Activation Energy Of Cu Research Articles

Experimental investigation of electromigration failure in Cu–Sn–Cu micropads in 3D integrated circuits

Inter-die electrical communication in vertically-stacked three-dimensional integrated circuits (3D ICs) is facilitated by inter-die micro bumps. The electromigration reliability of micro bumps is critical for developing an understanding of reliability of 3D IC based microelectronic systems. This paper reports experimental investigation of electromigration reliability of Cu–Sn–Cu microbumps formed between two die by thermo-compression bonding. The two-die 3D IC is assembled in wire bond ceramic packages and electromigration tests are conducted in both air and nitrogen ambient at various temperatures. Failure lifetime and Mean Time To Failure (MTTF) of microconnect chains and Kelvin structures are measured. Results indicate that the intrinsic activation energy of Cu–Sn microconnects is between 0.87eV and 1.02eV. Based on failure analysis, possible failure mechanisms are proposed. Results presented in this work are expected to improve the fundamental understanding of electromigration reliability in 3D ICs and facilitate the development of robust and reliable microelectronic systems based on 3D ICs.

Kinetics and equilibrium adsorption of copper(II) and nickel(II) ions from aqueous solution using sawdust xanthate modified with ethanediamine

Sawdust xanthate modified with ethanediamine was used for the removal of Cu(II) and Ni(II) from aqueous solution. The influence of various operating parameters such temperature and adsorbent dosage on the adsorption isotherms of modified sawdust was investigated. Thermodynamic parameters, namely Gibbs free energy (ΔGΘ), enthalpy (ΔHΘ) and entropy (ΔSΘ) of Cu(II) and Ni(II) adsorption process were calculated, showing that the adsorption is a spontaneous and exothermic process. The modified extended Langmuir equation approaches provide excellent prediction of the binary adsorption. In single and binary systems, the overall adsorption data were best described by the pseudo-second order kinetic model, then the calculated values of activation energy of Cu(II) and Ni(II) adsorption process were 59.12 and 55.92 kJ/mol respectively. The results show that the affinity of each metal ion onto the modified sawdust surface is influenced by the presence of the other one.

Adsorptive remediation of Cu(II) and Cd(II) contaminated water using manganese nodule leaching residue

Investigations carried out for the application of manganese nodule leaching residue in the removal of Cu(II) and Cd(II) from aqueous solution by adsorption are described. Several parameters, namely pH of solution, time, initial concentration of adsorbate metal ion, residue dose, etc., have been varied to study the feasibility of using residue as potential adsorbent for remediation of Cu(II) and Cd(II) contaminated water. The adsorption kinetics followed pseudo-second-order equation and the rate of adsorption increased with solution temperature. The equilibrium data was best fitted into Langmuir adsorption isotherm and the maximum adsorption capacities of washed manganese nodule residue (wMNR) towards Cu(II) and Cd(II) were found to be 26.95 and 32.26 mg g−1, at pH 5.5 and temperature 303 K, which improved to 40.32 and 38.17 mg g−1, respectively, upon raising the solution temperature to 323 K. Negative values of ΔG° indicated that adsorption of Cu(II) and Cd(II) onto wMNR was spontaneous. The activation energy for Cu(II) and Cd(II) adsorption onto wMNR ranged between 40 and 65 kJ mol−1. A mixed-type uptake mechanism involving chemical interaction and diffusion inside adsorbent particle is discussed. This study would be useful for future application of this material in the remediation of copper and cadmium contaminated wastewater.

Self-Assembled Nano-Stuffing Structure in CVD and ALD Co(W) Films as a Single-Layered Barrier/Liner for Future Cu-Interconnects

Cobalt film with tungsten [Co(W)] has the potential to be an effective single-layered barrier/liner in interconnects, due to its good adhesion with Cu, low resistivity compared with TaN, and comparable barrier properties to TaN. To reduce the resistivity of Co(W), oxygen-free Co(W) was fabricated from oxygen-free precursors, bis(N-tert-butyl-N′-ethylpropionamidinato) cobalt and bis(tert-butylimino)bis(dimethylamino) tungsten, by chemical vapor deposition (CVD) and atomic layer deposition (ALD). Our results showed that W addition improved the barrier properties of both CVD-Co(W) and ALD-Co(W) against Cu diffusion. The diffusion coefficient of Cu in Co(W) was reduced by W addition. The activation energy of Cu in CVD-Co(W) and ALD-Co(W) was 1.5 eV and 1.7–1.8 eV, respectively; whereas that in CVD-Co was 1.0 eV. Improvement in the barrier properties of Co(W) was attributed to the amorphous-like structure created by W. High-resolution transmission electron microscopy and multivariate spectral analysis of the nanoscale properties of Co(W) revealed that the improvement in the barrier properties was due to the self-assembled segregation of W atoms at the grain boundary. The segregated W atoms in both CVD-Co(W) and ALD-Co(W) films may act as a stuffing material. These results suggest Co(W), especially ALD-Co(W), as a promising material for Cu-interconnects in future ultra-large-scale integrated circuits.

