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

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 ====Procces flow description====
-The substrates for the samples were fabricated by depositing 1 μm of Si<sub>3</sub>N<sub>4</sub> (the resonator layer) on 100 mm silicon < 100 > wafers using low-pressure chemical vapor deposition. The process was carried out at 780C with ammonia (NH<sub>3</sub>) and dichlorosilane (SiH<sub>2</sub>Cl<sub>2</sub>) as reactive gases. Thickness and refractive index of the deposited silicon nitride was measured and confirmed using spectroscopic ellipsometry. The deposited Si<sub>3</sub>N<sub>4</sub> film was carefully analyzed for existence of cracks, particles and other defects using dark field optical microscopy. The best-quality wafer with Si<sub>3</sub>N<sub>4</sub> was selected and cleaved in pieces, which were used as substrates for the deposition of Al<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> multilayers. Before inserting each substrate into the ALD reactor, it was placed on a Si carrier wafer. Therefore the Al<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> multilayers were grown not only on the Si<sub>3</sub>N<sub>4</sub> layer but also on the dummy carrier wafer. After the ALD process was completed, the dummy was cleaved and its cross-section was characterized using scanning electron microscopy (SEM). The SEM images reveal high-quality homogeneous, conformal coatings, as seen in the examples in Figs 1. Such a method of deposited multilayers characterization turned out to be more feasible than the direct SEM characterization of multilayers on Si<sub>3</sub>N<sub>4</sub>, since the latter suffers from issues related to charge accumulation on the silicon nitride.
+A 500 μm-thick wafer of silica (SiO<sub>2</sub>) goes through RCA clean and low-pressure chemical vapor deposition (LPCVD) (furnace from Tempress) based on SiH<sub>4</sub> (silane) at 560<sup>◦</sup>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 deposition of 150 nm of the resist CSAR was done followed by exposure to Electron Beam Lithography (EBL) (JEOL JBX-9500 Electron-beam) [Fig. 1] generating a mask of Si with concentric ring patterns. After development, the wafer was submitted to advanced silicon etch (ASE). To form the trenches of the structures, a thin film of TiO<sub>2</sub> was deposited using the ALD technique in a hot-wall system (Picosun R200), working with 2000 cycles at 150<sup>◦</sup>C [Fig.1]. The precursors used were titanium tetrachloride (TiCl<sub>4</sub>) and H<sub>2</sub>O (supplied by Strem Chemicals Equipment). The process was followed by Ar<sup>+</sup> ion beam etching (IBE) on both sides of the wafer to remove excess[Fig. 1]. At the top most TiO<sub>2</sub> layer the physical sputtering of the sample using Ar<sup>+</sup> ions was performed in order to get access to Si core. On the backside, the Ar<sup>+</sup> ions were used to remove the deposited TiO<sub>2</sub>. Finally, we performed a reactive ion etch on silicon, leaving only the TiO<su2>2</sub> structures. The final system comprehends a base of SiO<sub>2</sub> with nano-structures of TiO<sub>2</sub> on it. Figure 2 shows the image of the system taken from scanning electron microscope (SEM) and conventional optical microscope. Figure 3 illustrates SEM cross-sectional image of the prepared q-plate.
 <gallery caption="" widths="1000px" heights="600px" perrow="1">
-image:Q_plates_fab__sheme.jpg| High aspect ratio Al<sub>2</sub>O<sub>3</sub> and TiO<sub>2</sub> nanogratings.
+image:Q_plates_fab_sheme.jpg| Figure 1. Scheme of fabrication flow.
 </gallery>
 <gallery caption="" widths="1000px" heights="600px" perrow="2">
-image:TiO2nanorings.jpg| High aspect ratio Al<sub>2</sub>O<sub>3</sub> and TiO<sub>2</sub> nanogratings.
+image:TiO2nanorings.jpg| Figure 2. TiO<sub>2</sub> concentric nanorings acting as a q-plate. Insets show optical and SEM images of the whole plate.
-image:Q_plates_cross_section.jpg| High aspect ratio Al<sub>2</sub>O<sub>3</sub> and TiO<sub>2</sub> nanogratings.
+image:Q_plates_cross_section.jpg| Figure 3. Cross-sectional SEM image of the TiO<sub>2</sub> q-plate.
 </gallery>