The Fraunhofer Institute for Photonic Microsystems (IPMS) is researching the use of nano-imprint lithography for the volume production of nanometre-scale devices and systems.
Structures in semiconductor devices have become smaller and smaller - so small that they cannot be fabricated by means of traditional photo lithographic processes any more, as even in the deep ultraviolet spectral range the wavelength of light is not short enough.
State-of-the-art methods of fabricating nanometre-scale patterns use excimer lasers with emission of a laser wavelength of 193nm in order to produce the commercially available integrated circuits at a minimum structural size of 35nm.
Features of sizes down to 22nm are possible to realise and the race for further miniaturisation continues.
An alternative technique to generate such small structures is electron beam lithography.
However, for volume production this process lasts far too long.
A solution is nano-imprint lithography.
To produce the required nanometre-scale structures, this technique uses 'stamps' with desired patterns manufactured by means of electron beam lithography.
The stamps are then imprinted multiple times into a very thin layer of plastic on a wafer, which subsequently is cured by irradiation with ultraviolet light.
By using such a nano-imprint lithography process high-resolution structures can be realised at high speed and low cost.
The Fraunhofer Institute for Photonic Microsystems in Dresden has state-of-the art nano-imprint lithography equipment that allows producing small batches of desired fine structures with high throughput.
The research and development activities are focused on applications in fields such as photonic crystals and micro resonators.
Photonic crystals are periodic dielectrics that suppress light propagation in certain frequency ranges (photonic band gaps) in complete analogy to electronic band gaps of crystalline solids.
Thus, light can be confined to specific functional defects that may act, for example, as sharp-bending waveguides or optical switches.
The research initiative of the Fraunhofer Institute started in early 2007 and focused on CMOS-compatible planar photonic crystals fabricated by 365nm photolithography and silicon-on-insulator (SOI) technology.
In the future, the equipment will make possible the fabrication of fibre-coupled photonic chips with a large variety of functionalities as well as integrated light sources and detectors.
Applications may be developed in the areas of gas or liquid sensing, optical telecommunication or micro-optical components.
Ring-shaped micro resonators are a promising starting point for applications in the field of bioanalytics as well as diagnosis of pathogens.
Using nano-imprint lithography, high-quality resonators can be fabricated at low cost.
The detection of biological particles such as viruses, proteins or DNA is based on a decreasing electrical field, which is surrounded by a ring resonator.
If this electrical field is linked with, for example, an influenza virus or other types of biological species, the behaviour of the optical system changes and the change of the ring resonators resonance frequency can be measured.
The Fraunhofer IPMS is currently developing a demonstrator that allows for detecting biological particles.
The target of the project is to reliably and quickly analyse pathogens directly by family physicians or in hospitals without having to send samples to specialised laboratories.
Besides the new nano-imprint lithography equipment, Fraunhofer IPMS has at its disposal in its cleanroom facility (class 10, US standard) all of the essential processes needed for the development and fabrication of semiconductor devices and microsystems (MEMS, MOEMS) such as photolithography, plasma etching, sputtering, thermal deposition, as well as wet chemical etching and cleaning.
Furthermore, Fraunhofer IPMS has built a laboratory in its cleanroom dedicated to optical characterisation via laser/optical experiments, Fourier-transform infrared micro-spectroscopy and scanning optical near-field microscopy.
