Thermal desorption of oxides on Si(100): A case study for the scanning photoelectron microscope at MAX-LAB

A scanning photoelectron microscope, utilizing a focused beam of monochromatized photons in the energy range from 15 to 150 eV, has been used to study the thermal desorption of oxide layers on Si(100). The instrument can provide high-resolution photoelectron spectra from selected parts of the surface as well as images showing the lateral distribution (on a micrometer scale) of elements in different chemical states by monitoring the photoemission intensity of chemically shifted core levels. Both native (10-15 Angstrom) and thick (200-400 Angstrom) oxides have been studied. The desorption (at 840 degrees C) of the native oxide proceeds through a phase of irregular (on a micrometer scale) and diminishing areas of dioxide until a clean surface is obtained. For the thick oxide, annealing to 1100 degrees C creates circular voids in the oxide layer which grow linearly in diameter with annealing time. The surface in these voids mainly consists of clean silicon but a small amount of remaining SiO2 is observed. This remaining dioxide most probably consists of small clusters or particles. For both types of oxide, we find, during and after desorption, a surface-shifted component in the Si 2p core level spectra indicating that at least parts of the surface have an ordered structure which most probably is a 2 x 1 reconstruction. (C) 1997 Elsevier Science B.V.