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Synchrotron X-Ray Microdiffraction Investigation of Scaling Effects on Plasticity and the Correlation to TSV Extrusion

The reliability of copper through-silicon vias (TSVs) has been shown to be largely determined by the microstructure and extrusion statistics, and the mechanism for this requires further investigation. Synchrotron x-ray microdiffraction is an advantageous technique for TSV measurements due to its high beam intensity, which allows for full stress derivation with submicron resolution, and its nondestructive sample preparation. Since copper is highly elastically anisotropic, the grain structure and corresponding mechanical properties are crucial in determining the thermomechanical response. In this paper, microdiffraction is used to investigate the TSV scaling effect on plastic deformation and its correlation to the grain growth and extrusion behavior. Electron backscatter diffraction results indicate that the grain growth mechanism is not largely affected by scaling in the range of 10µm to 2µm diameter TSVs. However, the magnitude and statistical spread of the via extrusion for the 2µm TSVs is higher than that of the 5µm TSVs. Microdiffraction results reveal that the magnitude and variation of the plasticity is also higher for the 2µm TSVs, and that the plastic deformation is correlated to the microstructure. These results, validated by thermomechanical simulation, demonstrate that scaling TSV dimensions does not improve stress and reliability for the via middle process, where further annealing beyond the post-plating anneal is required.