Effects of post–deposition annealing on the material characteristics of ultrathin HfO2 films on silicon

High quality HfO2 films were deposited on p-type Si(100) wafers by an atomic layer deposition scheme. The deposited films were smooth, amorphous, and stoichiometric, as determined by atomic force microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy, respectively. The as-deposited films showed a very small interfacial layer between the HfO2 and silicon. The index of refraction of the film was determined to be slightly smaller than that of bulk HfO2 by spectroscopic ellipsometry. The films annealed in O2 and NH3 at 800°C showed a growth of the interfacial layer, which resembles a SiO2-rich dielectric layer. Short-range order in the as-deposited films was determined to be monoclinic by the extended x-ray absorption fine structure measurements, and signs of crystallization were observed in the O2 annealed sample. The films appeared to be polycrystalline upon high temperature (800°C) annealing as confirmed by high-resolution transmission electron microscopy. Annealing in the forming gas (450°C) ...