Influence of Dopant on Growth of Intermetallic Layers in Sn-Ag-Cu Solder Joints

The interfacial interaction between Cu substrates and Sn-3.5Ag-0.7Cu-xSb (x = 0, 0.2, 0.5, 0.8, 1.0, 1.5, and 2.0) solder alloys has been investigated under different isothermal aging temperatures of 100°C, 150°C, and 190°C. Scanning electron microscopy (SEM) was used to measure the thickness of the intermetallic compound (IMC) layer and observe the microstructural evolution of the solder joints. The IMC phases were identified by energy-dispersive x-ray spectroscopy (EDX) and x-ray diffractometry (XRD). The growth of both the Cu 6 Sn 5 and Cu 3 Sn IMC layers at the interface between the Cu substrate and the solder fits a power-law relationship with the exponent ranging from 0.42 to 0.83, which suggests that the IMC growth is primarily controlled by diffusion but may also be influenced by interface reactions. The activation energies and interdiffusion coefficients of the IMC formation of seven solder alloys were determined. The addition of Sb has a strong influence on the growth of the Cu 6 Sn 5 layer, but very little influence on the formation of the Cu 3 Sn IMC phase. The thickness of the Cu 3 Sn layer rapidly increases with aging time and temperature, whereas the thickness of the Cu 6 Sn 5 layer increases slowly. This is probably due to the formation of Cu 3 Sn at the interface between two IMC phases, which occurs with consumption of Cu 6 Sn 5 . Adding antimony to Sn-3.5Ag-0.7Cu solder can evidently increase the activation energy of Cu 6 Sn 5 IMC formation, reduce the atomic diffusion rate, and thus inhibit excessive growth of Cu 6 Sn 5 IMCs. This study suggests that grain boundary pinning is one of the most important mechanisms for inhibiting the growth of Cu 6 Sn 5 IMCs in such solder joints when Sb is added.

Cu 22Bi 12S 21Cl 16—A mixed conductor with fast one-dimensional copper(I) ion transport

Melting reactions of Cu, CuCl, S, and Bi 2S 3 yield black, shiny needles of Cu 22(1)Bi 12S 21(1)Cl 16(1). The compound decomposes peritectically at 649(5) K. Oxidation state +I of the copper atoms is supported by Cu– K-XANES. The compound crystallizes in the hexagonal space group P6/ m with a=2116.7(7) pm and c=395.17(5) pm. Seven anions coordinate each of the two independent bismuth cations in the shape of mono-capped trigonal prisms. These polyhedra share edges and faces to form trigonal and hexagonal tubes running along [0 0 1]. The hexagonal tubes are centered by chloride ions, which are surrounded by disordered copper cations. The majority of copper cations are distributed over numerous sites between the tubes. The Joint Probability Density Function (JPDF) reveals a continuous pathway along [0 0 1]. The high mobility of the copper cations along [0 0 1] was demonstrated by impedance spectroscopy and DC polarization measurements on single crystals. The ionic conductivity at 450 K is about σ ion=0.06 S cm −1, and the activation energy for Cu + ion conduction is E a=0.44 eV. The chemical diffusion coefficient of copper is in the order of D cu δ =10 19 cm −3 at 420 K. The electronic band gap (p-type conductor) was determined as E g=0.06 eV. At room temperature the thermal conductivity of a pressed pellet is about κ=0.3 W K −1 m −1 and the Seebeck coefficient is S=43 μV K −1.

Activated states for cross-slip at screw dislocation intersections in face-centered cubic nickel and copper via atomistic simulation

We extend our recent simulation studies where a screw dislocation in face-centered cubic (fcc) Ni was found to spontaneously attain a low energy partially cross-slipped configuration upon intersecting a forest dislocation. Using atomistic (molecular statics) simulations with embedded atom potentials, we evaluated the activation barrier for a dislocation to transform from fully residing on the glide plane to fully residing on a cross-slip plane intersecting a forest dislocation in both Ni and Cu. The activation energies were obtained by determining equilibrium configurations (energies) when variable pure tensile or compressive stresses were applied along the [111] direction on the partially cross-slipped state. We show that the activation energy is a factor of 2–5 lower than that for cross-slip in isolation via the Escaig process. The cross-slip activation energies obtained at the intersection in Cu were in reasonable accord with the experimentally determined cross-slip activation energy for Cu. Further, the activation barrier for cross-slip at these intersections was shown to be linearly proportional to (d/b)[ln(3d/b)]1/2, as in the Escaig process, where d is the Shockley partial dislocation spacing and b is the Burgers vector of the screw dislocation. These results suggest that cross-slip should be preferentially observed at selected screw dislocation intersections in fcc materials.

