. Vanadium doping is optimized to yield SI material with very high resistivity and low capacitance.

Crystal quality of the substrates is evaluated using a wide variety of techniques. Specific defects, their interaction and evolution during growth are described with emphasis on micropipes and dislocations. The current quality of the 6H SI and 4H n+ crystals grown at II-VI is summarized.
Non-destructive Detection and Visualization of Extended Defects in 4H-SiC Epilayers
Authors: Feng Gan , Suda Jun , Kimoto Tsunenobu
Published: August 2010

The extended defects, such as dislocations and in-grown stacking faults (IGSFs), in 4H-SiC epilayers have been detected and visualized by a non-destructive method, the micro photoluminescence (μ-PL) intensity mapping method, at room temperature. The one-to-one correspondence between the extended defects and the μ-PL mapping contrast has been successfully obtained. A threading dislocation corresponds to a dark circle with the reduced intensity in the μ-PL mapping image performed at 390 nm, while a basal plane dislocation dissociates into a single Shockley SF during the measurements. Three kinds of IGSFs have been identified in the samples. Each kind of IGSF shows the distinct PL emission located at 460 nm, 480 nm, and 500 nm, respectively. The shapes and distributions of IGSFs have also been profiled by μ-PL intensity mapping.
Systematic first principles calculations of the effects of stacking faults defects on the 4H-SiC band structure
Authors: Camarda Massimo , delugas pietro , Canino Andrea , Severino Andrea , piluso nicolo , La Magna Antonino , La Via Francesco
Published: August 2010

Shockley-type Stacking faults (SSF) in hexagonal Silicon Carbide polytypes have received considerable attention in recent years since it has been found that these defects are responsible for the degradation of forward I-V characteristics in p-i-n diodes. In order to extend the knowledge on these kind of defects and theoretically support experimental findings (specifically, photoluminescence spectral analysis), we have determined the Kohn-Sham electronic band structures, along the closed path Γ-M-K-Γ, using density functional theory. We have also determined the energies of the SSFs with respect to the perfect crystal finding that the (35) and (44) SSFs have unexpectedly low formation energies, for this reason we could expect these two defects to be easily generated/expanded either during the growth or post-growth process steps.
Monolithic a-SiC:H Stack Architectures as Tunable Optical Filters for Spectral Analysis
Authors: Vieira Manuela , Louro Paula , Vieira M. A. , Costa João , Fernandes Miguel , Vygranenko Yury , Barata Manuel
Published: August 2010

The characteristics of a tunable wavelength filter in a-SiC:H multilayered stack p-i'i-n graded cells are studied both theoretically and experimentally. Three different architectures are tested for proper fine tuning of the spectral sensitivity. The simplest configuration is a two terminal p-i-n photodiode where the active intrinsic layer is a double layered a-SiC:H/a-Si:H thin film. In the others the active device consists of a p-i'(a-SiC:H)-n / p-i(a-Si:H)-n heterostructures where the doped layers can have high or low conductivities. The spectral analysis of the device is performed under different optical and electrical applied bias and frequencies. Results show that, depending on the architecture and time window used, the device acts as an optical filter, an amplifier or a multiplexer /demultiplexer for optical signal processing, wavelength conversion, signal demultiplexing, and pattern recognition. A theoretical analysis supported by numerical and electrical simulations is presented. The analysis uses simple phototransistor and photodiode equations to explain the response of the device under different optical signals, and to compare the generated photocurrent with the experimental data.
Pulse Performance and Reliability Analysis of a 1.0 cm24H-SiC GTO
Authors: O'Brien Heather , Ogunniyi Aderinto , Zhang Qingchun Jon , Agarwal Anant
Published: August 2010

A 1.0 cm2silicon carbide Super-GTO was designed and fabricated for Army pulsed power applications. It is a milestone, being the first SiC Super-GTO of this size. The design is the culmination of several years of research into material improvement, termination and gate patterns, optimizing device size, and calibrating pulse performance. The SGTO's forward blocking voltage is 9.0 kV, and its on-state voltage is 2.9 V at turn-on. Six devices were evaluated for pulse capability in a high-energy RLC circuit that was designed to produce a 1-ms wide half-sine shaped pulse. The maximum safe operating current for each of the six Super-GTOs varied from 2.2 kA to 3.4 kA, with 13 V being the typical VAKat a current of 3.0 kA. Two of the GTOs were also tested for pulse reliability and repeatability. They were individually switched in the pulse circuit for >500 pulses at very low duty cycle. This study is base-level research on pulse capability of the newest generation of SiC Super-GTOs and as such strives to identify the defining characteristics of an optimal device as well as the predominant modes of device failure.
Passivation by N Implantation of the SiO2/SiC Acceptor Interface States: Impact on the Oxide Hole Traps and the Gate Oxide Reliability
Authors: Poggi Antonella , Moscatelli Francesco , Solmi Sandro , Nipoti Roberta
Published: August 2010

