Copper On-Chip Interconnections: A Breakthrough in Electrodeposition to Make Better Chips

On-chip interconnections comprise a multilevel structure of fine wiring located on the top of the transistor circuitry of logic or memory chips, whose role is to connect circuits together as shown in Fig. 1. To avoid significant degradation of circuit speed, on-chip interconnections should permit rapid signal transmission among the various parts of the circuitry. Ever since the development of the integrated circuit about 40 years ago, the most pervasively used materials for the fabrication of the wiring structure have been aluminum as the conductor (or more recently an aluminum-copper alloy for better reliability) and silicon dioxide as the insulator. The transition to copper as the conductor and to a better insulator began with IBM’s announcement in September 1997 and product shipment since June 1998. This signals one of the most important changes in materials that the semiconductor industry has experienced since its creation. Copper metallization was implemented first since significant gains can be obtained by copper alone.