bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructure and Electrical Characteristics of La1−xSrxMnO3 (0.19≤x≤0.31) Thin Films Prepared by Sputter Techniques
Authors: Heo H. , Lim S.J. , Sung G.Y. , Cho N.-H.
Published: April 2011

La1−x SrxMnO3(0.19≤x≤0.31) thin films were prepared on silicon wafers by sputter techniques. The effect of substrate temperature, chemical composition and post-deposition heat-treatment on the crystalline structure and electrical characteristics of the films was investigated. The films grown at a substrate temperature of 500°C were found to be of the pseudo-tetragonal system (0.97≤a/c≤1) and exhibited a strong tendency of {001} planes to lie parallel to substrate surface. With the increase of x, the electrical resistivity of the films decreased and the transition temperature between the metallic and semiconducting electrical transport behaviors shifted to high temperature. With a magnetic field of 0.18 Tesla, the maximum magneto-resistance ratio (MR%) of La0.69Sr0.31MnO3 polycrystalline thin films was about 390%.
Structural and Dielectric Properties of Pulsed Laser Deposited Pb[Yb1/2Nb1/2]O3-PbTiO3 Thin Films
Authors: Bornand Véronique , Trolier-McKinstry Susan
Published: April 2011

Heterostructures consisting of (001) LaAlO3 or (111) SrTiO3 substrates, SrRuO3 metallic oxide bottom electrodes and Pb[Yb1/2Nb1/2]O3-PbTiO3 ferroelectric films were deposited by pulsed laser deposition. The combination of oxidic perovskite-type materials results in highly <001>- or <111>-heteroepitaxial capacitors with well-defined and homogeneous columnar microstructures. Most of the films show room temperature dielectric constant greater than 1500 associated with low dielectric loss (tgδ < 4%) and exhibit saturated hysteresis loops with remanent polarizations up to Pr ∼ 50µC.cm−2. It was found that the ferroelectric characteristics and, in particular, the fatigue phenomena greatly depend on the orientation and crystalline quality of the as-grown films. The stabilization of the <001>-orientation enhances the fatigue resistance and a good endurance up to 1011 cycles has been determined for highly <001>-textured samples. In contrast, fatigue tests performed on strongly <111>-oriented capacitors have revealed poor fatigue performances, with a progressive decrease in the switchable polarization by ac voltage cycling.
Electronic Structure of Tunable Materials MnAl and MnGa
Authors: Chantis A. N. , Demchenko D. O. , Petukhov A. G. , Lambrecht W. R. L.
Published: April 2011

We present first-principle calculations of equilibrium lattice constants, band structures, densities of states and magnetocrystaline anisotropy energy for bulk MnAl and MnGa. The linear-muffin-tin-orbital (LMTO) method has been used within the framework of the local spin density approximation (LSDA). Both the atomic sphere approximation (ASA) and the full-potential (FP) versions of the LMTO method were employed. Calculations of the equilibrium structures were performed both for paramagnetic and ferromagnetic phases of MnAl and MnGa. The results of these calculations indicate that the large tetragonal distortion of the crystal structure is caused by the spin polarization of the electronic subsystem. The magnetocrystalline anisotropy energy per unit cell for MnAl and MnGa is shown to be 0.244 meV and 0.422 meV respectively. This is in good agreement with previous calculations and some experimental data. Magnetic moments, density of states and dependence of magnetocrystalline anisotropy energy on the lattice constant ration c/a are also found to be in good agreement with previous results.
Mechanisms of Dielectric Loss in Microwave Materials
Authors: Tagantsev Alexander
Published: April 2011

The present knowledge on mechanisms for dielectric loss at microwave and higher frequencies is reviewed. A special attention is paid to the intrinsic loss mechanisms. Relation between the loss and the dielectric permittivity as well as the effect of dc electric field on the loss are discussed. The theoretical knowledge is compared to the existing experimental data.
Analysis and Optimization of Thin-Film Ferroelectric Phase Shifters
Authors: Romanofsky R. R. , Keuls F. W. Van , Warner J. D. , Mueller C. H. , Alterovitz S. A. , Miranda F. A. , Qureshi A. H.
Published: April 2011

Microwave phase shifters have been fabricated from (YBa2Cu3 O7-δ or Au)/SrTiO3 and Au/BaxSr1−xTiO3 films on LaAlO3 and MgO substrates. These coupled microstrip devices rival the performance of their semiconductor counterparts at Ku- and K-band frequencies. Typical insertion loss for room temperature ferroelectric phase shifters at K-band is ≈5 dB. An experimental and theoretical investigation of these novel devices explains the role of the ferroelectric film in overall device performance. A roadmap to the development of a 3 dB insertion loss phase shifter that would enable a new type of phased array antenna is discussed.
First Demonstration of a Periodically Loaded Line Phase Shifter Using BST Capacitors
Authors: Nagra Amit S. , Taylor Troy R. , Periaswamy Padmini , Speck James , York Robert A.
Published: April 2011

Periodically loaded line phase shifter circuits using voltage tunable BaSrTiO3 (BST) parallel plate capacitors have been demonstrated at X-band. The first such phase shifter circuit was capable of 100° of phase shift with an insertion loss of 7.6 dB at 10 GHz. Subsequently, the monolithic fabrication procedure was refined resulting in an improved phase shifter circuit with 200° of phase shift and an insertion loss of 6.2 dB at 10 GHz. In addition to promising loss performance (32°/dB) at 10 GHz, the circuits reported here have several desirable features such as moderate control voltages (20 V), room temperature operation, and compatibility with monolithic fabrication techniques.
In-Plane Uniaxial Magnetic Anisotropy of Cobalt Doped Y3Fe5O12 Epitaxial Films
Authors: Dale Darren , Hu G. , Balbarin Vincent , Suzuki Y.
Published: April 2011

