bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of the Effects of Heavy-Ion Radiation on Nanocomposite Carbon Films
Authors: Kristian Kathleen E. , Medina-Emmanuelli Nadia M. , Ortiz Oscar O. , González Adolfo , González Juan A. , Jesús JoelDe , Vargas Iris M. , Weiner Brad R. , Morell Gerardo
Published: June 2019

The compositional and microstructural transformations induced by heavy ions (GeV/amu Fe and Si ions) on nanocomposite carbon (n-C) films were investigated by Raman Spectroscopy (RS), Atomic Force Microscopy (AFM), and X-ray Photoelectron Spectrscopy (XPS). Two identical sets of n-C films were prepared in a sulfur-assisted hot filament chemical vapor deposition (HFCVD) system using methane, hydrogen and hydrogen sulfide. Films with various sp3 C and sp2 C bonding distributions were present within each set, which were obtained by varying the substrate temperature (400-600 °C). One set of films was submitted to a 20 krad dose of energetic Si and Fe ions at the NASA space radiation simulation facility hosted in Brookhaven National Laboratory's Alternating Gradient Synchrotron (AGS). All the films showed the characteristic diamond (tetragonal sp3 C) band at around 1332 cm-1 and the graphitic (trigonal sp2 C) D and G bands at around 1350 and 1590 cm-1, respectively, evidencing their composite nature. The results indicate that sp2 C ←sp3 C interconversions take place in the nanocomposite carbon material during heavy ion irradiation. A mechanism is proposed to explain this behavior. The overall results imply that there could be a range of sp3/sp2 C ratios for which carbon bonding interconversion takes place under ion radiation without significant changes to the average composition of the material. Nanocomposite carbon materials with this characteristic would be radiation insensitive. A technique could be developed based on this carbon bonding interconversion property by using focused energetic beams onto carbon films to produce a robust information storage technology that would survive catastrophic events.
Observation of ion-induced ripples in Cu(001)
Authors: Chan Wai Lun , Pavenayotin Niravun , Chason Eric
Published: June 2019

A linear instability theory proposed by Bradley and Harper accounts for many of the features of ripple formation on amorphous and semiconductor surfaces, but it is not consistent with measurements of sputtered metal surfaces. In the present work, we report observations of sputter ripples on Cu(001) surfaces which are similar to amorphous and semiconductor systems. By using higher ion flux and temperature than previously used, we have produced ripples in which the wavelength is independent of time and the amplitude increases exponentially during the early stages of growth. The ripple evolution was measured using in situ light scattering during sputtering.
Ion beam lithographic fabrication of ordered VO2 nanoparticle arrays
Authors: Lopez R. , Suh J. Y. , Feldman L. C. , Haglund R. F.
Published: June 2019

Long-range ordered arrays of vanadium dioxide nanoparticles are fabricated by pulsed laser deposition in a patterned layer of poly(methyl methacrylate) resist. The two- dimensional arbitrary pattern is created by focused ion beam exposure of the resist, followed by pulsed laser deposition and thermal annealing. Interaction of light with the nanoparticles is controlled by their geometrical arrangement as well as by the difference in optical properties displayed between the metallic and semiconducting phases of VO2. Arrays like this open opportunities to study optical resonances and interactions for nanoparticles in close proximity, in the framework of the metal-semiconductor phase transition in VO2.
Two-Dimensional Differential Adherence and Myoblast Alignment Driven Fabrication of Engineered C2C12 Muscle Organoids
Authors: Patz Tim M. , Doraiswamy Anand , Narayan Roger , Modi Rohit , Chrisey Douglas
Published: June 2019

Differential adherent surfaces were used to induce attachment of C2C12 myoblasts that later would form engineered muscle organoids. Narrow channels, 60–400 μm wide, were micromachined in a 2% agarose gel using an ArF laser, and subsequently filled with extracellular matrix. Upon addition of 1 mL of a 2×104 cells/mL myoblast suspension, cells selectively adhered to the ECM lined channels in a non-confluent manner and we monitored their growth at various time points. The adherent myoblasts were flourescently imaged with a propidium iodide live/dead assay, which revealed that the cells were alive within the channels. After 72 hours growth, the myoblasts grew, proliferated and differentiated into myotubes. Myoblasts residing in the narrow channels (60–150 μm wide) aligned parallel to the channel, while myoblasts adhered to the wide channel (400 μm) were randomly aligned within the channel. The fully-grown 1 cm long organoids maintained an aspect ratio on the order of 100:1. These results provide the foundation for future three-dimensional tissue growth using differential adherent
Direct Laser Sintering of metal parts: characterisation and evaluation of joining mechanisms
Authors: Bassoli E. , Gatto A. , Iuliano L. , Atzeni E.
Published: June 2019

Rapid Prototyping and Tooling are playing a more and more important role in the achievement of compressed time-to-market solutions, where prototype parts and tools are produced directly from the CAD model. In particular, Selective Laser Sintering (SLS) of metal powders with liquid phase is frequently applied for the production of inserts for injection moulding of plastic parts.

An experimental campaign has been planned to investigate the surface finish and mechanical performances of Direct Laser Sintering technique, with particular regard to the effect of the laser sintering strategy on the anisotropy of the final part. Tensile specimens of DirectMetal 20 and DirectSteel 20 materials have been produced, with different orientations in regard to laser path.

