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With the thermodynamic driving forces in mind, the observed microstructures and microstructural evolution that follows nonequilibrium solidification are discussed, with consideration of defect formation, intermetallic phases, and the influence of surface finish and microalloying on microstructure evolution.

The geometry of interconnections used in current electronic systems is described, and issues related to the reflow process that melts and re-solidifies the solder to make the interconnection are introduced.

Expanding use of electronic systems in close proximity to biological systems, marine environments, and polluted air introduce elements that attack solder joints. Mechanisms that cause damage and their effects on the lifetime of electronic system are discussed.

On-off operation of electronic systems leads to thermal cycling, which introduces thermal and strain energy into solder joints, resulting in microstructural evolution mechanisms of recovery, recrystallization and damage nucleation. The thermal strain history is very sensitive to the package design. The effects of microalloying on microstructure evolution bring both a challenge and an opportunity to improve the reliability of solder joints.

Understanding multifaceted microstructural evolution mechanisms is a key enabling foundation that will enable computational modeling and prediction of electronic system lifetimes before anything is built.

The mechanical stability of solder joints with SnAgCu alloy on various board thicknesses were investigated in a high G level shock environment. A test vehicle with 31mil, 62mil and 93mil board thickness, which has three different strain and shock level condition combination per board, was used to identify the joint stability and failure modes. The results revealed that joint stability is sensitive to board thickness and that the first failure location shift from the corner location near the stand off to the center with increased board thickness. Also the impact of isothermal aging and fine grain structure transformation on mechanical shock performance of solder joints were investigated. The results revealed that joint stability during shock loading is sensitive to the level of shock that can be absorbed during each shock cycle based on the capability of single to multi grain transformation. The localized fine grain structure distributions were analyzed to identify correlations between the microstructure evolution and shock performance.

This paper reports the fatigue properties of Sn-Ag-Cu (SAC) and Pb-Sn solder alloys determined from isothermal shear fatigue testing and analysis of resulting data using modified Coffin-Manson fatigue model. In our study, a series of cyclic shear fatigue testing was conducted on the solder joints in PBGA assembly with variation in testing temperature, strain range, and strain rate (or cycle frequency). The number of cycles to the first joint failure in the assembly was determined from the resistance of each solder joint and taken as the fatigue life of the assembly. Analysis of the resulting data reveals that isothermal fatigue behavior of both SAC (Sn-Ag-Cu) and Pb-Sn alloys follow the classic Coffin-Manson fatigue model and provide constants indicative of fatigue properties of the alloy, namely fatigue ductility coefficient and ductility exponent. These fatigue constants are consistent with what is generally expected from a metallic fatigue system except for their dependence on temperature. This deviation, attributable to the involvement of the thermal strain that is added to the applied mechanical shear strain, suggests that consideration of the thermal strain effect needs to be included in the fatigue analysis of solder joints even if the major fatigue mode appears to be pure mechanical shear. The fatigue constants gained from our study provide insights helpful in understanding the mechanism behind variation in fatigue reliability with solder alloy compositions and solder microstructure.

Electromigration in Cu thin films is studied in a cross-strip configuration. Cu lines with isolated areas of Cu(Al) or Cu(Sn) are tested between 250 and 390 °C with the following results. The hillock and void marker motion indicates that Sn moves in the direction of electron flow. The marker polarity indicates that it decreases the grain boundary electromigration of Cu, in agreement with previous studies. This study also finds evidence of active surface migration in Cu. During tests in forming gas, hillocks and voids form adjacent to a native Al2O3 layer at all temperatures, indicating the likelihood that Cu migrates faster through the Cu free surface than the interface between the surface layer of Al2O3 and Cu(Al). Active surface migration in Cu thin films is also evidenced by the growth of hillocks with highly developed facets, most of which are attached to the underlying film by narrow necks.

This article introduces a simple and effective technique for conducting electromigration testing of a number of samples using a single current source. It is based on a configuration where all samples are serially connected to a single current source, allowing them to be subjected to identical current conditions. In this design, each sample has a current bypass circuit, consisting essentially of a computer controlled shunt relay and a Zener diode, to enable continuation of testing without any interruption in the test current when samples fail. With this technique, a large number of samples can be tested with the same current and excellent current stability, making it suitable for both reliability assessment and scientific investigation of electromigration mechanisms. Initial results show high correlation with industry standard testing systems.

