Reverse polarity effect and cross-solder interaction in Cu/Sn–9Zn/Ni interconnect during liquid–solid electromigration

The diffusion behavior of Zn atoms and Cu–Ni cross-solder interaction in Cu/Sn–9Zn/Ni interconnects during liquid–solid electromigration were investigated under a current density of 5.0 × 10³ A/cm² at 230 °C. Under the combined effect of chemical potential gradient and electron wind, Zn atoms with positive effective charge number would directionally diffuse toward the Cu interface under both flowing directions of electrons. When electrons flowed from Cu substrate to Ni substrate, EM significantly enhanced the diffusion of Cu atoms to the opposite Ni interface, resulting in the formation of interfacial Cu₅Zn₈; while no Ni atoms diffused to the opposite Cu interface. When electrons flowed from Ni substrate to Cu substrate, only a small amount of Cu atoms diffused to the opposite Ni interface, resulting in the formation of a thin interfacial (NiCu)₃(SnZn)₄ (containing 3 wt% Cu); EM significantly accelerated the diffusion of Ni atoms to the Cu interface, resulting in the formation of a large amount of (NiCu)₃(SnZn)₄ at the Cu interface. Even under downwind diffusion, no apparent consumption of Cu substrate was observed due to the formation of a thick and dense Cu₅Zn₈ layer at the Cu interface. It is more damaging with electrons flowing from Ni to Cu than that from Cu to Ni.     

A theory of suppressed nitrogen solubility in Fe–Z–N ternary alloy systems in the relatively high range of concentration of Z (Z=Si or C)

It was shown in earlier work that, for the FeZ_zN_x in the relatively low range of z, the solubility pattern of N as a function of temperature T and nitrogen partial pressure p(N₂) can be interpreted in terms of decreased number θ of available interstitial sites for occupation by N atoms per Fe atom in the Fe lattice in proportion to increased z under the assumption of negligible interaction between two interstitial constituents, N and Z (Z=Si or C). In the present work, solubility reduction of N in ternary FeZ_zN_x with increasing z in the relatively high range of z were analysed on the basis of statistical thermodynamics. The present analysis for molten FeSi_zN_x in the relatively high range of z showed that a correction to the θ versus z relation for the relatively high range of z was desirable taking into account overlapping of blocked interstitial sites for occupation of N atoms in order to reproduce the observed equilibrium pressure–temperature–composition (PTC) relation for this system while the interaction between N and Si remains negligible. On the other hand, for the simulation of equilibrium PTC relation for austenitic FeC_zN_x alloy over the entire range of z analysed, significant N–C interaction was important in addition to the blockage effect for the available interstitial sites for occupation of N atoms.     

A simple model of radiation swelling of silicon

The radiation swelling of silicon is explained as a diffusion-like process where the flux of interstitials out of the plane is defined by the gradient of the concentration of interstitials and the gradient of mechanical stresses in the ion-implanted region of the solid. This model was applied to describe the dynamics and the main regularities (dependence of strain on the ion flux density, ion energy, substrate temperature) of ion implanted silicon (Ni⁺, E = 40–160 keV, j = 5–180 μA cm⁻²). It is demonstrated that suppression of radiation swelling at high temperatures of the substrate or high ion beam current density can be explained by the annihilation of radiation defects.     

Studies on the formation of Langmuir monolayer and Langmuir–Blodgett films of octadecyl amine-bromocresol purple dye complex

Properties of the monolayer of octadecyl amine (ODA) molecules on aqueous solution of bromocresol purple (Bcp) dye have been studied over a wide range of pH by measuring the surface pressure-area isotherms. A strong interaction of ODA molecule was observed with the dye molecule in the pH range of 4–9. Under the present study, the dye molecules were adsorbed on the ODA monolayer at the water surface and subsequently a Langmuir–Blodgett (LB) film of ODA–dye complex was transferred from the air–water interface onto a solid substrate. Alternatively, dye molecules were incorporated into LB film by immersing the predeposited LB film of pure ODA into the dye solution, i.e. by adsorption of dye molecule at the solid–liquid interface. The adsorption behavior of ODA–Bcp dye complexes obtained through these two different routes was characterised with the help of UV–Visible spectroscopy. The nature of the ODA–dye complex deposited from air–water interface using the LB technique was found to be quite different from that of the complex formed by the adsorption of the dye into the pure ODA LB film. The adsorption spectra of the ODA–dye complex obtained from the air–water interface did not change with pH, while those of the ODA–dye complex formed from the solid–liquid interface showed pH dependence.     