Rupture surfaces after the tensile tests were observed at the SEM, in order to understand failure mechanisms, whereas the observation of polished sections helped investigating joining phenomena between the particles. The proposed experimental methodology allowed correlating the macroscopic performances to the micro-mechanisms ruling the process, proving that no considerable differences can be noticed between samples produced in the X and Y direction within the plane of powder deposition.
Effect of Ink Properties through Various Sol-Gel Synthesis Routes for the Ink-Jet Deposition of YBa2Cu3O7−δ Superconducting Layers
Authors: Mouganie T. , Glowacki B. A.
Published: June 2019

The development of ink synthesis for YBa2Cu3O7−δ (YBCO) coated conductors is discussed in detail. These chemical solution deposition (CSD) processes are for drop-on-demand ink-jet coating and ink-jet printing allowing non-vacuum formation of multi-layer superconducting patterns on metal substrates (with and without the aid of buffer layers).

Printing and substrate parameters that alter solid-liquid interface properties were investigated, and the sol-inks synthesised were aqueous and non-aqueous based therefore allowing variable chemical properties depending on what was required from the deposition process. The formation and the stability of the sol-inks has been studied and discussed, with the various synthesis steps and additives yielding the properties required to produce coatings.

Characterisation of the inks was by Differential Thermal Analysis and Thermal Gravimetry whilst characterisation of the coatings and products was by X-Ray Diffraction and Scanning Electron Microscopy. AC susceptibility was used to assess the superconductivity of the printed samples.
Characterisation of innovative materials for Direct Laser Sintering
Authors: Bassoli E. , Gatto A. , Iuliano L. , Atzeni E.
Published: June 2019

The performances achieved by Rapid Prototyping techniques are progressively leading towards Rapid Manufacturing, that is the capability to produce end products, directly from the CAD model. Even so, the diffusion of these techniques is hardly supported by scientific knowledge about the micro-mechanisms ruling the macroscopic performances of the part. In the present research, mechanical performances of new materials produced by Direct Laser Sintering technique have been studied: a Polyamide and an innovative Polyamide-Aluminium composite (Alumide). Specimens were produced with different orientations in regard to powder deposition plane and laser path, to investigate how the manufacturing anisotropy affects the part performances.
Broadening Middle-School Students' Images of Science and Scientists
Authors: Leslie-Pelecky Diandra L. , Buck Gayle A. , Zabawa Angela
Published: June 2019

The ‘mad scientist’ stereotype is alive and well – and not an image most K-12 students can (or want to) embrace. Project Fulcrum, a National Science Foundation-funded GK-12 program, partners math, science and engineering graduate students with elementary and middle-level teachers. One project goal – broadening student images of science and scientists –is addressed by projects developed by the teacher/scientist teams that are focused on the specific needs of their students. The projects developed focus on scientists, the use of science in different types of jobs, and developing scientific skills. Pre-project research, in which teachers probe the motivation behind their students’ attitudes, is a critical component of developing a successful project. Although determining the specific impact of this project on student attitudes is complicated by its being part of a larger project, teachers and scientists report enhanced awareness of student attitudes and the reasons underlying those attitudes, and generated ideas to address those motivations.
A study of V3+ and the Vanadium acceptor level in semi-insulating 6H-SiC
Authors: Lee Wonwoo , Zvanut Mary E.
Published: June 2019

Infrared absorption (IR) and electron paramagnetic resonance (EPR) spectroscopies are used to study the V3+ impurity and the vanadium acceptor level in 6H semi-insulating SiC. IR and EPR data obtained from samples cut from the same wafer support the assignment of the 0.60 and 0.62 eV IR absorption lines to substitutional V3+. Photo-induced EPR measurements reveal identical photo-thresholds for V3+ and V4+ ions. A peak at 0.8 eV, where the intensity of the three plus charge state decreases and the four plus charge state increases by an equal amount, is thought to represent excitation of an electron from V3+ to the conduction band edge. The 0.8 eV peak is therefore attributed to the V3+/4+ level. The difference between the optically measured value reported here and that measured previously using temperature dependent techniques is attributed thermal relaxation.
Role of the Substrate Doping in the Activation of Fe2+ centers in Fe implanted InP
Authors: Cesca T. , Gasparotto A. , Mattei G. , Verna A. , Fraboni B. , Impellizzeri G. , Priolo F.
Published: June 2019

We have investigated the structural and electrical behavior of Fe centers introduced in InP by high temperature ion implantation. The lattice location of the Fe atoms and the effect of postimplantation annealing treatments have been studied by PIXE-channeling measurements. I-V, CV and DLTS analyses have been used to characterize the electrical properties related to the presence Fe2+/3+ deep traps. The results show that the background n-doping density play a crucial role in controlling the annealing behavior and the electrical activation of the Fe centers. The same effect has been observed in samples containing Fe concentrations both above and below the Fe solubility threshold in InP.
A Pulsed EDMR Study of Charge Trapping at Pb Centers
Authors: Boehme Christoph , Friedrich Felice , Lips Klaus
Published: June 2019

