bluuebunny/crossref_metadata_2025 huggingface dataset:
Low gap Amorphous (Si,Ge) Solar Cells
Authors: Dalal Vikram L. , Zhou Zhiyang
Published: April 2011

We report on the growth and fabrication of low-gap a-(Si,Ge) solar cells, including cells made from a-Ge:H. The cells were deposited from silane and germane, or germane alone, using a high dilution of hydrogen in a remote ECR plasma reactor. We have been able to achieve a Tauc gap of as low as 1.15 eV with good device properties. The fill factors were in the 50%-60% range, and the Urbach energies measured in devices were in the range of 45 meV. The devices were of the p/i/n type with light entering the p layer. The devices were fabricated on stainless steel substrates. We also report on experiments to improve graded gap solar cells in a- (Si,Ge) using a novel combination of ppm-boron dopant and bandgap grading. It is shown that this grading significantly improves the device performance, both voltage and fill factor.
Diamagnetic Susceptibility of Micron Thick a-Si:H Films Measured via Proton NMR: A Probe of Structural Disorder
Authors: Baugh J. , Han D. X. , Kleinhammes A. , Wang Q. , Wu Y.
Published: April 2011

Magnetic susceptibility is predicted to be sensitive to structural disorder in the group IV elemental semiconductors. A proton nuclear magnetic resonance (NMR) technique is shown to precisely measure bulk magnetic susceptibilities (χ) of hot-wire (HW) CVD a-Si:H films as- deposited on quartz substrates. Differences in χ correlate with growth rate, but not with hydrogen content or deposition temperature. Qualitative agreement is found between smaller diamagnetic susceptibility (less average disorder) and desirable electronic properties measured by photo- and dark conductivity on the same samples. Comparing films with similar hydrogen distribution and content (as evidenced by the NMR spectra) allows the unambiguous identification of the importance of overall Si network structural disorder in the metastability of a-Si:H.
Silicon-Carbon Alloys Synthesized by Electron Cyclotron Resonance Chemical Vapor Deposition
Authors: Moran Mark B. , Johnson Linda F.
Published: April 2011

Silicon-carbon alloys were deposited by electron cyclotron resonance chemical vapor deposition (ECR-CVD) using either halogenated or non-halogenated precursors for the Si and C sources. Halogenated precursors were chosen for initial experiments to try to reduce the H content and to improve the microstructure of the silicon carbide (SiCx) films. While a wide range of compositions has been deposited using the halogenated precursors, only a limited range has been deposited so far with the non-halogenated precursors. Electron spectroscopy for chemical analysis (ESCA) and Fourier transform infrared (FTIR) spectroscopy show that compositions ranging from near-stoichiometric SiCx to extremely C-rich can be deposited by controlling the deposition temperature, plasma power and C/Si ratio of the halogenated precursors. At the highest C/Si-precursor ratio, the deposited film is electrically conductive with a measured resistivity of 0.067ω-cm, contains only 3-atomic-percent Si and should be considered a Si-doped carbon (C:Si) film. The excellent transparency, especially that of the C:Si films, allowed the assignment of FTIR absorption bands that are usually masked by graphitic inclusions and other impurities. A weak absorption band at 1180cm−1 was found to correlate with the electrical conductivity of the films and was attributed to the asymmetric “bond-and-a-half” Si=C stretch in a Si=C=C functional group where the pi electrons are distributed equally between the three atoms. Additional results show etching of the substrate by reactive Cl from the halogenated precursors can have a dramatic effect on the microstructure, porosity and moisture stability of the films. For experiments involving halogenated precursors, the C:Si films are much more stable than the near-stoichiometric SiCx because C:Si is deposited at lower plasma powers that do not etch the Si substrate. Finally, preliminary results show that near-stoichiometric SiCx films deposited using non-halogenated precursors are much more stable with respect to moisture incorporation than those deposited with halogenated precursors.
Capacitance Voltage Characteristics of Polysilicon–Polysilicon Oxide–Polysilicon Structures for Three-Dimensional Memory
Authors: Lindsey John R. , Kalkur T. S.
Published: April 2011

Three-dimensional integration offers a dramatic reduction in chip area required per bit and has long been a research objective. Three-dimensional integration with thin film transistors (TFTs) requires detailed parametric analysis with techniques such as Capacitance-Voltage (CV) Characterization. CV analysis of polysilicon TFTs uses polysilicon-oxide-polysilicon thin film structures. Most of the CV analysis involving polysilicon available to date, however, is with polysilicon-oxide-bulk silicon structures. In this paper, we report the results of modeling andmeasurement of the CV characteristics of polysilicon-polysilicon oxide-polysilicon for doped and undoped polysilicon. To increase the conductivity of the polysilicon, elevated temperatures were used for measurement. CV measurements matching the theoretical curves were made for these polysilicon thin films. Oxide thickness, series and shunt resistance were extracted and correlated to process problems and splits.
A Junction Field Effect Transistor Based on Hydrogenated Amorphous Silicon
Authors: Caputo D. , Cesare G. de , Nascetti A. , Kellezi V. , Palma F.
Published: April 2011

An hydrogenated amorphous silicon junction field effect transistor suitable for analog and digital applications is presented. The device is constituted by a p+ - i - n− junction, with the drain and source contacts patterned on the n-doped layer and the gate electrode patterned on the p+ doped layer. As in the crystalline case, the device is a voltage-controlled resistor, and its drain-source resistance can be varied, with a voltage applied to the gate electrode, by modulating the width of the depletion layer extending into the n-type channel.

