The technique of optical lithography or photolithography uses ultraviolet (UV) radiation to sensitize a photosensitive resin, known as photoresist. During the development step, areas radiated by light are removed, creating a binary profile on the substrate (with and without photoresist).

The main components of the photoresist are: polymer (base resin), sensitizer and solvent. After exposure to radiation with a specific wavelength, the polymer changes the size of the structural chain through new bonds or breakage of molecules. In the case of positive photoresists, where light is radiated, fragmentation of the molecular chain occurs, leaving this region with a higher dissolution rate than the other shaded regions. With negative photoresists, however, the opposite occurs, the regions that were affected by light trigger a reaction that increases the size of the chain, a process known as crosslinking. Thus, these regions are dissolved at a lower rate than the other areas not sensitized by light.

Two techniques are available for exposing patterns: masked and unmasked (rapid prototyping). In the first case, a transparent substrate containing regions that allow the passage of light and regions protected with metal (preventing the passage of light) is used, also known as a photomask. In the case of rapid prototyping, a system uses projection lenses combined with micrometer-accurate scanning engines to selectively expose regions of the substrate, without the need for a physical mask. Standards for direct projection are defined by a virtual mask previously designed in dedicated software.