Photomask is a high-precision plate with micro circuit, which is made of quartz plate or glass plate with a layer of chromium on the surface. The residual chromium after etching is the designed micro electrogram, which is called light transmission in the mask industry.

Photomask is used in chip manufacturing, mainly IC (integrated circuit) chip, as well as flat panel display, thin film head and PC board.

The function of photomask is similar to that of negative film to photo. Photolithography develops on chip by photomask. If the pattern is developed multiple times on both sides of the chip through a mask, this method is known as exposure, and the mask at this time can also be called a mask.