Mask set
Beginner
The set of stencils used to print a chip’s patterns onto silicon. A new design needs a new set.
Novice
The photomasks, plates that each carry the pattern of one layer, that the factory uses to print a design onto wafers. A design needs at least one per patterned layer, and making the set is a large one-time cost that grows with each newer process.
Expert
Mask count rises with the number of layers and with multiple patterning (printing one layer in several exposures), so masks are a large part of the one-time cost at advanced processes. A fix confined to the upper metal wiring layers replaces only those masks, which is why designs scatter unused spare cells that a later wiring change can connect.