ELECTRON-IRRADIATION-INDUCED CHANGES IN THE SURFACE-TOPOGRAPHY OF SILICON DIOXIDE

The irradiation of crystalline (alpha-SiO2) and amorphous (a-SiO2) sil icon dioxide with a stationary electron beam produces characteristic c hanges in the surface topography. The development of these changes has been investigated using cathodoluminescence spectroscopy and microsco py, scanning probe (atomic force) microscopy, and scanning electron mi croscopy. Electron irradiation produces a permanent volume increase on (crystalline) alpha-SiO2, while in (amorphous) a-SiO? an initial smal l volume increase is followed by volume loss as irradiation continues. The observed changes are consistent with electromigration of oxygen u nder the influence of the electric field induced by charge trapping at preexisting or irradiation-induced defects. Oxygen enrichment may pro duce expansion of the surface region due to the formation of peroxy li nkage defects. In a-SiO2, charges trapped by defects at grain boundari es produce enhanced electric fields which may result in volume reducti on at the surface, when critical field strengths are exceeded. The obs erved volume reductions may be attributed to electron stimulated desor ption of constituents, in particular oxygen mass loss, and densificati on of the surface region associated with the formation of oxygen-defic ient defect centers. (C) 1996 American Institute of Physics.