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.

This paper presented a comprehensive experimental and simulation study for thermomigration (TM) accompanying electromigration (EM) at elevated current densities. Both Blech and standard wafer-level electromigration acceleration test (SWEAT)-like test structures, with aluminum (Al) as a carrier, were used for testing and analysis. In Part I of our study (Cui et al., 2023a), the experimental and numerical results with the current density of 1 MA/cm² were presented. We observed that Al stripes with a SWEAT structure did not show damage in the entire length, while Blech structures showed void and hillock formations only at the cathode and anode, respectively. The temperature gradient owing to Joule heating was neglected in our previous simulations, and the predicted results agreed well with the experimental observations. However, we have not theoretically verified the effect of the temperature gradient. In this paper, we first reported the new experimental data under the elevated current densities of 3 and 5 MA/cm². In both Blech and SWEAT structures, the spreading of voids in the middle region of conductors was observed. Moreover, in Blech structures, voiding in the middle region occurred after a period of time when voids/hillocks were formed at the cathode and anode, while the SWEAT structures did not show damage at the two ends. Next, based on the coupled 3D theory (Cui et al., 2023a), new analytical one-dimensional (1D) solutions were derived for the Blech and SWEAT structures in the un-passivated configuration considering TM. We found that TM played a significant role in the EM development in the middle of conductors under the elevated current density. The numerical results were in excellent agreement with the experimental data with the consideration of TM. We further established new EM failure's threshold criteria for the SWEAT structures in the form of the product of current density and square of conductor length. This is a major departure from the original Blech's theory in which only mechanical stress gradient was considered. We also studied the acceleration factor of the current density exponent and presented an insight into failure mechanisms associated with TM.

In this paper, we apply the Eshelby's solution to study the effect of passivation layer on electromigration (EM) failure in a conductor. The passivation layer is considered as an elastic material, not a rigid layer anymore. Thus, the deformation and stress evolution in the conductor during EM are related to the mechanical property of the passivation layer. One-dimensional (1D) analytical solution for the passivated conductor is obtained. The numerical results show that the conductor covered with the stiffer passivation layer has much less EM damage. And the steady-state solution shows that the magnitude of (jL)c increases with increasing Young's modulus of passivation material. The present study provides a way to predict the EM performances taking into account various passivation materials.

The continuous downscaling of microelectronics has introduced many reliability issues on interconnect. Electromigration and dewetting are major reliability concerns in high-temperature micro- and nanoscale devices. In this paper, the local dewetting of copper thin film during the electromigration test was first found and investigated. When the high current was applied, the dewetted copper forming around the edge was observed at the cathode of the conductor. Furthermore, the effect of temperature and conductor size on local dewetting was investigated. Our proposed mechanism for local dewetting is in good agreement with experimental findings.

Understanding the atomic diffusion features in metallic material is significant to explain the diffusion-controlled physical processes. In this paper, using electromigration experiments and molecular dynamic (MD) simulations, we investigate the effects of grain size and temperature on the self-diffusion of polycrystalline aluminium (Al). The mass transport due to electromigration are accelerated by increasing temperature and decreasing grain size. Magnitudes of effective diffusivity (Deff) and grain boundary diffusivity (DGBs) are experimentally determined, in which theDeffchanges as a function of grain size and temperature, butDGBsis independent of the grain size, only affected by the temperature. Moreover, MD simulations of atomic diffusion in polycrystalline Al demonstrate those observations from experiments. Based on MD results, the Arrhenius equation ofDGBsand empirical formula of the thickness of grain boundaries at various temperatures are obtained. In total,DeffandDGBsobtained in the present study agree with literature results, and a comprehensive result of diffusivities related to the grain size is presented.

In a light-emitting diode (LED) package, silicone encapsulant serves as a chip protector and enables the light to transmit, since it exhibits the advantages of high light transmittance, high refractive index, and high thermal stability. However, its reliability is still challenged under harsh operation conditions. In this study, the optical and mechanical properties of silicone encapsulant, including appearance, light transmittance, Young’s modulus, and tensile strength, were experimentally monitored during the sulfur-rich ageing process. Meanwhile, the Fourier transform infrared (FTIR) spectroscopy and molecular dynamics (MD) simulation were used to reveal its degradation mechanism. The results show that 1) in the sulfur (S₈)-rich ageing process, the severe vulcanization reaction occurred in silicone encapsulant assisted only by high temperature and high moisture, with the existence of H₂S as the reaction product of S₈ and H₂O vapor. 2) Vulcanization characterized by the formation of the sulfhydryl (-SH) group lowered both optical and mechanical properties of silicone encapsulant. 3) The hydrolysis reaction featured by the formation of the hydroxyl (-OH) group decreased the mechanical performances of silicone encapsulant but brought slight harm to its optical performances.

