Metal Electromigration Research Articles

The Understanding and Compact Modeling of Reliability in Modern Metal-Oxide-Semiconductor Field-Effect Transistors: From Single-Mode to Mixed-Mode Mechanisms.

With the technological scaling of metal-oxide-semiconductor field-effect transistors (MOSFETs) and the scarcity of circuit design margins, the characteristics of device reliability have garnered widespread attention. Traditional single-mode reliability mechanisms and modeling are less sufficient to meet the demands of resilient circuit designs. Mixed-mode reliability mechanisms and modeling have become a focal point of future designs for reliability. This paper reviews the mechanisms and compact aging models of mixed-mode reliability. The mechanism and modeling method of mixed-mode reliability are discussed, including hot carrier degradation (HCD) with self-heating effect, mixed-mode aging of HCD and Bias Temperature Instability (BTI), off-state degradation (OSD), on-state time-dependent dielectric breakdown (TDDB), and metal electromigration (EM). The impact of alternating HCD-BTI stress conditions is also discussed. The results indicate that single-mode reliability analysis is insufficient for predicting the lifetime of advanced technology and circuits and provides guidance for future mixed-mode reliability analysis and modeling.

Electromigration reliability and activation energy of Bi2Te3 thermoelectric film

Reliability problems caused by metal electromigration failure have attracted much attention, but it is barely investigated for thermoelectric semiconductors with increased current density in micro thermoelectric devices. Herein, we investigate electromigration reliability of a Bi2Te3 thermoelectric film with the current densities of ∼104 A/cm2. The failure mechanism and thermoelectric performance change of the Bi2Te3 film at different current densities by controlling the temperature are discussed, indicating the reliability issue is a comprehensive problem involving multiphysics effects. In addition, the activation energy of Bi2Te3 materials, as an essential electromigration parameter, is measured and calculated to be about 0.8 eV by the resistance change method. This work provides much guidance to the reliable service of thin-film TE devices operating under high current density.

Connecting the phase-field-crystal model of electromigration with electronic and continuum theories

Electromigration (EM) is the motion of lattice atoms under high-density electric current. It is an important mechanism for structural changes in nanoelectronic devices and a major contributor to the electroplastic effect in structural metals. Recently, a phase-field-crystal (PFC) model for studying EM in metals was developed and shown to successfully capture many important EM-driven structural evolutions at experimentally relevant timescales. In this work, connections between the previous PFC EM model and existing EM theories are established. It is shown that the PFC model can be linked to both the electron-density-based quantum EM theory and the drift-diffusion-based continuum EM theory, therefore filling an important gap in the theoretical and computational study of EM-related phenomena. The numerical method for implementing the PFC EM model is discussed in detail. The well-established Blech effect is quantitatively reproduced using the model.

A model for electromigration induced flow in liquid metals

Electromigration in liquid metals can be used for mass transport over a considerable length with micro- and nano-scale flow features. Exploitation of this phenomenon, however, requires a sound understanding of the liquid metal flow under an applied electric field. Depending on the sign of the effective charge number, Z*, liquid metals flow along a set direction under the applied electric field. A few liquid metals, e.g. Ga, Sn, etc, flow in the direction of the electric field, while a few others, e.g. Pb, flow in the opposite direction. Here, we propose a new model for predicting the direction of the aforementioned flow for a given liquid metal. Our model incorporates Lennard-Jones potential into the cell model of liquids in order to calculate the value of Z* as a function of temperature. We then carry out experiments on a few metals to validate the model and show that it indeed correctly predicts the ensuing flow.

Phase-Field-Crystal Model for Electromigration in Metal Interconnects.

We propose an atomistic model of electromigration (EM) in metals based on a recently developed phase-field-crystal (PFC) technique. By coupling the PFC model's atomic density field with an applied electric field through the EM effective charge parameter, EM is successfully captured on diffusive time scales. Our framework reproduces the well-established EM phenomena known as Black's equation and the Blech effect, and also naturally captures commonly observed phenomena such as void nucleation and migration in bulk crystals. A resistivity dipole field arising from electron scattering on void surfaces is shown to contribute significantly to void migration velocity. With an intrinsic time scale set by atomic diffusion rather than atomic oscillations or hopping events, as in conventional atomistic methods, our theoretical approach makes it possible to investigate EM-induced circuit failure at atomic spatial resolution and experimentally relevant time scales.

