bluuebunny/crossref_metadata_2025 huggingface dataset:
Mocvd Growth and Properties of Erbium Doped GaAs
Authors: Langer Dietrich W. , Li Yabo , Fang Xiao M. , Coon Victoria
Published: March 2011

Erbium doped GaAs was grown by metalorganic chemical vapor deposition using a novel liquid precursor: Tris(n-butylcyclopentadienyl)erbium, Er(C4H9C5H4)3. Growth parameter, i.e. temperature, V/III ratio, Er-vapor flow, were investigated. The maximum erbium incorporation in layers with excellent morphology was 1.2× 1019cm−3. The erbium-related photoluminescence intensity and the incorporated concentrations, as measured by secondary ion mass spectrometry, were correlated. Based on a simple model for, the excitation dependence of the emission, the non-radiative Auger-type process was estimated to be nearly five times that of the energy transfer process from bound excitons to the Er3+ ions, which subsequently resulted in the Er-related light emission. Temperature induced quenching of the emission was found to be dominated by transitions with an activation energy of 74meV.
Effects of Ytterbium Addition on Liquid Phase Epitaxial Growth of InGaAs/InP Heterostructures
Authors: Davis A. , Dauplaise H.M. , Lorenzo J.P. , Ramseyer G.O. , Horrigan J. A.
Published: March 2011

We have investigated the effects of Yb addition to melts used for the growth of InGaAs/InP heterostructures by liquid phase epitaxy. Our results indicate that impurities in the Yb play an important role in determining the changes in electrical properties observed in the epilayers after Yb treatment of the melt. We have examined samples using double-crystal x-ray diffractometry, photoluminescence, Hall/van der Pauw measurements, and secondary-ion mass spectroscopy. After Yb treatment, the residual carrier concentrations of the epilayers were reduced by more than one order of magnitude and the samples luminesced more strongly; while the lattice matching and crystal quality of the epilayers were not measurably affected by the Yb. There was a smaller-thanexpected ncrease in the 77K mobility and a marked increase in the compensation ratio of the epilayers grown after the addition of Yb to the melt. We believe the Yb is both acting as a scavenging agent in the melt, combining with impurities that otherwise would have been incorporated in the epilayers, and introducing deep level impurities of its own, which are incorporated into the grown layers.
Optical Activity of Yb3+ in MeV Ion-Implanted InP.
Authors: Uekusa S. , Majima A. , Katsumata H. , Noyori Y. , Kumagai M.
Published: March 2011

For the evaluation of an implanted layer, photoluminescence (PL) and photoluminescence excitation (PLE) measurements, which are nondestructive and sensitive methods for identifying impurities and defects, were performed. Yb3+ -related sharp luminescence was observed at a wavelength of 1002nm, due to the transitions which occurred between the spin-orbit levels 2F5/2→2F7/2 of Yb3+ (4f13). Most efficient luminescence of Yb3+ was achieved at an excitation wavelength of around 880nm. The luminescence intensity of this peak (Yb3+) decreased with an increase in annealing temperature. Since the peak has not been observed for good samples in crystallinity, it may indicate that new, efficient energy transfer processes to rare-earth ions occur through the defect energy level. Especially, for the sample annealed at 600°C, Yb-related luminescence intensity excited by the photon energy below the band gap is about 3 times larger than that of excited by the photon energy above the band gap.
Tm Doping of Lead Telluride
Authors: Ryabova Ludmila I. , Tamm Marina E.
Published: March 2011

Doping with the rare earth elements is widely used for the improvement of parameters of the PbTe-based lasers. It has been found that Tm is a donor in PbTe, and the solubility of TmTe in PbTe does not exceed 7 - 8 mol.%. Electron concentration in obtained PbTe(Tm) crystals reaches 4.1020 cm-3 and depends on Tm content and on deviation from stoichiometry. The analysis of the magnetoresistance oscillation picture shows no variation of the energy spectrum parameters for Tm contents less than I at.%. The g-factor does not change as well. This may be due to a rather small exchange interaction between Tm atom, which is magnetic in both +2 and +3 valence states, and band electrons. The experimental data for PbTe(Tm) are compared with the properties of semimagnetic PbTe(Cr) with quite the same electron consentration value.
Excitation and De-Excitation Mechanisms of Rare-Earth Ions in III-V Compounds: Optically Detected Microwave-Induced Impact Ionization of Yb Dopant in Inp
Authors: Gregorkiewicz T. , Liesertr B.J. Heijmink , Tsimperidis I. , de Maat-Gersdorf I. , Ammerlaan C.A.J. , Godlewski M. , Scholz F.
Published: March 2011

The excitation mechanisms of rare-earth dopants in III-V semiconductors are being reviewed. The discussion is focused on ytterbium-doped InP crystals for which a particularly large amount of experimental data has been gathered. Here, the results obtained recently by optically detected microwave-induced impact ionization are being examined in detail. On the basis of the experimental findings it is argued that the intrashell luminescence is excited by an intermediate state involving binding of an exciton. Direct evidence for the existence of such a state, of pseudoacceptor type, will be given. The nonradiative recombination channel responsible for the fast decay of Yb luminescence will also be discussed and, for the first time, evidence for an Auger process will be presented. It will also be shown that the nonradiative channel may be effectively blocked by impact ionization of a participating carrier.
Luminescence Properties of Yb-Doped Inp
Authors: Lozykowski H. J. , Alshawa A. K. , Pomrenke G. , Brown I.
Published: March 2011

