X-RAY ABSORPTION NEAR EDGE STRUCTURES OF INTERMEDIATE OXIDATION-STATES OF SILICON IN SILICON-OXIDES DURING THERMAL-DESORPTION

X-ray absorption near edge structure (XANES) spectra are measured from silicon oxides using a photoemission microscope. Native oxide overlayers on Si (100) and Si(111) crystals are studied at various stages of the thermal desorption process. Because of the very high energy resolution inherent in the microscope, we are able to resolve for the first time the spin-orbit splitting of the core exciton structure in SiO2. The spectroscopic signature of this transition is unique, and it has enabled us to identify the core exciton XANES structures of two intermediate oxidation states of silicon (Si2+ andSi3+). We have found the Si2+ and Si3+ states existing at the Si SiO2 interface. We have also found, for the first time, that Si2+ can exist independently on the silicon surface apart from any SiO2. © 1990, American Vacuum Society. All rights reserved.