bluuebunny/crossref_metadata_2025 huggingface dataset:
Persistent photoconductivity in AlGaN films Grown by mocvd
Authors: Polyakov A. Y. , Smirnov N. B. , Govorkov A. V. , Redwing J. M.
Published: April 2011

Photocurrent transients due to illumination by above-bandgap and subbandgap light were studied for Si doped and undoped films of AlGaN grown by MOCVD on sapphire and having compositions ranging from 0% to 60% of Al. It is shown that in Si doped layers the decay of photoconductivity takes extremely long time (hundreds and thousands seconds, depending on temperature, composition and illumination conditions). Both the kinetics of rise and fall of photoconductivity are best described by stretched exponents. The characteristic decay times are virtually temperature independent for temperatures below 270–290K and have activation energy of 0.14–0.26 eV (depending on composition) for higher temperatures. The decay times become longer with decreased light intensity and increase when above-bandgap light excitation is replaced by subbandgap light excitation (the photocurrent values from which the decay starts being equivalent). The results cannot be quantitatively explained by the effects of changing of the quasi-Fermi level position well known for DX-centers in AlGaAs. No persistent photoconductivity could be observed in high resistivity undoped AlGaN films with 5%, 15% and 25% of Al.
Ion Scattering Studies of Defects In Gan Thin Films on C-Oriented Sapphire
Authors: Holländer B. , Mantl S. , Mayer M. , Kirchner C. , Pelzmann A. , Kamp M. , Christiansen S. , Albrecht M. , Strunk H. P.
Published: April 2011

Epitaxial GaN films grown by metal organic vapour phase epitaxy (MOVPE) or gas source molecular beam epitaxy (GSMBE) have opened up new applications in short wavelength photonic devices as well as high-power and high-temperature devices. The large lattice mismatch of 14% between GaN and sapphire, which is frequently used as the substrate, and the different thermal expansion coefficients generally lead to high densities of structural defects. We investigate the defect structure of MOVPE- and GSMBE-grown GaN layers on sapphire by Rutherford backscattering and ion channeling measurements. Channeling along the c-axis revealed χmin-values as low as 1.2% even in samples with dislocation densities in the order of 109 cm−2. Channeling measurements along different crystal planes were performed in order to improve the sensitivity to dechanneling by crystalline defects. Angular yield scans around the c-axis indicate clearly the hexagonal symmetry of the GaN lattice. Dechanneling results were combined with transmission electron microscopy investigations (TEM). The results suggest that the dechanneling-cross-section of edge dislocations is about 4 times larger than the dechannelingcross-section of screw dislocations. screw dislocations.
A Semi-Analytical Interpretation of Transient Electron Transport in Gallium Nitride, Indium Nitride, and Aluminum Nitride
Authors: Foutz B. E. , O'Leary S. K. , Shur M. S. , Eastman L. F.
Published: April 2011

The energy dependent momentum and energy relaxation times, and the effective single valley energy dependent effective mass, are extracted from Monte Carlo simulations of gallium nitride, indium nitride, and aluminum nitride. A simple semi-analytical energy model, which uses these dependencies, is in good agreement with the results of transient Monte Carlo simulations. Both the Monte Carlo and the semi-analytical simulations show that the overshoot effects are most pronounced when the electric field abruptly changes from a value below a critical field to one above. This is attributed to the relatively large difference between the effective energy and momentum relaxation times for such a variation of electric field. Our calculations indicate that gallium nitride and indium nitride should have the most pronounced transient effects. A calculation of the transit times as a function of the gate length shows that an upper bound for the maximum expected cut-off frequencies are 260 GHz and 440 GHz for 0.2 μm gallium nitride and indium nitride field effect transistors, respectively.
An Erda Study on Proton Migration Induced by Electric Potential in SrZrO3,SrCeO3 and BaCeO3 Oxides:Measurements of Proton Transport Number and Proton Diffusivity
Authors: Kunimatsu A. , Arai T. , Takahiro K. , Nagata S. , Yamaguchi S. , Akiyama Y. , Sata N. , Ishigame M.
Published: April 2011

Migration of protons dissolved in acceptor doped SrZrO3, SrCeO3 and BaCeO3 oxides has been examined under an applied electric potential over a range of temperature from 25 to 220°C. Protons which dissolved in these oxides migrated to the cathode, and they were trapped there when the cathode material had a good ability to getter the migrating hydrogen. The amount of hydrogen accumulated in the cathode could be measured by the ERDA method using a highenergy 4He beam. We measured the amount of hydrogen in the cathode while monitoring the dc current passed through the oxide specimen. The proton transport number was determined from the ratio of the number of hydrogen in the cathode to the total numbers of charge through the specimen. The diffusion coefficient of proton was evaluated using the proton transport number and proton concentration in the specimen.
A Two-Step Low-Temperature Process For A P-N Junction Formation Due To Hydrogen Enhanced Thermal Donor Formation In P-Type Czochralski Silicon
Authors: Job R. , Fahrner W. R. , Kazuchits N. M. , Ulyashin A. G.
Published: April 2011

