Electromigration Test Research Articles

Electromigration in Cu–Cu joints: Measurement of activation energy and polarity effect

Electromigration (EM) has been a pivotal reliability challenge for interconnects, but there are only few studies on EM in Cu–Cu joints. In this work, accelerated EM tests for the Cu–Cu joints were conducted at three temperatures (150 °C, 179 °C, and 208 °C) and the temperature-dependent failures were discussed. The polarity effect of the grain growth behaviors at the bonding interfaces was observed at the opposite electron flows, which may be attributed to the difference in EM-build-up stress conditions and the divergence in atomic fluxes. Moreover, the activation energy (Ea) extrapolated from the three EM temperatures was derived as 0.9 eV. As compared to the solder joints with same dimensions, the Cu–Cu joints possess more than ten times of time-to-failures (TTFs) under the same EM condition.

The Effect of Bi Addition on the Electromigration Properties of Sn-3.0Ag-0.5Cu Lead-Free Solder

As electronic packaging technology advances towards miniaturization and integration, the issue of electromigration (EM) in lead-free solder joints has become a significant factor affecting solder joint reliability. In this study, a Sn-3.0Ag-0.5Cu (SAC305) alloy was used as the base, and different Bi content alloys, SAC305-xBi (x = 0, 0.5, 0.75, 1.0 wt.%), were prepared for tensile strength, hardness, and wetting tests. Copper wire was used to prepare EM test samples, which were subjected to EM tests at a current density of approximately 0.6 × 104 A/cm2 for varying durations. The interface microstructure of the SAC305-xBi alloys after the EM test was observed using an optical microscope. The results showed that the 0.5 wt.% Bi alloy exhibited the highest ultimate tensile strength and microhardness, improving by 33.3% and 11.8% compared to SAC305, respectively, with similar fracture strain. This alloy also displayed enhanced wettability. EM tests revealed the formation of Cu6Sn5 and Cu3Sn intermetallic compounds (IMCs) at both the cathode and anode interfaces of the solder alloy. The addition of Bi inhibited the diffusion rate of Sn in Cu6Sn5, resulting in similar total IMC thickness at the anode interface across different Bi contents under the same test conditions. However, the total IMC thickness at the cathode interface decreased and stabilized with increasing EM time, with the SAC305-0.75Bi alloy demonstrating the best resistance to EM.

The impact of titanium alloying on altering nanomechanical properties and grain structures of sputter-deposited cobalt for electromigration reliability enhancement

Cobalt (Co) has recently become a highlighted on-chip interconnection material for advanced metallization scheme of microelectronic circuits. Here, electromigration behaviors of sputter-deposited Co and Co(Ti; 0.9 at%) interconnection lines embedded in Si are comparatively studied. These lines were annealed (500 °C/30 min) prior to further accelerated electromigration testing under high current densities in the range of 3 × 107–9 × 108 A cm−2. A collection of the obtained electromigration failure lifetimes, current scaling factors and activation energies confirms a noticeable enhancement in the electromigration reliability of the Co lines by the added Ti. Results by scanning transmission electron microscopy (STEM) and nanoscratch testing reveal that 3–5 nm-sized Ti crystallites are uniformly dispersed in the Co-interconnect matrix, effectively inhibiting Co grain growth, promoting the formation of nanotwinned Co and elevating film’s mechanical properties for ensuring the electromigration reliability. With deteriorated hardness and adhesion energy, reduced planar defects and many big grains all spanning transversely the entire interconnect line, Co is vulnerable to electromigration failures, also giving accelerated thermally-induced interfacial diffusion and chemical reactions with the surrounding Si, as proven by depth-profiling secondary spectrometry and STEM analysis.

Electromigration of Power Devices Part 2: Power Device in Applications in Controlled Environment

In the power semiconductor industry, there is a continuous development toward a higher current capability of devices while device’s dimensions shrink. Although higher current is preferred, the reliability risk of the electromigration (EM) remains challenging. In the present study, a special EM test vehicle is used to investigate the pure EM behavior of power device, following our previous work. The selection of the test condition is discussed in detail, which is defined based on the temperature and current profiles of the device in the actual application, focusing on the applications of the power devices in a controlled environment, i.e., data centers or telecommunication servers. The current and temperature profiles of the device are discussed based on the device’s maximum power dissipation and its respective thermal design. The results show that the different combinations of currents and temperatures can lead to different ratios of acceleration factor between the temperature and the current. Consequently, an inappropriate selection of the testing condition can result in the over-domination of temperature over the current, leading to wrong conclusions. The effects of the PCB surface finish (both Ni and Sn plating) as well as different electron flow directions on the EM were studied. It is concluded that the maximum current that can be applied to a power device in the application within a controlled environment is rather limited by the cooling capability of the system than the EM induced device failure.

