bluuebunny/crossref_metadata_2025 huggingface dataset:
Ab Intio Simulations of Quatum Transport: Si Clusters and Fullerene Chains
Authors: Roland Christopher , Meunier Vincent , Larade Brian , Taylor Jeremy , Guo Hong
Published: June 2019

The I-V characteristics of small Sin clusters and short C20 chains between atomistic Al leads were calculated using a new ab initio transport code based on a nonequilibrium Greens function formalism. All of the Si diaplay metallic I-V characteristics with typical conductances ranging between tow and three (units Go = 2e2/h). The transport properties of these molecular devices may be understood in terms of both the bandstructure ofelectrodes, and the molecular levels of the clusters as modified by the lead environment. Turning to the short C20 chains, these behave as short C20 chains, these behave as short nanowires whose tranmission depends sensitively on the orientation and distance between the individual C20 molecules. Transport through the molecular chains is accompained by a significant amount of charge transfer, which however remains localized at the electrode/molecular interface.
Atomic and Electronic Structure of Interfaces at Sic Studied by Indirect Super Hrtem and Electron Spectroscopyn Imaging
Authors: Yan J. Y. , Ichinose Hideki , Chen Fu-Rong , Kai J. J. , Takuma Eriko
Published: June 2019

Obtaining electronic and atomic structure of material simultaneously is very important for developing the nano-technology. In this paper, we demonstrate that atomic and electronic structure of an interface can be extracted with combination of Gerchberg-Saxton indirect microscopy and electron spectroscopy imaging (ESI) technique. Basically, Gerchberg-Saxton algorithm includes two projections. Projection in the real space is a maximum entropy (ME) de-convolution process and in reciprocal space is an amplitude substitution process. It has been shown that Gerchberg-Saxton algorithm can extend the structural resolution to near 0.1nm. An application case of Gerchberg-Saxton algorithm to solve the atomic structure for 3C-polytypic SiC boundary is shown.

ESI spectrum processed by FFT interpolation, maximum entropy de-convolution and wavelet transformation allow us to extract 2-dimensional map of the sp2/sp3 with a sub-nanometer resolution. Grain boundary and interface at SiC are good candidates for this study, since the bond distance of Si-C is slightly less than 0.1nm which is not routinely resolvable using a FEG TEM and Si-L (99eV) and C-K-edges (283 eV) locate in a reasonable energy range. The resultant electronic structure can be compared with that calculated using WIEN97. An example of quantitative analysis on 2-dimensional sp3/sp2 map deduced from the C K-edge of ESI spectra acquired from 6H-SiC is given.
Green's Function Method for Calculation of Strain Field Due to a Quantum Dot in a Semi-Infinite Anisotropic Solid
Authors: Tewary V.K.
Published: June 2019

A computationally convenient Green's function method is described for calculation of strain characteristics of quantum dots in an anisotropic semi- infinite solid containing a free surface. Semi-analytic expressions are derived for the strain field due to a quantum dot, strain energy of a quantum dot, and strain- field interaction between 2 quantum dots. Numerical results are presented for the strain field due to a quantum dot in GaAs. It is shown that the effect of the free surface, which has been neglected in earlier calculations using Green's function methods, is quite significant.
Chemical Structure Analysis of a Σ 9 Grain Boundary in α-SiC by Arhvtem
Authors: Takuma Eriko , Ichinose Hideki
Published: June 2019

Grain boundary chemical structure of high purity α silicon carbide was investigated by an atomic resolution high voltage transmission electron microscope (ARHVTEM). Each of a ‘darker’ spots and each of the ‘brighter’ spots in the image have been identified to be silicon (Si) and carbon (C). Two (0001)/(1107) Σ 9 CSL grain boundaries were observed. One boundary showed a rigid body translation of 1/3 <1100> to the component crystals and the other did not. The unit period of the boundary was determined to 2.26 nm along >1120<. Two 6-membered, four 5-membered and 7-membered rings build up the boundary. Each ring consists of three C-C pairs, one Si-Si pair and non-paired Si atoms. In the case without the rigid body translation the number of lone Si atoms are four and only two Si atoms were determined in the other case. The observed structures suggest that the chemical structure of a grain boundary dominantly influences the grain boundary energy.
Ultraviolet Luminescence Emitted From ZnO Nanostructural Films by KrF Pulsed Laser Deposition
Authors: Ebihara Kenji , Ohshima Tamiko , Ikegami Tomoaki , Thareja Raj K.
Published: June 2019

Zinc Oxide (ZnO) thin films have been deposited on silicon (100), quartz glass, sapphire (0001), and glass substrates by pulsed laser deposition over a range of process conditions such as versus ambient oxygen gas pressure and substrate temperature. Photoluminescence measurements have been carried out to characterize ZnO thin films for optical device applications. We have also studied the influence of the process conditions on crystal structure and morphology of the grown films. Ultraviolet luminescence near the band gap at 3.25 eV was obtained from the optical pumped grown films. And ZnO thin films deposited on sapphire single crystal substrates exhibited strong stimulated emission around 3.12 eV with increasing pumping energy. ZnO thin films deposited at ambient oxygen gas pressure of 5 mTorr and a substrate temperature of 550 °C were predominantly c-axis oriented regardless of substrate material. The crystallite size of 22.7-49.8 nm was estimated using Scherrer's formula. AFM images of films grown on sapphire substrates display hexagonally shaped grains at various sizes.
Novel Nanosized Patterning Techniques Using An Electropulsed Scanning Probe Microscope
Authors: Melo L. V. , Brogueira P.
Published: June 2019

