Fabrication Process of 3D-photonic crystals via UV-Nanoimprint Lithography

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UV-based Nanoimprint Lithography (UV-NIL) offers several decisive technical advantages concerning overlay alignment accuracy, simultaneous imprinting of micro- and nanostructures and tool design. A variety of potential applications has been demonstrated by using Nanoimprint Lithography (e.g. SAW devices, vias and contact layers with dual damascene imprinting process, Bragg structures, patterned media) [1,2]. 3D-photonic crystals have been fabricated by using e-beam lithography [3] with high precision alignment stages for achieving sub-100 nm overlay alignment needed to exhibit full photonic bandgap structures for woodpile rod line width ranging from 200 nm to 400 nm. In order to increase the patterned area which is clearly restricted to about 100×100 µm in case of e-beam lithography to an area in the range of 25×25 mm UV-NIL has been selected for this application. Quartz glass templates were designed in such a way that the first layer as well as subsequent layers can be imprinted with the same stamp by rotating the stamp by 90° and a following optical alignment procedure. The alignment is performed in 3 stages using Vernier and Moiré pattern resulting in overlay alignment accuracies better than 100 nm [4,5]. Alignment marks are defined in the 0th layer by photolithography and lift-off which will be used as reference for all layers to be stacked. The template contains 16 squares (each 3×3 mm²) with elevated structures with a height of nominally 200 nm respectively 400 nm and periods ranging from 800 nm to 2400 nm (lines are ranging from 200 nm to 600 nm). After imprinting in UV-NIL resists [Figure1&2] the structures are transferred into SiO2 by dry etching techniques. Subsequently poly-Si is deposited on the sample. Then a planarization process is carried out by chemical mechanical polishing, defining a planar surface for building up the next, 90° rotated layer. Our contribution will demonstrate a concept for the fabrication of the woodpile structure as an example for 3D-structuring. Recently achieved results will be presented.

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Journal: TechConnect Briefs
Volume: 1, Technical Proceedings of the 2007 NSTI Nanotechnology Conference and Trade Show, Volume 1
Published: May 20, 2007
Pages: 96 - 99
Industry sectors: Advanced Materials & Manufacturing | Sensors, MEMS, Electronics
Topicss: Nanoelectronics, Photonic Materials & Devices
ISBN: 1-4200-6182-8