bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectroscopic Investigations of Dithienyl Polyenes
Authors: Cooper Thomas M. , Sowards Laura A. , Natarajan Lalgudi V. , Kirkpatrick Sean , Chandra Suresh , Mclean Daniel G. , Spangler Charles W.
Published: April 2011

To understand the properties of light-sensitive compounds used in optical limiters having photoinduced charge transfer mechanisms, we have investigated the photophysics of a series of di(2-thienyl-3,4–butyl)polyenes. Spectroscopic measurements were obtained as a function of the number of double bonds(n = 1–8). From analysis of the bandshape of the emission spectra, we found evidence of vibronic coupling between the S1 and S2 excited states. The degree of coupling increased with solvents of high refractive index. The appearance of the cis band in absorption spectra of dithienyl polyenes having 6–8 double bonds suggested equilibria between scis and s-trans conformors. The cis band intensity increased in lower polarity solvents, implying solvent-induced conformation changes in these dyes. Trends in the data reflected the ordering, energy gap between and mixing of 1Bu* and 1Ag* excited state configurations.
Optical Limiting Characteristics of Dendrons and Dendrimers Incorporating Dithienylpolyene Moieties
Authors: Ozer B. , Kang B.-S. , Spangler C. W.
Published: April 2011

Over the past decade there has been considerable progress in the design of new chromophores for potential optical limiting applications. Most of the focus has been centered on molecules that are capable of efficient excited state absorptions whose cross-sections are larger than the original π–π* excitation cross-section, usually referred to as reverse saturable absorbers (RSAs). The vast majority of chromophores having RSA characteristics depend on efficient intersystem crossing from the excited state singlet (S1) to a highly absorbing and relatively long-lived triplet state (T1). However, much less attention has been paid to alternative excited state absorptions, particularly from charge states such as polaronic radical-ions and bipolaronic diions. In this presentation, we propose that monodisperse dendrimers based on dendron coupling to core molecules such as bisphenol A are potential optical limiting materials based on photo-generation of such charge states in the dendron-attached chromophores, such as dithienylpolyenes. The design and syntheses of these dendrons and dendrimers are presented, and the absorption characteristics of the most likely charge states discussed from an optical limiting perspective.
Effects of Purification and Addition of Electron Acceptor Dyes to Solutions of Macrocyclic Dyes
Authors: Allen W J D , Bahra G S , Healy W
Published: April 2011

This paper will deal with the electronic and physical effects of purification of a macrocyclic dye, 2,3-napthalocyanine bis(trihexylsiloxide) (SiNC), on the optical limiting performance.

The changes in optical limiting performance of SiNC, a carbocyanine dye (1,1′,3,3,3′,3′,- Hexamethylindocarbocyanine iodide (HITCI) and two metallated porphyrins upon the addition of an electron acceptor material, methyl viologen dichloride (MV) (1,1′-dimethyl-4,4′ bipyridinium dichloride), are also shown and the results discussed.
Silica-Based Planar Lightwave Circuits
Authors: Himeno Akira
Published: April 2011

Silica-based planar lightwave circuits (PLC) provide various important devices for both optical wavelength division multiplexing (WDM) networks and optical access networks. This paper is an overview of recent progress in PLC technology including optical power splitters, arrayed-waveguide gratings, thermo-optic switches, and hybrid integrated PLCs.
Femtosecond to Nanosecond Characterization of Optical Limiting Mechanisms in Power Limiting Liquids and Solids
Authors: Malko A. , Xu S. , Wang H-L. , Kohlman R. , Smilowitz L. , Klimov V. , McBranch D. W. , Nogues J.-L. , Moreshead W. , Hagan D. , Yang S. , Stryland E. Van
Published: April 2011

We present our recent advances toward the development of high-performance solid-state optical limiting devices using reverse saturable absorption (RSA) dyes doped into optical host materials. Femtosecond transient absorption spectroscopy was employed to determine both the spectral regions of strong RSA, and the singlet-triplet excited-state dynamics. The optical limiting in the visible spectrum in both metallo-phthalocyanines and metallo-porphyrins is due to a combination of singlet and triplet RSA. Optical limiting performance was studied for RSA dyes in dual tandem limiters (both in solution and solid-state). Our best results in the solid-state yielded an attenuation of 400x, and a damage threshold of up to several mJ at f/5 focusing. The optical limiting at f/5 is further enhanced, particularly in the solid-state, by self-defocusing thermal nonlinearities.
Processing and Characterization of Inorganic Films for Optical Waveguide Components
Authors: Ponoth S. , Agarwal N. , Huang X. , Persans P. D. , Plawsky J.
Published: April 2011

Optical communications are becoming technologically important on progressively shorter length scales. As computer chip speeds increase longer metal wire interconnects become problematic and may limit device performance. Wide bandwidth optical interconnects may be used to address this problem. Silicon oxide and silicon nitride were explored as prospective optical and processing materials in the making of optical interconnects. Etching of slopes, which would be an important process for making optical interconnects, was studied. Slopes with angles ranging from 5 to 50 degrees were fabricated using a silicon oxide / silicon nitride stack.
Molecular Orbital Study of Apatite Nucleation at Silica Bioceramic Surfaces
Authors: Sahai N. , Tossell J. A.
Published: April 2011

We have used Hartree-Fock molecular orbital calculations to model the interactions of Ca2+, H2PO41-, HPO42- and H2O with bioceramic reactive surface sites represented by [Si3O6H6] to determine the reaction sequence for apatite precipitation at bioceramic surfaces. By comparing predicted reaction energies, viberational frequencies, abd NMR shifts for 29Si, and 31P with experimental values we were able to identify stable intermediates during reaction progress.