Scanning Probe Microscopes (SPM) have been used to change surfaces at nanometer scales. We report the deposition of user defined patterns in a controlled manner using an electropulsed SPM. The patterns were fabricated by applying -12 V electrical pulses in the 10 to 40 Hz range between a commercial CoCr conductive tip and a crystalline n-doped Si wafer. The tip damage during deposition is negligible as measurements on the same surface region before and after deposition show no detectable differences. Immediately after deposition the same tip is used for measuring the fabricated patterns. Applying one isolated electrical pulse results in a pixel with a typical size of the order of 30 nm. By combining the scanning ability of the SPM with the atmospheric deposition induced by electrical pulses on the tip, patterns can be fabricated. For example, by applying electrical pulses during a 25 nm x 800 nm tip scan in AFM tapping mode, at 40 Hz, lines with 65 nm width by 828 nm length were obtained (in good agreement with the expected dimensions of 55 nm x 830 nm derived from the pixel size and the scan range). The height of the deposited patterns is of the order of 2 to 3 nm, and was found to increase with the density of scan lines. The RMS roughness of the deposited material is shown to be strongly dependent on the electrical pulse frequency. The smoother pattern surface results from the 40 Hz pulse frequency. No deposition was observed at higher frequencies.
Fabrication of Periodic Arrays of Nanoscale Square Helices
Authors: Jensen Martin O. , Kennedy Scott R. , Brett Michael J.
Published: June 2019

We demonstrate fabrication of periodic arrays of nanometre scale square helices, with potential applications in three-dimensional photonic bandgap (PBG) materials. Processing is performed using a thin film deposition method known as Glancing Angle Deposition (GLAD). Through advanced substrate motion, this technique allows for controlled growth of square helices in a variety of inorganic materials. Organization of the helices into periodic twodimensional geometries is achieved by prepatterning the substrate surface using electron beam lithography. The regular turns of the helices yield periodicity in the third dimension, perpendicular to the substrate. We present studies of tetragonal and trigonal arrays of silicon helices, with lattice constants as low as 300 nm. By deliberately adding or leaving out seeds in the substrate pattern, we have succeeded in engineering line defects. Our periodic nanoscale structure closely matches an ideal photonic band gap architecture, as recently proposed by Toader and John. While our fabrication technique is simpler than most suggested PBG schemes, it is highly versatile. A wide range of materials can be used for GLAD, manipulation of lattice constant and helix pitch ensures optical tunability, and the GLAD films are robust to micromachining.
Mixed Abrasive CMP: A Study on Metal and Dielectric Films
Authors: Jindal Anurag , Hegde Sharath , Babu S.V.
Published: June 2019

Mixed abrasive slurries (MAS) containing alumina/silica and alumina/ceria abrasives were evaluated for CMP of metal and dielectric films, respectively. MAS with 0.5wt% calcined alumina and 2.5wt% silica (fumed and colloidal) abrasives were highly selective to tantalum polishing over copper and oxide. Similarly, MAS containing 1.5wt% calcined alumina and 3wt% colloidal ceria particles offered a polish rate selectivity between silicon dioxide and silicon nitride films of more than 30, without any additives, without compromising finished surface quality. This improved performance appears to be a result of modified surface morphology as well as synergistic interactions between the chemical activity of silica or ceria and the hardness of the alumina.
Photoelectron Spectroscopy Measurements of the Valence Band Structures of C60 Thin Films on Single Crystal Silicon and Polycrystalline Copper
Authors: Ha B. , Rhee J. H. , Li Y. , Singh D. , Sharma S. C.
Published: June 2019

We have used photoelectron spectroscopy to study possible modifications in the electronic valence band structures of thin films of C60 due to their deposition on single crystal silicon and polycrystalline copper. The C60 thin films were deposited by thermal evaporation under high vacuum and further characterized by using Raman spectroscopy. We observe significant differences in the valence band structures of C60 thin films deposited on these substrates and attribute them to interactions at the interface.
Influence of Filament and Substrate Temperatures on Structural and Optoelectronic Properties of Narrow Gap a-SiGe:H Alloys Deposited by Hot-Wire CVD
Authors: Xu Yueqin , Nelson Brent P. , Williamson D.L. , Gedvilas Lynn M. , Reedy Robert C.
Published: June 2019

We have found that narrow-bandgap—1.25 < Tauc Gap < 1.50 eV—amorphous silicon germanium (a-SiGe:H) alloys grown by hot-wire chemical vapor deposition (hot-wire CVD) can be improved by lowering both substrate and filament temperatures. We systematically study films deposited using a one-tungsten filament, decreasing filament temperature (Tf) from our standard temperature of 2150° down to 1750°C, and fixing all other deposition parameters. By decreasing Tfat the fixed substrate temperature (Ts) of 180°C, the Ge-H bonding increases, whereas the Si-H2bonding is eliminated. Films with higher Ge-H bonding and less Si-H2have improved photoconductivity. For the series of films deposited using the same germane gas fraction at 35%, the energy where the optical absorption is 1x104(E04) drops from 1.54 to 1.41 eV with decreasing Tf. This is mainly due to the combination of an increasing Ge solid fraction (x) in the film, and an improved homogeneity and compactness due to significant reduction of microvoids, which was confirmed by small angle X-ray scattering (SAXS). We also studied a series of films grown by decreasing the Tsfrom our previous standard temperature of 350°C down to 125°C, fixing all other deposition parameters including Tfat 1800°C. By decreasing Ts, both the total hydrogen content (CH) and the Ge-H bonding increased, but the Si-H2bonding is not measurable in the Tsrange of 180°-300°C. The E04 increases from 1.40 to 1.51 eV as Tsdecreased from 350° to 125°C, mainly due to the increased total hydrogen content (CH). At the same time, the photo-to-dark conductivity ratio increases almost three orders of magnitude over this range of Ts.
Numerical Studies Of The Dynamics Of Silicon: Relaxation, Nucleation And Energy Landscape
Authors: Mousseau Normand , Beaucage Philippe , Valiquette Francis
Published: June 2019