Research on Crystal Structure Evolution and Failure Mechanism during TSV-Metal Line Electromigration Process

The combined use of Through Silicon Via (TSV) and metal lines, referred to as TSV-metal lines, is an essential structure in three-dimensional integrated circuits. In-depth research into the electromigration failure mechanism of TSV and the microstructure evolution can serve as theoretical guidance for optimizing three-dimensional stacking. This article conducted electromigration experiments on TSV-metal line structural samples at current densities of 1.0 × 105 A/cm2, 5 × 105 A/cm2, and 1 × 106 A/cm2. Additionally, Electron Back Scattered Diffraction (EBSD) technology was employed to systematically investigate the microstructural evolution of the TSV-metal line structure profiles before and after the application of electrical testing. The results indicate that the current induces a change in the crystal orientation at the TSV-metal interface (TSV/metal interface) and the bottom metal line. This phenomenon notably depends on the initial angle between the grain orientation and the current flow direction. When the angle between the current direction and the grain orientations [001] and [010] is relatively large, the crystals are more likely to deviate in the direction where the angle between the grain orientation and the current is smaller. This is because, at this point, the current direction is precisely perpendicular to the <100> crystal plane family, where the atomic density is lowest, and the energy required for electron transport is minimal. Therefore, the current readily rotates in the direction of this crystal orientation. Before the electromigration tests, areas with a high level of misorientation were primarily concentrated at the TSV/metal interface and the corners of the TSV-metal line. However, these areas were found to be more prone to developing voids after the tests. It is conjectured that the high misorientation level leads to elevated stress gradients, which are the primary cause of cracking failures in the TSV-metal line. As the current density increases from 5 × 105 A/cm2 to 1 × 106 A/cm2, the electromigration failure phenomena in the TSV become even more severe.

Understanding electromigration failure behaviors of narrow cobalt lines and the mechanism of reliability enhancement for extremely dilute alloying of manganese oxide

Self-forming barriers for copper (Cu) interconnect metallization are well developed. However, the self-forming-barrier process and associated electromigration behaviors of narrow lines of cobalt (Co), a new interconnect wiring material for sub-10-nm semiconductor device nodes, are yet to be explored. In this study, we present an all-wet electroless trench-filling process to fabricate narrow (100 nm) lines of Co and MnO-added Co [Co(MnO)], then thermally annealed to some extent (400 °C/30 min) prior to electromigration testing. Empirical data obtained from accelerated electromigration testing, including failure lifetimes, current-density scaling factors, activation energies and physical failure profiles, consistently show that electromigration reliability of the Co lines is markedly enhanced by 0.1% added MnO. Transmission electron microscopy and focused ion beam imaging, along with dynamic adhesion strength data, reveal that the enhancement is related to annealing-induced segregation and dispersion of MnO particles at the interface with SiO2, ensuring adhesion of Co on SiO2, preventing interfacial interdiffusion and stuffing electromigration pathways. The adhesion strength, microstructures and Joule-heating data of Co and Co(MnO) are provided for the discussion of the differences in their electromigration performance and failure mechanism. Comments on electroless-plated Co as a new interconnect material are also given.

Anisotropic Grain Growth of Al-Si Wire Under Electromigration Tests in Power Devices

Anisotropic Grain Growth of Al-Si Wire Under Electromigration Tests in Power Devices

The electromigration study of thin-film structured Sn3.5Ag and Ag using continuous observation and reliability enhancement approach

Thin-film materials have been widely used in advanced technologies because of their flexible structure and superior working performance. However, the reliability of thin films that are employed in electronic devices has become an increasing concern. In this study, thin-film-structured Ag and Sn3.5Ag samples were prepared to observe their reliability behaviors during electromigration (EM) tests at low and high current densities. Under a low current density (8.89 × 104 A/cm2), the Ag stripe shows good resistance to EM, and microstructural changes are only observed in the Sn3.5Ag sample. In the high current density test (8.89 × 105 A/cm2), the microstructures of both samples undergo a significant change; however, the Ag sample shows superior performance than the Sn3.5Ag sample in terms of total experimental duration. Ag exhibits a better EM resistivity than Sn3.5Ag owing to the difference in EM activation energy causing the difference in atomic diffusivity. Moreover, it shows that pre-heating is an efficient method to enhance the EM resistivity of thin-film metals. The findings of this study provide a criterion for manufacturers to select suitable thin-film metals as far as EM is concerned and how to minimize the impact due to EM.

