Ion bombardment during the deposition of a thin film has been observed to modify strongly some of the properties of the thin film. This paper examines the effects of low energy ion beam bombardment during the deposition of a thin film by either sputtering or evaporation. The ion bombardment can cause physical changes in the film, such as a change in the grain size, the degree or direction of orientation, the film density and number of voids, the film stress, and other related properties such as the electrical resistivity, the dielectric constant, and the stability of the film. Chemical changes can also be induced, such as the formation of compounds or the incorporation of gas into the film. The understanding of these phenomena is at an early stage. Models have been presented which examine such features as the change in density and void structure, or the changes in stress and resistivity. © 1988.