High-density layer at the SiO2/Si interface observed by difference x-ray reflectivity

We have developed a high-accuracy difference X-ray reflectivity (DXR) method using intense synchrotron radiation for the evaluation of ultrathin thermal oxides on Si(100). By carefully analyzing DXR data for gate oxides with thicknesses of 40 Angstrom and 70 Angstrom grown at 800 degrees C to 1000 degrees C, the existence of a dense (similar to 2.4 g/cm(3)), thin (similar to 10 Angstrom) layer at the SiO2/Si interface has been revealed. The thickness of the interfacial layer decreases with increasing oxidation temperature. Oxides grown in O-3 or HCl/O-2 have a thinner interfacial layer compared to those grown in O-2.