Effect of De-ionized Water Rinse in AlCu Line Post Etch Asher Residue Removal Process Using Fluoride Containing Stripper

Compared with hydroxylamine-based stripper process, De-ionized water rinse becomes more critical due to intermediate solvent rinse elimination in the fluoride containing stripper process. In this paper, an integrated AlCu line photoresist strip de-ionized water rinse process utilizing a fluoride containing stripper is studied systematically in following aspects: a. CO2 bubble flow rate effects to metal galvanic corrosion, metal sidewall roughness and electromigration; b. de-ionized water rinse time effects to metal post-corrosion in wet box and metal electromigration; c. de-ionized water dump time effects to metal resistivity and electromigration. The data show de-ionized water rinse optimization along with CO2 bubble flow rate fine-tuning is essential to provide effective metal corrosion prevention, smooth metal sidewall and good electro-migration.

Electro-migration of heavy metals in an aged electroplating contaminated soil affected by the coexisting hexavalent chromium

Cr(VI) was often reported to oxidize soil organic matter at acidic environments due to its high ORP, probably thus changing cationic metal species bound to soil organic matter, and influencing their electro-migration patterns. However, such an effect on the electro-migration was not confirmed in most previous studies. Therefore, this study applied a fixed voltage direct current field on an aged electroplating contaminated clayed soil, with a special interest in the direct or indirect influence of Cr(VI) on the electro-migration of other coexisting metals. After 353h electrokinetic process, 81% of Zn, 53% of Ni and 22% of Cu in the original soil were electro-migrated into the electrolyte, and most of the remaining concentrated near the cathode. The Cr(VI) oxidized some soil organic matter along its migration pathway, with a pronounced reaction occurred near the anode at low pHs. The resulting Cr(III) reversed its original movement, and migrated towards the cathode, leading to the occurrence of a second Cr concentration peak in the soil. Metal species analyses showed that the amount of metals bound to soil organic matter significantly decreased, while a substantial increase in the Cr species bound to Fe/Mn (hydro-)oxides was observed, suggesting an enhancement of cationic metal electro-migration by the reduction of Cr(VI) into Cr(III). However, the Cr(VI) may form some stable lead chromate precipitates, and in turn demobilize Pb in the soil, as the results showed a low Pb removal and an increase in its acid-extractable and residual fractions after electrokinetic remediation.

W-plug via electromigration in CMOS process

We analyze the failure mechanism of W-plug via electromigration made in a 0.5-μm CMOS SPTM process. Failure occurs at the top or bottom of a W-plug via. We design a series of via chains, whose size ranges from 0.35 to 0.55 μm. The structure for the via electromigration test is a long via chain, and the layer in the via is Ti/TiN/W/TiN. Using a self-heated resistor to raise the temperature of the via chain allows the structure to be stressed at lower current densities, which does not cause significant joule heating in the plugs. This reduces the interaction between the plug and the plug contact resistance and the time-to-failure for the via chain. The lifetime of a W-plug via electromigration is on the order of 3 × 107 s, i.e., far below the lifetime of metal electromigration. The study on W-plug via electromigraion in this paper is beneficial for wafer level reliability monitoring of the ultra-deep submicron CMOS multilayer metal interconnect process.

Study on 1/<i>f</i> <sup>γ</sup> Noise Characterization of Metallic Interconnection Electromigration

Metallic interconnection electromigration is a common phenomenon in integral circuit, and it influences circuit reliability seriously as rapid miniaturization of circuit size. Resistance is a traditional electromigration characterization parameter, but it requires strict testing condition, and it is not sensitive to vacancies accumulation at early stage of electromigration. Some recent researches show that noise is very sensitive to metallic thin film electromigration, it can be used as an effective inspect method for electromigration. So noise wais used to characterize damage degree of Al thin film electromigration in this paper., Tthe results showeds both noise amplitude and frequency exponent increased during electromigration process, and when void nucleation occuredhappens, frequency exponent increased sharply. noise can also reflect electromigration degree under different environment temperature. Through comparing with resistance, noise can be proved a better characterization parameter for electromigration

Maintaining Cu metal integrity on low-k IMDs with a nanometer thick a-SiC:H film obtained by HWCVD