The photoluminescence, time resolved spectra and kinetics of Yb implanted InP samples are studied under pulsed and CW excitations (above and below band-gap) at different temperatures and excitation intensity. The photoluminescence intensity and decay time as a function of temperature is explained by a proposed new quenching mechanism involving Fe ion. The rise and decay times depend on excitation intensity. The above experimental facts was explained using the kinetics model developed by H.J. Lozykowski [2]. The numerically simulated luminescence rise and decay times show a good quantitative agreement with experiment, over a wide range of generation rates. The electric field InP:Yb photoluminescence quenching was investigated and reported for the first time.
Excitation and Relaxation Processes of Impact Excitation Emission of Er3+ Ions in InP
Authors: Kimura T. , Ishida H. , Yugo S. , Saito R. , Isshiki H. , Ikoma T.
Published: March 2011

Time-resolved excitation and relaxation processes of the impact excitation emission (EL) at 1.54μm of Er3+ ions doped in InP were investigated in the temperature range from 77K to 330K. The decay process was almost exponential in all the measured temperature range and showed little thermal quenching. The decay time of 2ms at 77K decreased only to tms at 330K. This result contrasted with the large thermal quenching and nonexponential characteristics of the photoluminescence (PL) time decay at higher temperatures, suggesting different Er3+ centers excited between EL and PL. A two-emission-center model is proposed and the different behaviors of thermal quenching and time decay between EL and PL emissions are consistently explained.
Impact excitation of Er-doped GaAs and the rare-earth sites in III-V compound semiconductors
Authors: Chang S. J. , Takahei K. , Nakata J. , Su Y. K.
Published: March 2011

We report the first study of impact excitation of Er ions in GaAs. The MOCVDgrown, p+-n structured EL devices were fabricated by growing, at different temperatures, GaAs:Er layers on top of the n+ GaAs substrates. P+ layers were made by Zn diffusion from the top surfaces. When we forward biased these diodes, their EL spectra were similar to their respective PL spectra for each sample but different from each other's. However, when we reverse biased these diodes, EL spectra obtained from all samples are the same, which were different from their PL spectra. These results indicate that the Er center(s) excited by direct impact is different from the Er center(s) excited through electron-hole recombination and subsequent energy transfer. By using RBS channeling, we found that most of the Er ions, in our MOCVD-grown GaAs:Er samples, occupy a displaced tetrahedral interstitial site. From these PL, EL and RBS results, we conclude that only a small amount of Er ions emit luminescence when they are indirectly excited through energy transfer.
Movpe of Rare Earth Doped III-V Semiconductors
Authors: Scholz F. , Weber J. , Pressel K. , Dörnen A.
Published: March 2011

Different III-V compound semiconductors have been doped with the rare earth (RE) elements Yb, Er, and Tm using atmospheric pressure metalorganic vapor phase epitaxy. Best results have been obtained using the novel metalorganic compounds tris-isopropyl-cyclopentadienyl-RE as precursors which have an acceptable vapor pressure and can be used as liquids at bubbler temperatures of 60°-90°C. Only Yb has been found to occupy a regular lattice site in InP, whereas the other RE show complex optical spectra because of their incorporation in form of different centers and clusters.
Rare-Earths Applications in III-V Crystal Growth Technology.
Authors: Zakharenkov Leo
Published: March 2011

The problem of manufacturing high purity semiconductor materials with super high electron mobility is among important, though technologically difficult ones.

Traditional with regard to III-V compounds this problem has been solved using the following technique

- the choice of alternative crucible material

- the application of high purity initial materials

- oxygen doping for shallow donors removal

- isoelectronic doping (e.g. bismuth)

We can also mention other attractive directions in this sphere of activity, such as secondary methods of influence upon the crystals grown - heat treatment and purification by radiation methods, the latter ones still wanting being explored.

From the late 70's we have been carrying out the investigations of the rare-earths (RE) influence upon the electrical characteristics of InP, and later - of GaAs.

In this work submitted are the results of comprehensive investigation of RE applications in bulk III-V crystal growth technology with the aim of purification and heavy doping of the crystals.
Erbium Doped Gallium Arsenide a Self-Organising Low Dimensional System
Authors: Peaker A.R. , Efeoglu H. , Langer J.M. , Wright A.C. , Poole I. , Singer K.E.
Published: March 2011

The growth of erbium doped gallium arsenide by MBE at normal substrate temperatures (∼580°C) is constrained by a solubility limit of 8×1017 cm−3. This is much less than is desirable for optical emitters using the forbidden 4f transitions of Er3+ to produce radiation at 1.54μm. We have developed an MBE technique where it is possible to produce spherical mesoscopic precipitates containing erbium as a matrix element within the gallium arsenide. Structural and analytical studies indicate that the precipitate is cubic (rock salt) erbium arsenide. The physical size of the precipitates is self limiting as a result of surface migration occurring during MBE growth. By adjusting the growth conditions it is possible to produce an array of uniform erbium arsenide quantum dots of a size chosen from the range 10-20Å. The dot density can be varied by changing the erbium flux.
EuTe/PbTe Superlattices: Mbe Growth and Optical Characterization
Authors: Springholz G. , Yuan Shu , Bauer G. , Kriechbaum M. , Krenn H.
Published: March 2011