In an effort to develop a magnetic biasing layer for potential applications in integrated devices, we have grown thin films of Y3Fe5O12 with increased uniaxial anisotropy by doping with varying Co2+, concentration. To compensate for the charge differential between Co2+ and Fe3+, Ge4+ and Ce4+ are substituted for Fe3+ and y3+, respectively. These garnet films, prepared using pulsed laser deposition on (110) oriented Gd3Ga5O12 substrates, exhibit excellent crystallinity as determined from X-ray diffraction and Rutherford backscattering spectroscopy. The addition of Co2+ in Y3Fe5O12 films enhances the in-plane uniaxial anisotropy over an order of magnitude, depending on composition.
Defect Reduction in Laser Thermal Processing
Authors: Banisaukas Heather , Jones Kevin S. , Talwar Somit , Falk Scott , Downey Dan F.
Published: April 2011

Laser thermal processing (LTP) of Si involves laser melting a preamorphized layer in order to activate dopants and create a low resistivity contact. Defects are often observed to form during the recrystallization of the molten layer. This work focuses on varying the implant conditions and the pre-LTP annealing conditions in an effort to reduce these defect concentrations. The effect of very low temperature anneals (VLTA) and varying dose rates on the amorphous/crystalline interface roughness prior to LTP and the defect density after LTP have been investigated. The amorphous layer was created by a 10 keV 1×1015/cm2 Si+ implant. VLTA were conducted in a nitrogen gas furnace at temperatures between 400°C and 450°C for times between 5 minutes and 60 minutes. These anneals were chosen to minimize recrystallization of the amorphous layer by solid phase epitaxial regrowth. Variation in the dose rate from 0.06 mA/cm2 to 0.48 mA/cm2 was achieved by changing the beam current in the ion implanter. High-resolution crosssectional transmission electron microscopy (HR-XTEM) was used to analyze the effect of the VLTA or dose rate on the amorphous/crystalline interface. Results show that the 400°C 60 minute VLTA or the 0.48 mA/cm2 dose rate reduced the roughness of the amorphous/crystalline interface from over 45Å to around 15Å. This reduction in amorphous/crystalline interface roughness prior to laser thermal processing results in a reduction in LTP recrystallization defects by as much as an order of magnitude.
A Physically Based Modeling of Boron TED in Amorphised Si
Authors: Lampin Evelyne , Senez Vincent , Claveriel Alain
Published: April 2011

We have developed a physically based modeling of TED of implanted boron in amorphised Si. The simulation starts with a supersaturation of Si free interstitials located below the amorphous/crystalline interface which, upon annealing, tend to diffuse out or to precipitate in the form of extended defects (clusters, {113}s, dislocation loops). The modeling of the nucleation and growth of these defects is divided into three distinct stages: the nucleation, the “pure growth” and the Ostwald ripening. This system can interact with a surface (characterized by a given recombination velocity for Si interstitials) only after the SPE regrowth is completed. Implementation of this model into a process simulator allows to describe the isothermal and isochronal evolutions of the sizes and of the densities of dislocation loops in agreement with TEM observations. Assuming that boron diffusion is caused by the concomitant time and space variations of the free interstitial supersaturation in the wafer, TED can be accurately predicted for a variety of experimental conditions.
On the Energetics of Extrinsic Defects in Si and their Role in Nonequilibrium Dopant Diffusion
Authors: Claverie Alain , Cristiano Filadelfo , Colombeau Benjamin , Cowern Nicholas
Published: April 2011

In this paper, we discuss the mechanisms by which small clusters evolve through “magic” sizes into {113} defects and then, at sufficiently high dose levels, transform into dislocation loops of two types. This ripening process is mediated by the interchange of free Si(int)s between different extended defects, leading to a decrease of their formation energy. The calculation of the supersaturation of free Si-interstitials in dynamical equilibrium with these defects shows a hierarchy of levels of nonequilibrium diffusion, ranging from supersaturations S of about 106 in the presence of small clusters, through 103 in the presence of {113} defects, to S in the range 100 down to 1 as loops are formed, evolve and finally evaporate. A detailed analysis of defect energetics has been carried out and it is shown that Ostwald ripening is the key concept for understanding and modelling defect interactions during TED of dopants in silicon.
Effect of N+ Ion Implantation and Gox Process on in and B Channel Profile
Authors: Curello G. , Rengarajan R. , Faul J. , Wurzer H. , Amon J. , Gaertner T. , Henke D. , Schmeide M. , Kieslich A.
Published: April 2011

In this work, we report on the effect of different dual gate oxide (DGox) processes on the electrical properties of CMOS devices in deep submicron embedded DRAM (eDRAM) technology. Also discussed, is the effect of N+ Ion Implantation on the diffusion / segregation behaviour of B and In channel dopants. In particular, it will be shown that the N+ dose required to obtain a certain combination of dual gate oxide thickness varies with the gate oxide process. Effects of N+ dose on the In and B channel profiles are studied using SIMS. The impact of “thickness-equivalent” DGox processes on short channel effect (SCE) and carrier mobility is analyzed and tradeoffs for optimization of device performances are discussed.
Junction Depth Reduction of ion Implanted Boron in Silicon Through Fluorine ion Implantation
Authors: Robertson L. S. , Warnes P. N. , Jones K. S. , Earles S. K. , Law M. E. , Downey D. F. , Falk S. , Liu J.
Published: April 2011

