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Nanolithography is the branch of nanotechnology concerned with the study and application of fabricating nanometer-scale structures, meaning patterns with at least one lateral dimension between the size of an individual atom and approximately 100 nm. Nanolithography is used during the fabrication of leading-edge semiconductor integrated circuits (nanocircuitry) or nanoelectromechanical systems (NEMS).
As of 2015, nanolithography is a very active area of research in academia and in industry.
Optical lithography, which has been the predominant patterning technique since the advent of the semiconductor age, is capable of producing sub-100-nm patterns with the use of very short wavelengths (currently 193 nm). Optical lithography will require the use of liquid immersion and a host of resolution enhancement technologies (phase-shift masks (PSM), optical proximity correction (OPC)) at the 32 nm node. Most experts feel that traditional optical lithography techniques will not be cost effective below 22 nm. At that point, it may be replaced by a next-generation lithography (NGL) technique. A new one, Quantum Optical Lithography announced a resolution of 2 nm half-pitch lines at SPIE Advanced Lithography 2012. Applications of nanolithography include:
- Miniaturization of FET
- Surface gated quantum devices
- Quantum dots
- Zone plates
- Mask making
Other nanolithography techniques
- X-ray lithography can be extended to an optical resolution of 15 nm by using the short wavelengths of 1 nm for the illumination. This is implemented by the proximity printing approach. The technique is developed to the extent of batch processing. The extension of the method relies on Near Field X-rays in Fresnel diffraction: a clear mask feature is "demagnified" by proximity to a wafer that is set near to a "Critical Condition". This Condition determines the mask-to-wafer Gap and depends on both the size of the clear mask feature and on the wavelength. The method is simple because it requires no lenses.
- Double patterning is a method of increasing the pitch resolution of a lithographic process by printing new features in between pre-printed features on the same layer. It is flexible because it can be adapted for any exposure or patterning technique. The feature size is reduced by non-lithographic techniques such as etching or sidewall spacers. It has been used in commercial production of microprocessors since the 32nm process node. "Multiple Patterning" is expected to be used in future process nodes, until next generation lithography technologies become practical.
- Work is in progress on an optical maskless lithography tool. This uses a digital micro-mirror array to directly manipulate reflected light without the need for an intervening mask. Throughput is inherently low, but the elimination of mask-related production costs - which are rising exponentially with every technology generation - means that such a system might be more cost effective in the case of small production runs of state of the art circuits, such as in a research lab, where tool throughput is not a concern.
- The most common nanolithographic technique is Electron-Beam Direct-Write Lithography (EBDW), the use of a beam of electrons to produce a pattern — typically in a polymeric resist such as PMMA.
- Extreme ultraviolet lithography (EUV) is a form of optical lithography using ultrashort wavelengths (13.5 nm). It is the most popularly considered NGL technique.
- Laser Printing of Single Nanoparticles In this method, the optical forces induced via scattering and absorption of photons on nanoparticles are used to direct single nanoparticles to specific locations on substrates and attach them via van-der Waals forces. This technique has been demonstrated on metallic nanoparticles, which are easier to print due to their large plasmonically-induced scattering and absorption cross sections, in both serial and parallel printing methods.
- Charged-particle lithography, such as ion- or electron-projection lithographies (PREVAIL, SCALPEL, LEEPL), are also capable of very-high-resolution patterning. Ion beam lithography uses a focused or broad beam of energetic lightweight ions (like He+) for transferring pattern to a surface. Using Ion Beam Proximity Lithography (IBL) nano-scale features can be transferred on non-planar surfaces.
- Neutral Particle Lithography(NPL) uses a broad beam of energetic neutral particle for pattern transfer on a surface.
- Nanoimprint lithography (NIL), and its variants, such as Step-and-Flash Imprint Lithography, LISA and LADI are promising nanopattern replication technologies. This technique can be combined with contact printingand cold welding.
- Scanning probe lithography (SPL) is a promising tool for patterning at the deep nanometer-scale. For example, individual atoms may be manipulated using the tip of a scanning tunneling microscope (STM). Dip-Pen Nanolithography (DPN) is the first commercially available SPL technology based on atomic force microscopy.
- Atomic Force Microscopic Nanolithography (AFM) is a chemomechanical surface patterning technique that uses an atomic force microscope.
- Thermochemical Nanolithography (TCNL) is an atomic force microscopy based technique, which uses hot tips to activate chemical reactions at the nanoscale. it was used to create arrays of proteins, DNA, graphene-like nanostructures, PPV nanowires, and piezoelectric nanoarrays.
- Magnetolithography (ML) based on applying a magnetic field on the substrate using paramagnetic metal masks call "magnetic mask". Magnetic mask which is analog to photomask define the spatial distribution and shape of the applied magnetic field. The second component is ferromagnetic nanoparticles (analog to the photoresist) that are assembled onto the substrate according to the field induced by the magnetic mask.
- Nanosphere lithography uses self-assembled monolayers of spheres (typically made of polystyrene) as evaporation masks. This method has been used to fabricate arrays of gold nanodots with precisely controlled spacings.
It is possible that molecular self-assembly methods will take over as the primary nanolithography approach, due to ever-increasing complexity of the top-down approaches listed above. Self-assembly of dense lines less than 20 nm wide in large pre-patterned trenches has been demonstrated. The degree of dimension and orientation control as well as prevention of lamella merging still need to be addressed for this to be an effective patterning technique. The important issue of line edge roughness is also highlighted by this technique.
Self-assembled ripple patterns and dot arrays formed by low-energy ion-beam sputtering are another emerging form of bottom-up lithography. Aligned arrays of plasmonic  and magnetic wires and nanoparticles are deposited on these templates via oblique evaporation. The templates are easily produced over large areas with periods down to 25 nm.
- Alexander S. Urban, Andrey A. Lutich, Fenando D. Stefani, and Jochen Feldmann, "Laser Printing Single Gold Nanoparticles", Nano Letters, VOL. 10, NO. 12, OCTOBER 2010
- Spas Nedev, Alexander S. Urban, Andrey A. Lutich, and Jochen Feldmann, "Optical Force Stamping Lithography", Nano Letters, VOL. 11, NO. 11, OCTOBER 2011
- Dhara Parikh, Barry Craver, Hatem N. Nounu, Fu-On Fong, and John C. Wolfe, "Nanoscale Pattern Definition on Nonplanar Surfaces Using Ion Beam Proximity Lithography and Conformal Plasma-Deposited Resist", Journal of Microelectromechanical Systems, VOL. 17, NO. 3, JUNE 2008
- J C Wolfe and B P Craver, "Neutral particle lithography: a simple solution to charge-related artefacts in ion beam proximity printing", J. Phys. D: Appl. Phys. 41 (2008) 024007 (12pp)
- R. C. Davis et al. (2003). "Chemomechanical surface patterning and functionalization of silicon surfaces using an atomic force microscope". Appl. Phys. Lett. 82 (5): 808–810. doi:10.1063/1.1535267. Related article
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- A. Hatzor-de Picciotto, A. D. Wissner-Gross, G. Lavallee, P. S. Weiss (2007). "Arrays of Cu(2+)-complexed organic clusters grown on gold nano dots" (PDF). Journal of Experimental Nanoscience 2: 3–11. doi:10.1080/17458080600925807.
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