Removal of Cu(II) in aqueous media by biosorption using water hyacinth roots as a biosorbent material

Water hyacinth roots were employed as a biosorbent to remove Cu(II) in aqueous media. Nitrogen adsorption/desorption analysis revealed that the biosorbent was mesoporous with a relatively small surface area. Equilibrium biosorption isotherms showed that the water hyacinth roots possessed a high affinity and sorption capacity for Cu(II) with a monolayer sorption capacity of 22.7 mg g −1 at initial pH 5.5. Kinetics study at different temperatures revealed that the sorption was a rapid and endothermic process. The activation energy for Cu(II) sorption was estimated to be 30.8 kJ mol −1, which is typical of activated chemisorption processes. The sorption mechanism was investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, effect of pH and calcium release. These analyses suggested that the biosorption mainly involved the ion exchange of Cu(II) with cations and complex formation with functional groups on the surface of the roots. All the results showed that water hyacinth roots are an alternative low-cost biosorbent for the removal of Cu(II) from aqueous media.

Biosorption of bivalent metal ions from aqueous solution by an agricultural waste: Kinetics, thermodynamics and environmental effects

The ability of Neem oil cake (NOC), a bio-waste material to remove Cu(II) and Cd(II) ions from aqueous solution was investigated. The influence of pH, sorbent dose, concentration, temperature, and contact time on the sorption of Cu(II) and Cd(II) on NOC has been studied by batch process. The sorption was found to be maximum in acidic medium and increases with increase in initial concentration. Percent deviation ( P) and regression coefficient ( r 2) for Langmuir and Freundlich sorption isotherms shows better fitting of the models. Thermodynamics parameters indicate that the process is endothermic and spontaneous. Activation energies for Cu(II) and Cd(II) were calculated from Dubinin–Redushkevich (D–R) isotherms are high 8.3–8.7 and 7.17–11.4 kJ mol −1 showing that chemisorption is involved. The sorption kinetics was found to follow pseudo-second-order model.

Electromigration Reliability in Nanoscale Cu Interconnects

AbstractElectromigration behavior in Cu damascene wires was studied for various Cu grain struc-tures. The grain size was modulated by Cu linewidth and thickness, and by adjusting the wafer annealing process step after Cu electroplating and before Cu chemical mechanical polishing. A larger variation of Cu grain size between the samples was achieved on CMOS 65 nm node tech-nology than previous nodes which was due to the finer line width and thinner metal thickness. The Cu lifetime and mass flow in samples with bamboo, near bamboo, bamboo-polycrystalline mixture, and polycrystalline grain structures were measured. The effects of a Cu(2.5 wt.% Ti) alloy seed, Cu surface pre-clean, and selective electroless CoWP deposition techniques on Cu electromigration were also observed and a significantly improved Cu lifetime was found. The electromigration activation energies for Cu in Cu(Ti) alloy, along Cu/amorphous a-SiCxNyHz in-terface and grain boundary were found to be 1.3, 0.95 and 0.79 ± 0.05 eV, respectively. In addition the Cu line size effect on the Cu conductivity for Cu area less than 4×104 nm2 was found to be a linear function of the Cu line area.

Solid state diffusion in Cu–Sn and Ni–Sn diffusion couples with flip-chip scale dimensions

The formation and growth rate of intermetallics of frequently used metallisation systems for flip-chip bumping have been studied and are reported for many years. However, no data are available on diffusion couples with flip-chip processing methods and actual flip-chip scale dimensions. In this paper, the interdiffusion coefficients and activation energies of Cu–Sn and Ni–Sn intermetallic formations are measured on flip-chip bumps with 40 μm bond pad diameter. Also the morphology of the metallurgical reactions is described. Furthermore, the ideal case of a binary diffusion system is seldom present in real-life. In practice, the presence of additional alloying elements has an impact on the intermetallic stoichiometry and even on intermetallic growth and morphology. It is shown that small quantities of Cu in a Ni–Sn system can have a beneficial effect on the Ni consumption but larger quantities result in extreme scalloping of the intermetallic interface.

