A liquid or solid film which can be developed after exposure to preferably UV light. Positive photoresists are dissolved or chemically modified (change in acid character) by exposure so that the exposed areas are stripped by special developers (chlorinated hydrocarbons, diluted caustic soda lye or soda solution, warm water, etc.). With negative photoresists, the process is reversed: The cross-linking in the exposed areas is increased. Depending on the thickness and chemical behaviour, galvanic or etching photoresists are differentiated.
With etching of fine structures, areas masked with photoresists are not etched. The photoresists themselves can be removed by plasma etching. entfernt werden.