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This paper reports experimental observations showing that a current flow produces an effect of strengthening a solder joint against a shear load. This conclusion is found from a single-joint shear test conducted on Sn–1Ag–0.5Cu wt% (SAC 105) joints with in situ current stressing varied from 700 to 1400 A/cm2 at room temperature. To isolate the current effect from the Joule heat effect, the same type of tests were conducted at room temperature, 40, 50, and 80 °C, without current applied to the joint, thus mimicking the condition of steady-state temperature resulting from Joule heating. Comparative testing was also conducted after aging the samples at 150 °C for 200 h. These tests produced indications suggesting that the current flow causes the maximum shear load to increase, while the rise in temperature by the Joule heat effect results in the opposite effect. Experimentally, as much as a 9.5% increase in the maximum shear load was observed from the isothermally aged sample tested under a current density of 700 A/cm2, while an ~ 25% reduction was estimated to result from a temperature increase by Joule heating. The potential mechanism for these observations is discussed.

ZnO/graphene oxide core-shell nanoparticles (ZGNPs) were prepared by via in-situ chemical synthesis and electrolysis. This report addresses the disagreement in the photocatalytic and photoluminescence behavior in this system. XRD, Raman, HRTEM, PL and UV–Vis were able to confirm ZnO nanoparticles and core-shell structures formation at various temperatures. A little shift was observed in Raman for ZGNPs after conjugating. PL showed a few peaks that were not related to the graphene, which depends on the synthesis route and defects. After conjugating between ZnO and Graphene, two mechanisms are suggested. The first is band structure modification in the boundary of core and shell. The second one is diffusion of functional group in GO as a dopant on ZnO surface.

This paper reports experimental observations evidencing that the intermetallic compound phase interfaced with Cu in the Al-Cu diffusion couple is most likely α2-Cu3Al phase, not γ-Cu9Al4 phase as previously assumed, and that its growth to a critical thickness may result in interface failure by stress-driven fracture. These conclusions are made based on an interdiffusion study of a diffusion couple made of a thick Cu plate coated with ∼ 2-μm-thick Al thin film. The interface microstructure and lattice parameter were characterized using scanning electron microscopy and x-ray diffraction analysis. Specimens aged at temperature between 623 K (350°C) and 723 K (450°C) for various hours produced consistent results supporting the main conclusions. It is found that disordered α2-Cu3Al phase grows in a similar manner to solid-state epitaxy, probably owing to its structural similarity to the Cu lattice. The increase in the interface strain that accompanies the α2-Cu3Al phase growth ultimately leads to interface fracture proceeding from crack initiation and growth along the interface. This mechanism provides the most consistent explanation for interface failures observed in other studies.

The mechanical stability of Sn-Ag-Cu interconnects with low and high silver content against mechanical shock at room and elevated temperatures was investigated. With a heating element-embedded printed circuit board design, a test temperature from room temperature to 80°C was established. High impact shock tests were applied to isothermally pre-conditioned ball-grid array interconnects. Under cyclic shock testing, degradation and improved shock performances were identified associated with test temperature variation and non-solder mask defined and solder-mask defined pad design configuration differences. Different crack propagation paths were observed, induced by the effect of the elevated temperature test conditions and isothermal aging pre-conditions.

The mechanical stability and thermo-mechanical fatigue performance of solder joints with low silver content Sn-1.0Ag-0.5Cu (wt.%) (SAC105) alloy based on different cooling rates are investigated in high G level shock environment and thermal cycling conditions. The cooling rate-controlled samples ranging from 1°C/min to 75°C/min cooling rate, not only show differences in microstructure, where a fine poly-granular microstructure develops in the case of fast cooling versus normal cooling, but also show various shock performances based on the microstructure changes. The fast cooling rate improves the high G shock performance by over 90% compared to the normal cooled SAC105 alloy air-cooling environment commonly used after assembly reflow. The microstructure effect on thermal cycling performance is also discussed, which is analyzed based on the Sn grain orientation, interconnect stability, and solder joint bulk microstructure.