The doping value of this layer has been chosen as a trade-off between high value of channel conductivity and a relatively low defect density in the material. The manufactured device, with W/L=5000/200 μm, shows the typical current-voltage curves of a JFET. In particular, at low VDS, the current presents the linear behavior of the triode zone, where the JFET operates as a linear resistance whose value is controlled by the gate voltage. At higher VDS the JFET works in the pinch-off region as a dependent current generator.

First results are very encouraging, since we have achieved transconductance values of 10−6 V/A, which are comparable to those of state of the art TFT.
Response Time Measurements and Flying Spot Technique in Microcrystalline Silicon Solar Cells
Authors: Schwarz R. , Sanguino P. , Koynov S. , Fernandes M. , Maçarico F. , Louro P. , Vieira M.
Published: April 2011

Transverse charge collection in a p-i-n structure based on microcrystalline silicon and lateral transport in a single intrinsic layer were analyzed using transient photoconductivity (TPC), steady-state photocarrier grating analysis (SSPG), and the flying spot technique (FST). Photocurrents were excited either with HeNe laser light (633 nm, intensity about 20 mW/cm2) or with 5 ns pulses from a Nd:YAG laser (532 nm, peak power of about 500 kW/cm2 with 5 mJ pulses). The response time τR varied greatly from about 3 ms at low intensity down to a few μs under pulsed laser excitation. The minority carrier diffusion length LD measured by FST in diode structures was usually larger than values obtained from the SSPG method applied to intrinsic microcrystalline layers.
Resistivity and Hall Voltage Investigation of Phosphorus Segregation in Polycrystalline Si1-xGex Thin Films
Authors: Qin W. , Ast D. G. , Kamins T. I.
Published: April 2011

Dopant segregation in atmospheric-pressure, chemically vapor deposited (APCVD), ~300 nm thick, polycrystalline Si0.95Ge0.5 and Si0.9Ge0.1 thin films, implanted at 80 KeV with 6×1013 to 5×1014 P/cm2 and annealed at 800 °C for 1 hr, was investigated using a combination of Hall and conductivity vs. temperature measurements. Hall measurements, feasible only in heavier doped films, showed that 29% of the phosphorus in Si0.9Ge0.1 and 42% of phosphorus in Si0.95Ge0.05 was electrically inactive. The loss was attributed to dopant segregating to grain boundaries. The density of grain boundaries states was also found to increase slightly with increasing Ge content, from 3.6×1012/cm2 in Si0.95Ge0.05 to 4.4×1012/cm2 in Si0.9Ge0.1.
Polycrystalline Silicon Thin Films For Microelectronic Applications
Authors: Guliants Elena A. , Song Young J. , Anderson Wayne A.
Published: April 2011

Polycrystalline silicon thin films with a thickness of 0.5-2μm were grown on 25nm thick Ni prelayers by d.c. magnetron sputtering from a Si target. In contrast to the conventional sputtering, the use of a thin Ni film allows the production of high crystallinity silicon at a temperature of 475°C and higher. The Ni disilicide grains formed at the Ni - growing Si film interface provide sufficient sites for the epitaxial growth of Si. The Si films with resistivity of 102-103Ω-cm possess a carrier lifetime of up to 11μs and a diffusion length of up to 3.4 μm, which makes them applicable to various microelectronic devices. As an example, Schottky diodes fabricated on 0.5μm thick Si films exhibit a forward-to-reverse current ratio of 107. The technique is easily implemented on a variety of substrates.
Nanoscale Elastic Imaging of Aluminum/Low-k Dielectric Interconnect Structures
Authors: Shekhawat G. S. , Kolosov O.V. , Briggs G.A.D. , Shaffer E. O. , Martin S. , Geer R. E.
Published: April 2011

A new characterization tool based on ultrasonic force microscopy (UFM) has been developed to image the nanometer scale mechanical properties of aluminum/low-k polymer damascence integrated circuit (IC) test structures. Aluminum and polymer regions are differentiated on the basis of elastic modulus with a spatial resolution ≤ 10 nm. This technique reveals a reactive-ion etch (RIE)-induced hardening of the low-k polymer that is manifested in the final IC test structure by a region of increased hardness at the aluminum/polymer interface. The ability to characterize nanometer scale mechanical properties of materials used for IC back-end-of-line (BEOL) manufacture offers new opportunities for metrological reliability evaluation of low-k integration processes.
Circuit-Level and Layout-Specific Interconnect Reliability Assessments
Authors: Hau-Riege S.P. , Thompson C.V. , Hau-Riege C.S. , Andleigh V.K. , Chery Y. , Troxel D.
Published: April 2011

We have developed a methodology and a prototype tool for making computationally efficient circuit-level assessments of interconnect reliability. A key component of this process has been the development of simple analytic models that relate the reliability of the complex structures in layouts to the simpler straight, junction-free lines of uniform width that are typically used in lifetime tests. We have considered interconnect trees as the fundamental reliability units, where trees can have multiple junctions and limbs, and can also have width variations. We have developed analytic methods for identifying trees which are immune to failure, and have demonstrated that computationally simple techniques lead to the identification of a large fraction of the trees in a circuit as immune to failure (i.e., that they are ‘immortal’). These trees therefore need not be considered in further analyses. Using simulations and analytic treatments we have also developed default models which allow estimation of the reliability of the remaining trees. These models have been tested and validated them through experiments on simple tree structures with junctions and line-width transitions. Our prototype circuit-level reliability analysis tool projects the reliability of circuits based on specific layouts, and provides a rank listing of the reliability of mortal trees. This allows the user to accept the assessment as is, to carry out more accurate but computationally-intensive analyses of the least reliable trees, or to modify the layout or process to address reliability concerns and reanalyze the reliability.
Stressmigration Behavior of Multilevel Ulsi Alcu-Metallizations
Authors: Fischer A.H. , Zitzelsberger A.E. , Hommel M. , von Glasow A.
Published: April 2011

