Thermal instability and silicidation of ultrathin HfO2x on Si(001)

Abstract

The thermal instability and silicidation behaviors of ultrathin HfOx on Si(001) were studied by using scanning tunneling microscopy (STM) with in-situ X-ray photoelectron spectroscopy (XPS). A 1.5-nm-thick HfOx layer was grown on Si(001) by using Hf deposition in an oxidizing ambient. In the low temperature (600 similar to 800 degreesC) region, hafnium oxide near the interface region easily reacted with the substrate silicon ions in order to form a silicate structure (Hf-O-Si bonding units). When the SiO evaporation proceeded in the high-temperature (greater than or equal to 900 degreesC) region, silicon migration from the substrate became kinctically remarkable and transformed the Hf-O-Si units into Hf- Si bonds with some remnant Si-O bonds. In contrast with the multi-phase feature of crystalline HfSi2 that has been reported to occur by annealing hafnium metal on ultrathin SiO2, our STM study reveals the formation of "irregularly shaped" silicides upon silicidation. These silicides contain some oxygen in the form of Si-O bonds, so they exhibit a, slightly insulating behavior in the spectroscope mode of STM.