Vacuum-Assisted Through Silicon via Filling Method With Ag-Based Epoxy

Abstract

In the field of 3-D integration, Cu electroplating has become the most popular method to metallize the through silicon via, due to the higher conductivity of Cu compared to W and doped poly-silicon and the good compatibility with other microfabrication procedures. However, many problems embedded in this technique, such as long deposition time, relatively high complexity, and environmental pollution, are still unsolved. In this paper, we utilized the Ag-based epoxy to fill the vias with the assistance of vacuum pressure to solve all these problems. It was found that the vacuum level played a more important role than the suction time in this process, as the filling depth for the vias with a diameter of 100 $\mu \text{m}$ and a depth of 500 $\mu \text{m}$ grew more visibly in a fixed lifespan when the vacuum pressure elevated from 0.2 to 1.6 kPa, and to realize a 100% filling ratio, 1.6 kPa and 3 s would be needed at least. By running the basic two-point probe test for two times without any printed circuit board, the volume resistance of fully filled vias was measured, and the results indicated that the average resistance was $\sim 25~\Omega $ . During the temperature increase from room temperature to 120 °C, this material established good stability in resistivity as the change in via resistance was negligible. The adhesion quality between this material and Cu-based bonding pad was tested as well, and the result was acceptable.