bluuebunny/crossref_metadata_2025 huggingface dataset:
Equilibrium structure of decagonal AlNiCo
Authors: Naidu S. , Mihalkovič M. , Widom M.
Published: April 2011

We investigate the high temperature decagonal quasicrystalline phase of Al72Ni20Co8 using a quasilattice gas Monte-Carlo simulation. To avoid biasing towards a specific model we use an over-dense site list with a large fraction of free sites, permitting the simulation to explore an extended region of perpendicular space. Representing the atomic surface occupancy in a basis of harmonic functions directly reveals the 5-fold symmetric component of our data. Occupancy is examined in physical and perpendicular space.
Amorphisation and Devitrification of Al-Transition Metal- Rare Earth Alloys
Authors: Battezzati Livio , Baricco Marcello , Kusy' Martin , Palumbo Mauro , Rizzi Paola , Ronto' Viktoria
Published: April 2011

Amorphisation studies by rapid solidification of Al-based alloys containing a transition metal (TM) and a rare earth element (RE) are reported. Results on primary formation of Al nanocrystals are given and discussed in relation to possible nucleation mechanisms considering the effect of various RE elements (RE = La, Ce, Nd and Sm) in Al87Ni7RE6 alloys. Ti or Zr, immiscible with RE's, are added to the ternary alloys with the aim of revealing possible phase separation in the melt. Calculations of ternary Al-Ni-Ce metastable phase equilibria are helpful in understanding the transformation sequence. Composition profiles ahead of nanocrystals are computed using the DICTRA software which correctly predicts the occurrence of composition gradients.

The surface fracture of mechanically tested samples are observed in TEM to check whether crystallisation is induced by deformation.
An isotropic glass phase in Al-Fe-Si formed by a first order transition
Authors: Cahn John W. , Bendersky Leonid A.
Published: April 2011

We present evidence of the nucleation and growth of a metallic glass phase from the melt, as if by a first-order transition. Microstructures of a number of rapidly solidified Al-Fe-Si alloys demonstrate that this glassy phase, which we term q-glass, is not a kinetically frozen liquid. It is the first phase to form from the melt as isolated nuclei that grow and deplete the melt of iron and silicon. From the nucleation behavior and the compositional partitioning, we infer an interface between the q-glass and the melt, and that, in a narrow composition range, the q-glass has a lower energy and entropy (is more ordered) than a conventional glass.
The Mn effect on magnetic structure of FeMn-B amorphous metals
Authors: Wang Yang , Nicholson D. M. C. , Widom M. , Fuentes-Cabrera M. , Mihalkovic M.
Published: April 2011

Fe-rich Fe-B amorphous metals exhibit approximately collinear magnetic structure. When a certain amount of Fe atoms are replaced with Mn, the magnetic structure of the alloys is found to become non-collinear. We performed electronic structure calculations using the locally self-consistent multiple scattering (LSMS) method for supercell samples generated by ab initio molecular dynamics simulation using the Vienna Ab-initio Simulation Package (VASP). We present the distribution of moment sizes and angular distributions in the FeMn-B amorphous metal samples. We discuss the Mn effect on the magnetic structure of the alloys.
The Prospects for Mechanical Ratcheting of Bulk Metallic Glasses
Authors: Wright Wendelin J. , Dauskardt R. H. , Nix W. D.
Published: April 2011

The major mechanical shortcoming of metallic glasses is their limited ductility at room temperature. Monolithic metallic glasses sustain only a few percent plastic strain when subjected to uniaxial compression and essentially no plastic strain under tension. Here we describe a room temperature deformation process that may have the potential to overcome the limited ductility of monolithic metallic glasses and achieve large plastic strains. By subjecting a metallic glass sample to cyclic torsion, the glass is brought to the yield surface; the superposition of a small uniaxial stress (much smaller than the yield stress) should then produce increments in plastic strain along the tensile axis. This accumulation of strain during cyclic loading, commonly known as ratcheting, has been extensively investigated in stainless and carbon steel alloys, but has not been previously studied in metallic glasses. We have successfully demonstrated the application of this ratcheting technique of cyclic torsion with superimposed tension for polycrystalline Ti–6Al–4V. Our stability analyses indicate that the plastic deformation of materials exhibiting elastic–perfectly plastic constitutive behavior such as metallic glasses should be stable under cyclic torsion, however, results obtained thus far are inconclusive.
Synthesis and Characterization of Amorphous Metallic Alloy Thin Films for MEMS Applications
Authors: Sambandam Senthil N , Bhansali Shekhar , Bhethanabotla Venkat R.
Published: April 2011

Microstructures of multi-component amorphous metallic glass alloys are becoming increasingly important due to their excellent mechanical properties and low coefficient of friction. In this work, thin films of Zr-Ti-Cu-Ni-Be have been deposited by DC magnetron sputtering in view of exploring their potential technological applications in fields such as Micro Electro Mechanical Systems (MEMS). Their structure, composition, surface morphology, mechanical properties viz., hardness and Young's modulus were analyzed using X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Nanoindentation. Influence of the deposition parameters of sputtering pressure and power upon the composition and surface morphology of these films has been evidenced by SEM, and AFM analysis, showing that such a process yields very smooth films with target composition at low sputtering pressures. These studies are useful in understanding the multicomponent sputtering process.
Deposition of Silver Nanoparticles on Yttrium Manganese Oxide Powders.
Authors: L. C. Roman , Castellanos R. M. A. , Diaz D.
Published: April 2011

