Nanoimprint lithography

The nano- imprint lithography (English nanoimprint lithography, short NIL ) is a nanolithography technique for low-cost manufacturing of nanostructures using a nanostructured stamp. Monomers or polymers are commonly used as a positive, which must be cured after embossing. Common applications for the nano- imprint lithography in the fabrication of (opto ) electronic devices.

History

The technique of nano imprint lithography was invented in the early 1990s by the group of Walter Bacher at the Institute for Microstructure Technology at the Forschungszentrum Karlsruhe and has already been used at this time for the production of nanostructures. Since then, the technique is the subject of current research and is provided by the International Technology Roadmap for Semiconductors 2014 for chip manufacturing at 20 nm. Technology Review listed the nano- imprint lithography in 2003 as " one of the ten emerging technologies that will change the world." Since 2006 Stamp exist for the production of three-dimensional nanostructures with a vertical resolution in the sub-nanometer range, ie less than a nanometer.

Manufacturing processes

Nanoimprint

For the production of nanostructures by nanoimprint lithography, you need a positive, usually a monomer or polymer, and a nanostructured stamp. The stamp itself can be produced by nanolithography or etching again. The positive is applied to a substrate and subsequently heated above the temperature of glass transition, i.e., it becomes liquid, before pushing the punch. To achieve a controllable ( and momentarily ) heating, laser or UV light are often used, which is necessary particularly in the preparation in several process steps, since otherwise the negative also melts.

Due to the viscosity of the positive when heating the interstices of the die are completely filled with it. After cooling, the stamp is removed. This means that the adhesion between positive and stamp is an important parameter ( in addition to temperature and injection pressure ). At the University of Kassel, a method was developed in which the dies are coated with a monomolecular coating so that they can be easily detached from the material.

If the embossed depth profile into the substrate or the actual layer is to be transmitted, the positive must be pre- etched (step 4 in the illustration ).

In nanoimprint lithography with UV light can work with lower contact pressures, also the process can take place at room temperature.

Stamp

The structuring of the stamp for lithography in turn can happen with nanoimprint, but also with other nanolithography techniques. As materials thereby find glass or light transparent plastics application. Due to the small feature size of the stamp is not atomic force microscope can be used for the quality control, since due to the size of the probe tip, the image sizes may not be played correctly. Instead, the seal may be examined using a scanning electron microscope, which, however, an electrically conductive coating (for example indium tin oxide) of the stamp requires.

Applications

The nano- imprint lithography is used to produce two - and three-dimensional organic or semiconductor nanostructures for optics, electronics, photonics and biology. Applications in optics and photonics, optical filters, polarizers, micromirror arrays, non-reflective structures or photonic circuits. Quantum wires and dots are for optical semiconductor elements such as laser diodes or of interest. Similarly, let electronic circuits such as MOSFETs, realize organic TFTs, or single-electron memory cheaper and easier than using techniques such as electron beam or EUV lithography. In biology nanostructures are of interest, inter alia, for the transport of liquids and the separation of biomolecules.

Pros and Cons

Nanoimprint may be used in silicon technology, with a resolution beyond the diffraction limit of light to the cost of producing nanostructures, such as integrated circuits. Also the production of multilayer structures ( multi-layer ) is also possible with this technique.

In the manufacturing process, however, is the temperature resistance and pressure resistance of the materials to be observed.