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Acreo logo with nano scale features
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Lithography is a key fabrication step for pattern generation, specifically in the top-down approach.
The desired patterns are generated in a suitable mask layer that is subsequently transferred to the underlying layers by etching. In the fabrication of nanostructures by the top-down approach, there are currently several established and emerging techniques, such as, electron-beam lithography, EUV-lithography (Extreme Ultraviolet), nanoimprint lithography (NIL) and proximity probe based techniques. NIL is an emerging method that has recently received considerable attention as an alternative, simple and cost-effective method for nano-structure fabrication. This technology is suitable for both academic research works and industry applications.
In NIL technology the nanostructures are defined by a stamp (mold) with nanoscale patterns pressed physically into a deformable material (resist) on the substrate, which is not only different from e-beam lithography, but also different from optical lithography nowadays. Whereas the resolution of the normal optical lithography is limited to about one micron due to the UV light wavelength range, NIL can define nanostructures smaller than 10 nm since it is not limited by diffraction. It also enables a wafer scale process, which reduces process cost significantly in comparison with e-beam lithography, and in addition avoids e-beam radiation on the wafers.
NIL is highly valuable for photonics, which would certainly have a great impact on the progress of research in the photonics integration area. Particularly, it will be of significant importance for nano-photonics, such as photonic crystals, nano-structured functional surfaces, advanced optoelectronic devices employing nanostructures.
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EVG 620 UV NIL
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A few nanophotonic applications by using NIL are described as follows:
- Pattern generation for Photonic crystals (PhCs) and PhCsbased devices
- Opto-electronic devices using nano-structures: Low dimensional semiconductor devices, for instance quantum
wire (QWR) and quantum dot (QD) lasers and detectors are currently attracting worldwide attention due to their fascinating physical properties and device performance. Compared with self assembled QD and QWR materials grown by MBE or MOVPE techniques, nano-structures defined by NIL has the advantages of controllable QD or QWR locations, good uniformity and flexible definition of nano structure size and shape.
- Epitaxial routes for fabricating ordered nano-structures: NIL can be used for generating patterns on substrates which can then be used as templates for selective area epitaxy. Similarly, such templates can be used to create a substrate with special topography (for example, by etching): This modified surface topography can be used for initiating selective/preferential formation of quantum dots or wires.
- Bio-photonics can also be foreseen. For example, by using periodic structures (e.g. PhCs) to enhance florescence from bio-molecules, driving towards cost-effective bio-chip solutions, and by using NIL for generating nano-structured functional surfaces.
An EVG 620 UV NIL equipment for high precision and high resolution replication on up to 6’’ wafers is available in the Electrum Laboratory. Acreo has developed a NIL process that was financed by the Kista Photonic Research Center (KPRC) for photonic device applications. Apart from the NIL equipment, ELab has other key required facilities for fabricating such devices, such as metal deposition, Si3N4 and SiO2 deposition, dry etching and antisticking layer coating etc equipment.