Fabrication of High Aspect Ratio Silicon Nanostructure with Sphere Lithography and Metal-Assisted Chemical Etching and its Wettability
Nobuyuki Moronuki*, Nguyen Phan*,†, and Norito Keyaki**
*Tokyo Metropolitan University
6-6 Asahigaoka, Hino, Tokyo 191-0065, Japan
**Mitsubishi Plastics, Inc.
5-8 Mitsuya, Nagahama, Shiga 526-8660, Japan
Metal-assisted chemical etching (MACE) is a site-selective etching process produced by a catalyst reaction at the interface between noble metal and silicon. This paper aims to make clear the applicability of sphere lithography and MACE to the fabrication of high aspect ratio Si nanostructures. The capacity to control the etched profiles and the scale extension are investigated. First, silica particles (e.g. φ1 μm) were self-assembled on a Si substrate. After the reduction of particle size via argon ion bombardment, a gold layer was deposited using the particles as a mask. The substrate was then etched with a mixture of hydrofluoric acid and hydrogen peroxide. It was found that an array of nanopillars with a regular pitch, good separation, and an aspect ratio of about 52 was produced. The effects of MACE conditions on final profiles were clarified. A limitation of this approach is the small (several millimeters) area fabricated due to the dependence on the vacuum technique (ion bombardment, Au deposition), and the size of the area limits its practical applications. Thus, Ag nanoparticles (e.g. φ150 nm) were applied. The relationship between the concentration of the Ag suspension, the Ag assembled layer, and the morphology of MACE structures was made clear. A spray method was applied to extend the deposited area of Ag particles up to φ100 mm. Finally, the effects of the cross-sectional profile on the contact angle of a water droplet were examined. By applying a high aspect ratio nanostructure on the substrate, the water contact angle increased up to 153 degrees while that without the structure is 58 degrees.
-  T. Liu, and C.-J. Kim, “Turning a surface superrepellent even to completely wetting liquids,” Science, Vol.346, pp. 1096-1100, 2014.
-  N. Moronuki, A. Takayama, and A. Kaneko, “Design of surface texture for the control of wettability,” Trans. JSME, Vol.70, pp. 1244-1249, 2004.
-  W. Chern et al., “Nonlithographic Patterning and Metal-Assisted Chemical Etching for Manufacturing of Tunable Light-Emitting Silicon Nanowire Arrays,” Nano Letters, Vol.10, pp. 1582-1588, 2010.
-  K. Q. Peng et al., “Silicon nanowires for advanced energy conversion and storage,” Nanotoday, Vol.8, pp. 75-79, 2013.
-  N. Moronuki, “Functional texture design and texturing processes,” Int. J. Automation Technol., Vol.10, pp. 4-15, 2016.
-  S. A. McAuley, H. Ashraf, L. Atabo, A. Chambers, S. Hall, J. Hopkins, and G. Nicholls, “Silicon micromachining using a high density plasma source,” J. Phys. D: Appl. Phys., Vol.34, pp. 2769-2774, 2001.
-  Y. Xiu, S. Zhang, V. Yelundur, A. Rohatgi, D. W. Hess, and C. P. Wong, “Superhydrophobic and low light reflectivity silicon surfaces fabricated by hierarchical etching,” Langmuir, Vol.24, pp. 10421-10426, 2008.
-  Z. Zhang, T. Shimizu, S. Senz, and U. Gosele, “Ordered high-density Si  nanowires arrays epitaxially grown by bottom imprint method,” Adv. Mater., Vol.21, pp. 2824-2828, 2009.
-  M. Nishio, N. Moronuki, and M. Abasaki, “Fabrication of patterned Ag and Au inverse opal structures through repeated self-assembly of fine particles,” Int. J. Automation Technol., Vol.8, pp. 755-760, 2014.
-  Z. Huang, H. Fang, and J. Zhu, “Fabrication of silicon nanowire arrays with controlled diameter, length and density,” Adv. Mater., Vol.19, pp. 744-748, 2007.
-  K. Peng, M. Zhang, A. Lu, N.-B. Wong, R. Zhang, and S.-T. Lee, “Ordered silicon nanowire arrays via nanosphere lithography and metal induced etching,” App. Phys. Lett., Vol.90, pp. 163123-163123-3, 2007.
-  D. Qi, N. Lu, H. Xu, B. Yang, C. Huang, M. Xu, L. Gao, Z. Wang, and L. Chi, “Simple approach to wafer-scale self-cleaning antireflective silicon surfaces,” Langmuir, Vol.25, pp. 7769-7772, 2009.
-  N. Geyer, B. Fuhrmann, Z. Huang, J. Boor, H. S. Leipner, and P. Werner, “Model for mass transport during metal-assisted chemical etching with contiguous metal films as catalyst,” J. Phys. Chem. C, Vol.116, pp. 13446-13451, 2012.
-  N. Hussing and U. Schubert, “Aerogel – airy material: chemistry, structure, and properties,” Angew. Chem. Int. Ed., Vol.37, pp. 22-45, 1998.
-  H. Jin, M. Kettunen, A. Laiho, H. Pynnonen, J. Paltakari, A. Marmur, O. Ikkala, and R. H. A. Ras, “Superhydrophobic nanocellulose aerogel membranes as bioinspired cargo carriers on water and oil,” Langmuir, Vol.27, pp. 1930-1934, 2011.
-  S-W. Chang, V. P. Chuang, S. T. Boles, C. A. Ross, and C. V. Thompson, “Densely packed arrays of ultra-high-aspect-ratio silicon nanowires fabricated using block-copolymer lithography and metal-assisted chemical etching,” Adv. Funct. Mater., Vol.19, pp. 2495-2500, 2009.
-  K. Balasundaram et al., “Porosity control in metal-assisted chemical etching of degenerately doped silicon nanowires,” Nanotechnology, Vol.23, pp. 305304-305310, 2012.
-  R. N. Wenzel, “Resistance of solid surfaces to wetting by water,” Ind. Eng. Chem., Vol.28, pp. 988-994, 1936.
-  A. B. D. Cassie, and S. Baxter, “Large contact angles of plant and animal surfaces,” Nature, Vol.155, pp. 21-22, 1945.
-  B. S. Kim, S. Shin, S. J. Shin, K. M. Kim, and H. H. Cho, “Control of superhydrophilicity/superhydrophobicity using silicon nanowires via electroless etching method and fluorine carbon coatings,” Langmuir, Vol.27, pp. 10148-10156, 2011.
-  H. Hu et al., “Hierachically structured re-entrant microstructures for superhydrophobic surfaces with extremely low hysteresis,” J. Micromech. Microeng, Vol.24, pp. 095023-095030, 2014.
-  S. R. Wasserman, Y. T. Tao, and G. M. Whitesides, “Structure and reactivity of alkylsiloxane monolayers formed by reaction of alkyltrichlorosilanes on silicon substrate,” Langmuir, Vol.5, pp. 1074-1087, 1989.
-  C. Lee and C. Kim, “Maximizing the giant liquid slip on superhydrophobic microstructures by nanostructuring their sidewalls,” Langmuir, Vol.25, pp. 12812-12818, 2009.
-  A. Kaneko and I. Takeda, “Textured surface of self-assembled particles as a scaffold for selective cell adhesion and growth,” Int. J. Automation Technol., Vol.10, pp. 62-68, 2016.