The heteroepitaxial growth of EuTe on PbTe (111) by molecular beam epitaxy (MBE) was investigated using in situ reflection high energy electron diffraction (RHEED). As a function of substrate temperature and Te2 flux rate, the resulting EuTe (111) surfaces exhibit several different surface reconstructions corresponding to Te-stabilized or Eu-stabilized surfaces. The Eustabilized surface shows a (2√3 × 2√3)R30° surface reconstruction. Because of the strain induced tendency for 3D islanding, only in a narrow window of MBE growth parameters perfect 2D layer-by-layer heteroepitaxial growth exists. Using such optimized MBE growth conditions, we have fabricated a series of PbTe/EuTe superlattices. In such superlattices the wide band gap EuTe layers act as barriers and the narrow band gap PbTe as quantum wells. The superlattices were investigated by high resolution x-ray diffraction, showing their high structural perfection. Modulated low temperature Fourier transform infrared reflection measurements were performed in order to determine the confined energy levels in the PbTe quantum wells. The measurements indicate that mini-subbands are formed in the PbTe quantum wells with a mini-band width of 22 meV in agreement with envelope function calculations.
Electron Structure and Mechanism of Excitation of the Rare-Earth ions in the III-V Semiconductors
Authors: Masterov Vadim F.
Published: March 2011

The review of results of KPR, ODMR, RBS and PL investigations of the III-V semiconductors doped with rare-earth elements is represented. The possible sites of RE related centers in hostare discussed. The possible mechanism of excitation of intrashell f-f transitions is considered. The simple theoretical model of the substitutional RE center in a binary semiconductors is discussed.
The Theory of Rare-Earth Impurities in Semiconductors
Authors: Lannoo Michel , Delerue C.
Published: March 2011

The chemical trends of rare-earth impurities in semiconductors are analyzed on the basis of a selfconsistent tight-binding Green's function technique. The 4f states are treated as a frozen core and we get essentially no 5d derived states in the gap. We calculate the 4f ionization levels in the solid and conclude that the stable state is mostly 3+. We then describe the results of a LDA calculation for Er in silicon which we find to be stable in the interstitial position. Finally we consider in some detail the case of Yb in InP where we discusss the possible origin of the shallow gap levels and the mechanisms for luminescence excitation and quenching.
Kinetics of the Luminescence of Isoelectronic Rare-Earth Ions In III-V Semiconductors
Authors: Lozykowski H.J.
Published: March 2011

In this work we have developed a model for the kinetics of the energy transfer from the host lattice to the localized core excited states of rare earth isoelectronic structured traps (REI-trap). We have derive a set of differential equations for semi-insulating semiconductor governing the kinetics of rare earth luminescence. The numerically simulated rise and decay times of luminescence show a good quantitative agreement with the experimental data obtained for InP:Yb, over a wide range of generation rates.
Erbium Doped Semiconductor Thin Films Prepared by Rf Magnetron Sputtering
Authors: Kim Hong Koo , Li Cheng Chung , Fang Xiao Ming , Solomon James , Nykolak Gerald , Becker Philippe C.
Published: March 2011

Highly Er-doped (∼ 1020 atoms/cm3) silicon and silica films were deposited by RF magnetron sputtering. Erbium was doped into the host material by co-sputtering technique. Deposited films (0.5 - 1.2 µm thick) were characterized by photoluminescence (PL), secondary ion mass spectroscopy (SIMS), and fluorescence decay measurements. Er-doped silica glass films show a strong, room-temperature luminescence at 1.54 µm wavelength. In contrast, Er-doped silicon films show a weak luminescence at room temperature. However, a big enhancement in the Er3+ luminescence was observed after a proper annealing, for example, 900 °C for 30 to 120 min in air ambient, resulting in the luminescence intensities comparable with that of the Er-doped silica films. This enhancement is attributed to the oxygen incorporation into the Si host film during the annealing, thus forming an Er-doped oxide layer on top of the film. The result suggests that Er-O bonding plays important role in forming optically active erbium ions. Erdoped, three-component silicate glass (SiO2 + A12O3 + MgO) films were also sputter deposited to investigate the dependence of Er3+ luminescence on the host material's composition. Even stronger luminescence was observed from the Er-doped, three component silicate glass films compared with the Er-doped SiO2 films.
Er3+-Doped Silicon Prepared by Laser Doping
Authors: Asatsuma T. , Dodd P. , Donegan J. F. , Lunney J. G. , Hegarty J.
Published: March 2011

We have carried out an investigation of the laser doping of Si with rare-earth ions. In this technique a silicon surface coated with a thin layer of the rare-earth metal is melted with a pulsed laser, the dopant is mixed in the molten layer, and incorporated in the crystal during regrowth. Er was chosen for the main part of our work as it is the best characterized of the rare-earth ions in Si. Luminescence is observed around 1.54µm and is assigned to optical transitions on Er3+ ions. This preliminary study shows that this new technique is viable for the production of optically active Er3+ in Si.
Ic Compatible Processing of Si:Er for optoelectronics
Authors: Ren F. Y. G. , Michel J. , Sun-Paduano Q. , Zheng B. , Kitagawa H. , Jacobson D.C. , Poate J.M. , Kimerling L. C.
Published: March 2011