Low temperature pulsed electrically detected magnetic resonance (pEDMR) measurements of charge trapping and recombination transitions involving Pb centers at the c-Si (111)/SiO2 interface are presented. The results of these experiments show that when a conduction electron is trapped, it forms a strongly coupled spin pair with the defect electron prior to its readjustment into the charged Pb ground state. The data reveals that the Landé factors of the two electrons within these pairs are almost identical (difference < 0.002) and that they are, within the measurement accuracy, identical to the Landé factor of the uncharged, singly occupied Pb center. From this, it is concluded that trapping and recombination at Pb defects is dominated by direct charge capture and not by tunneling or hopping transitions from other localized states. Different cross sections attributed in previous studies to different interface defects at the c-Si/SiO2 interface can be explained by readjustment out of different spin configurations of the charged Pb-* defect.
Investigation of GaNAsSb/GaAs and GaInNAsSb/GaNAs/GaAs Band Offsets
Authors: Yuen Homan B. , Kudrawiec Robert , Ryczko K. , Bank S.R. , Wistey M.A. , Bae H.P. , Misiewicz J. , Harris J.S.
Published: June 2019

Heterojunction band offsets of GaNAsSb/GaAs, GaInNAsSb/GaAs, and GaInNAsSb/GaNAs/GaAs quantum well (QW) structures were measured by photoreflectance (PR) spectroscopy. These samples were grown by solid-source molecular beam epitaxy using a radio-frequency nitrogen plasma source. PR spectra were collected from the QW structures and the energy transitions were obtained. The experimental data of the QW energy transitions were analyzed by theoretical calculations. Using predetermined values such as QW thickness and composition, unknown factors such as the heterojunction band offsets were able to be determined. For the GaN0.02As0.87Sb0.11/GaAs structure, we found that Qc≈0.5. For Ga0.62In0.38N0.026As0.954Sb0.02/GaAs, we found that Qc≈0.8. This value is similar to the antimony free dilute-nitride material GaInNAs since the small amount of antimony does not affect the band offsets. For the technologically important Ga0.61In0.39N0.023As0.957Sb0.02/GaN0.027As0.973/GaAs laser structure, we found that the GaInNAsSb/GaNAs QW had a conduction band offset of 144 meV and a valence band offset of 127 meV. With a greater understanding of the band structure, more advanced GaInNAsSb laser devices can be obtained.
Various Methods to Reduce Defect States in Tantalum Oxide Capacitors for DRAM Applications
Authors: Lau W.S. , Zhang G. , Leong L.L. , Qian P.W. , Han Taejoon , Das J. , Sandler Nathan P. , Chu P.K.
Published: June 2019

Tantalum oxide has attracted world-wide interest for DRAM (dynamic random access memory) capacitor applications because of its relative high dielectric constant compared to silicon dioxide or nitride. We would like to point out that tantalum oxide behaves very much like a large bandgap n-type semiconductor with 3 main types of donors responsible for leakage current. Native oxygen vacancies are very deep double donors with Ec – Ed = 0.8 eV approximately, where Ec is the bottom of the conduction band and Ed is the energy leVel of the defect state. Si-O vacancy complexes are relatively shallow single donors with Ec – Ed = 0.2-0.4 eV. C-O vacancy complexes are relatively shallow single donors with Ec – Ed = 0.5-0.6 eV. The key points regarding how to suppress these 3 types of donor defects will be discussed for the purpose of leakage current reduction.
Analysis of Nanoscale Deformation in GaAs(100): Towards Patterned Growth of Quantum Dots
Authors: Taylor Curtis R. , Stach Eric A. , Malshe Ajay P. , Salamo Gregory
Published: June 2019

Nanoindentations were created in the GaAs(100) surface to act as strain centers for the controlled nucleation and patterning of InAs quantum dots. A systematic approach is taken to understand the indent deformation processes that may lead to precision patterning capabilities for a broad range of nanostructures. Indents were generated using loads below 450 μN with a sharp cube corner indenter. Site-specific cross-sectional thinning of nanoindents (down to 100 nm in size) has been achieved using the in-situ ‘lift-out’ technique. This allowed for observation of subsurface deformation by transmission electron microscopy (TEM). The crystal was observed to deform solely by dislocation activity with no evidence of amorphization, twinning, fracture, or phase transformation. It is shown that the single phase deformation of GaAs can be well characterized and controlled, which should allow for exploitation of the dislocation strain field to bias nucleation of self-assembled quantum dots.
Silicon Wafer Defect Self-Characterization with CCD Image Sensors
Authors: McColgin William C. , Perryy Alexa M. , Seidler Dean J. , Lavine James P.
Published: June 2019

Today's CCD image sensors can provide very high image quality. However, used as a tool, they can also provide a sensitive window into defects in silicon, either intrinsic to the starting wafers or introduced during fabrication. In this paper, we examine some cases of known silicon defects and show how they can appear in, and be studied by, CCD imagers. As examples, we discuss epi-layer defects, slip defects, and dark-current rings.
A Comparison of Lattice-Matched GaInNAs and Metamorphic InGaAs Photodetector Devices
Authors: Jackrel David B. , Yuen Homan B. , Bank Seth R. , Wisteyy Mark A. , Yu Xiaojun , Fu Junxian , Rao Zhilong , Harris James S.
Published: June 2019