This study compares p-MOS capacitors fabricated on N+ implanted and on virgin 4H-SiC. The former sample have N at the SiO2/SiC interface, the latter have not. To investigate the presence of deep and shallow hole traps at the SiO2/SiC interface, high frequency and quasi-static capacitance voltage measurements under dark have been compared for bias sweeping from accumulation to depletion and from depletion to accumulation, the latter after white light illumination. The presence of N has an effect on the density of the shallow donor like traps but none effect on the deep ones. The positive charge trapped in the oxide and/or at the oxide interface after equivalent tunneling hole injection have been compared and are equivalent. Time dependent dielectric breakdown tests have been compared too. The oxide grown on N+implanted SiC broken at lower electric field.
Micromachining of thin 3C-SiC films for mechanical properties investigation
Authors: Michaud Jean-Francois , Jiao Sai , Bazin Anne-Elisabeth , Portail Marc , Chassagne Thierry , Zielinski Marcin , Alquier Daniel
Published: August 2010

In this work, the mechanical properties of cubic silicon carbide are explored through the analysis of the static and dynamic behavior of 3C-SiC cantilevers. The investigated structures were micro-machined using Inductively Coupled Plasma (ICP) etching of thin 3C-SiC films grown on silicon. The aim was to evaluate the influence of some basic parameters (film orientation, film thickness, defect density) on the mechanical properties of the material.

X-Ray Diffraction was used to evaluate the crystalline quality of the epilayers. Scanning Electron Microscopy observations of static cantilever deflection highlight the major difference between the stress states of (100) and (111) oriented layers for which the intrinsic stresses are of opposite signs. The cantilever deflection is highly dependent on the film thickness, as stated for (100) oriented epilayers. The lowest deflection is obtained for the thickest layer. The Young's modulus of 3C-SiC is calculated from the resonance frequency of clamped-free cantilevers, measured by laser Doppler vibrometry. The relatively low and orientation independent value of Young's modulus (~350GPa) found on the samples is probably associated with the high defect density usually observed in very thin 3C-SiC films grown on Si.
CMP for Copper TSV Applications
Authors: Gage Max , Liu Feng , Xu Kun , Wang You , Wang Yuchun , Xia Sherry , Tu Wen-Chiang , Karuppiah Lakshmanan
Published: August 2010

Through-silicon via (TSV) 3-D packaging and integration present many new opportunities and challenges for metals CMP applications. For front-side TSV polishing, challenges include the removal of large amounts of copper overburden, dishing control during copper clearing steps, and removal of large amounts of barrier metal and dielectric layers while still maintaining control over topography and defectivity. Additionally, the choice of barrier material can have significant impact on polishing in terms of the mechanical reliability regarding adhesion between the barrier metal and underlying dielectric layers. This paper will address many of these challenges with an emphasis on innovative technologies for superior process and endpoint controls, such as real-time profile control for thick copper films up to 6μm or more in thickness and automatic endpoint controls for barrier removal and dielectric stopping. The paper will also discuss some salient challenges for back-side TSV polishing, including the handling and polishing of bonded wafer pairs and strategies to minimize handling and polishing damage to the potentially fragile thinned device wafer. Additionally, the development of slurries with highly tunable copper-to-dielectric selectivity will be critical for enabling a wide range of final topographies, depending on requirements for subsequent bonding steps.
Effect of Mechanical and Chemical Wear on Consistency of Conditioning in Diamonds
Authors: Yamada Yohei , Kadomura Kazunori , Kawakubo Masanori , Sugaya Takahiro , Hirai Osamu , Tsugane Ken
Published: August 2010

We evaluated the effects of the edge degradation of diamonds in terms of their cutting ability from the viewpoint of mechanical, chemical and chemical-mechanical wear in chemical-mechanical polishing (CMP) systems for high-volume manufacturing. The results showed that both micro-chipping on the cutting edges of diamonds caused by a mechanical shock test and the rounding off of the sharp edges of diamonds in a marathon wear test degraded the pad cut rate, while no adverse effects on the cutting ability were observed during an acidic slurry immersion test. We also examined in situ coefficient of friction (COF) monitoring for use in identifying the tribology of the pad conditioning. Furthermore, we demonstrated the usefulness of measuring the height ratio of the asperity called “top surface area (TSA) ratio” as an appropriate topographical parameter to study the dependence of COF during conditioning on the decay of the tungsten removal rate. We presented a clear correlation between the pad cut rate degradation and the TSA ratio after CMP in order to elucidate an increase in the conditioning COF related to truncation of the asperity tip by wear and plastic deformation.
Influence of Ionic Strength and pH-value on the Silicon Dioxide Polishing Behaviour of Slurries Based on Pure Silica Suspensions
Authors: Kuenzelmann Ulrich , Estel Kathrin , Bartha Johann W , Meyer Erwin-Peter , Barthel Herbert
Published: August 2010