Using various simulation techniques, such as molecular dynamics and the activation-relaxation technique, we are slowly developing a consistent picture of the dynamical properties of amorphous silicon. For example, results of an extensive search for the activated events surrounding a single minimum, in a well-relaxed model represented by a modified Stillinger-Weber potential, confirm that barrier height at the transition point, for activated mechanisms, is determined essentially by the binding energy of a single bond and not the details of the mechanism. We will discuss these results in some detail as well as recent simulations of nucleation in liquid and amorphous silicon.
Stress Effects on Nanocrystal Formation by Ni-Induced Crystallization of Amorphous Si
Authors: Liu Yaocheng , Deal Michael D. , Sultana Mahmooda , Plummer James D.
Published: June 2019

Metal-induced crystallization (MIC) of amorphous Si is gaining increased interest because of its potential use for low-temperature fabrication of integrated circuits. In this work, the MIC technique was used to make Si nanocrystals and the effects of stress on the crystallization were studied. Amorphous Si films were deposited onto the Si substrate with thermal oxides on top by low-pressure chemical vapor deposition (LPCVD) and then patterned into nanoscale pillars by electron beam lithography and reactive ion etching. A conformal low-temperature oxide (LTO) layer was deposited to cover the pillars, followed by an anisotropic etch back to form a spacer, leaving only the top surface of the pillars exposed to the 5 nm Ni sputtering deposition afterwards. An HF dip was used to partially remove the LTO spacers on the pillars, leading to different LTO thicknesses on different samples. These samples were then annealed to crystallize the amorphous Si pillars, forming Si nanocrystals. Transmission electron microscope (TEM) observations after anneal found a clear dependence of the crystallization rate on the pillar size as well as the LTO thickness. The crystallization rate was lower for pillars with thicker LTO spacers, while for the same LTO thickness the crystallization rate was lower for pillars with narrower width. A model based on the stress in the pillars is proposed to explain this dependence. This model suggests some methods to control the nickel-induced crystallization process and achieve higher quality Si nanocrystals.
Formation of Large, Orientation-Controlled, Nearly Single Crystalline Si Thin Films on SiO2 Using Contact Printing of Rolled and Annealed Nickel Tapes
Authors: Huh Hwang , Shin Jung H.
Published: June 2019

Amorphous silicon (a-Si) films prepared on oxidized silicon wafer were crystallized to a highly textured form using contact printing of rolled and annealed nickel tapes. Crystallization was achieved by first annealing the a-Si film in contact with patterned Ni tape at 600°C for 20 min in a flowing forming gas (90 % N2, 10 % H2) environment, then removing the Ni tape and further annealing the a-Si film in vacuum for2hrsat600°C. An array of crystalline regions with diameters of up to 20 μm could be formed. Electron microscopy indicates that the regions are essentially single-crystalline except for the presence of twins and/or type A-B formations, and that all regions have the same orientation in all 3 directions even when separated by more than hundreds of microns. High resolution TEM analysis shows that formation of such orientation-controlled, nearly single crystalline regions is due to formation of nearly single crystalline NiSi2 under the point of contact, which then acts as the template for silicide-induced lateral crystallization. Furthermore, the orientation relationship between Si grains and Ni tape is observed to be Si (110) || Ni (001)
Scattering Rings in Birefringent Porous Silicon
Authors: Oton Claudio J. , Gaburro Zeno , Ghulinyan Mher , Daldosso Nicola , Pancheri Lucio , Bettotti Paolo , Negro Luca Dal , Pavesi Lorenzo
Published: June 2019

We report the observation of strongly anisotropic scattering of laser light at oblique incidence on (100)-oriented porous silicon layers. We performed angle-resolved light scattering measurements and three concentric rings were observed. Modeling porous silicon by means of nanometric columnar air pores and an effective anisotropic uniaxial dielectric constant explains the observed phenomenon, and besides, the observation of the angle aperture of these rings allows a direct measurement of relative birefringence. We finally study the changes of optical anisotropy after different modifications of the structure.
Direct Electrical Characterization of Metal Induced Lateral Crystallization Regions by Spreading Resistance Probe Measurements
Authors: Myasnikov Alexandre M. , Poon Vincent M.C. , Leung Vincent T.C. , Chan Mansun , Cheng Lawrence C.F.
Published: June 2019