The incorporation of hydrogen into standard p-type Czochralski (Cz) silicon (≥1 Ωcm) by a 110 MHz plasma treatment at 260°C leads to the formation of an n-type region due to hydrogen enhanced thermal donor (TD) formation in hydrogenated regions of the wafer, if a subsequent annealing in air is applied at 450°C. Spreading resistance probe (SRP) and light beam induced current (LBIC) measurements were used for the experimental analysis. The p-n junction depth, i. e. the counter doping by TDs, depends on the initial doping level of the p-type substrate, and therefore on the post-hydrogenation annealing time. The penetration of the n-type region into the wafer bulk is driven by a rapid hydrogen diffusion. The essential process for a TD generation is the creation of metastable hydrogen molecular species around 260°C and their decay at 450°C.
Hydrogen in a-Si:H Deposited by 55 kHz PECVD
Authors: Budaguan B. G. , Aivazov A. A.
Published: April 2011

In this work the mechanism of hydrogen incorporation and structural stability of a-Si:H films deposited by LF 55 kHz glow discharge in a wide range of technological parameters have been investigated. The analysis of plasma emission spectra and microstructure of films measured by IR spectroscopy and atomic force microscopy were carried out. It was shown that hydrogen desorption controls the growth rate in a wide range of substrate temperature (40–325°C ) and at low values of LF power (50–200W). At the same time the abnormal increase of hydrogen content due to ion-molecule surface reactions with the increase of substrate temperature was observed. The kinetics of hydrogen diffusion and thermodynamics of defect formation in a-SiH films were determined from modeling of differential scanning calorimetry data. It is concluded that the mechanism of hydrogen incorporation leads to formation of strong Sill bonds in the material bulk and to increase of structural stability with the increase of substrate temperature despite of the increase of hydrogen content.
Electronic Structure and Energetics of LaNi5, α-La2Ni10H and β-La2Ni10H14
Authors: Nakamura H. , Nguyen-Manh D. , Pettifor D. G.
Published: April 2011

The electronic structure and energetics of LaNi5, its hydrogen solution (α-La2Ni10H) and its hydride (β-La2Ni10H14) were investigated by means of the tight-binding linear muffin-tin orbitals method within the atomic sphere approximation (TB-LMTO-ASA). Preferred site occupancy by the absorbed hydrogen atoms was investigated in terms of the charge density of the interstitial sites and the total energy, both of which indicate that the 6m site in the P6/mmm symmetry is the most preferred. A negative heat of formation of La2Ni10H14 was obtained from the total energy calculations.
Hydrogen Adsorption of Ruthenium: Isosteres of Solubility of Adsorbed Hydrogen
Authors: Zaginaichenko S. Yu. , Matysina Z. A. , Schur D. V. , Pishuk V. K.
Published: April 2011

The theoretical investigation of solubility isosteres of adsorbed hydrogen has been performed for free face (0001) of crystals with hexagonal close-packed lattice A3 of Mg type. The face free energy has been calculated and its dependence on temperature, pressure, hydrogen concentration and character of hydrogen atoms distribution over surface interstitial sites of different type has been defined. The equations of thermodynamic equilibrium and solubility of adsorbed hydrogen have been defined. The plots of isosteres in the region of phase transition from isotropic to anisotropic state have been constructed and it has been established that in anisotropic state the order in distribution of hydrogen atoms over interstitial sites of different type must become apparent. Comparison of the theoretical isosteres with experimental for ruthenium has been carried out, the isotropic-anisotropic state transition can stipulate a stepwise and break-like change in isosteres.
Al Dual Damascene Technology for Multilevel Interconnects
Authors: Kikuta Kuniko
Published: April 2011

As the device dimension decreases, the number of metal layers increases and the metal pitch decreases, Al dual damascene has been known to achieve low fabrication cost because the fabrication processes can be simplified by using Al sputter-filling technology and Al CMP. However, from the electrical characteristics and reliability point of view, it was not clear if the Al dual damascene is suitable for fine pitch metallization. In this paper, we compare via characteristics among W-plug, Al-plug and Al dual damascene for multilevel interconnects.

We investigated the via resistance and electomigration characteristics. Al dual damascene was formed by Al hot sputtering to fill via and trench, and by subsequent Al-CMP. The electromigration lifetime for via holes with misalignment between the 1st and 2nd Al for dual damascene is larger than that for conventional Al plug. On the dual damascene structure, via holes are opened first, then 2nd metal trench are patterned. Even misalignment between the 1st via and the 2nd Al occurs, contact area for dual damascene become large because of making contact at both of the via top and the side wall of the 2nd Al. The electromigration lifetime is longer for dual damascene with misalignment, in compared with that for Al plug and W plug with misalignment. Via resistance for dual damascene is almost the same as the via resistance for Al plug, which is lower than W plug. Via yield for dual damascene with misalignment is better than that for Al plug and W plug.