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 lattice misfit at the island-cap interface in two In0.15Ga0.85As p-i-n devices, with 5 layers of InAs quantum dots (QDs), was modified by depositing 2.1 and 3.2 ML of InAs while maintaining near identical capping layers. The device with 35 ± 3 nm island size distribution exhibited photoluminescence activity in the near infra-red range from 975 to 1150 nm while the device with 42 ± 12 nm size islands recorded lower PL intensity over a narrower range of 1000-1100 nm suggesting (a) increased island-cap interface misfit, (b) truncation of the islands, and (c) generation of structural defects.

This paper reports the findings supporting that solder joint grain structure within an assembly is not fixed but varies with the joint location and cooling rate. Also reported is the fact that such change in grain structure can make the joint fatigue resistance to be increased. These conclusions are made by comparing the grain structure and fatigue kinetics of the joints in BGA assembly with variation in cooling rate after thermal aging. Our study finds that the grain structure changes with cooling rate because of the kinetic interplay between plastic deformation by thermal strain and its relaxation process other than dislocation glide. The variation in the spontaneous plastic deformation and its storage in the solder promote recrystallization in one extreme, while the process of dynamic relaxation releases the stored energy and make the joint maintain its original grain structure in another extreme. Mechanical fatigue testing of these samples reveals that failure prone joint, corner joint, becomes immune to fatigue failure when its grain structure is changed to polygranular structure. The degree of reliability gain is not possible to quantify at the present moment because the failed joint is shifted to non-recrystallized joint and the failure kinetics is also affected by the amount of residual stress which is also affected by the cooling rate. However, there are many of indications that the joint with polygranular structure is much less susceptible to fatigue failure. Some of highlighting evidences are presented in this paper.

Epitaxially formed indium arsenide quantum dot (QD) structures formed by the Stranski-Krastanov growth mode have been investigated with respect to how quantum confinement and lattice strain behavior affects the optoelectronic performance in p-i-n type InGaAs devices. The introduction of a correction layer and the proper selection of the QD capping layer’s alloy and thickness parameters allowed the control and management of the lattice misfit in two QD structures, which led to reduced defects and improved dark current behavior under forward bias conditions when compared to an InGaAs p-n homojunction (HOM) device without quantum-dots. Although the dark-current of the HOM devices behaved as expected under forward and reverse biases, the QD device structures displayed an apparent anomalous behavior in their dark-current densities under forward and reverse biases. Closer analysis reveals that this behavior is not anomalous; instead the information gained can be used to extract greater understanding about how to optimize the optoelectronic performance in quantum confined structures. In addition, the analysis suggests that lattice strain behavior continues to be a critical benchmark for defining and optimizing the performance of epitaxially formed= QD devices.

The possibility is addressed of improving the electromigration resistance of Al and Al–Cu thin‐film conductors with ‘‘quasi‐bamboo’’ structures by post‐pattern anneals that decrease the maximum polygranular segment length. Pure Al, Al–2Cu, and Al–2Cu–1Si lines were patterned and annealed at temperatures high enough to stimulate grain growth. Appropriate anneals led to predominantly bamboo structures with short polygranular segments. These grain structures had a high median time to failure with a relatively low deviation of the time to failure. Metallographic analyses showed that polygranular segment length was a dominant factor in determining the failure site. Post‐pattern annealing promotes a preferential shortening of the relatively long polygranular segments that cause early failures. However, even after annealing, failure occurred at the longest residual polygranular segments, even when these were significantly shorter than the ‘‘Blech length’’ under the test conditions. Statistical analysis of the failure of alloy lines revealed a simple exponential relation between the failure time and the longest polygranular segment length within a line, which is functionally identical to that previously found for lines tested in the as‐patterned condition.

Electromigration is a serious potential source of failure in the narrow, thin-film Al-Cu conductors used in modern microelectronic devices. The problem has become more acute as line widths have shrunk to below one micrometer, creating lines with quasi-bamboo microstructures. The usual mechanism of internal electromigration failure in such lines involves the formation of a transgranular void across a bamboo grain at the upstream end of a long, polygranular segment, preceded by the depletion of copper from both the polygranular segment and the upstream bamboo grain. At least three metallurgical mechanisms are available to inhibit this failure mechanism and improve the useful lifetime of the line, Each of these methods has been demonstrated in the laboratory environment.

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.

