Improvement in structural and dielectric properties of sputtered Ta2O5 thin film by post-deposition annealing

In current years, the growth of high-k dielectric thin films with reduced charge density and leakage current has drawn tremendous attention for microelectronic devices. Ta2O5 thin film is deposited on p-type silicon substrate using radio frequency sputtering deposition technique for high-k dielectric applications. The as-deposited films undergo post-deposition annealing treatment at temperatures ranging from 600 degrees C to 900 degrees C for 1 h in air ambient. X-ray diffraction analysis revealed the formation of a polycrystalline orthorhombic beta - Ta2O5 structure in the annealed films. The RMS roughness of the film is found to be increased from 2.3 nm to 3.7 nm with the increase in annealing temperature to 900 degrees C. Metal-oxide-semiconductor (Al/Ta2O5/p-Si) structures are fabricated using thermal evaporation for electrical characterizations. The capacitance-voltage (at 1 MHz) of this structure is measured for the sweep voltage from - 4 V to + 4 V. The oxide charge density and interface charge density of the film have been calculated from the C-V curve and found to decrease with the increase in annealing temperature. The highest dielectric constant value of 24.5 at 1 MHz is found for film annealed at 800 degrees C. The leakage current is measured from the current-voltage measurement and found to be minimum for the film annealed at 800 degrees C.