Fabrication of flexible UV nanoimprint mold with fluorinated polymer-coated PET film
© Shin et al; licensee Springer. 2011
Received: 14 April 2011
Accepted: 18 July 2011
Published: 18 July 2011
UV curing nanoimprint lithography is one of the most promising techniques for the fabrication of micro- to nano-sized patterns on various substrates with high throughput and a low production cost. The UV nanoimprint process requires a transparent template with micro- to nano-sized surface protrusions, having a low surface energy and good flexibility. Therefore, the development of low-cost, transparent, and flexible templates is essential. In this study, a flexible polyethylene terephthalate (PET) film coated with a fluorinated polymer material was used as an imprinting mold. Micro- and nano-sized surface protrusion patterns were formed on the fluorinated polymer layer by the hot embossing process from a Si master template. Then, the replicated pattern of the fluorinated polymer, coated on the flexible PET film, was used as a template for the UV nanoimprint process without any anti-stiction coating process. In this way, the micro- to nano-sized patterns of the original master Si template were replicated on various substrates, including a flat Si substrate and curved acryl substrate, with high fidelity using UV nanoimprint lithography.
In order to form micro- to nano-sized patterns, various lithographic technologies have been used, such as DUV photolithography , e-beam lithography [2, 3], X-ray lithography [4, 5], laser holographic lithography , nanosphere lithography , scanning probe microscopy lithography , and so on. Except for DUV photolithography, these conventional lithography technologies require either a complicated patterning system with a high process cost or offer limited throughput and, thus, are not suitable for mass production. None of these technologies allow micro- to nano-sized patterns to be formed on a non-flat surface. Recently, nanoimprint lithography [9–11] has emerged as one of the most effective technologies to fabricate micro- to nano-sized patterns. Due to its low process cost and high throughput, nanoimprint technology can be used for the mass production of nano-sized patterns [12, 13].
UV nanoimprint templates need to have high stiffness in order for the nano-sized protrusion patterns to be transferred to the substrate and sufficient flexibility for conformal contact to be achieved over a large-sized substrate. Flexible templates can be applied to non-planar substrates. In addition, high transparency to UV is required for the template to be used for UV nanoimprint lithography. A sufficiently low surface energy is also necessary to avoid the need for an anti-sticking coating on the template, which would require the extra deposition of a Si oxide layer [14, 15],
In this study, a fluorinated polymer layer was coated on a flexible polyethylene terephthalate (PET) film, since micro- to nano-sized patterns can easily be formed on a fluorinated polymer layer by the hot embossing process [16, 17], and fluorinated polymers have a very low surface energy [18, 19]. With this fluorinated polymer-coated flexible PET mold, micro- to nano-sized patterns were fabricated on a flat Si substrate and curved acryl substrate with high fidelity using UV nanoimprint lithography.
Fabrication of flexible UV nanoimprint mold
Imprinting process using replicated flexible UV nanoimprint mold
Results and discussion
The micro- and nano-sized surface protrusion patterns of the master template were transferred with high fidelity to the flexible PET film, coated with the fluorinated polymer material, by the hot embossing process.
Since the surface energy of fluorinated polymers is as high as 105° for DI water, a flexible PET film with a patterned fluorinated polymer can be used as a stamp for the UV nanoimprint process without the need for an anti-stiction coating.
Due to the uniform pressing of the flexible PET film mold over either the flat Si wafer or curved acryl substrate, the micro- and nano-sized patterns of the embossed PET film were successfully imprinted onto the substrates using the UV nanoimprint process.
1This work was supported by the Nano Research and Development program through the Korea Science and Engineering Foundation funded by the Ministry of Education, Science and Technology (2010-0019152) and Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (NRF-2011- 0004819).
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