In conclusion, we compared W-plug, A plug and Al dual damascene for multilevel interconnects. Al dual damascene was found to be durable and reliable in structure and process against misalignment in terms of electromigtration lifetime and via resistance, as well as yield. Al dual damascene is the most promising technology for fine-pitch metallization.
Investigation of the Homovalent Impurity in Aluminum to Form Alloys With Enhanced Interconnect Reliability
Authors: Kailasam Sridhar K. , Murarka S. P. , Glicksman M. E. , Merchant S. M.
Published: April 2011

Diffusion-induced failures such as stress-induced voiding and electromigration (EM) are a major concern for interconnect metallization in silicon integrated circuits. The addition of solute elements to aluminum interconnects often leads to “blocking” of high diffusivity paths such as grain boundaries and thus to an improvement in the resistance to electromigration failure. This research investigates Al-In, Al-La, and Al-In-La alloys to improve interconnect EM resistance. The choice of these alloying elements is based on the fact that they have negligible solid solubility in aluminum and are homovalent. Lower solubilities may lead to grain boundary stuffing and hence to improved EM resistance. In addition, the homovalency minimizes the adverse effect on the metal resistivity from addition of impurities to aluminum. Multicomponent diffusion principles are used to tailor aluminum-based ternary alloy compositions which would exhibit the multicomponent effect of zero flux planes (ZFPs), or regions in the reaction zone of a diffusion couple where the flux of a component goes to zero. This study involves modeling the occurrence of ZFPs for aluminum in several diffusion couples of Al-In-La, thus limiting the bulk diffusive spreading of aluminum so that the electromigration behavior can be inhibited or eliminated. This paper presents our experimental findings and discusses the modeling approach to determine ternary alloys exhibiting ZFPs.
Simulators of Thin Film Deposition for Silicon Device Processing
Authors: Gilmer G. H. , Baumann F. H. , Rubia T. Diaz de la
Published: April 2011

We discuss simulators of the deposition of metal films onto substrates containing vias and trenches. Our Monte Carlo simulations of Al are based on extensive first-principles and molecular dynamics (MD) data for atomic-level energetics and transport rates. We find that surface mobilities are highly anisotropic, and that this has a pronounced influence on film morphology. We have investigated the effects of faceting and grain boundary grooving on step coverage, together with the variation of morphology with deposition rate, temperature, and length scale. Mass transport across low index facets is extremely slow near equilibrium, and this can inhibit the smoothening of surfaces and the elimination of depressions during annealing. The MC model also predicts grain structures during polycrystalline film formation, and the generation of preferred crystallographic orientations (texture). We present MC simulations for a range of conditions, and provide comparisons with experiments on the sputter deposition of Al and TiN films. Results from the MC model are being incorporated into a continuum model based on level-set methods, and we expect that this will form the basis for a simulator that can efficiently explore a wide range of conditions.
Study of Factor and Interaction Effects During Programmed Rate Chemical Vapor Deposition of Aluminum
Authors: Yang D. , Jonnalagaddal R. , Rogers B. R. , Hillman J. T. , Foster R. F. , Cale T. S.
Published: April 2011

Results from a statistically designed experiment studying the effects of initial substrate temperature (A), precursor pulse time (B), diluent gas flow rate (C), and their interactions on film properties of programmed rate chemical vapor deposited aluminum are presented. Deposition rate, reflectivity, absolute and normalized roughness, and grain orientation were the response variables investigated. A two level, three factor (23) full factorial experimental design was used. Five center cell replicates were used to estimate cell standard deviations. The experiments were conducted using tri-isobutyl aluminum (TIBA) as the precursor in a lowpressure chemical vapor deposition (LPCVD) cold wall reactor. Effects were considered significant at the 95% confidence level. Initial substrate temperature (A) affected deposition rate and reflectivity. Diluent gas flow rate (C) affected deposition rate, normalized roughness and film texture. The precursor pulse time/diluent gas flow rate interaction (BC) affected film reflectivity and absolute surface roughness, while the initial substrate temperature/diluent gas flow rate interaction (AC) affected film texture.
Debonding of Interfaces in Multilayer Interconnect Structures
Authors: Lane Michael , Ni Winnie , Dauskardt Reiner H. , Ma Qing , Fujimoto Harry , Krishna Nety
Published: April 2011

The reliability of microelectronic devices containing multilayer structures is profoundly influenced by the interfacial strength (adhesion) and resistance to fracture (debonding) of the many resulting bimaterial interfaces. Adhesion and consequent structural integrity are closely related to composition and processing conditions which determine key interfacial parameters, such as interfacial impurities, morphology and adjoining microstructures. Residual stresses, thermo-mechanical cycling and mechanical loading may drive time dependent fracture in these multilayer interconnect structures. Moisture present in the atmosphere and perhaps moisture present in the layers themselves can lead to premature failure and reduced lifetimes of these devices. We present unique data showing the effects of interface non-planarity on the interface fracture energy and the time-dependent delamination processes. Data is presented showing the effects of the phase angle of loading on the interface fracture energy and subcritical debonding processes. Behavior is rationalized in terms of the salient chemical reaction rate occurring at the debond tip. Implications for life prediction of devices are discussed.
Kinetics of the C49-C54 transformation in patterned and blanket TiSi2 films: a comparison.
Authors: Via F. La , Privitera S. , Grimaldi M. G. , Raineri V. , Galli M. , Marabelli F. , Iannuzzil M. , Miglio L.
Published: April 2011