The dilute-nitride GaInNAs shows great promise in becoming the next choice for 1 eV photodetector and multi-junction photovoltaic applications due to the ability for it to be grown lattice-matched on GaAs substrates. This paper will present results from high-power photodetector devices fabricated from high-quality thick GaInNAs and metamorphic InGaAs materials grown by MBE. The internal quantum efficiency of rear-illuminated PIN photodiodes with thick GaInNAs films as the intrinsic region (roughly 62% at 1064 nm) is somewhat lower than comparable metamorphic InGaAs devices (roughly 75% at 1064 nm). However, the dark current density of the GaInNAs devices is also somewhat lower (roughly 3 μA/cm2 at 2×104 V/cm bias) than the InGaAs devices (roughly 20 μA/cm2 at 2×104 V/cm bias), while the breakdown voltages (beyond -20 V) are comparable. Materials characterization of each structure, including x-ray diffraction and room-temperature as well as temperature-dependent photoluminescence studies will be presented in order to explain the characteristics observed in the devices composed of the two different material systems.
Mutual Passivation in Dilute GaNxAs1-x Alloys
Authors: Yu K. M. , Walukiewicz W. , Wu J. , Mars D. E. , Scarpulla M. A. , Dubon O. D. , Ridgway M. C. , Geisz J. F.
Published: June 2019

The dilute GaNxAs1-x alloys (with x up to 0.05) have exhibited many unusual properties as compared to the conventional binary and ternary semiconductor alloys. We report on a new effect in the GaNxAs1-x alloy system in which electrically active substitutional group IV donors and isoelectronic N atoms passivate each other's activity. This mutual passivation occurs in dilute GaNxAs1-x doped with group IV donors through the formation of nearest neighbor IVGa- NAs pairs when the samples are annealed under conditions such that the diffusion length of the donors is greater than or equal to the average distance between donor and N atoms. The passivation of the shallow donors and the NAs atoms is manifested in a drastic reduction in the free electron concentration and, simultaneously, an increase in the fundamental bandgap. This mutual passivation effect is demonstrated in both Si and Ge doped GaNxAs1-x alloys. Analytical calculations of the passivation process based on Ga vacancy mediated diffusion show good agreement with the experimental results.
Effects of Silicon Nitride Passivation Layer on Mean Dark Current and Quantum Efficiency of CMOS Active Pixel Sensors
Authors: Benoit D. , Morin P. , Cohen M. , Bulkin P. , Regolini J. L.
Published: June 2019

In the present study, we have analyzed the influence of the silicon nitride (SiN) passivation layer properties on the mean dark current and the quantum efficiency of CMOS APS (Active Pixel Sensor) through electrical characterization of lot wafers processed with three different SiN passivation films. The SiN layers were characterized by Spectroscopic Ellipsometry (SE) and Fourier Transform Infra Red (FTIR) spectroscopy to get the optical indices and the hydrogen content of the films, respectively. Hydrogen desorption was also studied by Thermal Desorption Spectrometry (TDS) experiments.

The different chemical bond concentrations enable to explain the device performance. It is shown that high [Si-H] and low [Si-N] bonds concentrations lead to high hydrogen desorption from the SiN films. Thus, the lowest dark current values have also been obtained with such silicon nitride passivation layers. Consequently, results are in agreement with the hydrogen passivation of defects being responsible of thermally generated carriers. Concerning the quantum efficiency (QE), it is highly influenced by the optical indices of the SiN passivation layer.

Actually, the thickness and complex refractive index of the SiN layer affect the light reflection, while the light absorption, in the visible range, is controlled by the [Si-Si] bonds concentration. There are also competing requirements to minimize dark current and to maximize quantum efficiency. In fact, high [Si-H] and low [Si-N] bonds concentrations (for good passivation) are generally observed in silicon-rich SiN films, which also contain high amount of [Si-Si] bonds (inducing high absorption, thus low QE). Increasing simultaneously the [Si-H] and [N-H] bonds concentrations in the passivation layer can be a way to have high hydrogen desorption during passivation anneal just preserving a transparent layer.
Effect of Deuterium Diffusion on the Electrical Properties of AlGaN/GaN Heterostructures
Authors: Arroyo Jaime Mimila , Barbé Michel , Jomard François , Ballutaud Dominique , Chevallier Jacques , Poisson Marie-Antoinette , Delage Sylvain , Dua Christian , Cordier Yvon , Hugues Maxime , Semond Fabrice , Natali Franck , Lorenzini Philippe , Massies Jean
Published: June 2019

We have studied the influence of a deuterium diffusion on the electrical characteristics of the 2D gas present in AlGaN/GaN heterostructures. The deuterium diffusion is performed by exposing the structures to a rf remote deuterium plasma. We find that both the sheet carrier concentration and the electron mobility decrease and that these effects are partly reversible under thermal annealing. These results suggest that deuterium behave as acceptors in the 2D gas region. The negatively charged deuterium act as additional scattering centers for electrons.
High Resolution Site-Selective Studies of Erbium-Centers in GaN and GaN:Mg.
Authors: Glukhanyuk V. , Przybylińska H. , Kozanecki A. , Jantsch W.
Published: June 2019

In this work the high resolution optical spectroscopy is used in order to determine the positions of the Stark split 4I15/2, 4I11/2 and 4I9/2 energy levels of Er3+ in GaN and GaN:Mg. Photoluminescence and photoluminescence excitation spectra were measured at energies corresponding to the 4I15/2→4I9/2 and 4I15/2→4I11/2 absorption transitions. Low Er implant doses were applied to reduce the number of possible defects. In undoped GaN only a single Er-center was observed and no influence of Mg doping on the energy level splittings of this center in GaN:Mg was found. Numerical analysis based on point charge model was used to calculate parameters of the local crystal field (CF) acting on Er3+ ions. The splittings of the 4I9/2 and 4I11/2 energy levels were calculated in weak CF approach and good agreement with experimental results was obtained. The calculations confirmed that the symmetry of the erbium center in hexagonal GaN is C3v.
Luminescence and Lifetime Properties of Europium Doped Gallium Nitride Compatible with CMOS Technology
Authors: Poitras Carl B. , Lipson Michal , Wu Huaqiang , Spencer Michael G.
Published: June 2019