We have fabricated the first Si:Er LED, operating at 300 K, based on an understanding of the Si-Er-O materials system. Er-doped Si (Si:Er) provides an exciting opportunity for the monolithic integration of Si based opto-electronics. In this paper, Er-Si reactivity, and Er diffusivity and solubility have been studied to establish Si:Er process compatibility with a silicon IC fabline. Er3 Si5 is the most stable silicid formed; and it can be oxidized into Er2O3 at high temperature under any oxidizing conditions. Among Er compounds, Er2O3 luminesces and Er3Si5 and ErN do not. The diffusivity of Er in Si is low and SIMS analysis yields a diffusivity D(Er) ∼ 10−12cm2/s at 1300 C and ∼ 10−15cm2/s at 900 C, and a migration enthalpy of δHm(Er) ∼ 4.6 eV. The equilibrium solubility of Er in Si is in the range of 1016 cm−3 at 1300 C. The Si:Er LED performance is compared with GaAs LEDs to demonstrate its feasibility.
Characterization of Two Electromigration Failure Modes In Submicron Vlsi
Authors: Atakov Em , Clement JJ. , Miner B.
Published: March 2011

Grain-bondary erosion-type voids and transgranular slit-like voids are found to be two competing electromigration failure modes in VLSI interconnects. The effects of interconnect linewidth, microstructure, process variables and stress conditions on the two failure modes were studied.
Reliability Study of TiN/AlCu/TiN Interconnect in Submicron Cmos Process
Authors: Kuo Arthur T. , Choudhury Ratan , Hata William
Published: March 2011

In this paper, the effect of thin film deposition conditions on the multilayer interconnect reliability was studied. Experimental results indicated the most reliable TiN/AICu/TiN interconnect was obtained at the deposition temperature of 350 °C without any substrate bias. This observation was in close agreement with thin film characteristics such as resistivity, grain size and intermetallic formation seen for those deposition conditions. SEM pictures showed the anti-reflective coating (ARC) TiN film did successfully suppress inter-plane extrusion during electromigration test. The failure mechanism for electromigration was also revealed to be mass transport as the result of the grain boundary diffusion instead of catastrophic open failures. The stress migration studies found that TiN/AICu/TiN had superior stress migration resistance than AICu alone.
Effect of TiW As Adhesion Layer And Underlying Metal On Electromigration Characteristics of Tungsten Via Plugs
Authors: Gadepally Kamesh , Reddy Padala Krishna , Niew Siew , Merrill Richard , Lahri Rajeeva , Biswal Madan
Published: March 2011

The use of Tungsten plug technology to obtain good step coverage in vias and contacts is a well know fact. The effect of TiW as an adhesion layer between the plug and the overlying Aluminum is shown in this paper to have a significant impact on the electromigration characteristics of this scheme. A comparison between plug and non-plug technology is also made keeping the aspect ratios the same. Also discussed in this paper will be the effect of the first metal (Tungsten vs Aluminum) on electromigration characteristics. Constant current DC electromigration stressing was performed on via chains and the results are discussed. Discussed, also, are SEM cross sections (XSEM) of the stressed vias indicating the failure modes. An idealized metal scheme will be presented and discussed.
Stress Gradient and Relaxation Measurements in Al and Oxygen-Implanted al Films.
Authors: Besser Paul R. , Bader Stefan , Venkatraman Ramnath , Bravman John C.
Published: March 2011

Synchrotron radiation has been used in the grazing incidence geometry to determine the stress gradients and stress relaxation in 0.6 μm thick Al uniform films. We have examined both pure Al and Al implanted with 3 at% oxygen. The films were cycled between 23°C and 400°C. The surface of the pure Al films was more highly stressed, on average, than the film as a whole, both in tension and in compression. In contrast, the surface of the oxygen-implanted film was relaxed relative to the average film stress in compression but was more stressed in tension. The larger gradient in stress in the implanted films reduces during subsequent thermal cycling. These differences are attributed to the microstructures of the films. The 0-implanted film develops a small, non-columnar grain structure and forms small AI2O3 particles during annealing. The small grain size allows diffusional relaxation to occur in compression, relieving the stress in areas close to the film surface.
Stress in Copper thin Films With Barrier Layers
Authors: Vinci Richard P. , Bravman John C.
Published: March 2011

Wafer curvature and grazing incidence x-ray scattering (GIXS) techniques were used to investigate the biaxial stresses induced in blanket Cu films during a thermal cycle to 460°C and back to room temperature. Cu was deposited by DC sputtering at ambient temperature. Several different barrier layer materials — SiO2, W, Ta, TiN, and Si3N4 — were used to compare any effect barrier choice might have on Cu microstructure evolution and mechanical behavior. Ta and Si3N4 encouraged a strong (111) Cu texture. A W barrier led to an untextured microstructure which underwent large, uneven grain growth during thermal cycling. Several samples were capped with a Ta layer which affected the stress behavior during cooling by inhibiting dislocation motion. An inverse relationship between strength and thickness was also documented.
Stress Mapping Near Simulated Defects in Thin Film Wiring Using X-ray Microbeam Diffraction
Authors: Dehaven Patrick , Goldsmith Charles
Published: March 2011

The stress distribution about a series of deliberately fabricated defects in a Cu/Ni/Au/Cr redundant metal stack deposited on a Cr/Cu/Cr serpentine has been studied via x-ray microbeam diffraction using the sin2 ψ, technique. Strong directional anisotropies in the stress were found for both the second level nickel and copper. The extent of nickel stress relaxation from the edge of a defect far exceeded that predicted by a simple metal on substrate model. The size of the defect did not appear to significantly influence the stress distribution in the second level metal; however, the data suggest that the linewidth may influence the magnitude of the stress along the length of a line when near a defect or other sharp discontinuity.
X-ray Determination and Finite-Element Modeling of Stress in Passivated Al-0.5%Cu Lines During Thermal Cycling.
Authors: Besser Paul R. , Mack Anne Sauter , Fraser David , Bravman John C.
Published: March 2011

