bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical Activity and Order in Luminescent Langmuir-Blodgett Poly(ρ-Phenylene Vinylene) Films
Authors: Marletta A. , Guimãraes F.E.G. , Gonçalves D. , Campana P.T. , Nascimento O.R. , Oliveira O.N. , Faria R.M.
Published: April 2011

Langmuir-Blodgett (LB) PPV films of poly(ρ-phenylene vinylene) (PPV) have been obtained using a mixture of a PPV precursor, poly(xylylidene tetrahydrothiophenium chloride) (PTHT), with the sodium salt of dodecylsulfonic acid (DBSA) as the spreading solution. Spincoated films were prepared in order to compare their properties with those of LB films. A large circular dichroism was observed for LB films but not for spin-coated ones. Optical activity of PPV films was characterized by circular dichroism technique, while optical properties were evaluated by optical absorption and luminescence measurements at various temperatures. Overall, the results obtained allowed us to conclude that the layer-by-layer LB process yields a high degree of molecular order in the PPV films with low interchain interaction. Polarized absorption and circular dichroism measurements demonstrate a preferential chain orientation along the dipping direction in the LB processing. The origin of the CD in the PPV-LB can be ascribed to convenient packing of individual monolayers given by the Z-type deposition.
Thermal Shift and Broadening of Spectral Lines in Neodymium Doped Garnets
Authors: Chen Xuesheng , Bartolo Baldassare Di
Published: April 2011

Thermal shift and broadening of sharp luminescence lines in three Nd-doped laser garnet crystals, GGG, GSGG, and CYMGG, are investigated in a temperature range of 78 to 600K. These lines are due to the 4F3/2 → 4I9/2 (∼0.94μ) and 4F3/2 → 4I11/2 (∼lμ) transitions. Line widths and positions at different temperatures are reported for the lines of RI→Yl, RI→Y2, R2→Y3, RI→Z5 in GGG:Nd, RI→Y1, RI→Y2, R2→Y1, R2→Y3, RI→Y6, R2→Y6, RI→Z5 in GSGG:Nd,Cr, and R2→Y1, RI→Z5 in CYMGG:Nd,Cr. We observed that all the lines shift to longer wavelengths (red shift) with increasing temperature except for the R1,2 →Z5 lines that shift to shorter wavelength (blue shift) in all the three garnet crystals. For the widths, all the lines become broader with increasing temperature. It was also observed that the line width in the germanium garnet CYMGG is much broader than in GGG and GSGG.
Understanding the Photoluminescence of Copper Aluminum Halide Phosphors
Authors: Sullivan Roger M. , Martin James D.
Published: April 2011

Ambient temperature blue luminescence was observed under both UV and X-ray excitation during our investigation of the chemisorption of small molecules into both α- and β CuAIC14. The optical properties of the CuAIX4 (X=CI, Br) indicate a copper centered phosphorescence mechanism. The thermal history of the sample influences both which polymorph is formed and the color of the luminescence. The sorption of small molecules into the framework quenches the blue photoluminescence, which provides a useful probe of the interaction between the metal-halide framework and sorbed gases.
Sputtering Luminescent Ta2Zn3O8 Thin Films
Authors: Rack Philip D. , Potter Michael D. , Woodard Andrew , Kurinec Santosh
Published: April 2011

Thin films have been deposited by rf magnetron sputtering from a stoichiometric Ta2Zn3O8 ceramic target (3ZnO + 1Ta2O5). Negative ion re-sputtering effects have been observed in the stoichiometric Ta2Zn3O8 target and have been attributed to O ion formation from primarily Ta-O bonds. Zinc deficient thin films were deposited as a result of the preferential re- sputtering of Zn versus Ta. The negative ion re-sputtering effects are exacerbated at higher powers and lower pressure. This observation is correlated to the oxygen ion transport through the dark space and the plasma, which ultimately controls the energy distribution of the oxygen particles that arrive at the substrate. To circumvent the negative ion re-sputtering, a mosaic ZnO-Ta target was sputtered, which resulted in stoichiometric and luminescent thin films.
Modeling of Cathodoluminescence and Photoluminescence Properties of Pulsed Laser-Deposited Europium-Activated Yttrium Oxide thin Film Phosphors
Authors: Cho K.G. , Kumar D. , Chen Z. , Holloway P. H. , Singh R. K.
Published: April 2011

Europium-activated yttrium oxide (Eu:Y2O3) thin films were deposited on (100) silicon and (0001) sapphire substrates using 248 nm KrF pulsed laser. To investigate the effect of the Eu:Y2O3 film roughness on cathodoluminescence (CL) and photoluminescence (PL) properties, the substrate surfaces with various roughnesses were used. The roughness was found to play an important role in determining CL and PL brightness of the Eu:Y2O3 films. The improvement in brightness by increasing the film roughness is due to increase in total portion of light that escapes from the surface of the phosphor film. A model has been proposed which supports strongly this explanation. Our results show that depositions with slower growth rate and lower laser energy are more important parameters than increasing the roughness to improve CL brightness of the Eu:Y2O3 thin film phosphors.
Electrostatic Self-Assembly of Multilayer Noncentrosymmetric Thin Films and Devices
Authors: Lenahan K. M. , Zenga T. , Liu Y. , Wang Y.-X. , Zhao W. , Claus R.O.
Published: April 2011

