We have explored the direct use of anodized alumina (AAO) fabricated on an Si wafer as a mold for the nanoimprint lithography (NIL). The AAO mold has been fabricated over more than 10?cm2 area with two different pore diameters of ?nm and ?nm. One of the key challenges of the lack of bonding between the antisticking self-assembled monolayer (SAM) and the AAO has been overcome by modifying the surface chemistry of the fabricated AAO mold by coating it with thin SiO2 layer. Then we have applied the commonly used silane-based self-assembled monolayer (SAM) on these SiO2-coated AAO molds and achieved successful imprinting of resist pillars with feature size of ?nm by using the mold with a pore diameter of ?nm. Finally, we have achieved (001) oriented L10 FePt patterned structure with a dot diameter of ?nm by using a AAO mold with a pore diameter of ?nm. The perpendicular Hc of the unpatterned and patterned FePt is about 3.3?kOe and 12?kOe, respectively. These results indicate that AAO mold can potentially be used in NIL for fabricating patterned nanostructures over large area. 1. Introduction Nanoimprint lithography (NIL) has attracted enormous attentions [1–6] of the nanofabrication community since its innovation in 1995 [7] and regarded as a next generation nanofabrication tool for fabricating sub-10?nm features [3–5]. The NIL is a high-throughput and low-cost lithographic technique that showed its potential in many emerging fields, such as electronics [8], photonics [9], bit-patterned media [10, 11], and biological applications [12]. Bit patterned media is of particular interest due its potential in increasing the areal densities in magnetic data storage devices [13, 14]. The mold (also known as template or stamp) is the crucial part of the NIL that determines the throughput and resolution of the later in practical applications. Usually electron beam lithography or focused ion beam lithography followed by the pattern transfer using reactive ion etching (RIE) are used for making the mold. The high cost and low throughput of these methods limit the usefulness of the NIL for fabricating nanopatterns over large area for both of the research and practical applications. Therefore, exploring the fabrication of low-cost and highly robust large-area mold is a must to enjoy the full potential of the NIL. However, to date, only very few works have been reported in this highly demanding area. Park et al. [15] fabricated the large-area mold by using block-copolymer lithography that involved an extra-pattern transfer step. Kim et al. [2] and Lee et al. [16] used AAO
References
[1]
D. R. Barbero, M. S. M. Saifullah, P. Hoffmann et al., “High resolution nanoimprinting with a robust and reusable polymer mold,” Advanced Functional Materials, vol. 17, no. 14, pp. 2419–2425, 2007.
[2]
Y. S. Kim, K. Lee, J. S. Lee, G. Y. Jung, and W. B. Kim, “Nanoimprint lithography patterns with a vertically aligned nanoscale tubular carbon structure,” Nanotechnology, vol. 19, no. 36, Article ID 365305, 2008.
[3]
Z. Li, Y. Gu, L. Wangs et al., “Hybrid nanoimprint-soft lithography with sub-15 nm resolution,” Nano Letters, vol. 9, no. 6, pp. 2306–2310, 2009.
[4]
M. Schvartzman and S. J. Wind, “Robust pattern transfer of nanoimprinted features for sub-5-nm fabrication,” Nano Letters, vol. 9, no. 10, pp. 3629–3634, 2009.
[5]
J. Haisma, M. Verheijen, K. Van Den Heuvel, and J. Van Den Berg, “Mold-assisted nanolithography: a process for reliable pattern replication,” Journal of Vacuum Science and Technology B, vol. 14, no. 6, pp. 4124–4128, 1996.
[6]
P. F. Murphy, K. J. Morton, Z. Fu, and S. Y. Chou, “Nanoimprint mold fabrication and replication by room-temperature conformal chemical vapor deposition,” Applied Physics Letters, vol. 90, no. 20, Article ID 203115, 2007.
[7]
S. Y. Chou, P. R. Krauss, and P. J. Renstrom, “Imprint of sub-25 nm vias and trenches in polymers,” Applied Physics Letters, vol. 67, p. 3114, 1995.
[8]
E. Menard, M. A. Meitl, Y. Sun et al., “Micro- and nanopatterning techniques for organic electronic and optoelectronic systems,” Chemical Reviews, vol. 107, no. 4, pp. 1117–1160, 2007.
[9]
L. J. Guo, “Recent progress in nanoimprint technology and its applications,” Journal of Physics D, vol. 37, no. 11, pp. R123–R141, 2004.
[10]
P. R. Krauss and S. Y. Chou, “Nano-compact disks with 400 Gbit/in2 storage density fabricated using nanoimprint lithography and read with proximal probe,” Applied Physics Letters, vol. 71, no. 21, pp. 3174–3176, 1997.