At the pH of blood, our calculations predict that (i) the 3-ring is the active surface site, (ii) formation of [SiO-Ca-OPO3H] bonds is energetically preferred over direct Si-O-P bonds, and (iii) an acidic precursor with bidentate Ca>OPO3H bonds, [Si3O6H5CaHPO4(H2O)3]1-, nucleates rapidly (minutes to 1 hour) at the bioceramic surface. Predicted precursor complex, [Si3O6H5CaHPO4(H2O)3]1-, and young bone share unique IR bands at 631 and 1125–1145 cm-1. Going beyond the scope of our calculations, a literature survey suggests that subsequent slow (1–2 weeks) aggregation of oligomers by H-bonds between surface Si-OH and HPO4 groups results in apatite formation. Analogously, carboxyl and phosphoryl groups on sialoprotein and hydroxyl-terminations on collagen may provide the nucleation and H-bonding sites for natural bone formation in the absence of the bioceramic.
Control and Characterization of Protein Adsorption on Ceramic Surfaces
Authors: Read M. J. , Burkett S. L. , Mayes A. M.
Published: April 2011

Protein adsorption to ceramic surfaces is an important early step in the function of implants. The types and amounts of adsorbed protein and the resulting conformational changes could mediate subsequent cell adhesion and inorganic deposition. Microporous silicoalumino-phosphates, which allow variations in surface composition within the same crystal structure, have been used as model surfaces. Effects of surface composition on adsorption isotherms, elutability, and biological activity of the adsorbed protein layer have been studied using lysozyme, a model protein. Control over protein adsorption mechanisms using well-characterized surface properties could be used to predict the biological properties of surfaces, and engineer coatings for a desired response.
Nanocrystalline Apatites for Bone Reconstruction
Authors: Casalbou S. , Midy V. , Tofighi A. , Lee D. , Dard M. , Rey C.
Published: April 2011

Poorly crystalline apatites (PCA) are characterized by a non-stoichiometric composition, a high specific surface area and the existence of labile, non-apatitic environments detected by spectroscopic techniques. These environments have been shown to belong mainly to an hydrated layer at the surface of the crystals and determine their surface and bulk reactivity. PCA can be easily synthesized in aqueous media and the amount of labile, non-apatitic environments can be modulated by using apatites at different maturation stage. PCA can adsorb many active proteins or drugs, Growth factors (FGF-2, for example), were strongly bound and remained mostly attached to the surface. Several mineral ions which have been shown to have a biological activity such as strontium, can also be trapped at the surface or into the lattice of poorly crystalline apatites. Due to their reactivity, PCA cannot be shaped easily into materials, however, they have the ability to agglomerate irreversibly into solid body at low temperature. These low temperature ceramics show a variable amount of pores (30 to 60 %) and pore size (5 to 25 nm) in which organic components can be trapped and are released only by the dissolution of the ceramic.
Evidence of Anisotropic Thermoelectric Properties in La2/3Ca1/3MnO3 Thin Films Studied by Laser-Induced Transient Voltages
Authors: Habermeier H.-U. , Li Xiaohang , Zhang Pengxiang
Published: April 2011

Pulsed UV laser illumination of doped LaMnO3 thin films deposited on vicinal cut SrTiO3 [ STO ] substrates causes unexpected transient voltages at room temperature in remarkable analogy to those observed for intrinsically anisotropic YBa3Cu3O7−x, [YBCO] thin films. The experimental data for La2/3Ca1/3MnO3 [LCMO] thin films are consistent with the description of thermoelectric fields caused by off-diagonal elements of the Seebeck tensor. Systematic measurements of the dependence of the laser-induced signal on the geometry of the sample, the temperature and doping dependence suggest that the anisotropy of the Seebeck tensor is due to combination of long range co-operative Jahn-Teller distortions and substrate-induced biaxial strain effects.
rf Susceptibility of La1−xSrxMnO3 Single Crystals: Magnetic Signatures of Structural Changes
Authors: Parimi P.V. , Srikanth H. , Bailleul M. , Sridhar S. , Suryanarayanan R. , Pinsard L. , Revcolevschi A.
Published: April 2011

A sensitive tunnel diode oscillator (TDO) technique operating at 4MHz is used to probe the dynamic response of La1−xSrxMnO3 single crystals for x = 0.125, 0.175, 0.28 and 0.33 doping. Systematics of the measured change in reactance (δX) as a function of temperature (30K < T < 320K) and DC magnetic field (0 < H < 6kOe) reveal distinct temperature and field scales associated with the dynamic response of spin. It is notable that these features are far more striking than the corresponding features in static measurements. The results are discussed in the context of structural changes leading to polaron ordering.
Magnetism and CMR in Electron Doped Perovskite and Layered Manganites
Authors: Maignan A. , Martin C. , Hervieu M. , Raveau B.
Published: April 2011

From the magnetic phase diagrams established for Ln1−xAExMnO3 manganites with x>0.5, it is shown that the magnetoresistance is only obtained for compositions of smallest average Asite cations . The magnetic structure study reveals that the small  favors the coexistence of ferromagnetism with G-type antiferromagnetism. It is also shown that ferromagnetism can be induced in the Ln2−xAExMnO4 type electron doped manganites by using compositions with small Ln and AE cations and x values close to 1.90. Finally, manganse site doping by Cr, Co, Ni can be used to weaken the charge-ordering of the Mn4+ rich perovskite manganites (0.5<x≤0.8) and thus to induce CMR properties.
Transport Properties and Magnetism of β-MnO2
Authors: Sato H. , Enoki T. , Wakiya K. , Isobe M. , Ueda Y. , Kiyama T. , Wakabayashi Y. , Nakao H. , Murakami Y.
Published: April 2011