Characterization of planar waveguides obtained by proton exchange in lithium iodate

Due to its non-linear optical properties, lithium iodate is commonly used in optical devices. By proton exchange, performed by immersing z-cuts LiIO₃ single crystals in a molten hydrated nitrate salt, we formed a solid solution Li_1−xH_xIO₃ layer close to the surface. This modification of the structure increases the refractive index so that a waveguide is created. The index profile obtained by m-lines spectroscopy combined with structure characterization by μ-Raman and X-ray diffraction experiments allows us to describe the diffusion process of hydrogen in LiIO₃.     

Pulsed high energy density plasma processing silicon surface

Pulsed high energy density plasma (PHEDP) is a new material modification technique, which has the features of: high energy density (1–10 J/cm²), high plasma density (10¹⁴–10¹⁶ cm⁻³), high electron temperature (10–100 eV), high directed plasma velocity (10–100 km/s) and short pulse duration (10–100 μs). PHEDP interacting with material will result in rapid melting and re-solidification of surface layer with a quenching rate up to 10⁸ K/s; thus the material surface properties are modified. At the same time, PHEDP contains condensable ions or/and atoms, so a thin film layer can be formed on the modified surface and the deposited layer can be mixed with the substrate (or previous deposited layer) during following pulses. Therefore, this technique actually combines film deposition and mixing into one step. In this paper, we have reported the research results on the metallization of Si by PHEDP. The Ti---Si reactions under PHEDP are also discussed.     

Investigation of Brazing Structure of Bulk Graphite to a W-Re Substrate

The brazing structure of bulk graphite to a W-Re substrate has been investigated in the present paper. The brazing specimens used were a W-15Re substrate with a sintered density of 17.97g/cm³, and bulk graphite with a density of 1.86g/cm³. Titanium foil with a thickness of 0.05–1.5mm was used as the brazing agent. W-Re substrate and bulk graphite were brazed in a vacuum furnace. After brazing, the phase composition and structure of brazed layer were analyzed. The test results show that W-Re substrate and bulk graphite can be joined together when titanium was used as the brazing agent. Titanium and graphite react and form TiC, which has a higher melting point during brazing. The phase compositions of the brazed layer were a W-Re solid solution, TiC, and residual carbon. The metallographic structure of the brazed layer was made up of a W-Re solid solution and TiC.     

Interfacial evolution in Sn–58Bi solder joints during liquid electromigration

For Sn–58Bi low temperature solder alloy, local molten induced from electromigration Joule heating might change the atomic diffusion and interfacial behavior. In this paper, the diffusion behavior and interfacial evolution of Cu/Sn–58Bi/Cu joints were studied under liquid–solid (L–S) electromigration in molten solder and were compared with the interfacial behaviors in solid–solid (S–S) electromigration in solid solder. L–S or S–S electromigration was realized by applying a current density of 1.0?×?10⁴ A/cm² to molten solder at 150 °C or solid solder at 25 °C, respectively. During S–S electromigration, Bi atoms were driven towards anode side under electromigration induced flux and then accumulated to form Bi-rich layer near anode interface with current stressing time increasing. During L–S electromigration, Bi atoms were reversely migrated from anode to cathode to produce Bi segregation at cathode interface, while Cu atoms were rapidly dissolved into molten solder from cathode and migrated to form large amounts of Cu₆Sn₅ rod-like phases near anode interface. The reversal in the direction of Bi atoms may be attributed to the reversal in the direction of electromigration induced flux and correspondingly the change on effective charge number of Bi atoms from negative to positive.     

Solid–liquid interdiffusion bonding between In-coated silver thick films

Solid–liquid interdiffusion (SLID) bonding between two pieces of In-coated silver thick films was investigated. The silver thick film was prepared by screen-printing of silver paste on an aluminum oxide substrate. Indium was coated in thickness ranging from 3 to 12 μm onto the silver thick films using thermal deposition (in vacuum). Two pieces of the In-coated thick films were placed in intimate contact (with a compressive stress of 0.04 MPa) and heated (at 180–250 °C) for various durations (600–3600 s) to undergo SLID bonding. Measurement of the bonding strength indicated that the SLID bond in 3-μm-In-coated thick-film couples is stronger than that in 8-μm-In-coated couples. X-Ray diffraction, scanning electron microscopy and electron probe microanalysis were used to analyze the bond. The stronger bond comprises a central zone of γ-Ag₂In sandwiched by two Ag films; the weaker bond comprises a central zone of AgIn₂ sandwiched by two layers of γ-Ag₂In. In the latter case, diffusion of excess indium from the coat into the interface between the silver film and alumina substrates is responsible for bond weakening. The development of microstructures in the SLID process for both strong and weak bonds is proposed.     

