Application of a metal oxide as a gate dielectric for Si CMOS
requires an understanding of the materials reactions that occur with
thermal processing. A number of metal oxides have been examined for
use as a gate dielectric, with varying degrees of reactivity.
Reactions between Y and La oxides and SiO2 are facile, forming
interfacial silicates that can extend many nanometers. For the case of
Y2O3, this reaction can completely consume an SiO2 or SiOxNy buffer
layer, resulting in a silicate/Si(001) interface with no interfacial
layer detectable by medium energy ion scattering (MEIS). In contrast,
Zr and Hf oxides tend to remain unmixed with SiO2, due to the marginal
stability of the silicates. We will report MEIS results for gate
dielectric stacks, using in situ processing to illustrate the
materials reactions that are commonly encountered.