Interfacial structure and electrical properties of ultrathin HfO2 dielectric films on Si substrates by surface sol–gel method

Abstract

Ultrathin HfO2 films with about ∼3 nm thickness were deposited on n-type (1 0 0) silicon substrates using hafnium chloride (HfCl4) source by the surface sol–gel method and post-deposition annealing (PDA). The interfacial structure and electrical properties of ultrathin HfO2 films were investigated. The HfO2 films show amorphous structures and smooth surface morphologies with a very thin interfacial oxide layer of ∼0.5 nm and small surface roughness (∼0.45 nm). The 500 °C PDA treatment forms stronger Hf–O bonds, leading to passivated traps, and the interfacial layer is mainly Hf silicate (HfxSiyOz). Equivalent oxide thickness of around 0.84 nm of HfO2/Si has been obtained with a leakage current density of 0.7 A cm−2 at Vfb + 1 V after 500 °C PDA. It was found that the current conduction mechanism of HfO2/Si varied from Schottky–Richardson emission to Fowler–Nordheim tunnelling at an applied higher positive voltage due to the activated partial traps remaining in the ultrathin HfO2 films.