(Received December 27, 2004; accepted April 11, 2005; published August 5, 2005)
The oxidation mechanism at the HfO2/Si interface is discussed by investigating oxidation kinetics on the basis of experimental results that were obtained using the technique of grazing incidence X-ray reflectivity (GIXR) in combination with spectroscopic ellipsometry (SE) measurements. In a relatively thick HfO2 region, the interface layer growth shows a logarithmic dependence on annealing time, while the activation energy of oxidation is very small compared with that of conventional oxidation. These results clearly indicate that the oxidation mechanism at the HfO2/Si interface is different from that at the Si surface. Moreover, it is also reported that the oxidation at the HfO2/Si interface has no surface orientation dependence, no HfO2 thickness dependence and a slight O2 pressure dependence. All of the results obtained in this work suggest that atomic oxygen is involved in the oxidation at the HfO2/Si interface and the diffusion of oxygen atoms in the interface layer limits oxidation rate in a relatively thick HfO2 region. On the other hand, in an ultra-thin HfO2 region, HfO2 thickness dependence and Si surface orientation dependence are observed. These results suggest that both atomic oxygen and molecular oxygen are involved in the interface oxidation in an ultra-thin HfO2 region. On the basis of the results, we propose a kinetic model for the oxidation associated with both atomic oxygen and molecular oxygen at the HfO2/Si interface.
KEYWORDS:HfO2, interface layer, Si oxidation, surface orientation, atomic oxygen