Phase Stability, Phase Transformations, and Reactive Phase Formation in Electronic Materials XVI: Electromigration
Sponsored by: TMS Functional Materials Division, TMS: Alloy Phases Committee
Program Organizers: Shih-kang Lin, National Cheng Kung University; Chao-hong Wang, National Chung Cheng University; Jae-Ho Lee, Hongik University; Ikuo Ohnuma, National Institute for Materials Science (NIMS); Chih-Ming Chen, National Chung Hsing University; Thomas Reichmann, Karlsruhe Institute of Technology; Yu Zhong, Florida International University; Shijo Nagao, Osaka University; Shien Ping Tony Feng, The University of Hong Kong; Yee-wen Yen, National Taiwan Univ of Science & Tech

Tuesday 8:30 AM
February 28, 2017
Room: 25A
Location: San Diego Convention Ctr

Session Chair: Shih-kang Lin, National Cheng Kung University; Ming-Tzer Lin, National Chung Hsing University; Chao-hong Wang, National Chung Cheng University

8:30 AM  Invited
Electromigration Enhanced Intermetallic Growth and Damage Formation in Pb-free Solder Joints: Paul Ho1; Brook Huang-Lin Chao1; Seung-Hyun Chae1; Xuefeng Zhang1; 1The University of Texas at Austin
    EM enhanced intermetallic compound (IMC) growth and void formation for Sn-based Pb-free solder joints were analyzed taking into account Cu–Sn interdiffusion and current stressing effects. A new simulated annealing (SA) approach was developed to derive atomic diffusivities and effective charge numbers for this multi-phase multi-component system. A consistent set of parameters were obtained and used in a finite difference model to numerically solve the IMC growth kinetics and the result accurately correlated with the experiment. EM reliability test revealed that solder joint failure was caused by extensive void formation and subsequent crack propagation at the intermetallic interface. This damage formation mechanism was analyzed by considering vacancy transport under current stressing, then followed by a finite element analysis on the crack driving force induced by void formation. Implications on the structural reliability of the through-Si-via in 3D interconnects will be discussed.

9:00 AM  
Investigation of the Influence of Ni Content on Electromigration Resistance of (Pd,Ni)Sn4: Chao-hong Wang1; Kuan-ting Li1; 1National Chung Cheng University
    The insertion of Pd layer, i.e, ENEPIG, was found to be capable of effectively retarding the electromigration-induced Ni consumption in the flip-chip solder joints. During soldering process, the Pd layer was transformed to the (Pd,Ni)Sn4 phase at the interface. In this study, several interfacial structures, Sn/Pd(1 or 3μm)/Ni and Sn/Cu(3μm)/Pd(1μm)/Ni, were prepared to form the (Pd,Ni)Sn4 with different Ni contents. The electromigration test was conducted at 180oC and at a current density of 5000 A/cm2. In the Sn/Pd(1 or 3μm)/Ni sample, the (Pd,Ni)Sn4 layer with a high Ni solubility (~17at.%) was massively migrated into the solder matrix and the Ni substrate was considerably consumed. In contrast, in the Sn/Cu(3μm)/Pd(1μm)/Ni sample without the occurrence of rapid Pd dissolution, the (Pd,Ni)Sn4 layer with a low Ni content (< 3at.%) remained layer-structured, indicating that it can effectively retard electromigration. The (Pd,Ni)Sn4 phase clearly exhibited a better electromigration resistance when the Ni content decreased.

9:20 AM  
Ab Initio Critical Product of Blech Distance and Current Density: Yu-chen Liu1; Shih-kang Lin1; 1National Cheng Kung University
    Blech distance generally elucidated the occurrence of electromigration (EM) effect in terms of plastic deformation. However, no existing model had approached the EM occurrence from elastic deformation, and thus correlating the mechanical properties of materials and EM effect. In this work, we combined in situ synchrotron radiation XRD current experiment and ab initio calculation to reveal the critical point of EM occurrence in terms of mechanical point of view. Under electric current, metals would first undergo elastic tensile deformation at both anode and cathode side. The tensile strain would be originated from electron flow as revealed by ab initio calculation. The strain gradient for atomic diffusion under electric current agreed very much well with the ones obtained from literature. New approach to the Blech critical length-current density product from elastic deformation is derived. This combinatorial study provided novel insights on the correlation of the mechanical property and EM occurrence.

