Electronic devices are formed on a substrate that is advanced stepwise through a plurality of deposition vessels. Each deposition vessel includes a source of deposition material and has at least two shadow masks associated therewith. Each of the two masks is alternately positioned within the corresponding deposition vessel for patterning the deposition material onto the substrate through apertures in the mask positioned therein, and positioned in an adjacent cleaning vessel for mask cleaning. The patterning onto the substrate and the cleaning of at least one of the masks are performed concurrently.