With decreasing geometries of metal interconnects the demands on metallization reliability increase rapidly. In addition to electromigration, stress-induced voiding becomes a major problem, influencing lifetime and functionality of integrated circuits. This paper summarizes our studies on stressmigration behavior of various AlCu-multilevel metallizations. A model for an estimation of the median time to failure is presented.
Structure and Property Characterization of Porous Low-k Dielectric Constant Thin Films using X-ray Reflectivity and Small Angle Neutron Scattering
Authors: Lin Eric K. , Wu Wen-li , Jin Changming , Wetzel Jeffrey T.
Published: April 2011

High-resolution X-ray reflectivity and small angle neutron scattering measurements are used as complementary techniques to characterize the structure and properties of porous thin films for use as low-k interlevel dielectric (ILD) materials. With the addition of elemental composition information, the average pore size, porosity, pore connectivity, matrix density, average film density, film thickness, coefficient of thermal expansion, and moisture uptake of porous thin films are determined. Examples from different classes of materials and two analysis methods for small angle neutron scattering data are presented and discussed.
Fabrication of Air-Gaps Between Cu Interconnects for Low Intralevel k.
Authors: Bhusari Dhananjay M. , Wedlake Michael D. , Kohl Paul A. , Case Carlye , Klemens Fred P. , Miner John , Lee Byung-Chan , Gutmann Ronald J. , Lee J.J. , Shick Robert , Rhodes L.
Published: April 2011

We present here a method for fabrication of air-gaps between Cu-interconnects to achieve low intralevel dielectric constant, using a sacrificial polymer as a ‘place holder’. IC compatible metallization and CMP processes were used in a single damascene process. The air-gap occupies the entire intralevel volume between the copper lines with fully densified SiO2 as the planer interlevel dielectric. The width of the air-gaps was 286 nm and the width of the copper lines was 650 nm. The effective intralevel dielectric constant was calculated to be 2.19. The thickness of the interlevel SiO2 and copper lines were 1100 nm and 700 nm, respectively. Further reduction in the value of intralevel dielectric constant is possible by optimization of the geometry of the metal/air-gap structure, and by use of a low k interlevel dielectric material.

In this method of forming air-gaps, the layer of sacrificial polymer was spin-coated onto the substrate and formed into the desired pattern using an oxide or metal mask and reactive-ion-etching. The intralevel Cu trench is then inlaid using a damascene process. After the CMP of copper, interlevel SiO2 is deposited by plasma-CVD. Finally, the polymer place-holder is thermally decomposed with the decomposition products permeating through the interlevel dielectric material. The major advantages of this method over other reported methods of formation of air-gaps are excellent control over the geometry of the air-gaps; no protrusion of air-gaps into the interlevel dielectric; no deposition of SiO2 over the side-walls, and no degradation of the interlevel dielectric during the formation of air-gap.
Characterization and Integration in Cu Damascene Structures of AURORA, an Inorganic Low-k Dielectric
Authors: Donaton R. A. , Coenegrachts B. , Sleeckx E. , Schaekers M. , Sophie G. , Matsuki N. , Baklanov M. R. , Struyf H. , Lepage M. , Vanhaelemeersch S. , Beyer G. , Stucchi M. , Roest D. De , Maex K.
Published: April 2011

AURORA films, which have a Si-O-Si network with –CH3 terminations, were characterized and integrated into Cu single damascene structures. The relatively low carbon concentration (∼ 20%) and the very small pore size (∼ 0.6 nm) found could be advantageous during integration of AURORA. Integration of AURORA into Cu single damascene structures was successfully achieved. Suitable resist strip processes, which are critical for Si-O-C type materials, were developed, resulting in trenches with satisfactory profiles. After a complete single damascene process, a interline dielectric constant value of 2.7 was found for line spacing down to 0.25 µm.
A Three-phase Model for the Structure of Porous Thin Films Determined by X-ray Reflectivity and Small-Angle Neutron Scattering
Authors: Wu Wen-li , Lin Eric K. , Jin Changming , Wetzel Jeffrey T.
Published: April 2011

A methodology to characterize nanoporous thin films based on a novel combination of high-resolution specular x-ray reflectivity and small-angle neutron scattering has been advanced to accommodate heterogeneities within the material surrounding nanoscale voids. More specifically, the average pore size, pore connectivity, film thickness, wall or matrix density, coefficient of thermal expansion, and moisture uptake of nanoporous thin films with non-homogeneous solid matrices can be measured. The measurements can be performed directly on films up to 1.5 µm thick while supported on silicon substrates. This method has been successfully applied to a wide range of industrially developed materials for use as low-k interlayer dielectrics.
Electromigration-Induced Stress Interaction between Via and Polygranular Cluster
Authors: Park Young-Joon , Choi In-Suk , Joo Young-Chang
Published: April 2011

