XPS study on the effects of thermal annealing on CeO₂/La₂O₃ stacked gate dielectrics

Effects of thermal annealing on the interface reactions and the bonding structures of several CeO₂/La₂O₃ stacked dielectrics were studied in detail based on x-ray photoelectron spectroscopy (XPS) measurements. Results indicated that the high-temperature annealing can enhance O, Ce, La, and Si diffusion and result in the intermixing of CeO₂/La₂O₃ stack, growth of interfacial silicates layer at the La₂O₃/Si interface. A small amount of Ce³⁺ re-oxidation and significant interface oxidation were found for thermal annealing at 600 °C. Based on these observations, reactions taken place at both the CeO₂/La₂O₃ and La₂O₃/Si interfaces during thermal annealing are proposed. The growth of low-k interfacial layer undoubtedly brings a great challenge for achieving the smallest equivalent oxide thickness (EOT) with superior interface properties. This investigation provides some additional information for possible performance optimization of the high-k gate dielectrics in the subnanometer EOT era.