In high power electronics packaging, sintered silver nanoparticle joints suffer from thermal-humidity- electrical-chemical joint driven corrosion in extreme environments. In this paper, we conducted aging tests on sintered silver nanoparticles under high-temperature, high-humidity, and high-sulphur conditions. The results show that: (1) the sample under the dry high-sulphur conditions at a high temperature exhibited the highest degree of sulphidation; (2) Reactive force field (ReaxFF) molecular dynamics (MD) simulations of sintered silver nanoparticle sulphidation revealed the sulphidation layer was formed by silver atoms upward migration. This work paves the way for further investigation on sintered silver nanoparticles corrosion considering multi-physics coupling effects.

This paper analyzes the mechanical properties of tungsten disulfide (WS2) by means of multiscale simulation, including density functional theory (DFT), molecular dynamic (MD) analysis, and finite element analysis (FEA). We first conducted MD analysis to calculate the mechanical properties (i.e., Young's modulus and critical stress) of WS2. The influence of different defect types (i.e., point defects and line defects) on the mechanical properties are discussed. The results reveal that WS2 has a high Young's modulus and high critical stress. Next, the effects of defect density and temperature on the mechanical properties of the material were analyzed. The results show that a lower defect density results in improved performance and a higher temperature results in better ductility, which indicate that WS2 can potentially be a strain sensor. Based on this result, FEA was employed to analyze the WS2 stress sensor and then fabricate and analyze the device for benchmarking. It is found that the FEA model proposed in this work can be used for further optimization of the device. According to the DFT results, a narrower band gap WS2 is found with the existence of defects and the applied strain. The proposed multiscale simulation method can effectively analyze the mechanical properties of WS2 and optimize the design. Moreover, this method can be extended to other 2D/nanomaterials, providing a reference for a rapid and effective systematic design from the nanoscale to macroscale.

The CaAlSiN₃:Eu²⁺ red phosphor and its silicone/phosphor composite are very promising materials used in the high color rendering white light-emitting diode (LED) packaging. However, the reliabilities of CaAlSiN₃:Eu²⁺ and its composite are still being challenged by phosphor hydrolysis at high humidity application condition. A fundamental understanding of the interface adhesion between silicone and CaAlSiN₃:Eu²⁺ is significant for the developments and applications of this material. In this work, the mechanical properties of silicone/pristine CaAlSiN₃:Eu²⁺ and silicone/hydrolyzed CaAlSiN₃:Eu²⁺ composites are experimentally measured and compared firstly, in which both the tensile strength and Young's modulus of composite are increased after the hydrolysis reaction. Then, the first principles Density Functional Theory (DFT) calculations are used to investigate the adhesion behaviors of the silicone molecular on both the pristine and the hydrolyzed CaAlSiN₃[0 1 0] at atomic level. The results show that: (1) The silicone molecular is weakly adsorbed on the pristine CaAlSiN₃[0 1 0] via Van der Waals (vdW) interactions, while silicone molecular is much stronger absorbed on the hydrolyzed CaAlSiN₃[0 1 0] due to the formation of hydrogen bonding at the interface; (2) The transient state calculations indicate that the sliding energy barrier of silicone on the hydrolyzed CaAlSiN₃[0 1 0] is higher than that on the pristine one, as the increased adsorption energy and surface roughness. Generally, the findings in this paper can guide the phosphor selection, storage and process in LED packaging, and also assist in improving the reliability design of LED package used in high moisture condition.

In this paper, a recently developed theory - general coupling model of electromigration, is implemented in ANSYS. We first identify several errors provided in ANSYS manual for electromigration modeling. Then the general coupling model is implemented in ANSYS and the detailed description is presented. Finally, a 1-D confined metal line with a perfectly blocking condition is presented as a benchmark problem, in which the finite element solutions are in excellent agreement with the analytical solutions.