[11]
J. S. Sohn, D. Lee, E. Cho et al., “The fabrication of Co-Pt electro-deposited bit patterned media with nanoimprint lithography,” Nanotechnology, vol. 20, no. 2, Article ID 025302, 2009.
[12]
V. N. Truskett and M. P. C. Watts, “Trends in imprint lithography for biological applications,” Trends in Biotechnology, vol. 24, no. 7, pp. 312–317, 2006.
[13]
C. A. Ross, “Patterned magnetic recording media,” Annual Review of Materials Science, vol. 31, pp. 203–235, 2001.
[14]
B. D. Terris and T. Thomson, “Nanofabricated and self-assembled magnetic structures as data storage media,” Journal of Physics D, vol. 38, no. 12, pp. R199–R222, 2005.
[15]
H. J. Park, M. G. Kang, and L. J. Guo, “Large area high density sub-20 nm SiO2 nanostructures fabricated by block copolymer template for nanoimprint lithography,” ACS Nano, vol. 3, no. 9, pp. 2601–2608, 2009.
[16]
P. S. Lee, O. J. Lee, S. K. Hwang, S. H. Jung, S. E. Jee, and K. H. Lee, “Vertically aligned nanopillar arrays with hard skins using anodic aluminum oxide for nano imprint lithography,” Chemistry of Materials, vol. 17, no. 24, pp. 6181–6185, 2005.
[17]
M. T. Rahman, R. K. Dumas, N. Eibagi et al., “Controlling magnetization reversal in Co/Pt nanostructures with perpendicular anisotropy,” Applied Physics Letters, vol. 94, no. 4, Article ID 042507, 2009.
[18]
M. T. Rahman, N. N. Shams, C. H. Lai, J. Fidler, and D. Suess, “Co/Pt perpendicular antidot arrays with engineered feature size and magnetic properties fabricated on anodic aluminum oxide templates,” Physical Review B, vol. 81, no. 1, Article ID 014418, 2010.
[19]
M. T. Rahman, N. N. Shams, and C. H. Lai, “A large-area mesoporous array of magnetic nanostructure with perpendicular anisotropy integrated on Si wafers,” Nanotechnology, vol. 19, no. 32, Article ID 325302, 2008.
[20]
H. Masuda, K. Yada, and A. Osaka, “Self-ordering of cell configuration of anodic porous alumina with large-size pores in phosphoric acid solution,” Japanese Journal of Applied Physics, vol. 37, no. 11, pp. L1340–L1342, 1998.
[21]
A. P. Li, F. Müller, A. Bimer, K. Nielsch, and U. G?sele, “Hexagonal pore arrays with a 50-420 nm interpore distance formed by self-organization in anodic alumina,” Journal of Applied Physics, vol. 84, no. 11, pp. 6023–6026, 1998.
[22]
K. I. Nakamatsu, N. Yamada, K. Kanda, Y. Haruyama, and S. Matsui, “Fluorinated diamond-like carbon coating as antisticking layer on nanoimprint mold,” Japanese Journal of Applied Physics, vol. 45, no. 33-36, pp. L954–L956, 2006.
[23]
K. J. Byeon, K. Y. Yang, and H. Lee, “Thermal imprint lithography using sub-micron sized nickel template coated with thin SiO2 layer,” Microelectronic Engineering, vol. 84, no. 5-8, pp. 1003–1006, 2007.
[24]
B. Ma, H. Wang, H. Zhao, C. Sun, R. Acharya, and J. P. Wang, “L10 FePt/Fe exchange coupled composite structure on MgO substrates,” IEEE Transactions on Magnetics, vol. 46, no. 6, Article ID 5467459, pp. 2345–2348, 2010.
[25]
J. P. Wang, W. Shen, and S. Y. Hong, “Fabrication and characterization of exchange coupled composite media,” IEEE Transactions on Magnetics, vol. 43, no. 2, pp. 682–686, 2007.
[26]
T. Seki, T. Shima, K. Yakushiji, K. Takanashi, G. Q. Li, and S. Ishio, “Improvement of hard magnetic properties in microfabricated L1 0-FePt dot arrays upon post-annealing,” IEEE Transactions on Magnetics, vol. 41, no. 10, pp. 3604–3606, 2005.
[27]
J. M. Shaw, S. E. Russek, T. Thomson et al., “Reversal mechanisms in perpendicularly magnetized nanostructures,” Physical Review B, vol. 78, no. 2, Article ID 024414, 2008.