The electrostatic self-assembly of multilayer thin films by alternate adsorption from polyelectrolyte solutions spontaneously leads to the formation of noncentrosymmetric structures if the molecules themselves have net dipole moments. Significant second-order nonlinear optical susceptibility has been observed in such films, using both commercially available chromophores and molecules specifically designed to yield an enhanced net dipole moment. Recent results indicate the capability to fabricate piezoelectric films using the same method. The nature of the deposition process results in an alignment of the chromophores that is stable over time and to temperatures up to 150°C, in contrast with poled polymers. ESA films offer the additional major advantages of excellent homogeneity and low optical loss, high thermal and chemical stability, and low cost.
Towards the Synthesis of Mono- and Bi-Functional Amphiphilic Oligothiophenes: Organic Materials for Opto-Electronic Applications
Authors: Advincula R.C. , Inaoka S. , Park M. , Phillips D. , Shin D.M.
Published: April 2011

In this report, we describe our initial synthesis and characterization of mono-functional and bi-functional dibromoalkyl oligothiophenes to achieve amphiphilicity and telechelic functionality. Oligothiophenes are an important class of organic materials for opto-electronic devices and display applications. We have mono-functionalized oligothiophenes by the synthesis of a quinquethiophene bromoalkyl derivative. A bi-functional sexithiophene was derived primarily by the symmetrical coupling of terthiophene derivatives. Both were synthesized using Grignard coupling and lithiation reaction methodologies. UV-Vis, IR, NMR, MALDI-TOF-MS, and DSC confirmed the structure and physical properties of the oligomers. In addition, we have also synthesized an amphiphilic diamine derivative from the reaction of hexamethylenediamine with a bromoalkyl terthiophene derivative. Using photoluminescence, the photophysical properties of the oligomers were found to be that of typical oligothiophenes. Processing as ultrathin films for devices is currently being investigated.
Two Photon Spectroscopy of Dithienyl Polyenes
Authors: Cooper Thomas M. , Fleitz Paul A. , Sowards Laura A. , Natarajan Lalgudi V. , Kirkpatricky Sean , Chandra Suresh , 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-3,3'-butyl)polyenes. Spectroscopic measurements, including UV/Vis, fluorescence, fluorescence lifetimes, fluorescence quantum yields, triplet state lifetime, solvent effects and two-photon absorption coefficient were obtained as a function of the number of double bonds(n = 1-5). Trends in the data reflected the ordering, energy gap between and mixing of 1Bu* and 1Ag* excited state configurations.
Electromigration in Sputter Deposited Copper/Zirconium Alloys
Authors: McCusker N. D. , McCusker N. D. , Armstrong B. M.
Published: April 2011

RF-magnetron sputter deposited copper/zirconium alloy films have been characterised in terms of resistivity, composition, microstructure, texture and stress. The properties and electromigration reliability of these alloys have been compared to those of pure sputtered copper films. The surface segregation of zirconium within the films after annealing has been studied. We have proposed a mechanism in which zirconium at the copper surface can influence the electromigration damage process, enhancing reliability.
In Situ Stem Technique for Characterization of Nanoscale Interconnects During Electromigration Testing
Authors: Gobulukoglu Ismail , Robertson Brian W.
Published: April 2011

A technique for observing microstructure and morphology changes during annealing or electromigration of 100 nm-scale and smaller interconnects is presented. The technique is based on dynamic in situ characterization using a UHV field-emission scanning transmission electron microscope (STEM) and can enable full microstructural characterization (images, diffraction patterns and compositions) during electromigration testing. Initial steps in the validation of the approach include in situ electron-beam OMCVD of Al-containing wires and observation of these wires. Although the deposition conditions were not optimized, Al-containing wires, with high edge acuity, thickness uniformity, and with minimum interconnect widths as small as 15 nm have successfully been deposited. In situ imaging of the annealing of 100 nm Al films on 25 nm Si3N4 substrates at 350°C demonstrates that an image resolution of 10 nm should readily be attainable in passivated nanoscale interconnects during electromigration.
X-Ray Diffraction Determination of Texture and Stress in Damascene Fabricated Copper Interconnects
Authors: Winter Delrose , Besser Paul R.
Published: April 2011

X-Ray diffraction (XRD) provides an excellent tool for the measurement of both stress and texture (preferred orientation) on fabricated damascene interconnect structures. Since x-ray diffraction provides a direct measurement of lattice spacings, film strain can be measured directly. Also, since the intensity of diffracted x-rays is proportional to the density of lattice planes oriented in diffracting condition with respect to the incident beam, both the direction and extent of preferred orientation can be accurately measured. Special techniques and considerations are necessary when examining damascene interconnect structures with XRD which are not necessary with blanket films. These techniques are discussed and described in order to aid in obtaining meaningful XRD data and a correct interpretation of the results.
The Effect of Film Stress on Indentation Modulus/Hardness for Silicon Oxide Films
Authors: Sun Brad , Lee Jin , Kofron Patrick , Ma Qing
Published: April 2011

A controlled experiment was performed to determine whether residual stresses in silicon oxide films affect the apparent modulus and hardness of the films measured using microindentation. A set of wafers, each with a SiO2 film of different residual stress, were produced by PECVD deposition using different RF power settings. Residual stresses, determined by curvature measurement, were shown to become more compressive with the increase of the RF power. Correlation between indentation modulus/hardness and residual stress was established because the modulus was also observed to be trending with the RF power. To determine whether the residual stress change is the cause for the change of indentation modulus/hardness, one of the wafers was cut to pieces and bonded to steel substrates of different thickness at elevated temperatures. Because of the thermal mismatch between silicon and steel, the silicon pieces were stressed by the steel substrates and therefore provided additional stresses to the SiO2 film on the top surface. The applied stresses were determined using Raman piezospectroscopy. Micro-indentation tests performed on these samples showed no appreciable change of modulus/hardness due to additional stresses. It was concluded that the material change, such as density, was behind the correlation between indentation modulus and residual stress.
Analytical Methodology and Design of Advanced Test Structure for the Mechanical Characteristics of Microactuator Materials
Authors: Lee Se-Ho , Park Byung Woo , Pak Yukeun , Kwon Dongil
Published: April 2011

