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The flat band voltage in metal/HfLaO x /SiO 2 /Si capacitors has been investigated as a function of La concentration in HfLaO x . We have found that with an increase of La concentration, the flat band voltage shifts to the negative direction. Furthermore, we demonstrate that the flat band voltage in this system is determined by the La concentration at HfLaO x /SiO 2 interface. This result suggests that the flat band voltage shift is due to the dipole layer formed at the HfLaO x /SiO 2 interface rather than the Fermi-level pinning at the metal/HfLaO x interface.

Thin HfLaOx films on Si(100) have been investigated as an alternative gate insulator. The introduction of La2O3 into HfO2 causes an increase of crystallization temperature. Furthermore, unlike other Hf-based amorphous materials such as HfSiOx or HfAlOx, the permittivity of HfLaOx keeps a high value (>20). The capacitance-voltage curve of metal oxide semiconductor capacitor using the HfLaOx dielectric film has shown a negligible hysteresis and no frequency dispersion, indicating very small degradations of both interface and bulk properties. In addition, a very low fixed charge density in HfLaOx films is demonstrated from a very small film thickness dependence of the flatband voltage.

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In this work, we discuss doping effects of other metal oxides into HfO2 as a function of annealing temperature or doping concentration, and demonstrate a dramatic change of dielectric properties of doped HfO2 films. In addition to the relative dielectric constant (k-value), crystallization/amorphous characteristics have been also studied. One case induces easier crystallization than the pure HfO2, while the other case keeps amorphous up to 900 ºC without nitrogen introduction. From those observations, we discuss a general guideline for obtaining higher-k dielectric films.