LARGE-AREA FABRICATION OF SUB-30 NM PERIODIC NANOSTRUCTURES
H. Le-The1, E. Berenschot2, R.M. Tiggelaar3, N.R. Tas2, A. van den Berg1, and J.C.T. Eijkel1 1 BIOS Lab on a Chip, 2Mesoscale Chemical Systems, and 3NanoLab Cleanroom, MESA+ Institute for Nanotechnology, University of Twente, THE NETHERLANDS ABSTRACT We demonstrate a robust and high-yield fabrication method without deep-UV laser source by combining displacement Talbot lithography (DTL) using a monochromatic UV beam with dryetching techniques to pattern sub-30 nm periodic nanostructures over large-areas. Using this fabrication method, we fabricated 30-100 nm nanocolumns arrays of photoresist and sub-30 nm gold (Au) nanoparticle arrays. KEYWORDS: PhableR 100, Displacement Talbot Lithography, Photoresist Shrinkage INTRODUCTION Recently, displacement Talbot lithography (DTL) has been introduced, providing high-resolution photo-lithography for rapid patterning periodic nanostructures, i.e. regular patterns of lines, holes or dots in photoresist, over large-areas [1]. However, for patterning sub-100 nm periodic nanostructures with this technique, a deep-UV source is needed, i.e. an ArF laser at 193 nm. Here, we report and demonstrate an alternative approach without laser use to fabricate size-tunable large-area periodic nanostructures, which have many potential applications in photonics, electronics, biosensors, smart surfaces, catalysis, and biomedical analysis [2, 3]. EXPERIMENTAL An 3×3 cm2 array of photoresist nanocolumns (102±4 nm diameter, 250 nm pitch) was patterned by DTL (PhableR 100C, EULITHA) in a layer of PFI88 photoresist (Figure 1b-d), and subsequently transferred to a bottom anti-reflection layer coating (BARC) layer (AZ® BARLi® II 200) by using different plasma etchings (Figure 1e). These BARC nanocolumns were then used to fabricate sub-30 nm Au nanoparticle arrays using ion beam etching (Figure 1f-g).
Figure 1: Fabrication process of an array of Au nanoparticles supported on an amorphous fused-silica substrate using the combination of displacement Talbot lithography (DTL) [1] and dry-etching methods (plasma etching and ion beam etching). (a) A ~20 nm Au layer was sputtered on a fused-silica wafer. (b-d) The photoresist nanocolumns were patterned by DTL, and (e) subsequently transferred at a 1:1 ratio into the BARC by using N2 plasma etching for 9:30 min [4]. (f) The Au layer was inclined etched with ion beam etching (IBE, Oxford i300) with 5 sccm Ar, and 50-55 mA. (g) Over inclined IBE of the fused-silica substrate.
RESULTS AND DISCUSSION The photoresist nanocolumns (Figure 1d) can be even shrunk to smaller high aspect-ratio BARC nanocolumns by subsequently using reactive plasma etching with a O2/N2 (40/50 sccm) gas mixture (12 mTorr, 25 W). Using this recipe for 135 s, photoresist nanocolumns (102±4 nm diameter) were transferred to BARC nanocolumns (30±2 nm diameter), as shown in Figure 2(a). The etching of 978-0-9798064-9-0/µTAS 2016/$20©16CBMS-0001
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20th International Conference on Miniaturized Systems for Chemistry and Life Sciences 9-13 October, 2016, Dublin, Ireland
BARC using different plasma etchings versus etching time is shown in Figure 2(b). It is highly remarkable that the verticality of these nanocolumns remains during N2/O2 plasma shrink-etching. By controlling this shrink-etching process, BARC nanocolumn arrays can be produced at diameters ranging from ~100 nm to ~30 nm, enabling the large-footprint fabrication of size-tunable periodic nanostructures such as supported metal nanoparticle arrays for catalysis. (b)
(a)
Figure 2: (a) HR-SEM images of shrink-etching of BARC at different etching times, using reactive plasma etching with O2/N2 (40/50 sccm) gas mixture, 12 mTorr, and 25 W. (b) Etching of BARC versus etching time.
Figure 3 shows an array of Au nanoparticles (24±4 nm diameter, 250 nm pitch) supported on cone-shaped fused-silica features fabricated by over inclined IBE of the fused-silica substrate for 10 min (Figure 1g). The Au nanoparticle diameter can be tuned from ~90 nm to ~30 nm by adjusting the ion beam etching parameters, i.e. etching time and the incident angle of the beam. (a)
(c)
(b)
Figure 3: (a-b) AFM and (c) HR-SEM images of an array of Au nanoparticles (bright spots) supported on cone-shaped fused-silica features (inclined ion beam etching).
CONCLUSION A robust fabrication method has been reported combining DTL using a monochromatic UV beam with dry-etching techniques, enabling the fabrication of large-area arrays of 30-100 nm periodic nanostructures. With easy operation, this method is suitable for batch-production at low-cost. ACKNOWLEDGEMENTS This work was supported by the Netherlands Center for Multiscale Catalytic Energy Conversion (MCEC), and NWO Gravitation programme funded by the Ministry of Education, Culture and Science of the government of the Netherlands. The authors thank Mark Smithers for making high resolution SEM images. REFERENCES [1] H.H. Solak, C. Dais, and F. Clune, “Displacement Talbot lithography: a new method for highresolution patterning of large areas,” Opt. Express, 19, 10686-10691, 2011. [2] J.N. Anker, W.P. Hall, O. Lyandres, N.C. Shah, J. Zhao, and R.P.V. Duyne, “Biosensing with plasmonic nanosensors,” Nat. Mater., 7, 442-453, 2008. [3] A.N. Shipway, E. Katz, and I. Willner, “Nanoparticle arrays on surfaces for electronic, optical, and sensor applications,” ChemPhysChem., 1, 18-52, 2000. [4] S. Gupta, and C.F. Lyons, “Selective I-line BARL etch process,” U.S. Patent, no. 5807790, 1998. CONTACT * H. Le-The; phone: +31-659-604-540;
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