The interaction between boron and excess silicon interstitials caused by ion implantation hinders the formation of ultra-shallow, low resistivity junctions. Previous studies have shown that fluorine reduces boron transient enhanced diffusion, however it is unclear whether this observed phenomenon is due to the fluorine interacting with the boron atoms or silicon self-interstitials. Amorphization of a n-type Czochralski wafer was achieved with a 70 keV Si+ implantation at a dose of 1×1015/cm2. The Si+ implant produced a 1500Å deep amorphous layer, which was then implanted with 1.12 keV 1×1015/cm2 B+. The samples were then implanted with a dose of 2×1015/cm2F+ at various energies ranging from 2 keV to 36 keV. Ellipsometry measurements showed no increase in the amorphous layer thickness from either the boron or fluorine implants. The experimental conditions allowed the chemical species effect to be studied independent of the implant damage caused by the fluorine implant. Post-implantation anneals were performed in a tube furnace at 750° C. Secondary ion mass spectrometry was used to monitor the dopant diffusion after annealing. Transmission electron microscopy (TEM) was used to study the end-of-range defect evolution. The addition of fluorine reduces the boron transient enhanced diffusion for all fluorine energies. It was observed that both the magnitude of the boron diffusivity and the concentration gradient of the boron profile vary as a function of fluorine energy.
Vacancy Enhanced Boron Activation during Room Temperature Implantation and Low Temperature Annealing
Authors: Jina Jian-Yue , Rusakova Irene , Li Qinmian , Liu Jiarui , Chu Wei-Kan
Published: April 2011

Low temperature annealing combined with pre-damage (or preamorphization) implantation is a very promising method to overcome the activation barrier in ultra-shallow junction formation. We have made a 32 nm p+/n junction with sheet resistance of 290 /sq. using 20 keV 4×1014 Ω/cm2 Si followed by 2 keV 1×1015 at./cm2 B implantation and 10 minutes 550 °C annealing. This paper studies the boron activation mechanism during low temperature annealing. The result shows that placing B profile in the vacancyrich region has much better boron activation than placing B profile in interstitial-rich region or without pre-damage. It also shows that a significant portion of boron is in substitutional positions before annealing. The amount of substitutional boron is correlated to the amount of vacancies (damage) by the pre-damage Si implantation. The result supports our speculation that vacancy enhances boron activation.
Boron Implantation into Silicon Subject to Hydrogen Plasma
Authors: Rangan Sanjay , Horn Mark , Ashok S.
Published: April 2011

Alleviating transient enhanced diffusion (TED) is one among several issues that has to be solved to realize deep sub-micron CMOS. In this paper we present the influence of hydrogen plasma on TED of boron, along with deep level transient spectroscopic (DLTS) studies on defect evolution as a function of anneal temperature. The studies reveal that TED monotonically increases as a function of anneal temperature up to 650°C, where maximum TED occurs. Further increase in anneal temperature reveals TED reduction. The DLTS reveals a corresponding increase in defect density up to 650°C and then decreases when annealed at 850°C for the same amount of time.
Effect of Nitrogen Implants on Boron Transient Enhanced Diffusion
Authors: Dokumaci Omer , Ronsheim Paul , Hegde Suri , Chidambarrao Dureseti , Shaik-Adam Lahir , Law Mark E.
Published: April 2011

The effect of nitrogen implants on boron transient enhanced diffusion was studied for nitrogen-only, boron-only, and boron plus nitrogen implants. A boron buried layer was used as a detector for interstitial supersaturation in the samples. Boron dose ranged from 1×1014 to 1×1015 cm−2 and N2+ dose from 5×1013 and 5×1014 cm−2. The energies were chosen such that the location of the nitrogen and boron peaks matched. After the implants, RTA and low temperature furnace anneals were carried out. The diffusivity enhancements were extracted from the buried layer profiles by simulation. Nitrogen-only implants were found to cause significant enhanced diffusion on the buried boron layer. For lower doses, the enhancement of the nitrogen implant is about half as that of boron whereas the enhancements are equal at higher doses. Nitrogen coimplant with boron increases the transient enhanced diffusion of boron at low boron doses, which implies that nitrogen does not act as a strong sink for excess interstitials unlike carbon. At high boron doses, nitrogen co-implant does not significantly change boron diffusion. Sheet resistance measurements indicate that low nitrogen doses do not affect the activation of boron whereas high nitrogen doses either reduce the activation of boron or the mobility of the holes.
Transient Enhanced Diffusion of Arsenic by Self-Implantation —The role of As-I clusters—
Authors: Kim Ryangsu , Aoki Takenori , Furuta Yoshikazu , Kobyashi Hiroyuki , Xia Jianxin , Saito Tomoya , Kamakura Yoshinari , Taniguchi Kenji
Published: April 2011

Transient enhanced diffusion of implanted arsenic in silicon with/without additional self-implantation has been investigated. The experimental results show the suppression of As diffusion with Si self-implantation during initial stage of annealing in contrast to the prediction of conventional models. The results suggest that the arsenic and self-interstitial atoms might form immobile clusters during Si implantation or initial stage of annealing. After the clusters dissolve for further annealing, the transient enhanced diffusion of As increases with silicon implantation dose as expected from the “+1” model. These results clarify that interstitials/ As-I clusters play a major role in transient arsenic diffusion.
The Structure of Plasma-Deposited and Annealed Pseudo-Binary ZrO2-SiO2 Alloys
Authors: Rayner G. , Therrien R. , Lucovsky G.
Published: April 2011

