Scanning Auger electron microprobe line scan analysis was used to determine the surface mobility of Al atoms on (111) Si substrates which were cut 4º off-axis in the [1¯10] direction. Such substrates were believed to have clusters of single atomic layer steps which were oriented normal to the [1¯10] direction. The Al films, which were about 6nm thick, were deposited from an ionized cluster beam source. The slot was oriented with its long axis in the [1¯1¯2] direction (normal to the [1¯10] direction). Auger line scans showed that the surface mobility of the Al was anisotropic, and that the anisotropy changed as the acceleration voltage was increased from 0 to 3kV and as the substrate temperature was increased from 50 to 400C (table 3). The anisotropy was attributed to a higher probability for Al atoms to be absorbed or reflected at steps in the ascending direction. In the descending direction, the passage of Al atoms over steps was facilitated by the higher thermal energies which were provided by an increased substrate temperature or ion acceleration. An increased evaporation of Al at high temperatures resulted in a decrease in diffusion distance above 200C.

Anisotropic Surface Mobility of Aluminum on Si(111) during the Initial Stage of Vapor Deposition. L.L.Levenson, H.Usui, I.Yamada, T.Takagi, A.B.Swartzlander: Journal of Vacuum Science and Technology A, 1989, 7[3], 1206-9

Table 3

Diffusion of Al on Si Surfaces [4º off (111)]

as a Function of Acceleration Voltage and Substrate Temperature