Photomask facts for kids
In electronics manufacturing, a photomask is a special stencil which is used in photolithography to create a printed circuit board or integrated circuit. When light is shone through the photomask, certain parts where the light hits the unused circuit board are strengthened, much like what toothpaste does to the hard surfaces your teeth. When a circuit board is put through an acid bath, the parts where the light shone through the photomask stay in place, while the parts that were covered by the shadow of the photomask are eaten away by the acid. There are two prominent types of masks. "Contact" masks, which touch the surface of the silicon wafer directly. These masks are cheaper, at the price of being less precise. "Proximity" masks are placed near to, but not touching the wafer. These masks are much more expensive, but also a lot more precise. Another type is "Projection" masks, also known as "reticles", which only contain the pattern of one chip, instead of the pattern of the whole wafer.
Images for kids
A simulated photomask. The thicker features are the integrated circuit that is desired to be printed on the wafer. The thinner features are assists that do not print themselves, but help the integrated circuit print better out-of-focus. The zig-zag appearance of the photomask is because optical proximity correction was applied to it to create a better print.
Photomask Facts for Kids. Kiddle Encyclopedia.