Low-cost technique for etching nanoholes in silicon could underpin new filtration and nanophotonic devices

December 22, 2017, Agency for Science, Technology and Research (A*STAR), Singapore
Low-cost technique for etching nanoholes in silicon could underpin new filtration and nanophotonic devices
An example of directional etching for nanohole arrays of less than 500nm in diameter. Credit: © 2017 A*STAR Institute of Materials Research and Engineering

Metal-assisted chemical etching, or 'MacEtch', is used to fabricate a range of nanostructures, but damaging movements of the catalyst during vertical etching processes hamper its wider use. Now, a team led by A*STAR have developed a technique that improves catalyst stability, paving the way for wider application.

MacEtch is a wet etching method for fabricating nanostructures from patterned metal film. The simplicity, versatility, and cost effectiveness of MacEtch in silicon and other semiconductors have led to its use in the manufacture of a wide range of products, from electronic and optoelectronic devices to biological and chemical sensors, as well as energy harvesting technologies. These applications, however, use relatively large mesh structures.

When catalysts with smaller dimensions are used, forces acting on the catalyst cause it to move during the etching process, which limits their use in the fabrication of structures with high aspect ratios, such as nanoholes.

"Previously, it has been very difficult to achieve directional isolate catalyst etching, and [this] has been a major roadblock in its development," explains Sing Yang Chiam from A*STAR's Institute of Materials Research and Engineering. "Small feature sizes are especially important for fabricating filtration devices, but at these dimensions, etching becomes very challenging."

Now, a technique for controlling the catalyst during the etching process, allowing for the fabrication of nanoholes in silicon with unprecedented aspect ratios, has been developed by Chiam and colleagues in collaboration with the National University of Singapore and the University of Illinois at Urbana−Champaign in the United States.

The researchers investigated isolate catalyst etching of regular gold disks of identical array spacing and catalyst thickness, formed using laser interference lithography. This allowed the team to study precise and isolated effects of the parameters, such as the etchant and doping concentrations, to understand the interface forces on the catalyst.

They found that higher ratios of hydrofluoric acid to hydrogen peroxide, or higher p-type silicon doping levels, reduce catalyst motion, and attributed this to a lowering of the interface Van der Waals forces caused by the creation of porous silicon.

The researchers demonstrated their technique by fabricating large-area, regularly ordered, nanoholes arrays in with an aspect ratio of around 12. This new method enables the fabrication of new biological and water filters, and nanophotonic devices.

"We plan to use our findings to make a simple filtration device, and then see how much further we can take deep trenching," says Chiam.

Explore further: Better understanding the principles of silicon etching leads to improved surface patterning

More information: Lingyu Kong et al. Minimizing Isolate Catalyst Motion in Metal-Assisted Chemical Etching for Deep Trenching of Silicon Nanohole Array, ACS Applied Materials & Interfaces (2017). DOI: 10.1021/acsami.7b04565

Related Stories

Chemical etching method helps transistors stand tall

July 26, 2016

Smaller and faster has been the trend for electronic devices since the inception of the computer chip, but flat transistors have gotten about as small as physically possible. For researchers pushing for even faster speeds ...

Eco-friendly production of silicon nanowires

October 19, 2016

Physicists from the Lomonosov Moscow State University have worked out a new and more eco-friendly method of obtaining silicon nanowires that replaces hydrofluoric acid (HF) with ammonium fluoride (NH4F).

Recommended for you

Shining light on the separation of rare earth metals

October 18, 2018

Inside smartphones and computer displays are metals known as the rare earths. Mining and purifying these metals involves waste- and energy-intense processes. Better processes are needed. Previous work has shown that specific ...

Placing atoms for optimum catalysts

October 18, 2018

Fuels, plastics, and other products are made using catalysts, materials that drive chemical reactions. To design a better catalyst, scientists must get the right atoms in the right spot. Positioning the atoms can be difficult, ...

A chemical criterion for rating movies

October 18, 2018

A measurable criterion now exists for determining the age rating of films. A group of scientists at the Max Planck Institute for Chemistry in Mainz has found that the concentration of isoprene in cinema air correlates with ...

Chemists test a new nanocatalyst for obtaining hydrogen

October 17, 2018

A chemist from RUDN was the first to use catalysts with ruthenium nanoparticles to obtain hydrogen under the influence of visible light and UV radiation. In the future, such catalysts may be used for large-scale production ...

Cellular clean-up crews linked to how body handles sugar

October 17, 2018

How our bodies handle glucose—the simple sugar that provides energy from the food we eat—appears to be intertwined with how cells keep themselves functioning normally, according to new University of Chicago research.


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.