A comprehensive study of transport properties and magnetism on β-MnO2reveals the strong coupling between the conduction electrons and the localized spins which are supposed to form a magnetic helix below TN∼ 92 K. We also show the direct evidences of the helical magnetism by means of the measurements of the anisotropy in the magnetic susceptibility and the observation of x ray magnetic scatterings on a single crystal of β-MnO2. These results are consistent with proper-type helix model proposed by Yoshimori [J. Phys. Soc. Jpn. 14, p. 807 (1959)]. This model also qualitatively agrees with the anisotropy in magnetoresistance that appears belowTN. The pitch of the magnetic helix is not commensurate to the lattice and it is slightly temperature dependent. The intensity of several Bragg peaks drastically changes atTNsuggesting that the magnetic ordering is accompanied by a lattice distortion.
Anomalous Magnetoresistance Effect in Strained Manganite Ultrathin Films
Authors: Li Qi , Wang H. S. , Hu Y. F. , Wertz E.
Published: April 2011

Magnetotransport properties of strained epitaxial Pr2/3Sr1/3MnOz (PSMO) ultrathin films have been studied. The strains are controlled by growing PSMO films on different lattice-mismatched substrates which impose biaxial compressive-, tensile-, and very little strain in the films, respectively. Distinctive magnetoresistance effects in low magnetic field (LFMR) have been observed in films with different types of strain. The films with compressive strain show very large negative LFMR (> 1000 % at 2500 Oe) and significant magnetoresistance hysteresis when a magnetic field is applied perpendicular to the film plane. In a parallel field, the LFMR is much smaller with almost no hysteresis. In contrast, the tensile-strained ultrathin films show positive LFMR at low temperatures in a perpendicular field and a negative LFMR in a parallel field. In comparison, the almost strain-free ultrathin films show very small LFMR (< 2 %) as in single crystal samples at similar temperatures and magnetic fields. In the compressive-strained samples, the large LFMR decreases rapidly with increasing film thickness. These results are interpreted based on spin dependent scattering at the domain walls and domain-rotation.
Artificial Control of Magnetic and Magnetoresistive Properties in the Perovskite Manganites Superlattices and Their Multilayers With Organics
Authors: Tabata H. , Ueda K. , Matsui H. , Saeki H. , Kawai T.
Published: April 2011

Artificial superlattice of LaFeO3-LaMnO3 have been formed on SrTiO3(111), (110) and (100) substrates with various stacking periodicity using pulsed laser deposition. Their magnetic properties have been controlled by altering the ordering of magnetic ions (Fe or Mn). Charge disproportionate behaviors are also observed in these superlattices. For the superlattices on (111) plane, all the samples showed ferromagnetic (or ferrimagnetic) behaviors and the same Curie temperature of 230K. In the case of other superlattices formed on (110) and (100), oh the other hand, the increase of the spin frustration effect between LFO-LMO interface with decrease of the stacking periodicity causes reduction of Tc and magnetization. Specially, spin glass like behaviors observed in the superlattices of less than 3/3 stacking periodicity Furthermore, we have constructed heterostructures of Organic/Inorganic multilayers with a sequence of Copper phthalocyanine(CuPc), BaTiO3 and (LaSr)MnO3. In this system, magnetoresistant properties have been controlled by the photo irradiation through the lattice strain and/or induced charges caused by the piezo effect and electric field effect. That is magnetoresistance in the (LaSr)MnO3 layer can be controlled by the shining the light.
Prospects of Room-Temperature Microbolometer Based on CMR Thin Films
Authors: Verevkin A. , Noginova N. , Gillman E.S.
Published: April 2011

We discuss performance of CMR-based bolometers for pulse and modulated electromagnetic radiation detection. Ultimate characteristics of CMR thin film-based bolometers are considered based of current experimental studies of photoresponse.
Magnetoresistance in Thin Films of Silver Chalcogenides
Authors: Chuprakov I.S. , Lyalikov V.B. , Dahmen K.-H. , Xiong P.
Published: April 2011

Oriented and non-oriented thin films of silver(I) telluride, Ag2Te, were prepared by e-beam evaporation, vapor transport technique and Chemical Vapor Deposition (CVD). Crystallinity and orientation of the films were studied by Θ−2Θ XRD, rocking curve and pole figure measurements. The origin and conditions for the oriented growth are discussed. Special microdevice was prepared by photolitography from the oriented films of Ag2Te in order to investigate magnetoresistance (MR) in this material. It was proved that the reported earlier negative MR in Ag2Te films is a completely geometrical effect, which can be observed using non-linear arrangement of current and voltage contacts.
Narrow-Linewidth Yttrium Iron Garnet Films for Heterogeneous Integration
Authors: Levy M. , Osgood R.M. , Rachford F. J. , Kumar A. , Bakhru H.
Published: April 2011

We report on the fabrication and characterization of single-crystal films of yttrium iron garnet (YIG) for heterogeneous integration onto growth-incompatible substrates. The process entails the implantation of energetic helium ions into the material, resulting in the formation of a fast etching sacrificial layer. Separation from the growth substrate is followed by an annealing step, yielding a ferromagnetic resonance (FMR) linewidth of 0.70 Oe from a virgin sample of linewidth 0.55 Oe. Magnetization measurements show a distinct softening of the in-plane response to an applied field.
Performance of a Ferroelectric Tunable Pre-Select Filter/Low Noise Amplifier Hybrid Circuit
Authors: Subramanyam Guru , Miranda Felix A. , Romanofsky Robert R. , Keuls Fred Van , Chen Chonglin
Published: April 2011

