IRRADIATION-INDUCED DECOMPOSITION OF AL2O3 DURING AUGER-ELECTRON SPECTROSCOPY ANALYSIS

The effect of electron fluence on the decomposition of sapphire (Al2O3 ) was studied in situ by Auger electron spectroscopy (AES). The decomp osition was primarily detected by monitoring the evolution of the low kinetic energy Auger transitions of aluminum in Al2O3 (54 eV) and in m etallic aluminum (68 eV). The decomposition of sputter-cleaned sapphir e started at a fluence of similar to 4.9 x 10(19) electrons/cm(2) (7.8 C/cm(2)). This fluence was independent of the electron fluxes used in this work, except the lowest, which indicates that heating due to ele ctron bombardment does not significantly affect the decomposition beha vior. Electron-induced decomposition takes place in a minimum of the f irst five atomic layers of the substrate, as revealed by the evolution during irradiation of the high energy Al peaks associated with Al2O3 (1388 eV) and metallic aluminum (1396 eV). Comparison of the evolution of low and high kinetic energy Auger transitions demonstrates that th e decomposition kinetics are much faster for the first monolayer than for the subjacent atomic layers. The surface condition strongly influe nces the decomposition kinetics. Thus, a carbon layer adsorbed at the alumina surface significantly increases the threshold dose for decompo sition. The carbon layer most probably acts as a diffusion barrier for the oxygen produced during decomposition. An equation for the decompo sition rate of the first monolayer of alumina is established. The inte gral of this equation gives a good fitting to the experimental data. I t is found that the Auger signal of aluminum from sapphire does not di sappear even if the entire region has been decomposed. This effect is due to backscattered electrons that promote Auger electron excitations outside the irradiated region. (C) 1996 American Vacuum Society.