We have measured the principal strain state of AI-0.5%Cu lines passivated with silicon nitride directly and used it to calculate the stress state. The stress was determined as the lines were thermally cycled from room temperature to 450°C. The general stress-temperature behavior shows good fundamental agreement with that calculated using finite-element methods, although the magnitude of the stresses measured with x-rays is less than that predicted by modeling due to stressinduced voiding in the lines. This is shown with a high voltage scanning transmission electron microscope (STEM) operated in the backscattering mode.
Electromigration Induced Resistance Changes in Passivated Aluminum Thin Film Conductors
Authors: Möckl U.E. , Lloyd J.R. , Arzt E.
Published: March 2011

The relative change in resistance due to electromigration was studied in thin (0.7 μm) film conductors of AI-0.5% Cu Alloy passivated with a 1 μm thick glass passivation using a sensitive AC bridge technique. In contrast to previous experiments performed on unpassivated structures where a roughly linear resistance increase was observed, a saturation value for the resistance increase was observed which was seen to be a function of temperature and the applied current density. The results were found to be consistent with a Shatzkes and Lloyd electromigration model.
Effect of Line Width on Electromigration of Textured Pure Aluminum Films
Authors: Knorr D.B. , Rodbell K.P.
Published: March 2011

Three conditions of pure aluminum films were deposited, patterned into electromigration test structures, and annealed at 400°C for I hour. The grain size distribution was essentially the same for all conditions, but the textures were substantially different. Electromigration failure distributions were developed at 225°C and 1 MA/cm2for line widths of both 1.8 μm and 0.5 μm. Three conditions were tested at the wider line width while the strongest and weakest textures were evaluated in the narrow line width. Texture exerts a dominant effect at the wider line width where the lines are polycrystalline. The values of t50increase as texture becomes stronger although σ varies from <0.5 for strong textures to >1 for a bimodal failure distribution in the weakest texture. In the narrow lines, the texture effect is substantially reduced, and the failure distributions are bimodal with a few early fails followed by a monomodal distribution characterized by a low cr. The electromigration behavior is discussed in terms of both texture and the line width to grain size ratio.
Characterization of Oxides and Thin Films
Authors: Baikie Iain D. , Bruggink Gerrit H.
Published: March 2011

Using a new, high resolution, microscopic Scanning Kelvin Probe (SKP), work function topographies of metal, semiconductor and metal/semionductor surfaces have been studied in both Ultra-High-Vacuum (UHV) and air environments.

The work function is a very sensitive indicator of surface and Interface condition and has been previously utilized to examine preparation methods, surface roughness, adsorption processes, thin film monitoring and residual surface contamination.

Extension of the basic method, via Illumination of the semiconductor surface under the tip allows one to probe the local density of states (LDOS). Variations in LDOS can be used to monitor metal contamination, interface traps, bulk contamination, oxide imperfections, etc.

Work function topographies generated in this fashion have application in quality control at all stages of the manufacturing process. The Kelvin method of measuring work function is non-contact and non-destructive, utilizing neither high fields nor large currents. It can be applied to a variety of environments ranging from UHV to air and at a wide range of temperatures.
The Effect of Cu Alloying on Al Alloy Thin Films: Microstructural Mechanisms That Enhance Electromigration Resistance
Authors: Frear D. R. , Michael J. R. , Romig A. D.
Published: March 2011

The microstructural evolution of unpatterned Al-2wt.%Cu thin films has been examined to elucidate the mechanism by which copper improves electromigration resistance. After annealing at 425°C and cooling to room temperature at a rate of approximately 1°C/min., the microstructure of the Al-Cu films consisted of 1 μm aluminum grains with θ-phase Al2Cu precipitates at grain boundaries and triple points. The grain size and precipitation distribution did not change with subsequent isothermal heat treatments in the temperature range of 200° to 400°C. Al-Cu thin films annealed at 400°C, a temperature just below the Al/Al+θ solvus, exhibited microstructures in which the aluminum grain boundaries were depleted in copper except for the presence of the pre-existing large, widely dispersed AI2Cu precipitates. Al-Cu thin films annealed at 200° to 300°C were enriched with copper at the aluminum grain boundaries. The large, widely dispersed Al2Cu precipitates remained after the lower temperature anneals. From these results, it is proposed that the presence of copper in aluminum thin films improves electromigration resistance due to the precipitation of a thin film of Al2Cu, or a substoichiometric precursor, along the grain boundaries. The grain boundary phase retards grain boundary diffusion in the thin films, thereby reducing total mass transport and improving electromigration resistance.
Microstructure, Damage and Resistance during Electromigration Life-Testing of Al-Cu Interconnects
Authors: Shih W.C. , Greer A.L. , Xu Y.Z. , Jones B.K.
Published: March 2011

Unpassivated 1.4 mm long lines of Al-4wt.%Cu metallization have been successively imaged (by scanning electron microscopy) and electromigration stressed until failure. The resistance of lines, evolution of line microstructure and the development of electromigration damage are thus discontinuously recorded through the accelerated life-testing (260°C, 2 × 1010 A m-2). Correlations are made among microstructure evolution, electromigration damage development and line resistance. The probable mechanisms of damage development are discussed.
IN-SITU Analysis Of The Microstructure of Thermally Treated Thin Copper Films
Authors: Nucci J. , Neves H. , Shacham Y. , Eisenbraun E. , Zheng B. , Kaloyeros A.
Published: March 2011

