ELECTRON-EMISSION FROM ION-BOMBARDED SIO2 THIN-FILMS

The electron yield from SiO2 films on Si was measured as a function of oxide thickness and ion energy for 150-300 keV H+, He+, N+, Ne+, Ar+, Kr+, and Xe+ ions. For oxide films thicker than 200 Angstrom, the electron yield was found to be approximately independent of oxide thickness. The electron yield from the thick oxide increased as a function of the energy deposited D in electronic excitations with approximately the form D-0.65 and not D as expected from theory. Close to the SiO2/Si interface, unexpected variations in the electron yield with oxide thickness, dependent on ion mass and energy, were found. Experiments were performed to investigate whether or not the oxide surface was charged by the ion beam, but such effects could not be observed. However, a satisfactory interpretation of the data could be obtained with a model previously suggested for explaining the dependence of the electron yield on the angle of ion incidence. In this model, the positive charge left behind in the oxide by the liberated electrons within the electron cascades of individual ions, causes the probability of escape of electrons to decrease with increasing electron yield.