Following a novel silver nanoparticles synthesis pathway, pre-synthesized silver nanoparticles (4.4 nm of average diameter) were deposited on a substrate of yttrium manganese oxide. The method takes advantage of the spontaneous reduction of silver 2-ethylhexanoate in dimethyl sulfoxide (DMSO) at 50° C. Sodium citrate was used as capping agent. Silver nanoparticles dispersions mixed with yttrium manganite were kept for several days, at room temperature, in an Erlenmeyer flask wrapped in aluminum foil. Pure yttrium manganese oxide was prepared by solid state reaction of stoichiometric mixtures. The characterization of the samples mainly involved X-ray powder diffractometry and electron microscopy. Magnetic susceptibility was measured using a Quantum Design MPMS-5S SQUID magnetometer. Two samples were prepared: (I) YMnO3/Ag (1×10-3 M) and (II) YMnO3/Ag (5×10-2 M). The Ag nanoparticles deposition of (I) was confirmed by an increase in the surface area and a qualitative elemental analysis for silver. In (II) <10 nm silver nanoparticles were clearly appreciated by XRD and images of High Resolution Transmission Electron Microscopy. The measured value of magnetic susceptibility of (II) is slightly larger than pure YMnO3.
Nano-Mechanical Study of Mechanically Alloyed Zr-Cu-Al-Ni Glass Composite Containing Second-Phase ZrC Particles
Authors: Alcalá Germán , Mato Sonia , Deledda Stefano , Knieps Martin , Hangen Ude , Eckert Jürgen , Gebert Annett , Schultz Ludwig
Published: April 2011

Metallic glasses exhibit generally high hardness and elastic modulus values at the expense of very limited plasticity. The incorporation of crystalline particles within an amorphous metallic matrix has been widely reported to improve the performance of these materials by reducing crack propagation. The present work analyzes the influence of nanometer-size ZrC particles on the nano-mechanical behavior of mechanically alloyed Zr55Cu30Al10Ni5 glassy matrix composites. The volume fraction of ZrC particles ranged from zero up to 20 vol. %, showing a critical change in the mechanical behavior between 10 and 20 vol. %, particularly in the elastic response.
A Survey of Defects in Strained Si Layers
Authors: Bedell S. W. , Chen H. , Sadana D. K. , Fogel K. , Domenicucci A.
Published: April 2011

A new method for highlighting defects in thin Si/SiGe layers is used to investigate the densities of various types of defects present in strained Si layers grown on relaxed SiGe layers. Defect densities were measured in strained Si layers formed on graded SiGe buffer layers (bulk), as well as silicon germanium-on-insulator substrates (SGOI), from both external and internal sources. The result of this investigation indicates that in addition to threading dislocations (TDs) and dislocation pile-ups, planar defects, i.e., stacking faults, are present in all but one of the materials studied. Due to the larger crystalline area affected by these planar defects, citation of only TD density as an indication of material quality is inadequate. A better measure of crystalline quality should include the density of TDs, pile-up clusters and planar defects (stacking faults) as well as some indication of the length distribution of the pile-ups and stacking faults.
Atomically Controlled Impurity Doping in Si-Based CVD Epitaxial Growth
Authors: Murota Junichi , Sakuraba Masao , Tillack Bernd
Published: April 2011

Atomic-order surface reaction processes on the group IV semiconductor surface are formulated based on the Langmuir-type surface adsorption and reaction scheme. In in-situ doped Si1−xGex epitaxial growth on the (100) surface in a SiH4-GeH4-dopant (PH3, or B2H6 or SiH3CH3)-H2 gas mixture, the deposition rate, the Ge fraction and the dopant concentration are explained quantitatively assuming that the reactant gas adsorption/reaction depends on the surface site materials and that the dopant incorporation in the grown film is determined by Henry's law. Self-limiting formation of 1-3 monolayers of group IV or related atoms in the thermal adsorption and reaction of hydride gases (SiH4, GeH4, NH3, PH3, CH4 and SiH3CH3) on Si(100) and Ge(100) are generalized based on the Langmuir-type model. Epitaxial Si or SiGe grown on N, P or B layers already-formed on Si(100) or SiGe(100) surface is achieved. It is found that higher level of electrical active P atoms exist in such film, compared with doping under thermal equilibrium conditions. Furthermore, the capability of atomically controlled processing for doping of advanced devices with critical requirements for dopant dose and location control is demonstrated for the base doping of SiGe:C heterojunction bipolar transistors (HBTs). These results open the way to atomically controlled technology for ultra-large-scale integrations.
Stress Metrology : The challenge for the next generation of engineered wafers
Authors: Tiberj Antoine , Paillard Vincent , Aulnette Cécile , Daval Nicolas , Bourdelle Konstantin K. , Moreau Myriam , Kennard Mark , Cayrefourcq Ian
Published: April 2011

Raman spectroscopy is a powerful and versatile technique for stress measurements in complex stacks of thin crystalline layers at macroscopic and microscopic scales. Using such a technique we show that thick SiGe layers epitaxially grown using graded buffer method are fully relaxed (>95%) at a macroscopic scale but exhibit a small strain modulation at a microscopic scale. For the first time we report the results of Raman micro-mapping of stress distribution in SGOI wafers produced by Smart Cut™ technology. We conclude that Smart Cut™ is a unique method to manufacture the next generation of engineered wafers that can combine strained and/or relaxed SiGe alloys, Si and Ge films, while keeping their initial strain properties at both scales. It is important to develop Raman spectroscopy tool for in-line process control in fabrication of strained Silicon On Insulator (sSOI) wafers.
Interference-enhanced Raman Scattering in Strain Characterization of Ultra-thin Strained SiGe and Si Films on Insulator
Authors: Yin Haizhou , Hobart K.D. , Shieh S.R. , Peterson R.L. , Duffy T.S. , Sturm J.C.
Published: April 2011

