An ionized cluster beam (ICB) source was used to deposit Al onto SiO2 substrates. A 60 gtm diameter wire held at the substrate served as a mask. After Al deposition, the wire was removed and the masked area was examined by scanning electron microscopy (SEM) and by scanning Auger microprobe (SAM). The ICB source was operated at 0, 3, and 6 kV acceleration voltages. The substrate was held at 80°, 200°, and 400°C during Al depositions. The Al deposition rate averaged 240 A per min. The chamber pressure during deposition was 2×10-6 Torr. The diffusion distance of Al under the mask edge was determined from the SEM micrographs and SAM line scans. The maximum diffusion distance for all acceleration voltages occured at a substate temperature of 200°C. The maximum diffusion distance at 200°C was 29 μm at 6 kV acceleration voltage. The minimum diffusion distance was 12 μm at 400°C for an acceleration voltage of 6 kV.