Copper seed layer repair using an electroplating process for through silicon via metallization

Through silicon via (TSV) is a key technology for three-dimensional chip stacking, which serves as a bridge to connect multiple devices in the z-direction. Void-free copper deposition in a TSV is essential for reliable TSV fabrication. Deep reactive ion etching (DRIE) process (i.e., the Bosch process) has been widely used for deep TSV formation because of its high aspect-ratio etching capability. However, the sidewall of a TSV is not flat after the DRIE process, which frequently results in a so-called “scallop” structure on the sidewall. After a copper seed layer is deposited on the TSV sidewall by sputtering, the step coverage of the copper seed layer is poor, especially at a high aspect ratio. To solve this problem, we use a copper electroplating process to repair the discontinuous seed layer caused by the “scallop” structure. The seed layer repair formula that contains a polymer additive allows the growth of an electroplated copper seed layer to be faster in the horizontal direction (parallel to the sidewall surface) than in the vertical direction (normal to the sidewall). The polymer additive is a crosslinked polyamide that bears organic functional groups of R1NH2 and R2CONHR3, which prefers to stay on the terraces of copper crystals to inhibit the vertical copper deposition and correspondingly facilitate the horizontal copper deposition. After the repair plating process, the discontinuous seed layer becomes continuous, so that TSVs with diameters of 20 μm, which originally failed to achieve copper superfilling, are fully filled by means of copper electroplating.

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► Bosch process results in a “scallop” structure on the sidewall of a TSV.
► The “scallop” structure leads to a discontinuous Cu seed layer.
► The discontinuous Cu seed layer is repairable using a specific Cu plating formula.
► The repair plating formula enhances Cu nucleation along the sidewall of a TSV.
► The seed layer enhancement is due to the addition of polyamide in the plating solution.