Researchers from the Swiss Nanoscience Institute (SNI) Network have significantly advanced an etching method for producing precise silicon nanostructures. As part of a project funded by the SNI PhD School, they successfully created dense silicon nanostructures with extremely high and narrow structures using optimized metal-assisted chemical etching (MacEtch). The key to their success was a thin interlayer between the photoresist and the metallic catalyst. This innovation could revolutionize the production of semiconductor components, sensors and X-ray optics – all without plasma, but with unprecedented precision.

In micro- and nanotechnology, highly precise components with tall, narrow structures (high aspect ratios) made from semiconductor materials like silicon are of great importance. A promising method for their fabrication is metal-assisted chemical etching (MacEtch) in gas phase. In this plasma-free process, a thin metal layer defines the pattern on the silicon substrate. The actual etching step takes place in a chemical environment, where the etching reaction occurs only at the interface between the metal and silicon. The metal catalyst gradually sinks into the silicon, further directing the etching deeper.

For precise results, the catalyst must maintain its shape and activity throughout the entire process. Problems arise when the catalyst is contaminated or locally pinned, as this leads to irregular structures, defects, or unwanted porosity.

Dr. Lucia Romano and the research team at Paul Scherrer Institute (PSI) developed an innovative process that overcomes pattern instabilities and enables higher fidelity by introducing a thin interlayer made of chromium, aluminum oxide, and/or silicon dioxide between the photoresist and the metallic catalyst. This layer separates the two materials and allows for thorough cleaning of the surface before the catalyst is applied, keeping it clean and ensuring more uniform etching.

"With this method, we have succeeded in producing dense nanostructures that cover up to 50% of the area and are 250 times taller than they are wide," explains Bryan Benz, first author of the study and a PhD student at the SNI Doctoral School.

The researchers recently published their findings in the scientific journal Small Methods. They demonstrated that various materials for the interlayer and different patterning methods work effectively. Applications such as X-ray optics could benefit from this precise technology in the future.

Original Publication:
B. P. J. Benz, M. Stampanoni, and L. Romano
Interlayer-Catalyst Method for Metal-Assisted Chemical Etching of Ultra-High Aspect Ratio Silicon Nanostructures.
Small Methods (2026): e70833.
https://doi.org/10.1002/smtd.70833