The electrostatic test structure was presented to measure the micromechanical properties of micromaterials as thin films forming the microactuators. The test structure was fabricated by using the surface micromachining processes and driven by the electrostatic force. In order to measure the fracture toughness, the sharp notch in the test structure was introduced by using the etching process. The displacement and deflection of the test structure under the electrostatic force was on the basis of the beam bending theory. An analytical model was proposed to evaluate the fracture toughness by experimental determination of crack propagation from the variations of capacitance and voltage. Additionally, an acceleration test for evaluation of the long-term reliability of the microactuator device was performed to predict the lifetime of a gold micromirror plane used in DVD (Digital Video Disk) by analyzing the resonant frequency and capacitance.
On the Methodology of Numerical Etching
Authors: Wang X. H. , Shyu K. , Chang C.-T. , Zheng D. W. , Wen Weijia
Published: April 2011

A methodology to study the stress distribution of a patterned thin film residing on a silicon wafer was developed. Si underlying the pattern was thinned down through etching so that the deformation caused by residual stress in the microstructure could be detected by a Twyman- Green interferometer. A procedure called "numerical etching" was implemented to simulate the etching process, which linked the stress state of the microstructure on a regular wafer to that on a Si diaphragm. An initial stress field on the pattern was assumed, and its effect on the deformation of the Si diaphragm beneath was calculated and compared with experimental results. The discrepancy between them was used to modify the initially assumed stress field and repeated until a satisfactory match was achieved. The stress field from numerical analysis accurately predicts the actual stress distribution in and around the patterned structure under investigation. The stress distribution in a Ti pad on a Si3N4/ SiO2/Si composite diaphragm is used as an example.
Interfacial Diffusivity of Moisture Along A SiO2/Tin Interface Measured Using Imaging Secondary Ion Mass Spectroscopy (SIMS)
Authors: Xu Guanghai , Mates T. E. , Clarke D. R. , Ma Qing , Fujimoto Harry
Published: April 2011

The SiO2/TiN interface is prone to sub-critical decohesion by crack extension along the interface when exposed to moisture. As with conventional sub-critical crack growth in bulk silica, the rate of decohesion is dependent on both the relative humidity and the strain energy release rate. One of the unusual observations we have noted is that the decohesion velocity of narrow strips is highly sensitive to the exposure time in the humid environment, suggesting that the moisture diffuses into the interface ahead of the propagating decohesion crack, causing a form of hydrolytic weakening of the interface. In seeking to establish the origin of this behavior, we report measurements of moisture diffusion along the SiO2/TiN interface using Imaging Secondary Ion Mass Spectroscopy (SIMS) after immersion in water containing radioactive tracers, 2D and 18O. Analysis of images formed using 2D and 18O revealed that both diffuse along the interface with a diffusivity of (6 ±2)×10−13 cm2/sec, a value about 104 times faster than the bulk diffusion in the SiO2 dielectric.
Adhesion and Progressive Debonding of Polymer/Metal Interfaces: Effects of Temperature and Environment
Authors: Kook Seung-Yeop , Kirtikar Amol , Dauskardt Reinhold H.
Published: April 2011

The interfacial fracture properties of a representative polymer/metal interface commonly found in microelectronic applications are examined. The double cantilever beam (DCB) configuration was used to investigate the effects of environmental variables on interfacial adhesion and progressive delamination under monotonic and cyclic fatigue loading conditions. The steady-state interfacial fracture energy, Gss, taken from the plateau of the R-curve, of a representative silica-filled Phenol-Novolac epoxy on a Nielectroplated Cu substrate showed little sensitivity to the presence of moisture. On the other hand, both the initiation interfacial fracture energy, Gi, and the entire progressive debond curve under fatigue loading were remarkably sensitive to moisture and temperature, respectively. Debonding is modeled in terms of interface structure, chemistry using chemical reaction rate theory, and relaxation process at the debond tip. The activation energy for stage I debond growth is found to be 140 kJ/mol and 63 kJ/mol for stage II for the current polymer/metal interface.
Acoustic Emission Analysis of Fracture Events in Cu Films with W Overlayers
Authors: Volinsky Alex A. , Gerberich William W.
Published: April 2011

Indentation-induced delamination of thin films provides the basis for adhesion calculations. In the case of ductile Cu films plastic deformation usually prevents a film from debonding from the substrate. Deadhesion is facilitated by the use of a hard W superlayer, which promotes indenter-induced Cu film failure, increasing the delamination area by an order of magnitude. Radial as well as annular cracking acts like a secondary mechanism in the strain energy release, and can be resolved from excursions on the load-displacement curves. For the thicker Cu films no excursions were observed, though radial cracking took place. It is important to identify fracture events as they occur in order to understand the system behavior and accurately apply the analysis. An acoustic emission signal is used to detect the magnitude of fracture events in thin Cu films. For the films of different thickness from 40 nm to 3 microns the corresponding interfacial fracture energy ranged from 0.2 to over 100 J/m2. Limits of plastic energy dissipation are determined with the lower limit, the true work of adhesion, being associated with a dislocation emission criterion. Crack arrest marks were found upon the blister removal, and are proposed to represent the shape of the crack tip. Total acoustic emission energy was found to be inversely proportional to the strain energy release rate.
Measurement of Bonding Stress in Silicon High Power Device Structures by Infrared Photoelasticity Method
Authors: Peng H. J. , Wong S. P. , Lau W. F. , Ke N. , Zhao Shounan
Published: April 2011