Continuous-wave and time resolved photoluminescence measurements on europium doped gallium nitride in the form of a powder are presented. The powder is obtained from reacting NH3 and a melt of gallium and europium with bismuth as a wetting agent. Photoluminescence from continuous wave excitation above the GaN bandgap reveals that an optimal concentration of about 1 at.% of Eu gives the most intense emission at 621 nm. Above gap time resolved photoluminescence reveals that energy transfer between the host material (GaN) and the rare earth ions occurs at a faster rate than previously reported for MBE grown GaN:Eu. Applications of the powder are directed towards CMOS compatible light emitters that are spun on silicon. A high temperature anneal of the powder shows no change in the CW photoluminescence spectrum of the powder, confirming CMOS compatibility.
On 2.7 νm Emission from Er-doped Large Bandgap Hosts
Authors: Vrielinck H. , Izeddin I. , Ivanov V.Y. , Gregorkiewicz T. , Callens F. , Lee D. S. , Steckl A. J. , Khaidukov N. M.
Published: June 2019

The potential of Er-doped Cs2NaYF6 and GaN for mid-infrared emission at λ≈ 2.7 ν is investigated using time-resolved optical spectroscopy. This emission results from electronic transitions between the second (4I11/2) and first (4I13/2) excited states of the Er3+ ion. By recording the photoluminescence transients for the 4I11/2 → 4I15/2 and 4I13/2 → 4I15/2 transitions after pulsed excitation, we determine the lifetime of the 4I11/2 level and demonstrate that the 4I13/2 state is populated from this level. Our results indicate that both host lattices should enable 2.7 νm emission, which is temperature-stable but subject to concentration quenching.
Energy-Back-Transfer Process in Rare-Earth Doped AlGaN
Authors: Wakahara A. , Fujiwara T. , Okada H. , Yoshida A. , Ohshima T. , Itho H.
Published: June 2019

Temperature dependence of time-resolved photoluminescence (PL) properties for rare-earth ions (REIs: Eu, Tb, and Er) implanted AlxGa1-xN (x=0∼1) is investigated. Thermal quenching for RE-related PL becomes small when increasing the Al contents. The PL decay time of REIs used in the present work becomes shorter when increasing the temperature and/or PL peak energy. The temperature dependence of PL intensity and the decay time are analysed by assuming phonon assisted energy-back-transfer model, in which the energy in REIs escape to trap levels. From the results, the improvement of PL properties can be well explained by the model, in which the activation energy for energy-back-transfer process is increased as increasing the Al contents.
Influence of Rapid Thermal Annealing on Self-assembled Quantum-dot Superluminescent Diodes
Authors: Zhang Z.Y. , Tsui Y.Y. , Fedosejevs R. , Wang Z.G.
Published: June 2019

Superluminescent diodes (SLD) have great potential for application as light sources including optical gyroscopes and sensors, optical time domain reflectometers (OTDR) and wavelength-division multiplexing (WDM) system testing. High output power and large spectral bandwidth are key features for SLD. High output power has been attempted by antireflection coating of the facet and utilizing the tapered active region. In addition, as the spectral width broadened, the coherence length is reduced. The short coherence length can reduce the Rayleigh backscattering in fiber gyroscope systems and can improve the spatial resolution in OTDR application. Therefore, broadening spectral width of SLD offers an advantage for obtaining the ultimate sensitivity in these applications.
Tm-Er Codoping Al2O3 Thin Films: Activation by Annealing
Authors: Xiao Zhisong , Serna R. , Afonso C. N. , Vickridge I.
Published: June 2019

Amorphous aluminum oxide (Al2O3) thin films codoped with Tm3+ and Er3+ have been prepared by pulsed laser deposition. A broad emission band with a full-width half maximum (FWHM) up to 230 nm was observed in Tm-Er codoped film. The spectrum shows two peaks located at 1540 nm corresponding to Er3+ emission and 1640 nm due to Tm3+ emission. The luminescence intensity dependence on the annealing temperature was investigated. It is shown that the annealing temperature and energy transfer between Tm3+ and Er3+ ions play an important role in the definition of the luminescent response.
The Impact of Deposition Parameters on the Optical and Compositional Properties of Er Doped SRSO Thin Films Deposited by ECR-PECVD
Authors: Flynn Michael , Wojcik Jacek , Gujrathi Subhash , Irving Edward , Mascher Peter
Published: June 2019

Silicon rich silicon oxide films were fabricated by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD). The films were doped in situ using an organometallic precursor. Optical measurements show that the refractive indices of the films are determined by the silane to oxygen flow rate ratio used during the depositions. The erbium content as measured by elastic recoil detection (ERD) is also strongly dependent on the oxygen flow rate, with more erbium being incorporated in the more highly oxygenated films. The erbium content was also found to vary inversely with plasma power, which did not have a significant effect on the silicon to oxygen ratio. This allows the erbium and excess silicon levels of the films to be controlled independently.
Hafnium-related Photoluminescence in Single Crystal Silicon
Authors: Sachdeva R. , Istratov A. A. , Shan Wei , Deenapanray P. N. K. , Weber E.R.
Published: June 2019

