Photolithography

Photolithography (also known as optical lithography) is a process used in the manufacturing of <a href="/facts/Integrated_circuit/fjn6vg7C">integrated circuits</a>. It involves using <a href="/facts/Light/jeofpMn4">light</a> to transfer a pattern onto a substrate, typically a <a href="/facts/Silicon_wafer/lCBJAoUL">silicon wafer</a>.
The process begins with a photosensitive material, called a <a href="/facts/Photoresist/XNnIkCjU">photoresist</a>, being applied to the substrate. A <a href="/facts/Photomask/xCdRhIod">photomask</a> that contains the desired pattern is then placed over the photoresist. Light is shone through the photomask, exposing the photoresist in certain areas. The exposed areas undergo a chemical change, making them either soluble or insoluble in a developer solution. After development, the pattern is transferred onto the substrate through <a href="/facts/Etching/PM0FmoSb">etching</a>, <a href="/facts/Chemical_vapor_deposition/7khLxeU5">chemical vapor deposition</a>, or <a href="/facts/Ion_implantation/PHMokNUf">ion implantation</a> processes.
<a href="/facts/Ultraviolet/kncBUqn5">Ultraviolet (UV)</a> light is typically used.
Photolithography processes can be classified according to the type of light used, including ultraviolet lithography, deep ultraviolet lithography, <a href="/facts/Extreme_ultraviolet_lithography/NHpdP37J">extreme ultraviolet lithography (EUVL)</a>, and <a href="/facts/X-ray_lithography/7QnsUC6d">X-ray lithography</a>. The wavelength of light used determines the minimum <a href="/facts/Semiconductor_device_fabrication/Jd23Mu1z">feature size</a> that can be formed in the photoresist.
Photolithography is the most common method for the <a href="/facts/Semiconductor_fabrication/Jd23Mu1z">semiconductor fabrication</a> of integrated circuits ("ICs" or "chips"), such as <a href="/facts/Solid_state_memory/aMHBy8gU">solid-state memories</a> and <a href="/facts/Microprocessor/Fx9CaQht">microprocessors</a>. It can create extremely small patterns, down to a few <a href="/facts/Nanometer/a98sjHyu">nanometers</a> in size. It provides precise control of the shape and size of the objects it creates. It can create patterns over an entire wafer in a single step, quickly and with relatively low cost. In complex integrated circuits, a wafer may go through the photolithographic cycle as many as 50 times. It is also an important technique for <a href="/facts/Microfabrication/TzGo63pr">microfabrication</a> in general, such as the fabrication of <a href="/facts/Microelectromechanical_systems/TkhEzDpm">microelectromechanical systems</a>. However, photolithography cannot be used to produce masks on surfaces that are not perfectly flat. And, like all chip manufacturing processes, it requires extremely clean operating conditions.
Photolithography is a subclass of <a href="/facts/Microlithography/LFwpJbE7">microlithography</a>, the general term for processes that generate patterned thin films. Other technologies in this broader class include the use of <a href="/facts/Electron_beam_lithography/KILHHdKk">steerable electron beams</a>, or more rarely, <a href="/facts/Nanoimprint_lithography/n2f09DKo">nanoimprinting</a>, <a href="/facts/Interference_lithography/nG1r3Hrw">interference</a>, <a href="/facts/Magnetolithography/FsnldUSo">magnetic fields</a>, or <a href="/facts/Scanning_probe_lithography/6WtJeCf5">scanning probes</a>. On a broader level, it may compete with <a href="/facts/Directed_assembly_of_micro-_and_nano-structures/JMkw3KER">directed self-assembly</a> of micro- and nanostructures.
Photolithography shares some fundamental principles with <a href="/facts/Photography/ezLPT43M">photography</a> in that the pattern in the photoresist is created by exposing it to light — either directly by <a href="/facts/Projection_(physics)/ENlzoaCx">projection</a> through a <a href="/facts/Lens/ejlH6n5c">lens</a>, or by illuminating a mask placed directly over the substrate, as in <a href="/facts/Contact_printing/LL18PPaY">contact printing</a>. The technique can also be seen as a high precision version of the method used to make <a href="/facts/Printed_circuit_board/muSR2p43">printed circuit boards</a>. The name originated from a loose analogy with the traditional photographic method of producing plates for <a href="/facts/Lithography/LFwpJbE7">lithographic printing</a> on paper; however, subsequent stages in the process have more in common with etching than with traditional lithography.
Conventional photoresists typically consist of three components: resin, sensitizer, and solvent.

Photolithography open-in-new

Photolithography