The internal structures of various (ZrO2)x(SiO2)1-x alloys (x ≤ 0.5) were investigated. A remote plasma enhanced-metal organic chemical vapor deposition (RPEMOCVD) process was used to deposit films with varying alloy composition on Si(100) substrates. This study indicates that for the glassy silicate phase, g-ZrSiO4, a glass transition temperature, Tg, exists between 800°C and 900°C at which phase separation into the end-member components, SiO2 and ZrO2, occurs.
Physical and Electrical Properties of Yttrium Silicate Thin Films
Authors: Chambers James J. , Parsons Gregory N.
Published: April 2011

This article reports on the physical and electrical properties of yttrium silicate, which is a possible high-k replacement for the SiO2 gate dielectric in CMOS devices. The yttrium silicate (Y-O-Si) films are formed by sputtering yttrium onto clean silicon, annealing in vacuum to form yttrium silicide and then oxidizing in N2O to form the silicate. Shifts in the Y 3d, Si 2p and O 1s photoelectron spectra with respect to Y2O3 and SiO2 indicate that the films are fully oxidized yttrium silicate. FTIR results that reveal a Si-O stretching mode at 950 cm−1 and Y-O stretching modes in the far-IR are consistent with XPS. XPS and FTIR results are in accordance with the donation of electron density from the yttrium to the Si-O bond in the silicate. The yttrium silicate films contain a fixed charge density of ∼9×1010 cm−2 negative charges as calculated from measured C-V behavior. The properties of ultra-thin yttrium silicate films with an equivalent silicon dioxide thickness (electrical) of ∼1.0 nm will be discussed elsewhere.
Electrical Characteristics of TaOxNy for High-k MOS Gate Dielectric Applications
Authors: Im Kiju , Jung Hyungsuk , Jeon Sanghun , Yang Dooyoung , Hwang Hyunsang
Published: April 2011

In this paper, we report a process for the preparation of high quality amorphous tantalum oxynitride (TaOxNy) via ammonia annealing of Ta2O5 followed by wet reoxidation for use in gate dielectric applications. Compared with tantalum oxide(Ta2O5), a significant improvement in the dielectric constant was obtained by the ammonia treatment followed by light reoxidation in a wet ambient. We confirmed nitrogen incorporation in the tantalum oxynitride (TaOxNy) by Auger Electron Spectroscopy. By optimizing the nitridation and reoxidation process, we obtained an equivalent oxide thickness of less than 1.6nm and a leakage current of less than 10mA/cm2 at -1.5V. Compared with NH3 nitridation, nitridation of Ta2O5 in ND3 improve charge trapping and charge-to-breakdown characteristics of tantalum oxynitride.
Ultra-thin Gate Oxide Prepared by Nitridation in ND3 for MOS Device Applications
Authors: Kwon Hyungshin , Hwang Hyunsang
Published: April 2011

The electrical and reliability characteristics of ultra-thin gate oxide, annealed in ND3 gas, have been investigated. Compared with a control oxide, which had been annealed in NH3, the ND3-nitrided oxide exhibits a significant reduction in charge trapping and interface state generation. The improvement of electrical and reliability characteristics can be explained by the strong Si-D bond at the Si/SiO2 interface. This nitridation process of gate dielectric using ND3 has considerable potential for future ultra large scaled integration (ULSI) device applications.
Zr Oxide Based Gate Dielectrics with Equivalent SiO2 Thickness of Less than 1.0 nm and Device Integration with Pt Gate Electrode
Authors: Ma Yanjun , Ono Yoshi
Published: April 2011

ZrO2 films are investigated as an alternative to SiO2 gate dielectric below 1.5nm. A maximum accumulation capacitance ∼35 fF/μm2 with a leakage current of less than 0.1 A/cm2 has been achieved for a 3 nm Zr-O film, suggesting that ZrO2 can be scaled to below an equivalent oxide thickness of 0.5 nm. Al and Si doping is also investigated to reduce leakage currents and to increase the crystallization temperature of the film. Submicron MOSFETs with TiN or Pt gate electrodes have been fabricated with these gate dielectrics with excellent characteristics, demonstrating the feasibility of CMOS process integration. In particular, Pt damascene gate PMOS is shown to have the proper threshold voltage for dual metal gate CMOS application.
Low-Oxygen Nitride Layers Produced by UHV Ammonia Nitridation of Silicon
Authors: Shriver Mark A. , Higman T.K. , Campbell S.A. , Taylor Charles J. , Roberts Jeffrey
Published: April 2011

If chemically vapor deposited high permittivity materials such as TiO2 and Ta2O5 are to gain wide acceptance as alternatives to SiO2 gates in silicon MOSFETs, the interface between the deposited high-k material and the silicon must be abrupt and have a low density of electrically active defects. Unfortunately, the process for depositing these materials often produces an unacceptably thick, low-permittivity amorphous layer at the interface, which reduces the effectiveness of the high-k material and often contains unacceptably large numbers of charge states. One way to prevent this layer from forming is to deliberately introduce a very thin layer of Si3N4 to act as a diffusion barrier prior to deposition of the high-k material. Previous work has shown nitrides to have high concentrations of traps and interface states, but these films also had considerable oxygen contamination, particularly at the nitride-silicon interface. In this paper, we show that direct thermal nitridation of the silicon surface in ammonia can provide a low interface state density surface that is also an excellent diffusion barrier. A key feature of this process is the various techniques needed to obtain very low oxygen incorporation in the Si3N4. Even at the Si3N4-Si interface, the oxygen content was near the detection limits (0.5%) of Auger Electron Spectroscopy (AES). The nitride films were grown in a range of temperatures that resulted in self-limited thicknesses from a few monolayers to a few nanometers. These films were then characterized by Auger, Time-of-Flight SIMS, and in the case of the thicker films, capacitance-voltage techniques on both n- and p-type silicon substrates. The data shows very low levels of oxygen contamination in the nitride films and low interface state densities in capacitors fabricated from this material.
Integration Challenges for Advanced Salicide Processes and their Impact on CMOS Device Performance
Authors: Wieczorek K. , Horstmann M. , Engelmann H.-J. , Dittmar K. , Blum W. , Sultan A. , Besser P. , Frenkel A.
Published: April 2011

