Direct heteroepitaxy of crystalline Y2O3 on Si (001) for high-k gate dielectric applications

This work focuses on the microstructural characteristics of Y2O3 thin films and interfaces, which is related to their suitability as high-k replacement for SiO2 gate dielectrics in future transistor devices. The films were grown directly on silicon (001) substrates by electron-beam evaporation in a molecular beam epitaxy chamber under ultrahigh vacuum conditions. At an optimum growth temperature, ∼450 °C, high crystalline quality films were obtained, albeit with a heteroepitaxial relationship Y2O3 (110)//Si (001) and Y2O3 [001]//Si 〈110〉, which favors the formation of a potentially harmful complex microstructure. The latter consists of large (submicron-sized) domains containing smaller (10–30 nm) inclusions with perpendicular crystal orientations. Despite predictions for thermodynamic stability and low O2 partial pressure in the chamber, the chemical reaction of Y2O3 with Si could not be avoided. Indeed, a nonuniform interfacial amorphous layer with thickness 5–15 Å was observed, while YSi2 was formed at a moderate growth temperature (610 °C).