Material characterization of metal induced lateral crystallization (MILC) process of amorphous silicon (a-Si) has been performed by using the spreading resistance probe (SRP) measurements. It was found that carrier mobility in boron ion implanted layer, formed in MILC region, is up to 65 % in comparison with mobility in boron ion implanted layer, formed in single crystalline silicon. It was also observed in this work that prolongation of MILC process from 1 hour to 2 hours had induced the increasing of mobility from 24 cm2/Vs to 34 cm2/Vs.
Laser Interference Structuring of a-GeN for the Production of Optical Diffraction Gratings
Authors: Mulato M. , Zanatta A. R. , Toet D. , Chambouleyron I. E.
Published: June 2019

In this work, we study the pulsed laser crystallization of hydrogen-free amorphous germanium-nitrogen alloys (a-GeN). We discuss the role of nitrogen during phase transitions and the possible application of the resulting structure as an optical diffraction grating. The crystallized region results of pure microcrystalline germanium (μc-Ge). An indication that Ge-N bonds have broken and nitrogen outdiffused of the film is obtained from infrared spectroscopy and confirmed by Raman spectra. A pattern of alternating a-GeN and μc-Ge lines with a period of about 4 μm acts as an optical diffraction grating due to the difference in optical properties between the two materials, and the three dimensional surface profile, caused by N2 effusion, that is formed on the sample.
Performance of Thin-Film Silicon MEMS Resonators in Vacuum
Authors: Gaspar J. , Chu V. , Conde J. P.
Published: June 2019

This paper reports on the fabrication and characterization of microelectromechanical bridge resonators on glass substrates using thin-film technology and surface micromachining. All the processing steps are performed at temperatures below 110°C. The microbridges consist of either a single layer of heavily doped n-type amorphous silicon (n+-a-Si:H) or bilayers of aluminum (Al) and intrinsic a-Si:H. The bridge is suspended over a gate electrode with a 1 μm air-gap. Applying a voltage between the bridge and an underlying Al gate electrode electrostatically actuates the microstructures. The resulting deflection is monitored optically. The resonance of the microbridges is measured in air and in vacuum. Resonance frequencies up to 70 MHz and quality factors up to 3000 are obtained at pressures below 1 Torr. The energy dissipation mechanisms of the resonators are discussed.
Above-Threshold Parameter Extraction Including Contact Resistance Effects for a-Si:H TFTs on Glass and Plastic
Authors: Servati Peyman , Striakhilev Denis , Nathan Arokia
Published: June 2019

This paper presents a fast and accurate method for extraction of the above-threshold physical parameters (such as threshold voltage, power parameter, effective mobility, and contact resistance) from measurement data in the linear and saturation regions of hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) fabricated on glass and plastic substrates. The method of extraction is different from techniques that are currently used by virtue of the departure from the square law dependence of the current-voltage characteristics. In addition, a broader range of process-induced variation in material properties is expected, which is accentuated by the effects of different substrates, leading to wide-ranging device parameters. In particular, non-ideal parameters such as contact resistance may vary by orders of magnitude due to process variations, thus strongly influencing the extracted values of TFT parameters if its effect is not considered in the extraction method. In this paper, the effect of contact resistance and other non-ideal parameters is systematically identified and eliminated using TFTs with different channel length. The extracted values for TFTs on glass and plastic substrates clearly highlights the differences in material properties stemming from the different process conditions and substrate properties, and provide insight that is invaluable for subsequent device/process optimization.
Depth Profiling of Light-Induced Defects in Hydrogenated Amorphous Silicon by Transient Photocurrent Spectroscopy
Authors: Reynolds Steve , Main Charlie , Brüggemann Rudi
Published: June 2019

The sensitivity of transient photocurrent measurements to the spatial location of native and metastable electronic defects in hydrogenated amorphous silicon films is demonstrated. The technique utilises red and green laser excitation to generate excess carriers in the bulk and at the surfaces of the film, respectively. In annealed films the defect density is found to be higher in the surface regions. Following white light soaking, the metastable defect density at the surface at which the light is incident is greater than that in the bulk, which in turn is greater than that at the exit surface. This is attributed to the white light absorption profile within the film. Green light soaking creates metastable defects at the incident surface, with the bulk of the film largely unaffected.
Micro-Raman Studies of Mixed-phase Hydrogenated Silicon Solar Cells
Authors: Owens Jessica M. , Han Daxing , Yan Baojie , Yang Jeffrey , Lord Kenneth , Guha Subhendu
Published: June 2019

The open-circuit voltage (Voc) of mixed-phase hydrogenated silicon solar cells has been found to increase after light soaking. In this study, we use micro-Raman to investigate the heterogeneous structure of solar cells in the amorphous-to-nanocrystalline transition region. For a cell with Voc = 0.981 V, Raman spectra show a typical broad Gaussian lineshape around 480 cm-1, a signature of typical amorphous material. A cell with Voc = 0.674 V displays a sharp Lorentzian peak around 516 cm-1, indicative of nanocrystallinity. A cell with Voc = 0.767 V was systematically scanned for 20 different positions in 500 μm increments. Most spectra show a typical Gaussian lineshape around 480 cm-1, several spectra reveal a hint of a nanocrystalline shoulder around 512 cm-1, and one spectrum exhibits a distinct nanocrystalline peak. We conclude that the nanocrystallite distribution in the mixed-phase material is very non-uniform even within a mm dot. This result provides direct evidence supporting a recently proposed two-diode equivalent-circuit model to explain the light-induced effect.
Metamict Transformation of Silica
Authors: Cheng Ju-Yin , Treacy M.M. J. , Keblinski P. J.
Published: June 2019

