Nanolithography

Nanolithography — or lithography at the nanometer scale — refers to the fabrication of 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 or nanoelectromechanical systems (NEMS).

As of 2006, nanolithography is a very active area of research in academia and in industry.

Optical lithography

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 photomask 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 30 nm. At that point, it may be replaced by a next-generation lithography (NGL) technique.

Other nanolithography techniques

• 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.

• Charged-particle lithography, such as ion- or electron-projection lithographies (PREVAIL, SCALPEL, LEEPL), are also capable of very-high-resolution patterning.

• 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 printing.

• Scanning Probe Lithographies (SPL) are promising tools 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.

• The furthest developed NGL remains X-ray lithography which is extensible to 15 nm resolution by use of "demagnification" in the Near Field.

Bottom-up Methods

It is possible that 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 (see e.g., D. Sundrani et. al., Langmuir, vol. 20, 5091-5099 (2004)). 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.

CATEGORIES: Nanoengineering