Photolithography

This article is about semiconductor manufacturing. For printing on paper, see lithography. For similar processes for metals, see photochemical machining.

Photolithography (also known as optical lithography) is a process used in the manufacturing of integrated circuits. It involves using light to transfer a pattern onto a substrate, typically a silicon wafer.

The process begins with a photosensitive material, called a photoresist, being applied to the substrate. A photomask 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 etching, chemical vapor deposition, or ion implantation processes.

Ultraviolet (UV) light is typically used.[1]

Photolithography processes can be classified according to the type of light used, including ultraviolet lithography, deep ultraviolet lithography, extreme ultraviolet lithography (EUVL), and X-ray lithography. The wavelength of light used determines the minimum feature size that can be formed in the photoresist.

Photolithography is the most common method for the semiconductor fabrication of integrated circuits ("ICs" or "chips"), such as solid-state memories and microprocessors. It can create extremely small patterns, down to a few nanometers 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 microfabrication in general, such as the fabrication of microelectromechanical systems. 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 microlithography, the general term for processes that generate patterned thin films. Other technologies in this broader class include the use of steerable electron beams, or more rarely, nanoimprinting, interference, magnetic fields, or scanning probes. On a broader level, it may compete with directed self-assembly of micro- and nanostructures.[2]

Photolithography shares some fundamental principles with photography in that the pattern in the photoresist is created by exposing it to light — either directly by projection through a lens, or by illuminating a mask placed directly over the substrate, as in contact printing. The technique can also be seen as a high precision version of the method used to make printed circuit boards. The name originated from a loose analogy with the traditional photographic method of producing plates for lithographic printing on paper;[3] 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.

  1. ^ Carroll, Gregory T.; Turro, Nicholas J.; Mammana, Angela; Koberstein, Jeffrey T. (2017). "Photochemical Immobilization of Polymers on a Surface: Controlling Film Thickness and Wettability". Photochemistry and Photobiology. 93 (5): 1165–1169. doi:10.1111/php.12751. ISSN 0031-8655. PMID 28295380. S2CID 32105803.
  2. ^ "DSA Re-Enters Litho Picture". March 15, 2018.
  3. ^ Cite error: The named reference comus2018 was invoked but never defined (see the help page).