Replication of mold for UV-nanoimprint lithography using AAO membrane

doi:10.1016/j.apsusc.2009.05.006

Applied Surface Science

Volume 255, Issue 18, 30 June 2009, Pages 8019-8022

https://doi.org/10.1016/j.apsusc.2009.05.006 Get rights and content

Abstract

A simple and highly effective method to the replication of soft mold based on the anodic aluminum oxide (AAO) membrane was developed. The soft mold with nanopillar arrays was composed of the toluene diluted PDMS layer supported by the soft PDMS. A water contact angle as high as 114° was achieved. The hexagonally well-order arrays of holes of nanometer dimensions, ∼100 nm pore diameter and 125 nm center-to-center pore, could be gained over large areas by UV-nanoimprint lithography (UV-NIL) with the replicated soft PDMS mold. It is expected that the developed soft mold would find applications in light emitting diodes devices.

Introduction

UV-nanoimprint lithography (NIL) has been regarded as one of the most promising next generation lithography (NGL) technologies for high throughput nanoscale pattern with high resolution [1], [2], [3], [4], [5]. A transparent hard stamp of quartz glass [6] or soft elastomeric stamp (for instance PDMS) [7], [8], [9] is done the resin cured by UV-light exposure. However, it is of importance to fabricate the desired stamp in nanoimprint lithography process. The stamp for NIL can be currently fabricated by focused ion beam (FIB) or electron beam lithography (EBL) methods, which is very tedious and time-consuming. Moreover, at the smallest resolution, the throughput is very slow. It can be said without exaggeration that the fabrication technology for stamp is one of the critical bottlenecks to NIL progress.

Recently, some novel methods for fabricating the stamp were developed intensively. One of the key technologies, soft lithography invented by Whitesides’ group is the most useful for patterning features and for fabricating structures below 100 nm [10], [11], even excellent replication of carbon nanotube [12]. Based on the method, the modified methods for replicating PDMS were reported in some literatures. The PDMS flexible mold was prepared easily by pressure-assisted molding method based on the silicon master contains nanopillar arrays ranging from 500 nm to 50 nm [8]. Interestingly, the bio-inspired approaches to nanostructures exist in nature providing a simple and fast method of replicating the novel nanostructures. Cicada wings [13], beetle Plusiotis boucardi [14], moth's eye [15], Gecko foot-hair [16] and lotus surface [17] were successfully mold and the fabricated novel nanostructures would be used in nano-sensor and self-cleaning product.

Since a porous alumina membranes (AAO) was fabricated in 1995, it is increasingly finding a role in the preparing of nanostructure materials, the field of sensing and storage, such as aligned nanowires [18], aligned carbon nanotube [19] or metal and metal oxide nanotubes [20], dots arrays [21] and 2D photonic crystal [22]. Besides, AAO films have been acted as a mask for etching Si and GaAs substrates to gain nano-patterning surfaces [23], [24]. To our knowledge, little attention was paid to the replicated mold by virtue of AAO master for its application in UV-NIL process.

In the paper, we reported the AAO as a master mold for replicating daughter mold. After peeling off the poly (dimethylsiloxane) (PDMS) from AAO film, an array of nanopillar with the pattern of AAO was successfully obtained. The hexagonally well-order arrays of holes were imprinted by the soft PDMS mold, which was performed on UV-NIL of EVG 620(EVG Group, Austria). The developed technology can be applied for reproduction of nanopatterns over large areas.

Section snippets

Preparation of AAO membrane

The AAO membrane was fabricated through the well-known, two-step anodization process [25]. In brief, the pre-handled Al sheet was placed in the solution of oxalic acid for 5–6 h for a first anodization, followed by the 6% H₃PO₄ + 1.8% H₂CrO₄ aqueous solution for removing the oxide layer. And the following second anodization last for 10–12 h, the Al on the AAO membrane was eliminated by CuCl₂ solution. The removing of the barrier layer and the diameter of nanopore could be decided by 5% H₃PO₄

Results and discussion

A piece of 30 mm diameter AAO membrane was obtained by two-step anodization process .A representative scanning electron microscopy image (SEM) of AAO formed by two step anodization process is shown in Fig. 2. The highly regular nanopores with ∼100 nm in diameter are seen clearly. Furthermore, the interval spacing of two neighboring holes is about 120 nm (the insert of Fig. 2). It is easily calculated that a pore density of 2 × 10¹²/cm² are well formed on the whole AAO membrane.

Fig. 3 shows SEM image

Conclusion

In summary, we developed a novel application of AAO membranes for UV-nanoimprint lithography. The soft imprinted mold could be easily fabricated on the AAO surface as template by the PDMS diluted toluene. The high fidelity polymer substrate with hexagonally arranged nanopores arrays was achieved through UV-NIL with the replicated soft stamp. It is expected that the simple, highly effective and inexpensive fabrication of soft mold over large scale areas would be suitable for a broad range of

Acknowledgements

This work was jointly supported by National 973 Program (2007CB935400), China Postdoctoral Scientific Foundation Funded Project (20070420105), Science and Technology Committee of Shanghai (0652nm052 0752nm013, 0752nm014), and Shanghai Postdoctoral Scientific Program (07R214204, 08R214211).

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Replication of mold for UV-nanoimprint lithography using AAO membrane

Abstract

Introduction

Section snippets

Preparation of AAO membrane

Results and discussion

Conclusion

Acknowledgements

Microelectron. Eng.

Microelectron. Eng.

Microelectron. Eng.

Microelectron. Eng.

Science

Adv. Mater.

Mater. Sci. Eng. C

J. Vac. Sci. Technol. B

Nano. Lett.

Nanotechnology

J. Vac. Sci. Technol. B

Angew. Chem. Int. Ed.

Langmuir

Nano Lett.