Analysis of Electromechanically-Induced Failure of Metallic Thin Films Mediated by Void Dynamics

[201319] maroudas现代集成电路中的器件互连由金属线组成，其横截面以亚微米长度尺度为特征。这类金属线的机电致失效是微电子学中主要的材料可靠性问题。失效通常是由存在于这些金属线中的微孔的动力学引起的。电迁移、曲率驱动的表面扩散和应力诱导的表面扩散以及应变金属薄膜中的塑性流动驱动了空洞的迁移、生长和形态变化。对这种微观结构尺度动力学现象的基本理解和用于其定量分析的计算工具的开发对于使工程策略能够提高互连可靠性是必要的。为此，提出的研究系统地解决了互连线所受机电条件范围内延展性金属薄膜中复杂的非线性空洞动力学问题。将探讨涉及单空洞和多空洞动力学的若干相互关联的问题，包括：(i)电迁移和机械应力对单个孔洞迁移和形态稳定性的综合影响，（ii）电流诱导波在单个孔洞表面的传播，（iii）可能导致孔洞破裂和聚并现象的孔洞-孔洞相互作用，（iv）围绕演化孔洞的塑性变形机制，以及(v)塑性流动在互连破坏中的作用。提出的研究计划强调在电场和应力场作用下，由于表面质量传递和塑性流动而导致的空洞表面演化的自一致的介观公式，以及系统的参数研究，以确定可能触发破坏模式的不稳定性的开始。自洽模型的计算实现将基于新的边界积分方法、标准有限元方法和最近开发的跟踪移动界面的方法。这种介观模型的预测能力将通过根据多体原子间势对表面和界面性质进行原子计算而得到增强。此外，将进行数百万原子分子动力学（MD）模拟，以探索在应变韧性金属体系中控制空洞附近塑性变形的纳米尺度机制。MD结果的分析将提供解决细观尺度问题所需的塑性变形的本构关系

0201319MaroudasDevice interconnections in modern integrated circuits consist of metallic lines with cross-sections characterized by sub-micron length scales. Electromechanically-induced failure of such metallic lines is a major materials reliability problem in microelectronics. Failure is commonly mediated by the dynamics of microvoids that exist in these metallic lines. Void migration, growth, and morphological change are driven by electromigration, curvature-driven surface diffusion, and stress-induced surface diffusion, coupled with plastic flow in the strained metallic film. Fundamental understanding of such microstructural-scale dynamical phenomena and development of computational tools for their quantitative analysis are necessary for enabling engineering strategies to improve interconnect reliability. Toward this end, the proposed research addresses systematically the complex, nonlinear void dynamics in ductile metallic thin films over the range of electromechanical conditions that interconnect lines are subjected to. A number of interrelated problems will be pursued that involve single- and multiple-void dynamics, including: (i) combined effects of electromigration and mechanical stress on the migration and morphological stability of single voids, (ii) current-induced wave propagation on single void surfaces, (iii) void-void interactions that may lead to void breakup and coalescence phenomena, (iv) plastic deformation mechanisms around evolving voids, and (v) the role of plastic flow in interconnect failure. The proposed research plan emphasizes a self-consistent mesoscopic formulation of void surface evolution due to surface mass transport and plastic flow under the action of electric and stress fields, as well as systematic parametric studies to determine the onset of instabilities that may trigger failure modes. Computational implementation of the self-consistent model will be based on novel boundary-integral methods, standard finite-element methods, and recently developed methods for tracking moving interfaces. The predictive capabilities of this mesoscopic modeling will be enhanced by atomistic calculations of surface and interface properties according to many-body interatomic potentials. In addition, multi-million-atom molecular-dynamics (MD) simulations will be carried out to probe the nano-scale mechanisms that govern plastic deformation in the vicinity of voids in strained ductile metallic systems. Analysis of the MD results will provide the constitutive relations for plastic deformation required for the closure of the meso-scale problem.***