Characterization of bias magnetron sputtered tantalum oxide films for capacitors

Tantalum oxide films have been deposited by sputtering of tantalum target in an oxygen partial pressure of 2x10 mbar under various substrate bias voltages in the range from 0 to -150 V on glass and silicon substrates held at room temperature. The influence of substrate bias voltage on the chemical binding configuration, crystallographic structure, electrical and dielectric properties has been systematically studied. The X-ray photoelectron spectroscopic studies reveal that the films are stoichiometric. The X-ray diffraction and Fourier transform infrared spectroscopic studies indicate that the films deposited under unbiased condition are amorphous in nature, whereas those formed at substrate bias voltages > -75 V are polycrystalline with orthorhombic β-phase. The electrical and dielectric properties of Ta2O5 films have been studied on the metal / insulator / metal (MIM) structure of Al/Ta2O5/Al. The dielectric constant of the films formed at unbiased condition has been found to be 15, while for those prepared at higher substrate bias voltage of -150 V has been found to be 23 due to the improvement in the crystallinity and packing density. The voltage current measurements on the MIM structure indicate the decrease of leakage current density with the increase of substrate bias voltage.