In this paper we discuss the performance of a proof-of-concept of a tunable band pass filter (BPF)/Low Noise Amplifier (LNA) hybrid circuit for a possible gain-compensated down-converter targeted for the next generation of K-band satellite communication systems. Electrical tunability of the filter is obtained through the nonlinear electric field dependence of the relative dielectric constant of a ferroelectric thin-film such as strontium titanate (SrTiO3) or barium strontium titanate (BaxSr1−xTiO3). Experimental results show that the BPFs are tunable by more than 5%, with a bipolar biasing scheme employed. The BPF/LNA tunable hybrid circuit was used to study the effect of tuning on the hybrid circuit's performance especially on the amplifier's noise-figure and the gain.
Junctions for Deep Sub-100 NM MOS: How Far will Ion Implantation Take Us?
Authors: Gossmann H.-J. , Rafferty C. S. , Keys P.
Published: April 2011

We analyze the requirements that the International Technology Roadmap for Semiconductors (ITRS) implicitly imposes on the two-dimensional source/drain (SD) dopant profile and translate the results into implant parameters (energy, dose, peak concentration). We do this by determining the voltage drop that the SD current develops across the three main (exclusive of the channel) resistive components in the current path: the spreading resistance in the extension region; the metal-semiconductor contact; and the resistance in the link-up region where the SDregion meets the channel. The largest resistance occurs in the link-up region, followed by the resistance of the contact; the extension contribution is the smallest. The extension resistance requirement can be satisfied by ion-implantation for all generations of the ITRS. The link-up region requires very abrupt lateral profiles, not demonstrated so far by ion-implantation. It is found that such resistance cannot be reduced without impacting the intrinsic device behavior. The contact eventually necessitates dopant concentrations in excess of solid solubility and for NMOS in excess of the fundamental limit of dopant activation.
Ultrashallow Junction Formation and Gate Activation in Deep-Submicron CMOS
Authors: Stolk P. A. , Cubaynes F. N. , Meyssen V. M. H. , Mannino G. , Cowern N. E. B. , Zijl J. P. van , Roozeboom F. , Verhoeven J. F. C. , Berkum J. G. M. van , Wijgert W. M. van de , Schmitz J. , Tuinhout H.P. , Woerlee P. H.
Published: April 2011

This paper addresses the optimization of ion implantation and rapid thermal annealing for the fabrication of shallow junctions and the activation of polycrystalline silicon gates in deepsubmicron CMOS transistors. Achieving ultrashallow, low-resistance junctions was studied by combining low-energy B and As implantation with spike annealing. In addition, experiments using B doping marker superlattices were performed to identify the critical physical effects underlying dopant activation and diffusion. The combination of high ramp rates (∼100 °C/s) and ∼1 s cycles at temperatures as high as 1100 °C can be used to improve dopant activation without inducing significant thermal diffusion after TED has completed. MOS capacitors were used to identify the implantation and annealing conditions needed for adequate activation of the gate electrode. In comparison to the conventional recrystallized amorphous Si gates, it was found that fine-grained poly-Si allows for the use of lower processing temperatures or shorter annealing times while improving the gate activation level. The fine-grained crystal structure enhances the de-activation of B dopants in PMOS gates during the thermal treatments following gate activation. Yet, the resulting dopant loss stays within acceptable limits as verified by excellent 0.18 μm device performance. The feasibility of spike annealing and poly-Si gate materials for 100-nm technology was proven by full integration using gate lengths down to 80 nm.
Analysis and Suppression of Process-Induced Defects in Memory Devices.
Authors: Annunziata R. , Bottini R. , Colpani P. , Cremonesi C. , Ghidini G. , Gomiero E. , Pavia G. , Pio F. , Polignano M. L. , Servalli G. , Higgs V.
Published: April 2011

In this paper we show that dopant decoration of process-induced defects is responsible for a failure mechanism of memory devices. From the electrical point-of-view, the defect-related failure consists in a source-to-drain resistive path formed by junction piping. This mechanism is made active by the very close spacing which is typical of present device structures. A device-like test structure is used for defect detection. This structure proves to be a very effective tool for studying the impact of various process steps on defect generation, in that it allowes statistical data about the formation of these defects to be collected. TEM analyses are extensively used for studying the evolution of end-of-range defects during subsequent thermal treatments and for measuring the amorphous layer width under various implantation conditions.

The role of high dose implantations in the generation of this sort of defects is discussed. Even if the amorphous layer is completely recovered by a suitable recristallization annealing, residual defects grow and become dopant-decorated during post-implantation thermal treatments. Defect density is increased by oxidizing treatments. In this case point defect injection is active both in enhancing dopant diffusion and in growing defects.

