| Cu/low-k material interconnects are a solution to overcome problems that occur in deep submicron Al/SiO2 based interconnects. Several challenges have to be resolved before successfully integrating copper and low-k dielectric materials into interconnects. In this work, Cu and several low-k polymers were used for interconnect applications and their effects on interconnect performance were investigated. Dielectric anisotropy is one of the factors that affect interconnect performance. Two fluorinated polymers, a rigid rod-like polyimide (Dupont FPI-136M) and a flexible poly(aryl ether) (Allied Signal FLARE 1.51) were used to investigate the relationship between dielectric anisotropy and molecular orientation. The dielectric anisotropy of the rigid rod-like polyimide was reduced relative to that in blanket films when it was confined in submicron trenches. Such a reduction was not observed in the flexible polymer. Polarized FTIR experiments showed that when rigid rod-like polymer was confined in submicron trenches polymer chains preferentially oriented parallel to metal lines. The preferential orientation reduced the in-plane dielectric constant of the polymer. A barrier layer has to be used to prevent Cu diffusion into an interlayer dielectric material. Ta, TaN, and TaSiN were used to investigate the relationship between barrier capability and microstructures using a bias temperature stress. TaSiN performed best because TaSiN was amorphous, followed by TaN then Ta because TaN had impurities segregated in grain boundaries. When Cu/BCB interconnects were fabricated and their reliability was investigated with the bias temperature stress, some of the interconnect structures performed properly and their life times were comparable to those of Cu/SiO2 interconnects, while other interconnect structures rapidly failed because the Cu readily diffused through defects in the barrier. The defects were introduced during chemical-mechanical polishing and plasma etching processes. |
