Thermodynamic considerations in the stability of binary oxides for alternative gate dielectrics in complementary metal–oxide–semiconductors

Abstract

A number of binary oxides have been predicted to be thermodynamically stable in contact with Si and are candidates to replace SiO2 in complementary metal–oxide–semiconductors. However, reactions leading to the formation of interfacial silicide, silicate, or SiO2 layers have been reported when these oxides are exposed to high temperatures during device processing. Different pathways have been proposed in the literature to explain these reactions. In this article, a thermodynamic analysis of the proposed reactions is performed. The analysis includes gaseous species, because typical gate dielectrics are ultrathin layers and diffusivities for species from the surrounding atmosphere, such as oxygen, may be high. Furthermore, nonstoichiometry of the high-k oxide, as may be resulting from nonequilibrium deposition processes or reducing atmospheres during processing is also considered. Studies are proposed to distinguish between possible reaction mechanisms. Finally guidelines for stable interfaces are presented.