Fundamental understanding and modeling of reactive sputtering processes

Reactive sputtering is a commonly used process to fabricate compound thin film coatings on a wide variety of different substrates. The industrial applications request high rate deposition processes. To meet this demand, it is necessary to have very good process control of such processes. The deposition rate is extremely sensitive to the supply of the reactive gas. A too low supply of the reactive gas will cause high rate metallic sputtering, but may give rise to an understoichiometric composition of the deposited film. A too high supply of the reactive gas will allow for stoichiometric composition of the deposited film, but will cause poisoning of the target surface, which may reduce the deposition rate significantly. This behaviour points out that there may exist optimum processing conditions where both high rate and stoichiometric film composition may be obtained. The purpose of this article is to explain how different parameters affect the reactive sputtering process. A simple model for the reactive sputtering process is described. Based on this model, it is possible to predict the processing behaviour for many different ways of carrying out this process. It is also possible to use the results of the modeling work to scale processes from laboratory size to large industrial processes. The focus will be to obtain as simple a model that will still quite correctly describe most experimental findings. Despite some quite crude approximations, we believe that the model presented satisfies this criterion. (c) 2004 Elsevier B.V. All rights reserved.