Innovative etching method for silicon: Higher precision through interlayer

In the realm of micro- and nanotechnology, creating components with tall, narrow structures from semiconductor materials like silicon is crucial. Gas-phase metal-assisted chemical etching (MacEtch) stands out as a promising fabrication technique for this purpose. This plasma-free process involves a thin metal layer that defines the pattern on the silicon substrate, with the etching occurring in a chemical environment at the metal-silicon interface.

To achieve more precise results, the metal catalyst must maintain its shape and activity throughout the process, which can be challenging if the catalyst is contaminated or locally pinned, resulting in irregular structures, defects, or unwanted porosity.

Dr. Lucia Romano and her team at Paul Scherrer Institute (PSI) have developed a process that addresses these issues by introducing a thin interlayer between the photoresist and the metal catalyst. This interlayer, composed of chromium, aluminum oxide, and/or silicon dioxide, separates the two materials, enabling thorough surface cleaning before the catalyst is applied. This separation ensures a cleaner catalyst and more uniform etching, leading to denser nanostructures with higher aspect ratios.

Dr. Romano's research team successfully produced nanostructures that cover up to 50% of the surface area, with heights 250 times taller than their widths. These findings were published in the journal Small Methods. The researchers demonstrated that various interlayer materials and patterning methods work effectively in this MacEtch process. Potential applications include X-ray optics, where precise technology like this could prove beneficial.