CoSi2 has emerged as the silicide of choice for 0.18μm CMOS technologies and below. Robustness and scaling-performance of an integrated CoSi2-module, however, is shown to critically depend upon careful optimization of each individual process-step. The impact of surface-preparation, capping layer, initial Co-thickness and thermal processing will be discussed. The scalability of an optimized process meeting all major requirements for application to ULSI devices is demonstrated for gate-length down to 60nm.
Effect of a thin Ta layer on the C49-C54 transition.
Authors: Via F. La , Mammoliti F. , Grimaldi M.G. , Quilici S. , Meinardi F.
Published: April 2011

The effect of a thin Ta layer at the Ti/Si interface on the kinetic of the C49-C54 transition will be shown in detail. The transformation kinetic has been monitored by in situ sheet resistance measurements that, coupled to structural characterisation, allowed to evidence the presence of an intermediate phase before the C54 formation. The temperature of the C54 phase formation decreases with a Ta concentration of 4.5·1015 cm−2 and μ-Raman images of partially transformed samples indicates that the density of C54 grains in presence of Ta is about one order of magnitude higher with respect to pure Ti/Si samples.
Hot Wall Isothermal RTP for Gate Oxide Growth and Nitridation
Authors: Laser Allan , Ratliff Christopher , Yao Jack , Bailey Jeff , Passefort Jean-Claude , Vaughan Eric , Page Larry
Published: April 2011

A new system that incorporates many benefits of large batch furnaces (high quality films, growth of wet and dry oxides, chlorine capability, and low cost) into a single wafer processing module has been developed at SVG Thermal Systems. The problems associated with wafer temperature measurement and control in traditional lamp based RTP systems are avoided by utilizing a hot wall isothermal processing chamber. Unique fixturing is used to minimize thermal stress on the wafer during ramping. High quality gate oxides ranging in thickness from 20Å to 40Å have been grown in this system using both wet and dry oxidation ambients, with and without chlorine. Thin oxides grown in dry oxygen had 1-sigma uniformities in the range of 0.72-0.95%, while oxides grown in oxygen/HCl (1-3%) had uniformities of 0.80%. Steam grown oxides demonstrated growth rates of 100Å/min at 900°C and uniformities of 0.62%. Dry oxides annealed in NO and N2O had peak nitrogen incorporation levels ranging from 0.5 to 5.1 atomic percent depending on anneal ambient, temperature and time.
On the Template Mechanism of Enhanced C54-TiSi2 Formation
Authors: Kappius L. , Tung R. T.
Published: April 2011

The enhanced formation of the C54-TiSi2 phase by the addition of small amounts of refractory metal (Tm = Mo, Ta, Nb,..) has often been ascribed to a template mechanism from the C40 TixRm1−xSi2 or the (Ti,Rm)5Si3 phase. Due to lattice matching conditions, the presence of either of these phases is thought to lower the interface energies with certain orientations of the C54-TiSi2 grain and, thereby, possibly lower the nucleation barrier of the C54-TiSi2 phase. These proposed template mechanisms are specifically tested in the present work through a study of the nucleation of TiSi2 phase(s) in contact with a pre-existing C40 Ti0.4Mo0.6Si2 or Ti5Si3 layer. No identifiable enhancement in the C54-TiSi2 nucleation was observed which could be attributed to templates. Instead, the nucleation temperature of the C54-TiSi2 phase appeared to be correlated with the grain size of the C49-TiSi2 layer, independent of whether Rm was present. These results are suggestive that the primary mechanism for the enhanced formation of the C54 phase by refractory metals is a reduction in the grain size of the C49 TiSi2phase, likely due to altered kinetics.
Modeling on Mechanical Properties of Polishing Pads in CMP Process
Authors: Nishioka Takeshi , Iwami Satoko , Kawakami Takashi , Tateyama Yoshikuni , Ohtani Hiroshi , Miyashita Naoto
Published: April 2011

Chemical mechanical polishing is an essential process for achieving a high degree of planarization. The planarity after CMP sensitively depends on pattern scales, pattern densities and mechanical properties of polishing pads. In order to simulate the topography after CMP, a numerical model for the polishing pad is proposed. In this model, the surface roughness layer of the polishing pad is assumed as a flat soft layer. The distribution of the contact pressure between the patterned wafer and the polishing pad is calculated with finite element method, and the pattern topography is modified based on the pressure dependency of the polishing rate. The iterations of the contact pressure analyses and the topography modifications give the progress of the polishing process numerically. The model is applied to oxide CMP process with silica slurry and stacked pad of polyurethane and non-woven fabric. The compressive elastic moduli of polyurethane layer and non-woven fabric layer are measured dynamically. The elastic modulus of the soft layer is treated as a fitting parameter between the experimental results and the numerical model. The models with the elastic modulus of 10 MPa for the soft layer show good agreements with the experimental results in both of a short range, where the compressive deformation of the pad is dominant, and a long range, where the bending deformation is dominant. Static measurements for the surface elasticity of the polyurethane layer also give a good agreement with the model. The proposed pad model should be useful for the topography simulation, and it also guides the development of new polishing pads.
On Extreme Density of Data Storage in Patterned Magnetic Media
Authors: Meilikhov E. , Aronzon B. , Gurovich B. , Kuleshova E.
Published: April 2011

