Solving the Challenges of Nanoimprinting for Micro and Nano Optics

Nanoimprint lithography [1][2][3] is a verified production technology for a range of applications, from the creation of microlenses [4] to its use in the production of vertical cavity surface emitting lasers (VCSELs) [5].

In the majority of these applications, nanoimprint is executed on wafer scale. Roller-based nanoimprint has been suggested very early on for larger areas [6]. Roll-to-roll based nanoimprint [7][8][9] has undergone several developments, much less has been refined in the case of roll-to-plate NIL utilizing rigid substrates.

To solve the limitations of large area nanoimprinting on opaque and rigid substrates, Stensborg is currently organizing and investigating a roll-to-plate nanoimprint tool based on UV light.

It is established on the concept of [10] and includes a substrate translation stage and a transparent roller. A translucent printing plate or stamp can be joined to the roller. 

The source of UV light is found within this roller. A water-cooled range of UV-LEDs emit light that is directed to the nip, which is the location where the substrate and the roller meet.

The device is produced to manage substrates with a thickness of up to 10 mm and sizes leading to 30 x 60 cm². The speed of printing can vary from 1 m per minute to 10 m per minute.

The tool is not yet fully complete, as slot die coating and inkjet printing equipment still has to be installed to specifically include coating abilities for large areas.

Stensborg has already performed the initial printing tests. A glass plate was fixed onto the granite substrate table to carry out these investigations. A polymer foil was put on top of the glass-plate and covered with an imprint material that was UV-curable.

Characteristics with a wide range of dimensions were successfully replicated. Figure 1 demonstrates a line scan of a micro optical test structure, while Figure 2 shows a line scan of a test-hologram.

Linescan (Profilometer) of a roll-to-plate imprinted micro optical test structure, feature height approximately 45 µm, period approximately 100 µm.

Figure 1. Linescan (Profilometer) of a roll-to-plate imprinted micro optical test structure, feature height approximately 45 µm, period approximately 100 µm. Image Credit: Stensborg 

Linescan (AFM) of a roll-to-plate imprinted holographic test structure, feature height approximately 350 nm, period approximately 880 nm.

Figure 2. Linescan (AFM) of a roll-to-plate imprinted holographic test structure, feature height approximately 350 nm, period approximately 880 nm. Image Credit: Stensborg 

The period of the features along with the height varies by multiple orders of magnitude. Figure 3 displays a standard printed hologram structure. In Figure 4, an image of the device throughout UV-imprinting, including the printing plate, can be observed.

Optical micrograph of a hologram test pattern corresponding to Figure 2.

Figure 3. Optical micrograph of a hologram test pattern corresponding to Figure 2. Image Credit: Stensborg 

Photograph of the roller during imprinting with a printing plate mounted to the roller.

Figure 4. Photograph of the roller during imprinting with a printing plate mounted to the roller. Image Credit: Stensborg 

Separation was very simple due to the material combinations that were evaluated. The foils did not need to be mounted on the glass plate at all to enable effective automatic separation after the imprinting.

Printing plates produced from either UV-curable PDMS or a UV-curable resin material, along with Stensborg’s X29 imprinting resist were used. Separation was instant in both combinations, so the foil isolated itself from the printing plate.

Stensborg will publish additional printing results with a greater range of micro- and nanoscale characteristics, and additionally the initial results of large area coating of UV-curable materials.

The authors would like to thank the rollerNIL and ePaper projects for their funding (financed by FFG, the Austrian Research Promotion Agency).

Acknowledgements

Produced from materials originally authored by L. Yde1, L. Lindvold1, J. Stensborg1, T. Voglhuber2, H. Außerhuber2, S. Wögerer2, T. Fischinger2, M. Mühlberger2, and W. Hackl3 from Stensborg1, PROFACTOR GmbH2 and Forster Verkehr- und Werbetechnik GmbH3.

References and Further Reading

[1] Chou, S.Y., et al., J Vac Sci Technol B 14 (1996) 4129.
[2] Haisma, J., et al. J Vac Sci Technol B 14 (1996), 4124.
[3] Schift, H., J Vac Sci Technol B26 (2008) 458.
[4] e.g. Heptagon, http://hptg.com (last accessed 4.4.2016)
[5] Verschuuren, M.A., presented at NNT2011
[6] Tan, H., et al,. J Vac Sci Technol B 16 (1998) 3926.
[7] Thesen, M.W., et al. Microel Eng 123 (2014) 121.
[8] Ahn, S.H., et al., Advanced Materials 20 (2008) 2044.
[9] John, J., et al., Nanotechnology 24 (2013) 505307.
[10] Lindvold, L., Stensborg, J., Rassmussen, T., EP 1150843 B2.

This information has been sourced, reviewed and adapted from materials provided by Stensborg.

For more information on this source, please visit Stensborg.

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