Thermal stability of advanced gate stacks consisting of a Ru electrode and Hf-based gate dielectrics for CMOS technology

Metallic Ru and Hf-based dielectrics such as HfO2, HfSiOx and HfSiON, are promising materials for the gate electrode and gate dielectrics, respectively. This paper reports on the thermal stability of gate stack systems comprised of Ru/Hf-based dielectrics. Layers of both types of material were prepared on Si substrate by metal-organic chemical vapour deposition (MOCVD). The stacks underwent exposure by rapid thermal annealing (RTA) in pure nitrogen ambience at temperatures 800, 900, and 1000 °C for 10 s. The samples were analysed using Rutherford backscattering spectrometry (RBS). Small changes were found in the stacks treated at 800 and 900 °C. The most stable stack was found to be one with a HfSiON dielectric layer, which was resistant also at temperature 900 °C. However, the annealing at 1000 °C induced massive diffusion at both interfaces for all types of stack. The results imply a limited thermal stability of the Ru/Hf-based dielectric gate stacks during the source/drain activation step.