Fabrication and electrical characteristics of ultrathin (HfO2)x(SiO2)1−x films by surface sol–gel method and reaction-anneal treatment

Hafnium oxide (HfO2) films were deposited on Si substrates with a pre-grown oxide layer using hafnium chloride (HfCl4) source by surface sol–gel process, then ultrathin (HfO2)x(SiO2)1−x films were fabricated due to the reaction of SiO2 layer with HfO2 under the appropriate reaction-anneal treatment. The observation of high-resolution transmission electron microscopy indicates that the ultrathin films show amorphous nature. X-ray photoelectron spectroscopy analyses reveal that surface sol–gel derived ultrathin films are Hf–Si–O alloy instead of HfO2 and pre-grown SiO2 layer, and the composition was Hf0.52Si0.48O2 under 500 °C reaction-anneal. The lowest equivalent oxide thickness (EOT) value of 0.9 nm of film annealed at 500 °C has been obtained with small flatband voltage of −0.31 V. The experimental results indicate that a simple and feasible solution route to fabricate (HfO2)x(SiO2)1−x composite films has been developed by means of combination of surface sol–gel and reaction-anneal treatment.