Novel dielectric insulators for next generation microelectronic devices

The characteristics of barium strontium titanate (BST) thin films grown directly on Si substrates by an in-situ ultraviolet (UV)-assisted pulsed laser deposition (UVPLD) technique are reported in this paper. In comparison with BST films grown by conventional pulsed laser deposition (PLD) under similar conditions, but without UV illumination, the UVPLD grown films exhibited improved stoichiometry, structural, electrical, and optical properties. The dielectric constant of a 40-nm thick film deposited at 650 °C by UVPLD was determined to be 281, the leakage current density was approximately 4×10^-8 A/cm² at 100 kV/cm, and the density of interface states at the flat-band voltage was found to be approximately 5.6×10¹¹ eV^-1cm^-2. The equivalent silicon dioxide thickness of the best BST films grown was found to be around 10 angstroms. X-ray photoelectron spectroscopy investigations found out that the surface of the BST films contained Ba atoms in a new chemical state besides BST, believed to be caused by stress and/or oxygen vacancies. The amount of this new phase was always smaller for UVPLD grown films, which may explain their better overall properties. UV radiation, by providing more reactive gaseous species such as ozone and atomic oxygen and increasing the surface mobility of adatoms can contribute to the crystalline and stoichiometric growth of the films, especially at moderate processing temperatures, where the thermal energy available for the growth process is low.