Through-Silicon Via

The through-silicon via (TSV) is composed of a conductor, also named “nail” or “plug,” crossing the Si substrate of the stacked dies. The conductor [common material choices include copper (Cu), tungsten (W), and polysilicon] is electrically insulated from the substrate by a dielectric layer (usually SiO2) and interconnects the metal wires of the stacked dies.

The geometry of the TSV conductor may vary depending on the 3D stacking technology. The area crossed by current may have different shapes (squared, rectangular, circular, elliptical, and polygonal). Also, the lateral surface of the conductor can be cylindrical or conical. The TSV interconnection of metal wires in adjacent dies within a 3D stack can follow different schemes. For example, TSVs can connect a Metal 1 (M1) wire of the top die with the topmost MN wire of the bottom die when the latter features N-level wire hierarchy. Another scheme may foresee the connection of both the topmost MN layers of two adjacent stacked dies. The electrical link established by a TSV between dies can be utilized for any of the typical functions supported by standard 2D interconnects: signal (analog and/or digital), clock, and power supply/ground links. In general, the geometry and the materials used in all the TSVs crossing a die are the same and this simplifies the optimization of the 3D technology process.

Once the TSV technology is fixed, the only degree of freedom in achieving different design requirements in the electrical characteristics of TSV links is to employ more TSVs in parallel in the same link. For example, this can be utilized in power supply distribution networks, where high DC current capability is required and low-resistance interconnects are desirable. Connecting multiple TSVs in parallel can decrease the resistance of power/ground links among the stacked dies. In addition, an increase in the parasitic TSV capacitance due to multiple parallel TSVs can also contribute to compensating dI/dt effects, similar to the effect of inserting large decoupling capacitors.

The electrical parameters of a TSV, namely, RTSV , LTSV , and CTSV would strongly depend on the TSV structure (both geometry and materials).