The impact of isothermal aging and recrystallized grain structure distribution on mechanical shock and thermal cycling performance of solder joints with 1% and 3% silver content Sn-Ag-Cu interconnects were investigated. Localized recrystallized grain structure distributions were analyzed to identify correlations between the microstructure evolution and shock performance. The results reveal that the shock tolerance depends on the amount of shock energy that can be absorbed during each shock cycle, which depends on microstructural features. Based on the recrystallized grain distribution, additional isothermal aging in 1% silver Sn-Ag-Cu interconnects shows improved shock performance, whereas degraded shock performance was observed in 3% Sn-Ag-Cu interconnects. Using the same grain boundary distribution analysis on thermally cycled samples, relationships between the particle size distribution, localized recrystallized grain structure development, shock, and thermomechanical performance were identified: finer particle spacing is beneficial for thermal cycling as it resists grain boundary generation, while conversely, wider particle spacing facilitates recrystallization and grain boundary mobility that allows Sn to absorb shock energy.

The improved control of lattice strain in the quantum-dot (QD) region of p – i – n structures using a modified epitaxial growth procedure has been observed and analyzed. Strain in the QD region was managed by (a) inserting a correction layer (CL) with a lattice constant that was intermediate between the lattice constant of the QD region and the lattice constant of the underlying substrate, (b) capping the QD islands with a layer that had the same lattice constant as the CL, and (c) the utilization of only three atomic elements in the growth of the QD intrinsic region. These results were demonstrated in In x Ga 1− x As/InAs/In x Ga 1− x As p–i–n devices with five InAs QD layers and then compared with In x Ga 1− x As p–n (HOM) devices with identical ternary alloy compositions and no quantum dot layers. The layers in all of the devices were grown by molecular beam epitaxy. X-ray diffraction (XRD) measurements showed the interface dislocations in the QD samples were fewer than in the HOM samples and were isolated at the In x Ga 1− x As–GaAs interface, away from the optically active QD region. Cross-sectional, high-resolution transmission electron microscopy (HRTEM) images showed no evidence of threading dislocations in the QD region. Post-growth calculations of the average lattice constant of the QD region, using atomic force microscopy, XRD, and HRTEM data, indicated the QD region experienced a ∼3× reduction in its lattice misfit while increasing its critical thickness by more than 3×. Although the total misfit in the QD samples increased with the insertion of the CL and the average lattice constant of the QD region was not matched to the CL, the strain energy nevertheless was absorbed successfully without creating deleterious dislocations as seen in QD devices exhibiting lower dark current densities than in HOM control devices.

This paper examines the mechanics of ball shear testing with the objective of understanding the mechanism by which the maximum shear force and the rate of crack growth is dependent on the solder bump size. For this, Pb-Sn solder bumps with diameters between 460 lm and 760 lm are soldered to 400 lm-diameter Cu pads and subjected to ball shear testing. In spite of the constant interface area, the bump size significantly impacts the measured shear fracture force and the crack growth rate. Both the fracture force and the crack growth rate increase with bump size, and in the case of the fracture force, the increase is almost linear. Our analysis finds that the linear increase in the fracture force is a result of the bump deformation force, which increases with bump size. A simple model that accounts for the deformation force component is developed and used to extract the true interface fracture force. The estimated true interface fracture force is found to vary little with bump size, tightly converging to the 40 MPa to 48 MPa range. On the other hand, the dependence of crack growth rate on bump size is found to result from the higher degree of rotational moment associated with larger bumps.

This paper is concerned with the mechanics of interfacial fracture that are active in two common testing configurations of solder joint reliability. Utilizing eutectic Pb-Sn/Cu as a reference system and assuming the presence of a predefined crack size in the intermetallic compound (IMC) layer, stress intensity factors (K I and K II) at the crack are numerically calculated for the two given configurations. The analysis of the tensile test configuration reveals that the fracture occurs by the crack-opening mode (K I mode), as anticipated, but that it is greatly assisted by the viscoplasticity of the solder. With nonuniform viscoplastic deformation across the joint, K I is found to increase much more rapidly than it would without the solder, decreasing the critical crack size to the micron scale. The same mechanism is also responsible for the development of a K II comparable to K I at the crack tip, that is, |K I /K II| ~ 1. It is also found that the predominant fracture mode in the bump shear configuration is crack opening, not crack shearing. This is an unexpected result, but numerical analyses as well as experimental observations provide consistent indications that fracture occurs by crack opening. During shear testing, bump rotation due to nonzero rotational moment in the test configuration is found to be responsible for the change in the fracture mode because the rotation makes K I become dominant over K II. With rotational moment being affected by the geometry of the bump, it is further found that the fracture behavior may vary with bump size or shape.