We have investigated the stress interaction between via and polygranular cluster in the pure Al line using 1-dimensional computer simulation. The conventional belief was that the fastest stress evolution at the via occurs when the polygranular cluster is just below (or above) the via. However, the electromigration induced stress at the via would be faster when a cluster is apartfrom via because the stress interaction between via and clusters may assist electromigration. We simulated the time that the via reaches a certain stress value as a function of the distance of the cluster. It gives a specific distance where the time was minimum (i.e the fastest stress evolution). We named the position as the Fastest Stress Enhancing Polygranular cluster Position (FaSEPP). As a function of the current density, the FaSEPP decreases.
Real Time, In Situ Curvature Measurements of Epitaxial YBCO Films on MgO
Authors: Boyd D. , Tripathi A. , Gallivan M. , Musolf J. , Rosakis A. , Atwater H. , Goodwin D.
Published: April 2011

We have implemented coherent gradient sensing (CGS) to measure in situ, curvature and changes in curvature induced by temperature and O2 flow on thin film YBCO on MgO (001) substrates. CGS is a novel, real-time, full-field optical technique that provides a direct map of the components of the curvature tensor across the entire surface of the wafer. We have examined a well-characterized,700 nm thick YBCO film on a square 1”× 0.5mm MgO substrate with increasing temperature from 25 to 760°C and find the curvature increasing with temperature, although not always spatially uniform. By Stoney's equation, we relate the observed curvature to the thermal mismatch of the film and substrate where the maximum observed stress in orthogonal sample orientations is 1.2 and 1.4 GPa. For wafers under varying oxygen partial pressures, we observe dramatic local changes in the CGS interferograms, which we relate to the tetragonal to orthorhombic phase transformation YBCO exhibits as it cools in oxygen.
Simulation of 3D Films Deposited by Glancing Angle Deposition Using 3D-Films
Authors: Smy T. , Vick D. , Brett M. J. , Dew S. K. , Wu A. T. , Sit J.C. , Harris K. D.
Published: April 2011

A new fully three dimensional (3D) ballistic deposition simulator 3D-FILMS has been developed for the modeling of thin film deposition and structure. The simulator may be implemented using the memory resources available to workstations. In order to illustrate the capabilities of 3D-FILMS, we apply it to the growth of engineered porous thin films produced by the technique of GLancing Angle Deposition (GLAD).
Laser Ablation Of Solid Ozone
Authors: Nonaka Hidehiko , Nishiguchi Tetsuya , Morikawa Yoshiki , Miyamoto Masaharu , Ichimura Shingo
Published: April 2011

Species ablated from solid ozone by a UV laser were investigated using a time-of-flight method through a quadrupole mass filter. The results show that UV-laser ablation of solid ozone can produce a pulsed ozone beam with a translational energy far above that of room temperature. Highconcentration ozone from an ozone jet generator is solidified on a sapphire substrate attached to a copper block which is cooled to 30 to 60 K on a cryocooler head and the solid ozone is irradiated by pulsed laser light from a KrF laser (248 nm). The ablated species were a mixture of ozone and molecular oxygen as well as atomic oxygen due to photodissociation of ozone. At a substrate temperature of 30 K, the total amount of ablated ozone increases as the laser fluence increases to 13 mJcm−2. Beyond this fluence, enhanced decomposition of ozone occurs. Gaussian fitting of the time-of-flight signals of the ablated ozone reveals an average thermal energy exceeding 1,500 K. The velocity also increases when the laser fluence enters saturation at 2,300 K at 13 mJcm−2.
Optical and Structural Characteristics Of Gold Nanocrystallites Embedded in a Dielectric Matrix
Authors: Sharma A.K. , Muth J.F. , Kvit A. , Narayan J. , Kolbas R.M.
Published: April 2011

We have fabricated Gold (Au) crystallites in amorphous alumina matrix by pulsed laser deposition. The characterization of these multilayer sequences was performed by high resolution transmission electron microscopy (HRTEM) and optical transmission measurements. TEM studies revealed the morphology and the microstructure of these composites. The optical transmission spectra showed characteristic surface plasma resonance of Au particles confined by the host dielectric matrix. These resonances fall in the visible spectral range. The importance of pulsed laser deposition in fabricating these composite films is discussed.
Tantalum Nitride Thin Films Synthesized by Pulsed Nd:YAG Laser Deposition Method
Authors: Kawasaki Hiroharu , Namba Kazuya Doi. Jun , Suda Yoshiaki
Published: April 2011

Tantalum nitride (TAN) films have been deposited on silicon substrates by using a pulsed Nd:YAG laser deposition method. Experimental results suggest that the substrate temperature is one of the most important parameters to prepare crystalline tantalum nitride thin films. Glancing-angle X-ray diffraction patterns show that the films deposited at Ts ≤ 300 °C are almost amorphous. and crystalline Ta6N2.57 films are obtained at Ts ≥ 500 °C. Grain size of the film increases with increasing substrate temperature.
Laser Micromachining of Metallic Mold Inserts for Replication Techniques
Authors: Pfleging W. , Meier A. , Hanemann T. , Gruhn H. , Gahr K.-H. Zum
Published: April 2011

The laser microcaving (LMC) of steel is performed with cw Nd:YAG laser radiation. LMC enables a “clean” patterning process with only a small amount of debris and melt. During LMC the formation of a Ni-enriched interface layer and an oxide surface layer may be observed. The formation of these reaction layers as well as the etch rate and the surface quality strongly depend on the chemical composition of the steel and the process parameters. Surface qualities with an roughness of about Ra(center line average)=300 nm can be realised. The ablation rates are in the range of 106 µm3/s. With excimer laser radiation a further improvement of surface topographies can be achieved via laser planarisation. Mold inserts are manufactured by LMC, and microstructures composed of PMMA are successfully demolded by using the Ultraviolet light induced Reaction Injection Molding (UV-RIM) or Photomolding technique. CE(Capillary Electrophoresis)-Chips made of PMMA are successfully demolded, and the functionality of the CE-Chips is demonstrated.
Fluctuations of Step Positions at KDP Crystal Faces
Authors: Rashkovich Leonid N. , Shustin Oleg A. , Chernevich Tamara G.
Published: April 2011

