Nanolithography
Nanolithography is a growing field of techniques within nanotechnology dealing with the engineering of nanometer-scale structures on various materials.
The modern term reflects on a design of structures built in range of 10−9 to 10−6 meters, i.e. nanometer scale. Essentially, the field is a derivative of lithography, only covering very small structures. All NL methods can be categorized into four groups: photo lithography, scanning lithography, soft lithography and other miscellaneous techniques.
History
Nanolithography has evolved from the need to increase the number of sub-micrometer features in an integrated circuit in order to keep up with Moore's Law. While lithographic techniques have been around since the late 18th century, none were applied to nanoscale structures until the mid-1950s. With evolution of the semiconductor industry, demand for techniques capable of producing micro- and nano-scale structures skyrocketed. Photolithography was applied to these structures for the first time in 1958 beginning the age of nanolithography.Since then, photolithography has become the most commercially successful technique, capable of producing sub-100 nm patterns. There are several techniques associated with the field, each designed to serve its many uses in the medical and semiconductor industries. Breakthroughs in this field contribute significantly to the advancement of nanotechnology, and are increasingly important today as demand for smaller and smaller computer chips increases. Further areas of research deal with physical limitations of the field, energy harvesting, and photonics.
Etymology
From Greek, the word nanolithography can be broken up into three parts: "nano" meaning dwarf, "lith" meaning stone, and "graphy" meaning to write, or "tiny writing onto stone."Photolithography
As of 2021 photolithography is the most heavily used technique in mass production of microelectronics and semiconductor devices. It is characterized by both high production throughput and small-sized features of the patterns.Optical lithography
Optical Lithography is one of the most important and prevalent sets of techniques in the nanolithography field. Optical lithography contains several important derivative techniques, all that use very short light wavelengths in order to change the solubility of certain molecules, causing them to wash away in solution, leaving behind a desired structure. Several optical lithography techniques require the use of liquid immersion and a host of resolution enhancement technologies like phase-shift masks and optical proximity correction. Some of the included techniques in this set include multiphoton lithography, X-Ray lithography, light coupling nanolithography, and extreme ultraviolet lithography. This last technique is considered to be the most important next generation lithography technique due to its ability to produce structures accurately down below 30 nanometers at high throughput rates which makes it a viable option for commercial purposes.Quantum optical lithography
Quantum optical lithography, is a diffraction-unlimited method able to write at 1 nm resolution by optical means, using a red laser diode. Complex patterns like geometrical figures and letters were obtained at 3 nm resolution on resist substrate. The method was applied to nanopattern graphene at 20 nm resolution.Scanning lithography
Electron-beam lithography
Electron beam lithography or electron-beam direct-write lithography scans a focused beam of electrons on a surface covered with an electron-sensitive film or resist to draw custom shapes. By changing the solubility of the resist and subsequent selective removal of material by immersion in a solvent, sub-10 nm resolutions have been achieved. This form of direct-write, maskless lithography has high resolution and low throughput, limiting single-column e-beams to photomask fabrication, low-volume production of semiconductor devices, and research and development. Multiple-electron beam approaches have as a goal an increase of throughput for semiconductor mass-production.EBL can be utilized for selective protein nanopatterning on a solid substrate, aimed for ultrasensitive sensing. Resists for EBL can be hardened using sequential infiltration synthesis.