In classifying TSVs by when they are formed, which approach makes TSVs after forming transistors but before forming the multilayer interconnect?

Answer: B. Via-middle

By timing, TSVs are classified as via-first, made before transistors; via-middle, made after transistors and before the multilayer interconnect; and via-last, made after the interconnect or from the backside after thinning. Via-middle is widely used because it keeps copper TSVs away from high-temperature transistor steps while making them easy to connect to the wiring.

• A. Via-first forms them before transistors.
• B. Correct. They are formed between transistor and interconnect formation.
• C. Via-last forms them after the interconnect or after thinning.