In this paper we will demonstrate new approaches for failure analysis of memory devices with multiple stacked dies and TSV interconnects. Therefore, TSV specific failure modes are studied on daisy chain test samples. Two analysis flows for defect localization implementing Electron Beam Induced Current (EBAC) imaging and Lock-in-Thermography (LIT) as well as adapted Focused Ion Beam (FIB) preparation and defect characterization by electron microscopy will be discussed. The most challenging failure mode is an electrical short at the TSV sidewall isolation with sub-micrometer dimensions. It is shown that the leakage path to a certain TSV within the stack can firstly be located by applying LIT to a metallographic cross section and secondly pinpointing by FIB/SEM cross-sectioning. In order to evaluate the potential of non-destructive determination of the lateral defect position, as well as the defect depth from only one LIT measurement, 2D thermal simulations of TSV stacks with artificial leakages are performed calculating the phase shift values per die level.

In this paper different sample preparation strategies for fast and efficient failure analysis of 3D devices are reviewed and further explored. It will be shown that a combined workflow using laser ablation and plasma FIB milling provides best flexibility to cover most of the FA use cases. Laser ablation guarantees fast, coarse material removal and the subsequent plasma FIB milling provides fast removal of any damage or imperfections induced by the laser ablation, precise navigation to the region of interest, a high quality surface finish allowing direct SEM imaging and analytics such as EBSD and, if required the preparation of a thin lamella for TEM analysis.

In this paper the new Vion™ Plasma-FIB system, developed by FEI, is evaluated for cross sectioning of Cu filled Through Silicon Via (TSV) interconnects. The aim of the study presented in this paper is to evaluate and optimise different Plasma-FIB (P-FIB) milling strategies in terms of performance and cross section surface quality. The sufficient preservation of microstructures within cross sections is crucial for subsequent Electron Backscatter Diffraction (EBSD) grain structure analyses and a high resolution interface characterisation by TEM.