The effect of vacuum annealing on the microstructure, mechanical and electrical properties of tantalum films

• Phase transformation in vacuum annealed tantalum films was studied.
• The as-deposited 500 ± 2 nm thick tantalum film exhibited mixed (α and β) phases.
• Vacuum annealing (at 750 °C for 1 h) resulted in the transformation of β to α-phase.
• Electrical and mechanical properties were affected in vacuum annealed Ta films.

The microstructure, mechanical and electrical properties of vacuum annealed tantalum films were studied. X-ray diffraction spectra confirmed the presence of mixed (α and β) phases in the as-deposited Ta films. After vacuum annealing (at 750 °C for 1 h), the metastable β-phase was completely transformed to stable α-phase. The grain size increased (from 35 ± 3 nm to 92 ± 3 nm) with the increase in annealing temperature. The mixed (α and β) phases resulted in higher hardness and higher Young's modulus. The film annealed at 750 °C for 1 h exhibited lower resistivity (52 ± 4 μΩ-cm), lower hardness (H = 10.4 ± 1.3 GPa) and lower Young's modulus (Y = 185 ± 5 GPa) as compared to the as-deposited and annealed (at temperature < 750 °C) films. This is attributed to the phase transformation from β to α at an annealing temperature of 750 °C.