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Assessment of the Mechanical Integrity of the Si/TSV Interfacial Region in 3D Stacked Die Packages A Hierarchical Approach
Keywords: TSV, 3D, Molecular Dynamics
The continued miniaturization of the transistors has resulted in unparalleled growth of the electronics industry. Further performance improvement through size scaling; however, will not be cost-effective and difficult to manufacture. The need to integrate more devices in a small footprint (especially for modern handheld applications) has led to innovative packaging techniques such as 3-D (die stacking). The increased complexity of system-on-chip (SOC) semiconductor devices results in higher costs, thereby forcing to go 3-D TSV configurations. Through-Silicon-Via (TSV) is one of the key enabling technologies for 3-D systems allowing 3-D ICs to be interconnected directly and provide high speed signal processing, reduce interconnection power, increase communication frequency, improve design flexibility and enable seamless system-level integration of heterogeneous technologies [1]. TSVs filler material is usually copper; thereby inducing localized thermo-mechanical stresses at the TSV/Si interface due to significant CTE mismatch [2]. These stresses result in the degradation of the device performance, increase the transistor keep-out-zone (KOZ), and can cause fracture at the Si/TSV interfacial region. In this paper, molecular dynamics (MD) approach is leveraged to determine the interfacial strength of the TSV region (Si/TSV interface) at the molecular level. A molecular model of the Si/TSV interfacial region is formulated using DL_POLY graphical user interface (GUI), and the characteristic stress-strain curve is determined. A thermo-mechanical model of a 2 die 3-D TSV package is implemented to analyze the stress-strain distribution around the TSVs during package processing. Multi-level modeling (sub-modeling) and advanced element birth-death technique is leveraged to assess the damage at the continuum level. The sub-continuum response from the MD simulation is used as a failure criterion, and the numerical stress distribution from the ANSYS simulation is compared against the MD results. This work will provide valuable insight into the mechanical integrity of the TSVs during package processing.
Fahad Mirza, Research Assistant
University of Texas, Arlington
Arlington, TX

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