Fabrication of Ultra-High Aspect Ratio (>420:1) AlO Nanotube Arraysby Sidewall TransferMetal Assistant Chemical Etching.

We report a robust, sidewall transfer metal assistant chemical etching scheme for fabricating AlO nanotube arrays with an ultra-high aspect ratio. Electron beam lithography followed by low-temperature Au metal assisted chemical etching (MacEtch) is used to pattern high resolution, high aspect ratio, and vertical silicon nanostructures, used as a template. This template is subsequently transferred by an atomic layer deposition of the AlO layer, followed by an annealing process, anisotropic dry etching of the AlO layer, and a sacrificial silicon template. The process and characterization of the AlO nanotube arrays are discussed in detail. Vertical AlO nanotube arrays with line widths as small as 50 nm, heights of up to 21 μm, and aspect ratios up to 420:1 are fabricated on top of a silicon substrate. More importantly, such a sidewall transfer MacEtch approach is compatible with well-established silicon planar processes, and has the benefits of having a fully controllable linewidth and height, high reproducibility, and flexible design, making it attractive for a broad range of practical applications.