Applying atomic force microscopy in single string scanning mode, dependence of fluctuations of step shifts on KDP crystal faces on time was determined during crystallization from solution. It was shown that fluctuation amplitude grows proportionally to t1/4. On prism faces fluctuations at dissolving were bigger than at growth and bigger than on bipyramid faces. Amplitude of fluctuations was not dependent on distance between steps. Interpretation of experimental results and computation of elementary parameters of crystallization was done based on theory of V.V.Voronkov.
Epitaxial Oxide Thin-Film Phosphors for Low Voltage FED Applications
Authors: Lee Yong Eui , Norton David P. , Budai John D. , Rack Philip D. , Peterson Jeffrey , Potter Michael D.
Published: April 2011

Epitaxial ZnGa2O4 and Sr2CeO4 thin-film phosphors were successfully grown on (100) MgO, YSZ, and SrTiO3 single crystal substrates using pulsed laser ablation. Cathodoluminescence efficiency was remarkably enhanced by adding lithium in the ZnGa2O4 and ZnGa2O4:Mn for both blue and green light emitting thin-film phosphors. The highest efficiencies, in this experiment, were 0.35 and 0.29 lm/W at 1kV for as-deposited blue and green zinc gallate phosphor films, respectively. In case of Sr2CeO4 films, the highest luminescence was 0.14 lm/W at 1kV and 0.26 A/m2 for films annealed at 1000°C in air.
Intense Photoluminescence and Photoluminescence Enhancement upon Ultraviolet Irradiation in HYydrogenated Nanocrystalline Silicon Carbide
Authors: Yu M.B. , Rusli  , Yoon S.F. , Xu S.J. , Chew K. , Cui J. , Ahn J. , Zhang Q.
Published: April 2011

Hydrogenated nanocrystalline silicon carbide (nc-SiC:H) films were deposited in an electron cyclotron resonance chemical vapor deposition (ECR-CVD) system using silane (SiH4) and methane (CH4) as source gases. It was discovered that under the deposition conditions of strong hydrogen dilution and high microwave power, nanocrystalline grains embedded in an amorphous matrix can be obtained, as confirmed by TEM study. Steady state and time-resolved photoluminescence (PL) from these films were investigated. The films exhibit intense visible PL at room temperature under laser excitation. The PL emission peaks at 2.64 eV, which is higher in energy compared to the bandgap of cubic SiC. Temporal evolution of the emission peak exhibits a double-exponential decay. Two distinct decay times of 179 ps and 2.88 ns were identified, which are at least 2 orders of magnitude faster than that of bound excition transitions in bulk 3C- SiC at low temperature. It was found that upon ultraviolet irradiation using an Ar+ laser (351nm) the PL intensity of the films was enhanced. After 20 minutes irradiation, the PL intensity increased by about three times. This result suggests that the UV light may lead to modification of nonradiative recombination centers in the films. These nc-SiC:H films are promising for application in large area flat panel displays and in optoelectronic storage technology.
Uniform, High Performance Poly-Si TFTs Fabricated by Laser- Crystallization of PECVD-Grown a-SI:H
Authors: Toet D. , Sigmon T.W. , Takehara T. , Tsai C.C. , Harshbarger W.R.
Published: April 2011

Polycrystalline silicon thin film transistors (TFTs) were fabricated using laser crystallization of thin amorphous Si films grown by plasma-enhanced chemical vapor deposition. The films were exposed to a scanned XeCl excimer laser beam at 350 mJ/cm2. At this fluence the Si film com- pletely melted and crystallized in the form of uniformly distributed grains with an average size of 39 nm. One of the films was then subjected to a low fluence laser scan (250 mJ/cm2), which re- sulted in the melting of the top part of the film and lead to an increase in grain size. The TFTs fabricated without the partial melt method had good electrical properties and uniformities. The partial melt method lead to substantial improvements in most device characteristics, while the uniformity remained good.
Top Gate Self-Aligned μc-Si TFTs using Layer-by-Layer Method and Ion-doping Method
Authors: Nakata Yukihiko , Murata Yasuaki , Hijikigawa Masaya
Published: April 2011

We investigated the Layer-by-Layer method to obtain thin μc-Si films. Good quality μc-Si films can be obtained at a thickness of 600 Å Ion-doping of phosphor to i-type μc-Si was investigated to realize the top-gate, self-aligned μc-Si TFT. High conductivity, more than 1 ohm-cm, can be obtained. Using the combination of Layer-by-Layer deposition method and ion-doping method, we fabricated top gate self-aligned μc-Si TFTs. The mobility of TFTs with 600Å-thick μc-Si channel layer is 1.5 cm2/Vs, which is about three times that of a-Si TFT's mobility. The top gate self-aligned μc-Si TFT is very promising technology for large LCD with high mobility.
Space Based Applications for FEA Cathodes (FEAC)
Authors: Gilchrist B. E. , Michigan U. , Arbor Ann , Jensen K. L. , Gallimore A. D. , Michigan U. , Severns J. G.
Published: April 2011