A Measurement Amplification Method for TSV Weak Resistance

In the TSV electromigration test process, this paper has carried out relevant research on how to accurately measure TSV resistance and make it conducive to the observation of standard instruments, aiming at the problem that the resistance value of TSV reaches the magnitude of a microburst. Observing the resistance value change in the electromigration process is challenging. This paper analyzes and designs a measurement circuit for TSV. This circuit uses the cascade of an integrated amplifier. It combines with the four-probe method to amplify the TSV resistance change signal based on accurate measurement of TSV resistance, which is more conducive to the measurement of standard instruments and makes it easier to observe the change of resistance when TSV electromigration occurs.

Coupling model of electromigration and experimental verification – Part I: Effect of atomic concentration gradient

This paper presented integrated electromigration (EM) studies through experiment, theory, and simulation. First, extensive EM tests were performed using Blech and standard wafer-level electromigration acceleration test (SWEAT)-like structures, which were fabricated on four-inch wafers. Second, a molecular dynamics (MD) simulation-based diffusion-induced strain was incorporated into the existing coupled theory. Third, one-dimensional (1D) governing equations in terms of atomic concentration for un-passivated and passivated configurations were derived for void formation and growth, using a modified Eshelby's solution to consider the effect of passivation. Fourth, a systematic approach was established, including theoretical formulations and experimental methods, to obtain key material properties, i.e., critical atomic concentration and diffusivity. We then determined the material's properties from a specific set of experimental data, using aluminium (Al) as a carrier for demonstration. These properties were then used to predict the time to failure and void growth under various conditions. The theoretical results agreed well with the experimental data. Moreover, we theoretically determined the critical threshold products of current density and conductor length for the un-passivated and passivated configurations, respectively. Both experiment and theory showed that, in the absence of mechanical stress in un-passivated configurations, the atomic self-diffusion, which was opposite to electron wind, was significant in resisting EM development. However, when mechanical stress was present, such as in passivated configurations, stress migration played a dominant role in resisting EM development. Our numerical results showed that the current density exponent n in Black's law remained as 2 in the range of the current density greater than 0.2 MA/cm2 and rapidly approached infinity at a low level of current density.

Electromigration failure in inkjet-printed Ag conductive lines

Electromigration (EM) is crucial to the reliability of most conductive lines used in electronics. In the present study, the EM characteristics of inkjet-printed Ag conductive lines were analyzed under various EM acceleration conditions to comprehend the EM failure behaviors associated with inkjet-printed Ag lines with nanoparticle inks. The evolution of the porosity level in the microstructure of the inkjet-printed Ag lines during the EM test was investigated to locate the EM failure positions in the line and identify the main driving force for EM mass transport. Two theoretical models (resistometric and Black’s) were employed to analyze the activation energy and expected lifetime of inkjet-printed Ag lines. This study indicates that the EM of Ag cations is directed toward the cathode by the direct force resulting from the electric field–ion interaction, resulting in EM failure near the anode and hillock formation near the cathode of the inkjet-printed Ag lines. The activation energy computed from the theoretical models suggests that the surface diffusion of Ag through the inkjet-printed line plays an important part in the EM failure mechanism. This research was a pioneering attempt to experimentally investigate the EM performance of inkjet-printed Ag lines.

