Electromigration-induced damage in bamboo Al interconnects

Depletion and hillock formation were examined in-situ in a scanning electron microscope (SEM) during electromigration of bamboo Al interconnect segments. Hillocks formed directly at the anode ends of the segments by epitaxial addition of Al at the bottom Al/TiN interface. Depletion occurred nonuniformly from the cathode end and stopped once the distance between the leading void and the hillock reached the critical length for electromigration at the given current density. A modified equation for the drift velocity is proposed, which includes the effect of nonuniform depletion and predicts that interconnects with nonuniform depletion are more reliable than those with uniform depletion.     

Chiral separations by capillary electromigration techniques in nonaqueous media. I. Enantioselective nonaqueous capillary electrophoresis

Enantiomer separations by CE employing nonaqueous conditions are reviewed. The general focus of this article is directed towards solvent effects on chiral recognition and the separation mechanism. After a general discussion of solvent effects on the individual processes involved in CE enantiomer separation, specifics for various selector classes are discussed together with a few applications of enantioselective nonaqueous CE.     

静止化学反应界面：理论和验证

在静止中和反应界面的基础上，提出了静止化学反应界面的概念，导出了一些静止化学反应界面方程。这些方程显示：为了建立稳定的静止化学反应界面，正、负反应离子（比如氢离子和氢氧根离子）的迁移数必须相等。分析表明，方程的理论预测与下列事实定量吻合：（１）已建立的静止中和反应界面的实验，（２）基于Ｋｏｈｌｒａｕｓｃｈ′ｓ调整函数的计算机模拟。     

Electromigration reliability of open TSV structures

Through silicon vias are the components in three-dimensional integrated circuits, which are responsible for the vertical connection inside the dies. In this work we present studies about the reliability of open through silicon vias against electromigration. A two-step approach is followed. In the first step the stress development of a void free structure is analysed by means of simulation to find the locations, where voids due to stress are most probably nucleated. In the second step, voids are placed in the through silicon vias and their evolution is traced including the increase of resistance. The resistance raises more than linearly in time and shows an abrupt open circuit failure. These results are in good agreement with results of time accelerated electromigration tests.     

Migration of indium ions in amorphous indium-gallium-zinc-oxide thin film transistors

Electromigration of In in amorphous indium-gallium-zinc-oxide thin film transistors under repeated switching operation was investigated by analyzing the distribution of component elements. During the repeated switching operations up to 300 times, threshold voltage of this device increased gradually implying alteration to the internal device structures. Energy dispersive X-ray spectroscopy revealed noticeable redistribution of metallic components, especially In, in the channel layer beneath the source electrode during switching operations by the migration of metallic ions away from the source electrode, which is attributed to electromigrations similar to those observed in organic light emitting diodes having indium tin oxide electrodes.     

Power grid redundant path contribution in system on chip (SoC) robustness against electromigration

The miniaturisation of integrated circuits leads to reliability issues such as electromigration (EMG). This well-known phenomenon is checked at design level by CAD tools. The conventional EMG check methods are based on electrical parameters. However, the wire physical degradation depends also on the interconnection network structure. In order to improve the EMG check methodologies, we propose an accurate method based on failure mechanism and chip power grid configuration. Indeed, the power grid offers redundant paths in case of void in main power supply path. The principle of our method is to take into account the contribution of these redundant paths in power grid lifetime assessment. These effects are validated by silicon ageing tests on structures designed in 28 nm Full Depleted Silicon on Insulator (FDSOI). These accelerated tests results have confirmed the lifetime gain due to the redundancy. These results provide perspectives for the relaxation of wire current limits and improve the chip design toward EMG.     

Failure analysis on reflector blackening between lead frame electrodes in LEDs under WHTOL test

Blackening induced lumen decay in a QFN LED after WHTOL reliability test was reported and analyzed in this paper. A new LED blackening failure mechanism was proposed based on solid experimental results. We concluded that the failure process underwent delamination between lead frame and reflector polymer composites followed by chemical penetration, composite corrosion, silver migration, and finally caused blackening failure. Delamination and corrosive de-flash agent were the key factors for the failure mode. Besides, we also estimated the influence of the failure to the optical performance through simulation. Apart from other reported factors, this study highlighted that both composite corrosion and Ag migration could generate serious illumination decrease as well. The outcome of this study is valuable for LED manufacture and quality control in the future.     

Mathematical model of electromigration allowing the deviation from electroneutrality

The structure of the double layer on the boundary between solid and liquid phases is described by various models, of which the Stern–Gouy–Chapman model is still commonly accepted. Generally, the solid phase is charged, which also causes the distribution of the electric charge in the adjacent diffuse layer in the liquid phase. We propose a new mathematical model of electromigration considering the high deviation from electroneutrality in the diffuse layer of the double layer when the liquid phase is composed of solution of weak multivalent electrolytes of any valence and of any complexity. The mathematical model joins together the Poisson equation, the continuity equation for electric charge, the mass continuity equations, and the modified G-function. The model is able to calculate the volume charge density, electric potential, and concentration profiles of all ionic forms of all electrolytes in the diffuse part of the double layer, which consequently enables to calculate conductivity, pH, and deviation from electroneutrality. The model can easily be implemented into the numerical simulation software such as Comsol. Its outcome is demonstrated by the numerical simulation of the double layer composed of a charged silica surface and an adjacent liquid solution composed of weak multivalent electrolytes. The validity of the model is not limited only to the diffuse part of the double layer but is valid for electromigration of electrolytes in general.     

Temperature and current-density distributions in flip-chip solder joints with Cu traces

Three-dimensional simulation was performed to investigate the temperature and current density distribution in flip-chip solder joints with Cu traces during current stressing. It was found that the Cu traces can reduce the Joule heating effect significantly at high stressing currents. When the solder joints were stressed by 0.6 A, the average temperature increases in solder bumps with the Al traces was 26.7°C, and it was deceased to 18.7°C for the solder joint with the Cu traces. Hot spots exist in the solder near the entrance points of the Al or Cu traces. The temperature increases in the hot spot were 29.3°C and 20.6°C, for solder joints with the Al traces and Cu traces, respectively. As for current density distribution, the maximum current density inside the solder decreased slightly from 1.66×10⁵ A/cm² to 1.46×10⁵ A/cm² when the Al traces were replaced by the Cu traces. The solder joints with the Cu traces exhibited lower Joule heating and current crowding effects than those with the Al traces, which was mainly attributed to the lower electrical conductivity of the Cu traces. Therefore, the solder joints with the Cu traces are expected to have better electromigration resistance.