Alpha quartz can be transformed to a metamict phase in a physical reaction such as irradiation with fast ions, neutrons and electrons. As truly inspired by this fact, we design a simple experiment to produce disordered silica and at the same time watch the transformation using a transmission electron microscope. This work simply presents electron-damaged silica in dark field at Bragg reflection. Since the transformation is not complete, disordered silica (at the sample edge) and retained quartz can be compared in each image. Not surprisingly, more speckles are found in the quartz than in the disordered structure. But it is too early to say no medium-range ordering in amorphous silica because the experiment only shows one Bragg diffraction. Systematic work to complete and measure the disordering again is being pursued.
Toward understanding the degradation without light soaking in hot-wire a-Si:H thin films and solar cells
Authors: Wang Qi , Wang Keda , Han Daxing
Published: June 2019

The non-reversible degradation without light soaking has been observed in both thin films and solar cells fabricated using the hot-wire CVD technique. For solar cells, a 9.8% initial efficiency became 9.2% when measured after a few weeks of being stored in the dark. For the intrinsic layers, the conductivity increased in the air but remained steady in vacuum up to 700 hours. Also, the conductivity increased and activation energy decreases from an initial ∼0.95 eV to ~∼0.85 eV after several thermal cycles, even in a vacuum. We suggest that the degradation in both materials and solar cells come from the same origin: the upward shift of the Fermi-energy position from its initial value. In other words, the as-grown material is slightly p-type and gradually became slightly n-type after sitting in the air or after thermal annealing cycles in a vacuum. The shift in the Fermi-energy made the fill factor of the solar cell decrease and changes in the electronic properties of the i-layer. It is likely that adsorption of oxygen from water vapor is driving this degradation.
Nanocrystalline silicon ( nc-Si ) from single ion beam sputtering
Authors: Zhou Z.B. , Hadi G.M. , Cui R.Q. , Ding Z.M. , Li G.
Published: June 2019

Based on a small set of selected publications on the using of nanocrystalline silicon films (nc-Si) for solar cell from 1997 to 2001, this paper reviews the application of nc-Si films as intrinsic layers in p-i-n solar cells. The new structure of nc-Si films deposited at high chamber pressure and high hydrogen dilution have characters of nanocrystalline grains with dimension about several tens of nanometer embedded in matrix of amorphous tissue and a high volume fraction of crystallinity (60~80%). The new nc-Si material have optical gap of 1.89 eV. The efficiency of this single junction solar cell reaches 8.7%. This nc-Si layer can be used not only as an intrinsic layer and as a p-type layer. Also nanocrystalline layer may be used as a seed layer for the growth of polycrystalline Si films at a low temperature.

We used single ion beam sputtering methods to synthesize nanocrystalline silicon films successfully. The films were characterized with the technique of X-ray diffraction, Atomic Force Micrographs. We found that the films had a character of nc-amorphous double phase structure. Conductivity test at different temperatures presented the transportation of electrons dominated by different mechanism within different temperature ranges. Photoconductivity gains of the material were obtained in our recent investigation.
Investigation of the Causes and Variation of Leakage Currents in Amorphous Silicon P-I-N Diodes
Authors: Johnson Todd R. , Ganguly Gautam , Wood George S. , Carlson David E.
Published: June 2019

Excess leakage currents under reverse bias (known as shunting) and spontaneous reductions of this excess leakage under increased reverse bias (known as curing) were investigated in hydrogenated amorphous silicon (a-Si:H) based single junction p-i-n type diodes. An increase in the frequency of shunting was observed when the front contacts were switched from tin oxide to zinc oxide, most likely due to defects in the previously deposited zinc oxide coated glass was observed. Storage in the dark and light soaking up to 100 hours were both observed to independently increase the leakage current in previously leaking diodes. Models for the distribution of shunt-causing defects within a given cell area were considered. Comparing the measured frequency of shunting using cells of varying area (1 to 16 mm2) to the models' predictions indicate a distribution of point defects separated by relatively large average distances that are slightly larger for tin oxide (5-6 mm) than for zinc oxide (4 mm).
Room Temperature Recovery of Light Induced Changes in Amorphous Silicon Solar Cells
Authors: Ganguly G. , Carlson D.E. , Bennett M.S. , Willing F. , Arya R.R. , Stradins P.
Published: June 2019

We have observed the recovery of the performance of amorphous silicon (a-Si:H) based solar cell (especially the fill factor) at temperatures between 25°C and 170°C after ∼600 hours of light soaking under 1 sun illumination at ∼40°C. We find that there is some recovery of the fill factor of the cells even at temperatures below the temperature of light soaking. The recovery is significantly greater in cells of poor quality. There is also some evidence of enhancement of the recovery rate due to an external electric field. Above the light soaking temperature, a sort of thermally activated recovery of the fill factor is observed.
Calculations of SiH3 Diffusion and Growth Processes on a-Si:H Surfaces
Authors: Vigneron P , Peacock P W , Xiong K , Robertson J
Published: June 2019

Surface diffusion of a growth species is needed to give the observed smooth surface of hydrogenated amorphous silicon (a-Si:H). But what diffuses, the weakly bound SiH3 radical on the hydrogenated surface, or the bound SiH3 at a growth site. Diffusion is complicated by the change in the surface termination of a-Si:H as temperature rises. We use total energy pseudopotential calculations on a variety of periodic Si:H surface configurations to show that it is the weakly bound SiH3 that diffuses. We provide an overall energy scheme of the bound states and transport levels of SiH3 on a-Si:H surfaces.
Experimental Characterization of the Reliability of Multi-Terminal Dual-Damascene Copper Interconnect Trees
Authors: Gan C. L. , Thompson C.V. , Pey K. L. , Choi W. K. , Chang C. W. , Guo Q.
Published: June 2019

