Vacuum-assisted void-free copper filling of high-aspect-ratio through-glass vias for advanced interposers

초록

Void-free copper filling in high-aspect-ratio (AR) through-glass vias (TGVs) remains a critical challenge owing to void formation within geometrically confined structures. In this study, the effects of different pretreatment processes, such as sputtering, electroless plating, and vacuum-assisted wetting, on via filling behavior were systematically investigated. Electrochemical analyses employing cyclic voltammetry stripping (CVS) and linear sweep voltammetry (LSV) revealed that electrolytes containing additives exhibit mass transport-dependent adsorption behavior, which governs spatially dependent deposition behavior in high-AR vias. Additionally, contact angle measurements indicated that metal-coated surfaces and high-AR via structures exhibit reduced wettability compared to bare glass, thereby further limiting electrolyte infiltration. To overcome these limitations, a vacuum-assisted wetting process was introduced. Under reduced pressure, the pressure difference at the gas-liquid interface increases significantly, promoting bubble expansion and facilitating the removal of trapped gas from the via interior. As a result, uniform and void-free copper filling was achieved across a wide range of applied current densities in structures with AR values up to 10. Moreover, no defects such as voids or seams were observed after thermal shock testing (-55 degrees C to 125 degrees C, 100 cycles), thereby confirming the structural reliability of the fabricated vias. These results show that vacuum-assisted wetting is an effective pretreatment strategy for improving electrolyte infiltration and enabling consistent and reliable void-free filling in high-AR TGVs, offering a practical approach for advanced glass interposer applications.

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