We demonstrate a large-scale placement of nanoparticles through a scheme named "electrostatic funneling", in which charged nanoparticles are guided by an electrostatic potential energy gradient and placed on targeted locations with nanoscale precision. The guiding electrostatic structures are defined using current CMOS fabrication technology. The effectiveness of this scheme is demonstrated for a variety of geometries including one-dimensional and zero-dimensional patterns as well as three-dimensional step structures. Placement precision of 6 nm has been demonstrated using a one-dimensional guiding structure comprising alternatively charged lines with line width of approximately 100 nm. Detailed calculations using DLVO theory agree well with the observed long-range interactions and also estimate lateral forces as strong as (1-3) x 10(-7) dyn, which well explains the observed guided placement of Au nanoparticles.

This paper illustrates the influence of Au addition on the phase equilibria of Sn-Ag-Cu (SAC) near-eutectic alloys and on the interface reaction with the Cu substrate. From the thermal and microstructural characterization of Sn-3.8Ag-0.7Cu alloys containing various amounts of Au, it is found that the Au promotes the formation of a quaternary-eutectic reaction at 204.5°C ± 0.3°C. The equilibrium phases in the quaternary-eutectic microstructure are found to be AuSn4, Ag3Sn, βSn, and Cu6Sn5. While the addition of Au to Sn-3.8Ag-0.7Cu alloys is also found to increase liquidus temperature and the temperature ranges of the phase equilibria field for primary phases, such influences from Au are found to be less pronounced when the alloys were reacted with the Cu substrate. Because of the formation of the Au-Cu-Sn-ternary interface intermetallic, it is found that a majority of Au added to the solder is drained from the melt. The drainage of Au reduces the impact of Au on the phase equilibria of the solder alloys in the joint. It is further found that the involvement of Au in the interface reaction results in a change of the interface phase morphology from the conventional scallop structure to a compositelike structure consisting of (AuCu)6Sn5 grains and finely dispersed, βSn islands.

This paper is a study of the phase equilibria of the Sn-3.8Ag-0.7Cu alloy investigated by a differential cooling method. The difficulty in assessing phase equilibria of the Sn-Ag-Cu (SAC) system because of the insufficient resolution of conventional characterization techniques is solved by inducing preferential growth of a solid phase in a melt by holding the alloy at the solid-liquid phase-equilibrium field. Application of the technique to Sn-3.8Ag-0.7Cu with varying holding temperatures yielded results that the alloy is slightly off eutectic composition. The phase-formation sequence of the alloy during solidification was found to be Ag3Sn, β-Sn, and finally the ternary eutectic microstructure.

We report findings related to the HgTe nanodots fabricated from the precipitation phenomenon in the HgTe-PbTe quasi-binary system. With homogeneous nucleation and growth of HgTe phase, a well defined nanostructure is obtained, where the nanodots are three-dimensionally dispersed within the PbTe matrix. The nanodots prefer to take disk shape to relax a strong strain energy that resulted from the formation of disordered HgTe phase. With this facile and effective technique, the nanodots with various morphologies can be realized within any form of matrix, such as powder, bulk, or thin film, providing a new way to tailor the properties of the nanodots.

This paper presents a study of electron scattering in damascene-processed Cu interconnects. To understand the leading electron-scattering mechanism responsible for the size effect, Cu interconnects with varying physical widths, 80–750 nm, were made, and their resistivity characterized as a function of temperature, ranging from liquid He temperature (4.2 K) to 500 K. The resulting data suggest that surface scattering, contrary to expectations, was not the primary cause of the size effect observed in this investigation. Surface scattering was found to weaken with decreasing line width. Further analysis leads to the conclusion that a substantial fraction of the size effect originates from impurity content scaling inversely with width in these samples.