Interference-enhanced Raman scattering was utilized to characterize strain in ultra-thin strained silicon-germanium (SiGe) and silicon layers on insulator. Strained SiGe and silicon films with thickness ranging from 10 to 30 nm on insulating borophosphorosilicate glass (BPSG) were formed by layer transfer techniques and/or strain manipulation via lateral expansion of strained films. The optical interference of the multiple reflections at the BPSG interfaces can substantially boost the reflectivity at the interfaces. The reflection improves Raman signal from SiGe and/or silicon films by increasing excitation intensity and Raman signal collection in the thin films. With the use of interference-enhanced Raman scattering, strain can be characterized at visible wavelengths for films as thin as 10 nm.
Reduced Pressure - Chemical Vapor Deposition of Ge thick layers on Si(001) for microelectronics and optoelectronics purposes
Authors: Hartmann J.M. , Papon A.M. , Holliger P. , Rolland G. , Billon T. , Rouvière M. , Vivien L. , Laval S.
Published: April 2011

Ge-based photodetectors operating in the telecommunication wavelength range (1.3-1.6 μm) of silica fibers are highly desirable for the development of optical interconnections on SOI substrates. We have therefore investigated the structural and optical properties of Ge thick films grown directly onto Si(001) substrates using a production-compatible Reduced Pressure Chemical Vapor Deposition system. The thick Ge layers grown using a low-temperature / high temperature approach are in a definite tensile-strain configuration, with a threading dislocation density for as-grown layers of the order of 3×107 cm−2. The surface of those Ge thick layers is rather smooth, especially when considering the large lattice mismatch in-between Ge and Si. The root mean square roughness is indeed of the order of 2 nm only for as-grown layers. The layers produced are of high optical quality. An absorption coefficient α ≈10000 cm−1 @ 1.3μm (4500 cm−1 @ 1.55μm) has been found at room temperature for our Ge thick layers. A 30 meV bandgap shrinkage with respect to bulk Ge (0.77 eV ≎ 0.80 eV) is observed as well in those tensilestrained Ge epilayers.
Phosphorus and Boron Implantation into (100) Germanium
Authors: Suh Y. S. , Carroll M. S. , Levy R. A. , Sahiner A. , King C. A.
Published: April 2011

Boron and phosphorus were implanted into (100) Ge with energies ranging from 20-320 keV and doses of 5×1013 to 5×1016 cm−2. The as-implanted and annealed dopant profiles were examined using secondary ion mass spectrometry (SIMS) and spreading resistance profiling (SRP). The first four moments were extracted from the as-implanted profile for modeling with Pearson distributions over the entire energy range. The samples were annealed at 400, 600, or 800°C in nitrogen ambient. The dopant activation and diffusion were also examined and it was found that p-type sheet resistances immediately after boron implantation as low as 18 ohms/sq could be obtained without subsequent annealing.
Impact of Buffered Layer Growth Conditions on Grown-In Vacancy Concentrations in Molecular Beam Epitaxy Silicon Germanium
Authors: Shoukri Kareem M. , Haddara Yaser M. , Knights Andrew P. , Coleman Paul G. , Rahman Mohammad M. , Tatsuyama C.C.
Published: April 2011

Silicon-Germanium (SiGe) has become increasingly attractive to semiconductor manufacturers over the last decade for use in high performance devices. In order to produce thin layers of device grade SiGe with low concentrations of point defects and well-controlled doping profiles, advanced growth and deposition techniques such as molecular beam epitaxy (MBE) are used. One of the key issues in modeling dopant diffusion during subsequent processing is the concentration of grown-in point defects. The incorporation of vacancy clusters and vacancy point defects in 200nm SiGe/Si layers grown by molecular beam epitaxy over different buffer layers has been observed using beam-based positron annihilation spectroscopy. Variables included the type of buffer layer, the growth temperature and growth rate for the buffer, and the growth temperature and growth rate for the top layer. Different growth conditions resulted in different relaxation amounts in the top layer, but in all samples the dislocation density was below 106 cm−2. Preliminary results indicate a correlation between the size, type and concentration of vacancy defects and the buffer layer growth temperature. At high buffer layer growth temperature of 500°C the vacancy point defect concentration is below the PAS detectable limit of approximately 1015 cm−3. As the buffer layer growth is decreased to a minimum value of 300°C, large vacancy clusters are observed in the buffered layer and vacancy point defects are observed in the SiGe film. These results are relevant to the role played by point defects grown-in at temperatures below ∼350°C in modeling dopant diffusion during processing.
(A)thermal migration of Ge during junction formation in s-Si layers grown on thin SiGebuffer layers
Authors: Vandervorst W. , Pawlak B.J. , Janssens T. , Brijs B. , Delhougne R. , Caymax M. , Loo R.
Published: April 2011

Solid phase epitaxial regrowth (SPER) has been proven to be highly advantageous for ultra shallow junction formation in advanced technologies. Application of SPER to strained Si/SiGe structures raises the concern that the Ge may out diffuse during the implantation and/or anneal steps and thus reduce the strain in the top silicon layer.