A patterned magnetic medium is the next step to significantly increasing data storage density. To attain extreme density, it is necessary to deal with the smallest granules (each storing a bit of information) admissible from the physical point of view. It is well known that the volume of such granules, and their aspect ratio, have to be large enough to prevent thermally activated magnetization relaxation. However, these requirements are not exhaustive. A patterned recording medium is a set of closely-spaced, aligned magnetic granules, with the random (“up” and “down”) orientations of granules' magnetic moments. Though the exchange interactions between the granules may be neglected, there are long-range intergranular dipole-dipole interactions (DDI) which lead to significant lowering of activation barrier preventing thermal relaxation. Those interactions limit the acceptable density of ferromagnetic granules, and hence, reduce the extreme density of data storage. Our numerical calculations estimate the negative role of DDI for the particular case of a two-dimensional set of ellipsoidal magnetic granules and allow us to determine the extreme density of data storage.
Grain Size Relationships between the Magnetic Layer and the Underlayers in CoCrPtTa Recording Media
Authors: Ma Kai , Sinclair Robert , Bertero Gerardo , Cao Wei
Published: April 2011

This article presents a transmission electron microscopic (TEM) investigation of the relationship between the magnetic and underlayer grain sizes in CoCrPtTa/CrMo longitudinal magnetic recording media. A great deal of effort has been expended on decreasing the underlayer grain size in order to decrease that of the magnetic layer. However, our results show that the two grain sizes may not always correlate. When the underlayer (CrMo) grains are sufficiently small, the magnetic layer (CoCrPtTa) grain size does not necessarily decrease with further underlayer grain size reduction. By carefully controlling the processing conditions, CrMo grain sizes were made to vary from 16nm down to 10nm. However, the corresponding CoCrPtTa grain sizes remained nearly the same. As the underlayer grain size decreased, the ratio of magnetic to underlayer grain size increased from 0.9 to 1.4.
Magnetotransport and Magnetic Properties of La0.7MnO3−δ and Pr0.65Ba0.05Ca0.3MnO3−δ Superlattices
Authors: Pietambaram Srinivas V. , Kumar D. , Singh Rajiv K. , Lee C. B.
Published: April 2011

In an effort to achieve high magnetoresistance ratios at high temperature and low fields, we have fabricated superlattice structures consisting of La0.7MnO3−δ (LMO) and Pr0.65Ba0.05Ca0.3MnO3−δ (PBCMO) systems where La0.7MnO3−δ is believed to act as a ferromagnetic biasing source to Pr0.65Ba0.05Ca0.3MnO3−Δ. LMO and PBCMO individually transform to ferromagnetic states at 240 K and 60 K respectively. A series of samples, in which the thickness of La0.7MnO3−δ is fixed and that of Pr0.65Ba0.05Ca0.3MnO3−δ varied from 1 to 8 unit cells, have been grown in situ on (100) LaAlO3 substrates using a pulsed laser deposition technique. Microstructural characterization carried out on these films show the presence of characteristic intense satellite peaks indicating the chemical modulation of the superlattice structure. The insulator-to-metal transition and the MR ratio, defined as [R(0)-R(H)/R(H)], where R(0) and R(H) are resistances in zero and applied fields, is found to vary with the number of unit cells. The samples with 1, 2, 5 and 8 unit cells of Pr0.65Ba0.05Ca0.3MnO3−δ show a transition temperature of 240 K, 230 K, 150 K and 160 K and MR ratio of 540%, 592%, 3150% and 2875 % respectively. We have observed an enhancement of magnetoresistance ratio in case of superlattices with thickness of PBCMO greater than 5 unit cells. We attribute this enhancement to a ferromagnetic biasing provided by the LMO layers acting as a ferromagnetic film below its transition temperature.
Chemical Ordering and Microstructure of FePd Thin Films with perpendicular Magnetic Anisotropy
Authors: B. Gilles , F.F. Xu , D. Halley , A. Marty , Y. Samson , G. Patrat
Published: April 2011

FePd(001) thin films have been grown by the molecular beam epitaxy (MBE) technique. At room temperature, these films are chemically disordered whereas at 350 °C a well ordered L10 structure is found with the c-axis oriented in the growth direction. By combining RHEED, STM and Auger measurements, it is suggested that ordering occurs at the growing surface by the development of bi-atomic steps of the ordered structure. We have put in evidence that the surfactant behavior of the Pd atoms is mainly involved in the ordering process and selects the single orientation of the c-axis. For intermediate temperatures between RT and 350 °C, TEM and X-rays have evidenced a pseudo-periodic arrangement of anti-phased domains having a columnar shape. The variation of the long-range order parameter is related to the average size of these ordered domains.
Electrical And Microscopic Investigation Of E-Gun Evaporated Titanium Thin Films
Authors: Hofmann Karl , Luysberg Martina , Spangenberg Bernd , Kurz Heinrich
Published: April 2011

The deposition rate of titanium films plays a determining role for possible fabrication schemes of metallic SET structures. Depending on this rate the resistivities display a striking difference in their temperature dependence which is attributed to their different crystal structure as analyzed by transmission electron-beam microscopy. In addition a sharp rise in resistivity occurs below a critical thickness in films deposited at slow rates. This sharp increase can be used in combination with a step induced thinning to form tunnel junctions for single electron transistor structures.
Morphological Evolution in Highly Strained InSb/InAs(001)
Authors: Seshadri Aruna , Millunchick J. Mirecki
Published: April 2011

