Modeling of electromigration in through-silicon-via based 3D

Abstract Electromigration (EM) is a critical problem for interconnect reliability of modern IC design, especially as the feature size becomes smaller. In 3D IC technology, the EM problem becomes more severe due to drastic dimension mismatches between metal wires, through-silicon-vias (TSVs), and landing pads. Meanwhile, the thermo-mechanical stress due to TSV can further interact with EM and shorten the lifetime of the structure. However, there is very little study on EM issues with respect to TSV for 3D ICs. In this paper, we perform detailed and systematic studies on: (1) EM lifetime modeling of TSV structure, (2) impact of TSV stress on EM lifetime of BEOL wires, and (3) EM-robust design guidelines for TSV-based 3D ICs. Our results show EMinduced lifetime of TSV structure and neighboring wire largely depend on the TSV-induced stress. Also, lifetime of a wire can vary significantly depending on the relative position with the nearby TSV. I. Introduction As semiconductor technologies are pushed forward for higher performance with smaller power and area, threedimensional integrated circuits (3D ICs) have attracted a lot of attention from both academia and industry. 3D ICs can be realized with stacked dies and through-silicon-vias (TSVs) to communicate vertically. 3D ICs can help increase the bandwidth by reducing the interconnect length, reduce the footprint of the system, and achieve heterogeneous integration of the system. However 3D ICs introduce many new challenges, in particular the reliability issues which have become more critical. The temperature characteristics of 3D ICs can be worse, additional stress can be generated due to the coefficient of thermal expansion (CTE) mismatch between TSV and silicon materials, and current density of the interconnects needs to be increased to feed more transistors in spite of high loading capacitance of TSVs. Electromigration (EM) has been one of the major reliability problems even in conventional 2D IC designs. EM refers to the mass transport in metal structures. It is affected by geometrical shapes, temperature distribution, mechanical stress, current density, and material properties However in 3D ICs, despite of importance of EM which can shorten the lifetime of the system, only a few papers have been published regarding this issue. Shayan et al. considered mean time to failure (MTTF) due to the EM based on Black's equation, for a power distribution network (PDN) for 3D IC

Numerical analysis of lead-free solder joints: effects of thermal cycling and electromigration

To meet the requirements of miniaturization and multifunction in microelectronics, understanding of their reliability and performance has become an important research subject in order to characterise electronics served under various loadings. Along with the demands of the increasing miniaturization of electronic devices, various properties and the relevant thermo-mechanical-electrical response of the lead-free solder joints to thermal cycling and electro-migration become the critical factors, which affect the service life of microelectronics in different applications. However, due to the size and structure of solder interconnects in microelectronics, traditional methods based on experiments are not applicable in the evaluation of their reliability under complex joint loadings. This thesis presents an investigation, which is based on finite-element method, into the performance of lead-free solder interconnects under thermal fatigue and electro-migration, specifically in the areas as follows: (1) the investigation of thermal-mechanical performance and fatigue-life prediction of flip-chip package under different sizes to achieve a further understanding of IMC layer and size effects of a flip chip package under thermal cycling; (2) the establishment of a numerical method, simulating void-formation/crack-propagation based on the results of finite-element analysis, to allow the prediction of crack evolution and failure time for electro-migration reliability of solder bumps; (3) the establishment of a flow-based algorithm for combination effects of thermal-mechanical and electro-migration that was subsequent implemented in to an FE model to evaluate the reliability assessment of service lives associated with a flip chip package

Modeling the SAC microstructure evolution under thermal, thermomechanical and electrical constraints

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