Silicon high-power devices are commonly bonded to Mo electrodes using Al films. Bonding stress will inevitably be introduced into the Si substrate by such a process. In this work, the infrared (IR) photoelasticity (PE) method was employed to measure the stress distribution in the Si substrates induced by high temperature bonding process of Si/Al/Mo structures commonly used in the production of silicon thyristors. It is demonstrated that quantitative information on both the directions and magnitudes of the stress can be obtained. The dependence of the magnitude of the stress on the geometrical parameters of the structure has also been studied. The experimental results are shown to agree well with the calculated results derived from a theory of interlaminar stresses in composites.
Effects of Preexisting Stress Voids on Electromigration Stress Buildup and Flux Divergence
Authors: Shen Y. -L. , Minor C. A. , Guo Y. L.
Published: April 2011

Numerical modeling of electromigration stress buildup and flux divergence was undertaken. The objective is to provide a mechanistic understanding of the question: Do preexisting stress voids grow during later electromigration, to become potentially fatal? Conflicting experimental results have been reported. In this work the stress field in aluminum interconnects containing voids was first quantified using the finite element analysis. The averaged stress field then served as the initial condition in the one-dimensional partial differential equation of electromigration stress buildup. The finite difference method was employed to solve the evolving stress profile and the associated atomic flux and flux divergence along the conducting line. It was found that a large preexisting void suffers greater flux divergence and is therefore more prone to growth during electromigration. A single large stress void is more detrimental than populous small voids. Published experimental observations seem to support these findings.
Dimer Reconstruction at Metal-Silicide/Silicon Interfaces: A First-Principles Study
Authors: Yu B. D. , Miyamoto Y. , Sugino O. , Sakai A. , Sasaki T. , Ohno T.
Published: April 2011

By employing first-principles total-energy calculations we studied the atomic and chemical structure of NiSi2/Si(001) and CoSi2/Si(001) interfaces that are of great importance in understanding electronic properties, such as the Schottky-barrier height, of metal-silicide/silicon junctions. We found a new structural model that is more stable than previously proposed models of interface structures and well explains existing experimental data. The new interface model consists of sevenfold-coordinated interfacial metals and a 2×1 periodic array of interfacial Si dimers, similar to the Si(001) 2×1 surface reconstruction, reducing the number of dangling bonds.
Advanced CVD Barrier Technology for Copper Interconnect
Authors: Jain A. , Adetutu O. , Ekstrom B. , Hamilton G. , Herrick M. , Venkatraman R. , Weitzman E.
Published: April 2011

The adoption of copper (Cu) interconnects has imposed the challenge of developing a chemical vapor deposition (CVD) diffusion barrier technology that can be implemented for subhalf micron back-end design rules. Chemical vapor deposition (CVD) offers significantly higher film step coverage compared with sputter deposition processes. A number of materials have been proposed in literature for diffusion barriers of copper. However, the ability to suppress diffusion of Cu is only one of the barrier requirements out of a long list necessary for process integration. A number of other factors depend on the interaction of the barrier with Cu and with the underlying dielectric. We will begin with a review of some of the CVD candidate materials followed by a discussion on various interactions between barrier/Cu and barrier/dielectric that impact process reliability.

In addition there are manufacturing considerations ranging from availability of high purity precursor to complex issues of process compatibility, lowering defectivity, and reducing cost-ofownership (CoO). Ultimately, the choice may not necessarily be the most robust diffusion barrier but a process which provides adequate barrier properties and can be integrated easily and cost effectively to build Cu interconnect structures. Therefore, both materials and manufacturing requirements must be considered for selecting a barrier system.

A literature review is presented on some of the integration schemes and limitations they place on a barrier system. We will also share work done at Motorola on materials characterization and process development towards integration on some of the barrier processes. Finally, future trends in process development of diffusion barriers is presented.
Growth and Structure of Metallic Barrie Laye and Interconnect Films I: Exeriments
Authors: Windt D. L. , Torre J. Dalla , Gilmer G. H. , Sapjeta J. , Kalyanaraman R. , Baumann F. H. , O'Sullivan P. L. , Dunn D. , Hull R.
Published: April 2011

We present experimental results directed at understanding the growth and structure of metallic barrier layer and interconnect films. Numerical simulation results associated with this experimental work are presented in an accompanying paper in these proceedings. Here, thin films of Al, Ti, Cu and Ta have been grown by magnetron sputtering onto oxidized Si substrates. Using a specially-constructed substrate holder, the orientation of the substrate with respect to the growth direction was varied from horizontal to vertical. Films were grown at both low and high argon pressure; in the case of Ta, the cathode power was varied as well. The film structure and in particular the surface roughness was measured by X-ray reflectance and also by atomic force microscopy. We find that the surface roughness increases markedly with orientation angle in the case of Ta and Cu films, and in Ti films grown at high argon pressure. At low pressure, however, the Ti film surface roughness remains constant for all substrate orientations. No variation in roughness with either orientation angle or argon pressure was observed in the Al films. These results suggest that, under certain circumstances, shadowing effects and/or grain orientation (i.e., texture) competition during growth can give rise to lower density, more porous (and thus more rough) films, particularly at large orientation angles, as on sidewalls in sub-micron trenches.
Factors Affecting Passivation and Resistivity of Cu(Mg) Alloy Film
Authors: Cho Heung Lyul , Lee Jae Gab
Published: April 2011