Hydrogenated amorphous silicon carbon (a-SiC:H) ultra thin films obtained by Hot wire chemical vapor deposition (HWCVD) have been shown to act as efficient diffusion barriers for copper on inter metal dielectric (IMD) layers which are of great significance for ultra-large scale integration (ULSI) circuits. In this work, we have studied the influence of the a-SiC:H barrier layer obtained by HWCVD which has implications towards issues related to the resistance to electromigration of Cu in the low dielectric (low- k) hydrogen silsesquioxane (HSQ) film. The presence of the ultra thin a-SiC:H film maintains the integrity of the Cu metal not only by suppressing Cu diffusion but also by increasing its crystallinity, which would have implications with respect to the mean time to failure (MTF) arising from metal electromigration. Though, we demonstrate this aspect on the low- k (HSQ)/Cu system, this should yield similar benefits for other low- k dielectric materials too.

Research on noise correlation dimension of metallic interconnection electromigration

Research on noise correlation dimension of metallic interconnection electromigration

Fractal character of noise in electromigration in metel interconnection

Based on fractal theory , through the fractal dimension of electro-diffusion, the dimensions of noise time series and grain boundary are corelated. The change of noise dimension is shown to be useful for studying the damage mechanism and determining the parameters for electromigration. The picture of grain boundary becomes complicated in the early period of electromigration, but after the voids are informed, it becomes more regular. So the fractal dimension of time series increases during the early stage of electromigration and goes down after the voids are informed. The theoretical analysis is confirmed by experiment, the dimension of noise time series may be a new characteristic parameter for metallic interconnection electromigration.

Temporal Redundancy Based Encoding Technique for Peak Power and Delay Reduction of On-Chip Buses

Power consumption and delay are two of the most important constraints in current-day on-chip bus design. The two major sources of dynamic power dissipation on a bus are the self capacitance and the coupling capacitance. As technology scales, the interconnect resistance increases due to shrinking wire-width. At the same time, spacing between the interconnects decreases resulting in an increase in the coupling capacitance. This, in turn, leads to stronger crosstalk effects between the interconnects. In Deep SubMicron technology the coupling capacitance exceeds the self capacitance, which, in turn, cause more power consumption and delay on the bus. Recently, the interest has also shifted to minimizing peak power dissipation. The reason being that higher peak power leads to an undesired increase in switching noise, metal electromigration problems and operationinduced variations due to non-uniform temperature on the die. Thus, minimizing power consumption and delay are the most important design objectives for on-chip buses. Several bus encoding schemes have been proposed in the literature for reducing crosstalk. Most of these encoding techniques use spatial redundancy that requires additional transmission wires on the bus. In this paper, a new temporal encoding scheme is proposed, which uses self-shielding memory-less codes to completely eliminate worst-case crosstalk effects and hence significantly minimizes power consumption and delay of the bus. A major advantage of the proposed temporal redundancy based encoding scheme is the reduction in the number of wires of the on-chip bus. This reduction facilitates extra spacing between the bus wires, when compared with the normal bus, for a given area. This, in turn, leads to reduced crosstalk effects between the wires. The proposed encoding scheme is tested with the SPEC2000 CINT benchmarks. The experimental results, when compared to the transmission over a normal bus, show that on an average the proposed technique leads to a reduction in the peak-power consumption by 51% (28%), 51% (29%) and 52% (30%) in the data (address) bus for 90nm, 65nm and 45nm technologies, respectively. For a bus length of 10mm the proposed technique also achieves 17%, 31% and 37% reduction in the bus delay for 90nm, 65nm and 45nm technologies, respectively, when compared to what is incurred by the data transmission on a normal bus.

Novel applications of X-ray analysis to microelectronic materials and devices

X-ray analysis has been important for advanced understanding of many microelectronic materials. Examples described in this paper are drawn from work on metal conductor lines and on semiconductors. In situ studies of Al and Al(Cu) conductor lines by X-ray microbeam diffraction and fluorescence have been used to test models and to obtain key parameters for electromigration in polycrystalline metals and alloys. EXAFS and high resolution X-ray diffraction have given information about local strains, defect complexes and deformation potentials in studies of group III, IV, and V impurities in silicon. Real-time high resolution diffraction measurements of optically induced structural changes in GaAlAs:Sn and GaAlAs:Si have provided tests for structural models of the DX-center. Some of these examples illustrate advances in X-ray analysis made possible by high brightness synchrotron X-ray sources.

