Atomic transport and stability during annealing of HfO2 and HfAlO with an ultrathin layer of SiO2 on Si(001)

Abstract

A medium-energy ion scattering spectroscopy study has been carried out on HfO2/SiO2/Si and HfAlO/SiO2/Si stacks with 5-nm-thick dielectric layers prepared by atomic layer chemical vapor deposition at 300 °C. We observed that there are negligible interface strain and surface silicon for the as-deposited sample. After annealing in nitrogen, the crystallization of HfO2 started to occur between 500 °C and 600 °C. As the annealing temperature increased, a silicate layer is formed at the top of the HfO2 film. However, the HfAlO film with about 25% Al did not exhibit surface silicon and crystallization. Adding Al2O3 to HfO2 can suppress the existence of surface Si but can build up compressive strain at the oxide/Si interface layer. After annealing, excess Si that is prone to move may displace Al in order to relax the interface strain. On the other hand, HfAlO film exhibits much stronger resistance to oxygen diffusion than HfO2 and tends toward densification during N2 annealing.