In the present studies we expose 8-30 nm strained silicon layers grown on thin relaxed SiGe-buffers, to implant conditions and anneal cycles, characteristic for formation of the junctions by solid phase epitaxial regrowth and conventional spike activation. The resulting Geredistribution is measured using SIMS. Based on the outdiffused Ge-profiles the Ge-diffusion coefficient has been determined in the temperature range of 800-1100C from which an activation energy of ∼ 3.6 eV can be deduced. Up to 1050 C, 10 min, even a 30 nm strained film remains highly stable and shows only very moderate outdiffusion.

We also have observed a far more efficient, athermal Ge-redistribution process linked to the implantation step itself. This was studied by analysing the Ge-redistribution following an Asimplant (2-15 keV, 5 1014 – 3 1015 at/cm2). It is shown that the energy of the implant species (or more specifically the position of the damage distribution function relative to the Ge-edge) plays a determining factor with respect to the Ge-migration. For implants whereby the damage distribution overlaps with the Ge-edge, a very efficient transport of the Ge is observed, even prior to any anneal cycle. The migration is entirely correlated with the collision cascade and the resulting (forward!) Ge-recoil distribution. The scaling with dose for a given energy links the observed Ge-profile with a broadening mechanism related to the number of atom displacements induced in the sample within the vicinity of the Si-SiGe-transition.
Crystals (A Freshman Seminar): An Exercise on Cooperative and Peer Learning
Authors: Bokreta M. Krimo , Santiago-Avilés J. J.
Published: April 2011

We have found that dividing the class of 20 students in groups of four brings agility to the group logistics and minimizes “defocusing” socialization. These are the teams of peer teachers. Each is responsible in carrying its own weight in the education of the team. They select their own “management” structure, as well as their agenda. The course itself starts with a month of lectures by the instructors and by visitors from other germane departments. The students organize visits to research labs on campus where research on crystalline materials is being performed, and invite researchers in the field to lecture the class. Each meeting period involves discussion of homework problems, where the groups, informally, present their findings. After this initial month, each team selects a topic among a wide gamut of possibilities and clears, with the instructors, the particular focus it wishes to develop further. The selected themes tend to group in science, technology, as well the general “lore” of crystals. So the themes range from the growth of crystals in reduced gravity, through the economic aspects of synthetic diamonds, to the folklore of crystals in healing. The particular selection of a theme is not as important as the way they research the topic, develop it and present it. The teams first present a survey of their topic to the class. We evaluate the presentation in terms of intellectual content and delivery. The students not only receive our feedback but also that of their peers. They have the chance to incorporate the comments in a second report, three weeks after the first when they are supposed to focus more on the initial theme and select a part for a more in-depth study. Final oral and written reports are due at the end of the semester.

Through the semester the classroom atmosphere has been that of inquiry, critical thinking, accepting of all points of view and the pursuit of diverse perspectives. The students seem to be able to take with them these attitudes and maintain them in their team meetings and discussions.
Fundamental Study and Oxide Reliability of the MBE-Grown Ga2−xGdxO3 Dielectric Oxide for Compound Semiconductor MOSFETs
Authors: Kwo J. , Hong M. , Mannaerts J. P. , Lee Y. J. , Wu Y. D. , Lee W. G. , Milkap S. , Yang B. , Gustaffson T.
Published: April 2011

We have extended our invented high k dielectrics Ga2−xGdxO3 oxide to compound semiconductors of AlGaAs, InGaAs, and InP, and demonstrated the formation of low leakage, insulating barrier on the (100) surface. Fundamental studies of the MOS diodes consisting of Au/GGG mostly on InGaAs are reported, including the crystal-chemical and electrical properties to address the oxide reliability issue. An atomically abrupt interface between the oxide/GaAs interface was achieved by the MBE growth. Systematic post annealing studies of varying temperature and gas species were carried out to improve the dielectric performance such as the reduction of frequency dispersion, voltage hysteresis, and interfacial state density Dit. We show that our results are essential to device processing based on the oxide, and to establish a viable GaAs MOSFET technology.
Experimental Study of Etched Back Thermal Oxide for Optimization of the Si/High-k Interface
Authors: Barnett Joel , Moumen N. , Gutt J. , Gardner M. , Huffman C. , Majhi P. , Peterson J.J. , Gopalan S. , Foran B. , Li H.-J. , Lee B.H. , Bersuker G. , Zeitzoff P. M. , Brown G.A. , Lysaght P. , Young C. , Murto R.W. , Huff H. R.
Published: April 2011

We have demonstrated a uniform, robust interface for high-k deposition with significant improvements in device electrical performance compared to conventional surface preparation techniques. The interface was a thin thermal oxide that was grown and then etched back in a controlled manner to the desired thickness. Utilizing this approach, an equivalent oxide thickness (EOT) as low as 0.87 nm has been demonstrated on high-k gate stacks having improved electrical characteristics as compared to more conventionally prepared starting surfaces.
Next Generation of Thin Film Transistors Based on Zinc Oxide
Authors: Fortunato E. , Barquinha P. , Pimentel A. , Gonçalves A. , Pereira L. , Marques A. , Martins R.
Published: April 2011

