Plasma diagnostics in ion-assisted physical vapour deposition systems

Commonly used techniques in ion assisted physical vapour deposition systems include ion plating, activated evaporation, bias sputtering and other processes. Various plasma enhancement systems are frequently employed. In these processes, vapour deposition occurs in a gas discharge plasma and the substrate is simultaneously bombarded with energetic particles usually as a result of applied or self-induced bias. In such an environment complex interactions between discharge parameters make prediction and control of film properties difficult and usually the subject of much trial and error. In many cases altering the deposition rate itself leads to modification of plasma properties. In an attempt to isolate some of these interacting factors, a study is currently being made of plasma properties in an rf excited ion plating system. Measurements of dc bias, floating potential, plasma density and electron temperature have been made using a shielded Langmuir probe. The effect of the electron beam source power level and other parameters of the discharge on these measurements is demonstrated. It is shown that beyond a critical value of source power (and hence evaporation rate), a sharp increase in electron temperature and plasma density occurs which is related to the production of a critical vapour density over the surface of the melt. These results are of importance to an understanding of the interactions between the plasma and the growing film on the substrate and will assist in the prediction of the properties of thin films made by these methods. (author)