Polypyrrole-Montmorillonite Nanocomposite: A Composite Fast Ion Conductor

Cu(II)-exchanged montmorillonite [Cu(II)-MMT] takes up pyrrolium ions by ion exchange. Two pyrrolium ions are inserted for each Cu(II) ion expelled from its interlayers. These pyrrolium ions undergo spontaneous polymerization because of the remaining Cu(II) ions present within the intergalleries to form Cu(I)-polypyrrole-MMT nanocomposite. The polypyrrole (PPY) dispels any water already present within the intergalleries and the material becomes hydrophobic and reluctant to take up water. The inherent d-spacing due to anhydrous PPY present within the intergalleries is 16.0 A, which is a 6.4 A enhancement from the situation, which contains a bare inorganic ion. The material possesses unusually high mixed electrical conductivity. The conjugation length (and hence the electronic conductivity) decreases as the temperature is increased as confirmed by the Fourier transform infrared spectroscopy. However, the ionic component of the conductivity increases with temperature. The temperature dependence of conductivity shows Arrhenius behavior but two different activation regions are clearly visible. The activation energy for Cu(I) migration within the nanocomposite is much lower than 100 C (Ea1/4 0.09 eV). At the higher temperature region, the activation energy is 0.23 eV and this value is also comparatively low suggesting the favorable motion of Cu(I) ions within the PPY-MMT nanocomposite thus making it a fast Cu(I) ion conductor. The ionic conductivities are in the range 0.66-1.15 mS cm 1 in the temperature range from 25 to 120 C.

Initial oxidation kinetics and energetics of Cu 0.5Au 0.5 (0 0 1) film investigated by in situ ultrahigh vacuum transmission electron microscopy

The initial oxidation behavior of Cu 0.5Au 0.5 (0 0 1) thin film was investigated by in situ ultrahigh vacuum transmission electron microscopy to model nano-oxidation of alloys with one active component and one noble component. The formation of irregular-shaped octahedron Cu 2O islands with cube-on-cube crystallographic orientation to the substrate film was observed at all temperature studied. The energetics of Cu 2O nucleation for Cu and Cu 0.5Au 0.5 oxidation was compared. Cu 0.5Au 0.5 oxidation has lower nucleation activation energy due to the reduced mismatch strain between Cu 2O and Cu 0.5Au 0.5 films. On the other hand, the reaction kinetics for Cu 0.5Au 0.5 alloy oxidation is slower due to the higher diffusion activation energy of Cu.

Effect of metal liner on electromigration in Cu Damascene lines

Electromigration in Cu single Damascene lines capped with amorphous a-SiCxNyHz and fabricated with various Ta-based liners is investigated. The Ta-based liner layers were deposited using atomic layer and physical vapor deposition techniques. The crystallographic phases of the Ta liners were determined using x-ray and transmission electron diffraction. Although the Cu electromigration lifetimes are determined by % resistance increase failure criteria that are dependent on the liner resistance, the Cu void growth rate was found to be insensitive to the phases of Ta. This result is consistent with the dominant diffusion path being along the Cu∕a-SiCxNyHz interface in these samples. The activation energy for Cu along Cu∕a-SiCxNyHz interface diffusion was found to be 1.0±0.04eV.

Characterization of sputtered nano-crystalline zirconium carbide as a diffusion barrier for Cu metallization

Zirconium carbide (ZrC) films were grown on Si (100) substrates using magnetron sputtering where the growth temperature (Ts) was varied from 25°C to 290°C. The microstructure and resistivity of the as-deposited ZrC films were examined. The results reveal that nano-crystalline ZrC films with grain size less than 5 nm were fabricated only at 29°C, which can be explained by a repeated nucleation mechanism. For thermal stability characterization, the stacked structure of Cu/ZrC/Si was subsequently subject to thermal treatments at temperatures from 300°C to 900°C for 30 min in a vacuum tube. The stacked samples were shown to be thermally stable up to about 800°C from Auger electron spectroscopy (AES) and x-ray diffraction (XRD). The diffusion coefficient and activation energy of Cu and Si in the ZrC barrier were also derived. It indicated that Si has a lower activation energy than Cu resulting in faster diffusion. The device completely fails at 900°C, and the mechanism is discussed in this paper.

