LabAdviser/Technology Research/Fabrication of Hyperbolic Metamaterials using Atomic Layer Deposition/TIO ALU Gratings Procces flow

Procces flow description

The substrates for the samples were fabricated by depositing 1 μm of Si₃N₄ (the resonator layer) on 100 mm silicon < 100 > wafers using low-pressure chemical vapor deposition. The process was carried out at 780C with ammonia (NH₃) and dichlorosilane (SiH₂Cl₂) as reactive gases. Thickness and refractive index of the deposited silicon nitride was measured and confirmed using spectroscopic ellipsometry. The deposited Si₃N₄ film was carefully analyzed for existence of cracks, particles and other defects using dark field optical microscopy. The best-quality wafer with Si₃N₄ was selected and cleaved in pieces, which were used as substrates for the deposition of Al₂O₃/TiO₂ multilayers. Before inserting each substrate into the ALD reactor, it was placed on a Si carrier wafer. Therefore the Al₂O₃/TiO₂ multilayers were grown not only on the Si₃N₄ 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 Si₃N₄, since the latter suffers from issues related to charge accumulation on the silicon nitride.

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  High aspect ratio Al₂O₃ and TiO₂ nanogratings.

Process flow

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Step		Description	LabAdviser link	Image showing the step
1.1	Plasma surface treatment	To ensure clean surface, the 100 mm Si wafer is treated by O2/N2 plasma. (Optional step)	Plasma Asher 2
1.2	DUV Resist patterning	DUV	DUV Stepper Lithography.
1.3	Deep reactive ion etching (DRIE)	DRIE	DRIE Pegasus.
1.4	Plasma surface treatment	To ensure that remainings of DUV resist are gone, samples are treated by O2/N2 plasma. (Optional step)	Plasma Asher 2.	no image
1.5	Scanning Electron Microscopy inspection	By cleaving the sample it is possible to inspect DRIE etched Si trenches in cross-sectional mode	SEM Supra 2
1.6	Atomic Layer Deposition of either Al2O3 or TiO2	Deposition carried at 150C.Thickness is 90 nm.	Equipment used: ALD Picosun R200. Standard recipes used: Al2O3T and TiO2T .
1.7	Scanning Electron Microscopy inspection	By cleaving the sample it is possible to inspect ALD coatings deposited on Si trenches in cross-sectional mode	SEM Supra 2
1.8	Opening of deposited Al2O3 or TiO2 top layers.	Etching happens using ICP Metal etcher with Cl2/BCl3 process gasses.	Equipment used: Metal ICP Etcher.
1.9	Scanning Electron Microscopy inspection	By cleaving the sample it is possible to inspect ICP etcher results Si trenches in cross-sectional mode	SEM Supra 2
1.10	Selective etch of Si between ALD Al2O3 or TiO2 coatings.	Si etching proceeds using ICP Metal etcher with isotropic process based on SFf process gas.	Equipment used: Metal ICP Etcher.