Al surface mobility on Si(111) during initial stages of ionized cluster beam deposition

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Abstract
Al thin films were deposited from an ionized cluster beam onto Si(111) through a 50×1000-μm slot in a stainless-steel mask. The films were deposited under UHV conditions. The substrate temperatures were held at 50, 200, and 400 °C. The acceleration voltage applied to the beam was either 0 or 3 kV. Auger electron line scans across the Al strips were used to determine the distance Al atoms diffused along the surface under the mask in a direction normal to the slot. It was found that for a 0-kV beam (no ionization), Al atoms diffused 17 μm at 50 °C, 28 μm at 200 °C, and 12 μm at 400 °C. With a 3-kV beam, Al diffused 13 μm at 50 °C, 12 μm at 200 °C, and 12 μm at 400 °C. The film structures, as seen by scanning electron microscopy micrographs and by reflection medium-energy electron diffraction were similar for 50 and 200 °C substrates at 0 and 3 kV. However, for 400 °C substrates the film structures were significantly different for 0- and 3-kV beams. The Si(111) substrates were cut 4° off axis. Oriented platelets were formed by 3-kV beams on 200 and 400 °C substrates. The long axes of these platelets followed the direction of ledges, i.e., the [112] direction, probably because of anisotropic surface diffusion.

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