What is photoresist?
Photoresist is a liquid that, when exposed to light, changes its structure. Positive resist becomes mildly acidic and a basic solution, TetraMethylAmmoniumHydroxide (TMAH), dissolves away the exposed resist. The remaining resist is baked and becomes resistant to acid and/or plasma etching steps. A negative resist crosslinks and/or becomes harder when light hits it. The unexposed resist is washed away using a solvent that the resist material is carried in.