Influence of Electric Field on the Growth of Thin Metal Films

It has been found that an electric field applied in the plane of a metal film during deposition induces coalescence of the three-dimensional island-like structure at an earlier stage of the film growth than is obtained without the field. The surface area of the three dimensional islands is increased under applied electric field. The critical thickness, at which the electrically continuous film is obtained, decreases with the increase of electric field. The decrease is more rapid at higher substrate temperatures. Enhanced orientation effects and fewer structural defects have been observed in films deposited under applied field and are attributed to the recrystallization during induced coalescence. The observed short range order in the coalescence pattern indicates that the applied field transfers and redistributes the electrostatic charges on the islands. It is shown that the presence of a small number of electrostatic charges increases the surface energy and thus the surface area considerably. The electrostatic forces between two islands which either come very close to each other or carry significantly different charges of either polarity are predominantly attractive and are of sufficient magnitude to account for the physical merger. Coalescence as well as breakup of metal islands due to the presence of electrostatic charges on them have been observed on suitably prepared single-crystal lead films irradiated with the imaging electron beam inside an electron microscope.