Interconnect processes

What is the main purpose of placing a cap layer such as cobalt on top of copper wiring?

  1. ATo deliberately increase wire resistance
  2. BTo make the wiring transparent
  3. CTo suppress atom migration along the copper surface and improve electromigration resistance
Show answer and explanation

Answer: C. To suppress atom migration along the copper surface and improve electromigration resistance

Electromigration in copper wiring proceeds mainly by atom migration along the top surface (the interface with the dielectric). Covering the top with a metal cap such as cobalt strengthens interface bonding and makes atoms harder to move, improving electromigration resistance.

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More Interconnect processes questions

  1. In Black's equation for wire lifetime under electromigration, which factors shorten the lifetime?
  2. Which is closest to the number of wiring layers in advanced logic LSIs?
  3. What is an advantage of metals such as ruthenium (Ru), being considered as alternatives to copper for fine wiring?
  4. What is the film called that is formed on the top of a chip to protect the internal circuits from moisture, contamination and mechanical damage?
  5. Which metal has been used in many LSIs for the top-level bond pads where wire bonding is done?