optical lithography (rus. литография, оптическая otherwise фотолитография; photolitigraphy ) — technology of microelectronics; variant of lithography that includes transfer of the electronic component images from the mask (template) onto a semiconductor substrate coated with a film of photoresist (material sensitive to light radiation), followed by etching of the coating and doping of the substrate or deposition of films through windows in the layer of photoresist.


The usual substrate material is silicon wafers with oxidised surface. A thin film of SiO2 on the surface protects the silicon from further oxidation, and serves as an impermeable barrier to most impurities and as a good insulator. An advantage of the Si-SiO2 system is the possibility of selective etching with use of etchants that have an effect on only one of these two materials.

The photolithographic process includes chemical cleaning of the substrate surface from traces of different (organic, ionic, metallic) impurities, oxidation of the cleaned substrate surface with creation of a protective layer of SiO2, deposition of a thin film of photosensitive material (photoresist) on the oxidised surface, exposure of the photoresist through a mask and removal (etching) of negative photoresist from non-irradiated regions or of positive photoresist from irradiated regions. The most commonly used are positive photoresists enabling a more precise transfer of very fine geometric details of the image. In optical lithography all the details of the circuit are exposed simultaneously. The silicon wafer with a transferred pattern is placed in an environment, where dopant atoms are introduced into the silicon via windows in the photoresist. Repetition of the operations of oxidation, photolithography and doping allows selective introduction of p- and n-type dopant atoms in very small areas on the crystal surface. The pattern formed by photolithography also makes it possible to deposit the required metal and/or dielectric film coatings through the windows in the photoresist. The smallest size of elements that can be obtained using the classical optical photolithography is essentially limited by the wavelength of light. Photolithography using light with a wavelength of ~ 400 nm enables the mass-production of integrated circuits with a minimum size of 2-3 microns containing up to 105 transistors.


Main stages of lithographic process involving positive (left) and negative (right) photoresists:

Main stages of lithographic process involving positive (left) and negative (right) photoresists: a) oxidation and SiO2 surface layer buildup; b) resist coating; c) exposure; d) removal of exposed and nonexposed negative resists; e) SiO2 layer etching; f) complete removal of resist; (g) silicon substrate doping. 

(1) silicon substrate; (2) SiO2 surface layer; (3) photoresist layer; (4) photomask; (5) doping area.


  • Gusev Alexander I.


  1. Gusev A. I. Nanomaterials, Nanostructures, and Nanotechnologies (in Russian) // Fizmatlit, Moscow (2007) - 416 pp.

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