We report high performance ZnO thin film transistor (ZnO-TFT) fabricated by rf magnetron sputtering at room temperature with a bottom gate configuration. The ZnO-TFT operates in the enhancement mode with a threshold voltage of 19 V, a field effect mobility of 28 cm2/Vs, a gate voltage swing of 1.39 V/decade and an on/off ratio of 3×105. The ZnO-TFT present an average optical transmission (including the glass substrate) of 80 % in the visible part of the spectrum. The combination of transparency, high field-effect mobility and room temperature processing makes the ZnO-TFT a very promising low cost optoelectronic device for the next generation of invisible and flexible electronics.
Electrical properties of the La0.8Sr0.2MnO3 thin films on SrTiO3 substrate by an excimer laser metal organic deposition (ELMOD) process at low temperature
Authors: Tsuchiya T. , Yoshitake T. , Shimakawa Y. , Yamaguchi I. , Manabe T. , Kumagai T. , Kubo Y. , Mizuta S.
Published: April 2011

The electrical properties of epitaxial La0.8Sr0.2MnO3 films on a SrTiO3(STO) substrate prepared by changing the laser fluence, the irradiation time and the film thickness using excimer laser metal organic deposition(ELMOD) at 500/cm2, the film showed a 3.9 % maximum temperature coefficient of resistance (TCR: defined as 1/R•dR/dT) which was obtained by the ArF laser irradiation at 80mJ/cm2 for 10min. At a constant fluence of 80mJ/cm2, the Tm (temperature of the maximum TCR) of the La0.8Sr0.2MnO3 films increased from 225K to near 250K with an increase in the irradiation time to 90min at which the TCR was almost 3.9%. The La0.8Sr0.2MnO3 film that showed the maximum TCR of 4.0% at 275K was obtained by the ELMOD process at 500°C using the optimum conditions (Flence:80mJ/cm2, Irradiation time: 90min, Film thickness: 80nm).
Characteristic of hydrogenated Ga-doped ZnO films grown by DC magnetron sputtering using H2/Ar gas
Authors: Takeda Satoshi , Fukawa Makoto
Published: April 2011

We report characteristics of sputtered Ga-doped ZnO films grown in pure Ar (Ar-films) and H2/Ar gas mixture (H2/Ar-films). With increasing water partial pressure (PH2O), the resistivity of Ar-films significantly increased due to the decrease in both free carrier density and Hall mobility. The transmittance in the wavelength region of 300-400 nm for the films also increased with increasingPH2O. However, no significant PH2O dependence of the electrical and optical properties was observed for H2/Ar-films. Secondary ion mass spectrometry analysis revealed that hydrogen concentration in the Ar-films increased with increasing PH2O, indicating that the origin of the incorporated hydrogen is attributed to the residual water vapor in the coating chamber. On the contrary, the hydrogen concentration in H2/Ar-films was almost constant irrespective of PH2O and the concentration is obviously higher than that of Ar-films, indicating that the hydrogen primarily comes from H2 gas and the adsorption species due to H2 gas preferentially adsorb to the growing film surface over residual water vapor. Consequently, the effect of PH2O on the crystal growth was significantly reduced by H2 gas introduction, resulting in stability improvement.
Vibrational Lifetimes of Hydrogen in Silicon: Isotope Effects and MOSFET Reliability
Authors: Lüpke Gunter , Sun Baozhou , Tolk Norman H. , Feldman Leonard C.
Published: April 2011

Characterization of defect and impurity reactions, dissociation and migration in semiconductors requires detailed understanding of rates and pathways of vibrational energy flow, of energy transfer channels and of coupling mechanisms between local modes and the phonon bath of the host material. Significant progress in reaching this goal has been accomplished in recent landmark studies exploring the excitation and dynamics of vibrational states associated with hydrogen in silicon. We describe recent experiments which measure the vibrational lifetime of the Si-H bond in various defect configurations and show the relationship between these lifetimes and silicon MOSFET reliability.
Hydrogen diffusion in polycrystalline boron doped and undoped diamond.
Authors: Ballutaud D. , Boutry-Forveille A. , Laroche J.-M. , Simon N. , Girard H. , Herlem M. , Etcheberry A.
Published: April 2011

Hydrogen (deuterium used as tracer) diffusion experiments were performed on undoped and boron doped diamond films ([B] = 1019and 1020 cm−3) grown by plasma CVD or hot-filament assisted CVD. The samples were exposed either to a radiofrequency plasma or a microwave plasma at different temperatures between 400°C and 900°C. The deuterium profiles were analysed by secondary ion mass spectrometry (SIMS). The deuterium diffusion was explained mainly in term of trapping on intergranular defects. The passivation of boron acceptors, by B-D complex formation in the deuterium diffused superficial layers of the diamond films, was followed by electrochemical and mercury probe capacitance measurements. The results suggest a strong decrease of the free carrier density, which is in accordance with passivation of free carriers by deuterium trapping on dopant.
A Robust Process for Ion Implant Annealing of SiC in a Low-Pressure Silane Ambient
Authors: Rao S. , Saddow S.E. , Bergamini F. , Nipoti R. , Emirov Y. , Agrawal Anant
Published: April 2011

High-dose Al implants in n-type epitaxial layers have been successfully annealed at 1600°C without any evidence of step bunching. Anneals were conducted in a silane ambient and at a process pressure of 150 Torr. Silane, 3% premixed in 97% UHP Ar, was further diluted in a 6 slm Ar carrier gas and introduced into a CVD reactor where the sample was heated via RF induction. A 30 minute anneal was performed followed by a purge in Ar at which time the RF power was switched off. The samples were then studied via plan-view secondary electron microscopy (SEM) and atomic force microscopy (AFM). The resulting surface morphology was step- free and flat.
Homoepitaxial growth and characterization of thick SiC layers with a reduced micropipe density
Authors: Tsuchida H. , Kamata I. , Izumi S. , Tawara T. , Jikimoto T. , Miyanagi T. , Nakamura T. , Izumi K.
Published: April 2011