The kinetics of the C49-C54 polymorphic transformation in titanium disilicides thin films grown on amorphous Si substrate has been followed by sheet resistance and Infrared Spectroscopy measurements on both blanket samples and submicron lines. The transformation of a fine grained C49 films (davg=30 nm) into the C54 phase was complete after annealing for ∼300 s at a temperature of 700 °C in blanket samples and of 730 °C in submicron lines. The Avrami exponent decreases from n=3 in blanket films to n=l in stripes. The transformation time at a given temperature increases with decreasing linewidth in agreement with the nucleation density model. Infrared Spectroscopy shows no shift of the peaks of the C49 phonons going from blanket to patterned films, suggesting the lack of strain on TiSi2 patterned films. The different behavior between blanket and laterally limited samples has been explained in terms of the different surface energies.
Capacitance-Voltage, Current Voltage, and Thermal Stability of Copper Alloyed With Aluminum or Magnesium
Authors: Felipe T. Suwwan de , Murarka S. P. , Bedell S. , Lanford W. A.
Published: April 2011

Copper alloyed with small amounts of aluminum or magnesium has recently been suggested as a promising material for interconnect applications in silicon integrated circuits. This work reports the results of the investigation of the electrical (capacitance-voltage and current-voltage) stability of the metal-oxide-semiconductor capacitor made with copper-0.5 at. % aluminum and copper-2 at. % magnesium as metal, deposited on thermally oxidized silicon substrates. Effect of thermal treatment in vacuum ambient before and/or during the electrical testing was investigated. The resistance to oxidation of these alloys was also investigated. The results show that copper magnesium, after a thermal treatment of 350°C or higher, produces a passivating layer at the interfaces that has excellent corrosion resistance and very stable behavior in terms of capacitance-voltage and current-voltage measurements. Copper aluminum performed adequately, much better than pure copper but was inferior to copper magnesium.
Finite Element Modeling for Interconnect Materials and Structures
Authors: Bassman Lori , Pinsky Peter , Deal Michael
Published: April 2011

We present a Back-End Simulation Tool (BEST) developed to address important issues for modeling polycrystalline and multi-layered interconnect materials. During the temperature cycles of interconnect fabrication, diffusion and mechanical equilibrium processes are coupled. Accurate simulation of these systems leads to very large problems, and it is therefore necessary to partition the problem using a staggered scheme. We have developed an unconditionally stable algorithm which is crucial to the success of this approach. We are also able to consider the coupled effect of an electromigration driving force in conducting materials. In order to predict effectively the deformations and stresses which occur in structures fabricated from these materials, our work addresses the multiple length scales which characterize the problem. The simulations span from interconnect level structures to detailed descriptions of grain boundaries and material interfaces using continuously spatially varying material properties. The formulation naturally enforces segregation of impurities or vacancies (for metal self-diffusion) to and across interfaces and to surfaces. Our solutions of the coupled physical problems with the explicit inclusion of grain and layer structures make this a tool for efficient evaluation of the properties and reliability of new interconnect materials and layered structures. We will show some applications of our model to technologically relevant examples including hillock formation and interface stresses.
A Simple Co Salicide Process Using Silicidation by N2/H2 RTA
Authors: Sekiguchi Mitsuru , Moriwaki Masaru , Fujii Shinji , Mayumi Shuichi
Published: April 2011

For Co salicide process, a TiN cap layer is widely used to prevent oxidation of Co layers during silicidation by RTA. In this study, N2/H2 mixture ambient is used to eliminate the need for the TiN cap layer. The sheet resistance for the sample fabricated by N2 RTA without TiN cap layer shows large standard deviations for narrow N+ diffusion layers and shows 20% higher values and large standard deviations for P+ diffusion layers. On the other hand, the samples with N2/H2 RTA provides the same low and stable sheet resistance as those of the samples with TiN cap layer. XPS analysis shows that N2/H2 RTA suppresses oxidation of Co during the 1st RTA because of reduction by H2. B impurity in PMOS regions is known to retard silicidation of Co at 500°C. The retardation of silicidation seems to enhance oxidation of Co in PMOS regions by residual oxygen in the RTA chamber.
Process Windows of Titanium, Cobalt and Nickel Silicide In Deep Submicron Poly-Si Lines
Authors: Poon M. C. , Deng F. , Ho C. H. , Chan M. , Lau S. S.
Published: April 2011

Low resistivity (∼15μΩ-cm) TiSi2, CoSi2 and NiSi lines have been shown to be thermally stable and show no linewidth dependence after ∼850°C, 800°C and 700°C/1 hour annealing on poly-Si (B, As, and P-doped) with linewidths down to ∼0.43, 0.42 and 0.15 μm. Better thermal stability of silicides might be correlated to the larger poly grains formed after high dose implant and post-implant anneal.
High Resolution Auger Imaging Combined with Focused Ion Beam for the Investigation of Metal/GaAs Contacts in High Power Transistors
Authors: Etienne Patrick , Landesman Jean-Pierre , Wyczisk Frederic , Cassette Simone , Delage Sylvain
Published: April 2011

Inspecting and understanding the thermal stability of metal contacts in the context of reliability testing on high power transistors (especially in the GaAs technology) often necessitates to view atomic concentration profiles at deep interfaces. One common method for this purpose is the combined Auger spectroscopy/ion etching technique, where the region to be investigated is etched sequentially (with a “low” etch rate, typically in the Å/second regime) and Auger electron spectra (AES) are recorded at each step of the etching process. The 3 major resolution drawbacks of this approach are first that it is time-consuming, second that the spatial resolution is limited (atomic profiles on contact regions with lateral dimensions smaller that I R~m are difficult to obtain) and third that the interface of interest is “smoothed” during the etch process. The third point yields atomic concentration profiles with an apparent inter-mixing, which sometimes hinders observation of the details of interest for the interface under investigation.

