Interconnect processes

When a wire becomes narrower than its grains so that grain boundaries line up across the wire, what is this structure called, and how does it affect electromigration?

  1. AA porous structure, which lowers resistance
  2. BAn amorphous structure, which lowers resistance
  3. CA bamboo structure, which reduces grain-boundary diffusion paths along the wire and improves resistance
Show answer and explanation

Answer: C. A bamboo structure, which reduces grain-boundary diffusion paths along the wire and improves resistance

When the wire is narrower than the grain size, grain boundaries cross the wire like the nodes of bamboo. This structure removes most of the grain-boundary paths along the wire where atoms move fast, so electromigration by grain-boundary diffusion is suppressed. In Cu, however, interface diffusion becomes the dominant path.

  • A. A porous structure describes low-k films and the like.
  • B. Wiring metals are crystalline.
  • C. Correct. Fewer grain-boundary paths improve resistance.
Practice this topic Back to topic

More Interconnect processes questions

  1. When high-frequency signals flow in a wire, what is the phenomenon called in which current concentrates near the conductor surface and the effective resistance rises?
  2. What is the design practice called in which active devices and wiring are placed directly beneath the bond pads used for wire bonding and the like?
  3. Which technique deposits a Cu alloy with a small addition of manganese or similar and, through annealing, lets a thin barrier form spontaneously at the interface with the dielectric?
  4. For long, wide wires such as the clock network of a chip running at several GHz, which wire property must be considered in addition to resistance and capacitance?
  5. What is the main reason the wiring material of advanced LSIs was changed from aluminum (Al) to copper (Cu)?