LabAdviser/Technology Research/Fabrication of Hyperbolic Metamaterials using Atomic Layer Deposition/TiO2 Q plates: Difference between revisions

A 500 μm thick wafer of silica (SiO₂) goes through RCA clean and low-pressure chemical vapor deposition (LPCVD) (furnace from Tempress) based on SiH₄ (silane) at 560^◦C to form a layer of 300 nm of amorphous silicon (Si) [Fig. 1]. The back side of deposited Si was etched using KOH wet etch. In order to remove residues from the etching process, it was performed oxygen plasma cleaning. A CSAR resist was spin-coated to the thickness of 150 nm, followed by exposure of Electron Beam Lithography (EBL) (JEOL JBX-9500 Electron-beam) generating a mask with concentric ring patterns. After development, the wafer was submitted to advanced silicon etch (ASE). To form the trenches of the TiO₂ structures, a thin film of TiO₂ was deposited using the ALD technique in a hot-wall system (Picosun R200), working with 2000 cycles at 150^◦C [Fig.1]. The precursors used were titanium tetrachloride (TiCl₄) and H₂O (supplied by Strem Chemicals Equipment). The process was followed by Ar⁺ ion beam etching (IBE) on both sides of the wafer to remove excess of ALD deposited material. At the top most TiO₂ layer the physical sputtering of the sample using Ar⁺ ions was performed in order to get access to Si core. On the backside, the Ar⁺ ions were used to remove the deposited TiO₂. Finally, we performed a reactive ion etch on silicon, leaving only the TiO₂ structures. The final system comprehends a base of SiO₂ with nano-structures of TiO₂ on it. Figure 2 shows the image of the system taken using scanning electron microscope (SEM) and conventional optical microscope. Figure 3 illustrates SEM cross-sectional image of the prepared Q-plate .

image:Q_plates_fab_sheme_new.jpg| Figure 1. Scheme of fabrication flow.

<gallery caption="" widths="1000px" heights="600px" perrow="2">

image:TiO2nanorings.jpg| Figure 2. TiO₂ concentric nanorings acting as a Q-plate. Insets show optical and SEM images of the whole plate.

image:Q_plates_cross_section.jpg| Figure 3. Cross-sectional SEM image of the TiO₂ Q-plate. a) The low magnification image shows the whole plate b) High magnification allows to inspect individual rings cross-sections.