Optical absorption in ultrathin silicon oxide film

The reflectance spectra of ultrathin thermally grown silicon oxide films with thicknesses in the range from 6 to 18 nm were measured for the first time in vacuum ultraviolet using synchrotron orbital radiation. From the Kramers-Kronig analysis of these reflectance considering the multiple reflection in the oxide film, it has been found that the optical absorption in silicon oxide films below nearly 9 eV, which is the fundamental optical absorption edge of fused quartz, becomes appreciable with decreasing oxide film thickness or oxidation temperature.