We have investigated the variables affecting passivation and resistivities of Cu alloy, which was sputter prepared from a Cu(6 at.%Mg) target. The results show that oxidation of Cu(Mg) alloy includes the surface segregation of Mg and its preferential oxidation. Sufficient surface segregation of Mg is necessary to form the high quality, protective MgO layer on the surface. The interfacial oxide layer produced from the reaction of Mg and SiO2 does not serve as a barrier against Mg diffusion, thereby the generation of free Si seems to continue until Mg is exhausted in copper. Therefore, lowering the contents of Mg in copper is required to reduce the resistivity of Cu(Mg) alloy. In-situ heating of substrate is very effective to reduce the Mg contents in copper alloy and to enhance the surface segregation of Mg, thereby facilitating the passivation of Cu(Mg) alloy with the low resistivity, especially during the low temperature oxidation.
Mechanisms for Microstructure Evolution in Electroplated Copper Thin Films
Authors: Harper J. M. E. , Cabral C. , Andricacos P. C. , Gignac L. , Noyan I. C. , Rodbell K. P. , Hu C. K.
Published: April 2011

We present a model which accounts for the dramatic evolution in the microstructure of electroplated copper thin films near room temperature. Microstructure evolution occurs during a transient period of hours following deposition, and includes an increase in grain size, changes in preferred crystallographic texture, and decreases in resistivity, hardness and compressive stress. As the grain size increases from the as-deposited value of 0.05–0.1 μm up to several μm, the decreasing grain boundary contribution to electron scattering lowers the resistivity by tens of percent to near-bulk values. Concurrently, as the volume of grain boundaries decreases, the stress is shown to change in the tensile direction by tens of MPa. The as-deposited grain size is also shown to be consistent with grain boundary pinning.
In-Situ Characterisation of Precipitation in Al-Cu thin films
Authors: Lokker J. P. , Bottger A. J. , Janssen G. C. A. M. , Radelaar S.
Published: April 2011

The precipitate formation occurring in Al-Cu thin foils with copper concentrations of either 1.15 at.% or 0.3 at.%, has been studied. In-situ X-ray diffraction analysis and differential scanning calorimetry are applied to determine the phases formed and the enthalpy changes in the same samples. Both X-ray diffraction and differential scanning calorimetry indicate that the precipitation behaviour of thin films (about 500 nm thickness) differs significantly from that of bulk material. In the films studied the precipitation of Al2Cu occurs at a much lower temperature than expected on the basis of the (bulk) phase diagram. Moreover, no intermediate phases are observed prior to Al2Cu precipitation. Also the amount of Cu in solid solution (0.20 at%Cu) observed by electron-probe micro-analysis after slowly cooling from 500°C to room temperature, exceeds the solubility of bulk Al-Cu.
Integration of Low Dielectric Constant Materials in Advanced Aluminum and Copper Interconnects
Authors: Zhao Bin , Brongo Maureen
Published: April 2011

Advanced on-chip interconnects using new materials and new integration architectures are necessary for current and future IC chips in order to meet the requirements in performance, reliability and manufacturing cost. Insulating materials with low dielectric constant (low-κ) and conductive materials with low-resistivity have drawn significant attention for their possible applications in IC interconnects. Dual damascene interconnect integration architectures not only offer process simplification and low cost, but also enable the use of low-resistive Cu for interconnect wiring. Use of low-κ materials in dual damascene architecture is challenging due to material and processing issues. In this paper, the evolution of advanced interconnects, materials and technology options, and some recent achievements in advanced interconnect systems of low-κ dielectric and dual damascene architectures for both Al and Cu metallization are reviewed and discussed.
The Study of Fluorinated Amorphous Carbon as Low-K Dielectric Material and its Interface with Copper Metallization
Authors: Ariel N. , Eizenberg M. , Tzou E. Y.
Published: April 2011

In order to achieve better performance of devices, the interconnects RC delay time, the limiting factor of the device speed today, must be reduced. This calls for a new interconnect stack: lower resistivity Copper and low k materials (k<3) as dielectrics.

Fluorinated amorphous carbon (a-F:C) prepared by HDP- CVD is an attractive candidate as a low-k material. In this work we have studied the film, its stability and its interface with Copper metallization. The high density plasma CVD process resulted in a film which contains C and F at a ratio of 1:0.6 as determined by Nuclear Reactions Analysis. XPS analysis of the C Is transition indicated four types of bonds: C-C, C-CF, CF, and CF2. X-ray diffraction as well as high resolution TEM analyses proved that the film was amorphous at least up to 500°C anneal. For various applications, the advantage of adding a thin bi-layer of a-SiC/SiOx for adhesion promotion purposes was demonstrated. In addition, the interface of a-F:C and the adhesion promoter layer with Ta, TaN and Cu was studied. No interdiffusion was observed by SIMS after 400°C annealing. 500°C annealing caused F outdiffusion from the film and Cu diffusion into the adhesion promoter layer.
A New Low Dielectric Constant Polymer Material (k < 2): Microstructure, Electrical Properties, and Mechanical Properties
Authors: Tsai Yi-Pin , Liao C. N. , Xu Yuhuan , Tu K. N. , Zhao Bin , Liu Q.-Z. , Brongo Maureen
Published: April 2011