In this study, the effect of the addition of electrolytes in a given ionic strength to various high-purity silica suspensions was investigated by measurement of the removal rates (RR's) in CMP processes on oxide layers under the same experimental conditions. As so-called slurries the following suspensions were used: i) silica sols produced by the Stöber process, ii) conventional silica sols based on alkali silicate as well as iii) suspensions of fumed silica, with the same SiO2 concentration in each suspension. Ionic strength of the added electrolyte was adjusted to e.g. 0.065 mol/l, with the electrolytes being HCl, NH4Cl, KOH, or binary mixtures of these substances.

These investigations revealed significant differences of the polishing behaviour between the different types of silica dispersions as slurries. While for the Stöber sols investigated, the RR's are highest in the acidic range and almost negligible in the alkaline pH range, fumed silica suspensions show an entirely different behaviour: RR is very low for acidic pH-values, and increases with the alkalinity of the slurry. In contrast to these observations, the RR's of slurries based on conventional silica sols are highest around the neutral point, and show a decrease for both more alkaline and acidic pH-values. In comparison to the other two types of material, these suspensions have a high amount of electrolyte background, originating from their manufacturing process.

A model is developed to explain these results in a comprehensive manner. It involves effects of the electrolyte type and the ionic strengths as well as influences of the particle size.
The Mechanism of Low pH Colloidal Silica-based Oxide Slurries
Authors: White Michael L. , Jones Lamon , Romine Richard
Published: August 2010

The mechanism of oxide polishing at low pH in the presence of an organic cation is discussed. The role of the cation is thought to involve increasing the nucleophilicity of the silanolate active site on the particle surface by lowering the hydration state. Additionally, the activation energy of the reaction may be lowered by charge attraction between the particle and wafer surface and by increased hydrophobic interactions.
Characterization of Surface Processes During Oxide CMP by in situ FTIR Spectroscopy With Microstructured Reflection Elements at Silicon Wafers
Authors: Schumacher Henrik , Kuenzelmann Ulrich , Bartha Johann W
Published: August 2010

In situ investigations of the chemical and mechanical mechanisms during CMP processes require analytical access to the wafer surface while interacting with the slurry and the pad under polishing conditions. In this study me make use of novel, specifically prepared, and self-designed Si wafer called microstructured single reflection elements (mSRE) utilizing the IR transparency of silicon [1]. The mSRE's enable in and ex situ attenuated total reflection (ATR) Fourier transform infrared (FTIR) investigations at the interface between silicon and the ambient with an enhanced usable spectral range. So, a thin silicon oxide layer or the polishing slurry can be investigated in the entire mid and far infrared spectral region. These mSRE wafers were placed at a simple reflection accessory of a FTIR spectrometer and either wet etched by a buffered oxide etch or polished using a CMP equivalent polishing configuration. During CMP the change of typical vibration bands of SiO2 layers and slurry constituents are observed. It was shown that the sensitivity as well as the surface selectivity of the experimental setup enables slurry and thin-film characterisations within the thickness range of monolayers. Surprisingly, the spectral features of the pad have not been observed during the polishing investigations.
Effect of TaN Stoichiometry on Barrier Oxidation and Defect Density in 32nm Cu/Ultra-Low K Interconnects
Authors: Simon Andrew H. , Baumann Frieder H. , Bolom Tibor , Park Jong Guk , Child Craig , Kim Ben , DeHaven Patrick W. , Davis Robert E. , Ogunsola Oluwafemi O , Angyal Matthew S
Published: August 2010

The scaling of BEOL interconnect technology in ULSI circuitry requires the integration of Cu wiring with ultra-low K (ULK) dielectrics. We present the results of a study of the interaction between different-stoichiometry Ta(N)/Cu barrier processes and porous ULK dielectrics (k=2.4) at 32nm groundrules Auger and diffraction analysis of blanket wafers was used to benchmark two different stoichiometries of TaN barrier deposited using commercially-available ionized PVD sources. Comparison TEM and EDX/EELS images indicates that barrier oxidation is occurring in the low nitrogen-content Ta(N) barrier, which is absent at the higher stoichiometry. These differences are further manifested in defect-density analysis of patterned wafers comparing the two processes. These results illustrate the critical importance the TaN barrier properties play in enabling the integration of Cu/ULK interconnects at 32nm at beyond.
Interfacial Resistive Properties of Multi-layered Silicon-based Ohmic Contacts
Authors: Bhaskaran Madhu , Sriram Sharath , Holland Anthony Stephen
Published: August 2010