We have used a different approach for this aspect of metal contact testing, in which the interface to be studied is first “revealed” by focused ion beam (FIB) micro-sectioning. After this preparation step, chemical images of the interface are directly obtained by high resolution Auger electron spectra mapping. The different operating conditions for the FIB process (orientation of the cross-section with respect to the transistor surface, preliminary procedures to eliminate residual roughness as well as surface contamination) have been optimized in order to produce Auger spectra free of any artifact. The approach is demonstrated on Au/GeNiAu ohmics contacts to the emitter electrode of GaAs-based hererostructure bipolar transistor, designed for high power amplification in the microwave regime. Ultimate spatial resolution of 20 to 30 nm on the Ayuger chemical images is demonstrated on an Auger microscope equipped with a Schottky field emitting tip.
Low Temperature CVD Route to Binary and Ternary Diffusion Barrier Nitrides for Cu Metallization
Authors: Kaloyeros Alain E. , Kelsey Jean , Goldberg Cindy , Anjum Dalaver , Chen Xiaomeng , Mirza Jawid , Kumar Kaushik , Arkles Barry , Han Bin , Sullivan John J.
Published: April 2011

The identification of viable diffusion barrier/adhesion promoter material and associated deposition processes is a critical factor in the successful development of structurally and electrically reliable copper based metallization schemes. As feature sizes continue shrinking, such materials are expected to delivery enhanced performance at increasingly thinner layers to allow maximum space utilization by the actual conductor. In this respect, Ta and W based binary and ternary nitrides present promising solutions in view of their hardness, chemical inertness, and thermal stability to high temperatures. Additionally, their availability in amorphous form provides the added benefit of inherent absence of grain boundaries, which usually serve as a primary diffusion path. This paper presents finds from the development of low0temperature (,350°C) CVD processes for the growth of ultrathin Ta, W, Ta-Si, and WSinitride layers for sub−0.18 micron device structures. These processes employ novel inorganic and metal-organic source precursors which allow for the in-situ, one-step, growth of binary and ternary nitrides from appropriate mixtures of the corresponding source precursors. Results will also be discussed from diffusion barrier studies which established performance metris for the applicability of such materials in copper interconnect technologies.
Modelling of Failure Time Distributions for Interconnects Due to Stress Voiding and Electromigration
Authors: Wolfer W. G. , Bartelt M. C. , Dike J. J. , Hoyt J. J. , Gleixner R. J. , Nix W. D.
Published: April 2011

A status report is given on a comprehensive modeling project aimed at predicting failure time distributions of interconnect lines. We discuss our novel approach to calculate the evolution of stresses in lines using elastic response functions. It is argued that this approach makes it possible to model the stress and damage evolution in a large ensemble of lines efficiently so that statistically meaningful failure time distributions can be generated.

The elastic response functions enable us also to derive a generalized Korhonen equation which includes the effects of mass transport at remote locations. Basic features of this equation are demonstrated with a one-dimensional implementation and its results are compared with the classical Korhonen [8, 9, 10] model.
The Effects of Microstructures on Normal and Early Failures of Interconnects Caused by Electromigration
Authors: Liu Yongkun , Diefendorf R. J.
Published: April 2011

Microstructure plays a key role in reliability of interconnects. However, a quantitative correlation between microstructure and reliability of interconnects is lacking. This paper develops a statistical description of effective diffusivity of interconnects by considering grain boundaries, bulk lattice and line interface diffusion, and introduces a microstructure-based electromigration lifetime prediction model for normal failures of interconnects. Further, the probability of early failure of interconnects due to a severe microstructural inhomogeneity is calculated. Using the sub-population failure model, the mean time to failure of interconnects, with a range of microstructures from polycrystalline to hyper-bamboo, are simulated. The reported increase in lifetimes of wide polycrystalline lines with increasing w/d is mainly ascribed to reservoir effects of bonding pads in test structures. Reported lifetime prediction model may be used as guidance for circuit design and accelerated testing.
Determination of the Effects of Strain on Electrical Resistivity in Patterned Interconnects
Authors: Sanchez John E. , Reilly Christopher J.
Published: April 2011