A porous polymer material, which is made of a two-phase composite and contains 35% porosity with a pore size less than 50Å, is found to have a dielectric constant of 1.8. It absorbs almost no water. The electrical properties, such as capacitance and leakage current, do not change with time and temperature.
Preparation and Properties of Polysilsesquioxanes - Polysilsesquioxanes as a Candidate to a Low Dielectrics for Electronic Devices -
Authors: Abe Yoshimoto , Kagayama Keiko , Takamura Norihiro , Gunji Takahiro
Published: April 2011

Polysilsesquioxanes PSSQ as a candidate of coatings for interlayer low dielectric films were synthesized by acid and base catalyzed hydrolytic polycondensation of RSi(OMe)3 (R=methyl, vinyl, 3-methacryloxypropyl). Dip and spin coating of PSSQ on organic and inorganic substrates followed by curing at 100 °C, 400 °C, and 450 °C provided transparent and tough coating films of thickness 2000–9000 A. Polysilsesquioxanes adhered strongly to the substrates to form coating films of which the adhesion strength and hardness were 10 and 9H based on JIS K5400 comparable to ISO standard, as heating time and molecular weight increase. On curing at the elevated temperatures, they provided the films with a very smooth surface and the dielectric constants of 3.2∼3.6 (R=3-methacryloxypropyl), 3.8∼4.0 (R=vinyl), and 2.5∼2.7 (R=methyl) depending on film thickness and molecular weight of PSSQ. The films from PSSQ (R=methyl) were found to be porous compared with those from PSSQ (R=vinyl).
In-Situ Studies of the Formation of GA and AL Wires on SI(112) Facet Surfaces
Authors: Prokes S.M. , Glembocki O.J.
Published: April 2011

Reflectance difference anisotropy (RDA) and low energy electron diffraction (LEED)have been used to study the formation of Ga or Al chains and nanowires on the Si(112) surface. At T > 350°C, the Ga or Al chains form at the step edges by a self-limiting process, while at lower temperatures, Ga or Al nanowires form on the terraces in addition to the chains on the ledges. The process has been tracked in real time from the rapid change of the (2×1) Si(112) reconstruction under subcritical coverage to chain formation leading to a 5×1 reconstruction followed by a 6×1 reconstruction’. During sequential deposition of Ga and Al, we observe (in RDA and AES) that Ga atoms forming the chains can be replaced by Al, indicating a stronger Al-Si bond strength and confirming the chemical sensitivity of the light scattering in RDA. Low temperature depositions (in the 300’C range) are shown to lead to the formation of Al (or Ga) metallic wires on the Si(111) terraces. Continued deposition of less than 10 monolayers at T below 250°C leads to a very anisotropic but patterned Al or Ga structure in registry with the substrate which retains an unexpectedly large polarizability for coverages as thick as 40 ml.
Multifunctional Optical In Situ Monitoring of Semiconductor Film Growth
Authors: Bertness K. A. , Hays S. P. , Hickernell R. K.
Published: April 2011

We have modified a normal-incidence optical reflectance spectroscopy system to allow rapid switching between the measurement of sample reflectance and sample emission. The resulting optical system is capable of “smart” pyrometry, in which sample emissivity is measured rather than assumed. The emissivity measurement makes use of the principle of detailed balance, which states that for specular, opaque samples, the sum of the emissivity and reflectance at each wavelength is equal to 1. We present data based on multilayer III-V semiconductor structures grown by molecular beam epitaxy, but the optical system would function equally well in any growth or deposition system with optical access to the substrate. The “smart” pyrometry temperatures we measure typically differs from conventional pyrometry by 5 to 10°C, and occasionally as much as 20°C, for multilayer structures of AIGaAs and GaAs. We present details of the optical components and arrangement that minimize the effect of sample wobble and allow the system operator regular visual access to the sample. Calibration techniques for the combined system are also discussed.
Dislocation-Induced Surface Strain on (001) Silicon-On-Insulator
Authors: Sutter P. , Lagally M.G.
Published: April 2011

We demonstrate a novel technique, based on low-energy electron microscopy, by which inhomogeneous uniaxial strain at the (001) surface of Si can be mapped quantitatively. Using this technique on silicon-on-insulator wafers, we determine the surface strain field induced by a single 60° dislocation and show that such extended defects can be used as monitors of heteroepitaxy-induced changes in the surface strain.
Nucleation and Growth of Supported Metal Clusters at Defect Sites on Mgo and NaCl (001) Surfaces: The Cases of Pd and Ag
Authors: Venables J. A. , Haas G. , Brune H. , Harding J.H.
Published: April 2011

Nucleation and growth of metal clusters at defect sites is discussed in terms of rate equation models, which are applied to the cases of Pd and Ag on MgO(001) and NaCl(001) surfaces. Pd/MgO has been studied experimentally by variable temperature atomic force microscopy (AFM). The island density of Pd on Ar-cleaved surfaces was determined in-situ by AFM for a wide range of deposition temperature and flux, and stays constant over a remarkably wide range of parameters; for a particular flux, this plateau extends from 200 K ≤ T ≤ 600 K, but at higher temperatures the density decreases. The range of energies for defect trapping, adsorption, surface diffusion and pair binding are deduced, and compared with earlier data for Ag on NaCl, and with recent calculations for these metals on both NaCl and MgO
UHV-Investigation on MOCVD-grown InP(100) Surfaces
Authors: Visbeck S. , Hannappel T. , Vogt P. , Mahrt J. , Zorn M. , Knorr K. , Neges M. , Esser N. , Richter W. , Willig F.
Published: April 2011