Deposition and modification of titanium dioxide thin films by filtered arc deposition

Thin films of titanium dioxide have been deposited on glass substrates and conducting (100) silicon wafers by filtered arc deposition (FAD). The influence of the depositing Ti⁻ energy, substrate types and substrate temperature on the structure, density, mechanical and optical properties have been investigated. The results of X-ray diffraction (XRD) showed that with increasing substrate bias, the film structure on silicon substrates changes from anatase to amorphous and then to rutile phase without auxiliary heating, the transition to rutile occurring at a depositing particle energy of about 100 eV. However, in the case of the glass substrate, no changes in the structure and optical properties were observed with increasing substrate bias. The optical properties over the range of 300–800 nm were measured using spectroscopic elliosometery, and found to be strongly dependent on the substrate bias, film density and substrate type. The refractive index values of the amorphous, anatase and rutile films on Si were found to be 2.56, 2.62 and 2.72 at a wavelength of 550 nm, respectively. The hardness and elastic modulus of the films were found to be strongly dependent on the film density. Measurements of the mechanical properties and stress also confirmed the structural transitions. The hardness and elastic modulus range of TiO₂ films were found to be between 10–18 and 140–225 GPa, respectively. The compressive stress was found to vary from 0.7 to 2.6 GPa over the substrate bias range studied. The composition of the film was measured to be stoichiometric and no change was observed with increasing substrate bias. The density of the film varied with change in the substrate bias, and the density ranged between 3.62 and 4.09 g/cm³.     

Feasibility of Manufacturing A Solid Dosage Form Using A Liquid Nonvolatile Drug Carrier: A Physico-Chemical Characterization

Experiments were performed to determine the formulation and manufacturing feasibility of three model solid capsule formulations using a spray-on liquid drug carrier. Methylparaben was used as a model low-dose drug in the liquid drug carrier. Formulations containing different amounts of liquid drug carrier were successfully encapsulated on the H&K 400 capsule filling machine. The formulations contained varying ratios of liquid (methylparaben-propylene carbonate solution) to solid (compressible sugar, NF), which ranged from 10.0 - 20.0 μL/450 mg. Physical characteristics (i.e. weight variation, dissolution, etc.) of the filled capsules were evaluated. The 20.0 μL liquid/450 mg solid ratio was found to be the best hard gelatin capsule formulation based upon its rapid dissolution profile and was equivalent to all other formulations tested with respect to weight variation and content uniformity.     

Wetting behaviour of lead-free Sn-based alloys on Cu and Ni substrates

The present work was carried out in the framework of the study of new lead-free solder alloys for technical applications in electronic devices. In the focus of this characterisation the wetting behaviour of several Sn-rich alloys belonging to the In–Sn, Au–Sn and Cu–Sn systems has been studied by measuring the contact angle variations on Cu and Ni substrates as a function of time and temperature. The interface between the alloy and the substrate has been analysed by the use of optical microscopy and scanning electron microscopy combined with energy-dispersive X-ray spectrometry in order to study the reaction between the alloy and the solid substrate and the possible formation of different compounds at the interface. A remarkable effect of the two different substrates on the behaviour of the contact angle as a function of temperature and on the morphology of the interface between the liquid solder and the solid substrate was observed for the In–Sn and Cu–Sn, while the Au–Sn system shows a very similar wetting behaviour on Cu and Ni.     

Dynamic Motion of Superfluid Bubble in Solid 4He

We have observed an interesting motion of a superfluid bubble in solid ⁴ He with the solid/liquid interface through the video camera. The host hcp crystal was formed at around 0.8 K with c-axis oriented approximately 45 degrees from the horizontal solid/liquid interface. When a fairly strong power of 10 MHz pulsed sound was applied to a transducer in the solid, a small rounded liquid droplet was nucleated at one spot on the transducer. The droplet became larger as the sound pulse continued to be applied, developing over the entire transducer, and finally began to grow upwards. As it increased in size, the c-facet was observed in the bubble. At this time the shape of the bubble became something like a pyramid. When a top of the pyramidal shape of the bubble touched the interface, it changed its shape drastically, rapidly merged into the superfluid phase. The detailed motion was determined by careful observation of the video records. When the bubble size became pretty large, the horizontal interface moved upward to compensate the lower density of the bubble in order that total number of atoms in the cell should be retained.     

Variational Monte Carlo Calculations of 4He Adsorbed on Graphite

We present the results of variational Monte Carlo calculations of the solid ⁴ He monolayer adsorbed on a corrugated graphite substrate with the shadow wave function technique. We find that the solid monolayer at the commensurate density is tightly bound to the substrate and that the presence of corrugation localizes the Helium atoms in the direction parallel to the substrate around the sites of a triangular lattice where 1/3 of the adsorption sites of graphite are occupied. We have calculated the energy per particle, the density profile of the monolayer and the static structure factor. We have also studied the system in the presence of a defect (vacancy or interstitial) and we report the results for the one-body density matrix.     

