Thermal stability and structural characteristics of HfO2 films on Si (100) grown by atomic-layer deposition

The thermal stability and structural characteristics for gate stack structure of ${\mathrm{HfO}}_2$ dielectrics deposited by atomic-layer deposition (ALD) were investigated. The structural characteristics and chemical state of the ${\mathrm{HfO}}_2$ films in relation to the film thickness and postannealing temperature were examined by x-ray diffraction and x-ray photoelectron spectroscopy. An interfacial layer of hafnium silicate with an amorphous structure was grown on the oxidized Si substrate at an initial growth stage. The structural characteristics of the ${\mathrm{HfO}}_2$ films are closely affected by the interfacial layer and are depended on the thickness of the films. The 45 Å thick ${\mathrm{HfO}}_2$ film with an amorphous structure was changed into a polycrystalline structure after rapid temperature annealing of 750 °C for 5 min, while thicker films were grown into a polycrystalline structure of monoclinic or tetragonal crystal structure. The silicate layer grown at the interfacial region is not stable even at 700 °C under ultrahigh vacuum condition and changes into the silicide layers.