hardware//manufacturing//fab//photolithography

2026-10-04

Photolithography is how a fab prints the pattern of a chip onto a silicon wafer, and it is the step that lets thousands of identical structures (transistors, tracks, electrodes) be made at once instead of one by one. A wafer is a thin disc of silicon on which many chips are made side by side, and each layer of each chip is printed on it the same way.

The step works like a photograph. The wafer is coated with a light-sensitive film (the photoresist); light is projected through a mask carrying the drawing of one layer, a machine called a scanner shrinking the image onto the wafer; the exposed resist is developed away, and the uncovered material is etched or doped, after which the resist is removed. A chip is that sequence repeated for every layer, transistors first and then the stack of insulators and metal that wire them, which is how a CMOS die is built.

A mask prints every copy at once.

The 960 electrodes of a neural probe, like the billions of transistors of a processor, cost the same exposure as one, which is why chip making scales and hand work does not.

The process node names a generation of printing, never the size of the device. A 130 nm process makes features of that order in its smallest layers, while the chip itself can be centimetres long and its shank tens of micrometres wide.

The light sets how small a feature can be. Nodes down to about 7 nm print with deep-ultraviolet light (DUV, 248 or 193 nm wavelength); the smallest need extreme-ultraviolet light (EUV, 13.5 nm), whose scanners only ASML makes. ASML builds the machines and the fabs make the chips.

Shapes that are not flat need etching after the print. Carving a needle out of the wafer, for instance, is done with deep reactive ion etching, using a lithographic pattern as its guide.