Preparation of Pb-Bi film by alloy evaporation II. Microstructure and morphology

Abstract

In a previous paper, techniques were developed to obtain hexagonal-close-packed (27–32 wt.% Bi) Pb-Bi alloy films by evaporating from an alloy source. For the work reported here, Pb-Bi films were prepared under various evaporation rates, substrate temperatures, and residual gas pressures with a goal to obtain smooth and fine-grained films. Contrary to what is generally expected, the grain size, as measured at room temperature after sample warm up, increased by a factor of 3 to 5 when the substrate temperature Ts was lowered from 273 to — 180 K and below. Evidence to be presented suggests that although fine grains were obtained at low Ts, significant grain growth had occurred when the films were warmed from Ts< 200 K to room temperature. Grain sizes of Pb-Bi films prepared at 77 K were reduced when the films were doped with H20 during deposition or seeded with 5–10 nm thick layers of Pb-Bi or 02-doped Pb. But no grain size reduction was observed for films doped with 02 at 77 K or seeded with Au or Pd at 273 K. The dependence of film morphology on composition, deposition rate, and substrate temperature were also investigated. For fine-grained Pb-Bi films prepared as described above, hillocks and/or holes were typically observed. © 1983, American Vacuum Society. All rights reserved.