Defect formation is suppressed if the amorphous layer is made very shallow (≤ 50 nm) by suitable choices of the screen oxide and of the implantation energy. A binary collision code is used in order to estimate the dependence on energy of the self-interstitial excess outside the amorphous region. The results of these calculations indicate that defect suppression can be tentatively explained by point defect annihilation at the silicon surface.
Ultra - Shallow p+/n Junction Formed by Plasma Ion Implantation
Authors: Baek Sungkweon , Choi Chel-Jong , Seong Tae-Yeon , Hwang Hyunsang , Kim H. K. , Moon D. W.
Published: April 2011

We have investigated the electrical characteristics, junction depth and defect of ultrashallow junctions formed by using a plasma doping procedure. Compared with ultralow energy boron ion implantation at 500eV, the plasma doping process exhibits both a shallow junction depth and a low sheet resistance. The junction depths of the plasma doped samples were 15 nm and 33 nm after annealing for 10s at 900 °C and 950 °C, respectively. For the same junction depth, the sheet resistance of the B2H6 plasma doped sample is an order of magnitude less than that of the 500eV B ion implanted sample. Based on cross-sectional transmission electron microscope (TEM) and deep level transient spectroscopy (DLTS) analysis, the defects formed by the B2H6 plasma doping process can be completely removed by annealing at 950 °C for 10s.
Post-Oxidation Enhanced Diffusion of Low-Energy Implanted Boron in Ultra-Shallow P+/N Junctions Formation
Authors: Lenoble D. , Halimaoui A. , Grouillet A.
Published: April 2011

In this paper, we report for the first time the effect of sacrificial oxide (sacox) on the boron diffusion in ultra-shallow P+/N junctions. It is shown that the boron diffusivity is enhanced when low energy implantations are performed through sacrificial oxide. The various experimental data lead to conclude that the Post-Oxidation Enhanced Diffusion (POED) is due to a « mirror effect » seen by the Si interstitials incoming into the sacox layer. POED occurs even for sacox as thin as 1.5 nm. From a simple model, the reflection coefficient is estimated to be about 100 % for a 2.5 nm-thick sacox.
A Historical View of the Role of Ion-Implantation Defects in PN Junction Formation for Devices
Authors: Fair R.B.
Published: April 2011

The early use of ion bombardment of semiconductors for forming doped regions was viewed as a room-temperature process by solid-state scientists. Many interesting, but relatively useless devices were made by implanting species such as Na and Cs ions to form pn junctions from radiation damage or interstitial impurities. The revolutionary idea that one could implant Group III and V dopants into semiconductors and then heat the implanted substrate to above 800C didn't appear until 10 years after Shockley's 1954 patent. At that time, implantation damage became relatively unimportant as processes evolved with high temperature, long time diffusions. With the advent of rapid thermal processing, the attention shifted back to implantation-induced defects to explain transient-enhanced-diffusion effects. Today's challenges in forming ultra-shallow junctions by ion-implantation are in controlling and minimizing the damage structures that dominate junction activation and diffusion. Low-energy implants have been effective in this regard.
A Comparative Study of Dose Loss and Diffusion for B11 and BF2 Implants
Authors: Kasnavi Reza , Griffin Peter B. , Plummer James D.
Published: April 2011

We have studied dose loss for B11 and BF2 implants with energies ranging from 10 keV to 1keV for B11 and 45 keV to 2keV for BF2. We found that B11 implants during a 1050C-10s RTA anneal segregate mainly to the bulk of the oxide. High dose BF2 implants on the other hand, show significantly larger amounts of dose loss after stripping the oxide, due to a pile-up of boron at the Si/SiO2 interface. In order to simulate B11 diffusion we have introduced a simple average cluster size model to simulate Boron-Interstitial-Cluster (BIC) evolution. For BF2 implants, we have simulated the effect of F by reducing the damage and we have used interface traps to account for the dose loss observed experimentally. Using these models, we have been able to fit the SIMS profiles across the whole matrix of implant conditions for both B11 and BF2 implants.
Effect of Ge Pre-amorphization on Junction Characteristics for Low Energy B Implants
Authors: Liu Jinning , Mehta Sandeep
Published: April 2011

The drive towards developing deep sub-micron CMOS devices places more challenges on semiconductor processing. From the standpoint of doping technology, the challenge is to achieve ultra-shallow p+/n source/drain extension junctions for PMOS. Among the various approaches being pursued to meet this challenge, pre-amorphization was used to curtail channeling of the as-implanted Boron. The effect of pre-amorphization on junction depth and junction sheet resistance in the ultra-low implant energy regime is investigated in this study. Pre-amorphization was achieved with Ge implant. B was implanted at energies of 250eV to 5keV and at a dose of 1×1015cm−2 into crystalline and pre-amorphized wafers. Both spike anneal at 1050°C and furnace anneal at 500°C to 750°C were performed after B implants. In all spike anneal cases, the pre-amorphized wafers exhibit higher sheet resistance and shallower junction depth than crystalline wafers. In all furnace anneal cases, shallower junction depth as well as lower sheet resistance can be achieved with pre-amorphized wafers. Higher pre-amorphization energy induces lower sheet resistance after both furnace and rapid thermal anneal (RTA).
Non-destructive, In-line Characterization of Shallow Junction Processes
Authors: Kluth G. Jonathan , Bechtler Laurie , Borden Peter , Mi Jian
Published: April 2011

This paper describes the application of a novel optical metrology tool to in-line monitoring of shallow junction processes in a production setting. Recent results demonstrate the sensitivity of junction depth to implant dose and energy, as well as to annealing temperature and time. Results are also presented on monitoring of amorphizing implants and low dose implants. The in-line measurement has been performed on both bare wafers and product wafers. Measurements are compared with results obtained by destructive techniques such as SIMS and SRP. These results demonstrate that the optical method has the capability to provide in-line control of shallow junction processes.
Non-destructive Characterization of Activated Shallow B and as Implants in full NMOS and PMOS Process Flows
Authors: Borden Peter G. , Bechtler Laurie , Larson Lawrence , Murto Bob , Covington Billy , Ferguson Clarence , Nguyen Billy
Published: April 2011

A new method for non-destructive, small area characterization of ultra-shallow junctions, called Carrier Illumination™ (CI) has recently been developed. This work validates the CI measurement in full CMOS and NMOS process flows, with the aim of demonstrating its capability to provide in-line characterization of junction depth and uniformity on product wafers. Measurements have been carried out on both unpatterned and patterned wafers at various steps in the SEMATECH standard process flow. CI was used to characterize annealed 800 eV B11 PLDD implants into n-wells and annealed As75 NLDD source/drain (S/D) implants into p-wells. This work demonstrates correlation to dose, junction depth as measured with SIMS and SRP, and electrical properties of test structures.