Copper thin films were deposited by sputtering, electron beam evaporation, and electroless plating onto nitride membranes for TEM analysis. The samples were heat treated in-situ from room temperature to 600 °C for structural and chemical analysis. The as-deposited and heat treated microstructures were investigated. Orientation changes with heat treatment and reactions among the sample layers were analyzed by electron diffraction. This work provides baseline information for a study of the thermal evolution of copper lines.
The Effect of Thermal History On Interconnect Reliability
Authors: Thompson C.V.
Published: March 2011

The reliability of interconnects is strongly affected by their thermal history, including the deposition temperature, the temperature at which patterned films are passivated, and the temperature and cooling rates of the final packaging processes. The thermal history affects the stress, the grain structure, and the distribution of alloy additions, such as Cu. All of these affect the reliability of interconnects, especially as it is limited by electromigration. The postpatterning thermal history is especially important. For example, it is post-patterning annealing which leads to the evolution of electromigration resistant bamboo-microstructures. In Al-Cu alloy interconnects, pre- and post-patterning anneals can also affect the distribution of Cu in solution and in precipitates. This too can affect interconnect reliability. Experiments and modeling concerned with these effects of thermal history will be reviewed and discussed.
Grain Growth in Al-(Cu, Pd, Nb) Thin Films
Authors: Mis J.D. , Rodbell K.P.
Published: March 2011

The microstructure of 1 μim thick Al films containing 0.5 and 2%Cu (weight percent), 0.3%Pd, and 0.3%Pd-0.3%Nb were investigated by transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDS) as a function of isochronal and isothermal anneals. The grain size, grain size distribution, and precipitate morphology of these films was measured from 200 to 500ºC, with the activation energy for grain growth (Ea) determined for I h anneals at 200, 300, 400 and 500ºC. Normal grain growth was recorded for the A1Cu films annealed at temperatures ≤400ºC; however secondary grain growth occurred in the AI-2Cu film annealed for I h at 500ºC, with grains as large as 16 μm in diameter observed. Grain growth in the AI-0.3Pd films resulted in strongly bi-modal grain size distributions, with the onset ofsignificant grain growth retarded for I h anneals at temperatures ≤300ºC.The addition of Nb to the AI-0.3Pd film resulted in monomodal grain size distributions over the entire temperature range. The role of crystallographic texture on grain growth in thin films is discussed.
The Effect of Annealing on the Cu Distribution and AI2Cu Precipitation in Ai(Cu) Thin Films
Authors: Colgan E.G. , Rodbell K.P. , Vigliotti D.R.
Published: March 2011

The Cu distribution in AI(Cu) thin films has been examined in blanket and patterned samples as a function of annealing. The Cu concentration in the Al grains, measured at room temperature, closely follows the solubility at the anneal temperature when a high cooling rate is used (-100 or -200°C/min) from the annealing temperature. With fine lines, the room temperature Cu concentration follows the solubility at the anneal temperature only at low anneal temperatures, ≤350°C. With higher temperatureannealing, >400°C, the room temperature Cu concentration in the Al grains was substantially less than the solubility at the anneal temperature. These differences are attributed to the smaller grain size in fine lines, which reduces the distance to grain boundaries. With blanket films, the Θ-phase (Al2Cu) precipitate morphology depends on the Al grain size and annealing temperature. With small Al grains (100-300 nm), the Θ particles are small (100-200 nm) and round whereas with large Al grains (0.5-2μm), the precipitates are long and irregularly shaped. The morphology of the Θ precipitates is constrained by the Al grain size. With fine lines, having a bamboo structure, the Θ precipitates are “wedge” shaped along grain boundaries or span the width of the line. The electromigration lifetime was found to depend strongly on the heat treatment used, an increase of 3X in lifetime was obtained for samples rapidly cooled from a temperature above the solvus curve as compared with samples subjected to additional aging at low temperatures. This is believed to be dueto the different concentrations of Cu in solution and to the size and distribution of Θparticles in the patterned lines.
Corrosion and Protection of Thin Metallic Films
Authors: Brusic V. , Frankel G. S.
Published: March 2011

Well known principles governing metallic corrosion are summarized in this paper. Severalelectrochemical techniques that are suitable for evaluation of corrosion reactions and mechanisms are discussed. The challenge of minimizing metallic degradation in processing, in storage and during operation is discussed with examples drawn from thin films used inthe electronics industry.
A Spectromicroscopic Study of Corrosion in AI-Cu-Si Metallization
Authors: Liang S. , Ray-Chaudhuri A.K. , Ng W. , Singh S. , Welnak J.T. , Cerrina F.
Published: March 2011

Soft X-ray photoelectron spectromicroscopy has been employed to examine the microstructural chemistry of corrosion on thin films of AL-i%Cu-1%Si alloy. Cu-rich precipitates are formed after the film is annealed at around 320ºC Localized corrosion takes place around these precipitates, and circular microstructures have been observed. Energy distribution curves (EDCs) taken at specific points are analyzed and photoelectron images were obtained from different kinetic energies corresponding to the peaks in EDC. It was found that after corrosion the Al2Cu particles are revealed and distributed at the center of the corrosion structure with oxide as matrix, while the oxides form a ring-like band outside.
Agglomeration-Free Nanoscale Cobalt Silicide Film Formation Via Substrate Preamorphization
Authors: Pramanick S. , Patnaik B.K. , Rozgonyi G. A.
Published: March 2011

