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

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 µΩcm. The phases form in the order of α-Hf → HfN0.4 → ε-Hf3N2 → 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.