Hafnium and zirconium silicates for advanced gate dielectrics

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Abstract
Hafnium and zirconium silicate ( HfSi x O y and ZrSi x O y , respectively) gate dielectric films with metal contents ranging from ∼3 to 30 at. % Hf, or 2 to 27 at. % Zr (±1 at. % for Hf and Zr, respectively, within a given film), have been investigated, and films with ∼2–8 at. % Hf or Zr exhibit excellent electrical properties and high thermal stability in direct contact with Si. Capacitance–voltage measurements show an equivalent oxide thickness t ox of about 18 Å (21 Å) for a 50 Å HfSi x O y (50 Å ZrSi x O y ) film deposited directly on a Si substrate. Current–voltage measurements show for the same films a leakage current of less than 2×10 −6 A/cm 2 at 1.0 V bias. Hysteresis in these films is measured to be less than 10 mV, the breakdown field is measured to be E BD ∼10 MV/cm , and the midgap interface state density is estimated to be D it ∼1–5×10 11 cm −2 eV −1 . Au electrodes produce excellent electrical properties, while Al electrodes produce very good electrical results, but also react with the silicates, creating a lower ε layer at the metal interface. Transmission electron microscopy(TEM) and x-ray photoelectron spectroscopy indicate that the dielectric films are amorphous silicates, rather than crystalline or phase-separated silicide and oxide structures. TEM shows that these films remain amorphous and stable up to at least 1050 °C in direct contact with Si substrates.