Epitaxial InP(100)-films were prepared with TBP (tertiarybutylphosphine) and TMIn (trimethylindium) as precursors in a commercial MOCVD reactor. During growth, the V-III-ratio and TBP partial pressure were varied between 50 and 1 and possible changes of the surface structure monitored with the corresponding RAS (reflectance anisotropy spectroscopy) signal based on a correlation established with corresponding LEED measurements. Bulk properties of these films were investigated ex-situ with photoluminescence at 2 K, showing no noticeable difference between the samples. The MOCVD apparatus was modified to facilitate transfer of the sample from the MOCVD environment to UIHV in less than 20 seconds (to the 10−9 mbar range). After transfer, the same RA spectrum was recovered also in the critical case of the P-rich, as-grown surface. A corresponding Auger electron spectrum (AES) did not show any trace of contamination. Furthermore, the surface structure was investigated with LEED and STM. The LEED picture shows a clear (2×l)-pattern with a weak twofold symmetry along the [011] direction, STM pictures revealed a disordered surface terminated by P-dimers
Structural and Electrical Properties of Beryllium Implanted Silicon Carbide
Authors: Henkel T. , Tanaka Y. , Kobayashi N. , Tanoue H. , Gong M. , Chen X. D. , Fung S. , Beling C. D.
Published: April 2011

Structural and electrical properties of beryllium implanted silicon carbide have been investigated by secondary ion mass spectrometry, Rutherford backscattering as well as deep level transient spectroscopy, resistivity and Hall measurements. Strong redistributions of the beryllium profiles have been found after a short post-implantation anneal cycle at temperatures between 1500 °C and 1700 °C. In particular, diffusion towards the surface has been observed which caused severe depletion of beryllium in the surface region. The crystalline state of the implanted material is well recovered already after annealing at 1450 °C. However, four deep levels induced by the implantation process have been detected by deep level transient spectroscopy.
The Effect of Annealing on Argon Implanted Edge Terminations for 4H-SiC Schottky Diodes
Authors: Knights A P , Morrison D J , Wright N G , Johnson C M , O'Neill A G , Ortolland S , Homewood K P , Lourenço M A , Gwilliam R M , Coleman P G
Published: April 2011

The edge termination of SiC by the implantation of an inert ion species is used widely to increase the breakdown voltage of high power devices. We report results of the edge termination of Schottky barrier diodes using 30keV Ar+ ions with particular emphasis on the role of postimplant, relatively low temperature, annealing. The device leakage current measured at 100V is increased from 2.5nA to 7μA by the implantation of 30keV Ar+ ions at a dose of 1×1015 cm−2. This is reduced by two orders of magnitude following annealing at 600°C for 60 seconds, while a breakdown voltage in excess of 750V is maintained. The thermal evolution of the defects introduced by the implantation was monitored using positron annihilation spectroscopy (PAS) and deep-level-transient spectroscopy (DLTS). While a concentration of open-volume defects in excess of 1×1019cm−3 is measured using PAS in all samples, electrically active trapping sites are observed at concentrations ∼1×1015cm−3 using DLTS. The trap level is well-defined at Ec−Et = 0.9eV.
Characterization of P-Type Buffer Layers for SiC Microwave Device Applications
Authors: Konstantinov A. O. , Karlsson S. , Nilsson P.-Å , Saroukhan A.-M. , Svedberg J.-O. , Nordell N. , Harris C. I. , Eriksson J. , Rorsman N.
Published: April 2011

Low-loped p-type silicon carbide buffer layers are grown by chemical vapor deposition on conducting and semi-insulating substrates. Capacitance-voltage and electrical admittance techniques are developed for accurate non-destructive characterization. The electrical admittance techniques suggested are capable of measuring the resistivity in a very wide range, up to 7 orders of magnitude. MESFET devices using thick buffer layers on conducting substrates are reported with Ft=8.4 GHz and Fmax=32 GHz.
Growth of SiC Thin Films on (100) and (111) Silicon by Pulsed Laser Deposition Combined with a Vacuum Annealing Process
Authors: Huang Jipo , Wang Lianwei , Wen Jun , Wang Yuxia , Lin Chenglu , Zetterling Carl-Mikael , Ostling Mikael
Published: April 2011

Crystalline 3C-SiC thin films were successfully grown on (100) and (111) Si substrates by using ArF pulsed laser ablation from a SiC ceramic target combined with a vacuum annealing process. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were employed to study the effect of annealing on the structure of thin films deposited at 800°C. It was demonstrated that vacuum annealing could transform the amorphous SiC films into crystalline phase and that the crystallinity was strongly dependent on the annealing temperature. For the samples deposited on (100) and (111) Si, the optimum annealing temperatures were 980 and 920°C, respectively. Scanning electron microscope (SEM) micrographs exhibited different characteristic microstructure for the (100) and (111) Si cases, similar to that observed for the carbonization layer initially formed in chemical vapor deposition of SiC films on Si. This also showed the presence of the epitaxial relationship of 3C-SiC[100]//Si[100] and 3C-SiC[111]//Si[111] in the direction of growth.
On the Role of Foreign Atoms in the Optimization of 3C-SiC/Si Heterointerfaces
Authors: Masri P. , Moreaud N. , Averous M. , Stauden Th. , Wohner T. , Pezoldt J.
Published: April 2011

