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Nanoimprint lithography for novel 2- and 3- dimensional nanostructures

Final Report Summary - 3DNANOPRINT (Nanoimprint Lithography for Novel 2- and 3- dimensional Nanostructures)

One of the main problems in nanotechnology is the lack of methods for mass production. This is especially true for Small and medium-sized enterprises (SMEs), which do not have the ability to invest in expensive equipment for large-scale production of nanostructures. Nanoimprint lithography (NIL) is a tool that is comparably cheap and suited for mass production. The project 3DNANOPRINT aimed at the development of a complete process technology with the necessary tools to produce three-dimensional (3D) nanostructures with ultra high precision. In comparison to deep or extreme ultra violet lithography (abbreviated as DUV and EUV lithography, respectively) this research paved the way for the widespread use of a nanoscale production technology also by smaller companies, since the investment costs of nanoimprint production lines are significantly less than the ones for DUV or EUV lithography.

In nanoimprint lithography a micro- and / or nano-structured stamp is used to pattern a polymer. If necessary this polymer can then be used to transfer this pattern into a substrate by an etching process. The pattern replication is done under well controlled conditions by hardening the initially liquid polymer, while the stamp is still pressed into it, and subsequent separation of stamp and then hard polymer.

The project consisted of two levels, a directly process oriented part dealing with nanoimprint lithography itself, nanoimprint resists, reactive ion etching and alignment problems and a second more application oriented part.

In the second part requirements for nanoimprint lithography as production tool are defined, assuring that the final result of the project is a cost effective, high throughput, ultraprecise tool for the production of 3D nanostructures.

As a reference application 3D photonic crystals have been chosen, since such devices are extremely difficult to fabricate and therefore serve as an excellent indicator for the quality and suitability of the fabrication process. Other applications considered were micro- and nano-optical devices and glass scales and discs for position encoding and measurement.

The photonic crystal was built up in a woodpile structure, which required that the third layer was shifted by half the period d with respect of the first layer and layer five sat just at top layer 1 again. This led to very stringent alignment requirements, since the periodicity was in the range of a few 100 nm.

Additional critical issues were the residual layer thickness, the sidewall roughness and the imprinting polymer itself.

The residual layer after imprinting was the layer of imprint polymer, which remained after imprinting in the areas where the imprint polymer has been pressed down by the stamp. It could not be avoided but had to be as thin and as homogeneous as possible over the whole imprinting area to make a perfect pattern transfer in a subsequent etching process feasible.

In imprint experiments hard quartz stamps were mainly used to imprint spin coated layers on Si wafers.

The main objectives of the project were the following:
- development of a nanoimprint tool which allows the production of 3-dimensional nanostructures;
- development of the process technology to produce these nanostructures, which includes:
- improvement of layer-to-layer alignment accuracy;
- improvement of NIL resists;
- improvement of reactive ion etching.

This project should help to pave the way for the use of NIL as a production technology.