Micromechanical structures are used to investigate the effects of electron- and ion-beam irradiation on silicon dioxide. The devices are simple cantilever beams (50 μm long) fabricated from different types of silicon dioxide and integrated with two parallel driving electrodes. The electrically floating silicon dioxide beams oscillate only under electron-beam irradiation with an ac voltage applied to the driving electrodes at resonance. Accumulated charge produced by electron-beam irradiation in a scanning electron microscope (SEM) produces a driving force between the cantilever beam and the driving electrode. A time-resolved SEM technique is used to determine the resonant frequencies of these micro-cantilever beams. Electron- and ion-beam damage is measured by detecting the shift in the resonant frequency as a function of the irradiation time (electron-beam dose or sputtering time). Experimental results show that the resonant frequency of the silicon dioxide cantilever beam increases under electron-beam irradiation; this frequency rise indicates that material hardening or mass loss or both occur when the cantilever is subjected to electron-beam irradiation. We also observed differences in the rate of change of the frequency shift between thermally grown silicon dioxide films and plasma enhanced chemical vapor deposition silicon dioxide films. Under argon sputtering, the resonant frequency of the silicon dioxide cantilever beam decreases due to the change in the dimensions and mass of the cantilever beam caused by sputtering.
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Ogo et al. (1994) studied this question.