We have used preamorphization of silicon substrates as a process modification to suppress agglomeration during cobalt disilicide film formation. Planar, continuous and low resistivity (<21 μΩ-cm) silicide films less than 35 nm thick have been produced both on single crystal silicon and polysilicon. Nanoscale(<35 nm) silicide films are more susceptible to islanding phenomena since agglomeration is dependent onthe ratio of grain size to film thickness. Preamorphization prior to silicidation favorsa large increase in silicide nucleation rate, as well as reduction in critical nuclei size, both of which aid the formation of silicide with small grains. The resulting small grain silicides enable nanoscale films to remain below the critical grain size to thickness ratio for which thin films become morphologically unstable. An interphase void band which occurs between CoSi and CoSi2 layers, acts as a convenient diffusion marker and aids interpretation of the complex stability issues. Preamorphization prior to silicidation was also extended to heavily doped substrates to study the applicability of this approach for junctions and gate contacts. Silicidation of amorphized heavily boron doped substrates produces non uniform layers due to the collision of the advancing silicidation and SPE interfaces. A comparision of concurrent processing, i.e. simulatneous dopant activation and silicide formation, with conventional silicidation of Si+ preamorphized heavily doped(B) substrates is also presented.
Defects In GaAs Bulk Crystals and Multi-Layers Caused by In Diffusion
Authors: Werner P. , Liliental-Weber Z. , Swider W. , Sohn H. , Yau WaiFan , Baranowski J. , Weber E.R.
Published: March 2011

The objective of this work was to study by transmission electron microscopy the lattice defects in GaAs bulk crystals and heterostructures formed by In diffusion. In such samples hints for the existence of superconductivity have been found. Indium was found to move more than 100 μm into bulk GaAs during lh annealing at 550ºC (such conditions are typical for molecular beam epitaxy growth on GaAs wafers). This rapid diffusion is accompanied by the creation of dislocation networks and metallic In droplets that show evidence for lattice strain. To study the interaction of In with the GaAs lattice, In/GaAs multi-layers were grown by MBE at about 450ºC on a GaAs buffer layer. The interfaces of these structures showed misfit dislocations at islands of InAs besides the presence of lattice strain. Both types of samples showed microwave absorption signals typical for superconductivity. The most likely superconductive phases are small metastable inclusions, probably consisting of amorphous Ga or In.
Effect of TiN Anneal Ambient on The Microstructure and Electromigration Performance Of Al-Based Alloys
Authors: Olowolafe J. Olufemi , Lee Charles , Kawasaki Hisao , Gelatos Carol , Blumenthal Roc , Theodore N. David , Gregory R. B.
Published: March 2011

A strong correlation has been established between TiN substrate anneal ambient and electromigration performance of Al-based alloys. Excellent electromigration lifetimes were measured for AlSiCu (and AlCu) films on sputtered TiN substrates annealed in N2 and slowly cooled down in furnace. The films annealed in N2-O2 and N2-H2 showed poorer electromigration performance, in that order. Stronger Al (111) texture, larger median grain size and uniform grain size distribution have been responsible for the improved electromigration performance of the N2-annealed (furnace-cooled) films. On the contrary, Al alloy films on TiN substrates annealed in N2 (but air-cooled), N2-O2, or N2-H2 ambient showed weaker Al (111) textures and smaller median grain sizes.
An In Situ STM Investigation of Stranski - Krastanov Growth of Ag on Au (111) Electrodes
Authors: Corcoran S. G. , Chakarova G. S. , Sieradzki K.
Published: March 2011

We present in situ scanning tunneling Microscopy (STM) results which show the morphological aspects of Ag electrodeposition on Au (111). The experimental conditions enabled us to follow, in real time, with monolayer resolution, the morphological details of Stranski-Krastanov (SK) growth under a fixed electrochemical potential (constant supersaturation). Two epitaxial layers of Ag were sequentially formed prior to the heterogeneous nucleation of three-dimensional Ag crystallites. STM images are presented showing that the second silver monolayer has a coarsened (surface) diffusion-limited-aggregation growth front. IMMediately after the completion of the second silver monolayer which took approximately five Minutes, we observed the formation of 3D clusters preferentially at step edges. Our analysis of the SK growth process indicates that it is not well described by heterogeneous-nucleation thermodynamics owing to the almost identical lattice parameters of Ag and Au. Instead, we argue that the wetting-nonwetting transition we observed was kinetically stabilized by the relatively high activation energy involved with the motion of Ag adatoms over a descending Ag step.
Scanning Tunneling Microscopy Study of the Dynamic Scaling Properties of Rough Vapor-Deposited Silver Films
Authors: Palasantzas G. , Krim J.
Published: March 2011

We investigated the scaling behaviour of vapor-deposited silver films at room temperature by means of scanning tunneling Microscopy. The film-thickness range was ≈ 10 – 1000 nm. The roughness exponent H is observed to be H = 0.82 ± 0.05. The growth and dynamic scaling exponents are respectively observed to be β = 0.29 ± 0.06, and z = 2.53 ±0.50.
Temperature Dependence of morphology of InP Films Grown by metalorganic molecular Beam Epitaxy
Authors: Cotta M.A. , Hamm R.A. , Chu S.N.G. , Harriott L.R. , Temkin H.
Published: March 2011

