Characterization of bias magnetron sputtered tantalum oxide films for capacitors

Abstract

Tantalum oxide films have been deposited by sputtering of tantalum target in an oxygen partial pressure of 2x10⁻⁴ 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.