Photomask

A photomask (also simply called a mask) is an opaque plate with transparent areas that allow light to shine through in a defined pattern. Photomasks are commonly used in photolithography for the production of integrated circuits (ICs or "chips") to produce a pattern on a thin wafer of material (usually silicon). In semiconductor manufacturing, a mask is sometimes called a reticle.

In photolithography, several masks are used in turn, each one reproducing a layer of the completed design, and together known as a mask set.