The reliability of Cu dual-damascene interconnect trees with 3-terminal (dotted-I), 4-terminal (‘T’) and 5-terminal (‘+’) configurations has been investigated. The lifetime of multiterminal interconnect trees with the same current density through the common middle via was determined to be independent of the number of segments connected at the common junction. Furthermore, our experimental results on dotted-I test structures showed an increase in the reliability of the interconnect tree when the distribution of a same current was not equal in the two connected segments, especially for the cases where one of the segments was acting as a passive reservoir or active source of Cu atoms for the adjoining segment. Due to the low barrier for void nucleation at the Cu/Si3N4 interface, the presence of any small atomic source in neighboring segments will enhance the reliability of a connected segment in which Cu atoms are being drained away. As a consequence, failure can occur in a tree segment which is stressed at significantly lower current densities than more highly stressed adjoining segments.
Effect of barrier layers on the texture and microstructure of Copper films
Authors: Muppidi Tejodher , Field David P
Published: June 2019

The microstructure of interconnect material is know to influence its electromigration and stress-voiding properties. In addition to many factors responsible for the microstructure development, the barrier layer could be a major contributing factor as it forms the substrate for the copper films above. The microstructure of the barrier films based on its deposition technique could determine the final microstructure of the copper film. In the present work we examine the effect of two different barrier layers (Ta and TaN) and different stackings of these two materials on the microstructure on the copper seed (PVD) and electroplated films using EBSD, AFM and XRD. The results show that the plated films have a predominantly (111) texture and uniform grain size. But the (111) texture maximum varied with the barrier layer stacking underneath the plated film.
Electromigration of lower and upper Cu lines in dual-damascene Cu interconnects
Authors: Krishnamoorthy Ahila , Qiang Guo , Vairagar Anand V. , Mhaisalkar Subodh
Published: June 2019

Electromigration in upper M2 and lower M1 Cu lines in dual damascene interconnects was investigated by using two types of via terminated structures. Two different types of failures termed as abrupt and gradual failures were observed. Electromigration failures in M2 were mostly by gradual failures, while abrupt failures dominated in M1. Significantly different types of voids were observed in M1 as compared to those in M2, though similar resistance change was observed. Experimentally calculated activation energies for M1 and M2 indicated interfacial electromigration. Activation energy of M1 was found to be much lower than that of M2. This clearly demonstrates the asymmetry of electromigration in M2 and M1 Cu lines in dual damascene interconnects.
The formation of low temperature Cu3Si in Ag(Cu)/Si structure upon annealing and its effects on adhesion and resistivity
Authors: Hong Sungjin , Lee Seob , Ko Yeonkyu , Lee Jaegab
Published: June 2019

The annealing of Ag(40 at.% Cu) alloy films deposited on a Si substrate at 200 – 800 oC in vacuum has been conducted to investigate the formation of Cu3Si at the Ag-Si interface and its effects on adhesion and resistivity of Ag(Cu)/Si structure. Auger electron spectroscopy(AES) analysis showed that annealing at 200°C allowed a diffusion of Cu to the Si surface, leading to the significant reduction in Cu concentration in Ag(Cu) film and thus causing a rapid drop in resistivity. In addition, the segregated Cu to the Si surface reacts with Si, forming a continuous copper silicide at the Ag(Cu)/Si interface, which can contribute to an enhanced adhesion of Ag(Cu)/Si annealed at 200 oC. However, as the temperature increases above 300°C, the adhesion tends to decrease, which may be attributed to the agglomeration of copper silicide beginning at around 300°C.
Material and Electrical Characterization of HfO2 Films for MIM Capacitors Application
Authors: Hu Hang , Zhu Chunxiang , Lu Y. F. , Wu Y. H. , Liew T. , Li M. F. , Cho B.J. , Choi W. K. , Yakovlev N.
Published: June 2019

Thin films of HfO2 high-κ dielectric have been prepared by pulsed-laser deposition (PLD) at various deposition conditions. X-ray diffraction (XRD), atomic force microscopy (AFM), and secondary ion mass spectroscopy (SIMS) were used to characterize the deposited films. Experimental results show that substrate temperature has little effect on the stoichiometry, while deposition pressure plays an important role in determining the ratio of Hf and O. The electrical properties of HfO2 Metal-Insulator-Metal (MIM) capacitors were investigated at various deposition temperatures. It is shown that the HfO2 (56 nm) MIM capacitor fabricated at 200 oC shows an overall high performance, such as a high capacitance density of ∼3.0 fF/νm2, a low leakage current of 2x10-9 A/cm2 at 3 V, etc. All these indicate that the HfO2 MIM capacitors are very suitable for use in Si analog circuit applications.
Air Bridge Technology: A Comparison of Novel Interconnect Materials and Integration Schemes for Beyond 45 nm
Authors: Foster Kenneth , Waeterloos Joost , Frye Don , Froelicher Steve , Mills Mike
Published: June 2019

