Cobalt arrests copper’s impetus

Cobalt is the new copper. Semiconductor manufacturers are now finding that copper, the bee’s knees as one of the best bulk conductors of electricity, has its limitations.

The face centered cubic crystal arrangement – basically an atom at each corner of each face of the cu plus one in the center – has seen it being used for interconnects in the metallization layer, the Back-End Of Line (BEOL) in semiconductor manufacturing.

As Malcolm Penn, CEO of Future Horizons remarked: “Copper was supposed to be the ultimate and final interconnect solution.”

“The trouble is,” Penn continued, “as metallization geometries have shrunk copper no longer forms a nice conductive crystal.”

Enter stage left cobalt. At the IEEE International Electron Device Meeting (IEDM 2017) in San Francisco last December Intel announced it was using cobalt on the bottom two layers of its 10nm interconnect.

Explains Penn, “While cobalt is not such a good bulk conductor, it provides more reliable and repeatable conductivity in short interconnects where the resistance of the contact dominates, not interconnect length.”
Intel is using cobalt at the bottom two layers of metallizations as this where all the short inter-gate connections are made.

During the course of a technology update in London Penn also pointed out that another advantage of using cobalt is that it reduce electromigration.

“This allows tracks to be placed closer together with confidence they won’t short together within the expected lifetime of the IC,” he added.