Design and Fabrication of a Silicon Interposer With TSVs in Cavities for Three-Dimensional IC Packaging

Flip chip is one of the packaging techniques for high-performance components. There is a greater demand on integrating more functions in a smaller chip nowadays. This leads to the increase of I/O density. Organic substrate is the bottleneck of the high-density packaging. A silicon interposer with through-silicon vias (TSVs) is commonly used to provide a platform with a high wiring density to redistribute I/Os. After I/O redistribution, larger solder joints with a larger pitch can be used to connect the interposer to the organic substrate. In this paper, a TSV-based silicon interposer with a cavity and copper pillars for 3-D packaging is presented. The cavity hosts the flip-chip device. There are copper-filled TSVs in the cavity to provide the electrical interconnections to the backside of the interposer. Flip-chip solder bumps are electroplated on the copper pillars. Subsequent to the flip-chip assembly process, the device is seated in the cavity entirely. The backside of the flip chip is lower than that of the surface of the interposer. This provides a better environment for further die stacking on the surface of the interposer. The microfabrication process of the proposed silicon interposer with TSVs in cavities is discussed in detail.