Numerical simulation and twinning evolution mechanism of the deep through silicon via electroplated copper

Abstract

The microstructure is an important key factor for the reliability of deep through silicon via (TSV) electroplated copper. In the present study, the influence of current density on the surface physical field and microstructure in the electroplated copper were discussed using a combined method of numerical simulation and experiment. The results showed that the optimal electroplated parameters with the defect-free filling were confirmed to be at 0.1-0.17 Ampere per Square Decimeter (ASD) with an accelerator-to-suppressor ratio of 1:10 when the size of deep TSV was Φ20 μm × 200 μm with an aspect ratio of 10:1. The microstructure of TSVs exhibited a distinct distribution feature: fine grains along sidewalls and at the mouth, large columnar grains in mid-regions, and equiaxed grains at the bottom. The grain size and the quantity of Σ3 twin boundaries first decreased and then increased with increasing current density due to the competing effect of nucleation rate and grain growth by governing the polarization and suppressor desorption. Moreover, the intermediate 9R structure between the matrix and the twin was first observed in the electroplated copper, which provided a new way for strain accommodation in deep TSV electroplated copper, and the matrix→9R→twin pathway was proposed through the slip of Shockley partial dislocations. These findings served as a valuable reference for modeling microstructure evolution and laid a foundation for both microstructure prediction and control in deep TSV electroplated copper.

Keywords

Deep through silicon via electroplated copper / applied current density / numerical simulation / twinning mechanism / grain morphology

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