Diffusion mediated film growth on polycrystalline substrates

Mechanisms of island formation and growth are central issues in thin-film d eposition. The shape and size as well as the spatial distribution of stable islands in the first phases of growth determine a wide variety of film pro perties. In an earlier work, the growth mode of sputter-deposited tin (Sn) and lead (Pb) films on polycrystalline Al substrates was analyzed in the fr amework of the rate-equation theory. This analysis yielded Stranski-Krastan ov growth with the size of the critical nucleus in the range from 6 to 20 m onomers. The present study is devoted to a detailed experimental investigat ion of the mechanisms involved in the formation of Sn and Pb islands on pol ycrystalline aluminum (Al). All thin-film systems treated in this work were deposited on glass substrates by DC magnetron sputtering. They consist of a polycrystalline Al underlayer covered with a 100 Angstrom thick Sn or Pb films. The variation of the mean Sn and Pb island distance was determined a s a function of the deposition temperature and of the underlayer thickness. It varied from 0.5 to 20 mu m and showed an Arrhenius dependence on the de position temperature. A rate-equation analysis yielded activation energies for surface diffusion of single Sn and Pb atoms of approximately 0.5 eV. Is land size distributions (ISDs) were determined for different deposition tem peratures and were mostly found to be monomodal with a global maximum at th e mean island size. All these facts indicate that the mechanism of island f ormation is mediated by surface diffusion of the Sn or Pb monomers on the A l surface in a wide range of deposition temperatures. (C) 2000 Elsevier Sci ence B.V. All rights reserved.