Growth of sputtered vs evaporated metal films

Abstract

The early growth stages of sputtered (S) vs evaporated (E) Ag/mica and Ag/NaCl films have been studied by transmission electron microscopy and electron diffraction. The observed maximum density of the islands at thicknesses less than 20 Å is slightly higher for S films, although the order of magnitude is the same (∼10¹¹/cm²) for both the S and E films. Electrostatic charges carried by the S atoms and the point defects caused by the penetration of the energetic S atoms could account for the observed higher S-island density. As the film thickness increases, the S-island density at 25°C decreases rapidly to reach a constant value before the film becomes continuous. The corresponding E-island density decreases slowly. The higher mobility, as indicated by the rate of change of the island density, and the observed epitaxial growth of the S films at a temperature considerably lower than that obtained for E films, are attributed to the higher kinetic energy of the S atoms. The E-island density decreases rapidly as the substrate temperature is increased. The decrease in S-island density is, however, accompanied by an increase in the surface area of the islands and formation of bridges between the islands, thereby resulting in coalescence at a smaller nominal thickness than is observed in E films. These observations are explained on the basis of the effects of higher electrostatic charges and kinetic energy of the S atoms. The activation energies for the diffusion processes, calculated from the temperature dependence of the separation between the islands, are 0.1 and 0.15 eV for S and E films, respectively, at substrate temperature below 250°C. Above 250°C, the activation energies increase rapidly to 0.5 and 0.9 eV, respectively.