We investigated the morphological evolution of InSb grown on InAs (001) substrates (lattice mismatch = 6.9%) as a function of film thickness. Due to the very large lattice mismatch, growth proceeded via the Volmer-Weber mode. The morphological evolution of highly strained InSb films proceeds through several regimes as a function of thickness. The films initially nucleate isolated 3D islands even in the earliest stages of growth. The islands then coarsen and coalesce at slightly higher thicknesses, with some evidence of cooperative nucleation, or the sequential nucleation of islands and pits. Once the islands coalesce, the morphology evolves into long ridges aligned along the [110], however, those films are still discontinuous. At a thickness =100nm, the films finally become completely continuous and 2D growth proceeds via step flow of growth spirals present on the surface.
Cathodoluminescence Wavelength Imaging Study of Clustering in InAs/GaAs Self-Assembled Quantum Dots
Authors: Rich D. H. , Zhang C. , Mukhametzhanov I. , Madhukar A.
Published: April 2011

Cathodoluminescence wavelength imaging (CLWI) of InAs/GaAs self-assembled quantum dots (SAQDs) was performed to study the spatial variation in the spectral lineshape of the broadened quantum dot (QD) ensemble. The lineshape was found to vary on a scale of ∼μm, revealing attendant variations in the size distribution of SAQD clusters on this spatial scale. Energy variations in clusters of SAQDs are found to exhibit a spatial correlation with the efficiency of luminescence and the activation energy for thermal re-emission of carriers. A reduction in the energy variation of the QD clusters occurs when the thickness of the spacer layers in vertically self-organized samples is reduced or the number of stacks is increased. SAQDs were also prepared by punctuated island growth (PIG), in which deposition of the total desired amount is broken into two or more stages each separated by time delays. CLWI reveals a reduced variation in the energy of the dominant CL emission on a ∼μm spatial scale, correlating with a narrower size distribution of larger QDs for PIG, as measured in atomic force microscopy.
Improved Carrier Transport in Intermixed GaAs/AlGaAs Laser Structure With Multi-Quantum Wells Cladding
Authors: Teng J. H. , Chua S. J. , Liu W. , Wang X. C. , Choi H. W. , Dong J. R. , Li G. , Braddoc D.
Published: April 2011

A GaAs/A1GaAs laser structure with multi-quantum-well cladding layer has been employed to investigate the group III interdiffusion. With this structure the photoluminescence (PL) signals from both the top C doped cladding layers and the laser active region quantum wells can be observed simultaneously. In contrast to the depth dependence of the group III vacancy enhanced interdiffusion, the quantum wells in the thick top cladding layer showed a uniform layer intermixing and the extent of intermixing was less than that observed in the quantum wells of the laser active region. The Al-Ga interdiffusion coefficient, DAl-Ga, of the cladding layer is about 4 times less than that of the active region. A more efficient carrier transport from the cladding layer to the active region in the intermixed sample was deduced from the temperature varied PL spectra. The built-in electric field is proposed to enhance the vacancy diffusion in the active region
Scanning Tunneling Spectroscopy Investigation of the Strained Si1−xGex-on-Si Band Offsets
Authors: Chen Xiangdong , Wang Xiang-Dong , Liu Kou-Chen , Kim Dong-Won , Banerjee Sanjay
Published: April 2011

The band offsets and band gap are the most important parameters that determine the electrical and optical behavior of a heterojunction. In situscanning tunneling spectroscopy (STS) was employed to measure the valence band offset of strained Si1−xGex-on-Si (100) for the first time. The valence band offsets of strained Si0.77Ge0.23and Si0.59Ge0.41on Si(100) are found to be 0.21eV and 0.36eV, respectively. The results are in good agreement with theory and with results from other experimental methods. Due to band bending and surface states, it is difficult to determine the conduction band edge at the interface of Si1−xGex/Si exactly, but the conduction band offset is found to be much smaller than the valence band offset
Characterization of Morphology and Defects in Silicon-Germanium Virtual Substrates
Authors: Dilliway G.D.M. , Willoughby A.F.W. , Bonar J.M.
Published: April 2011

Silicon-germanium heterostructures incorporating virtual substrates are successfully used for both microelectronic and optoelectronic applications. However their use may be limited by the rough surface morphology and defect content, especially threading dislocations. High quality silicon-germanium heterostructures incorporating virtual substrates have been grown epitaxially using different techniques. Also various methods for improving the surface roughness and threading dislocation density have been reported. This study reports comparatively the effects of two different types of grading (linear and step wise) of the germanium concentration in the virtual substrate on the surface morphology and defect content of silicon-germanium heterostructures grown by Low Pressure Chemical Vapour Deposition (LPCVD) in the Southampton University Microelectronics Centre. Step-grading is demonstrated to produce superior virtual substrates
Uniformity Control of 3-Inch GaN/InGaN Layers Grown in Planetary Reactors®
Authors: Protzmann H. , Luenenbuerger M. , Bremser M. , Heuken M. , Juergensen H.
Published: April 2011