(1) Proceedings of the Fifth International Workshop on Measurement, Characterization and Modeling of Ultra-Shallow Doping Profiles in Semiconductors, usj-99, Research Triangle Park, NC, March 1999, pp. 314-18.
Energy Dependence of Transient Enhanced Diffusion and {311} Defect Kinetics
Authors: Saleh Hugo , Law Mark E. , Bharatan Sushil , Jones Kevin S. , Krishnamoorthy Wish , Buyuklimanli Temel
Published: April 2011

Boron, a P-type dopant, experiences Transient Enhanced Diffusion (TED) via interstitials. The Boron TED and {311} dissolution rates are explored as a function of implant energy dependence. Silicon implants of 1014/cm2 at 20, 40, 80, and 160 keV were used to damage the surface of a wafer with an epitaxially grown boron marker layer. Samples were annealed at 750°C for 15 to 135 minutes and 800°C for 10 to 30 minutes to observe the diffusion exhibited by the marker layer and to correlate this with the dissolution of {311} type defects. The diffusion enhancement depends strongly on implant energy but the {311} dissolution rate is weakly dependent.
Depth Profiles of High-energy Recoil Implantation of Boron into Silicon
Authors: Shao Lin , Lu Xinming , Jin Jianyue , Li Qinmian , Rusakova Irene , Liu Jiarui , Chu Wei-Kan
Published: April 2011

We have studied boron profiles by using the ion beam recoil implantation. A boron layer was first deposited onto Si, followed by irradiation with Si ions at various energies to knock the boron. Conventional belief is that the higher the implantation energy, the deeper the recoil profiles. While this is true for low-energy incident ions, we show here that the situation is reversed for incident Si ions of higher energy due to the fact that recoil probability at a given angle is a strong function of the energy of the primary projectile. Our experiments show that 500-keV high-energy recoil implantation produces a shallower B profile than lower-energy implantation such as 10 keV and 50 keV. The secondary-ion-massspectrometry (SIMS) analysis shows that the distribution of recoiled B atoms scattered by the energetic Si ions agrees with our calculation results. Sub-100 nm p+/n junctions have been realized with a 500-keV Si ion beam.
Influence of Carbon on the Diffusion of Interstitials and Boron in Silicon
Authors: Law Mark E. , Griglione Michelle D. , Northridge Misty
Published: April 2011

Carbon is a native impurity in Si which is known to trap self-interstitials and decrease their diffusivity. Carbon has also been observed to decrease B transient enhanced diffusion (TED) in Si through these interstitial interactions. Recently it has been proposed that vacancies must also be considered when accounting for the reduction of B TED. We have incorporated both the kick-out mechanism and the Frank-Turnbull (F-T) mechanism in simulations of interstitial diffusion and carbon diffusion, as well as experiments involving B diffusion in B doped superlattices (DSLs) with varying C concentration regions. We have used the binding energy between a carbon atom and a self-interstitial as a basis for the reaction rates for both mechanisms, and have found that an single energy of 2.25 eV best reproduces the results from several experiments, assuming equilibrium initial conditions for both mechanisms and ab-initio equilibrium values for all point defects.
Calibration of the Au Labeling Technique to Measure Vacancy Defects in Si
Authors: Kalyanaraman R. , Haynes T. E. , Venezia V. C. , Jacobson D. C. , Gossmann H.-J. , Rafferty C. S.
Published: April 2011

It has been shown recently that Au labeling can be used to profile vacancy-type defects located near half the projected range (½Rp) in MeV-implanted Si. In this work we have quantified the technique by determining the ratio of vacancies annihilated to decrease in the number of Au atoms trapped (calibration factor ‘k’) for the Au labeling technique. The 3 step experiment involved: 1) a high-energy Si-self implant (HEI) followed by an anneal to form stable vacancy clusters, 2) a controlled removal of vacancies via a medium energy Si self implant and interstitial-cluster dissolution anneal, and finally 3) Au labeling to count the change in vacancy concentration in the near surface region (0.1-1.6μm). It is seen that the Au concentration decreases linearly with increasing interstitial injection and the slope of this decrease determined the number of vacancies per trapped Au atom. The value of k was determined to be 1.2±0.2 vacancies per trapped Au atom.
Structural and Chemical Characterization of Tungsten Gate Stack for 1 Gb Dram
Authors: Gluschenkov O. , Benedict J. , Clevenger L.A. , DeHaven P. , Dziobkowski C. , Faltermeier J. , Lin C. , McStay I. , Wong K.
Published: April 2011

Material interaction during integration of tungsten gate stack for 1 Gb DRAM was investigated by Transition Electron Microscopy (TEM), X-ray Diffraction analysis (XRD) and Auger Electron Spectroscopy (AES). During selective side-wall oxidation tungsten gate conductor undergoes a structural transformation. The transformation results in the reduction of tungsten crystal lattice spacing, re-crystallization of tungsten and/or growth of grains. During a highly selective oxidation process, a relatively small but noticeable amount of oxygen was incorporated into the tungsten layer. The incorporation of oxygen is attributed to the formation of a stable WO x (x<2) composite.
Thin Ni-Silicides for Low Resistance Contacts and Growth of Thin Crystalline Si Layers
Authors: Guliants Elena A. , Anderson Wayne A.
Published: April 2011

