Effect of postdeposition annealing on the thermal stability and structural characteristics of sputtered HfO2 films on Si (1 0 0)

The thermal stability and structural characteristics for gate stack structure of HfO2 dielectrics grown by DC reactive magnetron sputtering were investigated. The structural characteristics and chemical states of the HfO2 films in relation to the postannealing temperature were examined by X-ray diffraction and X-ray photoelectron spectroscopy. XRD patterns demonstrate that the as-grown HfO2 films are amorphous and the structure of the annealed HfO2 films undergoes a transformation of tetragonal to monoclinic phase with increasing annealing temperature and forms a polycrystalline structure at high annealing temperature. Analysis of XPS of Hf4f and O1s gives evidence that the as-grown HfO2 film is nonstoichiometric. With increase of annealing temperature, both peaks of Hf4f and O1s keep on shifting towards lower binding energy, which indicates to be forming stoichiometric HfO2 film. Annealing the as-grown thin film at low temperature leads to the formation of silicate at the interfacial regime resulting from the reaction between the nonstoichiometric thin film and parts of SiOx formed at the interfacial regime, and the Si–O–Hf and Si–O bonds in the silicate and SiOx attributes greatly to the XPS O1s peaks. High temperature annealing process, the O-deficient HfO2 films will absorb oxygen atoms from the formed silicate interfacial layer and the oxygen ambient to form the fully oxidized HfO2 thin films.