Interfacial intermetallic compound modification to extend the electromigration lifetime of copper pillar joints

Electromigration is the massive metal atom transport due to electron flow, which could induce a disconnect in electronics. Due to the size of copper pillar bump reduction, the portion of interfacial intermetallic compound in solder joints is increasing obviously. However, there is lack of systematical research on the effects of intermetallic compound on the EM lifetime of solder joints. In this paper, the interfacial intermetallic compound of copper pillar joints is modified to extend the electromigration lifetime. The growth rate of intermetallic compound in solder joints sample is calculated firstly. From 230°C to 250°C, the growth rate of intermetallic compound increases from 0.09 μm/min to 0.19 μm/min. With a longer reaction time, the intermetallic compound layers continuously grow. Then electromigration tests were conducted under thermo-electric coupling loading of 100°C and 1.0 × 104 A/cm2. Compared with lifetime of thin and thick intermetallic compound samples, the lifetime of all intermetallic compound sample improved significantly. The lifetime of thin, thick, and all intermetallic compound samples is 400 min, 300 min, and 1,200 min, respectively. The failure mechanism for the thin intermetallic compound sample is massive voids generation and aggregation at the interface between solder joints and pads. For the thick intermetallic compound sample, the intermetallic compound distance is short between cathode and anode in solder joints, leading to lots of crack create in the middle of solder joints. As the all intermetallic compound sample can greatly reduce the number of voids generated by crystal structure transforming, the lifetime extend obviously.

Non-destructive micro analysis of electromigration failures in solder microbumps using 3D X-ray computed tomography

Three-dimensional (3D) X-ray was employed to characterize the electromigration (EM) induced failures (voids, cracks, and necking) in 30 μm Cu/Sn/Ni/Cu solder joints. The 3D X-ray is capable of mapping the positions and evolution of voids and morphology change in the solder joints caused by EM. Such an approach offers an alternatively non-destructive assessment for the reliability of large-area solder arrays. The EM-induced failures of hundreds of solder joints could be captured and characterized. The results show that large voids mostly formed near the entrance of electron flow. Two-step change of solder electrical resistance was found: a gradual increase (10.6% after 5.1 h) at the beginning EM stage due to slow nucleation of newly individual voids and a sharp increase (10.6% to 22.2% within 0.8 h) caused by the significant growth and coalescence of multiple voids and necking. We found that the total number of solder joints with obvious voids in plan-view CT images was larger than that in side-view micrographs indicating their better practical implementation. Additionally, we found that the total contact area of the solder joints gradually decreased due to solder necking after EM tests. It further expanded and merged with neighboring voids to generate cracks near solder edges. • 3D X-ray was used to map the positions of EM-induced voids and necking. • SEM was also employed to verify such EM-induced failures mapped by 3D X-ray. • EM-induced failures of hundreds of solder joints could be captured and characterized. • Voids formed at electron entrance, and the contact area gradually reduced due to solder necking. • It further expanded and merged with neighboring voids to generate cracks near solder edges.

Fast prediction of electromigration lifetime with modified mean-time-to-failure equation

• Based on Onsager’s entropy production equation, the mean-time-to-failure equation for electromigration is derived. • Only need one set of data to predict the electromigration lifetime with this equation. • The cost and time can be saved for electromigration tests. Black’s mean-time-to-failure (MTTF) equation has been applied to predict electromigration lifetime in electronics for decades. It is an empirical equation, and at least three sets of data tested under two temperatures and two current densities are needed to determine the parameter n, activation energy E , and pre-factor A in the equation. Based on Onsager’s entropy production theory, we derived a modified MTTF equation, in which n = 2 becomes definite. The activation energy E is intrinsic for materials; for SnAg solder joints, we can take it as 1 eV. Therefore, we only need one set of data (one temperature and one current density) to determine the perfector A , for predicting the electromigration lifetime of the test samples. Our modified MTTF equation provides a fast and cost-saving method for accurate prediction of the electromigration lifetime for electronic products.

Experimental and Numerical Investigation of Electromigration Behavior of Printed Silver Wire Under High Current Density

Abstract The electromigration (EM) damage is becoming a severe problem in the printed flexible electronics as the printed circuits are fabricated thinner and thinner due to the development of printing technology. In this work, the EM behavior of printed silver wires was investigated by EM experiments and numerical simulations. The EM tests showed that voids are generated in the cathode area and hillocks are formed in the anode area for a wire with a small length. However, with the increase of wire length, hillocks tend to occur on the two sides of the silver wire middle part. The results of numerical simulations based on the atomic flux divergence (AFD) method revealed that the formation of the hillocks on the printed wire is caused by not only the mechanism of electron wind but also the strong temperature gradient along the wire length and width direction. Also, it can be concluded that the temperature gradient induced by Joule heating plays a more important role than electron wind in the atomic migration of the printed silver wire subjected to a high current density. The influence of the printed silver wire size on the EM behavior was also analyzed by numerical simulation, and the results demonstrated that the printed silver wires with a larger length and a smaller width-to-thickness ratio are more likely to develop hillocks on the two sides of silver wire middle part while subjected to a high current density.