This article reports on the characterization of two- and three-layer ohmic contacts comprising of titanium disilicide and nickel silicide. Cross Kelvin resistor test structures were used to extract the specific contact resistivity (SCR) values for the different ohmic contacts fabricated. The SCR of aluminum to titanium silicide (Al-TiSi2) ohmic contacts was evaluated to be as low as 6.0 x 10-10 Ωcm2. Three-layer ohmic contacts were created using aluminum and nickel silicide thin films and doped silicon. SCR values as low as 5.0 x 10-9 Ωcm2 to antimony-doped silicon and 3.5 x 10-9 Ωcm2 to boron-doped silicon were evaluated.
Designing Ultra Low-k Dielectric Materials for Ease of Patterning
Authors: Antonelli George Andrew , Jiang Gengwei , Sriram Mandyam , Chattopadhyay Kaushik , Guo Wei , Sawin Herbert
Published: August 2010

Organosilicate materials with dielectric constants (k) ranging from 3.0 to 2.2 are in production or under development for use as interlayer dielectric materials in advanced interconnect logic technology. The dielectric constant of these materials is lowered through the addition of porosity which lowers the film density, making the patterning of these materials difficult. The etching kinetics and surface roughening of a series of low-k dielectric materials with varying porosity and composition were investigated as a function of ion beam angle in a 7% C4F8/Ar chemistry in an inductively-coupled plasma reactor. A similar set of low-k samples were patterned in a single damascene scheme. With a basic understanding of the etching process, we will show that it is possible to proactively design a low-k material that is optimized for a given patterning. A case study will be used to illustrate this point.
Low Temperature Bonding via Copper Nanowires for 3D Integrated Circuits
Authors: Chun Shu Rong , Sasangka Wardhana Aji , Gan Chee Lip , Cai Hui , Ng Chee Mang
Published: August 2010

Low temperature bonding is desired for compatibility with back-end-of-line processing (BEOL) conditions in order not to affect the three dimensional (3D) Integrated Circuits (IC) device performance. In this paper, the aim is to demonstrate that thermocompression bonding temperature can be lowered by changing the copper (Cu) film with Cu nanowires fabricated via electrodeposition through anodized aluminum oxide (AAO) template. A comparison was done between film-to-film (Film-Film) and nanowires-to-nanowires (NWs-NWs) bonding in terms of microstructure and shear strength. Cross-sectional images captured by Focused Ion Beam (FIB) revealed good interface between NWs-NWs bonding as the nanowires had fused together. Scanning Electron Microscope (SEM) images of samples after shear test also demonstrated that there is good adhesion between the bonding layers. Results from shear tests showed an increase in shear strength of NWs-NWs bonding as compared to that of Film-Film bonding at 200 °C. In addition, NWs-NWs bonding at 300 °C achieved higher shear strength than at 200 °C. In this study, it has been shown that copper nanowires fabricated via electrodeposition through porous AAO template can be a potential method to form a bonding intermediate layer for 3D ICs.
Silsesquioxane-based Photopatternable Porous Low-kDielectric Materials
Authors: Nelson Alshakim , Rathore Jitendra S , Davis Blake , Brock Phillip , Sooriyakumaran Ratnam , Miller Robert , Lin Qinghuang
Published: August 2010

The future resolution requirements for the semiconductor industry demand advanced lithographic techniques, such as immersion and extreme ultraviolet (EUV) technologies, which will increase the cost of microelectronics manufacturing. Currently, low-k dielectric materials, which are used as insulating layers between the copper wiring, are indirectly patterned using a set of sacrificial layers and etch processes. The sacrificial layers include a photoresist polymer that must first be imaged prior to transferring the pattern to the underlying layers, including the dielectric layer. In order to reduce the number of processing steps required for semiconductor manufacturing, we have developed a novel photo-patternable low-k dielectric material that (1) eliminates the need for sacrificial layers and (2) reduces the number of wafer processing steps. Silsesquioxane copolymers that undergo acid-catalyzed crosslinking when exposed to 193nm wavelength were synthesized. In addition to the direct photo-patternability, the patterned structures are suitable as a dielectric material with a dielectric constant as low as 2.4, and an appreciable elastic modulus (E > 4.0 GPa). These photo-patternable low-k materials represent a ‘greener' approach to semiconductor manufacturing which has the ability to reduce cost, waste materials, and energy consumption.
Annealing Effects on Si Nanocrystal Nonvolatile Memories
Authors: Dimitrakis Panagiotis , Bonafos Caroline , Schamm Sylvie , Normand Pascal , Assayag G. Ben
Published: August 2010

