Particle Bombardment Effects in Thin Film Deposition

Abstract

The properties of thin films are greatly affected by energetic particle bombardment during deposition. By its input of energy, particle bombardment creates a deposition environment somewhat similar to an elevated substrate temperature, but there are distinct features which make bombardment itself an important control parameter. This article reviews the flux and energy range of bombarding particles in thin film deposition, and relates their effects to those of substrate temperature. It is based on a lecture presented at the 1988 NATO Advanced Study Institute on Plasma-Surface Interaction and Processing of Materials. Wherever possible, the essential information is given in quantitative relationships and practical units, so that the reader may estimate the relative importance of each bombardment process. First, the vacuum environment is briefly described, followed by a summary of the sources of particle bombardment in sputtered film growth. Next, the material transfer processes are described at the sputtering cathode (target), at the growing film surface (substrate), and in the space between. After this review of basic phenomena, the general effects of substrate temperature and of particle bombardment on thin film properties are summarized. Then a series of examples is presented, to demonstrate the effects of temperature and bombardment on an increasingly complex series of materials. A single element (tungsten) is used as the first example, followed by metal alloys (Al-Cu, Gd-Co), compounds (A1N, TiN, Hf3N4), and multiple-phase materials (In-O, Y-Ba-Cu-O). The object is to introduce more complicated effects of ion bombardment with more complicated examples, keeping in mind that the simple effects are present in all cases.