Sensitive measurements of electromigration-induced resistance changes in metallization interconnects have been previously interpreted as due to precipitation effects, vacancy concentration changes and local stress changes (due to the piezoresistance effect). The latter have the potential for characterizing the early stages of electromigration-induced diffusive phenomena prior to larger scale effects such as voiding and subsequent localized joule heating which seriously complicate the interpretation of small resistance changes. However the utility of such “early" measurements is also hindered by lack of an accurate knowledge of the stress coefficient of resistivity as a proper characterization of the change in strain state of the Al. We present measurements of the effects of volumetric strain on the resistivity of Al interconnects where the strain is induced by thermal expansion mismatch between the Al and surrounding passivations. The piezoresistance effect is characterized by properly accounting for the degree of interconnect constraint (and volumetric strain) induced by thermal expansion mismatch as a function of temperature for both passivated and unpassivated lines. Sensitive interconnect resistance versus temperature measurements for differently constrained interconnects (with different volumetric strains) thus allows for the measurement of the piezoresistance effect. Other effects such as solute or vacancy concentration changes with temperature are minimized since the measurements are performed by cooling the passivated and unpassivated lines from room temperature to approximately 70K, rather than by significant heating above room temperature. We determine the piezoresistance coefficient, defined as dρ/dɛv, where ρ = resistivity and ɛv = volumetric strain, to be approximately 1.5−5 Ω-cm, in rough agreement with previous work. The interpretation of sensitive resistance measurements as volumetric strains in isolated sections of interconnects undergoing electromigration-induced diffusion processes is described for specialized test structures.
Critical Length and Resistance Saturation Effects in Al(Cu) Interconnects
Authors: Gall M. , Müller J. , Jawarani D. , Capasso C. , Hernandez R. , Kawasaki H.
Published: April 2011

A new test structure for electromigration failure analysis of via-interconnect metallization schemes was developed. Multi-via/interconnect chain arrays were used in a parallel/serial testing arrangement. Due to improved statistical sampling, the multi-via test structures enabled measurement of drift velocity phenomena at via/interconnect interfaces with a very limited number of test devices per stressing condition, and without reducing the signal to noise ratio. Furthermore, realistic, production-type metallization schemes can be characterized without usually required “traditional” drift velocity-type metal stacks incorporating highly resistive shunt-layers. Critical length effects were investigated as a function of line length and current density. At interconnect lengths close to the critical Blech-length, resistance saturation effects were encountered and used for calculations of the critical current density-length product, (jl)*. Furthermore, a new resistance saturation model was developed and found to correlate well with the acquired data. Critical length effects can accurately be measured and used for length-dependent interconnect performance evaluation on the device-level.
Local Channel Temperature Measurements on Pseudomorphic High Electron Mobility Transistors by Photoluminescence Spectroscopy
Authors: Landesman J.P. , Martin E. , Depret B. , Fily A. , Braun P.
Published: April 2011

The technique of spatially resolved photoluminescence (PL) spectroscopy was used to determine the local channel temperatures on GaAs/GaInAs/GaAlAs pseudomorphic high electron mobility transistors. By focusing a laser beam onto the different regions of the DC-biased transistor, it is shown that the channel temperature can be determined from the energy shift of one of the peaks in the PL spectra, with a spatial resolution of about 1 µm and a temperature resolution in the order of 1 °C. In particular, an asymmetry in the temperature distribution between the drain and source sides is observed. Using this approach, detailed temperature maps of the devices were obtained, as a function of the gate-source voltage VGS. These experimental temperature values are also compared with predictions derived from an analytical model of the thermal resistance in these devices.
Mems as Temperature Sensors During High Temperature Processing
Authors: Tada H. , Abramson A. R. , Nieva P. , Zavracky P. , Miaoulis I. N. , Wong P. Y.
Published: April 2011

In high temperature processing of microelectronics such as rapid thermal processing (RTP), an accurate measurement of temperature is critical in fabricating defect-free devices. Currently, temperatures during such processes are measured using thermocouples or pyrometers. However, accurate measurements with thermocouples are troublesome due to the difficulties in holding the thermocouples in place and maintaining good thermal contact. A further drawback for thermocouples is that they are highly intrusive. For pyrometers, optical interference effects and partial transparency limit their applicability and the local temperature of wafers near the electronic devices are difficult to measure using pyrometer due to relatively large spot size. Microelectromechanical systems (MEMS) technology is being used in developing innovative temperature sensor (T-MEMS), which allow an ex-situ examination of the maximum temperature reached during a thermal process by creating a permanent change in structure at high temperatures. The performance of the device relies on the thermophysical properties of the materials; specifically, the Young's modulus, thermal expansion coefficient, and the ultimate strength must be considered for silicon, and silicon nitride. Through careful experimental design and accurate modeling of their structural behavior, the high-temperature material properties can be determined using the T-MEMS and calibrated furnaces.
Finite-Element Modeling of Residual Stress in SiC Diaphragms
Authors: DeAnna Russell G. , Zorman Christian A. , Mehregany Mehran
Published: April 2011

