Photoresist

Notes

Supply is concentrated in Japanese chemical firms such as JSR, TOK, Shin-Etsu and Sumitomo.

Overview

Photoresist is the light-sensitive polymer film coated on a wafer during lithography, whose solubility changes where light falls on it, so that developing it leaves a patterned stencil for the etch or implant that follows. It turns the optical image of the mask into a physical pattern on the wafer. Each lithography wavelength needs its own resist chemistry, and resist performance limits how fine and how uniform printed features can be.

How it works

Resist is spun onto the wafer as a liquid to form a thin, even film, then baked to drive off solvent. After exposure, a post-exposure bake drives the chemical reaction, and a developer solution dissolves either the exposed areas, for a positive resist, or the unexposed areas, for a negative one. The remaining resist protects the wafer while the next step etches or implants the uncovered areas, and it is then stripped.

Early resists for mercury lamp light used novolac resin with a diazonaphthoquinone sensitiser. Deep ultraviolet lithography at 248 nm and 193 nm uses chemically amplified resists, in which light generates a small amount of acid that, during the bake, catalyses many reactions, giving high sensitivity. Extra layers are often added: anti-reflective coatings to stop reflections from distorting the image, and, for immersion lithography, top coats or water-resistant resists.

EUV lithography pushes resists hard. With few photons per feature, random variation causes rough edges and defects, so suppliers are developing both chemically amplified and metal oxide resists. Resists are supplied by specialist chemical companies such as Tokyo Ohka Kogyo, and a change of supplier or grade is treated as a significant process change.

Examples

• A positive chemically amplified resist used for 193 nm immersion lithography.
• A bottom anti-reflective coating applied under the resist to improve pattern fidelity.
• Metal oxide resists being evaluated for high-resolution EUV layers.
• A thick resist used to form tall solder bump openings in wafer-level packaging.
• A lot reworked by stripping the resist and repeating lithography after an overlay error.

Why it matters

Resist choice affects resolution, line edge roughness, defects and scanner throughput, so lithography process engineers, resist chemists and materials suppliers work on it constantly. A change of resist is a major process change that needs requalification.

In the chip lifecycle, resists are chosen and optimised during process development, qualified for production, and their supply and quality are monitored for every lot in manufacturing.

It matters most to: Lithography Process Engineer, Patterning and Resist Materials Researcher, Photoresist Chemist, Photoresist R&D Chemist, Strategic Sourcing Manager, Semiconductor Materials

Common confusions

Not the same as photomask

The photomask carries the pattern that is projected; the photoresist is the film on the wafer that records it. Photoresist vs photomask

Not the same as hard mask

A hard mask is a durable film, such as silicon nitride, patterned using resist and then used as the etch mask in its place.

Not the same as solder resist

Solder resist on circuit boards is a protective coating, also called solder mask, unrelated to lithography resist apart from being patterned.

Sources

1. Semiconductor Manufacturing Field (opens in a new tab), Tokyo Ohka Kogyo (TOK), 2026-10-22
2. Lithography principles (opens in a new tab), ASML, 2026-10-22
3. Lithography (opens in a new tab), Semiconductor Engineering, 2026-10-22
4. Photoresist (Wikipedia) (opens in a new tab), Wikimedia Foundation, 2026-10-22

Related terms

• CAR
• Metal-oxide resist
• Dose
• Track

Where it appears on the Hub

Used on 56 pages of the Hub. In each group, the pages that mention it most come first.