Lithography in the integrated circuit technology context is typically the transfer of a pattern to a photosensitive material by selective exposure to a radiation source such as light. A lithographic system includes exposure tool, mask, resist, and all of the processing steps to accomplish pattern transfer from a mask to a resist and then to devices. A photosensitive material is a material that experiences a change in its physical properties when exposed to a radiation source. If we selectively expose a photosensitive material to radiation (e.g. by masking some of the radiation), the pattern of the radiation on the material is transferred to the material exposed. If the resist is placed in a developer solution after selective exposure to a light source, it will etch away one of the two regions (exposed or unexposed). If the exposed material is etched away by the developer and the unexposed region is resilient, the material is considered a positive resist (shown in Fig 3.1). If the exposed material is resilient to the developer and the unexposed region is etched away, it is considered a negative resist.

From the 1960s, when integrated circuits had line widths of 5 µm, optical lithography has been used ubiquitously for manufacturing. Electron-beam (e-beam) and X-ray lithographies have been considered as alternatives to optical lithography. However, wafer throughput with e-beam lithography is too slow for use in current semiconductor wafer production. Currently e-beam lithography is regarded as complementary to optical lithography. Optical lithography depends on e-beam lithography to generate the masks. Because of its intrinsic high resolution, e-beam lithography is at present the primary lithographic technique used in sub-quarter-micron device research.