The electronics industry, in a continual drive for improved integrated device performance, is seeking increasingly lower dielectric constants (k) of the insulators that are used as interlayer dielectric (ILD) for advanced logic interconnects. As the industry continually seeks a stepwise reduction of the “effective” dielectric constant (keff), simple extendibility, leads to the consideration of the highest performance possible, namely air bridge technology. In this paper we will discuss requirements, integration schemes and properties for a novel class of materials that has been developed as part of an advanced technology probe into air bridge architecture. We will compare and contrast these potential technology offerings with other existing dense and porous ILD integration options, and show that the choice is neither trivial nor obvious.
3D System Integration Technologies
Authors: Ramm Peter , Klumpp Armin , Merkel Reinhard , Weber Josef , Wieland Robert , Ostmann Andreas , Wolf Jürgen
Published: June 2019

In the last years strong efforts were made to miniaturize microelectronic systems. Chip scale packages, flip chips and multichip modules are now commonly used in a great variety of products (e. g. mobile phones, hand-held computers and chip cards). Future microelectronic applications require significantly more complex devices with increased functionality and performance. Due to added device content, chip area will also increase. Performance, multi-functionality and reliability of microelectronic systems will be limited mainly by the wiring between the subsystems (so called “wiring crisis”), causing a critical performance bottleneck for future IC generations. 3D System Integration provides a base to overcome these drawbacks. Furthermore, systems with minimum volume and weight as well as reduced power consumption can be realized for portable applications. 3D integrated systems show reduced chip areas and enable optimized partitioning, both which decrease the fabrication cost of the system. An additional benefit is the enabling of minimal interconnection lengths and the elimination of speed-limiting inter-chip interconnects. 3D concepts which take advantage of wafer level processing to avoid increasing package sizes and expensive single component assembling processes have the potential to integrate passive devices resistors, inductors and capacitors into the manufacturing system and provide full advantage for system performance.

The ITRS roadmap predicts an increasing demand for systems-on-a-chip (SoC) [1]. Conventional fabrication is based on embedded technologies which are cost intensive. A new low cost fabrication approach for vertical system integration is introduced. The wafer-level 3D SoC technology, optimized to the capability for chip-to-wafer stacking has the potential to replace embedded technologies based on monolithic integration.
Expanding thermal plasma for low-k dielectrics deposition
Authors: Creatore M. , Barrell Y. , Kessels W.M.M. , Sanden M.C.M. van de
Published: June 2019

As the need for low-k dielectrics in the ULSI technology becomes urgent, the research primarily focuses on the deposition of novel materials with appropriate electrical properties and on the challenges concerning their integration with subsequent processing steps. In this framework we introduce the expanding thermal plasma as a novel remote technique for the deposition of low-k carbon-doped silicon dioxide films from argon/hexamethyldisiloxane/oxygen mixtures. We have obtained k values in the range 2.9-3.4 for films characterized by acceptable mechanical properties (hardness of 1 GPa).
Organofluorosilicate Glass (OFSG): A Dense Low K Dielectric with Superior Materials Properties
Authors: O'Neill M.L. , Cheng Y.L. , Lukas A.S. , Wang Y.L. , Karwacki E.J. , Feng M.S. , Vrtis R.N. , Vincent J.L. , Peterson B.K. , Bitner M.D.
Published: June 2019

Organofluorosilicate glass (OFSG) films with the composition Si:O:C:H:F were deposited via plasma-enhanced CVD from mixtures of trimethylsilane (3MS), silicon tetrafluoride (SiF4), and oxygen (O2). OFSG films have significantly enhanced mechanical strength, thermo-oxidative stability, and adhesion compared with OSG films deposited from 3MS and O2 alone. We propose that the increased density of OFSG, which helps improve mechanical strength, is balanced by the presence on non-polarizable Si-F functionalities, which serve to lower the dielectric constant.
Single walled 0.4 nm carbon nanotube bundles prepared by pyrolysis of n-hexane catalyzed by ferrocene
Authors: Wang Qixiang , Ning Guoqing , Wei Fei , Luoa Guohua
Published: June 2019

Bundles of single walled 0.4 nm carbon nanotubes were prepared by chemical vapor deposition using n-hexane as carbon source catalyzed by ferrocene with additives of thiophene at 1373 K. 8 cm long rope of single walled carbon nanotubes with diameters of 0.8-1.18 nm was also synthesized. The products were characterized by scanning electron microscopy, high resolution transmission electron microscopy and Raman spectroscopy.
Integration of Carbon Nanotubes Devices Into Microelectronics
Authors: Hoenlein W. , Kreupl F. , Duesberg G.S. , Graham A.P. , Liebau M. , Seidel R. , Unger E.
Published: June 2019

Carbon Nanotubes (CNTs) offer extraordinary properties for applications in microelectronics. We assess the methods used to grow CNTs for integration into microelectronics, in particular, metallic carbon nanotubes for vias and interconnects as well as semiconducting CNTs for fieldeffect devices are discussed. State-of-the-art CNTFETs are compared to Si-MOSFETs. A vertical CNTFET (VCNTFET) device concept is presented which offers better growth control, adding a new quality to microelectronics and making real 3-dimensional electronics possible.
The Magnetochiral Effect in Charge Transport in Carbon Nanotubes
Authors: Krstic Vojislav , Roth Siegmar , Burghard Marko , Kern Klaus , Rikken Geert L.J.A.
Published: June 2019

