Fabrication of 2-D and 3-D Photonic Bandgap Structures Using Laser-assisted Imprinting of Self-assembled Particles
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Fabrication of 2-D and 3-D Photonic Bandgap Structures Using Laser-assisted Imprinting of Self-assembled Particles Y.F. Lu*, L.P. Li, K.K. Mendu, J. Shi, D.W. Doerr, D.R. Alexander Department of Electrical Engineering, the University of Nebraska-Lincoln, NE 68588-0511 *Tel: (402) 472-8323, Fax: (402) 472-4732, Email: [email protected]
ABSTRACT Fabrication of 2-D and 3-D photonic bandgap (PBG) structures on silicon substrates using laser-assisted nanoimprinting of silica particles has been investigated. Monolayers of silica particles, with different diameters ranging from 160 nm to 5 µm, were deposited on silicon substrates by self-assembly. A quartz plate, which is transparent to the laser wavelength of 248 nm, was tightly placed on the substrate surface. A KrF excimer laser beam with the wavelength of 248 nm was vertically irradiated on the quartz/nanoparticle/silicon structure. The silica particles were imprinted into silicon substrates by the quartz to form a 2-D PBG structure due to the transient Si surface melting during the laser pulse. 3-D PBG structures can be fabricated by directly imprinting multilayer self-assembled silica particles into Si substrates. They can also be fabricated by repeating a process cycle of silica nanoparticles self-assembly, amorphous Si layer deposition, and simultaneous laser melting, imprinting and recrystallization. INTRODUCTION Photonic bandgap (PBG) crystals have unique military applications including infrared (IR) image control (thermal stealth), target identification, and signal recognition. Commercial applications in optical communications will lead to a totally new generation of silicon (Si) photonic devices that are integrated with current Si microelectronics, microelectromechanical systems, and sensors on a single chip. Examples of discrete Si photonic devices include highperformance low-cost lasers, light-emitting diodes, mirrors, waveguides, and optical filters. However, large gaps exist in further developing photonic crystal technologies due to the fact that low-cost and efficient manufacturing methods to fabricate large-scale photonic crystals are yet to be established. Various nanolithography techniques have been developed to produce 2-D and 3-D periodic structures on solid surfaces. Electron beam lithography is able to form high resolution of submicron features [1-3]. However, serial processing limits the throughput and the cost is high. X-ray lithography has high throughput [4,5] but it requires a high capital cost. UV photolithography [6, 7] is a widely used method; however, its feature sizes are limited by its diffraction-limit of λ/2 [8]. For the laser-assisted nanopatterning with scanning tunneling microscope (STM) [9] or atomic force microscope (AFM) [10], good feature size control can be obtained but the sample throughput is low. A number of new approaches for nanofabrication have been developed. Among them, nanoimprinting lithography has demonstrated to pattern sub10 nm features over a large area in a few minutes [3, 11]. This technique utilizes a reusab
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