Effect of Phase Formation Behavior on Thermal Stability of Hafnium-Based Thin Films for Copper Interconnects

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Hafnium (Hf) and hafnium nitride (Hf–N) flims were deposited on silicon wafers using a magnetron sputtering system. The as-deposited Hf film has a hexagonal close packed structure and a low resistivity of 101 μ$\Omega$cm. The phases form in the order of $\alpha$-Hf $\rightarrow$ HfN0.4 $\rightarrow$ $\varepsilon$-Hf3N2 $\rightarrow$ fcc-HfN with increasing nitrogen concentration in the Hf–N film. The thermal stabilities of Cu/Hf–N/Si contact systems are evaluated by thermal stressing at various annealing temperatures. In Cu/Hf/Si, a reaction between the Hf barrier layer and the Cu layer is observed, and copper–hafnium compounds form after annealing at 550°C. Moreover, highly resistive copper silicide is found after 600°C annealing. No copper–hafnium or copper silicide compounds are found in the Cu/HfN0.47/Si contact system even after annealing at 650°C. Incorporating nitrogen into the hafnium diffusion barrier can suppress the formation of copper–hafnium compounds and copper penetration, thus improving the barrier’s thermal stability.
2004-06-15