A new technological method of producing the Ni silicide with metal-like conductivity by deposition of a thin Si film over an ultrathin Ni prelayer at low temperature has been developed. The interaction of a metallic Ni with the Si atoms provided by the deposition source leads to the formation of the Ni-rich silicide phases immediately after the onset of Si deposition. Continued Si deposition results in the transformation of the Ni-rich silicide phases into the more Si-rich ones which implies that the phase composition is controlled by the Ni-to-Si concentration ratio rather than temperature. After Ni is completely consumed, the Si grains grow epitaxially on the disilicide crystals. The silicide layer has been studied in detail with respect to both the dynamics of the silicide growth and the electrical properties. The Ni silicide resistivity was found to be 2×10-4Ωcm. The technique has advantages in two respects: it provides a high crystallinity Si film and allows fabrication of an ohmic contact directly on the substrate thus leaving the front surface of the film available for the formation of the active device junction.
Effects of Nitridation by N2O or No on the Electrical Properties of Thin Gate or Tunnel Oxides
Authors: Gerardi C. , Rossetti T. , Melanotte M. , Lombardo S. , Crupi I.
Published: April 2011

We have studied the effects of nitridation on the leakage current of thin (7-8 nm) gate or tunnel oxides. A polarity dependence of the tunneling current has been found this behavior is related to the presence of a thin silicon oxynitride layer at the SiO2/Si-substrate interface. The oxynitride layer lowers the tunneling current when electrons are injected from the interface where the oxynitride is located (substrate injection). The current flowing across the oxide when electrons are injected from the opposite interface (gate injection) is not influenced by the oxynitride. The increase of nitrogen concentration leads to a decrease of the tunneling current for substrate electron injection.
Silicide engineering: influence of alloying elements on CoSi2 nucleation
Authors: Detavernier C. , Van Meirhaeghe R.L. , Maex K. , Cardon F.
Published: April 2011

Evidence is presented that the nucleation of CoSi2 can be influenced by the presence of small amounts of other elements. The presence of trace amounts of Ti in the CoSi (originating from either a Ti capping layer or interlayer) causes an increase in the CoSi2 nucleation temperature. Moreover, the presence of Ti in the CoSi induces a preferential orientation of the CoSi2 : for an increasing amount of Ti, we observed a transition from polycrystalline CoSi2 over preferential (220) orientation towards epitaxial (400) CoSi2. We observed similar effects for other elements (e.g. Ta, W, C, Mo, Cr). We were able to explain these findings based on the heterogeneous nucleation of CoSi2.
Modeling of Self-Aligned Silicidation in 2D and 3D: Growth Suppression by Oxygen Diffusion
Authors: Moroz Victor , Okada Takako
Published: April 2011

Stress-strain effects and physical processes during formation of the self-aligned silicides are analyzed. A new model for predictive simulation of the self-aligned silicidation is suggested. The model is based on suppression of diffusion and reaction rate of the silicon atoms inside silicide in the presence of oxygen atoms, injected into silicide from the neighbor oxide regions such as oxide spacer, TEOS at STI (Shallow Trench Isolation) and pad oxide. The model is demonstrated to explain the experimentally observed silicide shape.
Planarization of Cu and Ta Using Silica and Alumina Abrasives - A Comparison
Authors: Li Y. , Ramarajan S. , Hariharaputhiran M. , Her Y. S. , Babu S.V.
Published: April 2011

Experimental results on chemical mechanical polishing of copper and tantalum in the presence of different chemicals, such as Fe(NO3)3, H2O2 and glycine, using both silica and alumina abrasive particles are presented. The polish rates with alumina slurries vary in accordance with the hardness of the material being polished, suggesting a dominant role for a wear mechanism. However, polish rates with silica slurries do not relate directly to the hardness of the film, indicating a more complex removal mechanism.
Optical Characterization of Porous Membranes
Authors: Mujat Claudia , Denney Lorrene , Dogariu Aristide
Published: April 2011

Multiple light scattering techniques are intensively investigated as potential characterization tools for a broad range of applications. We are reporting on the noninvasive characterization of filters used in processes such as slurries filtering for CMP.

Filters are soft porous membranes characterized by their pore size distribution and thickness, and a noncontact, nondestructive optical procedure to measure these properties is highly desirable. Due to their internal inhomogeneity, porous media strongly scatter light and, therefore, a specific procedure needs to be developed.

In this work, low coherence interferometry is used to investigate light propagation in the filter and obtain the reflectivity as a function of optical pathlength for backscattered photons. This can be subsequently related to the optical properties of the sample using analytical and/or numerical models, and the porosity of the sample can be determined. In the case of filters with thicknesses much larger than the wavelength, a diffusion approximation for light propagation is used to infer the porosity information. For thinner membranes, numerical methods are used to describe the intermediate low-scattering regime that can not be represented analytically. As a direct result of the measurement, the thickness of the filter is determined independent of porosity.
Dynamic Mechanical Analysis (DMA) of CMP pad materials
Authors: Li Irene , Forsthoefel Kersten M. , Richardson Kathleen A. , Obeng Yaw S. , Easter William G. , Maury Alvaro
Published: April 2011

