Nanolithography – refers to the fabrication of structures of at least one transverse size between the size of an individual atom and approximately 100 nm.

Optical lithography, which has been the predominant pattern making method since the semiconductor era, is capable of creating patterns less than 100 nm using very short wavelengths. Optical lithography would require the use of immersion in a liquid and a host of photomask enhancement techniques (phase shift masks, optical approximation correction at the 32 nm node.

X-ray lithography can be extended to an optical resolution of 15 nm by using short wavelengths of 1 nm for illumination. This is realized using a non-contact printing method. The technology is developed to the degree of batch processing. The extension of the method is based on near-field X-rays in Fresnel diffraction: the clear feature of the mask is “blurred” by proximity to the plate, which is near the “Critical State”. This condition determines the gap between the mask and the plate and depends on both the size of the transparent mask feature and the wavelength. The method is simple because it does not require lenses.

A method for increasing the resolution in tone height that is gaining acceptance is double patterning. This method increases the density of objects by printing new objects between pre-printed objects on the same layer. It is a flexible method because it can be adapted to any exposure or drawing technique. The size of the element is reduced by using non-lithographic techniques such as etching or sidelaying.

The most common nanolithography technique is direct writing electron beam lithography, using a beam of electrons to produce a pattern.

Ultraviolet lithography is a form of optical lithography using ultrashort wavelengths (13.5 nm). It is the most popular NGL technology. Charged-particle lithography, such as ion or electron-projection lithography, is also capable of producing very high-resolution patterns. [1]

Scanning probe lithography is a promising tool for creating patterns at the deep nanometer scale. For example, individual atoms can be manipulated with the tip of a scanning tunneling microscope. Immersion pen nanolithography is the first commercially available SPL technology based on atomic force microscopy.

Another type of nanolithography is chemo-mechanical surface patterning using an atomic force microscope. [2]

Nanosphere lithography uses self-assembled monolayers of spheres (usually polystyrene) as evaporation masks. This method has been used to make arrays of gold nanodots with precisely controlled distances. [3]

It is possible that molecular self-assembly methods will become the main approach to nanolithography because of the ever increasing complexity of the top-down approaches listed above. The degree of size and orientation control as well as the prevention of lamella fusion still needs to be addressed in order for this to become an effective pattern forming method. This method also highlights the important problem of line edge roughness.

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