Experiments on the study of effect of microparticles anomalistic penetration into solid bodies

At certain conditions interaction between high velocity (up to 3 km/s) flows of microparticles with dimensions 20–70 μm and solid bodies could result in their super deep penetration (SDP) into those bodies. For SDP-effect to be studied a number of experiments were carried out. The X-ray analysis of microparticles acceleration has shown the advantage of acceleration of microparticles in mixture with the extender (porofor) because it makes it possible to regulate the flow density, its velocity and impact duration by means of the extender concentration variation. Experiments have been performed on the impact of microparticle flows with velocities in the range 1–2.6 km/s on copper and iron substrates. Results of metallographic investigations of cross-sectional and lengthwise grinds of substrates indicate that some tungsten particles penetrate into a target. The diameter of channels in the substrate material, which are formed due to particles penetration, is in the range 2–15 μm.     

Interface phenomena in the Y2O3/(Al–Cu) system

Wetting behavior and the interface reaction in the Y₂O₃/(Cu–Al) system were investigated at 1423 K. A contact angle of about 130° was measured in the Y₂O₃/Cu system. Aluminum addition to copper improves wetting and the transition from non-wetting to wetting (θ ≤ 90°) was observed for the alloy with 50 at.% Al. The microstructure examination of the interface indicates that Al reacts with yttria, yttrium dissolves in the melt and a crater of AlYO₃ is formed at the substrate. The interface interaction in the Y₂O₃/(Cu–Al) system is in a good agreement with the results of a thermodynamic analysis in the Y–Al–Cu–O system. The crater depth and the macroscopic final contact angles are correlated with the Y and Al activities in the melt.     

Influence of alloying elements on as-cast microstructure and strength of gray iron

Casting experiments were carried out to produce gray cast irons with compositions in the range (wt.%): Fe–3.2C–wCu–xMo–yMn–zSi, where w = 0.78–1.79, x = 0.11–1.17, y = 0.68–2.34 and z = 1.41–2.32. These key elements were varied systematically during sand casting into 30-mm diameter bars to assess their influence on the development of microstructure and mechanical properties. It was found that microstructures ranging from fully pearlitic to an intimate mixture of retained austenite and bainitic ferrite, termed ausferrite, were produced and a reasonable linear correlation was observed between ausferrite volume fraction and strength. The optimum combination of mechanical properties was achieved in an alloy of approximate composition Fe–3.2C–1.0Cu–0.7Mo–0.55Mn–2.0Si, which generated 100% ausferrite without alloy carbides. This alloy has a microstructure and mechanical properties comparable to austempered gray iron without many of the problems associated with austempering.     

Helium mixtures on weak binding substrates

It has been recently proposed that³He bound states may exist in the first non solid layer of liquid helium near a substrate [N. Pavloff and J. Treiner, J. Low Temp. Phys.83, 331 (1991)]. Detailed calculations show that for weak binding substrates on which helium remains liquid, the energy of this substrate state ₃ is in the range –4 to –5.5 K, whereas for stronger substrates on which one or two layers solidify, _s is larger than the energy of a³He atom in bulk⁴He (–2.8 K). As a special case, we find that³He atoms can be bound at the⁴He solid-liquid interface, with a binding energy of 3 K with respect to bulk. Experiments able to test these predictions are proposed.     

Fabrication and characterization of (1−x)SrBi2Ta2O9–xBi3TaTiO9 layered structure solid solution thin films for ferroelectric random access memory (FRAM) applications

We report on the properties of (1−x)SrBi₂Ta₂O₉–xBi₃TaTiO₉ solid solution thin films for ferroelectric non-volatile memory applications. The solid solution thin films fabricated by modified metalorganic solution deposition technique showed much improved properties compared to SrBi₂Ta₂O₉. A pyrochlore free crystalline phase was obtained at a low annealing temperature of 600°C and grain size was found to be considerably increased for the solid solution compositions. The film properties were found to be strongly dependent on the composition and annealing temperatures. The measured dielectric constant of the solid solution thin films was in the range 180–225 for films with 10–50% of Bi₃TaTiO₉ content in the solid solution. Ferroelectric properties of (1−x)SrBi₂Ta₂O₉–xBi₃TaTiO₉ thin films were significantly improved compared to SrBi₂Ta₂O₉. For example, the observed remanent polarization (2P_r) and coercive field (E_c) values for films with 0.7SrBi₂Ta₂O₉–0.3Bi₃TaTiO₉ composition, annealed at 650°C, were 12.4 μC/cm² and 80 kV/cm, respectively. The solid solution thin films showed less than 5% decay of the polarization charge after 10¹⁰ switching cycles and good memory retention characteristics after about 10⁶ s of memory retention. The improved microstructural and ferroelectric properties of (1−x)SrBi₂Ta₂O₉–xBi₃TaTiO₉ thin films compared to SrBi₂Ta₂O₉, especially at lower annealing temperatures, suggest their suitability for high density FRAM applications.