Characterization of plasticity and stresses in TSV structures in stacked dies using synchrotron x-ray microdiffraction

The characteristics of thermal stresses in a five-stacked memory dies containing through-silicon vias (TSVs) were measured with synchrotron x-ray microdiffraction. The measurements were performed in and around the Cu vias for both the top and bottom dies. With scanning white beam x-ray microdiffraction, high resolution mappings of stress distribution were obtained. The results provided a direct observation of the local plasticity in Cu TSV and the stress and deformation in the surrounding Si. Thermo-mechanical modeling using finite element analysis (FEA) was carried out for the stacked structure. Results from the modeling analysis were correlated to the synchrotron observation to examine the effect of the die stacking on the stress behavior of the TSV at different die levels. Overall, the stress distribution obtained by FEA showed good agreement with the synchrotron measurement. The presence of plasticity was predicted by FEA and confirmed by the synchrotron observation. The implication of the residual stress on reliability of the memory structure was discussed. The results from this work demonstrate the capability of synchrotron based x-ray technique in studying the stress characteristics of multi-stack TSV structures.