Cold cathodes such as field emitter arrays offer the potential to benefit or enable space-based applications of critical commercial, government, or military importance by providing an electron source that is low power, low cost, requires no consumables, potentially robust as well as highly reliable. Applications that would especially benefit from such cold cathodes include low power electric propulsion (EP) thruster technology, electrodyanamic tethers (ED) for propellantless propulsion in low-Earth orbit, and spacecraft negative potential charge control. In controlled environments, field emitter arrays have shown substantial capability, but have failed in harsher environments more typical of space applications. We argue that a combination of localized arc suppression coupled with a low work function, but nevertheless robust, coating such as zirconium carbide would provide the needed ruggedness to withstand energetic ions, oxygen fluxes, and adsorbates typical of a spacecraft environment. We have found that arc-protected and coated FEACs that can operate in a 1-10 microTorr pressure environment with current densities of less than 0.1 Amps/cm^2 and gate voltages between 50-100 Volts, would enable reliable, lowcost devices capable of operating in the required space environment.
A Concentric Circular Type in-situ Vacuum Sealed Lateral Feas Employing E-Beam Evaporator
Authors: Lim Moo-Sup , Han Min-Koo , Choi Yearn-Ik
Published: April 2011

In this paper, we propose concentric circular lateral field emitter structure which is more sstable in fabricating and maintaining vacuum conditions. The new FEAs have concentric circular shape while our previous FEAs are stripe type. The anode is formed at inner circle and the cathode is outer circle respectively. We use Molybdenum or Silicon dioxide as a sealing material. After we fabricating tips, Molybdenum or Silicon dioxide is deposited with e-beam evaporator at base pressure of 3.5×10−6Torr. In this process, the micro-cavity remains vacuum cavity without filling Molybdenum or oxide due to step coverage of evaporation. It should be noted that the vacuum level of the micro-cavity can be identical to the base pressure of the e-gun evaporator chamber. All of the two types of new FEAs show good reproducibility in fabricating and maintaining vacuum conditions. Field emitter structure that the anode is located at inner circle shows superior field emission characteristics. The measurements of long term stability for the anode current show that oxide is the most promising material for in-situ vacuum sealing.
Micro-Structural and Field Emission Characteristics of Nitrogen-Doped And Micro-Patterned Diamond-Like Carbon Films Prepared by Pulsed Laser Deposition
Authors: Shin Ik Ho , Choi Jae Hyoung , Lee Jeong Yong , Lee Taek Dong
Published: April 2011

Effect of nitrogen doping on field emission characteristics of patterned Diamond-like Carbon (DLC) films was studied. The patterned DLC films were fabricated by the method reported previously[1]. Nitrogen-doping in DLC film was carried out by introducing N2 gas into the vacuum chamber during deposition. Higher emission current density of 0.3∼0.4 mA/cm2 was observed for the films with 6 at % N than the undoped films but the emission current density decreased with further increase of N contents. Some changes in CN bonding characteristics with increasing N contents were observed. The CN bonding characteristics which seem to affect the electron emission properties of these films were studied by Raman spectroscopy, x-ray photoemission spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). The electrical resistivity and the optical band gap measurements showed consistence with the above analyses. High-resolution transmission electron microscopic (HRTEM) results also support the formation of graphite-like phase in 9 at % N-doped DLC film.
Colloidal Solution of Metal Nanoparticles as a Catalyst for Carbon Nanotube Growth
Authors: Ago Hiroki , Ohshima Satoshi , Komatsu Toshiki , Kuriki Yasunori , Yumura Motoo
Published: April 2011

Aligned multi-wall carbon nanotubes (MWNTs) were successfully grown on a Si substrate based on a thermal chemical vapor deposition (CVD) method. We employed Co metal nanoparticles as the catalyst for nanotube growth, which were prepared by a reverse micelle method. The reverse micelle method provides nanoparticles covered with surfactants so that they are dispersed in organic solvent and, thus highly processible. The present MWNT arrays are promising for application in field emission displays, because of much lower nanotube density compared with the previously reported arrays.
Purity and Solubility of Nanotubes in Arc Discharge Carbon Powder
Authors: Coleman Jonathan N. , Dalton Alan B. , McCarthy Brendan , Barklie Robert C. , Blau Werner J.
Published: April 2011

We have described a novel experimental technique to separate nanotubes from other unwanted carbon species in arc generated carbon soot. A conjugated polymer was used to bind to nanotubes in solution. The resultant hybrid was soluble while extraneous carbon material formed a sediment at the bottom of the sample bottle. This process was monitored using electron paramagnetic resonance (EPR) which showed that 63% of nanotubes were kept in solution while 98.1% of impurities were rejected. This allowed the calculation of the nanotube content in the carbon soot using EPR and thermo-gravitational analysis (TGA) yielding a purity value of 34% for the soot used in this study. This is compatible with estimates made using electron microscopy.
Quantum Transport Properties of Carbon Nanotubes in the Coulomb Blockade Regime
Authors: Mehrez H. , Guo Hong , Wang Jian , Roland Christopher
Published: April 2011

Recent experimental measurements on transport through carbon nanotubes in the Colomb Blockade regime showedm at zero bias and zero magnetic field, an alternation in the Coulomb peak heights as electrons are added to the nanotube. This surprsing peak-height alternation is shown to be related to the odd/even parity of the number of electrons in sider the nanotube. We invesitiaged this phenmenon theoretically with a new many-body apporach. and find that the anomalous behaviour may be attributed to the spin degenerate states. We alos show that asymmetric current saturation as a function of bias voltage polarity, also observed experimentally, is due to eigenstate relaxtions within the nanotube.
Solubility of carbon nanotubes
Authors: Panhuis Marc In Het , Coleman Jonathan N. , Blau Werner J.
Published: April 2011