This paper presents experimental evidence suggesting that electromigration (EM) can be a serious reliability threat when the dimension of Cu interconnects approaches the nanoscale range. To understand the failure mechanism prevailing in nanoscale Cu interconnects, single-level, 400-µm long interconnects with various effective widths, ranging from 750 nm to 80 nm, were made, EM tested, and characterized in this investigation. The results indicate that interface EM (Cu/barrier) may be the predominant EM mechanism in all line widths. The evidence supporting the active Cu/barrier interface EM includes the fact that the EM lifetime is inversely proportional to the interface area fraction. Microscopic analysis of the failure sites also supports the conclusion of interface EM because voids and hillocks are found at the ends of the test strip, which is not possible if lines fail by grain-boundary EM in the test structure used in this study. In addition, our study finds evidence that failure is assisted by a secondary mechanism. The influence of this factor is particularly significant when the feature size is small, resulting in more uniform distribution of failure time in narrower lines. Although limited, evidence suggests that the secondary factor is probably attributed to pre-existing defects or grain boundaries.

This report studies the electromigration performance of W-plug via structures under the reservoir effect. The lifetime improvement factor M was observed to be a weak function of the stressing current and approximately equal to 2. A Simple model is included in the report to explain this observation. The model also predicts the most effective reservoir length for electromigration lifetime improvement.

This paper reports the formation of intermetallic compounds in Au/Ni/Cu/Ti under-bump-metallization (UBM) structure reacted with Ag-Sn eutectic solder. In this study, UBM is prepared by evaporating Au(500 A)/Ni(1000 A)/Cu(7500 A) /Ti (700 A) thin films on top of Si substrates. It is then reacted with Ag-Sn eutectic solder at 260 C for various times to induce different stages of the interfacial reaction. Microstructural examination of the interface, using both chemical and crystallographic analysis, indicates that two types of intermetallic compounds are formed during the interfacial reaction. The first phase, formed at the intial stage of the reaction, is predominantly Ni3Sn4. At longer times the Ni3Sn4 phase transforms into (Cu, Ni)6Sn6, probably induced by interdiffusion of Cu and Ni. At this stage, the underlying Cu layer also reacts with Sn and forms the same phase, (Cu,Ni)6Sn5. As a result, the fully reacted interface is found to consist of two intermetallic layers with the same phase but different morphologies.

The present paper reports the results of the controlled precipitation for the HgTe nano-crystals in the PbTe semiconductor matrix and demonstrates its effectiveness in producing well-organized and crystallographically aligned semiconductor nano-crystals. Following the same procedure used in metallic alloys, the semiconductor alloys are treated at 600°C for 48 h, quenched and aged up to 400 h at 300°C and 400°C to induce homogeneous nucleation and growth of HgTe precipitates. Examination of the resulting precipitates using transmission electron microscopy (TEM) reveals that the coherent HgTe precipitates form as thin disks along the {1 0 0} habit planes of PbTe matrix. It is also found that the precipitate undergoes a gradual shape change without any noticeable coarsening, from a disk to a cube, as the aging time increases. The microstructure after full aging is found to contain almost equal sized HgTe cubes, roughly 7 nm, that maintain coherency with {1 0 0} planes of the matrix. These results combined with the extreme dimension of the precipitates and the simplicity of the formation process leads to a belief that controlled precipitation can be an effective method in preparing a desirable quantum-dot microstructure.

The work reported here concerns the effect of a brief exposure to a reversed current on the electromigration failure of narrow Al-Cu thin-film conducting lines. While the precise mechanism by which Cu retards electromigration in AlCu alloys is not fully understood, the consistent observation that electromigration failure is preceded by the sweeping of Cu from the failure site can be used to improve electromigration resistance by stabilizing the distribution of Cu. One way of doing this is to expose the Al-Cu line to a reverse current for some period of time. The present work shows that this method is particularly effective in thin lines with “quasi-bamboo” microstructures. It has the effect of building a reservoir of Cu at the upstream ends of the polygranular segments that are the preferred failure sites, and significantly increases both the mean time to failure, and the time to first failure of a distribution of lines. It can be inferred from these results that Al-Cu lines that conduct alternating current should be exceptionally resistant to electromigration failure.

A newly devised misfit management method was used to deftly balance the lattice strain in an InAs quantum dot (QD) based In 0.15 Ga 0.85 As p-i-n device. The photovoltaic behavior under AM0 conditions exhibited higher V oc and lower J sc in the QD-based device as compared to a control p-n device without quantum dots. To our knowledge, both of these observations are new and seemingly conflict with some of the current understanding of quantum-dot-based PV device physics. The PV behavior under infrared illumination confirms that the quantum-confined carriers of the InAs islands in the intrinsic region contribute to the photocurrent.

