Mask data preparation (MDP) is the step that translates an intended set of polygons on an integrated circuit layout into a form that can be physically written by the photomask writer. Usually this involves fracturing complex polygons into simpler shapes, often rectangles and trapezoids, that can be written by the mask writing hardware. Therefore this step was sometimes called mask fracturing, which is now but a part of the MDP.
Typically a design is delivered to mask data preparation in GDSII or OASIS format, and after fracturing is written out in a proprietary format specific to the mask writer.
Although previously a simple translation task, the changes required for resolution enhancement technologies (RET) and optical proximity correction (OPC) steps associated with design for manufacturability considerations can create huge data volume problems for the mask writer, so some care must be applied to mitigate these negative effects.