Thermal stability of TiO2, ZrO2, or HfO2 on Si(100) by photoelectron emission microscopy

Abstract

The thermal stability of thin films (3nm) of transition-metal (TM) oxides (TiO2, ZrO2, and HfO2) grown on ultrathin (∼0.5nm) SiO2 buffer layers on Si(100) surfaces was investigated with ultraviolet photoelectron emission microscopy (UV-PEEM). The decomposition of the TM oxides was observed in the PEEM during ultrahigh-vacuum annealing at temperatures of ∼870, ∼900, and ∼1000°C for the TiO2, ZrO2, and HfO2, respectively. Following the decomposition reaction, atomic force microscopy measurements of the annealed surfaces revealed a high density of islands in the decomposed regions. The degradation of the TM oxide films is attributed to a reaction occurring at defects at the TM oxide/SiO2∕Si interfaces, which forms SiO species. Once a portion of the interfacial SiO2 layer is desorbed as a result of this reaction, Si from the substrate can diffuse into contact with the TM oxide layer, resulting in the formation of a TM silicide and the evolution of SiO. This process continues until the entire TM oxide layer is consumed and only silicide islands remain.