An approach to control the dielectric properties of hafnium-based oxide films with an intentional structural phase transformation was proposed and demonstrated. Yttrium serves effectively as a dopant to induce a phase transformation from the monoclinic to the cubic phase even at 600°C. The yttrium-doped HfO2 films show higher permittivity than undoped HfO2, and the permittivity as high as 27 is obtained by 4at.% yttrium doping. The permittivity enhancement by yttrium doping can be explained by the shrinkage of molar volume due to the structural phase transformation. The advantage of yttrium doping is more pronounced at higher temperatures, since the permittivity of undoped HfO2 is reduced significantly, whereas that of 17at.% yttrium-doped film shows no change even at 1000°C.

An investigation of the inversion layer mobility characteristics on conditions with systematic combinations of three key parameters: surface orientations, in-plane channel directions, and mi-axial strains, was performed. A guiding principle for an optimum combination of above three key parameters in terms of electron and hole mobility enhancement is presented. In addition, it is found experimentally that the 'definition of the mobility universality should he changed with surface orientations and applied uni-axial strains.

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.

Effects of moisture absorption on permittivity and surface roughness of lanthanum oxide (La2O3) films were investigated. It was found that the moisture absorption deteriorates the permittivity (k) of La2O3 films on silicon because of the formation of hexagonal La(OH)3 with a low permittivity after films were exposed to the air. Therefore, the moisture absorption should be a very possible reason for the permittivity variation of La2O3 film in literatures reported, so far. Furthermore, a roughness enhancement was also observed after La2O3 films were exposed to the air for several hours. This observation should be another concern of hygroscopic La2O3 film application.

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.