The influence of surfactant-based liner post-treatment on the wetting and nucleation characteristics of ultra-thin copper (Cu) films has been examined, employing ultra-thin atomic layer deposited (ALD) tantalum nitride (TaNx) as liner material. This surfactant-based posttreatment consists of in-situ exposure of the liner to a metal-organic source containing a low surface free energy metal (Sn) surfactant, which is a potential candidate for enhancing the wetting of Cu on liner surfaces and subsequently suppressing island-type growth of Cu, due to both the high atomic volume and low surface free energy of the surfactant relative to Cu. A methodology involving thermally-enhanced de-wetting of Cu, promoted by annealing Cu/liner stacks in a forming gas (95% Ar, 5% H2) ambient under several applied thermal budgets (annealing at 350°C for 30 minutes, and at 600°C for 4, 12, and 48 hrs, respectively), was utilized to both elucidate and quantify the wetting properties of Cu on liners, via detailed analyses of the surface morphology of annealed stacks by atomic force microscopy (AFM) and scanning electron microscopy (SEM). By comparing stacks containing ALD TaNx liners to those that contain post-treated ALD TaNx liners, this method allowed an evaluation of the effectiveness of surfactant-based liner surface post-treatments in inhibiting Cu de-wetting.
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