Lithography

Overview

Lithography is the set of steps that copies a circuit pattern from a photomask onto a wafer, by projecting light through the mask onto a light-sensitive coating and then developing it. The developed pattern acts as a stencil, so the etch or implant step that follows changes the wafer only where the design says it should. It is repeated for every patterned layer of a chip, and it sets the smallest features a process can make.

How it works

A wafer is first coated with a thin film of photoresist. An exposure tool, usually a scanner, projects a reduced image of the mask onto one field of the wafer at a time and steps across the whole wafer. Where light falls, the chemistry of the resist changes, so the developer removes either the exposed or the unexposed areas. The wafer is then measured, and if the pattern is in the right place and the right size it moves on to etch or implant; if not, the resist can be stripped and the layer reworked.

How small a feature can be printed depends on the wavelength of the light, the numerical aperture of the optics and a process factor, a relationship known as the Rayleigh criterion. That is why the industry moved from mercury lamp light to deep ultraviolet lasers at 248 nm and 193 nm, then to immersion scanners with water between lens and wafer, and finally to extreme ultraviolet (EUV) light at 13.5 nm. Where one exposure cannot resolve a pattern, it is split across two or more exposures and etches, which is called multiple patterning.

Each new layer must also land precisely on the layers below it. This alignment, called overlay, is measured on every lot alongside critical dimension.

Examples

• A 193 nm immersion scanner printing the lower metal layers of a mature logic process.
• An EUV scanner printing the most critical layers of a leading-edge process in a single exposure.
• Self-aligned double patterning, in which spacers formed alongside printed lines double the line density.
• A lot sent back for rework after an overlay measurement shows a layer shifted beyond its limit.
• Optical proximity correction, where the mask shapes are deliberately distorted so the printed result matches the intended layout.

Why it matters

Lithography is often the most expensive and most closely watched module in a fab: the scanner fleet sets capacity, and lithography errors are a leading source of yield loss. Lithography process engineers, overlay control engineers and computational lithography engineers own the module, while designers feel its limits through design rules and restricted layout styles.

In the chip lifecycle, lithography capability is fixed during process development, shapes the design rules in the design kit, and is controlled lot by lot throughout volume manufacturing.

It matters most to: Computational Lithography Engineer, DUV Lithography Process Engineer, EUV Lithography Engineer, Lithography Overlay Control Engineer, Lithography Process Engineer

Common confusions

Not the same as photolithography

Photolithography is lithography with light, the form used in volume chipmaking. Lithography also covers electron beam writing, used mainly to make masks, and nanoimprint, which presses a pattern into resist.

Not the same as etch

Lithography only defines the pattern in resist. The etch step that follows transfers it into the film underneath.

Not the same as process node

A node name such as 3 nm is a generation label, not a printed dimension. The smallest features lithography prints on a given layer are usually larger than the name suggests.

Sources

1. Lithography principles (opens in a new tab), ASML, 2026-10-22
2. Lithography (opens in a new tab), Semiconductor Engineering, 2026-10-22
3. Photolithography (Wikipedia) (opens in a new tab), Wikimedia Foundation, 2026-10-22
4. Multiple patterning (Wikipedia) (opens in a new tab), Wikimedia Foundation, 2026-10-22

Related terms

• Photomask
• EUV
• Immersion lithography
• Photoresist

Where it appears on the Hub

Used on 180 pages of the Hub. In each group, the pages that mention it most come first.