Growth technique for thick SiC epilayers with a reduced micropipe density has been developed in a vertical hot-wall CVD reactor. Micropipe closing by growing an epilayer is possible with a nearly 100% probability for 4H-SiC substrates oriented (0001) and (000-1) off-cut towards either [11-20] or [1-100]. By applying the micropipe closing technique, a high-performance Schottky barrier diode (SBD) was demonstrated on a substrate including micropipes. Growth of low-doped and thick SiC epilayers is also possible with a good morphology at a high growth rate, and 14.4 kV blocking performance was demonstrated using a 210 μm-thick epilayer. Epitaxial growth on (000-1) substrates with low doping and a low epi-induced defect density was also demonstrated. Deep centers and impurities were investigated to determine the effective lifetime killer of the epilayers. Dislocations and stacking faults in epilayers grown on 4H-SiC substrates off-cut towards different directions were also investigated.
PVT Growth of 6H SiC Crystals and Defect Characterization
Authors: Dhanaraj Govindhan , Liu Feng , Dudley Michael , Zhang Hui , Prasad Vish
Published: April 2011

SiC single crystals have been grown by seeded sublimation method using physical vapor transport (PVT) system designed and fabricated in our laboratory. A novel multi-segmented graphite insulation has been used for improved heat containment in the hot-zone. Numerical modeling was used to obtain the temperature field and predict various growth parameters. The grown crystals were characterized using AFM, SWBXT and chemical etching.
Atomic Force Microscope Observation of Growth and Defects on As-Grown (111) 3C-SiC Mesa Surfaces
Authors: Neudeck Philip G. , Trunek Andrew J. , Powell J. Anthony
Published: April 2011

This paper presents experimental atomic force microscope (AFM) observations of the surface morphology of as-grown (111) silicon-face 3C-SiC mesa heterofilms. Wide variations in 3C surface step structure are observed as a function of film growth conditions and film defect content. The vast majority of as-grown 3C-SiC surfaces consisted of trains of single bilayer height (0.25 nm) steps. Macrostep formation (i.e., step-bunching) was rarely observed, and then only on mesa heterofilms with extended crystal defects. As supersaturation is lowered by decreasing precursor concentration, terrace nucleation on the top (111) surface becomes suppressed, sometimes enabling the formation of thin 3C-SiC film surfaces completely free of steps. For thicker films, propagation of steps inward from mesa edges is sometimes observed, suggesting that enlarging 3C mesa sidewall facets begin to play an increasingly important role in film growth. The AFM observation of stacking faults (SF's) and 0.25 nm Burgers vector screw component growth spirals on the as-grown surface of defective 3C films is reported.
Growth of Large Diameter Semi-Insulating 6H-SiC Crystals by Physical Vapor Transport
Authors: Yoganathan M. , Gupta A. , Semenas E. , Emorhokpor E. , Martin C. , Kerr T. , Zwieback I , Souzis A. E. , Anderson T.A. , Tanner C.D. , Chen J. , Barrett D.L. , Hopkins R.H. , Johnson C.J. , Yan Fei , Choyke W.J. , Devaty R.P.
Published: April 2011

Semi-insulating (SI) 6H-SiC boules up to 110mm in diameter have been grown by Physical Vapor Transport (PVT). SI properties have been achieved by vanadiumc compensation, which resulted in the room temperature electrical resistivity exceeding 2×1011ωcm. Low temperature photoluminescence (LTPL) data shows the presence of the deep intrinsic defect level UD-1 in addition to V4+. The nitrogen-bound exciton (NBE) luminescence is weak in heavily vanadium compensated 6H-SiC.
Coherent Chip-Scale Modeling for Copper CMP Pattern Dependence
Authors: Cai Hong , Park Tae , Boning Duane , Kim Hyungjun , Kang Youngsoo , Kim Sibum , Lee Jeong-Gun
Published: April 2011

In this research, we present an improved and coherent chip-scale model framework for copper bulk polishing, copper over-polishing, and barrier layer polishing. The integration of contact wear and density-step-height models is more seamlessly implemented and addresses inherent shortcomings of the previous model. In the new model, a local density is used instead of the effective density computed by way of a planarization length, and only a contact wear coefficient is used to characterize the long-range planarization capability, thus avoiding the conflict between the planarization length and the contact wear coefficient in capturing topography variation. In addition, the pressure computed for each 240×240 μm block using contact wear is further redistributed, using a linear height vs. pressure model, among 40×40 μm cells within that block. The same model framework is used for different polishing steps, so that it is possible to directly compare basic process characteristics, such as pad stiffness, of different polishing stages. Results with the new model show a significant improvement of the modeling accuracy to less than 100 Å of root mean square error. Furthermore, the new model framework can be adapted for the modeling of multi-level metallization processes.
Metrological Assessment of the Coefficient of Friction of Various Types of Silica Using the Motor Current During ILD-CMP
Authors: Jacobsen Harald , Stachowiak Eric , Zwicker Gerfried , Lortz Wolfgang , Brandes Ralph
Published: April 2011

In the work presented the coefficient of friction (COF) was firstly determined metrologically by a systematic assessment of motor currents for different products of pressure and velocity (p v). With all seven test slurries it could be shown that the inserted energy ECMP is proportional to the product of pressure and velocity. The COF of the parameter domain considered here does not depend on the inserted energy or the product of p v in a first approximation. For all tested slurries it was demonstrated that, both the COF and the removal rate (RR) behave analogously (low COF→ low RR).

