Characterization of Cu-Mn/Ta Layer as Cu Diffusion Barrier on a Low-k Dielectric

Abstract

Over the last several years, interconnections used in the semiconductor industry have advanced as feature size has gradually decreased. However, smaller feature sizes cause problems such as RC (resistive-capacitive) delay and difficulties in gap filling. To solve these problems, a low dielectric constant material was used as a substitute for SiO2 and Cu was used as an interconnectionmaterial to replace Al. However, Cu interconnections are required to prevent Cu diffusion into the dielectric layer. Therefore, various diffusion barrier layers were investigated to continue the trend of device scale-down. One such barrier layer is a self-forming diffusion barrier, which prevents Cu diffusion into dielectrics without barrier layer deposition. Self-forming diffusion barriers can also increase the Cu filling ratio, but they are very sensitive to the Cu alloy material composition and can cause Cu penetration before barrier layer formation. This phenomenon is particularly problematic when porous low-k dielectrics are used. In this work, a Cu-Mn alloy and Ta were used as the seed layer and sub-layer, respectively, on low-k substrates to address the problems mentioned above. A Cu-Mn/Ta/low-k structure was prepared and was annealed at 400 degrees C for 1 hr. Cu film and barrier layer properties were analyzed using four-point-probe measurements, transmission electron microscopy, atomic force microscopy and I-V analysis. We confirmed that the Ta layer is sufficient to prevent Cu diffusion into the dielectric during annealing. Moreover, its thermal stability is good compared to the self-forming barrier without a Ta layer. The results showed that a Cu-Mn/Ta layer on low-k substrates is suitable for use as a Cu diffusion barrier, and we expect this strategy can be used to enhance device performance.