The effect of thermal treatments in oxidizing ambient on the structural and electrical properties of low-energy Si-implanted thin SiO2 layers which previously suffered or not high temperature annealing in inert ambient was investigated. Based on TEM examination, charge trapping evaluation and FN conduction analysis of the resulting Si-NC SiO2 matrices, a model taking into account the healing of excess silicon atoms introduced by implantation and the generation of Si interstitials by oxidation above and below the viscoelastic temperature of SiO2 is proposed.
Ultra-Low Energy Ion Implantation of Si into HfO2 and HfSiO-based Structures for Non Volatile Memory Applications
Authors: Gloux Florence , Coulon Pierre-Eugène , Groenen Jesse , Schamm Sylvie , Benassayag Gerard , Pecassou Beatrice , Slaoui Abdelilah , Sahu Bhabani , Carrada Marzia , Lhostis Sandrine , Bonafos Caroline
Published: August 2010

The fabrication of Si nanocrystals (NCs) in multilayer structures based on HfO2 and alloys for memory applications is carried out using an innovative method, the ultra-low energy (1 keV) ion implantation followed by a post-implantation annealing. Si+ ions are implanted into SiO2 thin layers deposited on top of thin HfO2-based layers. After annealing at high temperature (1050°C), the implantation leads to the formation of a two dimensional array of Si NCs at a distance from the surface larger than expected, due to an anomalous oxidation of the implanted Si. Nevertheless, the best memory windows are obtained at lower thermal budget, when no nanocrystals are present in the layer. This suggests that electrical measurements should always be correlated to structural characterization in order to understand where charge storage occurs.
Charge Trapping Sites in nc-RuO Embedded ZrHfO High-k Nonvolatile Memories
Authors: Lin Chen-Han , Kuo Yue
Published: August 2010

Materials and electrical properties of the MOS capacitor containing nc-RuO embedded in the high-k ZrHfO dielectric film have been studied. The electron- and hole-trapping capacities and trapping sites in this kind of device were investigated using the constant voltage stress method, the frequency-dependent C-V measurement, and the retention characteristics. The negligible charge trapping phenomenon in the non-embedded device rules out the possibility of any trapping site in the bulk ZrHfO film or at the Si/ZrHfO interface. The electrical characterization result suggests that electrons are trapped in the bulk nc-RuO. However, holes have two possible trapping sites, i.e., in the bulk nc-RuO or at the nc-RuO/ZrHfO interface.
Study on C60 Doped PMMA for Organic Memory Devices
Authors: Charbonneau Micael , Tiron Raluca , Buckley Julien , Py Mathieu , Barnes Jean-paul , Derrough Samir , Constancias Christophe , Licitra Christophe , Sourd Claire , Ghibaudo Gerard , De Salvo Barbara
Published: August 2010

In this paper, fabrication of nanocomposite thin films with introduction of fullerene (C60) molecules in PolyMethyl MethAcrylate resist (PMMA) was investigated from a material and electrical point of view. The effective inclusion of C60 molecules in the samples was characterized by using UV-vis and Tof-SIMS instruments. The modified resist PMMA:C60 was also studied with Thermal analysis (TGA, DSC) where modification of physical properties is reported. Films were included in MIS and MIM devices and results on non volatile trapping of C60 doped PMMA are presented. Moreover, e-beam exposure tests showed that PMMA:C60 active layers for memory devices, were scalable in size.
Correlation Between Oxygen Composition and Electrical Properties in NiO Thin Films for Resistive Random Access Memory
Authors: Nishi Yusuke , Iwata Tatsuya , Kimoto Tsunenobu
Published: August 2010

Admittance spectroscopy measurement has been performed on NiOx thin films with various oxygen compositions (x=1.0-1.2) in order to characterize localized defect levels. The activation energy and concentration of localized defect levels in NiOx films with low oxygen composition (x≤1.07) are 120-170 meV and lower than 2×1019 cm-3, respectively. From I-V measurement of the Pt/NiOx/Pt structures, samples with high oxygen composition (x≥1.10) did not show resistance switching operation, while samples with low oxygen composition (x≤1.07) did. The best oxygen composition of NiOx thin films turned out to be 1.07 in order to realize repeatable and stable resistance switching operation.