Abstract: An improvement in an apparatus having an external casing defining a processing chamber for deposition of a film on a substrate and an opening in the processing chamber through which a substrate is introduced for deposition is described. The improvement comprises an internal casing member moveably mounted within the processing chamber for movement between a first position which allows deposition onto the substrate to occur and a second position at which the casing is in sealing engagement with the opening to form an isolation chamber within the processing chamber and effective to isolate the substrate from processing chamber. The invention also includes a method for reducing cross-contamination between processing chambers in such an apparatus and a method for reducing particulate contamination to media prepared in such a deposition apparatus.