Liquid or rigid substances which are sensitive against electromagnetic radiation. Fotoresists can be sensitive against visible light, those used for technical applications usually are sensitive against UV radiation. Fotoresists may become soluble or insolubel against photo developers where they have been exposed to the radiation.
The chemistry of positive resists is modified by the radiation that way, that it becomes soluble by a sodium hydroxide solution, i.e. the positive resist will be removed in the areas exposed.
Negative resists will be cross linked by the radiation so that they are no more soluble. The development process removes the resist in the areas where not exposed and remains in the areas where irradiated.
When treated by a solvent or by plasma a substrate remains unaffected where the fotoresist remains. Areas to be treated or to be protected are selected by a fotomask.
Fotoresists can be removed from a substrate by plasma ashing.