Structural phase transformation of Y2O3 doped HfO2 films grown on Si using atomic layer deposition

Hf O 2 and Y2O3 films, along with Y2O3-doped HfO2 composite films, have been deposited on Si by means of atomic layer deposition (ALD) using tetrakis(diethylamino)hafnium and tris(ethylcyclopentadienyl)yttrium with water vapor as the oxidizer. The growth rate and structural properties of these films have been investigated by spectral ellipsometry, grazing incidence x-ray diffraction, and x-ray photoelectron spectroscopy (XPS). The film growth temperature dependence of both HfO2 and Y2O3 films indicate overlapping ALD windows in the 250–285°C region, which is critical for ALD of Y2O3-doped HfO2 films. The composition of such films is controlled by altering precursor cycle ratios, and XPS analyses of the resulting films indicate strong correlation between the precursor cycle ratio and the film composition. From structural analyses, the as-deposited HfO2 was found to be amorphous but after annealing at 600°C or higher, it became monoclinic. In contrast, all Y2O3 films whether annealed or not had evidence of cubic crystallinity. Having a cycle ratio of at least 2.5% in a Y2O3-doped HfO2 composite film is observed to induce cubic phase crystallinity in the film after postdeposition annealing at 600°C or greater.