Enhancement of breakdown strength and electromigration reliability for cobalt lines lightly doped with boron

Abstract

Conventional copper interconnect is facing a considerable rise in electrical resistivity for applications in nanoscale devices due mainly to its significant-high electron mean free path. Cobalt, a metal with a shorter electron mean free path, has been suggested as the most promising interconnecting material for the next-generation device. Thus, this work studies alloying cobalt film with a small amount of boron as an electromigration retarder without sacrificing its electrical conductivity through evaluating its electrical properties, electromigration resistance, bonding structure, and thermal stability. Examining composition of the boron lightly-doped cobalt films shows that it can be intentionally controlled by the deposition power, yielding the incorporating boron not significantly increasing its electrical resistivity. Additionally, boron incorporation strongly intensifies the breakdown strength and electromigration reliability of the cobalt film. However, boron addition leads to a higher surface energy, and thus causes a degradation of the thermal stability. Nevertheless, the studied boron lightly-doped cobalt film is still thermally stable up to 600 °C, making it a promising interconnecting material for application in nanoscale devices.