9:40 AM  
Phase-field Modeling of Grain-boundary Grooving and Surface Drift under Homogeneous Electromigration: Arnab Mukherjee1; Kumar Ankit2; Britta Nestler2; 1Karlsruhe University of Applied Sciences; 2Karlsruhe Institute of Technology
    Comprehension of interplay between various diffusion pathways in polycrystalline interconnects during electromigration (EM) holds central importance in enhancing microelectronic reliability. Here, we investigate the role of potential diffusion pathways during EM in polycrystalline interconnects using a phase-field method that additionally accounts for electron wind force. Focusing on the homogeneous EM regime, we consider the evolution of grooves under the cumulative influence of capillary and electromigration-mediated surface diffusion (between the interconnect and the underlayer) and electromigration-induced grain-boundary diffusion (in the interconnect) on a drift test geometry. The groove morphology under EM-dominated regime is found to differ significantly when compared to the classical Mullins' profile. Furthermore, a detailed parametric study reveals the onset of EM modulated healing flux as the entire surface drifts with constant velocity. Finally, the role of grain coarsening on EM-induced damage in polycrystalline thin films is discussed.

10:00 AM Break

10:20 AM  Invited
An Industry Perspective on Electromigration in Microelectronics: Ping-Chuan Wang1; 1GlobalFoundries
    Electromigration remains as one of the major reliability concerns in semiconductor industry since it was first recognized more than half century ago. Significant resource and efforts have been devoted to the understanding and mitigation of electromigration and its adverse effect on the reliability of integrated circuit (IC) technologies. Such activities include fundamental material change in interconnects, modification of metallization stack and metallurgy, novel wiring structures to benefit from Blech effect, as well as implementing restrictions in circuit designs. In this talk, a brief overview will be given to illustrate the progress in improving electromigration reliability in the IC industry, including the evolution in interconnect materials and structures, as well as the implication of electromigration on device operation and design. Also, some examples of recent applications and ideas, taking advantage of electromigration as a controlled process to enable functional devices, will be introduced.

10:50 AM  
Electromigration Effects upon Interfacial Reactions in Electronic Solder Joints of Different Bump Heights and Different Electric Current Densities: Jing-wei Chen1; Sinn-wen Chen1; Yi-cheng Lin1; Tao-chih Chang2; 1National Tsing Hua University; 2Industrial Technology Research Institute
    Passage of electric current causes electromigration and joule heating at the electronic solder joints. Both effects elevate atomic fluxes and cause interfacial reactions. Interfacial reactions in the Sn-Ag/Ni/Sn-Ag, Sn-Ag/Cu/Sn-Ag and Ni/Sn-Ag/Cu samples were examined at 125, 150 and 200°C with and without passage of electric currents. The reaction couples were of different bump heights. Electric current of different densities and directions were applied to the samples under specific reaction temperatures. With or without current stressing, one reaction layer, Ni3Sn4, was formed at Ni/Sn-Ag interface, and two layers, Cu3Sn and Cu6Sn5, were formed at Cu/Sn-Ag interface. The thickness and structure of reaction layers varied with different current density and bump height. A one-dimensional mass transfer model was developed to describe the growth of the reaction phase layer. The effects of diffusion and electromigration upon the layer growth are compared and discussed. The electromigration effect is more significant at lower temperatures.

11:10 AM  
The Investigation of Electromigration Defects due to Currents Stress Effects between the Flip-chip Solder and Copper Substrate: Wei-Jhen Chen1; Yue-Lin Lee1; Ti-Yuan Wu1; Ang-Tin Tsai1; Ming-Tzer Lin1; 1National Chung Hsing University
    In this study, the investigation of electromigration defects due to currents stress effects between solder and copper substrate were performed. Experiments were tested during heating; heating and applied current; heating, applied current and applied stress. We observed micro-structural changes, measured resistivity changes and stress were provided by using four-point probe measurements. The results show that intermetallic compound thickness increases with increasing heating time both 100℃ and 200℃. For heat-treated only samples, the intermetallic compound growth mechanism controlled by grain boundary diffusion. For applied current and heating samples, the intermetallic compound growth mechanism was dominated by volume diffusion and interface reaction. For the heating, applied current and applied stress groups, the intermetallic compound growth mechanism were dominated by grain boundary diffusion with grain growth. The percentage increase in the resistivity changes linearly, as the temperature increases the slope increases, resistivity change with the film micro-structural changes are closely related.