Why Would Ruthenium Replace Copper Chip Wires?

Jack Kavalieros says ruthenium can replace copper on the tightest chip wires because ruthenium can be etched and does not need the liner copper requires, so it conducts better once the pitch is down around 20 nanometers.

A transistor is useful only once it is connected to other transistors. On a modern chip that takes more than a dozen layers of copper wires, called interconnect. Copper typically needs a liner, a glue or transition layer, so each deposit sticks to the copper below. On fine wires that liner used to be a large share of the conduction path. Ruthenium does not need one. Dropping that resistive liner is the crossover where ruthenium has better conductivity than copper. Half of a 20 nanometer pitch is the metal line and half is the dielectric that isolates it. Intel has since made the copper liner thinner, so copper comes back as a contender at some sizes. At 10 nanometer, Intel moved from copper to cobalt.

A new metal still has to do more than scale. It has to integrate with the many other pieces in the transistor stack before it is ready for high-volume manufacturing.