3C-SiC/Si structures with Ge incorporation are elaborated by solid source molecular beam epitaxy (SSMBE). A comparison of the flatness of the SiC-surface and the interface between SiC and Si by comparing the deposition with and without Ge is made. The results are analyzed within the framework of a theoretical approach based on the theory of elasticity.
Current Status of SiC Power Switching Devices: Diodes & GTOs
Authors: Seshadri S. , Agarwall A. K. , Hall W. B. , Mani S. S. , MacMillan M. F. , Rodrigues R. , Hanson T. , Khatri S. , Sanger P. A.
Published: April 2011

The progress that has been made in SiC diodes and GTOs is reviewed. A 100 A/1000 V SiC pi- n diode package, the highest current rating reported for any SiC device, a 69 A conduction/ 11 A turn-off of a SiC GTO and MTOTM, as well as the first all-SiC, 3 phase Pulse Width Modulated (PWM) inverter are reported, herein, for the first time. The inverter achieves voltage controlled turn off with a high temperature capable, hybrid SiC JFET. Material and process technology issues that will need to be addressed before device commercialization can be realized are discussed.
The influence of the sapphire substrate on the temperature dependence of the GaN bandgap
Authors: Krüiger Joachim , Shapiro Noad , Subramanya Sudhir , Kim Yihwan , Siegle Henrik , Perlin Piotr , Weber Eicke R. , Wong William S. , Sands Timothy , Cheung Nathan W. , Molnar Richard J.
Published: April 2011

This paper analyses the influence of the sapphire substrate on stress in GaN epilayers in the temperature range between 4K and 600K. Removal of the substrate by a laser assisted liftoff technique allows, for the first time, to distinguish between stress and other material specific temperature dependencies. In contrast to the prevailing assumption in the literature, that the difference in the thermal expansion coefficients is the main cause for stress it is found that the substrate has a rather small influence in the examined temperature range. The measured temperature dependence of stress is in contradiction to the published values for the thermal expansion coefficients for sapphire and GaN.
Enhanced Optical Emission from GaN Film Grown on Composite Intermediate Layers
Authors: Zhang Xiong , Chua Soo-Jin , Li Peng , Chong Kok-Boon
Published: April 2011

GaN films have been grown on silicon-(001) substrate with specially designed composite intermediate layers consisting of an ultra-thin amorphous silicon layer and a GaN/AlxGa1−xN (x=0.2) multilayered buffer by metal-organic chemical vapor deposition and characterized by photoluminescence and x-ray diffraction spectroscopy. It was found that the GaN films grown on the composite intermediate layers gave comparable or slightly stronger optical emission than those grown on sapphire substrate under identical reactor configuration. Moreover, the full width at half maximum for the GaN band-edge-related emission is 40 meV at room temperature. This fact indicates that, by using the proposed composite intermediate layers, the crystalline quality of GaN-based nitride grown on a silicon substrate can be significantly improved.
Growth and Characterization of InGaN/GaN Heterostructures Using Plasma-Assisted Molecular Beam Epitaxy
Authors: Shim K. H. , Hong S. E. , Kim K. H. , Paek M. C. , Cho K. I
Published: April 2011

Structural and optical properties of In0.2Ga0.8N/GaN heterostructures grown by plasma-assisted molecular beam epitaxy have been investigated as a function of rf plasma power. Indium incorporation resulted in the higher rf power level suppressing 3D island growth with reduced introduction of defects in In0.2Ga0 8N in comparison with GaN. Sharp morphology at interfaces and strong transitions in photoluminescence reveal the optimum rf power around 400 W in our experimental set up for the growth of In0.2Ga0.8N/GaN heterostructures. Our experimental observations suggest that the presence of indium on surface modulates the rate of plasma stimulated desorption and diffusion, and reduces the formation of damaged subsurface.
Electron Transport in the III-V Nitride Alloys
Authors: Foutz B. E. , Otleary S. K. , Shur M. S. , Eastman L. F.
Published: April 2011

We study electron transport in the alloys of aluminum nitride and gallium nitride and alloys of indium nitride and gallium nitride. In particular, employing Monte Carlo simulations we determine the velocity-field characteristics associated with these alloys for various alloy compositions. We also determine the dependence of the low-field mobility on the alloy composition. We find that while the low-field mobility is a strong function of the alloy composition, the peak and saturation drift velocities exhibit a more mild dependence. Transient electron transport is also considered. We find that the velocity overshoot characteristic is a strong function of the alloy composition. The device implications of these results are discussed.
High-Quality GaN Grown by Molecular Beam Epitaxy on Ge(001)
Authors: Siegle H. , Kim Y. , Sudhir G. S. , Kruger J. , Perlin P. , Ager J. W. , Kislelowski C. , Weber E. R.
Published: April 2011

We report on growth of GaN on Germanium as an alternative substrate material. The GaN films were deposited on Ge(001) substrates by plasma-assisted molecular beam epitaxy. Atomic force microscopy, x-ray diffraction, photoluminescence, and Raman spectroscopy were used to characterize the structural and optical properties of the films. We observed that the Ga/N ratio plays a crucial role in determining the phase purity and crystal quality. Under N-rich conditions the films were phase-mixed, containing cubic and hexagonal GaN, while in the Ga-rich regime they were purily hexagonal. The latter samples show bandedge luminescence with linewidths as small as 31 meV at low temperatures.