We have described a novel experimental technique to separate nanotubes from other unwanted carbon species in arc generated carbon soot. A conjugated polymer was used to bind to nanotubes in solution. The resultant hybrid was soluble while extraneous carbon material formed a sediment at the bottom of the sample bottle. This process was monitored using electron paramagnetic resonance (EPR) which showed that 63% of nanotubes were kept in solution while 98.1% of impurities were rejected. Optimal polymer characteristics for nanotube solubility were identified using geometry optimisation and experimental evidence. It was calculated that a successful polymer has a flat shaped helical backbone with solvent solubilising groups projected outwards. This is achieved with the following polymer characteristics, two solvent solubilising groups on a twist allowing π-conjugated backbone.
Polarized Raman Spectra of Carbon Nanotubes
Authors: Jorio Ado , Brown Sandra D.M , Dresselhaus Gene , Dresselhaus Mildred S. , Pimentap Marcos A. , Saito Riichiro , Rao Apparao M. , Kneipp Katrin
Published: April 2011

P olarizedresonant Raman spectra for the G-band were obtained from a rope of aligned semiconducting SWNTs and from nonaligned semiconducting and metallic SWNTs. Based on group theory analysis and related theoretical predictions, we assign the symmetry for the modes in the G-band of both metallic and semiconducting SWNTs. he frequency shifts of the tangential G modes from the 2D graphite-like E2g2 frequency are discussed in terms of the nanotube geometry.
High Resolution Resists for Next Generation Lithography: The Nanocomposite Approach
Authors: Gonsalves Kenneth E. , Wu Hengpeng , Hu Yongqi , Merhari Lhadi
Published: April 2011

The SIA roadmap predicts mass production of sub-100 nm resolution circuits by 2006. This not only imposes major constraints on next generation lithographic tools but also requires that new resists capable of accommodating such a high resolution be synthesized and developed concurrently. Except for ion beam lithography, DUV, X-ray, and in particular electron beam lithography suffer significantly from proximity effects, leading to severe degradation of resolution in classical resists. We report a new class of resists based on organic/inorganic nanocomposites having a structure that reduces the proximity effects. Synthetic routes are described for a ZEP520®nano-SiO2 resist where 47nm wide lines have been written with a 40 nm diameter, 20 keV electron beam at no sensitivity cost. Other resist systems based on polyhedral oligosilsesquioxane copolymerized with MMA, TBMA, MMA and a proprietary PAG are also presented. These nanocomposite resists suitable for DUV and electron beam lithography show enhancement in both contrast and RIE resistance in oxygen. Tentative mechanisms responsible for proximity effect reduction are also discussed.
Fabrication of Micro- and Nanostructures with Monodispersed Colloidal Spheres as the Active Components
Authors: Gates Byron , Mayers Brian , Li Zhi-Yuan , Xia Younan
Published: April 2011

Monodispersed colloidal spheres with dimensions in the range of 100 nm to 10 μm can be used as building blocks to fabricate highly ordered 3D micro- and nanostructures. For example, they can be self-assembled into closely packed lattices, which can be subsequently used as templates to generate 3D porous structures. Here we present the recent progress in our group regarding this approach.
Precise Characterization of Resists and Thin Gate Dielectrics in the VUV Range for 157nm Lithography
Authors: Boher Pierre , Evrard Patrick , Piel Jean Philippe , Defranoux Christophe , Stehlé Jean Louis
Published: April 2011

Spectroscopic ellipsometry is one of the most important tools for thin film metrology. It is now intensively used in microelectronics and especially for the microlithographic applications. Instrumentation for the next generation of VUV lithography at 157nm requires special optical setup since oxygen and water are extremely absorbing below 190nm. Recently a new ellipsometer included in a purged glove box to reduce the oxygen and water contamination in the part per million range has been developed. In the VUV range, roughness and interface diffusion become critical since the layer thickness is generally reduced. An independent characterization technique like the grazing x-ray reflectance is then extremely complementary to ellipsometry in this wavelength region. The present paper presents recent results on up to date lithography samples combining the two characterization techniques. Photoresists and gate dielectrics are successively examined.
Nanolithography by Electron Beam Resist-trimming Technique
Authors: Maeda Tatsuro , Ishii Kenichi , Suzuki Eiichi , Hiroshima Hiroshi , Iida Tsutomu , Takanashi Yoshihumi , Ahmet Parhat , Chikyow Toyohiro , Taguchi Hirohisa
Published: April 2011

We have investigated a resist-trimming process for SAL601 chemically amplified negative electron beam resist. Ultra-fine SAL601 resist patterns with a width of 16nm were obtained by an isotropic trimming process in oxygen plasma. This pattern resolution in SAL601 could not be obtained through direct electron beam lithography alone. Using the trimmed electron beam resists, we have successfully fabricated ultra-fine poly-silicon patterns of less than 20nm width. We applied this nanolithography technique to fabricating an ultra-small metal-oxide-semiconductor field-effect-transistor (MOSFET) and revealed that this trimming process is a useful method for nanometer-scale silicon device fabrication.
Fabrication of Helically Perforated Thin Films
Authors: Harris K.D. , Westra K.L. , Brett M.J.
Published: April 2011

Using glancing angle deposition and templating techniques, we have fabricated a number of unique thin film microstructures. Engineered columnar thin films having the inverse of the desired structure (i.e., arrays of helices or chevrons) were first deposited by glancing angle deposition. These films were then filled with a solution of the desired material, and allowed to cure. The template material was then removed by chemical etching, leaving a perforated thin film. Such films have been produced of photoresist and spin-on-glass, on both silicon and glass substrates. The perforations have taken the form of chevrons and helices of large and small pitch, and have been arranged in both random and periodic (1μm spacing) arrays.
Fabrication of Photonic Crystals Using Metal Clusters as Nuclei for Self-formation of Etching Masks
Authors: Tada Tetsuya , Poborchii Vladimir V. , Kanayama Toshihiko
Published: April 2011

