Fabrication and electrical characteristics of ultrathin (HfO 2) x(SiO 2) 1−x films by surface sol–gel method and reaction-anneal treatment

Abstract

Hafnium oxide (HfO 2) films were deposited on Si substrates with a pre-grown oxide layer using hafnium chloride (HfCl 4) source by surface sol–gel process, then ultrathin (HfO 2) x (SiO 2) 1− x films were fabricated due to the reaction of SiO 2 layer with HfO 2 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 HfO 2 and pre-grown SiO 2 layer, and the composition was Hf 0.52Si 0.48O 2 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 (HfO 2) x (SiO 2) 1− x composite films has been developed by means of combination of surface sol–gel and reaction-anneal treatment.