Probing the thermal decomposition behaviors of ultrathinHfO2 films by an in situ high temperature scanning tunneling microscope

Abstract

The thermal decomposition of ultrathinHfO2 films(∼0.6–1.2 nm) on Si by ultrahigh vacuum annealing (25–800 °C) is investigated in situ in real time by scanning tunneling microscopy. Twodistinct thickness-dependent decomposition behaviors are observed. When theHfO2 thicknessis ∼ 0.6 nm, no discernible morphological changes are found below ∼ 700 °C. Then an abruptreaction occurs at 750 °C with crystalline hafnium silicide nanostructures formed instantaneously.However, when the thickness is about 1.2 nm, the decomposition proceedsgradually with the creation and growth of two-dimensional voids at800 °C. The observed thickness-dependent behavior is closely related to the SiO desorption, whichis believed to be the rate-limiting step of the decomposition process.