In the semiconductor industry, there is a need to establish fundamental, mechanism-based, correlation(s) between process conditions, consumables (e.g., pads and slurries), and observed process performance in Chemical-Mechanical Polishing (CMP). In this paper, we present recent results of studies on polyurethane-based CMP pads in static and dynamic conditions using Dynamic Mechanical Analysis (DMA) to monitor modulus and energy damping changes. Two-layered, composite IC1000 on Suba IV pads, [IC1000 (cast and cured polyurethane elastomer) / Suba IV (polyurethane impregnated polyester felt)], were analyzed: prior to use (fresh); after a 24-hr soak in silica-containing oxide slurry (basic); and after oxide polishing (used). Upon comparison it was observed that a characteristic transition feature due to water is present at sub-ambient temperatures in both the slurry soaked and used pads. Exposure of as-received pads to basic oxide slurry results in a broad, high temperature transition thought to be the result of chemical-induced disruption of macrostructural units. Polishing (load-enhanced chemical exposure) introduces further changes to the polymer network represented by an apparent degradation to the structural species responsible for the high temperature transition in Suba IV.
An Evaluation of the Effects of Benzotriazole in NH4OH Slurry for Copper CMP
Authors: Len V.S.C. , Mcneill D.W. , Gamble H.S.
Published: April 2011

Chemical mechanical polishing (CMP) of copper using alumina-based NH4OH slurry containing benzotriazole (BTA) has been evaluated in terms of polish efficiency and viability. Dishing of damascene copper patterns can result from a combination of chemical dissolution and mechanical abrasion due to the deformed polishing pad bending into the recessed copper regions. The addition of at least 0.1 wt.% BTA to the slurry leads to the formation of a thin Cu(I)-BTA polymer on the copper surface during CMP. This polymer reduces the amount of dishing by an order of magnitude. At the same time, however, the CMP polish rate falls sharply with the addition of 0.1 - 0.25 wt.% BTA to the slurry. Above 0.25 wt.% BTA, the polish rate falls no further. Stability of alumina particles in the NH4OH slurry is found to deteriorate with the addition of BTA. Integrated copper/barrier electromigration resistance test structures with large contact areas (2×2mm) have been successfully patterned using a 2-step CMP/etching process scheme, using a BTA-containing slurry to minimise dishing.
Fundamental Study of Iodate and Iodine Based Slurries for Copper CMP
Authors: Lee Seung-Mahn , Mahajan Uday , Chen Zhan , Singh Rajiv K.
Published: April 2011

The chemical mechanical polishing of copper in several slurry chemistries based on iodate and iodine oxidizers has been investigated. Benzotriazole (BTA) and potassium iodide (KI) were used for preparing the polishing slurry chemistries based iodate. As observed by the anodic electrochemical behavior of copper and the surface analyses of EDS, it was determined that CuI layer formed in the iodate and iodine based solutions. Especially, in I2 slurry in pH 4, CuI layer formed very fast and uniformly, and passivated the copper. In addition, the highest removal rate using this slurry was obtained. These results were compared to H2O2 based slurries. From these experimental results, the slurry containing 0.1M KIO3 and 0.01M KI, and 0.01N I2 give better results than H2O2 based slurry in copper CMP.
Planarization of Copper Damascene Interconnects by Spin-Etch Process: A Chemical Approach
Authors: Mukherjee Shyama P. , Levert Joseph A. , DeBear Donald S.
Published: April 2011

The present work describes the process principles of “Spin-Etch Planarization” (SEP), an emerging method of planarization of dual damascene copper interconnects. The process involves a uniform removal of copper and the planarization of surface topography of copper interconnects by dispensing abrasive free etchants to a rotating wafer. The primary process parameters comprise of (a) Physics and chemistry of etchants, and (b) Nature of fluid flow on a spinning wafer. It is evident, that unlike conventional chemical-mechanical planarization, which has a large number of variables due to the presence of pads, normal load, and abrasives, SEP has a smaller number of process parameters and most of them are primary in nature. Based on our preliminary works, we have presented the basic technical parameters that contribute to the process and satisfy the basic requirements of planarization such as (a) Uniformity of removal (b) Removal rate (c) Degree of Planarization (d) Selectivity. The anticipated advantages and some inherent limitations are discussed in the context of process principles. We believe that when fully developed, SEP will be a simple, predictable and controllable process.
Structural Characterization of Epitaxial GMR Magnetic Multilayers and Spin Valves Grown by Sputter Deposition
Authors: Geng H. , Loloee R. , Heckman J.W. , Bass J. , Pratt W.P. , Crimp M.A.
Published: April 2011

Epitaxial Cu/Py/FeMn and (Cu/Co)×20 GMR magnetic multilayers were grown on single crystal (011) Nb that was deposited on (1121) Al2O3 substrates by dc magnetron sputtering. Electron backscatter patterns (EBSPs) revealed that the Cu films display two twin variants, corresponding to two stacking sequences of {111} planes in fcc. The epitaxial orientation relationship between the bcc Nb and both fcc Cu variants was the Nishiyama-Wasserman (N-W) relationship. Conventional TEM observations revealed epitaxial growth for both the Cu/Py/FeMn and (Cu/Co)×20 multilayers. High-resolution TEM confirmed epitaxial growth of close packed (011) Nb on (1120) Al2O3 substrates with [111]Nb∥[0001]Al2O3. Numerous small twins were observed in the Cu near the Cu-Nb interface of the Cu/Py/FeMn multilayer. In the Cu/Co multilayer, the growth planes of the Cu and Co were found to be {100} instead of the expected close-packed {111} planes of the fcc structure.