Nanotubes forming carbon atoms arrange differently, resulting into three main types of carbon nanotubes: armchair, zigzag, chiral. Thus, depending on their type, nanotubes may be regarded as chiral, molecular electrical conductors. As a consequence of symmetry arguments, the magnetoresistance of such tubes depends on the relative orientation of the traversing current and the external magnetic field. Magnetotransport measurements on single walled carbon nanotubes have been performed showing the expected dependence on both the current and magnetic field. Further, the quantum-mechanical model of a free electron on a helix in an external magnetic field is discussed in order to provide indicators to possible microscopic mechanisms.
Synthesis, Analysis, Transport and Field emission Measurements of Compound B-C-N Nanotubes
Authors: Golberg Dmitri , Bando Yoshio , Dorozhkin Pavel , Dong Zhen-Chao , Tang Cheng-Chun , Kurashima Keiji , Mitome Masanori
Published: June 2019

Multiwalled B-C-N nanotubes of various morphologies and chemical compositions were synthesized by reacting C-based nanotube templates with boron oxide and nitrogen at 1573 K- 2173 K. The nanotubes were thoroughly analysed using a high-resolution field-emission 300 kV transmission electron microscope (TEM), an energy-filtered field-emission 300 kV electron microscope (Omega filter), an electron energy loss spectrometer and an energy dispersion X-ray detector. Transport and field emission properties of the nanotubes were studied using a low energy electron point source microscope and via in-situ measurements in TEM equipped with a scanning tunnelling microscope (STM) unit.
Carbon-Nanotube Engineering for Probes and Tweezers Operating in Scanning Probe Microscope
Authors: Nakayama Yoshikazu , Akita Seiji
Published: June 2019

We have developed a series of processes for preparing carbon nanotube devices of probes and tweezers that operate in scanning probe microscope (SPM). The main developments are a nanotube cartridge where nanotubes are aligned at a knife-edge to be easily picked up one by one and a scanning-electron-microscope manipulator by which a nanotube is transferred from the nanotube cartridge onto a Si tip under observing its view.

We have also developed the electron ablation of a nanotube to adjust its length and the sharpening of a multiwall nanotube to have its inner layer with or without an end cap at the tip. For the sharpening process, the free end of a nanotube protruded from the cartridge was attached onto a metal-coated Si tip and the voltage was applied to the nanotube. At a high voltage giving the saturation of current, the current decreased stepwise in the temporal variation, indicating the sequential destruction of individual nanotube layers. The nanotube was finally cut at the middle of the nanotube bridge, and its tip was sharpened to have an inner layer with an opened end. Moving up the cartridge before cutting enables us to extract the inner layer with an end cap.

It is evidenced that the maximum current at each layer during the stepwise decrease depends on its circumference, and the force for extracting the inner layer with ∼ 5nm diameter is ∼ 4 nN.
Localized Fabrication of Mental Contacts and Electrical Measurements on Multi walled Carbon Nanotubes
Authors: Ziroff J. , Agnello G. , Rullan J. , Dovidenko K.
Published: June 2019

A Focused Ion Beam (FIB) microscope was to locally deposit platinum contacts on Multiwalled Carbon Nanotubes (MWNTs) for resistance and current carrying capability measurements. We have determined the resistivity of these ultra-thin Pt lines and the MWNT-Pt contact resistance to account for contributions to the MWNT measurements. We have studied the effects of secondary mental deposition around the contacts (‘halo’ effect) on the MENT electrical measurements as well as effects of ion beam exposure and possible ways to avoid/minimize them. Transmission Electron Microscopy data was used to evalutate MWNT surface modifications due to ion beam exposure and Pt deposition.
Deformation of Small Volumes of Material Studied Using Strained-Layer Superlattice Structures
Authors: P'ng K.M.Y. , Bushby A.J. , Dunstan D.J.
Published: June 2019

Mechanical studies of semiconductor superlattices have shown that the onset of plastic deformation under an inhomogeneous stress is a process that takes place simultaneously across a finite volume of the order of a micron across. The ability to incorporate known internal stresses, and to vary the stress and thickness of individual layers in a semiconductor superlattice, is a very powerful tool, opening up new possibilities for investigations that cannot be achieved by varying external stresses on a specimen that is sensibly homogeneous. In this way, from the initial yield stress of single-crystal strained-layer superlattices under indentation, we demonstrated a new criterion, of which the key feature is that it is to be averaged over a finite volume. Here we show that designing samples with individual layers in bands to form low yield-stress material within the structure can give information about the size and position of the initial yield volume.
Atomistic and Continuum Studies of Diffusional Creep and Associated Dislocation Mechanisms in thin Films on Substrates
Authors: Buehler Markus J. , Hartmaier Alexander , Gao Huajian
Published: June 2019

Motivated by recent theoretical and experimental progress, large-scale atomistic simulations are performed to study plastic deformation in sub-micron thin films. The studies reveal that stresses are relaxed by material transport from the surface into the grain boundary. This leads to the formation of a novel defect identified as diffusion wedge. Eventually, a crack-like stress field develops because the tractions along the grain boundary relax, but the adhesion of the film to the substrate prohibits strain relaxation close to the interface. This causes nucleation of unexpected parallel glide dislocations at the grain boundary-substrate interface, for which no driving force exists in the overall biaxial stress field. The observation of parallel glide dislocations in molecular dynamics studies closes the theory-experiment-simulation linkage. In this study, we also compare the nucleation of dislocations from a diffusion wedge with nucleation from a crack. Further, we present preliminary results of modeling constrained diffusional creep using discrete dislocation dynamics simulations.