A new photoluminescence (PL) band in the energy range of 700 meV to 950 meV associated with hafnium implanted in silicon is reported. A shift in the position of photoluminescence peaks observed on the samples implanted with two different isotopes of Hf confirms the Hfrelated origin of the observed photoluminescence band. Activation of the Hf-optical centers requires a 1000°C anneal step. The intensity of the PL lines depends on the cooling conditions. The spectrum consists of five peaks in the rapidly quenched sample as opposed to twenty one in the slowly cooled sample. Temperature dependent PL measurements and hydrostatic pressure measurements were performed to identify their nature.
Lattice Location of Rare Earth Ions in Semiconductors: Interpretation and Limitations of Using g Values
Authors: Carey David
Published: June 2019

The g values of rare earth ions obtained from either paramagnetic resonance or Zeeman measurements are often used to interpret the location and/or environment surrounding rare earth ions. In the case of centres with cubic symmetry the g value can be used to distinguish between substitutional and interstitial sites. For centres with less than cubic symmetry the average g value, taken as 1/3 trace of the g tensor, is often used as an indication of the lattice location and/or a measure of the strength of the local crystal field. This approach is widely used but is based on the assumption that the non-cubic terms in the total crystal field potential are small compared with the cubic crystal field. In this paper we have explored this assumption by calculating the principal g values in axial crystal fields for the Er3+ ion. We examine the limits over which the average g value approach is valid. Comparison is made with published results.
Novel Use of Surfactants in Copper Chemical Mechanical Polishing (CMP)
Authors: Hong Youngki , Patri Udaya B. , Ramakrishnan Suresh , Babu S.V.
Published: June 2019

In this study, the interaction between several kinds of surfactants and copper surface was examined to control the dissolution of copper during CMP. Among those surfactants, sodium dodecylsulfate (SDS), one of the conventional anionic surfactants, showed effective interaction with copper and significantly suppressed the dissolution of the copper at acidic and neutral pH ranges in a model copper CMP slurry system consisting of 3 wt% fumed silica, 1 wt% glycine, and 5 wt% hydrogen peroxide in deionized water. The inhibition performance of copper dissolution by SDS is better than that of Benzotriazole (BTA), a conventional inhibiting agent of copper dissolution in a copper CMP slurry.
Effect of Corrosion Inhibitor (BTA) in Citric Acid based Slurry on Cu CMP
Authors: Kim In-Kwon , Kang Young-Jae , Hong Yi-Koan , Park Jin-Goo
Published: June 2019

In this study, the effect of BTA on polishing behavior was investigated as functions of H2O2, slurry pH and abrasive particles. The addition of BTA effectively prevented Cu from etching by forming the passivation layer of Cu-BTA regardless of pH and H2O2 concentration in slurry. A thinner passivation layer was grown on Cu in BTA added slurry solutions with a higher contact angle of 60°. The dynamic etch rate, the removal rate with abrasive free slurry, also decreased when BTA was added in slurry at pH 2, 4 and 6. The removal rate of Cu was strongly dependent on types of abrasive particles in slurry. The larger hardness of slurry abrasive particles, the higher removal rates of Cu. The reduction of removal rates in BTA added slurry was determined by the competition between chemical dissolution rate and mechanical abrasion rate.
AFM Measurements of Adhesion between Actual CMP Slurry Particles and Various Substrates
Authors: Liu Yong , Zdyrko Bogdan , Tregub Alex , Moinpour Mansour , Buehler Mark , Luzinov Igor
Published: June 2019

One of the critical parameters in chemical mechanical polishing (CMP) technology is adhesion between abrasive particles and surfaces being polished. Accumulated up to date theoretical and experimental facts insist that development of advanced material removal and cleaning methods requires understanding and evaluation of particle adhesion in these processes. To this end, our research focuses on AFM studies of interaction between the slurry particles and different substrates treated by CMP processes. To conduct adhesion measurements, the particles present in a CMP system and model latex particle were first attached to the surface of silicon wafer covered with monolayer of polymer(s) having high affinity to particles and the silicon wafer. Glass/quartz sphere (10-60 microns) was attached to AFM cantilever with appropriate spring constant. (The sphere represented the surface of material being polished and might be covered with various materials during future investigations.) Next, AFM force volume mode, which utilizes the collection of the force-distance curves over selected surface areas, was used for the adhesion measurements.
Stress Characterization of Post-CMP Copper Films Planarized Using Novel Low-Shear and Surface-Engineered Pads
Authors: Deopura Manish , Hwang Edward , Misra Sudhanshu , Roy Pradip K.
Published: June 2019

A family of novel low-shear and surface-engineered pads for copper chemical mechanical planarization (CMP) are designed and evaluated for polishing characteristics and process induced stress. Tribological studies are carried out on blanket copper films using these low-shear/surface-engineered pads and comparison is made with state of the art commercial pads (IC1000 and JSR). Results indicate that low-shear surface-engineered pads exhibit vastly improved tribological performance. These pads exhibit a 40% lower coefficient of friction (COF) over a larger range of Sommerfeld numbers (So) compared to commercial pads. A simplified XRD line profiling technique has been utilized to characterize stress within post-CMP copper films. The (222) Bragg peak position obtained from the XRD spectra of films polished using low-shear surface-engineered pads indicates virtually no shift compared to the peak position for the unpolished copper films. This result establishes that almost no stress is incorporated during bulk Copper removal using the newly designed pads.
A Universal CMP Process Description Language for Standardization
Authors: Yoshida Takafumi
Published: June 2019

