Structural relaxation of SiO2/Si interfacial layer during annealing

We have studied the structural evolution of the high density interfacial layer around 10 Angstrom thick in 40 Angstrom thermal oxide observed by difference X-ray reflectivity (DXR) techniques during thermal annealing. Effects of interfacial stress are evaluated by grazing incidence X-ray diffraction. As the annealing proceeds, density of the interfacial layer decreased and got close to the value of the upper SiO2 layer after 2 h of annealing in Ar at 800 degrees C. At the same time, a slight increase in the thickness of the interfacial layer and the flattening of the Si interface are observed. These results indicate that during annealing, both the structural relaxation of oxide in the direction normal to the interface and an atomic rearrangement at the Si interface proceeds. Elastic deformation by stress can not be the dominant origin of the density change. The observed decrease of the interface state density D-it alone annealing may be linked to the decrease of structural defects accompanied with the structural relaxation at the interface.