Experimental research on performance degradation of TSV microstructure under thermal cycling, vibration and electrical stress

Through‑silicon-via (TSV) microstructure is the key structure of 3D integrated packaging, and its reliability during service plays a very important role in the long-term reliable operation of the chip. However, the failure mechanism and reliability evaluation of the TSV structure in the service process of the chip have not been fully elucidated. Chips inevitably bear various stresses during the service process, such as thermal stress, vibration stress, electrical stress, etc. In this paper, a TSV reliability test chip that can be easily loaded with various stresses was designed first, and the resistivity of the TSV microstructure was tested. It is found that the resistivity of TSV has a significant scale effect. Then, thermal cycling, vibration and electromigration tests were carried out, and the failure mode, performance degradation trend and failure distribution of TSV microstructure under thermal cycling, vibration and electrical stress were analyzed. Finally, the failure analysis of the tested chip was carried out by scanning electron microscope (SEM) and high-resolution industrial micro-CT, and the potential failure mechanism were analyzed and discussed.

A combined modelling approach to design test structures to study thermomigration in Cu interconnects

With the downscaling of microelectronic devices, thermal gradients become increasingly important, making thermomigration (TM) an important mass transport mechanism. We use a combination of thermal simulations using finite element (FE) methods and a 1D physics-based TM model to characterise and design test structures to study thermomigration in Cu interconnects. As the test structure, in order to locally heat a section of the Cu interconnect, we propose to add a W-heater below a classical electromigration (EM) test structure. Using experimentally calibrated FE thermal models, we study the temperature distribution and temperature gradients along the Cu interconnects for various configurations of the test structure. Subsequently, the 1D TM model is used to identify locations where the tensile stress would reach a critical stress, σcrit, which can lead to void nucleation induced by thermal gradients. By comparing different heater positions, we show that a higher thermal gradient is expected when the heater is positioned further away from the local heat sinks. Based on the outcome of the simulations, we propose a modified test structure where metal levels are inverted such that the Cu metal line is closer to the heater. Such structure shows a 4× increase in temperature gradient compared to the original structure, facilitating TM characterisation studies.

Enhancement of Electromigration Reliability of Electroless-Plated Nanoscaled Copper Interconnects by Complete Encapsulation of a 1 nm-Thin Self-Assembled Monolayer

The downsizing of integrated circuits for the upcoming technology nodes has brought attention to sub-2 nm thin organic/inorganic materials as an alternative to metallic barrier/capping layers for nanoscaled Cu interconnects. While self-assembled monolayers (SAMs) serving as the barrier materials for copper metalized films are well studied, electromigration (EM) of Cu interconnects encapsulated by SAMs is an untouched research topic. In this study, we report an all-wet encapsulating process involving SAM seeding/encapsulating and electroless narrow-gap filling to fabricate nanoscaled copper interconnects that are completely encapsulated by a 1 nm-thin amino-based SAM, subsequently annealed to some extents prior to EM testing. Both annealing and SAM encapsulation retard EM of the Cu interconnects tested at current densities on orders of 108–109 A cm−2. Particularly, SAM encapsulation quintuples the lifetime of, for example, as-fabricated Cu interconnects from 470 to 2,890 s. Electromigration failure mechanisms are elucidated from analyses of activation energies and current-density scale factors obtained from the accelerated EM testing. The importance of SAM qualities (e.g., ordering and layered structure) as a prerequisite for the reliability enhancement cannot be overestimated, and the results of the SAM quality evaluation are presented. The mechanism of reliability enhancement is also thoroughly discussed.

