Abstract
Cobalt film with tungsten addition [Co(W)] has the potential to be an effective single-layered barrier/liner in interconnects awing to its good adhesion with Cu, a lower resistivity than TaN, and an improved barrier property with respect to cobalt films. Our previous study on chemical-vapor-deposited (CVD) Co(W) using carbonyl precursors clarified, however, that WO3 included in the films increased the resistivity. In this current study, to reduce the resistivity of Co(W), oxygen-free Co(W) films were fabricated from two oxygen-free precursors, bis(cyclopentadienyl)cobalt and bis(cyclopentadienyl)tungstendihydride, by atomic layer deposition (ALD) using NH2 radicals generated using a hot filament. Results revealed that (a) W concentration in ALD-Co(W) could be controlled by adjusting the gas-feed sequences, (b) W addition improved the barrier property of ALD-Co(W) against Cu diffusion, (c) diffusion of Cu into ALD-Co(W) had a high activation energy, 2.0 eV, indicating interstitial diffusion, and (d) ALD-Co(W) consisted mainly of an amorphous-like phase, which is consistent with the high activation energy of Cu diffusion.
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