Measurements of the viscosity η have shown that η is not a constant in the shear rate range relevant for CMP. Using the obtained viscosity values a mean slurry film thickness in the range of 2,5 -C 6 μm could be calculated.
Effect of Particle Interaction on Agglomeration of Silica-Based CMP Slurries
Authors: Sorooshian A. , Ashwani R. , Choi H.K. , Moinpour M. , Oehler A. , Tregub A.
Published: April 2011

Chemical Mechanical Planarization has become a method of choice for planarization of metal and oxide layers in microelectronics industry. A CMP process includes up to 16 variables that need to be controlled to achieve a stable CMP process [1]. One of the major variables in CMP is related to slurry compositions. In particularly, a uniform distribution of the sizes of the abrasive particle in slurry is crucial for a stable CMP performance. The agglomerates can be unstable, since their size depends on addition of chemical additives and shearing during the CMP process.

In this work, the authors studied agglomeration of the fumed and colloidal silica-based slurries using dynamic rheometry, zeta potential tests, and an accusizer.

Slurry viscosity, determined using a steady state rheometry, was correlated to the particle charge, characterized by zeta potential, and to the particle sizes obtained using the particle size analyzer. Additionally, rheometer was used for slurry shearing to study effect of shear on slurry characteristics. Particle agglomeration due to slurry shearing and storage was observed and corroborated using rheometry, zeta potential, and particle size measurements.
Modeling CMP Transport and Kinetics at the Pad Groove Scale
Authors: Muldowney Gregory P.
Published: April 2011

A 3-D fluid flow and kinetics model of the full pad-wafer gap of a commercial CMP machine, including both grooves and land area flow properties, was developed to research the influence of these essential pad features at a scale not previously studied. Concentric circular grooves of two different dimensions were examined. Heat transfer and chemical reaction rates at the wafer surface were studied by including a combined frictional/chemical heat release model and firstorder kinetics for slurry activity. Results revealed sharp variations in velocity between the grooves and land areas, and a strong impact of groove depth and width on transient slurry mixing in the pad-wafer gap. These effects were more pronounced at higher polish pressures. Flow patterns in individual grooves beneath the rotating wafer were highly variable from one location to another such that fluid pathlines were dissimilar point to point even within the same groove. The effects of pad and wafer rotation, amplified by the unequal flow resistances of grooves and land areas, led to features in the steady-state temperature and concentration profiles at the same spacing as the groove pitch. This unusual finding identified a direct mechanism by which polish irregularities may be formed at the scale of the grooves.
Characterizing STI CMP Processes with an STI Test Mask Having Realistic Geometric Shapes
Authors: Xie Xiaolin , Park Tae , Boning Duane , Smith Aaron , Allard Paul , Patel Neil
Published: April 2011

Chemical mechanical polishing (CMP) has become the enabling planarization method for shallow trench isolation (STI) of sub 0.25μm technology. CMP is able to reduce topography over longer lateral distances than earlier techniques; however, CMP still suffers from pattern dependencies that result in large variation in the post-polish profile across a chip. In the STI process, insufficient polish will leave residue nitride and cause device failure, while excess dishing and erosion degrade device performance.

Our group has proposed several chip-scale CMP pattern density models [1], and a methodology using designed dielectric CMP test mask to characterize CMP processes [2]. The methodology has proven helpful in understanding STI CMP; however, it has several limitations as the existing test mask primarily consists of arrays of lines and spaces of large feature size varying from 10 to 100 μm. In this paper, we present a new STI characterization mask, which consists of various rectangular, L-shape, and X-shape structures of feature sizes down to submicron. The mask is designed to study advanced STI CMP processes better, as it is more representative of real STI structures. The small feature size amplifies the effects of edge acceleration and oxide deposition bias, and thus enables us to study their impact better. Experimental data from an STI CMP process is shown to verify the methodology, and these secondary effects are explored. The new mask and data guide ongoing development of improved pattern dependent STI CMP models.
A High Index Contrast Silicon Oxynitride Materials Platform for Er-doped Microphotonic Amplifiers
Authors: Saini Sajan , Sandland Jessica G. , Eshed Anat , Sparacin Daniel K. , Negro Luca Dal , Michel Jurgen , Kimerling Lionel C.
Published: April 2011

Er-based optical amplification continues to be the ideal low noise, WDM crosstalk free, broadband candidate for waveguide amplifiers. Design analysis of the applicability of Er-Doped Waveguide Amplifiers (EDWAs) for micron-scale integrated photonics in a planar lightwave circuit concludes: (i) an >80× increase in gain efficiency, and (ii) a >40×increase in device shrink can be realized, for a high index contrast EDWA (with a core-cladding index difference of δn=0.1↔0.7), compared to a conventional Er-doped fiber amplifier. The materials challenge now is to establish a robust materials system which meets this high index difference design requirement while simultaneously leveraging the capability of silicon (Si) processing: a host platform for EDWAs must be found which can integrate with Si Microphotonics. Silicon nitride (Si3N4), silicon oxide (SiO2) and a miscible silicon oxynitride alloy (SiON) of the two meet this materials challenge. We present the results of reactive and conventional magnetron sputtering based materials characterization for this high index host system. Room temperature and 4 K photo-luminescence studies for annealed samples show the reduction of non-radiative de-excitation centers while maintaining an amorphous host structure. Atomic force microscopy shows less than 1 nm peak-to-peak roughness in deposited films. Prism coupler measurements show a reliable reproducibility of host index of refraction with waveguide scattering loss <2 dB/cm. We conclude that the SiON host system forms an optimal waveguide core for an SiO2-clad EDWA. Initial gain measurements show a gain coefficient of approximately 3.9 dB/cm.
Optical and structural investigation on the energy transfer in a multicomponent glass co-doped with Si nanoaggregates and Er3+ ions
Authors: Enrichi Francesco , Mattei Giovanni , Sada Cinzia , Trave Enrico , Pacifici Domenico , Franzò Giorgia , Priolo Francesco , Iacona Fabio , Prassas Michel , Falconieri Mauro , Borsella Elisabetta
Published: April 2011

