A partially transparent film or glass plate that is used to
its transparent pattern by optical projection.
In the IC process, the designed circuit pattern is drawn in an
enlarged scale from several tens to nearly a hundred times, and reduced onto film or glass plate as
a photo mask. This original mask is directly used for exposure, copying to the wafer, or to produce
a working version with the same pattern as the original to be used for production purposes. The
material of the plate depends on the wavelength of the rays used in the projection process.