One of the important phenomena in Electromigration (EM) is Blech Effect. The existence of Threshold Current Density-Length Product or EM Threshold has such fundamental and technological consequences in the design, manufacture, and testing of electronics. Temperature-dependence of Blech Product had been thermodynamically established and the real behavior of such interconnect materials have been extensively studied. The present paper reviewed the temperature-dependence of EM threshold in metallization lines of different materials and structure as found in relevant published articles. It is expected that the reader can see a big picture from the compiled data, which might be overlooked when it was examined in pieces.

This letter presents evidence of an oxidation-driven failure mechanism in Cu interconnects integrated with ultralow-κ materials. It is found that the open pore structure of ultralow-κ materials allows oxidants in the ambient to reach the interconnect structure and induce oxidation of Cu. In contrast to a normal oxidation process where Cu is in contact with the oxidant, oxidation is controlled by the outdiffusion of Cu through the barrier layers, Ta and SiCN, to form Cu oxide in the pores of the dielectric material. The loss of Cu by outdiffusion induces extensive voiding and subsequent failure in Cu interconnects.

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.

This paper reports experimental evidences suggesting that fracture resistance of solder joints in packaging assembly is not necessarily uniform but can vary significantly with their locations in the assembly. Specifically, it is found that the solder joints located at the chip corner is much more prone to the fracture under thermo-mechanical or mechanical loads such as vibration and shock. This, the variation in fracture resistance, is found from the isothermal cyclic shear fatigue testing of 60Pb-40Sn, SAC305 and SAC105 solder alloys assembled in PBGA configuration. Under pure shear fatigue situation, the location of the joint failure should ideally be random because all joints are subjected to an identical shear strain. However, it is found that the solder joint that fails first is always the ones located at the corner site of chip. The inner joint, close to the center of the chip, shows much higher resistance against failure. Further study that investigates the joint microstructure with aging, produces evidences indicating that the corner is the place of high residual thermal stress or stored strain energy (by plastic deformation during cooling or heating). In an extreme case, where stored energy by plastic deformation is not released well by competing process, the stored energy triggers recrystallization, leading to polygranular structure of the corner joint solder. These results strongly suggest that the joints in package assembly have different reliability and microstructural evolution path depending on their location in the package and thermal history.

This paper presents the results of isothermal shear fatigue tests conducted on Sn-Ag-Cu lead-free and Pb-Sn solder alloys in fully assembled PBGA configurations. Our study, aimed to better understand the fatigue behaviors of solder alloys in the package assembly, reveals that the shear fatigue test is indeed capable of measuring the fatigue properties of the solder itself and may lead to material parameters necessary for the prediction of the solder joints fatigue reliability in general. The cyclic shear fatigue test conducted under various fatigue conditions yields the result suggesting the close linkage between the fatigue in PBGA and the fatigue property of solder alloy. This is a result of the existence of consistency in crack propagation path in solder joint, that is fixed to the chip-side of solder matrix (not interface), irrespective of test conditions that includes temperature, strain range, and frequency. As a result, fatigue failure of Pb-free and Pb-Sn solder can be fitted to the Coffin-Manson fatigue model with a reasonable consistency. The resulting numerical constants, namely ductility coefficient and ductility exponent, are consistent with what is expected from general consideration of metallic fatigue system. However, their temperature dependence shows a significant deviation from expectation, probably due to an addition of thermal strain to the shear strain and its variation with temperature.

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...

Sintered magnetoelectric composites generally exhibit reduced sensitivity due to: 1) breakage and aggregation of ferrite coating during compaction forming path of reduced resistivity, 2) coarsening of piezoelectric particle leading to interfacial porosity, and 3) inter-diffusion between piezoelectric and ferrite resulting in coherency loss. In order to overcome these problems, we are adopting following approach to synthesize core-shell nanocomposites: 1) create piezoelectric particles (sub-micron range) with crystallographic facets which will result in uniform stress.

