photoresists

Photoresists are light-sensitive polymeric materials used in lithography to transfer patterns onto substrates such as silicon wafers. When exposed to radiation or charged particles, photoresists undergo a chemical change that alters their solubility in a developer solution, enabling defined features to be etched or replicated.

There are two major classes: positive resists, which become more soluble in the developer at exposed regions, and negative resists, which become less soluble where exposed due to crosslinking or other reactions. In advanced processes, chemically amplified resists use a photoacid generator that, upon exposure, produces acid which catalyzes a reaction during a post-exposure bake, dramatically increasing sensitivity. Materials range from conventional polymer resists to molecular or inorganic variants, and they are available for ultraviolet, deep ultraviolet, EUV, and electron-beam lithography, among other modalities. Common examples include PMMA as a simple electron-beam resist and various chemically amplified resists for optical wavelengths.

The standard lithography workflow for resists includes coating a substrate by spin coating, prebake to remove solvent, exposure with masked radiation, post-exposure bake (for chemically amplified resists), development to remove soluble regions, rinse, and a hard bake or etch preparation as needed. Performance is described by sensitivity (dose required), contrast, resolution, line-edge roughness, adhesion, and etch resistance, as well as defect density and film quality.

Applications span semiconductor device fabrication, MEMS, microfluidics, and printed electronics, where precise pattern transfer at micron- to nanometer-scale resolutions is required. Ongoing developments seek lower processing temperatures, higher resolution at shorter wavelengths, reduced environmental impact, and better line uniformity.