The enhancement of the Er3+ ions photoluminescence (PL) emission at 1.54 μm in a Si and Er co-implanted aluminosilicate glass is investigated in details. Post-implantation annealing has been performed to recover the damage induced by the implantation process and to promote Si aggregation. It is shown that 1h treatment in N2 atmosphere is not sufficient to induce Si precipitation for the investigated temperatures, up to 500°C. Nevertheless, the most intense Er3+ PL emission at 1.54 μm is achieved at 400°C. Such emission has been investigated by pumping in and out of resonance. The results suggest that good energy transfer mediators could be small Si aggregates and not only crystalline clusters. The effective excitation cross section of Er3+ ions has been measured in the best performing sample yielding a value of ∼ 2 × 10−16 cm2, many orders of magnitude higher than the direct absorption cross section of Er3+ ions: about 10−21 cm2 in this glass. The structural and optical properties of this material are discussed and compared to those found for a standard silica substrate.
Optical Spectroscopy of Silicon-On-Insulator Waveguide Photonic Crystals
Authors: Bajoni D. , Galli M. , Belotti M. , Paleari F. , Patrini M. , Guizzetti G. , Gerace D. , Agio M. , Andreani L.C. , Chen Y.
Published: April 2011

We report on a complete optical investigation on two-dimensional silicon-on-insulator (SOI) waveguide photonic crystals obtained by electron beam lithography and reactive ion etching. The dispersion of photonic modes is fully investigated both above and below the light-line by means of angle- and polarization-resolved micro-reflectance and attenuated total reflectance measurements.

The investigated samples consisted in a) large area (300 × 300 μm2) two-dimensional (2D) triangular lattices of air holes containing repeated line–defects; b) small area triangular lattices of holes with different number of periods and /or line defects integrated in a ridge type waveguide structure.

In the case of large area samples, variable-angle reflectance and ATR is measured from the sample surface in a wide spectral range from 0.2 to 2 eV both in TE and TM polarizations. The sharp resonances observed in the polarized reflectance and ATR spectra allow mapping of the photonic dispersion of both radiative and guided modes. Experimentally determined and compared to those calculated by means of an expansion on the basis of the waveguide modes.

In the case of ridge type waveguide-integrated photonic crystals, transmission is measured in the 0.9-1.7 eV spectral range by an edge-coupling technique. Transmission spectra exhibit significant attenuation corresponding to the photonic gaps along the Γ–M and Γ–K directions respectively, even when a small number of hole periods is integrated in the ridge waveguide. Good agreement is obtained by comparing the measured transmission spectra with the calculated photonic bands.
Low loss silica waveguides containing Si nanocrystals
Authors: Garcia C. , Garrido B. , Pellegrino P. , Morante J.R. , Melchiorri M. , Daldosso N. , Pavesi L. , Scheid E. , Sarrabayrouse G.
Published: April 2011

We study the optical and structural properties of rib-loaded waveguides working in the 600-900 nm spectral range. A Si nanocrystal-rich SiOx with Si excess nominally ranging from 10 to 20% forms the active region of the waveguide. Starting materials were fused silica wafers and 2 μm-thick SiO2 thermally grown onto Si substrate. Si nanocrystals were precipitated by annealing at 1100°C after quadruple Si ion implantation to high doses in a flat profile. The complete phase separation and formation of Si nanocrystals were monitored by means of optical tools, such as Raman, optical absorption and photoluminescence. Grain size distribution was obtained by electron microscopy. The actual Si excess content was obtained by X-ray photoelectron spectroscopy. The rib-loaded structure of the waveguide was fabricated by photolitographic and reactive ion etching processes, with patterned rib widths ranging from 1 to 8 μm. M-lines spectroscopy measurements provided a direct measurement of the refractive index and thickness of the active layers versus Si excess. When coupling a probe signal at 780 nm or 633 nm into the waveguide, an attenuation of at least 11 dB/cm was observed. These propagation losses have been attributed to Mie scattering, waveguide irregularities and direct absorption by the silicon nanocrystals.
Structural properties of Si nanoclusters produced by thermal annealing of SiOx films
Authors: Boninelli Simona , Iacona Fabio , Bongiorno Corrado , Spinella Corrado , Priolo Francesco
Published: April 2011

The structural properties of Si nanoclusters embedded in SiO2, produced by high temperature annealing of SiOx films, have been investigated by energy filtered transmission electron microscopy. The presence of amorphous nanostructures, not detectable by using dark field transmission electron microscopy, has been demonstrated. By taking into account also this contribution, a quantitative description of the evolution of the samples upon thermal annealing has been accomplished. In particular, the nanocluster mean radius and the density of amorphous and crystalline clusters have been determined as a function of the annealing temperature.