This paper proposes a universal Chemical Mechanical Planarization (CMP) process description language. We discuss the appropriate attributes needed to describe complex CMP processes and the capability for the standardization of CMP. We show an implementation of the language based on an open standard.
Integration of CMP Fixed Abrasive Polishing into the Manufacturing of Thick Film SOI Substrates
Authors: Kulawski Martin , Luoto Hannu , Henttinen Kimmo , Suni Tommi , Weimar Frauke , Mäkinen Jari
Published: June 2019

The specification for the total thickness variation (TTV) of the device layers on thick-film silicon on insulator (SOI) wafers tighten for future applications. Therefore, the bulk removal polishing process of current technology after grinding cannot meet the demands in terms of flatness. The currently required amount of material removal for polishing out the induced sub surface damage (SSD) of the grinding is very high. Additionally, slurry-based CMP processes show unsatisfactory grindline and topography removal. This in turn reflects negatively to processing times, throughput and overall flatness performance.

Encouraging early results of FA pad use for silicon and SOI polishing have already been further developed [1]. Low SSD grinding has been introduced to silicon manufacturing [[1]]. In this work, an integrated manufacturing process sequence is presented. Starting from low SSD grinding of the bonded SOI wafer couple, an optimized FA CMP step is replacing the conventional bulk polishing with reduced removal. The SSD after FA CMP is investigated by oxide induced stacking fault (OISF) method [[2]] and results are used to adjust the final polishing step of the substrates. The overall process sequence is highly advantageous in terms of performance in TTV and provides a highly competitive and effective method for achieving best possible surface quality with minimized total silicon removal. This method is not only useful for SOI wafers but also in other areas of silicon processing.
CMP Compatibility of Partially Cured Benzocyclobutene (BCB) for a Via-First 3D IC Process
Authors: McMahon J. J. , Niklaus F. , Kumar R. J. , Yu J. , Lu J.Q. , Gutmann R. J.
Published: June 2019

Wafer-level three dimensional (3D) IC technology offers the promise of decreasing RC delays by reducing long interconnect lines in high performance ICs. This paper focuses on a viafirst 3D IC platform, which utilizes a back-end-of-line (BEOL) compatible damascene-patterned layer of copper and Benzocyclobutene (BCB). This damascene-patterned copper/BCB serves as a redistribution layer between two fully fabricated wafer sets of ICs and offers the potential of high bonding strength and low contact resistance for inter-wafer interconnects between the wafer pair. The process would thus combine the electrical advantages of 3D technology using Cu-to-Cu bonding with the mechanical advantages of 3D technology using BCB-to-BCB bonding.

In this work, partially cured BCB has been evaluated for copper damascene patterning using commercially available CMP slurries as a key process step for a via-first 3D process flow. BCB is spin-cast on 200 mm wafers and cured at temperatures ranging from 190°C to 250°C, providing a wide range of crosslink percentage. These films are evaluated for CMP removal rate, surface damage (surface scratching and embedded abrasives), and planarity with commercially available copper CMP slurries. Under baseline process parameters, erosion, and roughness changes are presented for single-level damascene test patterns. After wafers are bonded under controlled temperature and pressure, the bonding interface is inspected optically using glass-to-silicon bonded wafers, and the bond strength is evaluated by a razor blade test.
Modeling Pattern Effects in Oxide CMP
Authors: Rzehak R.
Published: June 2019

We present an extension of the density-stepheight model for pattern effects in oxide CMP which accounts for the roughness of the polishing pad's surface. The model is compared to polishing data for processes using different pressure and speed. Agreement with the data is improved especially in the initial regime of polishing before the pad contacts the down areas.
Yield Improvement via minimization of step height non-uniformity in Chemical Mechanical Planarization (CMP)
Authors: Kadavasal Muthukkumar , Eamkajornsiri Sutee , Chandra Abhijit , Bastawros Ashraf F.
Published: June 2019

Obtaining local and global planarity is one of the prime criteria in dielectric and metal planarizations. Although Chemical Mechanical Planarization (CMP) helps us achieve this criterion in constant pattern density surfaces, the same is not true for variable pattern density surfaces this results in formation of global step heights across the die. This paper provides a pressure open loop control algorithms for obtaining planarity across a die containing variations in pattern densities. Based on the variation of pattern density and surface heights across the die, the surfaces are separated into zones and the pressure is varied spatially and/or temporally to obtain uniform surface heights, with enhanced step height uniformity. One of the algorithms looks ahead and recalculates/modifies the pressure values by identifying the step heights that could be formed after a specified time step. The final surface predictions have improved uniformity on the upper surface as well as on the step heights across the entire die. The simulation would help us track the polishing process for each time step and guide us with the optimized pressure values that can be applied in order to an uniform final surface evolution.
Polishing Slurries with Aluminate-modified Colloidal Silica Abrasive
Authors: Belov Irina , Kim Joo-Yun , Watkins Paula , Perry Martin , Pierce Keith
Published: June 2019

This study has developed a route for increasing stability of colloidal silica particles in acidic polishing slurries. Drastic improvement in colloid stability has been achieved by using SiO2 particles with increased negative surface charge through doping/modification with metallate ions Me(OH)4–, particularly with aluminate ions. Novel Copper CMP slurries employing aluminate-doped colloidal silica provide high removal rates, good planarization and dishing performance, demonstrate required stability and long shelf life while preserving all the morphological advantages of colloidal abrasive particles. The developed route is also useful for production of acidic polishing slurries for other applications, such as Tungsten and STI CMP, as well as in polishing hard drive disks, fiber optic connectors, etc.
Characterization of the Chemical Effects of Ceria Slurries for Chemical Mechanical Polishing
Authors: Abiade J. T. , Yeruva S. , Moudgil B. , Kumar D. , Singh R. K.
Published: June 2019

