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 Å and 70 Å grown at 800° C to 1000° C, the existence of a dense ( ∼2.4 g/cm3), thin (∼10 Å) layer at the S i O 2/S i interface has been revealed. The thickness of the interfacial layer decreases with increasing oxidation temperature. Oxides grown in O3 or HCl/O2 have a thinner interfacial layer compared to those grown in O2.