Two regimes of growth are observed for epitaxial films of InP prepared by metalorganic molecular beam epitaxy. Below a minimum growth temperature, kinetic roughening is observed. At temperatures higher than smooth morphologies are obtained. From the dependence of on the substrate Misorientation, we estimate a value of ∼0.4–0.5eV for the Schwoebel barrier. At growth temperatures higher than we observe two types of defects: large oval defects related only to the initial conditions of the substrate surface and small defects with the density strongly dependent on the growth condition. Increasing temperature above or decreasing V/III ratio, results in increased density of these defects. In addition, their density increases with an activation energy that depends on the substrate Misorientation. The origin of the oval defects is attributed to non-stoichiometric, P-defficient, clusters on the growing surface, formed either by enhanced cracking of metalorganic s on the substrate due to the presence of contaminants or by a low V/III ratio used for growth.
Adhesion of Nanoscale Metal Clusters to Semiconductor Surfaces: A Scanning Tunneling Microscopy Examination
Authors: LIN SHIHCHER T. , ANDRES R. P.
Published: March 2011

Scanning tunneling Microscopy (STM) is used to investigate the initial stage of metal overlayer formation on semiconductor surfaces. STM scans are presented of preformed nanometer diameter Au clusters deposited at room temperature on molybdenum disulfide and hydrogen terminated silicon substrates. These scans show that the Au clusters are substantially deformed by interfacial forces between the cluster and substrate. The extent of deformation depends on the substrate.
the Microstructure and Electrical Resistivity of Cluster-Based thin Films
Authors: Bielefeld Jeffery D. , Andres Ronald P.
Published: March 2011

Cluster-assembled thin metal films exhibit properties which are different from those of films obtained by conventional atomic-deposition. We present TEM data on the evolution of 2-D Microstructure and SFM data on the evolution of 3-D Microstructure in thin films grown by vacuum deposition of preformed silver clusters and of preformed acetylene-silver clusters on flat SiO2, and Mica. Electrical resistivity measurements of cluster-based Ag and Ag/C2H2 films deposited on glass substrates with nominal film thicknesses of 5 nm - 50 nm are also presented and discussed.
the Critical Thickness of Dislocation-free Stranski-Krastanov Growth Atop a Deformabile Substrate
Authors: Grinfeld Michael
Published: March 2011

We investigate the influence of mass forces (in particular, of gravitation and van der Waals forces) on the critical film thickness of thin films attached to solid substrates and establish corresponding corrections of the earlier published formula Hcril = ΣΜ/τ2 (where Σ is the surface energy, Μ - the shear Modulus, and τ - the mismatch stress). It is assumed that the films’ particles are able to rearrange their relative positions in the lattices, and the equilibrium rearrangement is determined by minimizing the total static energy. Recently, it was demonstrated that morphological stability of interfaces in crystalline solids with the rearrangement is extremely sensitive to the presence of shear stresses. Equilibrium theory of elasticity of pre-stressed solids with the rearrangement of their material particles has already allowed the prediction of the appearance of corrugations in He4 films and to explain the dislocation-free Stranski-Krastanov pattern of epitaxial growth of thin solid films. The explicit asymptotic formulae announced here are especially useful in the case of small mass force, the effects of which can be detectable and even significant for some of the above mentioned phenomena.
Dynamic Scaling of the Island-Size Distribution and Percolation in a model of Sub-Monolayer Molecular Beam Epitaxy
Authors: Amar Jacques G. , Family Fereydoon , Lam Pui-Man
Published: March 2011

The results of a detailed study of the scaling and percolation behavior of the sub-Monolayer in a model of molecular beam epitaxy are presented. In our model adatoms are randomly deposited on a square lattice and then allowed to diffuse. Whenever an adatom encounters another adatom or an island, it is attached to them and becomes immobile. We have found and studied four distinct scaling regimes, corresponding to a low-coverage (nucleation) regime, intermediate-coverage regime, an aggregation regime, and coalescence and percolation regime. At low coverage the islands have a dendritic structure such as seen in Au/Ru (0001) while at higher coverages they become compact. The scaling of the cluster fractal dimension, island density, Monomer density, island size distribution, and structure factor and pair-correlation function are studied as a function of the coverage θ and the ratio R = D /F of the diffusion rate to the deposition rate.
Surface Evolution During Mbe Growth of Eute Studied by Uhv-Stm and Rheed Investigations
Authors: Frank N. , Springholz G. , Bauer G.
Published: March 2011

MBE growth of 2% lattice-Mismatched EuTe on PbTe (111) is studied combining in-situ reflection high-energy electron diffraction (RHEED) with UHV scanning tunneling Microscopy (STM) to investigate the evolution of the EuTe surface Morphology. Using RHEED we have found that 2D nucleation and layer-by-layer growth occurs only in a very narrow range of growth conditions as a result of a strain induced coherent islanding of the surface[l], which leads to a roughening transition at the critical layer thickness hc of 45 Monolayers (ML). Starting with a very smooth initial (111) PbTe surface with terrace widths of 50 to 200 nm, islands of monolayer height are formed due to 2D nucleation of EuTe. For EuTe layer thicknesses below hc, the root mean square roughness (RMS) is essentially constant and equal to about one ML. Beyond hc, the surface roughness increases strongly and islands of about 20 ML height are observed for an EuTe layer thickness of 66 ML.