For highly selective particle-based slurries or fixed abrasive pads, ceria has been identified as the abrasive of choice for the chemical mechanical polishing (CMP) step for shallow trench isolation (STI). The advantageous performance of ceria-based CMP consumables is usually attributed to enhanced chemical reactivity between ceria and oxide materials. In fact, this reaction is a central theme of all ceria polishing models from glass polishing to STI CMP. Previously, experimental evidence in support of the ceria-silica reaction during CMP was virtually non-existent. Recently, we proposed a pH-dependent ceria-silica polishing mechanism based on polishing results, in-situ friction force measurements, and spectroscopic and microscopic investigations. In this report, we have studied the chemical interactions between ceria and silica in the absence of particles using an atomic force microscope (AFM) and a scanning electron microscope (SEM). AFM silicon tapping mode cantilevers were functionalized by depositing a silica coating via chemical vapor deposition (CVD) and thermal oxidation. SEM imaging and compositional analysis was conducted on the cantilevers before and after wear against a ceria thin film, which was grown by pulsed laser deposition. The cantilever wear profile and elemental composition as a function of pH confirms our earlier polishing results and the pH-dependent CMP model for ceria-silica CMP.
In-situ Metrology for End Point Detection during Chemical Mechanical Polishing of Shallow Trench Isolation Structure
Authors: Zantye Parshuram B. , Mudhivarthi S. , Kumar Ashok , Evans David
Published: June 2019

Efficient end point detection (EPD) helps prevent numerous Chemical Mechanical Polishing (CMP) process defects such as dishing, erosion, excessive over-polish etc. During the CMP of Shallow Trench Isolation (STI) structures, the process should be effectively stopped at the buried Si3N4 layer to prevent any/all of the aforementioned process defects. In this research, novel in-situ metrology technique that used the real time tracking of Coefficient of Friction (COF) data during polishing was employed for EPD during STI-CMP. The experiments were performed on the CETR CP-4 CMP Tester using 1“X 1” sample coupons having a 2 ‘mu;m pitch STI pattern. The COF signal during polishing is a characteristic signature of the given process parameters and conditions. The in-situ EPD was based on the principle that the COF values are strongly dependent upon the surface of the materials that are being polished. Extended polishing to polish the underlying layer after the process end point was reached, can give an estimate of the polishing slurry selectivity with respect to the buried layer. The ex-situ surface characterization of coupons was performed at different points of the process using Atomic Force Microscopy (AFM). The repeatability and reliability of this technique was evaluated after carrying out multiple tests at similar process conditions. The demonstrated methodology can also be implemented for characterization of polishing pads and slurries besides STI-CMP process optimization.
High Planarization Efficiency and Wide Process Window Using Electro-chemical Mechanical Planarization (EcmpTM)
Authors: Liu Feng Q , Chen Liang , Duboust Alain , Tsai Stan , Manens Antoine , Wang Yan , Hsu Wei-Yung
Published: June 2019

EcmpTM is a revolutionary planarization technology uniquely combining removal rate controlled by charge with superior planarization efficiency in the near no shear regime. In addition, the electrochemical removal mechanism has excellent within-wafer profile control. Multiple electrical zones configuration combined with a precise end-point control by electric charge, make it more predictable to control the remaining thickness and profile of copper film. The factors affecting the planarization such as the concentration and the efficiency of the inhibitors will be discussed in this paper. Meanwhile a planarization mechanism for Ecmp will be proposed to match the high planarization efficiency. The effects of applied voltage on removal rate and planarization efficiency will be presented in this paper. The electrical feature allows Ecmp to be a planarization process with removal rate independent of down force, enabling a wide removal rate window based on applied voltage.
Influence of the Substrate Temperature on the Texture of MgO Films Grown by Ion Beam Assisted Deposition
Authors: Stan Liliana , Arendt Paul N. , DePaula Raymond F. , Usov Igor , Groves James R.
Published: June 2019

The variation in the substrate temperature during ion beam assisted deposition (IBAD), which employs the use of energetic ions to bombard a growing film, has been shown to influence the quality of crystalline texture in MgO films. Determining the acceptable deviation from the optimum ion to molecule ratio for different substrate temperatures establishes the optimum MgO deposition conditions. For each fixed deposition temperature, a set of samples was produced by varying the ion assist beam current from sample to sample while keeping the deposition rate constant. In this way, the ion to molecule ratio was modified and the range of achieving well textured films was determined. The investigation of the MgO texture dependence on the substrate temperature reveals that the best in-plane alignment is obtained at ˜ 25°C. At this temperature, MgO films with in-plane orientation distribution as low as 3.7° full width at half maximum (FWHM) have been attained. MgO films deposited at temperatures higher than 100°C have broad in-plane alignment. Although, the deposition at the lowest temperature (-150°C) did not improve the in-plane texture, the acceptable deviation from the optimum ion to molecule ratio for achieving biaxially textured films was the largest. As a trend, the acceptable ion to molecule deviation decreases with increasing substrate temperature. This is especially important for continuous IBAD MgO depositions where less restrictive conditions are desired.