Effects of Cu Metal Barrier on Electrical Characteristics of Porous Carbon-Doped Oxide Film

Porous carbon-doped oxide (CDO) film is a promising low-dielectric-constant (low-k) material that is used as an insulator in the back-end-of-line interconnects of integrated circuits for 45 nm or below technological nodes. In Cu/porous low-k integrated interconnects, a barrier is required to prevent the migration of Cu into the low-k insulating dielectric, avoiding electrical instability and degradation of reliability. Cobalt (Co) and ruthenium (Ru), deposited by physical vapor deposition (PVD), were evaluated as Cu barriers in this study. Their effects on the electrical characteristics of the porous CDO film were compared. Experimental results revealed that Co is a better barrier against Cu diffusion, enhances adhesion, and generates electric stress-induced traps at a lower rate. However, damage to the underlying porous CDO film during Co or Ru PVD sputtering deposition was observed. More damage was detected when a Co barrier was used because vacuum-ultraviolet light irradiation was emitted by Ar plasma for a longer time. Therefore, Co can serve as an alternative material for Cu barrier layer. However, the method of deposition of the Co barrier must be carefully chosen to alleviate damage to the contacting low-k insulating dielectric.