The Equilibrium and Kinetic Modelling of the Biosorption of Copper(II) Ions on Cladophora crispata

The biosorption of Cu(II) ions on Cladophora crispata was investigated as a function of the initial pH, temperature and initial Cu(II) ion concentration. Algal biomass exhibited the highest Cu(II) uptake capacity at 25∘C and at the initial pH of 4.5. Equilibrium data fitted very well to both the Langmuir and Freundlich isotherm models. The pseudo second order kinetic model was applied to describe the kinetic data and the rate constants were evaluated in the studied concentration range of Cu(II) ions at all the temperatures studied. The experimental data fitted well to the pseudo second order kinetic model with a high correlation coefficient (R 2 > 0.99), which indicates that the external mass transfer limitations in the system can be neglected and the chemical sorption is the rate-limiting step. The pseudo second order kinetic constants were also used to calculate the activation energy of Cu(II) biosorption.

Influence of the preferred orientation and thickness of zirconium nitride films on the diffusion property in copper

Zirconium nitride (ZrN) films of different preferred orientations are grown on Si (100) substrates at various substrate temperatures during deposition in a dc magnetron sputtering system. The thermal stability of the as-deposited ZrN films are shown to be stable with Si up to 900 °C annealing for 30 min. The structural characterization of the thin films is carried out by x-ray diffraction and the electrical resistivity is measured by four-point probe. The decrease of the resistivity in the as-deposited films upon annealing is ascribed to the release of the lattice strain. Subsequently, copper is deposited on top of the ZrN films and the interdiffusion of each species upon annealing is studied by Auger electron spectroscopy as a function of ZrN preferred orientation and thickness. The diffusion coefficient and activation energy of Cu in the ZrN barrier are derived. The results indicate that the thicker (111) oriented crystalline ZrN films with larger grain sizes provide a higher activation energy against Cu diffusion and can act as an excellent diffusion barrier for Cu up to 800 °C. The detailed mechanisms accounted for the better performance are discussed in terms of a proposed grain boundary model.

Modeling Copper Diffusion in Silicon Oxide, Nitride, and Carbide

AbstractDensity functional theory was applied to simulate copper diffusion in silicon oxide, nitride, and carbide (SiOx, SiNx, SiCx). Because copper drift into oxide is significantly enhanced by negative bias, copper ions are the active diffusing species. Clusters and, in some cases supercells, modeling various ring configurations of the amorphous networks of silicon oxide, nitride, and carbide were employed. Interactions of both neutral copper and its cation, Cu+, with the network were explored. Calculations revealed a strong binding of Cu+ to SiOx, SiCx, and SiNx in contrast with neutral Cu. The Cu+ attraction to carbide clusters is significantly lower than to SiOx and SiNx, explaining the effective barrier properties of SiCx. The estimated lower bounds for activation energies for Cu+ hops between stable ring clusters of SiOx and SiNx are similar. This implies that the difference in Cu diffusion properties between oxides and nitrides is likely due to a higher percentage of large rings in amorphous oxides compared with nitrides. An approach to increasing the resistance of oxides to Cu+ diffusion is suggested.

Dynamic Behavior of Group 13 Elements in Bromocomplexes as Studied by NQR and NMR

NMR, NQR, powder X-ray diffraction, DTA and AC conductivity were measured in RMBr4 (R = Ag, Cu; M = Al, Ga) and RM2Br7 (R = Li, Ag; M = Al, Ga). In RMBr4 , the activation energy of Cu+ diffusion was evaluated from 63Cu NMR and was in good agreement with that from 81Br NQR. In CuAlBr4 , the e2Qq/h value of 63Cu NMR and the η value of 27AI NMR changed linearly with decreasing temperature, although the e2Qq/h value of 27AI NMR did not change so much. These temperature dependences are supposed to be due to Cu+ diffusion and not to a variation of the lattice constants. In RM2Br7 , the activation energy was obtained from the spin-lattice relaxation time T1 of 81Br NQR and is ascribed to a modulation of the cation diffusion. The line width of 7Li NMR in LiAl2Br7 was about 5.9 kHz in the low-temperature phase and 0.4 kHz for the high-temperature phase. The 27AlNMR spectrum was broadened by the quadrupole interaction and unchanged up to 400 K, suggesting that diffusion of Li+ ions occurs in the high-temperature phase.

Molecular Dynamics Studies of Thin-Films of Sn On Cu

ABSTRACTUsing Molecular Dynamics, the evolution dynamics of Sn on the (111) and (100) surfaces of Cu have been investigated as a function of coverage and temperature. The interaction potentials are described by modified embedded atom method (MEAM) potentials. The calculated diffusion activation energies of Cu in Sn and Sn in Cu agree reasonably well with experimental values. We find that the structure of the overlayer depends on the morphology of the substrate and remains stable up to temperatures of the order of 70% of the melting temperature of the substrate at which diffusion of Sn into the substrate and Cu atoms onto the overlayer is observed.