Finite-element modeling of the residual stress due to expansion-coefficient mismatch between a 3C-SiC film and Si substrate is presented. The change in residual stress after bulk etching of the silicon substrate to create a suspended diaphragm is also presented. 1, 2, or 3 μm-thick 3C-SiC films are grown at 1600 K on a 100 mm diameter, 500 μm-thick, (100) Si substrate using atmospheric pressure chemical vapor deposition (APCVD) in a cold-wall, vertical-geometry, RF-induction-heated reactor. An axisymmetric, finite-element analysis (FEA) of the cooling and etching process is presented using the ANSYS54 finite-element package. The etching process is modeled by removing the Si elements in the etched region after cooling from film-growth to room temperature. The results show that residual stress in the diaphragm decreases from 3 to 8 percent after etching.
Resonance Method: An Attractive Way to Evaluate Mechanical Properties of Thin Gold Films
Authors: Attia P. , Hesto P.
Published: April 2011

Micromechanical test structures have been developed for evaluating mechanical properties of thin gold films. Using micromachining techniques, gold cantilever beams of different geometry (typically 40 to 100-µm-long, 2-µm-thick and around 1-µm-wide), were fabricated. These cantilevers were resonated by electrical excitation in a scanning electron microscope (SEM) and Young's modulus, Q-factor and fatigue properties were deduced from these experiments. The longest cantilevers showed a slight upward curvature which allowed the internal stress gradient to be evaluating.
Round-Robin Tests of Modulus and Strength of Polysilicou
Authors: Sharpe W. N. , Brown S. , Johnson G. C. , Knauss W.
Published: April 2011

The Young's modulus and strength of polysilicon specimens manufactured in the same production run were measured in four different laboratories. Specimens subjected to in-plane bending were tested at U. C. Berkeley and at Failure Analysis Associates, and tensile measurements were made at Caltech and Johns Hopkins. All specimens were produced at the Microelectronics Center of North Carolina (MCNC).

In bending, the Young's modulus for specimens nominally 2 µm thick was measured as 174 GPa and 137 GPa; whereas in tension, a value of 132 GPa was obtained. Modulus values of 136 GPa and 142 GPa were measured in tension on specimens nominally 1.5 µm and 3.5 µm thick. Strengths of the brittle polysilicon were 2.8 and 2.7 GPa in bending and 1.3 GPa for both thicknesses in tension.

These preliminary results were presented atSymposium N - Microelectromechanical Structures for Materials Researchat the Materials Research Society meeting in April 1998. This paper is a short overview of the test methods — each of which is described elsewhere — and a documentation of the results presented at that time.
Strength of Surface Micromachined Diaphragms
Authors: Yang Xing , Siu Frances M. , Tai Yu-Chong
Published: April 2011

This paper presents the study of the strength of surface micromachined diaphragms. It is found that the diaphragm strength strongly depends on the diaphragm boundary conditions. A new fabrication technique which does not change the mask and fabrication process is proposed to improve the common step-up boundary condition. Test diaphragms with diameters from 200 µm to 800 µm and three different boundary conditions have been fabricated using silicon nitride/PSG and silicon nitride/polysilicon surface micromachining processes. Experimentally, it is found that the strength of the diaphragms is significantly improved with the new boundary conditions. The application of this technique to other surface micromachined structures is also described.
Synthesis and Intermolecularly Mediated Assembly of Organic Pigment in Hybrid Coating Films
Authors: Yan Y. , Duan Z. , Chen D.-G. , Chaudhuri S. Ray
Published: April 2011

The insoluble, strongly hydrogen bonded organic pigment of 3,6-bis-(4-chlorphenyl)-l,4- diketopyrrolo [3,4-c] pyrrole was transiently blocked by adding carbamate groups, and consequently incorporated into organic-inorganic hybrid matrices by a sol-gel process. The homo- (pigment-pigment) and hetero-intermolecular (pigment-matrix) interactions were found to control both the assembly and dispersion of pigment molecules in the hybrid coating films. A weaker interaction between matrices and pigment molecules results in aggregation of the carbamate pigment in the methyl-silicate films. A stronger interaction forms a homogenous dispersion and coloration of the phenyl-silicate films. The as-prepared methyl- and phenylsilicate films doped with the organic pigment were distinguished by a morphology change and a blue (hypsochromic) shift in absorption from 550 to 460 nm. Thermal treatment can remove the carbamate groups and in-situ form the organic pigment in the hybrid films.
Nanocomposites From Polymers and Layered Minerals
Authors: Fischer H. R. , Gielgens L. H. , Koster T. P. M.
Published: April 2011

Composite materials consisting of polymeric matrix materials and natural or synthetic layered minerals like clays were prepared by using special compatibilizing agents between the two intrinsically non-miscible materials. These compatibiliseres are block- or graft copolymers combining one part of the polymer identically and/or completely miscible with the organic polymer (matrix compound) an another part compatible/miscible with the natural mineral. The interaction between the first part of the compatibiliser is preferentially an ionic interaction or an interaction via H-bonds. This interaction leads to a separation of the mineral into single sheets and a subsequent homogeneous incorporation of these sheets into the polymer matrix material.
Inorganic- Organic Hybrid Materials For Photonics
Authors: Lal M. , Joshi M. , Kumar D. N. , Friend C. S. , Winiarz J. , Asefa T. , Kim K. , Prasad Paras N.
Published: April 2011

