Interconnect processes

What is an advantage of metals such as ruthenium (Ru), being considered as alternatives to copper for fine wiring?

  1. ATheir resistivity rises relatively little in narrow wires, and the barrier layer may be made thinner (or unnecessary)
  2. BThey are much cheaper than copper
  3. CThey transmit light, making inspection easier
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Answer: A. Their resistivity rises relatively little in narrow wires, and the barrier layer may be made thinner (or unnecessary)

Copper has low resistivity in wide wires, but in very narrow wires surface and grain-boundary scattering increase and a thick barrier is needed, raising the effective resistance. Metals such as ruthenium and molybdenum have short electron mean free paths and may allow thinner barriers, so they are being considered for the narrowest wires.

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More Interconnect processes questions

  1. 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?
  2. Which metal has been used in many LSIs for the top-level bond pads where wire bonding is done?
  3. What is the method called that fills wiring trenches and vias with copper at the same time and finishes them with a single CMP step?
  4. What is the role of the thin copper film sputtered before filling copper by electroplating?
  5. What problems occur when copper filling is incomplete and a void remains in a via?