This work is principally concerned with the microstructure of electromigration failure in narrow Al‐2Cu‐1Si conducting lines on Si. Samples were patterned from 0.5‐μm‐thick vapor‐deposited films with mean grain size of 2.4 μm, and had linewidths of 1.3 μm (W/G≊0.5), 2 μm (W/G≊0.8), and 6 μm (W/G≊2.5). The lines were tested to failure at T=226 °C and j=2.5×106 A/cm2. Other samples were tested over a range of substrate temperatures and current densities to test the effect of these variables, and 1.3 μm lines were tested after preaging at 226 °C for various times to change the Cu‐precipitate distribution prior to testing. Three failure modes were observed: The 6 μm specimens failed by separation along grain boundaries with an apparent activation energy of 0.65 eV; the 1.3 μm specimens that were preaged for 24 h failed after very long times by gradual thinning to rupture; all other narrow lines failed by the transgranular‐slit mechanism with an activation energy near 0.93 eV. Microstructural studies suggest that the transgranular‐slit failure mechanism is due to the accumulation of a supersaturation of vacancies in the bamboo grains that terminate polygranular segments in the line. Failure occurs after Cu has been swept from the grain that fails. Failure happens first at the end of the longest polygranular segment of the line, at a time that decreases exponentially with the polygranular segment length. Preaging the line to create a more stable distribution of Cu lengthens the time required to sweep Cu from the longest polygranular segment, and significantly increases the time to failure. In the optimal case the transgranular‐slit failure mechanism is suppressed, and the bamboo grain fails by diffuse thinning to rupture. Preaging is particularly effective in increasing the lifetimes of lines that contain very long polygranular segments, and has the consequence that the time to first failure in an array of lines is much longer than predicted by a log‐normal fit to the distribution of failure times.

This paper reports the experimental and theoretical exploration of the fracture mechanism active in BGA lead-free solder assemblies under high speed shear fatigue test conditions. Our investigation finds that, contrary to common assumption, the crack growth in shear fatigue is not governed by shear stress but more by crack opening stress. Our theoretical analysis indicates that fracture by crack opening mode prevails because non-uniformity in the shear deformation of solder joint creates a body rotation which results in crack opening stress rather than shear. While the crack growth in shear fatigue is found to vary sensitively with variation in the mechanical constraints on the assembly, such as solder shape and elastic modulus of the chip mold, it is also sensitive to variation in solder microstructure. This, the sensitivity to the assembly constraints and solder microstructure, makes it ideal in investigating fatigue properties of solder joints as well as identifying the structural and microstructural features responsible for reliability failure.

This paper reports a study of the effect of Cu precipitation on electromigration failure in Al‐2Cu‐1Si thin‐film conducting lines. The films were 0.5 μm in thickness, and patterned to widths of 1.3 and 4 μm, providing width‐to‐grain‐size ratios (W/G) of approximately 0.5 and 2. The lines were aged for various times at 226 °C, and were then tested to failure at a current density of 2.5×106 A/cm2. Scanning and transmission electron microscopy were used to study the Cu precipitate distribution, its evolution during aging and electromigration, and the microstructural failure mechanism. Aging produces a dense distribution of intragranular θ’ (Al2Cu; coherent), with stable θ (Al2Cu; incoherent) in the grain boundaries. The θ’ is replaced by θ as aging proceeds. In the wide lines (W/G≊2), the mean time to failure (MTF) increases slowly and monotonically with prior aging time. The failure happens through the growth and coalescence of intergranular voids. In the narrow lines (W/G≊0.5), both the MTF and the time to...

This study concerns the failure mechanism of a lead-free SAC305 solder joint under the isothermal bending fatigue condition. For this, series of bending fatigue tests are carried out with the variations of bending displacement and frequency, and FEM analysis is conducted to examine the relationship between mechanical behavior of a solder joint and fatigue life cycle. The results of this investigation suggest that the isothermal fatigue of a solder joint is strongly affected by plastic deformation process of SAC solder. It is found that the failure life cycle ‘N f ’ fits well to the model suggested by Coffin-Manson, that is N f ∼ (Δe p )−2.3. This result indicates that fatigue failure is determined by accumulation of damage by plastic deformation of solder. The fractography of a solder joint also supports our conclusion because crack is found to propagate along the solder matrix near to IMC interface.

This paper presents findings evidencing that electromigration(EM) imparts significant influence on the kinetics of contact failure of Au wire bonded to an Al pad. Contact resistance between Au wire and Al pad at moderately accelerated test conditions (T=150–175°C; j=5×104A/cm2) revealed that the failure rate depends highly on the direction of electron flow across the contact: electron flow from Au to Al resulted in far faster failure rate than the opposite direction. Microscopic inspection of the contact interface indicated that the wirebond contact failure is related to the growth of Au-Al intermetallic compounds (IMC). EM was found to influence the failure kinetics because it accelerates or decelerates the growth rate of the IMC.

