Dose effects of cathodoluminescence in SiO₂ layers on Si

Cathodoluminescence (CL) of thermal SiO₂ layers is performed in a digital scanning electron microscope (SEM) and wavelength dispersed registered by a CCD-camera. The CL-spectrum of SiO₂ shows three characteristic bands at 650 nm (red), 460 nm (blue) and 285 nm (UV) that all change their intensity during the time of electron bombardment. This different excitation dose behaviour of the luminescence bands was investigated in a wide range of current densities (10^-5-10^-3 A cm^-2) and temperatures (90-500 K). Some interpretation is made by a model of precursor transformation and quenching. The UV and blue luminescence is attributed to twofold-coordinated silicon in SiO₂. Contrary to thermal SiO₂ films TEOS-CVD SiO₂ shows only the red band which is generally associated with non-bridging oxygen.