The Effects of Low Energy Ion Bombardment on the Growth of Thin Films: Model and Experiment

Low energy ion bombardment during the physical vapor deposition of thin films can modify film properties by varying the bombardment energy and current. Current industrial uses of ion assisted deposition (IAD) include densification of conducting and nonconducting films at low deposition temperatures for use as optical coatings. Future industrial applications may include filling of high aspect ratio vias for packaging applications. Thus, it is important to better understand the role ion bombardment plays in modifying thin film properties and thus gain insight into which ion energies are appropriate to certain classes of materials. In order to improve this understanding, the ion -solid interaction is studied microscopically with an emphasis estimating the time scale of the surface effect and on calculating post-bombardment surface effects. Arguments will be presented to show that ion bombardment of solids, can, under the proper circumstances, produce a fluid-like region in the solid. For the Noble metals, Al, and Mg, heat conduction out of the fluid-like region will be shown to be dominated by phonons. For these metals, the lifetimes of the fluid-like region and corresponding surface transient are shown to be larger than 10 and 100 ps, significantly longer than previously thought. Predictions of the existence of an optimum ion energy are made and are compared to experimental studies of the resistivities of the Ag^+/Ag, Al^+/Al, and Cu^+ /Cu systems. Methods for dynamic calculations of surface desorption and diffusion are also presented. The predictions of the model will be seen to robust for physically realistic variations of the model assumptions and initial conditions. Another aim of this thesis is to show that the type of IAD used in this thesis, the partially ionized beam technique, can control the microstructure of polycrystalline thin films. The microstructure of the films is shown to have important effects on the film resistivity and diffusion barrier properties. The x-ray fiber texture and Bragg -Bretano 2theta techniques are used to characterize the microstructure.