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

Abstract

This work focuses on the microstructural characteristics of Y 2 O 3 thin films and interfaces, which is related to their suitability as high-k replacement for SiO 2 gate dielectrics in future transistordevices. 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 Y 2 O 3 (110)//Si (001) and Y 2 O 3 [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 O 2 partial pressure in the chamber, the chemical reaction of Y 2 O 3 with Si could not be avoided. Indeed, a nonuniform interfacial amorphous layer with thickness 5–15 Å was observed, while YSi 2 was formed at a moderate growth temperature (610 °C).