Synthesis of sputtered thin films in low energy ion beams

Magnetron sputtering is a process which gives a highly energetic depositing species. The growing film can be further bombarded with ions of the heavy gas used for sputtering by directing a plasma of it onto the surface. This can be done quite simply by using an unbalanced magnetron. The immersion of an insulating or isolated substrate-film combination in this plasma leads to a self-bias of around 30 V appearing on it's surface and a bombardment of low energy ions of the sputtering gas of several milli-amps per square centimetre. If the residual gas contains a reactive component, to form a compound film, then the gas is made much more reactive and less is needed to form the stoichiometric film. This can take place in a continuously operating system made stable using partial pressure control of the reactive gas with plasma emission monitoring or something similar. It can also be operated when the process of deposition is separated in time from the process of reaction and is repeated to build the film. We have called this process successive-plasma-anodisation (SPA) and it can be achieved by mechanically transferring the substrate between two magnetrons, one to deposit the metal film and one, which is unbalanced, to provide an oxygen plasma. It can also be operated by pulsing the reactive gas under carefully controlled conditions. Examples are given of the synthesis of compound films using low energy ion bombardment with these techniques and it is demonstrated that excellent films of a large range of oxides and nitrides can be made.