Landauer fields in electron transport and electromigration

Landauer's classic 1957 paper on electron transport in the presence of localized scatterers has provided a powerful approach for analysing the local transport field and the driving force for electromigration in metals. This approach leads to local fields which are associated with residual resistivity dipoles and with carrier density modulation, and these Landauer fields contribute to the electromigration driving force. The nature of these fields and their role in electromigration are critically examined and comparisons are made with the results of more elaborate quantum-mechanical theories.

Tutorial: Electrolytic models for metallic electromigration failure mechanisms : Simeon J. Krumbein. IEEE Transactions on Reliability, 1995, 44(4), 539

The “W-Capped Aluminum Damascene Process” forms low-resistance wiring for the IBM/Siemens 64 MB dynamic random access memory (DRAM). Damascene wiring is fabricated by etching a trough in a dielectric, filling the trough with metal, and planarizing back to the dielectric surface. For the 64 Mb DRAM, collimation is used to enhance fill of the recessed features. This paper reports the results of our recent work to optimize the processes. Specifically, we have investigated the trough-fill capability of the Al and Ti films as a function of process parameters, deposition hardware, and the oxide trough aspect ratios. In addition, we have improved the manufacturability of these processes by modifying the collimator design to increase deposition rate and lengthen collimator life.Finally, we report the first demonstration of an Al-based dual-damascene structure combining collimated sputtering and chemical vapor deposition (CVD) W. Dual damascene combines fabrication of the wires and studs by etching both recesses in the same dielectric and filling them simultaneously, thereby simplifying the process flow and lowering fabrication costs.

Electrolytic models for metallic electromigration failure mechanisms

Metallic electromigration is the movement of metallic material across a nonmetallic medium, under the influence of an electric field. It is increasingly important in the performance and reliability of electronic systems as an underling cause of functional failures in electrical and electronic components. This tutorial discusses the characteristics of the various electromigration mechanisms, with primary emphasis on electrolytically-controlled processes that occur under low power and relatively ambient conditions.

Electrical Properties of Nichia AlGaN/InGaN/GaN Blue LEDs in a Wide Current/Temperature Range

ABSTRACTStudies of electrical characteristics of nitride-based light emitting diodes (LEDs) are of interest as they can shed light on carrier transport across the p-n heterojunction. In addition, they provide a convenient way of investigating degradation processes associated with high electrical stress. We present electrical characteristics of Nichia NLPB500 blue LEDs based on AlGaN/InGaN/GaN material system in the temperature range of 9-340 K. Two components of current are identified. High-density current stress leads to diode degradation by shunt formation caused by metal electromigration. At 8 K, blue emission was observed at currents as small as 20 nA.

An ERD based study of the electromigration of hydrogen in V, Ta, Nb, and Ti

Elastic recoil detection (ERD) has been successfully applied to the measurement of hydrogen and deuterium electromigration in metals. Besides providing a sensitive and direct measure of hydrogen isotope concentrations in the direction of transport, advantages over other techniques include excellent spatial resolution and the ability to distinguish between surface and bulk effects. Using incident 4He ions to determine the lateral redistribution of hydrogen due to the presence of a large electric current, we have measured the effective charge Z ∗ of H in α-Nb, Ta, and Ti under various conditions. We also demonstrate the simultaneous determination of Z ∗ of H and D in α-V. Data analysis methods and sample preparation are discussed.

Passivation Design / Electromigration Performance Correlations in Layered Aluminum Metallizations

ABSTRACTThe study presented in this paper establishes correlations between key passivation morphological characteristics and metal electromigration performance. This was done by using test structures including extrusion monitors which provided narrow gaps along both sides of the test stripes. The parameters studied were: (1) the nature of the gap filling (oxide process and step coverage), (2) local oxide planarization, and (3) oxide thickness above the leads tested. Failure analysis was conducted by SEM cross-sections of cracked passivation areas. We observed that in the case of aluminum metallizations capped by a thin anti-reflective coating (ARC) layer, failure occurred in all cases by aluminum extrusion from the top corners of the leads, and at 45 degree angles into the passivation. Ultimately, the lifetime was dependent on oxide thickness above the test leads rather than gap-filling characteristics.