Atomic scale model interfaces between high-k hafnium silicates and silicon

Hafnium silicates (HfySi1-yO2) are being considered as high-k gate dielectrics in field-effect transistors as a compromise between high permittivity and thermal stability on silicon during complementary metal-oxide-semiconductor processing. Using hafnon (HfSiO4) as a prototypical hafnium silicate, we have explored model abrupt interfaces at the atomic scale, employing various hafnon surfaces on Si(100) and Si(110) via a silicon suboxide interfacial layer. Relative stabilities are computed using molecular dynamics and geometry optimization at the density-functional theory level. The immiscibility of HfO2 and SiO2 means that the interface is intrinsically metastable, so that we predict a poor-quality interface under oxygen-poor conditions. On the other hand, the interface is stabilized under oxidizing conditions, leading eventually to the growth of the interfacial layer into the Si substrate. We find evidence that Si(110) resists oxidation more than Si(100). Structural features such as Hf-O-Si and Si-O-Si bridges are found to be common to all defect-free interfaces under all conditions. 4 angstrom is the minimum thickness of the defect-free suboxide interfacial layer.