Imprint Lithography at the Fraunhofer Institute for Photonic Microsystems in Dresden: Engineering and Volume Production of Nanometer Scale Devices and Systems
Structures in semiconductor devices become smaller and smaller – so small that they cannot be fabricated by means of traditional photo lithographic processes any more since even in the deep ultraviolet spectral range the wavelength of light is not short enough. State-of-the-art methods of fabricating nanometer scale patterns use excimer lasers with emission of a laser wavelength of 193 nm in order to produce the commercially available integrated circuits at a minimum structural size of 35 nm. Features of sizes down to 22 nm are to date possible to realize and the race for further miniaturization continues.
An alternative technique to generate such small structures is electron beam lithography. However, for volume production this process lasts far too long. An innovative solution is nanoimprint lithography. To produce the required nanometer 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 nanoimprint lithography process high resolution structures can be realized at high speed and low cost.
Since the end of 2008, the Fraunhofer Institute for Photonic Microsystems (Fraunhofer IPMS) in Dresden has state-of-the art nanoimprint lithography equipment which 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 which 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 focused on CMOS-compatible planar photonic crystals fabricated by 365 nm photolithography and silicon-on-insulator (SOI) technology. In the future, the new 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 very promising starting point for applications in the field of bio-analytics as well as diagnosis of pathogens. Using nanoimprint 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 behavior of the optical system changes and the change of the ring resonators resonance frequency can be measured. The Fraunhofer IPMS currently develops a demonstrator that allows for detecting biological particles. The target of the project is to reliably and quickly analyze pathogens directly by family physicians or in hospitals without having to send samples to specialized laboratories.
Besides the new nanoimprint lithography equipment, Fraunhofer IPMS has at its disposal in its clean room 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 photo-lithography, plasma etching, sputtering, thermal deposition as well as wet chemical etching and cleaning. Furthermore, Fraunhofer IPMS has built in its clean room a laboratory dedicated to optical characterization via laser/optical experiments, Fourier-transform infrared micro-spectroscopy and scanning optical near-field microscopy.