Aluminum surface mobility on silicon nitride and on several silicon oxides

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Abstract
This report concerns the measurement of Al atom surface mobility on various substrates during physical vapor and neutral cluster deposition. One objective is to determine Al surface mobility dependence on substrate type and temperature. Another objective is to compare Al diffusion distances produced by an effusive source and a cluster beam source. The experiment is done with a simple wire mask held on the substrates during Al deposition. During deposition, the substrates were held at constant temperatures between 80 and 400 °C. After the wire is removed, the shadowed areas are examined by optical and electron microscopy, mechanical profilometer, and Auger electron line scans. Measurements show that Al diffusion distances in the shadow zones are between 8 and 16 μm on oxidized Si films on Si substrates. The diffusion distance of Al on silicon nitride ranges from 20 to 25 μm. The diffusion distances of Al on all substrates can be understood in terms of the mean diffusion distance X=(2Dsτs)1/2, where Ds is the surface diffusion coefficient and τs is the mean time to desorption after Al atoms are deposited. These results show that on the micrometer scale the diffusion distance of Al atoms, while temperature and substrate dependent, is independent of the deposition method.

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