Chemical vapor deposition and characterization of HfO₂ films from organo-hafnium compounds

HfO₂ films were deposited on silicon substrates by the oxygen-assisted decomposition of hafnium β-diketonates at temperatures in the range 400-550 °C. These films were characterized by using transmission electron microscopy, X-ray diffraction, electron microprobe analysis and measurements of dielectric and optical properties. It was found that the films were fine-grained (approximately 325 Å) nearly stoichiometric monoclinic HfO₂. The films showed high resistance to most aqueous acids and bases. The deposits had a refractive index of 2.1 and an optical energy gap of 5.68 eV. The dielectric constant at 1 MHz was 22-25, and the dielectric strenght of the HfO₂ films varied between 2 × 10⁶ and 4.5 × 10⁶ V cm^-1. C-V measurements at 1 MHz indicated the presence of effective surface states which varied between 1.0 × 10¹¹ and 6 × 10¹¹ cm^t-2 for films that were deposited at temperatures higher than 500 °C or that were annealed at above 750 °C if deposited at 400-450 °C. The V_FB values were between -0.6 and 0 V. The annealed films or films grown above 500 °C showed good bias-temperature stability. When positive bias and elevated temperatures were applied, the original C-V curve moved towards higher positive field values (0.2-0.5 V). After applying negative bias at elevated temperatures the C-V curved moved back in the direction of the original C-V curve. Measurements of the dependence of the current I on the electric field showed a dependence of I ∝ V² over a wide range.