A photomask used in creating layers on a chip that is repeated (stepped) across the wafer. Light shines through the reticle to create a pattern on the light-sensitive photoresist applied to the wafer. The reticle is much larger than the final image so that its geometry can be precisely measured. Lenses in the stepper machine reduce the image down to the microscopic level. See
chip manufacturing and
EUV machine.
Although the terms reticle and photomask are used synonymously, a reticle implies that it is a photomask pattern for only a part of the wafer layer, and the process must be replicated many times by the stepper for that layer. The reticle pattern may cover a handful of chips, a single chip or part of a chip. See
ultraviolet light.
Before Reticles and Steppers
In the 1960s and 1970s, the photomasks were the size of the wafer, and there was no movement required. A "mask aligner" merely aligned the photomask with the wafer. However, the never-ending goal of making transistors smaller required turning the photomask into reticles and performing multiple steps. See
process technology.