Molecular materials comprised of inorganic:organic composites are of considerable interest in photonics, optoelectronics and biophotonics. We report broad band lasing and tunable filters in sol-gel processed poly (p-phenylene vinylene) PPV: Silica composites. Optical power limiting in near IR wavelength region is also reported in dye doped PPV: silica multiphasic nanocomposites. For making hybrid inorganic: organic composites the reverse micelle mediated synthesis technique has been exploited to synthesize dye encapsulated metal oxide particles, thiocresol capped CdS clusters, Cul and AgI nanoparticles. These particles were dispersed in polymeric matrix for applications in photoconductivity and photorefractive measurements.
Optical and Electronic Properties of Conjugated Polymer -Nanocluster Semiconductor Hybrid Systems
Authors: Narayan K. S. , Manoj A. G. , Nanda J. , Kuruvilla B. A. , Sarma D. D. , Claflin B. , Lucovsky G. , Claflin B. , Lucovsky G.
Published: April 2011

Conjugated polymers are intensively pursued as candidate materials for emission and detection devices with the optical range of interest determined by the chemical structure. On the other hand the optical range for emission and detection can also be tuned by size selection in semiconductor nanoclusters. The mechanisms for charge generation and separation upon optical excitation, and light emission are different for these systems. Hybrid systems based on these different class of materials reveal interesting electronic and optical properties and add further insight into the individual characteristics of the different components. Multilayer structures and blends of these materials on different substrates were prepared for absorption, photocurrent (Iph), photoluminescence (PL) and electroluminscence (EL) studies. Polymers chosen were derivatives of polythiophene (PT) and polyparaphenylenevinylene (PPV) along with nanoclusters of cadmium sulphide of average size 4.4 nm (CdS-44). The photocurrent spectral response in these systems followed the absorption response around the band edges for each of the components and revealed additional features, which depended on bias voltage, thickness of the layers and interfacial effects. The current-voltage curves showed multi-component features with emission varying for different regimes of voltage. The emission spectral response revealed additive features and is discussed in terms of excitonic mechanisms.
Controlling the Particle Size of Quantum Dots Incorporated in Hybrid Materials
Authors: Monte Francisco Del , Xu Yuhuan , Mackenzie John D. , Claflin B. , Lucovsky G.
Published: April 2011

Semiconductor PbS quantum dot-doped Ormocers were successfully prepared by the sol-gel technique. Ormocers preparation was based on the use of trifunctional silane precursors at the solution stage. Formation of PbS particles took place in the pores of the Ormocers through lead precursor reaction with H2S gas. It was observed that temperature was an important factor in the reaction leading to the first appearance of PbS particles. The dot size of PbS was controlled through chemical interaction with the non-hydrolyzed groups of the trifunctional silane precursors. These groups prevent uncontrolled nucleation and aggregation processes during the particle formation and growth. The control of particle size was studied at different conditions for nucleation and aggregation. Determination of the average particle size was done by XR-Diffraction. Optical absorption spectra were also measured at the UV-VIS wavelength range. Absorption edge blue shifts show the quantum confinement effect in these materials.
Physical Performance of Polymer Systems Containing Micro and Nano Fillers
Authors: Gao Z. Justin , Tsou Andy H. , Claflin B. , Lucovsky G.
Published: April 2011

This paper deals with polymer systems containing micro and nano organic/inorganic fillers. A general framework is established to study the effects of the filler and matrix properties on the physical performance of filled polymer systems. A model is proposed to predict elastic moduli, break strength and break strain of polymers containing fillers. The model, based on rigorous continuum mechanics principles, takes into consideration the filler/filler interactions, incorporates the nonlinear synergistic effects of fillers, and agrees very well with experimental measurements.
Synthesis and Characterization of Hybrid Materials Obtained Through Hydrolysis of Alkoxysilanes and Vanadium Alkoxides
Authors: Alonso B. , Maquet J. , Viana B. , Sanchez C.
Published: April 2011

New hybrid materials made of polydimethylsiloxane species (chains and cyclic species) crosslinked at the molecular level by O=V(O-)3 units with a very high degree of homogeneity and dispersion even for a V/Si ratio of 10% have been synthesized and characterized mainly by 29Si, 51V MAS NMR, DSC and DMA. The structure of these hybrids is very different from those proposed for the other dimethylsiloxane-transition metal oxide systems. These dimethylsiloxanevanadates copolymers exhibit higher glass transition temperatures than usual PDMS and a very sharp variation of the loss factor tanδ. These hybrid materials exhibit at low temperature a strong phosphorescence usually associated to a Ligand to Metal Charge Transfrer process.
Introduction of Organic Moieties into Transition-Metal Oxide Matrices via Phosphonate Groups
Authors: Mutin P.H. , Delenne C. , Medoukali D. , Corriu R. , Vioux A.
Published: April 2011

Transition metal oxide / phenylphosphonate hybrids with M/P ratios ranging from 1 to 5, (M= Ti, Zr) and metal phosphonates (M/P = 0.5) have been prepared by a sol-gel process involving in a first step the non-hydrolytic condensation between metal alkoxide and phosphonic acid leading to M-O-P bonds, followed by the hydrolysis-condensation of the remaining M-OR groups. The composition, texture and structure of the materials were investigated using EDX, TGA, XRD, IR and 31P NMR.