Anisotropic surface mobility of aluminum on Si(111) during the initial stage of vapor deposition

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Abstract
Scanning Auger electron microprobe line scan analysis was used to determine the surface mobility of Al atoms on Si(111) substrates cut 4° off axis in the [11̄0] direction. These substrates are expected to have clusters of one atomic layer steps oriented normal to the [11̄0] direction. The Al films, ∼6 nm thick, were deposited from an ionized cluster beam source through a 50×1000 μm slot in a stainless-steel mask. The slot was oriented with its long axis in the [11̄2̄] direction, i.e., normal to the [11̄0]. The Auger line scans show that the surface mobility of Al is anisotropic. Furthermore, the anisotropy changes as the acceleration voltage increases from 0 to 3 kV and as the substrate temperature increases from 50 to 400° C. This anisotropy can be explained by the higher probability of Al atoms to be absorbed or reflected at steps in the ascending direction. In the descending direction, the passage of Al atoms over steps is facilitated by higher thermal energies provided by increased substrate temperature or by ion acceleration. However, increased evaporation of Al at high temperatures results in a decrease in diffusion distance above 200 °C.

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