We developed a fabrication process of regular arrays of Si nanopillars using self-formation of etching masks with metal clusters as formation nuclei. When Si substrates deposited with metal clusters are subjected to electron cyclotron plasma etching with SF6 at around -130 °C, reaction products in the plasma, SxFy, condense preferentially at the clusters, leading to the self-formation of nanoscale etching masks. As a result, Si pillars, about 10 nm in diameter and 100 nm tall, are formed with remarkably narrow size-distributions when Au clusters of 1-3 nm diameter are used. This method can be easily combined with electron beam lithography technique, which enables us to define pillar positions. Using this process, we have fabricated 2 dimensional photonic crystals (square and triangular lattices of Si nanopillars) with photonic band gaps in the visible and near infrared regions. We measured reflection spectra of the photonic crystals and observed polarization-dependent reflection bands in the wavelength range consistent with theoretical calculations.
Formation of Nanostructures in Silicon by Nanosecond-Pulsed Laser Irradiation
Authors: Fowlkes J. D. , Pedraza A. J. , Jesse S. , Rouleau C. M. , Blom D. A.
Published: April 2011

Silicon nanoparticles are formed during pulsed laser ablation under a background atmosphere of Ar gas. In this paper we have characterized the nanoparticles that are backscattered via collisions in the gas phase and redeposited on the target surface. Clustering in an O2/Ar gas atmosphere resulted in the formation of unique nanostructures that photoluminesce in the violet and blue-green portions of the electromagnetic spectrum. Ablating a (001) Si target in the presence of ultra-high purity (UHP) argon produced Si nanoparticles outside the irradiated region. The mean diameter of these particles decreases from 50 nm to 5 nm with increasing distance from the laser spot. The nanoparticle distribution can be induced to self-organize in linear arrays by simultaneously irradiating the nanoparticles as they deposit.
Exciton-mediated excitation of Er3+ in Erbium-doped silicon rich silicon oxide
Authors: Seo Se-Young , Shin Jung H.
Published: April 2011

Exciton-mediated excitation of Er3+ in erbium doped silicon rich silicon oxide (SRSO) is investigated. Er-doped SRSO films were fabricated by electron cyclotron-resonance plasmaenhanced chemical vapor deposition of Er-doped SiOx (x < 2) using SiH4 and O2 as source gases and co-sputtering of Er, followed by an anneal at 950 °C. Very weak visible luminescence from Si nanocluster relative to Er3+ luminescence were observed, indicating a very efficient excitation of Er3+ ions by Si nanoclusters. From detailed modeling and analysis of time-resolved Er3+ luminescence as the excitation duration and excitation power, we conclude that exciton-erbium coupling is dominant over exciton-nanocluster. The results are consistent with the proposal that the luminescent Er3+ ions are located predominantly in the SiO2 layer.
Studies of Compositional Variations in Germanium Quantum Dots Grown on Silicon
Authors: Dunbar Alan D.F. , Halsall Matthew P. , Bangert Uschi , Harvey Alan , Dawson Philip , Joyce Bruce A. , Zhang Jing , Berbezier Isabel
Published: April 2011

We report optical and scanning transmission electron microscopy studies of germanium dots grown on silicon. In an attempt to control the self-organized growth process and promote dot size uniformity the dot layers were grown on a 4.5nm Si0.6Ge0.4 alloy template layer. Photoluminescence results indicate the formation of carrier confining Ge rich islands, whilst Raman scattering results indicate the presence of an alloy throughout the structures formed. The samples were studied in the UK high resolution scanning transmission electron microscopy facility at Liverpool, UK. Energy dispersive analysis of individual line scans through the sample show that the structures are composed of an alloy throughout with an asymmetric distribution of Germanium in the dots and in the wetting layer close to the dots. We discuss the results in the light of the proposed growth mode for these dots and conclude that attempts to manipulate the composition of these dots during growth may be problematic due to the self-organized nature of their formation.
Optical Photoluminescence due to the Recombination of Donor-Acceptor Pairs in Porous Silicon
Authors: Zheng J. P. , Wei X.
Published: April 2011

The temperature dependence of the intensity, peak-wavelength, and bandwidth of photoluminescence (PL) spectra was studied in the porous silicon (PS) sample. To explain the observed temperature dependence, we proposed a model for the origin of the PL in PS. At low temperatures, the photon emission was dominated by the recombination of donor-acceptor pairs with ionization energies of about 4 meV. The donor and the acceptor were spatially separated with a distance of about 3.8 nm, which was about the crystalline size of the PS. Whereas at high temperatures where thermal energy exceeded the ionization energy, the photon emission was mainly from the exciton recombination.
Photonic bandgap effect in Periodic Porous Silicon Planar Waveguides
Authors: Ferrand P. , Romestain R.
Published: April 2011

We have obtained a porous silicon optical planar waveguide, with a submicronic periodic modulation of the optical index along one direction of plane, using a holographic process. Near-infrared continuous transmission spectra of guided light across not less than 3000 periods show several strong stopbands, with a decrease of intensity by two orders of magnitude. By means of the coupled-mode theory, we were able to deduce from the spectra a realistic map of the optical index at a microscopic scale, demonstrating a strong photo-induced index contrast (Δn = 0.5) at a submicronic scale.