The rate of resistivity decay in Al‐2Cu‐1Si thin‐film conductors was studied as a function of temperature and grain size distribution. The decay kinetics were assumed to be governed by the rate of precipitate reconfiguration to grain boundaries. This assumption was confirmed by transmission electron microscopy (TEM) observations of the microstructure during resistance decay, and by studies of lines of two different widths. The results can be explained qualitatively from the microstructure of the lines. In particular, increasing the mean grain size slows the rate of resistivity decay, and establishing a bimodal distribution with a significant population of relatively large grains has the same effect. A simple model was developed to treat these effects quantitatively. The model assumes a cylindrical grain geometry and a uniform initial distribution of Cu and ignores the effect of intragranular precipitation. The model yields reasonable values for the activation energy for Cu diffusion in thin films, and pre...

Devices in which the transport and storage of single electrons are systematically controlled could lead to a new generation of nanoscale devices and sensors. The attractive features of these devices include operation at extremely low power, scalability to the sub-nanometre regime and extremely high charge sensitivity. However, the fabrication of single-electron devices requires nanoscale geometrical control, which has limited their fabrication to small numbers of devices at a time, significantly restricting their implementation in practical devices. Here we report the parallel fabrication of single-electron devices, which results in multiple, individually addressable, single-electron devices that operate at room temperature. This was made possible using CMOS fabrication technology and implementing self-alignment of the source and drain electrodes, which are vertically separated by thin dielectric films. We demonstrate clear Coulomb staircase/blockade and Coulomb oscillations at room temperature and also at low temperatures.

This letter reports the effects of via current density on electromigration (EM) failure in Al–0.5 Cu conductors. Two-level metallization structures, differing in the number of feeding vias (1, 6, and 15), were made with the same pattern of Al lines at two levels to allow simultaneous EM testing of upper- and lower-level lines. It was established that the lower-level lines were more susceptible to the impact of the via, resulting in a failure by the formation of a local void beneath a via and a strong dependence of EM lifetime on the via current density. The results led to a phenomenological equation that incorporates via structure into failure kinetics.

In previous work we proposed a simple constitutive equation that describes the electromigration failure kinetics in naturally passivated Al(Cu) quasi-bamboo lines. The time to failure, tf obeys the relation, tf = t0 exp (−l/t0), where t0 and l0 are characteristic constants and l is the length of the polygranular segment that causes failure (which is ordinarily the longest polygranular segment in the line). The present paper gathers the data supporting this relation, which includes tests on lines as-patterned and annealed at low and high temperature, and examines the dependence of the factors t0 and l0 on current density, test temperature, line geometry, and Al2Cu precipitate distribution. The experimental data suggest that to varies geometrically with j, with exponent n ≈ 2.8, and exponentially with T−1, with activation energy of ∼0.69 eV. It also varies with the line width and the distribution of Al2Cu precipitates. On the other hand, l0 is only weakly dependent on current density and temperature, but may vary with the ratio of line width to grain size (w/G).

In order to understand the role of Sc on electromigration (EM) failure, Al interconnects with 0.1 and 0.3 wt.% Sc were tested as a function of post-pattern annealing time. In response to the evolution of the line structure, the statistics of lifetime evolved. While the addition of Sc greatly reduces the rate of evolution of the failure statistics because the grain growth rate decreases, the MTF variation was found to be very similar to that of pure Al. These observations seem to show that Sc has little influence on the kinetics of Al EM; however, it has some influence on the EM resistance of the line since it is an efficient grain refiner. Unlike Cu in Al, Sc does not seem to migrate, which may explain its lack of influence on the kinetics of Al EM.

This letter reports the observation of the space charge limited current (SCLC) induced by injection and drift of Cu ions into porous low-k dielectrics. The SCLC, characterized by the momentary rise and fall of current with time, is found in all Cu interconnects having defective Ta barrier while it is absent in interconnects with intact barrier. This observation, combined with existing model on SCLC, leads to the conclusion that Cu ions can be injected through defects in Ta barrier and drift under electric field with the mobility as high as an order of 10−13 cm2/sec V at room temperature.