Although single-electron devices have many advantages over conventional electronic devices and are therefore expected to have important applications for military, space, and commercial use, many fabrication challenges associated with nanoscale geometrical control have limited their implementation for practical use. The aim of this project was to create new single-electron device architecture and its associated fabrication techniques to realize single-electron device fabrication on a large scale, thereby enabling their implementation for practical applications. We demonstrated 1) chip-level fabrication of single-electron transistors, 2) that they can be fabricated in completely parallel processing, with each device individually addressable, 3) clear I-V characteristics of Coulomb blockade/staircase and Coulomb oscillations, and 4) that they can operate at room temperature. These results show that fabrication of integrated systems of room-temperature single-electron devices is now possible, paving a pathway toward practical use of single-electron devices.

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.

Recent surgical management of cancer tends toward minimally invasive surgical techniques since tumors can be detected smaller than ever due to the advance of cancer diagnostic technologies. Many of these surgical procedures are thermal therapies where a localized freezing or heating zone (i.e. thermal lesion) is created to destroy tumors without damaging adjacent normal tissues. The outcomes of these innovative and less invasive surgeries, however, are significantly impaired by the limited image-guidance of the thermal lesion during the procedures. Since the primary clinical objective of these surgeries is to eradicate diseased tissues while sparing the adjacent normal tissue, accurate intra-operative monitoring of the thermal lesion is critical. Moreover, in many surgical situations, sparing adjacent tissue is not only desired, but imperative since major blood vessels, nerve bundles and surrounding organs are susceptible to thermal injury. However, currently available monitoring techniques have limited accuracy or accessibility, and/or are not capable of monitoring the lesion in real-time during the procedure. In our recent study [1], we demonstrated the feasibility of non-invasive thermometry using quantum dot (QD) as temperature probe. Although its feasibility was demonstrated, several limitations should be addressed before more rigorous clinical applications. Especially the lower quantum yield of core/shell QDs should be significantly improved for deeper tissue imaging. In the present study, QD-embedded nano-composite particles were developed for deeper tissue imaging and its temperature dependent fluorescence was characterized.

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.

This paper introduces new electrochemical cells and testing methods that are ideal for characterizing corrosion risk assessment of the components used for liquid cooling system with high surface to liquid volume ratio. Two cell configurations are described in this paper and they use three electrode and two electrode cells. These cells have the identical structure except for the number of electrodes. These cells are made by sandwiching the working electrode plate (sample) and the counter electrode plate (graphite) with a spacer (gasket), and by filling the cavity with the liquid under interest. In case of the three-electrode cell, the reference electrode is inserted through the hole in the graphite. The three-electrode cell is ideal for the quantitative characterization of the corrosion rate by utilizing conventional electrochemical techniques such as a Tafel method. The use of the two-electrode cell is similar to the case of the galvanic corrosion characterization as it measures the cell current that flows between the dissimilar metals that are in contact with the liquid. When coupled with computer assisted data acquisition, the two-electrode cell configuration allows the characterization of long-term corrosion reliability of a component with a variation in a large number of test variables. It is particularly useful in finding corrosion inhibitors.Copyright © 2006 by ASME

This paper reports the observation of HgTe precipitate formation and its subsequent evolution in a PbTe semiconductor matrix containing 4 mol. % HgTe (PbTe-4HgTe) produced by a controlled precipitation process. The controlled precipitation process is being developed as a new way to produce a large number of quality semiconductor nanocrystals more simply than the conventional methods. Characterization of the HgTe precipitates resulting from application of controlled precipitation to the PbTe-4HgTe alloy system provides evidence that this method is effective in generating nanocrystals. Transmission electron microscopy of the processed alloys reveals that HgTe precipitates are extremely small in size, maintain a coherent interface, and experience a unique shape evolution with aging.

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).

This letter reports experimental observations evidencing the viscoplasticity of porous organosilicate glass thin films under conditions pertinent to their application in advanced low-k/Cu interconnect technology. Specifically, it is found that porous SiCOH thin films exhibit a significant level of viscoplasticity with a rate sensitive to the porosity, the degree of plasma damage, and hydration reaction when tested using a ball indenter at 150–400 °C. The activation energy of the viscosity (1.25–1.45 eV) is measured to be far lower than the bulk glass (>4 eV), suggesting that the viscous flow is affected by the presence of defective bond-network such as Si–OH or Si–H bonds.

