Definition: photolithography

The lithographic technique used to transfer the design of circuit paths onto printed circuit boards and chips. Also called "optical lithography," photolithography is a critical step in chip making because it determines the minimum size of everything on a chip, including the transistor's internal elements. See process technology.

A Mask for Each Layer
A photomask is created with the design for each layer of the board or wafer (chip), and there are various techniques for adjusting the masks and the light (see computational lithography).

The board or wafer is coated with a light-sensitive film (photoresist) that is hardened when exposed to light shining through the photomask. The board or wafer is then exposed to an acid bath (wet processing) or hot ions (dry processing), and the unhardened areas are etched away. For more details, see chip manufacturing. See reticle and printed circuit board.

Masking Is the First Stage

The photomask stage is where the design of each layer is transferred to all the chips on the wafer. Today's state-of-the-art photomasking machines are modern miracles (see EUV machine).