Diffusion and interface growth in hafnium oxide and silicate ultrathin films on Si(001)

Medium energy ion scattering has been used in combination with ¹⁶O and ¹⁸O isotope tracing to determine elemental depth distributions and elucidate oxygen transport in 2--5 nm thick HfO₂ and HfSiOₓ films grown by atomic layer deposition on Si(001). Both the oxygen isotope exchange rate in the dielectric as well as the interfacial silicon oxide growth rates were examined as a function of time, temperature, film stoichiometry (HfO₂, HfSiOₓ, and HfSiOₓNy), and crystallinity. The amount of exchanged oxygen in the oxide was found to decrease with increasing SiO₂ content. When the SiO₂ to HfO₂ ratio reaches 1:1 in HfSiOₓ an almost full suppression of the oxygen exchange is observed. The activation barrier for the SiO₂ growth at the HfO₂/Si and HfSiOₓ/Si interfaces was found to be much lower than that in the SiO₂/Si and SiOₓNy/Si cases, which is attributed to distinctly different oxygen incorporation mechanisms. The primary route for oxygen delivery to the interface responsible for the SiO₂ growth is via exchange, however, direct oxidation by molecular oxygen cannot be discounted completely. In the presence of an interfacial nitride layer the ¹⁸O-¹⁶O exchange is replaced by the ¹⁸O-N exchange, which slows diffusion and reduces the oxidation rate.