We report on a collective body of work wherein we have studied the mass transport phenomena which are likely to be operative during stress driven changes in microstructure arising from electromigration and stress voiding. Our goal is to understand such microstructural evolution leading to failure of the metal lines or interconnects associated with integrated electronic circuits or chips. This work, when complete, will lead to improved electronics performance and reliability and faster product development arising from accurate and predictive models of wearout phenomena. We report on the role of thermal induced strain leading to hole and hillock formation, the influence of grains structure on the reliability of Al- based interconnects, and the observation of counter-current electromigration of Ua in Al grain boundaries.

This study investigates the effect of solute additions on electromigration in Al-based thin film binary alloys. The “cross-strip” technique was used to observe solute electromigration and its influence on Al electromigration. The results of electromigration tests on five alloy additions, Ag, Au, Cu, Pd and Ni, are presented. It is concluded that beneficial solutes have two characteristics. First, they have a large, negative effective valence (Z**). Second, they have sufficient solubility in Al at test temperature to provide a reservoir of mobile atoms. Ag and Au are relatively ineffective because of their low effective valence. Pd and Ni appears to be relatively ineffective because of their low solubility at test temperature. Only Cu satisfies both criteria.

Thin-film Al-2Cu conducting lines with “quasi-bamboo” microstructures were investigated to understand the microstructural mechanism of electromigration failure. Both conventional test structures and electron-transparent lines fabricated on silicon nitride windows were utilized to identify the “weakest” polygranular segments. Even when the current density was reduced to 0.75 MA/cm2 and the segment length was on the order of a few microns, failure occurs at the upstream termination of the longest polygranular segment in the line, at a time that decreases exponentially with the segment length. There is no apparent “Blech length” in quasi-bamboo Al- Cu lines; the longest segments are the failure sites, and their lifetime decreases with segment length in a regular way, even when the longest segments are only a few microns in length. It follows (and is observed) that the time-to-failure distribution of a group of lines is fixed by the distribution of the longest polygranular segments within them. This distribution can be effectively controlled by post-pattern annealing, which can refine the quasi-bamboo structure so that the longest polygranular segments are short and the distribution of longest polygranular segment lengths is narrow. Consequently, post pattern annealing is a very effective method for improving reliability by increasing the time to first failure.

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.

Al-Cu lines of submicron width ordinarily have quasi-bamboo microstructures that contain both bamboo grains and polygranular segments. The usual mechanism of internal electro-migration failure in such lines involves the formation of a transgranular void across a bamboo grain at the upstream end of a long, polygranular segment. The voiding is preceded by the depletion of Cu from both the polygranular segment and the upstream bamboo grain. At least three metallurgical mechanisms are available to inhibit this failure mechanism and improve the useful lifetime of the line. First, the line can be annealed after patterning to break up long polygranular segments. Second, the line can be aged at relatively low temperature to stabilize the distribution of Cu and retard its depletion from polygranular segments. Third, the line can be subjected to reverse currents to restore the distribution of Cu and provide a Cu reservoir. Each of these methods has been demonstrated in the laboratory environment.

The work reported here concerns the effect of grain structure on electromigration failure in pure Al and Al-2wt.%Cu-lwt.%Si lines. The grain structures of fine lines were controlled by annealing after patterning to promote the formation of "bamboo" structures. Significant improvements in the median time to failure (MTF) and the deviation of the time to failure (DTF) were observed with the development of near-bamboo structures with polygranular-segment lengths shorter than ~ 5 μm. The most common failure sites are voids or slits across bamboo grains at the upstream ends of polygranular segments. The time-to-failure decreases with the polygranular segment length, and can be significantly enhanced by controlling the grain structure.

not Available.

Microstructural studies of electromigration failure were performed on A1-2Cu-1Si interconnects with 1.3 μm width. The lines were tested to failure under controlled conditions after pre-aging for various times at three different temperatures. Examination of the microstructure of the failure sites suggests that the lines fail at the bamboo grains that terminate the longest polygranular segments in the line. Transgranular slit voids form after Cu has been swept from the grain that fails. Hence, pre-aging lines to create a more stable distribution of Cu lengthens the time required to sweep Cu and significantly increases the time to failure. The optimal microstructure has a maximum intragranular density of stable θ precipitates. In this case transgranular slit failure is suppressed, and the bamboo grain fails by diffuse thinning to rupture.