We report on recent results obtained using an AIX 2400G3HT production type Planetary Reactor® in the 5×3 inch configuration for growth of typical group-III nitride layer structures consisting of GaN, InGaN and AlGaN. The optimum reactor geometry has been found by extensive modeling of the reactor design. Increased thermal management allows maximum reactor temperatures above 1400°C. As a consequence of extensive reactor modeling, the process transfer from 6×2 inch to 5×3 inch configuration was carried out by simple scaling of the corresponding process parameters of the 6×2 inch configuration. The scaling factor is calculated with respect to the changed reactor geometry. We used optical reflectrometry for in-situ growth control during this process development and could confirm the theoretical scaling requirements for obtaining identical growth conditions as compared to the 6×2 inch reactor configuration. This is verified by the generation of identical reflectance spectrum features. This important issue of in-situ control is discussed in detail. The TMGa efficiency could be kept at about 17%. Switching to the 8×3 inch configuration the efficiency increases up to about 27%, which is an improvement of 63% as compared to the 6×2 inch configuration
Growth of GaInNAs by Plasma Assisted Molecular Beam Epitaxy
Authors: Gotthold David W. , Govindaraju Sridhar , Holmes Archie L. , Streetman Ben G.
Published: April 2011

The nitrogen containing alloy GaInNAs has attracted a great deal of interest recently for optoelectronic device applications at long wavelengths, especially 1.3µm, on GaAs substrates. What has been observed is that the material quality degrades rapidly with the addition of nitrogen. In this work we systematically explore the parameter space for the growth of GainNAs using plasma-assisted MBE and inert gas dilution. Inert gas dilution allows additional control of the production of active nitrogen; thus we can independently adjust RF power, gas flow rate, and nitrogen generation, which is used to study the effects of the plasma on the growth surface. In addition to examining the effects of plasma operating conditions, we will also explore the effects of other growth parameters (arsenic to nitrogen ratio and growth temperature) on the resultant structural and optical properties. These properties will be explored by photoluminescence, SIMS, and x-ray diffraction with the goal of understanding how nitrogen incorporation affects the resultant material properties. The resulting information is used to grow high quality layers for GaNAs avalanche photodiodes with a cut-off wavelength of 1.064µm
Atomic Force Microscopy Characterization of Interface Roughness of V-Shaped AlGaAs/GaAs Quantum Wire
Authors: Wang Xue-Lun , Voliotis Valia , Grousson Roger , Ogura Mutsuo
Published: April 2011

The influence of surface roughness on the initial V-grooved substrate on the interface uniformity of V-shaped AIGaAs/GaAs quantum wires (QWRs) is investigated by direct atomic force microscopy observation of V-groove surface. We found that roughness on the initial V-grooved substrate induced during V-groove preparation processes can severely affect the interface uniformity of QWRs grown on it. We also found that roughness on the initial substrate can be greatly reduced by a simple etching treatment using a NH4OH:H2O2:H2O=1:3:50 solution, and this resulted in significant improvement of QWR interface quality.
Island Coalescence Induced Substructure Within GaP Epitaxial Layers Grown on (001), (111), (110) and (113) Si
Authors: Narayanan V. , Mahajan S. , Bachmann K. J. , Woods V. , Dietz N.
Published: April 2011

GaP islands grown on selected surfaces of Si and their coalescence behavior have been investigated by transmission electron microscopy. These layers were grown by chemical beam epitaxy. A number of significant observations emerge from this study. First, planar defect formation has been shown to be related to stacking errors on the smaller P-terminated {111} facets of GaP islands. Amongst the four orientations, (111) epilayers have a higher density of stacking faults and first order twins because of more P-terminated {111} facets per island. Second, multiple twinning on exposed {111} facets can produce tilt boundaries and irregular growths when islands coalesce. Third, inversion domain boundaries lying on {110} planes have been shown to form during GaP island coalescence across monatomic steps on (001) Si. Image simulations have been performed to show that these boundaries can be seen in high resolution lattice images and the observed contrast is attributed to the presence of wrong Ga-Ga and P-P bonds at the inversion boundary.
Oxidation Kinetics in SrTiO3 Homoepitaxy
Authors: Zhu X.D. , Si Weidong , Xi X.X. , Jiang Qidu
Published: April 2011

Using an oblique-incidence optical reflectivity difference technique, we investigated kinetic processes in SrTiO3 homoepitaxy on SrTiO3(001) under pulsed laser deposition conditions. Depending upon growth temperature and oxygen ambient pressure, we found that the oxidation of an as-grown SrTiO3 monolayer may take a much longer time to complete than the recrystallization of the monolayer. The oxidation reaction was found to be characterized by an effective activation energy barrier of 1.35 eV and a large pre-exponential factor.
Optical Properties of Thin-Film SrTiO3 on Si Grown by MBE
Authors: Zollner Stefan , Demkov A.A. , Liu Ran , Curless J.A. , Yu Z. , Ramdani J. , Droopad R.
Published: April 2011

Oxides with perovskite crystal structure such as SrTiO3 are important candidates for ultrathin gate oxides because of their large DC dielectric constant. When SrTiO3 is deposited directly on Si, an amorphous non-stoichiometric interfacial layer is usually formed during the later stages of growth, which reduces the specific capacitance and is therefore undesirable. We have performed deep-UV spectroscopic ellipsometry measurements from 0.7 to 6.6 eV of SrTiO3 films grown on Si by MBE. This technique is very well suited to determine the thickness of SrTiO3 films between 75 and 200 Å. For thinner films, refractive index and thickness cannot be determined independently. Ellipsometry measures the total thickness (SrTiO3 plus amorphous interfacial layer). There is no signature in the data that can be used to determine the SrTiO3 and interfacial layer thicknesses independently. We find that the effective refractive index (averaged over the crystalline SrTiO3 and the interfacial layer) decreases with decreasing thickness due to the increasing importance of the interfacial layer, but the overall critical-points due to interband transitions are not eliminated, therefore the electronic structure stays mostly intact.