The field of lithography is a fundamental part of the electronics industry and nanotechnology. Currently, it is the only known process that can mass-produce microchips and other complex semiconductor devices. Similar to many other semiconductor processes, it's found a use in constructing nanostructures out of semiconductor materials.
Lithography is merely one step in the process of fabricating a semiconductor. However, it is vital because it effectively guides most of the other steps. The technique involves patterning a substrate or wafer (A thin, round slice of semiconductor material, typically silicon, from which microchips are made. Silicon is processed into large cylindrical ingots, sliced into ultra-thin wafers and then implanted with transistors before being cut into smaller semiconductor chips. ) with a specified layout.
First, the substrate is coated with photoresist (A film used in photolithography that temporarily holds the pattern of a circuit path or microscopic element of a chip. When exposed to light, it hardens and is resistant to the acid bath that washes away the unexposed areas.). Next, the substrate is carefully aligned with its 'mask'. The mask determines the patterning process. By selectively allowing light to pass through, only specified sections of the substrate are exposed. The light will either break down the layer of photoresist or harden it. The portions of photoresist that weaken subsequently is removed with acid. Any photoresist that remains simply acts as a barrier for ensuing processes such as epitaxy, doping, or etching, other steps in the construction of a semiconductor.
On any one wafer, hundreds of chips can be made simultaneously. The technique has been so well developed over the years that main participants in the chip making industry, such as Intel, can produce quantity as well as quality.
With regard to nanotechnology, lithography has proven to be extremely valuable in patterning a substrate for the selective growth of nanostructures. For example, substrates can be prepared so that they will grow nanowires and quantum dots solely in the chosen areas. Furthermore, lithography may prove to be the precursor to the construction of other nanostructures.
Unfortunately, the smallest features available in lithography are limited: the light used to pass through the “mask” has a fundamental restriction known as the 'diffraction limit of light' (A physical limit to how focused a beam of light can be). Many industry experts are concerned about this handicap, as the demands for faster computer chips continue to soar. Already, modern manufacturers are employing high-power lithography to push the limits of the technique. However, with extreme ultraviolet rays, it's only possible to have feature sizes of around 90 nm. While it is possible to generate lithographic machines that are capable of going slightly smaller, exorbitant costs are thwarting the efforts of all but the most powerful chipmakers at pursuing the necessary research.
Due to this limitation, the current methods of lithography will never be able to make nanostructures directly. However, this constitutes the reason why nanotechnology is so important for the future of electronics. Currently, it is one of the only acknowledged methods that future miniaturization of electronics can advance beyond the fundamental limits of lithography.
Currently, instruments used in nanolithography include the scanning probe microscope (SPM) and the atomic force microscope (ATM). The SPM permits surface viewing in detail without necessarily modifying it. Either the SPM or the ATM can be used to etch, write, or print on a surface in single-atom dimensions.
Nanolithography literally means 'writing on small rocks.' Our ability to carve smaller and smaller features has made it to the atomic level! Presently, the quality of computer chips is chiefly bounded by how small technology is able to write. Nanolithography is the subsequent step in minuaturization and rapid progress is ensuing.
References
Lithography. RingSurf. 23 Nov. 2005 <http://www.ringsurf.com/info/Technology_/Nanotechnology/Tools/Lithography_-_E-Beam__-_UV/>.
