Selective hierarchical patterning of silicon nanostructures via soft nanostencil lithography

Abstract

It is challenging to hierarchically pattern high-aspect-ratio nanostructures on microstructures using conventional lithographic techniques, where photoresist (PR) film is not able to uniformly cover on the microstructures as the aspect ratio increases. Such non-uniformity causes poor definition of nanopatterns over the microstructures. Nanostencil lithography can provide an alternative means to hierarchically construct nanostructures on microstructures via direct deposition or plasma etching through a free-standing nanoporous membrane. In this work, we demonstrate the multiscale hierarchical fabrication of high-aspect-ratio nanostructures on microstructures of silicon using a free-standing nanostencil, which is a nanoporous membrane consisting of metal (Cr), PR, and anti-reflective coating. The nanostencil membrane is used as a deposition mask to define Cr nanodot patterns on the predefined silicon microstructures. Then, deep reactive ion etching is used to hierarchically create nanostructures on the microstructures using the Cr nanodots as an etch mask. With simple modification of the main fabrication processes, high-aspect-ratio nanopillars are selectively defined only on top of the microstructures, on bottom, or on both top and bottom.

Freestanding Photoresist Film: A Versatile Template for Three‐Dimensional Micro‐ and Nanofabrication

“…This can be used to pattern nanostructures selectively on the top surface of the microstructures. [ 15 ] The flexibility of the PR film also allows it to fully cover the 3D surface of microgratings. The results show that this can be achieved by employing a simple evaporative process of a water droplet placed between the PR film and target substrate, where the surface tension force of the droplet leads the conformal deposition of the PR film during the evaporation.…”

“…Recently, nanolithographically defined ultrathin photoresist (PR) films have emerged as a new template for 3D nanofabrication. [13][14][15][16] Here, we show a novel process for the preparation of flexible and scalable soft PR films with uniform and periodic micro-and nanofeatures and their versatile applications. The micro-and nanopatterned PR film fabricated via conventional lithographic processes can be directly released from its supporting substrate through a novel sacrificial-layer-free (SLF) lifting-off process, in the form of an ultrathin freestanding film, and can be directly used as a conformable template for various 3D micro-and nanofabrication purposes.…”

Scalable Manufacturing of Single Nanowire Devices Using Crack-Defined Shadow Mask Lithography

“…To that end, several research groups have investigated wafer-scalable alternatives to produce nanoscale patterns for shadow mask lithography, including nanosphere lithography, interference lithography, and membrane stacking. − However, these techniques are limited to periodic arrays of identical structures, and achieving a fine dimensional control in the sub-100 nm range with this approach is still an open challenge. Moreover, the use of stencils formed with these techniques would lead to the formation of high-density vertical NWs, which is not ideal for the realization of single NW devices.…”

Manipulation of the Superhydrophobicity of Plasma-Etched Polymer Nanostructures

“…To increase the surface roughness, advanced nanopatterning techniques such as black silicon [ 13 ], metal-assisted chemical etching [ 14 ], and anodization [ 15 ] have been explored to realize such bio-inspired and high-aspect-ratio nanostructures. To further increase the surface roughness and achieve multiscale hierarchical micro- and nanostructures, a nanostencil lithography technique has also been employed, capable of patterning uniform and high-aspect-ratio nanostructures selectively on top, bottom, or both top and bottom of pre-patterned microstructures [ 16 , 17 , 18 , 19 , 20 ]. However, the minimum feature size of the nanostructures attainable in such a technique is limited by the resolution of the nanostencil.…”