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 replacemen t for SiO2 gate dielectrics in future transistor devices. The films were gr own directly on silicon (001) substrates by electron-beam evaporation in a molecular beam epitaxy chamber under ultrahigh vacuum conditions. At an opt imum growth temperature, similar to 450 degreesC, 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 poten tially harmful complex microstructure. The latter consists of large (submic ron-sized) domains containing smaller (10-30 nm) inclusions with perpendicu lar crystal orientations. Despite predictions for thermodynamic stability a nd low O-2 partial pressure in the chamber, the chemical reaction of Y2O3 w ith Si could not be avoided. Indeed, a nonuniform interfacial amorphous lay er with thickness 5-15 Angstrom was observed, while YSi2 was formed at a mo derate growth temperature (610 degreesC). (C) 2001 American Institute of Ph ysics.