Study on Lifetimes of Plasma Etched Ru Lines

Copper (Cu) is a widely used interconnect material in ULSICs, large area TFT LCDs, and other electronics. However, as the dimensions shrinks, electronic scattering at grain boundaries and surfaces causes the large increase of line resistance and the RC delay [1]. Also, the barrier layer occupies a large fraction of the interconnect line, which is an issue in conductance and reliability [2]. An alternative interconnect material for Cu is necessary. Ruthenium (Ru) is a possible material for this purpose because of its low resistivity, high resistant to oxidation, good heat dissipation, low diffusion and good adhesion to dielectrics [3–6]. Furthermore, it was reported that Ru has a low resistivity scaling [7], which suggested that it can be more conductive than Cu lines in advanced technology nodes. In this study, the reliability of the plasma etched Ru line is studied using the electromigration (EM) stress method [8].The Ru film was sputter deposited on top of the SiO2 coated layer Si <100> wafer and covered with a sputter deposited SiO2 layer as a hard mask layer. After the sample was lithographically defined into a 4-point test pattern, the SiO2 hard mask layer was etched at CF4 10 sccm, 60 mTorr, and 600 W. Then, the Ru layer was etched under the condition of O2 40 sccm, 50 mTorr, and 600W. All etches were carried out in a parallel-plate plasma reactor (PlasmaTherm 700) under the RIE mode at room temperature. The remaining SiO2 hard mask on top of the Ru film was removed by dipping in a dilute HF solution. The electromigration (EM) test was done at room temperature on a probe station (Signatone S-1160). The EM stress was conducted under the constant current density (J) condition. Separately, in order to facilitate the breakdown of the Ru line, the sample was stresses at the constant voltage (V) with a power supply (Agilent E3645A).Figure 1(a) and (b) show the top views of an electric stressed Ru line under the (a) bright and (b) dark fields of an optical microscope. The surface of the line is smooth and has a small edge roughness. In the bright field mode, few voids, which are voids generated in the line, are barely visible. However, in the dark field, the light is diverged into a cone. Light is scattered through the voids, which shows as bright dots [9]. Figure 1(c) shows a broken line that was generated under a large constant voltage. The color change near the center of the line is the broken spot, which indicates the high local temperature in the process.Figure 2 shows the resistance-time (R-t) curves of a plasma-etched TiW/Cu line stressed at J = 6.00 105 A/cm2 and a Ru line stressed at J = 1.25 106 A/cm2. The Cu line was broken before 10,000 sec. However, the Ru line was not broken after 12,000 sec and the resistance remained the same through the stress period. Therefore, the Ru line is much resistant to the EM stress than the Cu line even under a larger current density condition. Although voids were observed in the stressed Ru line, they did not cause the line broken, i.e., through a series of voids growth, merge, and connection steps [10,11]. Although no barrier layer was used for the Ru line, no line peel off was observed before and after the stress. This can be another advantage over the Cu line.More detailed discussion on the plasma etching of the Ru line and the EM phenomenon will be presented.1. A. F. Mayadas, et al., Appl. Phys. Lett., 14, 345 (1969).2. C.-K. Hu, et al., Microelectron. Eng., 70, 406 (2003).3. L. G. Wen, et al., 2016 IITC/AMC, 34 (2016).4. S. Dutta, et al., 2017 IITC, 1 (2017).5. O. V. Pedreira, et al.,, 2017 IRPS, 6B-2 (2017).6. T. Zhan, et al., ACS Appl. Mater. Interfaces, 12, 22347 (2020).7. E. Milosevic, et al., J. Appl. Phys., 124, 165105 (2018).8. G. Liu and Y. Kuo, J. Electrochem. Soc., 156, H579 (2009).9. J. Q. Su and Y. Kuo, MRS Advances, 5, 2827 (2020).10. J. R. Black, IEEE T. Electron Dev., 16, 338 (1969).11. S. C. Hau-Riege, Microelectron. Reliab., 44, 195 (2004). Figure 1

Enhancement of electromigration lifetime of copper lines by eliminating nanoscale grains in highly -oriented nanotwinned structures

In this study, we designed and electroplated various regular and nanotwinned copper (nt-Cu) lines. These Cu lines were then covered with a polyimide (PI) layer and heat-treated to some extents prior to electromigration (EM) testing. The results show that the EM lifetime of the nt-Cu lines is approximately 4.7 times longer than that of the regular ones. We found that the EM lifetime has been enhanced by 273% using a heat treatment. The improvement is attributed to the heat-treatment-led elimination of the nt–Cu transition layer (nanoscale grain region). The diffusion paths of Cu atoms at the nt-Cu line bottom were shortened as the number of continuous grain boundaries was decreased under the heat-treatment. Thus, the oxidation and void formation were further suppressed. Additionally, we discovered that the columnar microstructure of the nt-Cu lines remained unchanged under a high annealing temperature. These nt-Cu lines with high thermal stability and EM resistance can be widely used for advanced fine-pitch packaging due to its controlled microstructures.